Drivability = Nil

[90Brougham350]

As many of you know, I've been having drivability problems lately with the CE light coming on. When the vehicle is at normal operating temp, I can reproduce the effect which causes the CE light to turn on. If the vehicle is completely warm and 50+% throttle is applied, the CE immediately comes on, and drivability immediately plummets. Going up a hill while doing this increases the chance of the light coming on. It seems to do it most while in motion. Keep in mind I have to attempt it several times to get it to work, it doesn't happen all the time.

The vehicle bogs, and feels as if it has half its normal power. It's not steady either. The vehicle feels like it wants to go but there's something holding it back, but it is somewhat uneven.

While under medium to heavy acceleration and going up hills, the vehicle also acts this way, but not quite as bad as when the CE light comes on. The CE light doesn't always come on, but once it does, it stays on until the vehicle is shut off. Then, once its restarted, the problem can be recreated quickly. However, the light will remain on if not shut off and the same symptoms will be there, under any type of driving.

I pulled the codes today with a paper clip and got only one: 43. Knock Sensor. I figured the sensor must be going bad and retarding the timing which is why acceleration would feel sloppy and powerless. However, the vehicle was running on 7 cylinders for a while and I'm also wondering if the O2 sensor is bad or fouled. This could certainly put forth a lack of power and performance.

I disconnected the knock sensor to no avail. The knock sensor normally sends 0 volts to the ECM, so disconnecting it would give a perfectly normal reading to the computer. In another post, NODIH suggested either the fuel pump might be failing or the ignition coil might be the problem.

Any further thoughts? I'm going to take a look at the ignition coil but I'm not sure how to tell if it's bad or not. Same with the fuel pump. Anyone have any ideas? I could really use some, I have $00.00 right now and I can't afford to have a mechanic look at it. I bought a new O2 sensor but I haven't installed it yet. Thanks for the help as usual guys, this time, I really need it!

Brian

[carguy16]

not even a free estimate to see whats wrong at a small town shop? tell them its just a Chevy 350 giving you trouble.

Originally Posted by 90Brougham350

As many of you know, I've been having drivability problems lately with the CE light coming on. When the vehicle is at normal operating temp, I can reproduce the effect which causes the CE light to turn on. If the vehicle is completely warm and 50+% throttle is applied, the CE immediately comes on, and drivability immediately plummets. Going up a hill while doing this increases the chance of the light coming on. It seems to do it most while in motion. Keep in mind I have to attempt it several times to get it to work, it doesn't happen all the time.

The vehicle bogs, and feels as if it has half its normal power. It's not steady either. The vehicle feels like it wants to go but there's something holding it back, but it is somewhat uneven.

While under medium to heavy acceleration and going up hills, the vehicle also acts this way, but not quite as bad as when the CE light comes on. The CE light doesn't always come on, but once it does, it stays on until the vehicle is shut off. Then, once its restarted, the problem can be recreated quickly. However, the light will remain on if not shut off and the same symptoms will be there, under any type of driving.

I pulled the codes today with a paper clip and got only one: 43. Knock Sensor. I figured the sensor must be going bad and retarding the timing which is why acceleration would feel sloppy and powerless. However, the vehicle was running on 7 cylinders for a while and I'm also wondering if the O2 sensor is bad or fouled. This could certainly put forth a lack of power and performance.

I disconnected the knock sensor to no avail. The knock sensor normally sends 0 volts to the ECM, so disconnecting it would give a perfectly normal reading to the computer. In another post, NODIH suggested either the fuel pump might be failing or the ignition coil might be the problem.

Any further thoughts? I'm going to take a look at the ignition coil but I'm not sure how to tell if it's bad or not. Same with the fuel pump. Anyone have any ideas? I could really use some, I have $00.00 right now and I can't afford to have a mechanic look at it. I bought a new O2 sensor but I haven't installed it yet. Thanks for the help as usual guys, this time, I really need it!

Brian

[N0DIH]

Is the accelerator pump bad? You can depress it at idle and it should stall the engine.

The symptoms of an Accelerator pump are bog on acceleration, but normal cruise or decel. Might trigger knock sensor or lean fuel mix due to excessively lean mixture under acceleration, enough the ECM can't command enough fuel fast enough out of the Q-Jet. (Is the 350 Chevy in the Cad EFI or Carb? I haven't seen one to know for sure, if EFI, then fuel pump or regulator)

Be very cautious on lean mixtures, they can put holes in pistons!

Oh, an O2 won't cause driveability issues like this. You can rule out the ECM a lot by taking the coolant sensor and disconnect it and then short the 2 pins. This will trigger a fault and it will tell the ECM to stay in open loop, not using the O2 at all.

[90Brougham350]

lol, well, I replaced the O2 sensor tonight after dinner, and went for a short drive, and light throttle was somewhat noticeably better, but I managed to get the CE light back on with harder throttle. There's a throttle body sitting atop the ol' intake, so that rules out the Q-Jet. Thanks for the warning on lean mixtures, I've seen my share of poorly tuned Holleys burning the hell out of spark plugs. I bought the 350 because I wanted the additional torque and acceleration. I figured TBI would be easy to work on like a carburetor but no, I get stuck with sensors all over the damned place, computers here and there, why can't I just swap jets and turn a screw driver!

Brian

[Destroyer]

Originally Posted by 90Brougham350

lol, well, I replaced the O2 sensor tonight after dinner, and went for a short drive, and light throttle was somewhat noticeably better, but I managed to get the CE light back on with harder throttle. There's a throttle body sitting atop the ol' intake, so that rules out the Q-Jet. Thanks for the warning on lean mixtures, I've seen my share of poorly tuned Holleys burning the hell out of spark plugs. I bought the 350 because I wanted the additional torque and acceleration. I figured TBI would be easy to work on like a carburetor but no, I get stuck with sensors all over the damned place, computers here and there, why can't I just swap jets and turn a screw driver!

Brian

I just bought a Holley intake/Edelbrock carb for my 350 91 FWB. I'll let you know whats involved and how easy or hard it was when I'm done with it and how good or bad it runs. I too have had a hell of time with the TBI setup. I swapped out the stock 305 for a 350 and I figured this is the problem. I'm done messing with sensors and computers, lets get back to basics.

[N0DIH]

Be careful on the TBI to Carb, the electric fuel pump delivers around 10 psi, the carb can only handle 5-6. 7 if it is Q-Jet. And that is still on a good day. Does the TBI unit have a return line? You will need it for a regulator.

If you are going non ECM, you will need to modify the distributor to non ECM module and add a vacuum adv can and a center shaft that supports mechanical advance. I have a ESC distrib for a Chevy sitting in the basement. You anywhere near SE WI?

FWIW, I might be interested in your TBI setup for my 80 T/A. If you can actually part with the ECM. Not sure if the car will like that.

So in a nutshell, going from TBI to carb isn't quite a simple bolt on... But not hard either. Oh, and you will lose TCC lockup, which with the typical lazy gears GM likes, you will need to do manually or get a kit from one one of the trans shops. Else the converter will stall while at cruise, overheating the trans in short order.

[BluEyes]

Originally Posted by N0DIH

the carb can only handle 5-6. 7 if it is Q-Jet.

I have always been told that Q's take less pressure than other carbs, and have even heard people running as low as 2# without issue (not in a performance application obviously, but just to drive)
Really, as long as the fuel bowl stays full at WOT, a carb doesn't care how low the pressure gets since it doesn't operate on the fuel pressure like an injector does.

[N0DIH]

A AFB takes the least, Q-Jet the most stock, and the Holley likes around 6psi. More will keep the needle off of seat too much. Likely ok at WOT, but idle and decel will be a problem. Q-Jet's do well. Get Doe Roe's book on the Q-Jet. Well worth it. I think there is a similar one on Holleys.

[brougham]

Did you get codes the propery way to see if it says anything? I wouldn't get rid of the fuel injection just because it has a problem. It's probably easier to fix that then it is to put a carberator on it and it runs better with it too.

[90Brougham350]

That's true, and no matter how well a carburetor is tuneable, fuel injectors will always be able to atomize the fuel better for better economy. I've narrowed it down through the process of elimination to the point where I'm almost postive it's the coil / distributor. Now when I bought the car last December, they told me they'd done a few things to tune it up. I assumed this meant cap and rotor, plugs and wires. Well, the plugs and wires looked decent, but they were $1.09 Champions so I swapped out to Bosch +4 plugs and new wires as well (let's not start another debate on the +4's, we had one 3 months ago).

The car has 128 thousand on it, and from what the service manual tells me along with a gut feeling from the lack of codes, the inside of the cap must have enough carbon to make a new Star of Africa. The cat is also stock as well, so my plan is to go with a new cap and rotor, and straight pipe the cat. I'll drill a small hole for the EGR tube that currently runs into the cat right now so I don't get any emissions problems. I can't think of anything else that could cause the problems like this, because the service manual described perfectly the way the vehicle was acting during normal acceleration.

Thus, I'm just wondering if this will cure the problem, or make it somewhat better. Since resistance is heat and the coil will perform poorly when it gets too hot, could the extra heat generated by all the buildup in the cap, along with the sudden rush of air/gas mixture rushing in to be burned put that much effort on the coil to cause the CE light to come on? I'm hoping something along this path. Thank you all for the help and suggestions so far, you've been a lot more help than those lazy bums over at Chevy High Performance!

Brian

[N0DIH]

I have only had 2 spark plugs FAIL (in less than 14 days no less) and they were both Champions. I will never ever buy them again. Junk!

EGR Tube? There is an AIR tube, as in Air Injector Reactor, from the smog pump. Just plug it, heck, ditch the AIR system, it won't hurt and won't give a code. Don't bother, I just removed it on my 85 Cutlass and the ECM never had a clue. It it to provide addtional O2 to the converter to help with lightoff and converter efficiency.

Signs of plugged cat, fouled out plugs. It will likely idle ok, but get progressively worse as you go higher rpm (aka, higher airflow).

Something else to check. Most cars have a "Clear Flood Mode" which the fuel injectors are scaled back to 80:1 fuel mix when at WOT just before you start to crank the engine over. Try this, mash gas and hold, crank, and listen to the rythm of the engine, it should be balanced and smooth while cranking (if it tries to start back off immediately!!!). If you hear a crank crank crank ug crank crank crank crank crank then you might have a bad valve or a bad cyl. This tests the mechanical compression of the engine. A real compression check might not be a bad idea if this fails.

Cover the basics, plugs, cap/rotor, wires (ohm them out to be sure), weak coil, dirty injectors, bad injectors (Ohm them out, and use a timing light to observe the spray pattern, be careful! This is still gasoline here!!! It can ignite if sparked!!!), weak fuel pump, bad pressure regulator (get a vacuum pump and check, it should hold vacuum for at least 1 minute), check the fuel pressure, worn cam (unlikely if this is a roller cam engine), worn timing chain/gears (you can check for timing chain slack by turning engine one direction, remove cap, note rotor location, then turn engine other way till it moves again, if it is a lot it is worn and very sloppy), typically it just moves the powerband higher and higher, but too far gone and it will cause drivability issues, but in my experience, it will get replaced before then.

Make sure there is sufficient oil pressure, maybe oil pump weak and lifters not pumping up, but likely you will get valvetrain clatter first. Are the rocker arms out of adjustment? Go to zero lash, and turn tighten 1 full turn down. If you have poly locks or other locking type rocker nuts you can go to 1/4 to 1/2 turn beyond zero lash. This increases cam duration slightly. As much as 6 degrees depending on the cam specs.

I know some of this doesn't apply, but it is a random weird thought process of what can affect what.

Tell me this, does it do it at ALL when engine is cold? Ever? This isolates Closed Loop problem to Open Loop problem. To keep in open loop, disconnect coolant sensor and short leads together, tape off so you don't short to anything. This is a logic level, so no real current flows, but the ECM "sees" it as being VERY cold, and trips a fault saying shorted sensor, likely a Code 14. You will never go into closed loop, O2 will never be used, it will go to fixed data tables for spark/fuel. It will run richer and may be harder to start, but will run. An open sensor is interpreted as very hot and will run poorly, shorted is closer to -40F and will run on fixed values. If there is an air temp sensor, this will be used for calculations when the CTS is "bad". There should be one somewhere. Carbs don't have them, as they don't really need them.

How is the TPS, the Throttle Position Sensor. It can do some bizzare things too. If you have an ohm meter, check it at the sensor itself. Go slowly through the entire throttle range. It should have a smooth resistance. If you can, check it with the ignition on, engine off, and watch the voltage from the center pin to ground, it should very stable and linear. Ensure this is set to proper specs at idle. This is the reference point, later they made assumptions that if the car is cold started, the throttle is "closed" and that value is assumed to be the proper value and it just offsets if it needs to.

A weak cap can prematurely fail the coil, as it has soak up the high voltage that has no where to go. So it will eventually burn through the wire's insulation starting to short wire to wire, effectively reducing the number of turns the coil has, and voltage will drop off more and more till it runs like do do.

Something else to look at:
This is something of a tech tip from Mighty Auto parts to test a coolant temp sensor from http://www.mightyautoparts.com/pdf/articles/tt67.pdf:

MAKING YOUR OWN TESTER
A problem in the coolant sensor circuit can be very difficult to diagnose as the ECM, wiring and coolant sensor can reflect the same symptoms.
Here’s a nifty test to isolate the culprit in a GM vehicle. First obtain a 10,000 ohm variable resistor from an electrical supply such as Radio Shack.
With the resistor installed in the harness in place of the coolant sensor, ignition switch on and a scan tool attached to monitor the readings, turn the adjustment on the variable resistor while observing the readings on the scan tool. The readings on the scan tool should respond to the adjustment of the variable resistor. If not, check the wiring to the ECM. If the wiring is OK, replace the ECM. The same test can be performed on other vehicle manufacturer’s systems. However, refer to the test charts to determine the resistance value of the coolant sensor circuit. A variable resistor of a higher ohm value may be required. The variable resistor can be very helpful in diagnosing cold start-up related problems. Observe the code charts for the resistance value for a given temperature. With an ohm meter attached to the resistor, set the adjustment to the desired ohm value. Install the variable resistor in the harness in place of the coolant sensor. This saves much diagnostic time in attempting to cool a sensor down if your first diagnosis fails to identify the problem. In addition, it saves purchasing an expensive coolant sensor just to test with and it eliminates coolant spills. If you are testing in extreme cold conditions, a resistor with a resistance value greater than 10,000 ohms may be required. The variable resistor can also be very helpful in diagnosing vehicles equipped with ACT (air charge temperature) sensors.

So by all means this is not in any special order. I would attack electrical first, then fuel, then the rest.

Tom

[90Brougham350]

Thanks for the help! So my reasoning sounds logical? Well, I've hit another roadblock, the hold-down screw on the passenger side of the distributor cap has a truly F!ed-up head. Looks like someone used a vice grips or something on it, but there's no way in kingdom come I'm gonna be able to put a 7/32 socket on there now. Any ideas, keeping in mind the extreme lack of space to work around there?

Brian

[N0DIH]

They used the screw down cap? I thought that only the Vette and the Cad HT4x00's used those.

Can you add some comet to it to give you more bite?

Or get a dremel in there and make a std screwdriver slot and screw it out.

[90Brougham350]

Alright, well, I replaced the cap and the rotor today, and let's just say that I saw carbon aplenty. I'm surprised it even ran with that much carbon buildup. It idles and runs better, until I hit the gas when she's warm. Still doing the same damn thing. I have about a billion options to pursue, which is next guys? Is it possible the coil is bad? Is there a way to test it?

Brian