This thing is driving me nuts!!
 

Ok, still working on that stumbling problem on my 87 305 5spd. I've replaced the 02 sensor (helped a little) new TPS, (also helped a little), new CTS, and also found out that my fuel pump wasn't holding pressure, so just finished pulling the tank and replacing the pump. Also deleted the pulsator with the high pressure hose and clamps included with the AC delco pump. But the car still stumbles badly when warm. You push the throttle down and it almosts competely cuts out. Something I just noticed today was when it does this the tach needle drops about 900 rpm. The engine rpm doesn't drop, just the tach drops, then when you let off the throttle the tach jumps back up to the correct rpm reading. The car will cruise fine, just can't give it any throttle when warm.

Anyone have any thoughts on what to try next?? I think I'm to close to the problem to look at it logically. Maybe someone looking from the outside in will have a better perspective than I do.

Thanks-Dan

check this
 

i'm no big expert on ignition or anything, but since you say that the engine RPMs don't drop but the tach does, perhaps it's something in the ignition system, like the coil that is making the tach drop. i THINK i heard somewhere that the ECM uses engine RPM to adjust the air/fuel ratio...perhaps if whatever reads the RPMs is off, the ECM will be sending more or less fuel to the engine than what it should be.

kev:D

kev, Funny you should say check the coil. I was thinking the same thing. So I changed it out with one off a 90 caprice 350 I parted out, and it does exactly the same thing. Thanks for the response though. -Dan

How about your igintion module? Does it check out alright? There should be a test in the Chilton's or Hayne's manuals.

90iroc-Just pulled the module and replaced it with a new spare wells module I had. Didn't change anything.

I just called a place in town and they are open 7 days a week and he will scan it for $90. Also just found another guy that will do it for $65 on Monday. I'm really tempted to do this. Much as I hate to admit defeat, it's getting to the point it isn't fun anymore. It seems like I've become a parts changer and not a mechanic on this one. $90 might be a good investment.

I know what you're going through. I've pretty much done the same thing chasing down a bad fuel pump.

If your tach drops but the engine speed doesn't, there is definitely something wrong with your ignition system. If you can get ahold of a new distributor I think that may fix your problem. If you can borrow one to test, that would obviously be the best thing to do.

rezinn,

I have another distributor out of a 90 caprice ex-cop car with a 350/700R4. I parted it out about 6 months ago, but the engine was running perfectly (other than the rod knock). I bought it for the 700R4 and a set of 5 good year eagle tires and wheels I sold for $500. Paid $450 for the car, so can't complain much.

If I use my TPI ignition module, will this distributor interchange with the one in my 87? They look the same, but I've found out over the years that looks can be deceiving.

Thanks-Dan

P.S. I've got my plenum and runners off right now. I'm going to send the injectors off to cruizin performance to have them cleaned,tested, and matched. From reading posts on injectors it sounds like I'll be money ahead doing this. Also been doing some grinding work on the plenum and will have it jet cleaned before it goes back on. So it will be a week before I get the injectors back and can swap distributors. I don't want to change out the distributor until I get the intake and injectors back in and get the car running. That could create more problems. One thing at a time.