Car:
88 Vette, new 383, AFR 190s, LPE 219 cam, Hookers, 58mm TB, Superram plenum, 30lb used Ford Injectors, Ported Edelbrock hi-flow intake man, comp cams roller lifters and 1.6 roller rockers, Stock 165 comp, ABTP code with mods to MAF vs diags-Injector Const-fan temps. Has 2 O2 sensors. 1 in pipe #7 that runs a gauge in the dash, and a heated one in the Y pipe just past where it joins and 6-8 inches before the main and only cat that goes to the computer.
History:
Below 1000 rpms, it surges and has a very rough idle. Only suspect components were the distributor from original 130k engine and a used set of 30# injectors. Had the injectors flow tested, they are within 2%. Put in rebuilt distributer, new cap, new rotor and injectors and put it all back together. Disconnected the brown and black wire and set the base timeing to 6*. Runs much smoother than before. I plug the brown and black wire back in and it starts backfiring immediately, violently, and succesively. I have made no changes to the timing in the ABTP. I have reburned a new chip to see if that was the prob, but same thing. And yes, I reset the computer between chips.

Any ides? Is it mecanical or computer related? Why does it only happen when I plug the computer timing control back in?

Thanks,
Eric


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88 Z51 4+3 Corvette
94 Trans Am GT

 

Have you verified that the timing mark on the damper is truly at TDC?

 

Wel, the damper can only go on one way and there is only 1 mark. Also keep in mind that before the new distributer it was runinng, just rough. Now with the wire unplugged, its smoother than before. With it plugged in its backfiring and never did that before. Reason I swapped the distributer is that the old one had a lot of play in it.

 

warlock,
A couple items to check. Will the car idle at all with the dist wire plugged in???
If yes try to see what the timing is at with the dist (brown wire) plugged in.

What dist did you buy. How about a cap and coil?? I remember reading a guy with a vette have systems close to yours. His was he installed a camaro coil instead of a vette coil. One of them had red/yellow wires and the other is red/white.
With the worong coil installed when he plugged it back in the car ran bad,backfired etc.I belive the different coil reversed the timing.
A search on the vette forum may clear this up some.

Dennis

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85 vette,383,miniram,ZF6,4.10's..best ET 11.56@119.00 60' 1.59
w/100HP nirous 11.05@127
http://geocities.com/bowtie8
http://bowtye8.tzo.com

 

Wont even idle with the wire plugged in backfires instantly. I am using the same coil, just a rebuilt distributor and new cap and rotor. Everything looked right when I switched.

 

One problem I ran into with my 355 engine was that there are 2 different locations for the timing mark on SBC's when the engine is at TDC. One of them is with the timing mark straight up at 12 o'clock, and the other is with the timing mark facing the driver's side at about 2 o'clock. The only way to tell which one you have is comparing the timing mark to the crank key slot. The first type of balancer will have the timing mark about 70 degrees away from the key slot, while on the second type (common on F-body TPI engines) the timing mark is only 10 degrees away from the key slot. It's a very noticable difference, especially when you have the 2 types side by side. I had the wrong one initially, and wasn't able to set the timing using a light since it was so far off. We did it by ear and estimating where it should be until I bought and swapped on the correct balancer.

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Greg Westphal
'87 IROC 355TPI/A4

 

I have a similar setup. 383, TFS 23 degree heads, 11:1 SRP's, 30# Ford injectors, Accel intake, SLP runners, SLP .495/.502 cam, 1.5 RR. Running the stock ECM and PROM for now.

I ran with the 22# injectors for a month. Two weeks ago I installed the 30# injectors and although running quite rich, 108BLM most of the time, it ran fairly well and very good at WOT for a few days. Things started going downhill from there. I adjusted everything possible, (don't have programming equipment yet) and replaced the MAF, double check TPS and IAC and several other things. Yesterday, my buddy, said "put an ignition module in the distributor". I did, (had two spares) and now I'm back running exactly the way it did when I installed the 30# injectors, which leave me with needing to get my programming hardware!

Moral to the story is, that's why there were no codes, a bad ignition module doesn't set any and causes so many symptoms that point to other problems we experience with modified TPI setups.

Just a guess, hope it helps.

ps. I know, most of the time the modules just quit working but not this one! It just made it run really screwy.

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SMasterson

[This message has been edited by SMasterson (edited October 03, 2001).]