I have an 02 Z06 with 129k miles. I've been having a hesitation problem with my car for the past few weeks that i can't figure out. When it first started happening it would only appear a couple minutes after start up and then go away after the car reached operating temperature. Now it seems to happen any time but only under heavy acceleration, and the hesitation is hard until i let off the gas pedal, if i feather the throttle, it's fine. I don't have any codes present or history of codes. I've replaced the spark plugs and wires, replaced the fuel filter, replaced o2 sensors, MAF sensor, checked for vacuum leaks ,ran techron fuel cleaner through it, checked the fuel pressure (reads about 60psi) cleaned the throttle body, cleaned grounds in engine bay. I'm running out of ideas and just wondering if anyone else has ever come accross this problem or have any ideas on what to check....thanks

Update: I found a wire rubbing against the starter that wore through the insulation. I believe it goes to the crankshaft position sensor, most likely my problem. I will update again if this fixes my problem.

 

Do you have cats, if so have you ever replaced the catalytic converters? If you have original cats I bet if you try and go up a hill after it is warmed up WITHOUT a hard acceleration but trying to maintain speed around 50 mph or so it will do the same.

This is one thing that is not normally going to throw a code.

 

Yes, car is stock except for a k&n air filter. So you're saying my cats could be clogged?

 

Yes, clogged cats. If bad it is very normal that as they heat up it gets worse. You might be able to get the car in the air and hit the cats and hear loose beads in it. I think it is a high probability that cats are your issue with no codes. The mileage is also indicative of old cats starting to fail.

I had the same identical thing happen in my truck years ago. Same symptoms exactly and similar mileage. Ran at idle or constant speed with low rpm/flow but any increase in flow and the engine could not move enough exhaust and felt like it was stalling.

 

Well, i happen to have a set of catless xs power headers coming soon. Hopefully you're right and that will fix my problem! I appreciate the help man!!

 

I think it will solve your problem. I am sure you will update us and let us know so if we need to scratch our heads some more we can.

 

I will definitely update. In the meantime, I was thinking of removing the 02 sensors and taking the car out for a spin to see if the hesitation goes away. Any thoughts?

 

If you run without O2 sensors, your car may not run well at all when your in closed loop. When your in Power Enrichment (PE) it may show you something.

 

Ok, i only plan to run it a mile or two without them in. It won't damage anything right?

 

well, I opened up the exhaust before the cats and took it out for a spin and no help, so I guess the cats are not clogged. I also noticed that when the hesitation is happening the check engine light flashes. I checked for codes and still nothing. Getting frustrated!

 

Removing the front 02's may not give you accurate results for a restricted exhaust. Your engine breathes through two 2.5" pipes not two 5/8" holes. There is an easy accurate test for exhaust restriction. Connect a vacuum gauge to the intake manifold. In neutral, raise the rpm's to 2500. The vacuum should stay at 18". If it drops off steadily, the exhaust is restricted.
You may also have a fuel problem. Once your past 80% throttle, the ECM ignores the 02 signals(no codes). It runs in wot mode. Having 60psi at idle is good, but it doesn't tell the whole story. Engines need very little fuel to idle. You need to get a fuel pressure gauge up on the windshield where you can see it. Duct tape will hold it. Make sure it is not leaking first. Run the car in 2nd or 3rd gear and mat the throttle. If the pressure drops off, you found your problem. Before you change the pump, make sure you have 13-13.5 volts with the engine running at the pump. Measure at the voltage feed and fp ground wire. It would suck to change the pump if you have a bad power or ground.
If you have good fuel pressure and no restrictions, replace the MAF. It's quick and easy. If it doesn't work take it back. At that point I would install a new ac delco crank sensor. They can cause some weird problems and not set codes.
Good luck

 

The flashing check engine light is telling you that you have misfire in one or more cylinders. I would start with the basics and check the plugs and coil pack connections.

 

Too bad the cats were not an issue. Check Engine light indicates the issue is getting worse. Does seem like an ignition issue, not sure a fuel starvation from the filter/pump would cause the light to come on but I will do some checking.

Please pull your codes again since now you have had a CEL come on.

 

I checked my codes and nothing is showing. The CEL only flashes when the hesitation is occuring. I have put in new ac delco iridium plugs and gmpp wires. Is there a way to check the coils to see if one is weak?

 

Excellent Recommendations!!

Bill

 

Ok, i will try this ^. I appreciate all the help from this forum! Good bunch of guys!
I want to point out that the hesitation only seems to happen at WOT and only after the car has warmed up about 2-3 minutes. Maybe that will mean something.

 

Those are great instructions, best anywhere.

 

I am having the same issue as you with my 2000 c5 convertible, I was wondering if you found the problem yet?

 

http://forums.corvetteforum.com/c5-t...oil-packs.html

check the 3rd. post in this link
watch the video
AC Delco plug/coil tester