00 Cav z24
40k Miles

When I start my car, accelerate quickly from a dead stop, or hit about 2.5k RPM going uphill my car hesitates, as if it weren't recieving any gasoline. I was told by several sources that I have to get my engine timing adjusted.

I have no base knowledge of cars, and have been making an attempt to seld-educate myself lately. While searching the forums, the only thing I found that had to do with timing was a timing chain, and I don't know how this would be adjusted, or even if that's what needs to be done.

Any suggestions?

Timing is not adjustable on any modern day cars. This includes yours.

Your PCM could be retardating your timing, if it senses detonation, thats when it retards timing.

Hesitation can be caused by many many things. The first thing I'd be doing is checking exhaust backpressure, since you say it happens above 2500RPMs, or going up hill, in both cases the car is under more of a load than normal.

A clogged exhaust system would show symptons about that time.

Hesitation can also be caused by a weak fuel pump, clogged fuel filter, clogged air filter ( in some cases), the car simply needs a tuen up, plugs and wires if possible.

Good luck

Also your check engine light isnt on is it?




- 2004 Cavalier - 124k, owned since new

My CEL is not on.

I put some fuel injector cleaner in my tank yesterday, no hesitation so far but that doesn't mean the problem is fixed. Some days it's better than others, so I will keep running down the checklist if the problem continues.

How would I go about checking exhaust backpressure?

Also, this information might help the diagnosis: the hesitation can be heard when reving the engine in neutral, but the hesitation occurs at a lower rpm than 2500.

Could this make it more likely that it is infact my fuel injectors/fuel filter?

You can do two things to check for exhaust backpressure. I'm pretty sure you dont have an exhaust backpressure gauge so that is out.

You can remove your O2 sensor from the exhaust pipe, the one before the car. Yes, doing so the CEL will come on and all. Anyways if after removing it, and keeping it out and driving around, the hesitation is not felt you have a plugged exhaust system, actually a plugged cat.
hope that helps




- 2004 Cavalier - 124k, owned since new

Addam Tait wrote:My CEL is not on.

I put some fuel injector cleaner in my tank yesterday, no hesitation so far but that doesn't mean the problem is fixed. Some days it's better than others, so I will keep running down the checklist if the problem continues.

How would I go about checking exhaust backpressure?

Also, this information might help the diagnosis: the hesitation can be heard when reving the engine in neutral, but the hesitation occurs at a lower rpm than 2500.

Could this make it more likely that it is infact my fuel injectors/fuel filter?

Just keep driving the car and see what happens. The problem could have been the gas cap being loose. Now you've taken it off and put it back on, and it stopped doing so. Could be a bad gasket it the cap as well.

It's definitley not the gas cap, as this is an ongoing problem (several months).

After using the fuel injector cleaner I have had no problems at the usual 2500 RPM going up hill, however just a couple of minutes ago, I did a quick turnaround in a parkinglot to catch my friend going down the street, and after pulling in and romping on the gas it stuttered for about 3 seconds straight until I lifted my foot from the gas and pushed back down lightly.

I have heard of similiar problems being solved by replacing the ignitor coil cover. This is about $120 though, and other suggestion besides removing the exhaust sensor before sinking money into this?

how hard is it to remove the exhaust sensor

What, is the car an Auto? I bet it could be the Traction Control kicking in? Is your AC on when this happens too? AC tends to draw a bunch on the car. As for the O2 sensor, i wouldnt advise removing the one in the manifold, its used to tell the car air/fuel mixtures. The other one is on the side of the Cat past it under the car. I think a 19mm open end Wrench is what I used on mine.

Ender_Wiggin wrote:What, is the car an Auto? I bet it could be the Traction Control kicking in? Is your AC on when this happens too? AC tends to draw a bunch on the car. As for the O2 sensor, i wouldnt advise removing the one in the manifold, its used to tell the car air/fuel mixtures. The other one is on the side of the Cat past it under the car. I think a 19mm open end Wrench is what I used on mine.

Wow thats not good advice.

The T/C doesnt kick on unless it senses wheel slippage.

The A/C dosnt draw a bunch of power, normally 8-10HP is all that is lost with it on.

Now maybe since your so bright you can explain something to me.

I said above to check exhaust backpressure, so how the fark would remvoing the O2 sensor in the manifold check for exhaust backpressure, he needs to remove the one right before the car, as that is part of the exhaust stream.

To the original ignore the poster that I just railed on, he has no clue about cars. Maybe a mod will delete his post before someone else reads it and takes his bad advice.




- 2004 Cavalier - 124k, owned since new

Rob S wrote:

Ender_Wiggin wrote:What, is the car an Auto? I bet it could be the Traction Control kicking in? Is your AC on when this happens too? AC tends to draw a bunch on the car. As for the O2 sensor, i wouldnt advise removing the one in the manifold, its used to tell the car air/fuel mixtures. The other one is on the side of the Cat past it under the car. I think a 19mm open end Wrench is what I used on mine.

Wow thats not good advice.

The T/C doesnt kick on unless it senses wheel slippage.

The A/C dosnt draw a bunch of power, normally 8-10HP is all that is lost with it on.

Now maybe since your so bright you can explain something to me.

I said above to check exhaust backpressure, so how the fark would remvoing the O2 sensor in the manifold check for exhaust backpressure, he needs to remove the one right before the car, as that is part of the exhaust stream.

To the original ignore the poster that I just railed on, he has no clue about cars. Maybe a mod will delete his post before someone else reads it and takes his bad advice.

Apparently you cant read what you wrote, you said twice now, he needs to remove the O2 sensor right before the CAR, i assume you mean CAT, as the in the Catalytic Converter. Why would he remove the front O2 sensor in the Manifold? If i remember correctly, the rear Oxygen Sensor is after the Cat, and not before the CAR, so im not sure why you think im a total moron when it comes to cars. As for the A/C, my car used to do that at low RPM with the AC on, just needed to down shift or be in higher RPM. As for the T/C, it could be malfunctioning, and the car thinking that the wheels are slipping, thus retarding timing, which is a good valid thought. As for your post, maybe it should be deleted, not mine for trying to help the fellow in need.

Car is an auto

AC Is not on when this happens

Would my the TRAC OFF light come on if my TC was malfunctioning? What controls the tc? Is there a chip somewhere?

Addam Tait wrote:Car is an auto

AC Is not on when this happens

Would my the TRAC OFF light come on if my TC was malfunctioning? What controls the tc? Is there a chip somewhere?

If its not working, then yes the TRAC OFF light will come on (providing the switch isnt turned off). As for a chip no, its controlled by the PCM i think, along with the trans.

Yes I mean cat, as in catalyic convertor, dont be a spelling nazi.




- 2004 Cavalier - 124k, owned since new

Ender_Wiggin wrote:

Addam Tait wrote:Car is an auto

AC Is not on when this happens

Would my the TRAC OFF light come on if my TC was malfunctioning? What controls the tc? Is there a chip somewhere?

If its not working, then yes the TRAC OFF light will come on (providing the switch isnt turned off). As for a chip no, its controlled by the PCM i think, along with the trans.

The Z24 doesnt get the off switch like the Sunfire GT does. So, something is definatly being found as a fault in the system. And yes, it and the transmission, are controlled by the PCM.

Rob S wrote:Yes I mean cat, as in catalyic convertor, dont be a spelling nazi.

wasnt about spelling, it was about interpretation.

Stop fighting in my thread >.<

Gonna spring for the coil cover. Wish me luck.

Well I hope you find your problem before having to put all the money into it like I have. My car is doing pretty much the same thing. Go look at the forum "car bucks and dies" maybe a little info. will help you there plus you can see what all we have done and not found the problem.

Rob S wrote:

Ender_Wiggin wrote:What, is the car an Auto? I bet it could be the Traction Control kicking in? Is your AC on when this happens too? AC tends to draw a bunch on the car. As for the O2 sensor, i wouldnt advise removing the one in the manifold, its used to tell the car air/fuel mixtures. The other one is on the side of the Cat past it under the car. I think a 19mm open end Wrench is what I used on mine.

Wow thats not good advice.

The T/C doesnt kick on unless it senses wheel slippage.Unless it is malfunctioning. If the computer THINKS there is wheel slippage it will retard timing (or apply brakes, I have ZERO knowledge of the system chevy used since most of my knowledge is of pontiacs, but not j-bodys). A VERY real possibility is that a WSS is showing intermittent troubles which makes the computer think it is slipping. Since he mentions nothing of any trac lights I would say this is not the case.

The A/C dosnt draw a bunch of power, normally 8-10HP is all that is lost with it on.Do you realize in a car with right around 140 HP stock that is a 5-10% loss in power. Not saying the original poster is not in tune with his car, but I know many people that look at me blankly when they have the AC on and say their car feels so slow right now to them.

Now maybe since your so bright you can explain something to me.

I said above to check exhaust backpressure, so how the fark would remvoing the O2 sensor in the manifold check for exhaust backpressure, he needs to remove the one right before the car, as that is part of the exhaust stream.There are two sensors: one in the manifold and one BEHIND the cat. The one in the manifold aids in the A/F mixture. The one behind the cat tells the computer whether or not the cat is doing its job. It will throw a CEL if the cat is no longer "converting," but not if its clogged. So those are your choices...pick one. To me it sounds you want him to remove the one in the manifold, well guess what? His car will run like crap because it will default and run either rich or lean.

To the original ignore the poster that I just railed on, he has no clue about cars. Maybe a mod will delete his post before someone else reads it and takes his bad advice.

Look in the mirror buddy. You didn't rail on anyone, you just made yourself look ignorant.


"The Blue Bullet"

Addam, You see this is what happens when people give advice , but leave out important details, or they only know half of what they think they know.

To try to diagnose a car on here is next to impossible, Yet we still try it. Nothing beats having it right in front of me to work on.

Any way I wont tell you whats wrong for sure but, with 40k miles on it I would suggest that you have the fuel filter changed, and a tune up, if you havent done so already. If the problem persists try checking the fuel pressure.

Lots of luck,,,,
and guys stop fighting. The guy just wants advice, not an argueing match.


01 cav w/01 3400 gam gt 4t45e

I will tell you now it is your fuel pump, almost 100% sure.

My Gfs car was doing this since I got the car did the engine swap etc. It is the most frustration problem I have ever encountered. At first I thought the car was in need of an exhaust system so replaced it and checked the cat, flowed fine. Then the fuel filter, still nothing, then plugs and coil pack and still nothing. the car would have good days and then bad other days.

The pump is most likely not working properly thus leaning it out, the computer sees this and retards the timing slowing the car down dramatically. Her car lasted just over a year like this and the FP just quit yesterday.

LOOK INTO THE FP!!!



http://members.cardomain.com/vertz24 1998 Z24 Convertible

Chris Fontana wrote:I will tell you now it is your fuel pump, almost 100% sure.

My Gfs car was doing this since I got the car did the engine swap etc. It is the most frustration problem I have ever encountered. At first I thought the car was in need of an exhaust system so replaced it and checked the cat, flowed fine. Then the fuel filter, still nothing, then plugs and coil pack and still nothing. the car would have good days and then bad other days.

The pump is most likely not working properly thus leaning it out, the computer sees this and retards the timing slowing the car down dramatically. Her car lasted just over a year like this and the FP just quit yesterday.

LOOK INTO THE FP!!!

If the fuel pump is bad it will show up doing a KOEO, and KOER test of the fuel pressure.




- 2004 Cavalier - 124k, owned since new