: Having major issues during acceleration - 84 Deville HT4100



henrydean40
06-13-11, 06:13 AM
I've made a number of recent updates to my 84 Deville with HT4100 (with only 36,000 miles on it - she's a beauty) in an attempt to fix the acceleration problem I'm having (and also hopefully the extreme lack of power going uphill - I cant exceed 50mph going uphill), but nothing seems to be helping. When starting movement from a dead stop, if I push the accelerator a tiny bit the car starts to move slowly, but if I push the pedal any further there is a very drastic hesitation or lag...the car almost wants to die. I've noticed that it also happens when cruising down the road and pushing the pedal in attempt to accelerate, you can feel the hesitation. It seems that the problem is worse when the engine is hot.
Mieneke did an engine performance analysis and noted that the engine may have a misfire.

Any suggestions on what might be causing this?
Do you think it might be worn camshaft lobes? It almost seems starved for fuel...but how and why?

jayoldschool
06-13-11, 10:26 AM
Fuel filter, fuel pump, clogged cat, bad injector, bad fuel pressure regulator, incorrect timing are all possibilities (in order of my likely guesses). Also, could be the trans TV cable. Does the car downshift when you are in OD and floor the gas?

amunderdog
06-13-11, 10:54 AM
84 Cadillac Deville HT 4100
The engine and its electronic control module (ECM) were quite sophisticated, despite having a throttle body injection system (as opposed to port fuel injection.) Like the 6.0/368" DFI engines before it,
The HT4100 used an ECM that incorporated a detailed on-board computer. Every parameter of engine performance could be displayed on the Electronic Climate Control panel while the car was being driven.

Am looking to see how to use it.

csbuckn
06-13-11, 11:28 AM
My guess is also fuel related. What about that little solenoid by the TBI? Isnt that a throttle position sensor? A lot of people have had issues with that.

jayoldschool
06-13-11, 01:30 PM
TPS will throw a code.

Speaking of that... henry... any codes? Is the CEL on?

henrydean40
06-13-11, 04:09 PM
No, there are no error codes at the moment. The "service now" light appeared breifly while on my 1 hour trip over the weekend, but it went away. I'll run diagnostics again to see if there are any new codes.
When I was going up a long hill, the car would struggle to keep 50mph, and when I would push the pedal all the way to the floor I could hear the tranny kick down and the engine change gears...I wasn't sure what it was until I got home a read a little bit about it....still not exactly sure how its supposed to work and why - its the detent switch, right?

In response to jayoldschool: I recently changed the CAT to a magnaflow version, changed the fuel filter a couple months back, changed the base timin to 13 (to try to squeeze a little more power), and got new plug wires, dist cap and rotor. From your suggestions that leaves: fuel pump, bad injector(s), bad fuel pressure regulator, and TV cable.
I have a Haynes manual that discusses the TV cable a bit, so I'll go out and do an inspection on that. Maybe it needs adjustment. After that I'll try cleaning the injectors to see if that helps until I can buy a new fuel pump on Wednesday...

amunderdog
06-13-11, 04:22 PM
If it was fuel / wouldn't it be throwing lean codes.
That thing got electric fans or fan clutch?

henrydean40
06-13-11, 04:26 PM
Okay, i just ran diagnostics again and surpisingly it showed code 44. My haynes manual says the following for code 44:

Code 44....Oxygen Sensor.....The exhaust is lean. Indicated by the 02 sensor after the engine has run in closed loop, part throttle at road load up to five minutes. Check the ECM wiring connectors,. Chech for vacuum leakage at the base gasket, vacuum hoses or the intake manifold gasket. Replace o2 sensor

I replaced the o2 sensor 2months ago, so I know its working okay. I'm guessing that it may be a vacuum leak as suggested?? Would that cause the problems I'm having??

As for the electric fans or fan clutch, I'm not exactly sure. I've only had the sexy little thang for 6 months so I'm still learning a bit about her...

amunderdog
06-13-11, 04:33 PM
Find a can of throttle body cleaner.
With it idling spray all around the throttle body and vacuum hoses.
Pay attention to where you are spraying and listen for a change in RPM.
You can also take a piece of hose and hold one end to your ear probe around with the other end and try to hear the vacuum leak.

Good luck
Keep up the good work:)

While your in there see if the cooling fan is bolted to the front of motor......

jayoldschool
06-13-11, 08:26 PM
4100s are mechanical fan.

Why did you replace the cat with such low mileage?

henrydean40
06-13-11, 11:34 PM
Yep, the fan is attached to the motor...it is a mechanical fan.

I went ahead and sprayed the throttle body, linkage and shaft with the injector cleaner while idling, and I didn't notice any change in RPM. I've also taken a hose and tried to listen for leaks...there is a sound coming from near the TPS, but I'm not sure that it is a vacuum leak.

P.S. I replaced the stock CAT with a magnaflow version because I wanted to improve the power and performance as much as possible. Its just a small part of this giant project of mine to improve the throttle response and accelerating power so that she can travel okay on hills, but also to eliminate this drastic hesitation problem that is occuring right now when I press on the accelerator. The CAT was just one part on the list of parts that I've updated while chasing this 'hesitation' or 'lack of power' issue...

jayoldschool
06-14-11, 12:32 AM
Check the fuel pressure, and the timing.

henrydean40
06-14-11, 02:46 AM
I'll get a fuel pressure tester on loan from Schuck's on Wednesday and will test the fuel pressure then. I found out today that they loan out special tools such as that...its not even renting because all you do is put down a deposit (≈$35 for the fuel pressure tester) and all of the money is returned to you when you return the tool....I thought that was pretty awesome. They do that with all sorts of specialty tools: steering wheel pullers, compression testers, etc.

What are the target values that you would suggest for the timing and the fuel pressure??
I believe the timing is currently at 13 BTDC (bumped from 10 previously to squeeze out more hp).
Also, from what I've read i believe 10psi is the target value for the fuel pressure throughout the entire driving range and idle....do you agree with those??

henrydean40
06-14-11, 02:53 AM
To follow up on some earlier topics, using the haynes manual I went ahead and adjusted the TV cable, and then I changed the spark plugs. Those two (along with everything else) seemed to have helped quite a bit with the lack of power going uphill, however, I'm still getting the extremely rough acceleration or hesitation when accelerating from a stop.

I'll check the fuel pressure and double check the timing asap and post the results...

amunderdog
06-14-11, 03:50 AM
Correct fuel pressure should be 9-12 psi. "I read that somewhere".

Maybe it's just me
I quit using a timing light years ago.
I prefer a vacuum gauge - Set carb / throttle body and distributor up for highest steady vacuum possible.

Now back to that cooling fan. It has a viscous clutch. One way it can go bad is by locking up. When they do this they will suck HP and MPG will suffer.
So grab it by the blade and see how hard it is to turn. it should not spin freely or be overly difficult to turn.
While your shaking hands with it give it a little front to back shake. There should not be a lot of slop that way.

Looks like we are making progress:)

jayoldschool
06-14-11, 10:14 AM
I would put the timing back to stock to eliminate that as a possibility. Also, TBI engines require a special procedure to set timing, so if that wasn't followed, it may be way off what you think it is.

henrydean40
06-14-11, 06:13 PM
The switch from the timing light to the vacuum gauge seems like a great idea, especially since so much of this vehicle really relies on the vacuum lines. :thumbsup: 1. Where should I hook the vacuum gauge up to? And 2. when I get the gauge hooked up, do I just adjust the distributor until I have maximum vacuum (without pinging, of course)?.....is that how its done?

As for the cooling fan, there is really no slop back and forth, however the blade does spin pretty easily. With constant light pressure the fan will continue to spin, but when I give it a push to try to make it spin on its own it stops right when I let go.... Is that operating correctly??

I'm not sure if DFI is equivalent to TBI, but this one is DFI (digital fuel injection)...just as a sidenote. As for the procedure used to set the timing (I believe I used the right one): I set the base timing with the car in park, the green connector by the distributor unhooked, and the ALD jumper connected from A to B. And actually, I'm not sure if its the timing because this issue was there prior to me changing from the factory setting of 10BTDC to the current 13. I changed to 13 to see if it would help fix the problem, but it didn't fix it. Having said that, should I still drop it back down to 10?

jayoldschool
06-14-11, 07:11 PM
DFI is Cadillac's fancy name for TBI. Your timing procedure sounds right, going from memory. My FSMs are out in the garage.

You are running high octane fuel, correct? I would still put the timing back to stock. 4100s were spec'd for high octane, stock. That likely means that they can't handle much more timing before detonation.

henrydean40
06-14-11, 07:20 PM
Yep, High octane every chance I get. I'll bump down the timing to 10 next chance I get and see if there is any change in performance...

tqwrench
06-16-11, 02:41 AM
One thing to bear in mind: Oxygen sensors detect oxygen, not fuel. They infer from the amount of oxygen in the exhaust stream how rich/lean the system is. That being said, lean codes have a few sources, as discussed already, intake leaks (these were notorious for intake manifold problems), which creates unmetered air, or not enough fuel. If the camshaft was wiped I wouldn't expect a lean code. Lean tells me it's getting enough air which debunks a cam lobe wipeout. These are speed density systems which means it relies on a calculation from volumetric efficiency (fixed) and a MAP sensor (engine vacuum - variable) and engine RPM (variable) to calculate fuel delivery. Add in engine temp, barometric pressure, and some other items to trim the fuel plus a learned strategy.

Go towards fuel pressure, if that's ok and the injectors work, double check for air leaks. Worst case scenario, do like we did in the old days, tell the tech to put intake gaskets on it, invariably he'll find a broken vacuum hose when he snatches the intake anyway :alchi:

amunderdog
06-16-11, 12:01 PM
The switch from the timing light to the vacuum gauge seems like a great idea, especially since so much of this vehicle really relies on the vacuum lines. :thumbsup: 1. Where should I hook the vacuum gauge up to? And 2. when I get the gauge hooked up, do I just adjust the distributor until I have maximum vacuum (without pinging, of course)?.....is that how its done?

As for the cooling fan, there is really no slop back and forth, however the blade does spin pretty easily. With constant light pressure the fan will continue to spin, but when I give it a push to try to make it spin on its own it stops right when I let go.... Is that operating correctly??

I'm not sure if DFI is equivalent to TBI, but this one is DFI (digital fuel injection)...just as a sidenote. As for the procedure used to set the timing (I believe I used the right one): I set the base timing with the car in park, the green connector by the distributor unhooked, and the ALD jumper connected from A to B. And actually, I'm not sure if its the timing because this issue was there prior to me changing from the factory setting of 10BTDC to the current 13. I changed to 13 to see if it would help fix the problem, but it didn't fix it. Having said that, should I still drop it back down to 10?\

Sorry this thread dropped out on me.
Looks like you are getting good help:)
Hows it going today?

The Fan clutch sounds like it passed inspection.

About the Vacuum gauge tuning.
Yes it is as much by ear - feel - knowledge as by facts.
But it really not that hard to pick up if you understand basics like spark knock - rich - etc.
Type ( Tuning with a Vacuum gauge ) into your search engine.
Here is a short and long version.
http://www.classic-car-magazine.co.uk/articles/tuning-with-a-vacuum-gauge.html
http://www.centuryperformance.com/tuning-with-a-vacuum-gauge-spg-148.html

henrydean40
06-17-11, 05:34 PM
On tuesday I popped open the TBI and cleaned everything with throttle body & air intake cleaner. I then proceeded to change the spark plugs, and in the process I was amazed to find one of the spark plugs a bit loose (I suspected that one may be bad based on the performance). I made sure all were tight, and it seems to be performing MUCH better. The hesitation APPEARS to be gone and there is acceptable power (it'll never be hot-rod) throughout the driving speeds. It seems to be shifting at the right time now, and the I haven't felt the severe hesitation when starting from acceleration. I haven't tested on the freeway yet, but I will do this weekend and post back. I think the TV cable adjustment and the tightening of the loose plug played key roles in the improvements.

Since the changes resulted in the improvements, I never actually made it to testing the fuel pressure or adjusting the timing for maximum vacuum (maybe stock timing setting instead....haven't decided). However, there is still a slightly 'erratic idle' - where the engine seems to periodically rev up and down slightly when just sitting in park. As a result, I plan to test continue with the fuel pressure testing and vacuum inspection this weekend. I'm wondering if a faulty TPS is causing this issue and was part of the other issues - I ran the diagnostics it tripped error codes 13 and 44. The Haynes manual shows the following:

Code 13....Oxygen Sensor.....The engine must run up to five minutes at part throttle under road load before this code will set. Check for sticking or misadjusted throttle position sensor. Check the oxygen sensor wires and connectors. Replace the oxygen sensor if necessary.

Code 44....Oxygen Sensor.....The exhaust is lean. Indicated by the 02 sensor after the engine has run in closed loop, part throttle at road load up to five minutes. Check the ECM wiring connectors,. Chech for vacuum leakage at the base gasket, vacuum hoses or the intake manifold gasket. Replace o2 sensor

But I changed the o2 sensor a couple months ago.... :hmm:
I cleared the error codes last night, so we'll see if they are tripped again...

csbuckn
06-17-11, 07:01 PM
I still think you should put timing back to stock until everything is on the up and up. Once you are sure its running right, adjust your timing then. Glad to see you got the main issue fixed.

henrydean40
06-17-11, 09:56 PM
Hmmmmmm....I'm not so sure its fixed now. Actually, I'm sure its NOT fixed. I took it for a longer test drive today, and once it got warm the severe hesitation returned. She does have a bit more power and noticeably better throttle response (most of the time), but it definitely still has the hesitation.

I'll test the fuel pressure (as soon as I can get the gauge) and will look again for vacuum leaks. I will post the results as soon as I can get that done.

csbuckn
06-17-11, 10:03 PM
Does your car have a knock sensor?

henrydean40
06-17-11, 10:16 PM
I'm not sure. How can I tell?

csbuckn
06-17-11, 11:17 PM
Theres a sensor near the bottom of the block with a roundish plug. Not sure how to tell without being there. Its there to detect knock so if it does, it will change the timing another 5 degrees once its warm. Don't know if this is your problem(probably not) but its another ave.

jayoldschool
06-18-11, 01:29 PM
If it is ok cold, but bad when warmed up, it is definitely a closed loop problem. That means a sensor is bad. Open loop just ignores the sensors.

henrydean40
06-22-11, 09:42 PM
Since the issue is occuring when the engine warms up, which sensor do you think it might be?? Could it be the TPS (throttle position sensor) or the MAP sensor?? I'm just guessing...

68cadu
06-27-11, 10:38 PM
Hi henrydean40, I'm having identical problems with my 1984 Coupe Deville with 74,000 miles on it I've done everything you have done but can't seem to fix the hesitation. Please keep me posted if you figure this problem out. Thank you

Aron9000
06-27-11, 11:41 PM
I'd try changing the oxygen sensor again. What brand part did you use when you last changed it?? Some of the cheap Autozone parts are chinese made garbage.

sven914
06-28-11, 12:37 AM
^All of the cheap Autozone parts are Chinese made garbage.

You should get your electronics form Advance Auto because they are an authorized AC DELCO distributor. They don't have everything, but what they do have is factory original for your car.

CoupeDevilleRob
06-30-11, 02:41 AM
I experienced similar problems with my 83 Coupe. I essentially rebuilt the throttle body and it cured the problem some what. The hesitation still exists just not as bad. The conclusion I reached is the HT4100 sucks and I'm waiting to have some extra cash to do a small block Chevy swap. Glad you got your's sorted out though.

DouglasJRizzo
06-30-11, 09:34 PM
I drove an 82 Eldorado when it was brand new, 4100 equipped and bog slow. Couldn't get out of its own way. But..it was smooth and quiet. This engine is known for odd problems. Don't be surprised if there's an intake leak somewhere. If doing an engine swap, I've seen 425's and 368's dropped in that work fine, but I'd love to drop a built 472 in one of these and leave the "HT4100" badges on it..

henrydean40
06-30-11, 11:15 PM
Actually, I still haven't figured it out....its still a nasty battle at the moment :banghead: . I think I should maybe rebuild the TBI just to see if that helps. (However, I'm starting to believe that, just as everyone says, these ht4100's just suck ballz, they'll never have decent power and I may never eliminate the hesitation fully).

I plan to do the following:
1) Test the fuel pressure at the moment the problem is occuring (by maybe taping the gauge on the windsheild with the hood cracked slighly and see what the pressure is when the hesitation ACTUALLY happens).
2) Change the O2 sensor to higher performance - as Aron9000 suggested
3) Install the iridium spark plugs (≈$8 ea...ouch), but they are supposed to increase throttle resp and hp.
4) Rebuild the TBI unit to ensure there are no leaks.
5) search more for vacuum leaks (although I'm not finding squat)


My last and final option (that I'm aware of ......please if you have suggestions add to the list):
6) Swap out the engine with something that is compatible and will be perform better (if it's even worth it on this car). Does anyone have a rough estimate of how much a engine swap would be to get something in there that performs better than the pansy little ht4100??

Thanks everybody.

henrydean40
06-30-11, 11:19 PM
I drove an 82 Eldorado when it was brand new, 4100 equipped and bog slow. Couldn't get out of its own way. But..it was smooth and quiet. This engine is known for odd problems. Don't be surprised if there's an intake leak somewhere. If doing an engine swap, I've seen 425's and 368's dropped in that work fine, but I'd love to drop a built 472 in one of these and leave the "HT4100" badges on it..

Where would be a good place to start searching for the intake leak? Are there some locations that I should start with first and look extra closely?

Also, what do you think it might cost to swap to a 425, 368 or even a 472?? Are those the best ones/most compatibile to consider?

sven914
06-30-11, 11:41 PM
^All of those engines will swap in, but require you to change both the transmission and differential. Probably the most cost effective thing would be an Oldsmobile 307. It uses the same transmission and can't break the differential, so you won't need to swap out a lot of parts. You can sometimes find them on Craigslist or get them from a junk yard for around $500. The 307 isn't that much more powerful than the 4100, but because it's carburetted, you don't need the computer controls and it will be easier to tune.

For a little more power (and cash), you can also get an Olds 350 and still use the 4100 transmission and final drive; you just need to be careful about how much torque and horsepower it makes. One made after 1977 wouldn't have enough power to damage the transmission, but would be more responsive than the 307 or 4100.

68cadu
06-30-11, 11:44 PM
I'm going to eliminate my catalytic converter for now and check for leaks. I'm starting to think it's maybe the distributor, I did a full tune up and the engine still has a rough feel to it even under light acceleration. It's really dangerous these days now that it's so much worse when the ac is running.

cadillac kevin
06-30-11, 11:54 PM
the best (read cheapest/ bang for the buck) option for you is a chevy 350 and a 700r4. a 350 with a rv cam (similar to the grind used on GM crate motors), 76cc heads, and a 4bbl will get you at least 250 hp in the real world and probably about 17 mpg combined.
a second option (a bit more $ but more power) would be a vortec 350 with either the fuel injection setup and a 4l60e trans or with an aftermarket intake and carb and a 700r4 trans (probably cheaper to go with a carb and 700r4)
the 425 and 472's are a bit more expensive to rebuild but have more torque than the chevy 350 in stock trim). they're also great low rpm cruising motors, but dont get good mileage (I think they average about 14 or 15 mpg combined)

ponchoman49
07-01-11, 12:12 AM
I would highly recommend finding someone with a good high end scanner and running the car until it reaches
proper operating temp(closed loop). The scanner will read all the values such as engine temp, oxygen content in exhaust by the voltage at the sensor, TPS voltage at differing pedal inputs, engine idle vacuum, timing etc. My buddy hooked his scanner up to my 1990 Brougham which is suffering from lack of power and poor mileage with no check engine light and we found low idle vacuum, timing off by 10 degrees and improper
TPS voltage which was affecting other things. Again there was no check engine light and the engine idled
fine and ran ok otherwise. The HT 4100 is notorious for bad intake manifold gaskets so I wouldn't be
surprised if as others have stated that was were some of your vacuum leak was coming from.
Also keep in mind this engine is rated at only 135 HP and only 200 LBS Ft of torque to move around
3800-3900 LBS of car so it won't be a ball of fire even in perfect tune and hill climbing power and highway
passing response will both be tepid. The 3.42:1 rear final drive did help off the line response so that should be where this engine shines some. Bumping up the timing 2-3 degrees, replacing the factory cat with a high flow unit and a few other mods helps a bit too but those mods should only be on a perfectly running mill.

henrydean40
07-01-11, 01:06 AM
I'm going to eliminate my catalytic converter for now and check for leaks. I'm starting to think it's maybe the distributor, I did a full tune up and the engine still has a rough feel to it even under light acceleration. It's really dangerous these days now that it's so much worse when the ac is running.

I replaced my CAT with Magnaflow version recently - it seemed to help a bit. I also replaced the distributor cap, wires, plugs, fuel filter...and the list goes on - those also helped a bit. But the hesitation/lag is definitely still there.

henrydean40
07-03-11, 01:38 AM
Where would I find the intake manifold gaskets? Is the intake manifold the large peice thats under the TBI unit (that the rocker arm covers attach to)??

jayoldschool
07-03-11, 10:51 AM
Gaskets are available from any parts store. Rocker covers attach to the heads, not the intake.

Intake looks like this:

http://i183.photobucket.com/albums/x57/UrsusMorologus/45TBIintake.jpg

Engine with intake (and without valve covers). Viewed from the back.

http://eldorado.xlr8d.com/engine/4100_03.jpg

henrydean40
07-05-11, 08:50 PM
The severe hesitation is really bad now that hot weather is here. The only way I can get the car to move from a stop is to 1)lightly pump the throttle, or 2)almost floor it. It seems that when I use the 2nd method, the engine is actually kicking into overdrive, but it gets the car to move....some times. What are the chances that this is a problem with the Tranny??

One thing that makes me think its NOT the tranny, is that when I stop the car after a drive where I was experiencing these acceleration issues, (with the car in park) the engine will actually rev up and down a few times before ultimately dying on its own. Any suggestions on what might cause that??

jayoldschool
07-05-11, 09:20 PM
TPS throttle position sensor could be one.

68cadu
07-05-11, 11:30 PM
Is this with the ac on? My 84 has a hesitation also but it's really bad when the ac is on. Sometimes after a long drive on the highway when I finally come to a stop it's seems to get locked up in overdrive and then 3rd and 2nd, The car starts bucking while coming to a stop and then finally shifts roughly into 1st.

68cadu
07-05-11, 11:37 PM
If the TPS was bad would it throw a code? Would the idle be constantly rising and lowering on it's own? My idle seems to be ok it even raises like it's supposed to when I turn the ac on. THIS CAR IS DRIVING ME NUTS!!! My 01 S430 is easier to diagnose!

68cadu
07-05-11, 11:46 PM
Now come to think of it I'm getting a E44 code(O2 sensor lean) And a E53 (Distributor Signal Interrupt)
Can a 02 sensor cause hesitation? I would think it would just effect emissions and MPG. Not sure though

sven914
07-06-11, 02:34 AM
Yes.

If the O2 sensor is malfunctioning, the computer cannot meter the fuel correctly. When the sensor is reading lean, the computer reacts by dumping fuel into the engine. If the compute doesn't see a change in the sensor's reading, it goes into default fuel metering.

Either way, the engine would be running overly rich and not be able to perform. The computer is basically drowning the spark with gasoline so it can't ignite the cylinders properly.

henrydean40
07-06-11, 04:57 AM
Mine hesitates whether the AC is on or not, but its definitely worse with the AC on.
Is the Bosch O2 sensor a good replacement choice (≈$20 at Schucks)? Or should I shoot for higher end?

I think changing the o2 sensor is a good suggestion...even the ad for the bosch o2 sensors says "Can cause engine performance problems, such as surging and hesitating" when malfunctioning. Sounds a little familiar to what I'm fighting with for sure... I'm getting one tomorrow morning. Will post results...

sven914
07-06-11, 03:46 PM
Replace it with an AC DELCO sensor; DELCO is OEM for Cadillac. You don't need anything more higher end than that and a non-OEM sensor can give false readings to the computer.

schaefer
07-16-11, 07:56 PM
so, if you decide to replace the entire engine with a carb version, you dont need the computer at all?

csbuckn
07-16-11, 08:22 PM
You dont need a computer to run a carb'd car. You just need 12v to the coil with ignition on, and power to the starter. No sensors or computer stuff is needed. Dont know what the two smaller wires for the alternator are for though.

henrydean40
07-18-11, 04:48 AM
The non-computer version sounds pretty darn good right now :yup:, however, the other day I actually had everything working perfectly. Feeling like I finally solved the problem, I boasted for a few days to my brother about how it was "running like a cadillac again" and that I absolutely loved the car and wanted to hold onto it for a LONG time. It had significantly increased HP that was clearly noticeable, the hesitation was essentially gone, the throttle response was killer, I could pass on the freeways no problem, and I could accelerate from a stop without a hitch....... UNTIL.....2 days later I had to get out of someone's way and I tried to aggressively accelerate, all of a sudden I felt the dreaded hesitation come back again. The increase HP is still there, but the hesitation is definitely happening again.

I'm kind-of stumped at this point: I replaced the O2 sensor (it was a Bosch again because that's all they had, and I was hoping the one I got first might be defective. I plan to replace again with ACDelco ASAP). But I also replaced the spark plugs with Hi-perf iridium plugs ($6.50ea), hi performance Accel plug wires (one wire on the previous set had a broken distributor contact, so I was essentially running on 7 cylinders...that'll cause some hesitation for sure), Hi-performance ignition module and tightened a few bolts. All those changes resulted in two days of AMAZING PEFORMANCE by this HT4100. It fully renewed my hope that this setup can indeed be a car with decent performance and HP if everything is working correctly. But then when I got into the gas pedal and the issue came back......it makes me feel like it could be the intake manifold possibly leaking (which error codes have suggested) but it's a real hassle getting to the bolts. They are under the rocker arm covers, which are covered by hoses, fuel lines and all kinds of stuff. :banghead:

I'm also getting all the error codes as previous (13, 44, 52, 53), so I'm actually looking into replacing the ECM since most of the codes mention it as a potential cause for the error as well.

68cadu
07-18-11, 10:04 PM
I would think that since it runs fine and then runs like crap at other times it would be a computer issue. My 84 runs like crap all the time, but sometimes it's really bad. I'm going with a new ECM. For $50 you can't go wrong.

68cadu
07-18-11, 10:12 PM
I would think that since it runs fine and then runs like crap at other times it would be a computer issue. My 84 runs like crap all the time, but sometimes it's really bad. I'm going with a new ECM. For $50 you can't go wrong.

TheRedSharon
07-20-11, 02:23 AM
Similar problem with my '85, same engine. For me, it was the throttle position sensor; i replaced it, and haven't had any trouble since. If its not that, then I haven't any idea what it could be.

csbuckn
07-20-11, 02:47 AM
^Isn't there a way to test them? Sven might know, maybe with a DVOM? I know a few people here have had issues with them. I do know they cost a little more then your average TPS.

jzchen
07-20-11, 06:01 AM
The non-computer version sounds pretty darn good right now :yup:, however, the other day I actually had everything working perfectly. Feeling like I finally solved the problem, I boasted for a few days to my brother about how it was "running like a cadillac again" and that I absolutely loved the car and wanted to hold onto it for a LONG time. It had significantly increased HP that was clearly noticeable, the hesitation was essentially gone, the throttle response was killer, I could pass on the freeways no problem, and I could accelerate from a stop without a hitch....... UNTIL.....2 days later I had to get out of someone's way and I tried to aggressively accelerate, all of a sudden I felt the dreaded hesitation come back again. The increase HP is still there, but the hesitation is definitely happening again.

I'm kind-of stumped at this point: I replaced the O2 sensor (it was a Bosch again because that's all they had, and I was hoping the one I got first might be defective. I plan to replace again with ACDelco ASAP). But I also replaced the spark plugs with Hi-perf iridium plugs ($6.50ea), hi performance Accel plug wires (one wire on the previous set had a broken distributor contact, so I was essentially running on 7 cylinders...that'll cause some hesitation for sure), Hi-performance ignition module and tightened a few bolts. All those changes resulted in two days of AMAZING PEFORMANCE by this HT4100. It fully renewed my hope that this setup can indeed be a car with decent performance and HP if everything is working correctly. But then when I got into the gas pedal and the issue came back......it makes me feel like it could be the intake manifold possibly leaking (which error codes have suggested) but it's a real hassle getting to the bolts. They are under the rocker arm covers, which are covered by hoses, fuel lines and all kinds of stuff. :banghead:

I'm also getting all the error codes as previous (13, 44, 52, 53), so I'm actually looking into replacing the ECM since most of the codes mention it as a potential cause for the error as well.

This with 10 degrees or 13 degrees. (I would stick with 10 personally...)

TheRedSharon
07-20-11, 09:53 AM
^Isn't there a way to test them? Sven might know, maybe with a DVOM? I know a few people here have had issues with them. I do know they cost a little more then your average TPS.
I don't know how to test them. The idiot who screwed up my car actually managed to correctly diagnose the problem, and I did a burnout (accidentally) after he played with it.

jayoldschool
07-20-11, 11:33 AM
Yes, you test a TPS by measuring the output while open and closed. The procedure (and specs) are in the FSM.

henrydean40
09-10-11, 12:31 AM
ITS A MIRACLE!!!! :worship: There is a god!!
After months of replacing parts trying to fix this hesitation issue, I finally got it. It was just a couple of worn out fuel injectors that was causing me all of the headaches.

I finally caved in and took the car to Meineke to have the fuel system checked, they said that everything was fine except the fuel injectors were worn and it would cost $2000 to fix it.....yeah he really said that :cookoo:. (He said the he couldn't find the fuel injectors for any cheaper than $600ea and it would cost $800 in labor to replace them). After nearly crapping myself, I said no thanks and hopped right on Rockauto.com. And what do yah know?......they have OEM injectors for ≈$100ea, and even high performance versions for around $110ea. I just droppee them in today with about 45 minutes of very light, easy work ($800 my A**) and the car runs like an absolute dream - even better than I was hoping for. Its as smooth as can be, the hesitation is gone, the shifting is flawless, there is noticeable power difference, the fuel economy jumped from average 10.0mpg to 14mpg and it sounds like it purrs again..........she's back to running like a cadillac. I LOVE IT AGAIN :cloud9:

ROCKAUTO.COM RULES

csbuckn
09-10-11, 02:15 AM
Rockauto is pretty dang good. I always thought we should have a thread on them where you can post any discount codes they give you.

raiderromo2002
01-23-12, 09:05 PM
i have a 81 cad. eldorado biarratz..swapped the motor for a 1983 engine HT 4100 v8 not know all the issues with these motors. car ran great when we put the motor with the complete dash and computer. car sat awhile, and went to drive it and drove fine then, started to bogg down on acceleration. since then, i have done a complete tune up, wires, plugs, oil pressure sensor, map sensor, replace antifreeze, fuel pump, and filter, air filter, cap, rotor, distributor cap, coil inside of cap and components insides distributor condesor, rebuilt fuel injectors, replace TPS sensor, checked all vaccum lines, i am at a loss. tried to set the timming, my mechanic thinks that maybe the timming chain jumped a gear. it sounds good when its at idle, problem is that to start the car i have to spray engine start spray in carb. once on, it stays on. runs pretty smooth...once you hit the accelerator , it boggs down and wants to shut off, like its not getting enough fuel... this is so weird, because car ran great and all of a sudden it started to bogg down on acceleration. we did a compression test, and it needle didnt move and first crank, then showed about 150-160lbs. mechanic thinks valves are not opening and closing all the way...because of lack of use and oil changes. but vehicle was hardly driven. any suggestions on what to check??? next step is to check the timing chain, and maybe rebuild heads....i have dropped alot of money in this car. thinking maybe its time for a different engine, something without a computer..older chevy motor. this is not a daily driver...sunday driver..any help will be appreciated.. thanks

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was your caddy bogging down on accelation?? i had my fuel injectors rebuilt a shop. they seemed to spray the fuel better after i installed them, but problem still existed..dont know if i should just buy some like you did. it seems like my car is not getting enough fuel when i accelerate. just replaced the TPS sensor...(is there a special way to install that thing). seems like its just a bolt on. thanks for any info

camarotim
01-26-12, 01:40 PM
Have your mechanic pull the valve covers and check for broken valve springs. I had a 4100 in my 83 de ville and it did this. It idled good and didn't make any noise, but bogged bad and wouldn't hardly run if you tried to rev it up. Not sure if this is your problem, but it's worth a look before throwing more parts at it.