A stumbling problem

[Fifth87]

My '96 Olds Ciera, 3.1L, 77k.
Bought it cheap, as a project, with a lot of deferred maintenance.
Had the Check Engine light on when I got it, one code for EGR-insufficient flow detected, 2nd one for a misfire. Unfortunately I didn't write down the codes at the time.
It idles a little rough, and when you put it in drive it bogs down. Accelerating from a stop is very difficult, requiring feathering the pedal to get up to approximately 40mph. There is a pronounced hesitation, and stumbling/bucking when you try to accelerate normally. The warmer it gets, it will buck coasting on a slight downhill grade.
Changed what I suspect to be the original fuel filter. PO installed new Belden Plug wires. Swapped three known good coils and an EGR valve. Coils removed had two rusty/corroded looking terminals. Parts swapped in made no difference. Exhaust smells a bit rich. Testing the fuel pressure yielded 42-44psi key on, engine off, 38psi hot, with the gauge mostly staying steady at idle. Increasing engine speed also increases fuel pressure.
Vacuum hoses underhood don't look great, sprayed them with carb cleaner while running which made no change in idle speed.
I suspect the fuel system despite the pressure test results, but don't want to drop the tank in case I am overlooking something obvious.
Any ideas would be greatly appreciated.

 

[JohnnyG]

I have to agree. It sounds like fuel starvation to me. Is this throttle body injection? I'd clean the throttle body itself. Throttle position sensor is another possibility, as well as throttle position re-learn.
In my experience, fuel tank filter causes most issues at high load/high demand situations, not coming off of idle.

 

[Fifth87]

I have to agree. It sounds like fuel starvation to me. Is this throttle body injection? I'd clean the throttle body itself. Throttle position sensor is another possibility, as well as throttle position re-learn.
In my experience, fuel tank filter causes most issues at high load/high demand situations, not coming off of idle.

Port fuel injection. I haven't even looked at the throttle body, or considered the TPS. I can't get it up to any speed that would meet the definition of high load, aside from a hard take off from a stop, which it can't do. Hills are too much of a challenge right now. Bottom of a hill at the speed limit (35) half way up it is down to 15 and bucking/shaking violently unless you back off the throttle.

 

[mk378]

Does it run on all 6 at idle? Disconnect fuel injectors one at a time to test. Compression test would be good to check basic mechanical condition.

 

[Zaedock]

Intake manifold gaskets are a very common issue on these engines.

 

[chemman]

Check the fuel pressure regulator to make sure it's diaphragm is not ruptured.

 

[Fifth87]

It runs on all six at idle, I cannot reach the electrical connectors for the injectors without removing the upper intake manifold. I wish I could reach them to test that. I have checked/tested the Fuel Pressure Regulator and it tests ok, also no fuel in the vacuum connection to it. The intake manifold gasket issue is something I am aware of, no oil in coolant or vice versa. I do expect to do them at some point. I plan on borrowing a compression tester from a co-worker this week.
Mechanical condition... It has piston slap, bad- when it warms up, it diminishes, but at start-up it sounds ugly.

 

[Warstud]

You probably need to clean out the EGR passages. Start with the Throttle Body

 

[wolfox03SS]

Agreed here. Does the brake pedal also sink to the floor too easily?

A partially wedged open EGR can cause your symptoms and cause the brake to fall to the floor in stop and go traffic. Unbolting it, clearing the screen (if equipped) and leaving it aside - start the engine for a few seconds. It will be loud, but hopefully any carbon "rocks" and chunks will fly out. Clear the EGR valve pintle with compressed air and carb-n- choke cleaner, reinstall. Should be good until it plugs again.

 

[Fifth87]

That was my first line of thinking, EGR, especially with the code. I put on a used one I had which was known good. So I was disappointed that didn't. The code has not reappeared. Brake pedal is good, brakes replaced as they were metal to metal.

 

[tiger862]

Check for carbon on valves.

 

[71Chevyguy]

Dealt with something like this on a Monte Carlo once and it ended up being melted cats. It had a huge fart can exhaust on it and was really quiet. I did intake gaskets on it since that is a typical issue. Luckily I did because there was no sign of issues but when I drained the oil, coolant came out first then oil. They then had the cats replaced and the car ran perfectly after that.

 

[Fifth87]

The cat did come to mind. I am really hoping that isn't it. It does run quiet. Any idea how to test for excess exhaust back pressure?

 

[Fifth87]

Ok, some googling answered that question. I'll have to look into an exhaust back pressure tester

 

[Fifth87]

The back pressure tester I ordered showed up. Tested it this morning, that is the issue, a melted cat. Took it on a lap around the block as well with the oxygen sensor removed from the manifold and it accelerates normally.
I despise exhaust work so I am taking it to a local exhaust shop in the morning.

 

[350Rocket]

It runs on all six at idle, I cannot reach the electrical connectors for the injectors without removing the upper intake manifold. I wish I could reach them to test that. I have checked/tested the Fuel Pressure Regulator and it tests ok, also no fuel in the vacuum connection to it. The intake manifold gasket issue is something I am aware of, no oil in coolant or vice versa. I do expect to do them at some point. I plan on borrowing a compression tester from a co-worker this week.
Mechanical condition... It has piston slap, bad- when it warms up, it diminishes, but at start-up it sounds ugly.

I remember when I worked at an independent garage we had one of those cars in the shop running terrible. It turned out to be a cobweb in the MAF.
Piston slap is pretty well normal on those engines.

 

[Fifth87]

Wouldn't be surprised about cobwebs anywhere on this car. It looks like someone fired the parts cannon at it when it started running poorly then parked it.
The piston slap on this one is BAD. I think that is partially why I was able to get it cheap.

 

[Fifth87]

Cat replaced. It runs and drives....but it still stumbles, just not nearly as bad.
No codes set, EGR insufficient flow code has not reappeared.
It has, however, stalled out on four separate occasions, idling in park in my driveway.
No dip in the idle speed beforehand, it just stops as if the ignition was turned off.
I suspect the cat melted down from this pre existing issue. The lack of codes to point me in a direction is frustrating.

 

[350Rocket]

Cat replaced. It runs and drives....but it still stumbles, just not nearly as bad.
No codes set, EGR insufficient flow code has not reappeared.
It has, however, stalled out on four separate occasions, idling in park in my driveway.
No dip in the idle speed beforehand, it just stops as if the ignition was turned off.
I suspect the cat melted down from this pre existing issue. The lack of codes to point me in a direction is frustrating.

Sounds like an ignition issue at this point, if it just shuts right off. At least you made some progress.
I remember feeling really good that the issue was a cobweb on the one we dealt with as the owners didn't have a lot of money to fix it.

 

[Fifth87]

Per your suggestion I pulled the MAF sensor.
No cobwebs. I appreciate your support. I wish I felt like I made progress. I have priced the cam and crank sensors and have been reading the chapter on ignition in the FSM over and over. Very hesitant to fire the parts cannon. It did have a misfire code when I got it which has not reoccurred. But when you attach a scan tool to it you can see that it is, which makes me wonder fuel injectors.
I wanted a project to keep me busy when I quit drinking. Not a project that makes me want to drink!