Decided to start a fresh thread on this.

Same old problem...when the car is warmed up, it hesitates, bucks and stumbles from a stop, or getting going from low speed...here is what I've done:

I know that folks love to jump all over the opti for these issues. I have searched these forums over the last few weeks (yes WEEKS) and read literally hundreds of posts on this issue, and here is my assessment from the problems and solutions I've read about (BTW, not enough of you post your solutions when you find them):

1. Opti is usually NOT the problem (in a very small number of cases it has rectified all, but usually only some of the problem)
2. Coil and module is usually as above.
3. Plugs and wires: Some have had good luck with replacing these.
4. O2 sensors: almost never the problem
5. Header/exhaust leaks: A few have eliminated the stumble by finding these.
6. Bad grounds: Several members have eliminated the problem by removing and cleaning all grounds to the chassis.
7. MAF sensor: one or two members have had luck by cleaning the MAF.
8. IAT: some have reported that replacing this, even when the original one 'appeared' to be operating correctly corrected the problem completely.
9. Bad compression: At least one member, after years of troubleshooting found that 2 cylinders on one bank had terrible compression, causing the problem.
10. Knock sensor: At least a couple of guys found that they were getting terrible retard from knock...bad sensor.

So, it appears that there is no ONE solution, which is why this problem is SO DAMN PREVALENT!!!
MY suggestion: Don't change the Opti right off the bat, it appears very unlikely that it's the problem.

BTW: In my efforts to elimate my stumble (which is the same symptom as all of yours), I have done the following (to no avail):
New Opti (and water pump while I was there)
New O2 sensors
New coil
New module
New plugs (champion)gapped to FSM specs.
New Injectors (Accel 30lb) retuned PCM
New knock sensor
New 160* Thermostat
New IAT sensor
New Coolant Temp sensor
New MSD 8.5 MM wires, incl. coil wire
I'm running headers (this is in a Datsun 240Z) and my wires are routed over the valve covers and ARE NOT touching anything at all....
Checked Fuel pressure and it's in spec.
All EGR equip. is removed and blocked off and editted out of PCM (TunerCat)
No air pump or evap. purge
I have installed another (powdercoated) intake with all new gaskets. No vaccum leaks detected anywhere!

I am still hunting for a solution.

The saga continues.......

Tim

 

I have the same problem, I too would like to find a solution. I have replaced many of the same things that you have and going to replace the opti and seal the intake manifold next. If that dont fix it then I have no idea what it could be

 

Any ideas out there guys......
I've replaced EVERYTHING....

It appears to me to linked somehow to when the car goes into closed loop, but the symptoms are the same with the old and new O2 sensors.....what else comes alive at closed loop?


I'm starting to get just a little perturbed!!

TIm

 

When I was testing the supercharger I put in my car, I pulled out and matted the gas. When I let off, the engine almost stalled and the car at idle or while maintaining a speed stumbled and was running full rich. It ran fine when I floored the gas. Turned out I didn't tighten the clamp to the throttle body tight enough and while it looked like it was on, it was loose. Tightened the clamp and problem solved, ran absolutely perfectly. I know it sounds like a simple solution, but you never know....

 

Well,
I took off the TB and disassembled it and cleaned everything and tightened everything up pretty well. Everytime I do something, I am very careful and diligent about how/what I'm doing so that I am sure that I'm not creating any further problems......

Tim

 

Same problem, with some detonation under load. Would like to have a solution. I am trying the opti tomorrow, but after extensive testing it seems that it isnt getting spark from the opti to the #7 and randomly drops other cylinders? I also feel/hear like the #7 randomly igniting under load. Sounds like a mini explosion in right infront of the drivers seat. Yea yea I know thats not good at all. I dont know what the hell is going on. Good Luck man.

-Dustin-

 

Well, it seems that after all the stuff I replaced (see initial post above), I did two things today that seems to have solved the problem.

1.) I had put 6 inches of reflective heat protective sleeving on each of the plug wires, from the spark plug boot back...just for some added protection from the headers. Well, with the motor running, I was making sure the wires were secure in the loom brackets and I felt some very faint 'shock' when I was touching the sleeves on a couple of the wires.....huh? wierd!! Very faint mind you...actually felt pleasant. So I cut off the sleeves from all the wires. These are brand new MSD 8.5mm wires BTW!! I guess the sleeves were able to conduct some juice away from the plugs....but why? Shouldn't the wires be completely 'sealed'? Anyways.....

2.) I wrapped the threads of the knock sensor with about 8 loops of teflon tape. Then wrapped a wire around the top of the threads to create a good ground and attached the other side of the wire to block. Due to my headers (very tight to the block), I had to relocate the KS to the boss above the oil filter. Maybe the clutch/gearbox was creating a lot of false knock?

So after doing this and resealing all the joints in the exhaust with silicone and aluminum gaskets, I took it for a drive.....all around town stuff....lots of stop/start type stuff.....and low and behold....no stumble at all.....beautifully smooth!!!!


So that's that!!!


Now to pull the LT1/T56 out for something with a bit more grunt!!!

ha ha ha ......


Tim

 

Did you ever scan log the car? At least you would know if your getting a lot of (false) knock or not

 

Shot in the dark but:
how's your CAT (if you're running one)?

 

I could not scan the car while driving as my laptop battery was a bit 'dodgy' and I didn't want to risk causing any PCM problems. I was getting nothing 'funny' in the driveway...but that's not too surprising I suppose.

I have no Cat in the exhaust system...Long tube Tri-Y headers (home made) into dual 2.5 inch, into single 3" with one Dynomax at the rear.

Tim

 

Ah yea, laptops can be a pain in the butt battery wise once they age a bit

Using Freescan, it will be ok though even if it dies on you. Its just collecting a stream of data from the computer and not interacting with the computer at all. As long as its logging it to CSV is on, even if it dies when you turn it back on you should be able to grab that CSV of data and still look at it

 

Thanks for the heads up Toby. Reading teh warnings in the TunerCat documantation, it's put the fear of God into me about that happening, and FreeScan doesn't exactly have reems of documentation with it! I assume then that I select "listen" during a scan, and not "interact"?

Tim

 

Yup, i dont blame ya for being careful tho Would seriously suck to mess up the computer. But remember its designed for non-computerish type people too GM Techs!