My car stumbling at partial throttle in every gear and i don't know what else to check. The new motor ran great after i got it back from the dyno up untill about 3 days ago when it started studdering and missing while i was just driving along, but its not noticeable at WOT.
I put er up on blocks and checked the o2s for burned spots first (that happend at the dyno, had to replace one) they were (visually) ok, checked the wires real thourogh ok, took every spark plug out and cleaned/checked ok, ran 2 gallons of toluene with my 93 gas in case of KR, didn't help....the opti only has about 10k on it, i don't have egr crap to worry about clogging anymore...or cats...
I'm out of ideas and i wanted to take my car to the super chevy show on the 25thand try to get some 1/4 times and now i'm just ready to set it on fire Spending thousands of bucks on this car and having it run like shiz is my last straw.
The o2s have never been replaced, even the replacement for the burnt one at the dyno was used, so i may buy some. Is there something else i can do short of driving it down to NC again and having it checked out!?! I'll give $5 bucks to whoever nails this studder/missing prob.

 

have you ran the car in speed density mode?

does it stumble at all operating temps (in open and closed loops)?

have you put in a scanner?

 

how exactly do i run it in speed density mode? last time i tried to unplug the MAF it wouldn't even start?

I don't have a scanning tool to scan it with, and I don't think i can doesn't original OBD II cars have a different connector under the steering wheel than OBD I? (i did the conversion)

It seems to stumble only when its warmed up, but it warms up quick so its difficult to distinguish.

Tell me again how to check it in speed density mode. If it doesn't do it in speed density then that makes my o2s the suspect right?

 

my car is also a 96 and i have converted to OBD1, it has the same connector.

your car should start and run with the MAF unplugged, it will be in speed density.

if your problem is gone suspect your MAF is bad.....

 

Ok, it stumbled with the MAF unplugged, so does that rule out the o2's as well???

I replaced the coil with a spare one i had and unplugged the MSD Ign. and same results so they are ruled out.

It does it when its warmed up and under load keeping it at a constant light pedal/rpm ex: 5th gear/50 mph/around 2200rpm on a mild grade up hill.

hey qckz28 i may just give you the 5 bucks for being the only one to help me with this. thanks!

 

Have you checked the trottle position sensor. It may be goin out. What about your MAP sensor. I would find a guy in your area that has a scan tool and check your sensor readings to see if your o2s, MAP, IAT, TPS, and various other sensors are reading right.

Could also be an exhaust or intake leak.

Good luck with this.

-Stu

BTW: Dont set it on fire, i know a guy in jail right now that did just that.

 

So does the car still stumbling in speed density mode rule out the o2 sensors? Does speed density mode still use the o2s?

I just bought 2 new bosch ones (couldn't get ac delco) and need to know if i have to take them back or install them.

 

Speed density does not use MAF sensor, it uses the mainfold pressure sensor to determine the amount of air. Both systems use oxygen sensors.

I think you are confusing open and closed loop. Closed loop uses the o2 sensors, open does not.