: Hesitation



rrhayden
05-02-05, 01:42 PM
Hello,

I have a 94 STS with the nortstar engine. The car has developed an intermitant hesitation when the car is warm. Pulling out from a stop the engine will rev to about 1500 rpm then for a split second drop to 800 rpm, and then run fine. It will also hesitate if you are on the freeway and take your foot of it, and then press the gas again. It can go days and be fine then do it all day and stop again. I checked codes and none are recorded. I have changed the fuel filter, the car has 100,000 miles. Any help would be great, Thanks

mechanix
05-02-05, 05:36 PM
Isn't that typical? It gives you all kinds of codes when you think it's running fine, then won't give you ANY when you need one! *lol* Your problem could be any one of about 20 things, rrhayden. But I guess that's why you posted your problem. Right?! *lol* Let's see...air filter? Fuel pressure regulator? Gas tank vents clear? Purge cannister clogged? It sounds as though it may fuel or air related somehow. Can you give us any more symptoms or info?

rrhayden
05-02-05, 06:08 PM
You are right, how often do you wish you had a code !

The only symptom is loss of power for a split second. The best way to explain is that at a stop you accelorate and just as the tach passes 1500 rpm it is like the key is turned off for 1/2 a second then she goes again. There is no blink of the dash or lights to indicate a full power interuption and the tach only drops to 800 to a 1000 rpm. It only happens when she is warm and the rpm are passing through 1500. Could it be plugs and wires, or a bad ground?

mechanix
05-02-05, 06:38 PM
Hmmm...it really doesn't sound like plugs or wires to me. They tend to hesitate a lot more and "jerk" when they go bad. But you are about due for new ones anyway - it wouldn't be money wasted if you wanted to replace the plugs and wires. And a bad ground would almost certainly act up at any rpm range, not just 1500. I'm not real sharp on these computer cars, but I believe I would look at the fuel rail pressure regulator - pull the little vacuum hose off it and check for wet fuel - there shouldn't be any. And test the fuel rail pressure. The Helm manual tells you how to do all that. Or do a search for the appropriate thread on here. I used an old A/C R-12 filling hose to make a fuel rail pressure tester. I would sure take that charcoal cannister/purge/venting system apart and make sure all that is clear too. Check the EGR for deposits/sticking. Check all your electrical engine control plugs and wiring for fraying, chaffing, loose connections, oil saturation, corrosion, pinching, etc. Check for a vacuum line rubbing a hole in the side, or collapsing under vacuum. Just spend a little time under the hood looking at things with a good, strong light. Chances are, you will see something wrong, or at least something that looks odd to you. And don't forget that air filter! *lol* It sure sounds like a fuel flow or an air flow problem to me. Or in one or more of the sensors that provide air or fuel signals to the PCM. If not, then (perish the thought) it could be in the PCM itself. If you do all that and can't find anything, then I think I would find a mechanic with a scan tool, and who has experience interpreting it. They will reveal codes that don't show up on the on-board diagnostics. Put on the coveralls next Saturday and crawl all over that car! *lol* You're bound to find SOMETHING amiss! Good luck, and please keep us posted.