JeffD

So I had bad hesitation from a stop when accelerating. Started checking things on the engine and eventually found that the EGR valve wouldn't hold any vacuum. Order the replacement part and did a remove and replace. Got everything back together again and cranked the engine. Car catches but will not stay running. If I feather the gas to higher rpms it will stay running, but as soon as I go steady with the gas at any rpm the engine stalls. I have checked and rechecked vacuum lines, plug wires and am getting now where. I am convinced it has to be vacuum, but I am at a loss as to where to look now. Any ideas?

Jeff

five7kid

iTrader: (14)

Check the gaskets for the parts you took apart to get to the valve.

JeffD

Follow up to my initial problem. I had difficulty finding my vacuum leak because the car would start and then immediately cutoff. I went to the store and bought some incense sticks. I lit 2 of them and then put them in the general area where I suspected the vacuum leak. I had my son start the car. I found the leak by watching where the smoke went and it was going right to the cold start injector area. We took the driver side plenum off and also removed the CSI/CSV. We immediately noticed that the CSI mounting plate was bent right where the torx bolt goes thru to the intake. I suspect that when it was being tightened down it was "cocking" the CSI partially out of place giving me the vacuum leak. Now the car will start and stay running, but I am still back to my original problem of the hesitation from a stop. Even with the car parked when I do an engine rev, the engine almost acts like it can't get enough fuel or air for maybe 1/2 a sec then catches and revs up. I have also noticed that when I first start the car it runs with a rough idle for about 5 minutes and then idles fine...until i put it in gear and try to drive. Any additional ideas on what is causing this engine "cough"?

JeffD

I am attaching a video file of what my car is doing when I press the accelerator. The engine hesitates everytime I press the accelerator. You will hear some "pops" in the video that sound almost like small backfires. I can get a better audio/video file if that helps anyone out, but I hope this will get some ideas rolling. Thanks a bunch.

Jeff

The video is in .mpg format. I had to slaughter the quality to get it into a manageable download size.

bcmag

sounds alot like what mine was doing before i replaced maf.would also check fuel pressure.

JeffD

Update on what I am seeing so far. I hooked up a fuel pressure gage and found that I have anywhere from 26-32 psi while the engine is running. The needle is moving around quite a bit too. It fluctuates between the above readings. I do not have any noticeable pressure bleed off so I feel quite confident at this point that the injectors are not leaking. Should the needle for the pressure gage be moving around like that or should it be steady and rise or fall as engine speed increases?

jrfidencio

iTrader: (1)

your fuel pressure should go up or down and ur rpms go up or down but it sounds like ur fuel pressure is alittle low should be around 32-38psi. check for vaccume leaks first get some brake clean and spray around vaccume lines.

bcmag

pressure is definetly low.clamp return lie BRIEFLY and see what kind of pressure you get.may be weak pump or bad regulator.i would expect to see atleast 70 with pump dead headed.

wyochimneysweep

iTrader: (1)

Plugged filter. most of the time when i check fp its steady at one psi. i'd hook up a vacuum gauge and make sure vacuum isnt bouncing around also. how about your timing. is that correct or bolt come lose?

JeffD

Just came from the garage. Fuel pressure is bouncing steady between 28-32 psi. Car was idling rough, but I also heard a ticking noise from the PCV that seemed a bit unusual. I pulled it out and plugged the end with my thumb. Rev'd the engine to about 2000 rpm for ~30 sec and then put the PCV back in. The ticking noise went away and the car is idling a bit better now and the hesitation I had before is slightly better. I let the engine get good and hot and had my son watch the gage as I put it in gear to add a little load to the engine. Fuel pressure stayed about the same, but he did say it was bouncing around from about 38 down to 15 psi. The gage isn't liquid filled so I think a good portion of this is just overshoot. I am a bit puzzled as to which direction I should go in. Do I have a vacuum leak that is leading to the fuel regulator fluctuating fuel pressure or do I have a fuel pump or fuel filter issue?

I'll try pinching off the return line to see how the pressure responds.

JeffD

Where is a good spot to hook up the vacuum gage? What should I expect to read at idle?

JeffD

I checked engine vacuum and it was dead on 21 in.-Hg. While looking around the back side of the engine I heard another slight hissing sound. Started moving vacuum lines around and found that the vacuum line going to my cruise control had been laying over a spark plug wire and had worn through, but it was resting enough on it to not cause a bigger vacuum leak. Well in the process of replacing the EGR valve I bumped it off its "resting" point and now I had the "bigger" problem. Once that was fixed the car was running like a champ. No hesitation during acceleration and smooth idle. I also failed to mention that I let the car get up to full operating temp...good and hot. Right now everything appears ok. We'll see in the morning.

JeffD

Started the car this morning and I am back to my hesitation problem. Took my other car to work. I think I am going to let the car get back up to temp when I get home and see if that has any impact on what is going on (it was working great last night!). This is getting a bit frustrating...

Rayzor32

iTrader: (1)

Does it still stall when you disconnect the vacuum line from the EGR? The car will stall if the EGR opens on idle. Also did you use an aftermarket EGR?

JeffD

I will look at disconnecting the EGR when I get home and see if this has any impact. Also, the EGR valve is stamped with the letters GM + original part number.

Rayzor32

iTrader: (1)

Also when you do that check and see if the line connected to the egr is pulling any vacuum at idle. The reason I ask if it was aftermarket is Ive seen a lot of problems with the aftermarket ones as they are meant for lots of applications. You have to get one that is calibrated for your engine which is why i recommend always getting a genuine part for egr's.

JeffD

EGR is not pulling vacuum at idle. I am trying Ether around vacuum lines this evening. Already done some and nothing is showing up so far.

Rayzor32

iTrader: (1)

Well I guess you can rule out the egr coming on then, have you replaced the fuel filter yet?

JeffD

No I haven't replaced the fuel filter yet. I guess I am trying to figure out why when I first start the engine I get this "loping" effect like you hear in my video post, but once the car warms up good the problem goes away (or at least is hardly noticeable). Fuel pressure is steady at around 30-32 psi. I am just running out of ideas at this point. I sprayed Ether everywhere and it seems that there are no more vacuum leaks. No SES light. Just puzzled.

Rayzor32

iTrader: (1)

What is the spec for fuel pressure? Sometimes you might have good pressure but not the volume. Keep us informed

JeffD

Ok here is the latest. Put pressure gage back on the car and turned the ignition on. Gage only read 20 psi. Pinched the return fuel line and pressure did not increase. Pushed the pressure relief valve on the gage and had my son try to start the car and it either wouldn't start or would and then shut off again. Released pressure relief valve and the car would start. Tried one more time with the valve and it wouldn't start. At this point I am suspecting fuel flow and/or pressure. I'll change out the fuel filter first and go from there.

JeffD

Replaced fuel filter and I have the same result. 20 psi. Car will start and run (but rough) with relief valve on gage not pressed, but as soon as the valve is opened up the car runs for 1-2 sec rough and then shuts off. Going to go for the fuel pump now.

JeffD

Well I decided not to do the Fuel Pump yet. I have a little less than 1/4 tank of gas and I haven't decided how I want to get it out of the tank. I went ahead and put a new diaphragm into the fuel pressure regulator, but this has had no change (by the way you will need a T10 anti-tamper Torx bit to do this). Pressure is now reading 29-30 psi with engine running and still 20 psi with only key on. I think I am going to run the car out of gas and go for the fuel pump next. I have a couple questions/observations though:

I have noticed when the car is running rough that the fuel gage needle oscillates quite a bit 1-2 psi and that the PCV rattles like a rattle snake.

Should the car be able to run with the fuel pressure regulator vacuum disconnected?

Anyone done the fuel pump r/r before? Suggestions?

Thanks.

KNBlazer

have you checked your timing?

JeffD

Why would you recommend I check my timing?

nate perron

if his car is computer controlled will it run w/out the egr if your state does not smog test or does not dyno test I would just eliminate it I passed another car with just a cat converter and no other smog equipment why bother with some p.o.s part if you don't have to.

wyochimneysweep

iTrader: (1)

It could be the little rubber line in the tank between the pump and the tube out. i see a problem with the car stuting down when you pressure the vavle in. Do you got a massive stream out of it?

JeffD

What was interesting this evening is I decided to use the fuel gage pressure bleed off valve to bypass some of the gas into a gas can while the engine ran. I noticed that there seemed to be quite a bit of air bubbles moving through the line...not a solid stream. It got worse right towards the end before the car shut off because of no gas. I also noticed that when it was just about out of gas the pressure dropped to about 10 psi and the engine was also running very rough until it coughed a couple times and shut off.

Birdstheword

if you're going to go after that pump you're going to need this .
https://www.thirdgen.org/forums/tech...p-not-bad.html

wyochimneysweep

iTrader: (1)

I'd say pull the tank and look at the pump and the rubber hose and if you dont see anything sticking out like a sore thumb to replace the pump the hose and filter. i believe these engines are to be at 36 psi running?

JeffD

Need help on the tank removal. It doesn't seem like the rear axle is coming down far enough to get the tank out. I am a bit confused with some of the terms for the items needing to be removed. It looks like there is some kind of lower control arm that goes forward from the axle area to the frame on both sides. Do these control arms need to be removed as well? I am thinking they are holding my axle up right now because it won't drop anymore and I am not near close of putting the brake lines in danger. Help!!

On a side note I have read that for the TPIs the fuel pressure should be 40-47 psi with key on and just 2-3 (max) under when running. I have also read that the TPIs are very sensitive to line pressure and volume below what is normal, that even a few psi can cause problems like hesitation, lean fuel-to-air, stumbling, etc...

JeffD

So the fuel pump has been replaced. Not too bad of a job overall. Started the car and my fuel pressure now shows 39-40 psi (up from the 28-30 I had before). I will pinch off the return line to verify a pressure build later today when I get back in the garage. Once the tires and suspension get put back together it will get the road test. Right now I don't have any hesitation with the car in idle.

JeffD

Well I am 99.9% sure that the fuel pump was the problem. Not only is my hesitation gone, but the car is running great with much more pick-up off the line. I am convinced now that my car has been running lean for some time it has just slowly gotten worse until a critical point was reached with the fuel pressure and volume.