I ran a search and have been reading through threads for a while now and it sounds like my O2's are simply bad...

My car runs fine in open loop and as soon as it hits closed, it gets a really bad stumble and hesitation. Occasionally the SES light will come on and the problem will go away temporarily.

The problem started about a week ago when I had to drive the car in a pretty heavy rain storm. My O2's only have 15k miles on them (approximately 1.5yrs when I did my headers) however, I had to extend them to get them to reach when I installed my headers. My guess is that they got wet (only insulated w/ electrical tape) and are skrewed up now...

Is there anything else that could be causing this problem? What other sensors operate only in closed loop?

thanks!

-Jason

edit: my car is a 94 Formula M6 w/ H/C and tuned by PCMforLess

 

its probably your O2's.............mine went bad............i was in a bind to replace them, and the only ones available at the autoparts store was Bosch (2 day wait for AC Delcos, and i needed my car right away)

2 weeks later they are already starting to cause problems again.

from what ive read, the bosch are not properly designed to work with out cars, so if you do replace them, get the AC Delcos, theyre cheaper anyway.


as far as other possibilites........it could also be your MAP sensor.......do a search on it..........sometimes the sensor itself is bad.........or the little orange seal is bad (probably can make your own with liquid gasket). the MAP might also be dirty, some people solved their hesitation just by cleaning it out with some carb cleaner.

 

BWAHAHAHA...

I've got Bosch's in the car now...grrrrr

thanks!

 

just saw your edit...silly question: where is the MAP sensor on these cars? the pic on Rob's site wont load

thanks

 

its the little black box on top of the intake manifold, passenger side............it has one 4prong wire harness going into it...........be delicate when detaching the harness because it snaps easy.

after you dettach the wires, there are two socket bolts on top of the sensor itself that you unscrew, then the MAP sensor should lift off.

the sensor itself is just a little phallic shaped plastic tube thing that inserts into a hole on top of the intake manifold.

the tube is hollow and sometimes gets blocked up with carbon. you can clean it with carb cleaner.

mine wasnt blocked up, but i replaced the whole sensor just in case, it was only $30.

btw, around the tube thing is an orange sleeve gasket that seals it to the hole in the manifold.........alot of people found this gasket ruined/melted..........its hard to find it anywhere, even my dealerships did not have it. im guessing you could use liquid gasket from the autoparts store to repair/imitate it.

 

oh yeah, before you do all this, disconnect the negative terminal on the battery, and let it sit for awhile to reset the pcm.

my pcm needed 15 mins of driving after installing my O2's just to realize there wasnt a problem anymore.

 

You could also be burning through an O2 sensor wire with your header.

 

or a plug wire.


it seems alot of problems have a common symptom of stuttering/hesitation.

 

true, but my problems are only occuring in closed loop...WOT still hauls, etc...

 

thats why i said the MAP sensor...........from what ive read its a closed loop deal, just like the O2's.

althought id put money on your O2's being bad.........it doesnt hurt and only takes 5 mins to check/clean your MAP sensor.