Tonight my 92 LT1 Auto was stumbling under light acceleration.

car has recent plugs, wires, EGR, Injectors, even Oil and filter.

Scan showed that all sensors appear to working normally. O2's, MAP, etc. Though the ST and LT counts were floating quite a bit in Closed loop.

I read recently a discussion about someone's car stumbling under normal acceleration and it was a sign of the OPTI failing. The one time it Coughed and sputtered pretty bad. I thought I was going to die on me for a second. Everything looks ok That I can see.

Does anyone have and advice or should I just start saving now to replace distributor, Pump, gaskets etc. in hopes of a fix... I have access to FSM books 1 and 2. will continue to leaf through.

Thanks guys, any ideas would be a huge help.

 

OH, and no DTC's

 

O2s

 

My car also stumbled-- my opti was full of rust, when I seen how bad it was I was surprised the car ran as well as it did. Its hard to say for sure if that is what happening with yours but it may be.

Hope this helps

 

I was having a very slight skip in my 95. At hiway speeds you could hear just an ever so slight misfire.
In the past few months I have replaced the plug wires, coil, icm, opti cap , checked resistance on injectors ( they were all 13 ohms )cleaned injectors and added a new air filter. I checked codes and had no code but code 12 which is normal.
the last time I took it out for a cruise , after about 25 minutes of driving 45 mph or less I found a stretch of road to lean into the loud pedal. She sputtered and bogged and fell flat on her face.
So, after more and more web research it's come down to o2 sensors , iac or egr. It ran good in open loop but as soon as it went closed loop the miss started again.
As someone suggested on another forum, I took the fuse out for the o2 sensors to take them out of the equation, that seems to have made all the difference. I replaced the sensors shortly after I bought the car five years ago with Bosch units, I didn't realize the stigma they came with. I have about 40,000 miles on them and think they are going bad but not enough to throw a code , which I've read numerous times can and does happen with these sensors. I've ordered new denso units and hope to put them in tomorrow, I'll let you know how that goes.
So, short story long, remove the fuse and give that a shot, just don't drive that way for too long, you don't want to clog up catalytic converters , then there's more problems to fix if that happens.
Good luck

 

OK. Well given the price of O2 sensors and the age of the car, perhaps that would be the best place to start. For $36 for two delco sensors I'll swap them out. Manual says service interval of 50K miles on single wire units so I suppose with the age of the car it's time.

I'm surprised it would cause the car to run that rough.

still feeling pretty skeptical of the opti. Hopefully I'll have a chance to try wit new sensors next weekend.

Thanks for the responses!

 

It is unlikely that a failing opti would cause misfiring in closed loop operation, but not in open loop. Get a scanner on it, and see what all of the sensors are doing, etc.

Live well,

SJW

 

I forgot to add that I changed the fuel filter and the strainer on the fuel pump as well.
One other thing that was going on was that the transmission was having to hunt for OD and shifted slow. That seems to have gone away now with the o2 sensors disconnected ( I read that with the Ox sensors failing it could cause such a problem) My sensors came in this morning, so tomorrow will be the tale of the tape.
On a 21 year old car I was just replacing consumables while I had her up in stands so that I could basically have her back to a fresh start and then be able to enjoy her with piece of mind knowing that pretty much everything was new and hope it lasts another 20 years.

 

In my case I don't know that the problem necessarily occurred in closed and not in open loop. Though it was likely in closed loop at the time.

 

I replaced my Ox sensors yesterday. Seems to be much , much better. No stumbling at speed and although I haven't taken her for a long cruise, she seems like her power is back to normal and there's no hunting for gears. I'm attaching a pic, you can see the difference in design between Bosch ( used and on the right)
And the denso units. This is the drivers side with less than 50,000 miles, the passenger side was a little more "sooty".
Attachment 48018157

 

Good job

 

I tested my fuel pressure tonight, per FSM, it was right in the middle for spec. Waiting to get O2 sensors and replace fuel filter. Discovered a little coolant at water pump weep hole after a drive last night. A friend of mine rode with me a bit and agreed it was likely the distributor causing all the hesitation. May be awhile before I do the opti but I will report back when I do.

 

If your leaking it can kill your opti and getting the wires wet can mess you up too. Start soaking your pulley just in case.

 

Replaced both O2 sensors and the fuel filter. Car still behaves the same as far as the stumble when accelerating. I didn't think these were going to help but they needed done anyway and it was worth a shot.

Going to replace distributor, does anyone have a good suggestion on replacement. I believe Summit has a reman OE opti. Is this the safest way to go?

 

It worked on mine but I was not watering my opti. The opti really seems to be a crap shoot. I would try cap and wires first.

 

Going to order parts this week. PETRIS OPTI or Summit AC DELCO reman?? Either way I'm in around $375 to $400. Does anyone prefer one over the other. I'm leaning towards the PETRIS. Any advice is always appreciated.

 

New water pump. New PETRIS Opti. Injectors less than 1 year old. Intake was removed cleaned, reinstalled. New plugs. New wires. New EGR. New Fuel filter. New O2 sensors. New IAC.

This car still stumbles at times. This occurs when accelerating. Even had a pop pop from what seemed to be in the engine, intake I suppose. From a stop I floored it and it popped and stumbled bad, car fell on its face. Stopped the car after it only rolled a few feet, floored it again and it spun the tires right through 2nd as you would expect. I've tested the fuel pressure while parked and it was around 40 - 42 psi, removed vac from regulator and it went up like 10 psi. With the car off it held pressure for a few hours before I removed the gage. Sorry, someone will ask and I don't have a way currently to test fuel pressure while driving.

I suppose my question is, can this simply be a failing FPR or fuel pump, or should I suspect both? At this point everything else seems ok. I did drive it a vey small distance with the vac off the FPR and it got much worse, but I'm honestly not totally sure what that proves. Starts right up every time and idles great. Just wanting some advice before I replace the FPR and pump.

 

Oh, looks like a code 16 opti low resolution pulse. So that's pretty sweet.

 

Well, checked voltage, to opti and it's good. 4-6 vdc on terminal A. Reset code code and drove again. Still had issues. No codes were set this time at all. Lost...

Also, I'm also wondering if the ignition coil itself is getting weak.

 

ECM code H16. Drove the car all over today and it runs at speed fine. WOT from stop it burns tires. 1/2 throttle from stop and it stumbles, sometimes backfires, then gets going, mate smooth out over 3k rpm. Code H16. Low res pulse. Going to call PETRIS on Monday but could I really have a cam sensor issue??? I did not get this code before the new opti though I still had this problem. I'm lost. If anyone has advice please jump in. Not sure where I went wrong here.