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2005 STS 4.6L
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Discussion Starter #1
The white whale I have been chasing for a few years. My LH2 (~65k miles) has high LTFT (over 20%) on both banks during high engine vacuum, though bank 2 is higher and thus occasionally (maybe every four months) sets a P0174 after extended driving. At cruise or acceleration, LTFT are above 0% and below 10%. Engine vacuum is ~19.5 in/Hg on a warm engine at idle. No noticeable driveability issues and getting ~19.5 MPG. All components are stock, no aftermarket (oiled) air filter either. I have completed the following:

-Tested MAF against known good MAF, no problem found;
-Tested MAP against known good MAP, no problem found;
-Tested throttle body against known good throttle body, no problem found;
-Replaced intake manifold gaskets;
-Replaced fuel filter (overdue for change anyhow, and noticed line was holding strong pressure);
-Swapped bank 1 for bank 2 fuel injectors, no change in fuel trims;
-Disconnected canister purge solenoid to eliminate potential leaks in this system, no problem found;
-Three engine smoke tests (because I am becoming unhinged) using a Black and Mild on warm and cold engine, each time only saw a leak at airbox before MAF;
-Red Herring: camshaft actuator magnets are leaking oil so I replaced bank 1, no change in fuel trims. Will replace leaking magnets on bank 2 when I have the patience to remove the power steering pump

The way Torque Pro scan app reports these fuel trims is a textbook example of vacuum leak (I even created some to confirm the readings). But I cannot find any leaks. Any reason to suspect the accuracy of this app/ELM327 dongle? The LH2 has no EGR or PCV valves, and I inspected the PCV, throttle body to manifold, brake booster, and MAF to valve cover hoses and confirmed they are sealed.

I crawled under the car and inspected the exhaust and the pre-cat O2 sensors to the best of my ability. Though I could not see all of the exhaust, I did not find anything obvious. An exhaust leak and/or O2 sensor failure is all I can envision unless it were an ECM fault (reluctant to fire parts at the car). But those failures (along with the fuel pump) wouldn't jive with the high LTFT at high engine vacuum, would they?
 

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08 STS 1SG HUD ACC F55 AWD, 08 STS 1SG Platinum HUD ACC F55 RWD
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Just possibilities. Did You smoke test the exhaust system? And disconnect the large vacuum line at the brake booster and plug the hose. Drive the car in the way that produces the over 20 LTFT. Caution because you only have regular brakes (no vacuum assist) so do not get into a tight situation. I hope you find the LTFT is normal. Good Luck.

Another thought, was there a fuel shutoff on deceleration that was select-able with a TechII?
 

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2008 STS Northstar RWD, 2000 Trans Am WS6 6 spd, 1968 LeMans convertible 6.6
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234 Posts
I suspect bad O2 sensors, I'd replace the upstream pair first.
 

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2005 STS 4.6L
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Discussion Starter #4
Just possibilities. Did You smoke test the exhaust system? And disconnect the large vacuum line at the brake booster and plug the hose. Drive the car in the way that produces the over 20 LTFT. Caution because you only have regular brakes (no vacuum assist) so do not get into a tight situation. I hope you find the LTFT is normal. Good Luck.

Another thought, was there a fuel shutoff on deceleration that was select-able with a TechII?
Appreciate the input. The brake booster holds vacuum well with no apparent leaks and I wish Torque Pro had the capabilities of a Tech-II, but it's mostly read-only PIDs. Regarding smoke testing the exhaust, I have been mulling over how to do that. Given the large volume and that the smoke would have to overcome at least one muffler, resonator, and catalytic converter, do you think the cigar method would still work? Or is it time to use an actual machine? I suppose I could remove the post-cat O2 sensors and try to blow smoke in there. . .
 

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2005 STS 4.6L
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Discussion Starter #5
I suspect bad O2 sensors, I'd replace the upstream pair first.
I would like to at least swap bank 1 and bank 2 to see what happens. But they and their connectors are difficult to access from under the car. Do you know of any tricks for removal?
 

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08 STS 1SG HUD ACC F55 AWD, 08 STS 1SG Platinum HUD ACC F55 RWD
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Smoke machine - I made my own with a Qt mason jar and lid. Lined the bottom with aluminum foil (not flat but wrinkled up to form a cup in the bottom. Shredded cardboard in the cup smokes well after starting with a propane torch. Two holes drilled in the lid. Two hoses in the holes. One hose to a cheap tire pump (12 volt). smoke comes out of the other hose and with adapters (cloth wrapping) will fit the brake booster hose or the end of the exhaust pipe. Size the hoses to fit the pump and seal both hoses to the lid. Turn the pump on and off to keep the cardboard smoking but not actually flaming up. I do not believe the cigar method gives a good test but this does. Sometimes you have to push smoke for 5 min before the leak point shows up.
Swapping O2 sensors - Check the part numbers to be sure they are the same before removal. Different part numbers probably mean different length of the connecting wire. I think they actually connect high up behind the engine. There is a lock pin that has to be removed before you can push the tab to release the connector. Drivers side best access from below reaching up. Do not know about the passenger side. If both sides are showing 20 LTFT, how will swapping O2 sensors determine anything? Please report back with results. Good Luck
 

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2005 STS 4.6L
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Discussion Starter #7
Smoke machine - I made my own with a Qt mason jar and lid. Lined the bottom with aluminum foil (not flat but wrinkled up to form a cup in the bottom. Shredded cardboard in the cup smokes well after starting with a propane torch. Two holes drilled in the lid. Two hoses in the holes. One hose to a cheap tire pump (12 volt). smoke comes out of the other hose and with adapters (cloth wrapping) will fit the brake booster hose or the end of the exhaust pipe. Size the hoses to fit the pump and seal both hoses to the lid. Turn the pump on and off to keep the cardboard smoking but not actually flaming up. I do not believe the cigar method gives a good test but this does. Sometimes you have to push smoke for 5 min before the leak point shows up.
Swapping O2 sensors - Check the part numbers to be sure they are the same before removal. Different part numbers probably mean different length of the connecting wire. I think they actually connect high up behind the engine. There is a lock pin that has to be removed before you can push the tab to release the connector. Drivers side best access from below reaching up. Do not know about the passenger side. If both sides are showing 20 LTFT, how will swapping O2 sensors determine anything? Please report back with results. Good Luck

The sensors are the same, just a PITA to reach. Though they both read 20+ at high vacuum, Bank 2 is consistently higher (hence only the P0174). If I switch the two and the relationship does not change, I would be more inclined to believe the sensors are accurate. But it may be a moot point if I cannot remove them.

Never thought about burning cardboard. Thanks for the suggestion, I'll look into it.
 

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2005 STS N* 1SF
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When you changed the intake gaskets did you take a good look at the plenum duct hose? They tend to crack on the bottom under the clamp. If you smoke it chances you won't see the leak because the throttle body is closed. If you try smoke from the PCV hose that connects to Cai and close off at the maf you might see it.
 

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2005 STS 4.6L
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Discussion Starter #9
I was hopeful that would be the problem, but all hoses were intact when I inspected them.
 

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2006 Cadillac STS-4 1SG V8 PREM PERF V8
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Mines a 2006 1SG V8 and I'm dealing with 171&174 p0300 and has been on rare occasion tossing a 1101 and P0068 at me ..
it definitely seems like a vac leak . I did find one at the manifold for the brake assist.. oil had been getting at the rubber hose and swelled it loosie hoodie annnnd there is not a hose clamp Because it fits on a nipple in a recess in the way back of the manifold
I replaced the hose for 20 bucks I definitely stopped a larger leak for sure but the car actually runs worse although The idle is better 171 and 174 come up all the time now.. I'm at 152k now the problem is getting progressively worse ..
Long term fuel trims average at +10 b1 & +15 b2 but I've seen them over 20 particularly on a low load hot day idle . Shorts typically are +\- 5-10 but often hang out at 0 or +-1,2 my map sensor is reporting a baro of 14.3-14.7 with the map reading vac at idle all accessories off of like 6.3-6.5 i feel like it should report in the 4's somewhere ... mileage is about 18-20 depending on how horny she has me at the time .I get no black / gray or blue smoke at all .
and my clamp on Amp meter and scope show at least mostly even compression stroke draws from the battery
This car is still fun around town but sucks up hill as it's surging and cutting in and out while lacking power especially in manual mode 5th gear light load around 2000 rpm so I'm always over 2200 in operation which doesn't help my gas problems .
The car has had its scheduled maintenance
Mobil one 5-30 and always at 4000 miles and I did install denso double platinum plugs amd have about 20k on them now (was told it's the factory plug, ) they're not what I retrieved from the heads tho .
I had cleaned the throttle body and I did look at the coupler for the manifold -T/B, it all seems right when I did look but now this guy above has me wondering. No cracks but I didn't look under the clamp So i t may be the leak. so I'm with a 8mm now to go look so I'll fill everyone in if that bastard is the issue . I mean it looks tight and right and I'll be surprised if it's bad .
the maf sensor looked dingy so I tried to clean it thinking it was under reporting its intake
This helped but I found myself replacing it in the end .. it's a Carquest blue brand new unit
This seemed to solve the issue for about an hour .. I'm now hearing to only use the Vdo Siemens factory original unit . I'll take advise on anything any of you may have tried that worked or pinpointed the issues
I am seeing a significant knock retard in cylinders 5,6,7,8 and I was thinking she's starved for fuel on that driver bank#2 but it's numbered even and odd bank
But bank two is that deadheaded fuel rail so is it somehow catching little bits of air or not receiving enough pressure at the injector to support a good flow and atomized pattern
I also have a knocking up in the valve train
It's definitely driven by the cams rotation has anyone ever heard of a gm knock retard program that could be mistaking engine noise as detonation and as a result killing the timing making it pull power back
I know eventually ill
Figure this out. But if anyone has a trick to try or a diagnostic procedure that gets to he problem I'll even cash app some money for your time
I'd rather give it you rather then the parts store
Thanks so much
Dave
 

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08 STS 1SG HUD ACC F55 AWD, 08 STS 1SG Platinum HUD ACC F55 RWD
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Shots in the Dark - Have you changed your fuel filter? Maybe clogged fuel injectors?
 

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2005 STS 4.6L
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Discussion Starter #12 (Edited)
Dave-

Had a similar issue with oil swelling the booster hose at the back of the manifold. I replaced the hose, but no discernible difference to fuel trims. Not sure why oil was present there as it does not appear to be sucking in through the CV hose nor backing up through the ports. So it goes. I also had a similar experience with a new MAF. I replaced it and the fuel trims corrected for about 20 mins of highway driving before returning to their previous levels. Perhaps the delay had something to do with satisfying some enable criteria?

CWB mentioned the fuel filter. If you haven't, given your mileage, you may want to consider it regardless of whether it were the issue. I replaced mine, but again, no discernible difference to fuel trims. You can also try swapping bank 1 for bank 2 injectors to see if your knock retard changes to different cylinders.

Have you checked the seals on the dipstick and oil filler cap? Low probabilities for failure there, but they are easy to check off the inspection list. Eager to hear your solution. Crossing my fingers it isn't exhaust related.
 

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2006 Cadillac STS-4 1SG V8 PREM PERF V8
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Ok guys jut so you all have my background . I am 41 from New England Ive held ASE Master a1-a8 Certs , advances level engine performance specialist L1 and C1 for service consultant for 10 years Further I am an mass. & Ri safety and enhanced emissions inspector and part of the C.I.R.T. Emissions repair team in Rhode Island I am an excellent source of diagnostic information..
sadly a fuel filter isn't the issue ..I will change it but not unil after I pull he injectors ( I want to see if debris got past the original filter that gm supposedly installed correctly and cleanly!!
fuel pressure would drop out toward max flow requirements .. same with a weak pump or bad relay should it have corrosion across its terminals etc. my fuel pressure is within spec
I am thinkin we have clogged injectors
Thy deliver adequately at idle and under full vacuum but when vacuum drops and more fuel is needed they (some of them) do not have the required pressure to open as fast and stay open as long as needed to match up to an otherwise healthy injector due to a difference in pressure differential ..
I was reading about the grounding circuit having some level of voltage drop causing less then desirable voltage across the injector winding even tho the computer compensates continually for voltage that it detects ..
it's something I need to test because I hear it's an issue not many know about and , well it would cause this type of concern .
But before that and only because I hate digging for wires in this car I'm pulling out the injectors and see if he screen is clogged at all on these problem cylinders.. tsb's regard restricted injectors causing this issue
I will be (without wire digging) doing an injector power and ground voltage drop testing wih my 100mhz lab scope to true batt+ and batt-(at the injector convection) and I'll post that later today if I can get to doin it

Can someone give me actual readings from the map sensor on their LH2 at a specified idle speed and with zero and fully loaded electronic values
I would take the maf readings as well if someone has that info aswell
 

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2006 Cadillac STS-4 1SG V8 PREM PERF V8
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Ok guys , I pulled her apart as I told he wife she has to buy a car so we can get around ..just in case I pull it apart (I won't reassemble until I have root failure cause and a solution w/parts)
Her car went on he road couple of days now and it seems reliable
Pulled injectors and manifold off .. all but 2 bolts man/head were finger tight .. so loose that a 1/4" drive didn't even have a jerk as he tension left he bolt .. all he injectors are black inside with a graphite looking soot. And the spray head had noticeable deposits , even looked clogged or partially clogged

so I cleaned the manifold hot bath in The sink
Rinsed Thoroughly Replaced all gaskets and installed but while he manifold was off I took some wd40 to all the intake ports and valves I could access and cleaned them up as good as possible and vacuumed and blew them out
Lots of crud in this intake and ports
Especially seeing I've run a few intake cleaners thru it ..
I soaked all 8 injectors in seafoam for 8-10 hours then carefully cleaned them

then I emptied the fuel from the rail and filled it back up after I installed the injectors With a 70% mixture seafoam and Sunoco 94
70% seafoam
30% fuel
Then reinstalled it all
Car didn't want to start but eventually came I see it my way .. ran her for a day and she ran well
Then check engine light pops on with code p0171 p0174
Lookin at he fuel trims now we are at 20% plus fuel .. sometimes even 30
So as I'm fixing obvious vacuum leaks and making fuel more available it's gettin worse
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Well I said enough
The left side bank 2 has been making a timing noise for some time .. it's not bad but hey I've had position sensor failure codes and now I have a no cam crank correlation learned ..
well I have found a nylon shoe cut up the middle and dislodged from the aluminum slack adjuster
She's getting new timing components
Does anyone have a parts list and vendor that has proven reliability ?
I see cloye's on amazon butI'm looking for everything all the components not sure Ineed new sprockets but if you all say it is necessary I'll do them
 

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08 STS 1SG HUD ACC F55 AWD, 08 STS 1SG Platinum HUD ACC F55 RWD
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Wow - congratulations. Such a good catch on a problem that could have turned to catastrophe at any minute.

Your engine is so clean inside and out. Lucky car to be pampered by you.

Before you actually remove the chains, let us know if the timing is still correct. Good learning experience for the rest of us. I am curious as to the details of the noise you were hearing so I can correlate with this actual damage. Good Luck.
 

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2006 Cadillac STS-4 1SG V8 PREM PERF V8
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Well according to the manual you have to brin it tdc and lock the cams so I don't see me not noticing that .. I'm feelin with the correlation codes and low intake map readings the cams are severely retarded. I'm also thinking that has caused the compression to be reduced and all the forward and backward flow thru the intake and exhaust valves is causing the fuel trim issue
That noise I have been hearing is a knocking sound not so much a timing chain rattle it almost sounds like a main bearing but it's right up on top.. and I'm leaning toward a cam bouncing up and down as it ramps up and down the follower
A sort of " nugga nugga nugga "sound
I have to pull some cam main caps off and plastiguage the journals in The head
I don't see any bushings or bearings in there so that will be a cyl head replacement and a studded block
If the ol girl Pans out ok I'd like to put some beehive valve springs in and do they make better HLAV's (lifters) perhaps even wanna larger ratio cam follower upgrade and adjustable cam or crank sprockets ? I think another 2 deg intake cam advance will give her a nice bottom end that she could use.
Thank you for the compliments regarding Dillies hygiene .. it was riddled with crud because my aunt has no idea how to bring her vehicles for service
Seafoam high mileage 1 16 oz cam in The oil for 400 miles before a filter and oil change does that to most any motor.
look at the oil that comes out inthe attached photo .. looks like the motor had a spun bearing or ten lol I assure you it doesn't
584370
AED5B63A-9040-474A-9368-D278BE7C4F64.png
 
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