So i have a little misfire at any rpm, random no pattern. Everything that can be replaced has been replaced. when the EST bypass connector is disconnected it has no misfire whatsoever, just the usual, small idle fluctuation. The only thing left to replace is the ECM. Injectors are fine. Also im running the stock bin, for the 305 TPI 5 speed... Car now is a 350 TPI 5 speed, with the 193 heads/cam.. any ideas are greatly appreciated. Thanks, Boldguy

With the EST disconnected whats the timing set to?

Double check it so its 6deg.

6.000* deadballs on... quadruple checked.

Three stretches....

Was the key off, then pulled the connector, then checked the timing?

Have you confirmed that 0* on the mark is really 0? I've seen balancers slip, and marks be in the wrong place. Pull #1 plug, confirm actual TDC, then compare the marks.

Hate to say it, but.... are you sure you were on #1 plug?

Aren't the '193 heads swirl port? They require less spark timing then the stock TPI heads, which are not swirl port.

Try backing the distributor timing down to 0* BTDC. Then run the same calibration as you have been. This will remove 6* across the board. See if it helps alleviate the misfire issue.

Is this a SD or MAF setup? Are the injectors sized properly for the calibration/engine combination?

RBob.

I adjusted the timing to 0* BTDC and it seemed to do a little better. I think i will try running a bin for the added displacement and the injector size and see what happens.
It still hickups at idle. havent checked it with EST disconnected. It is a SD setup.

dr fiero Yes i did check the timing correctly and on the no.1 wire as long as you number them 1,3,5,7 .. 1 being most toward the radiator on the driver side.....

Haven't checked the balancer...

So i broke down at school and i replaced the ECM and the Distributor (again), and still i have a misfire. timing was set at 0*, but i believe it was causing me to overheat... ANY ideas, what else is there???

your base timing set at zero is not going to cause the car to overheat

setting it at 20 might though lol

I'd double check your firing order. Sounds like my car when I got #2 and 4 plug wires reversed

-jason

I'm betting 5 & 7 are swapped.
Check they are not real close to each other if they are correct anyway. Might be some crossing going on.

It's not a steady misfire though...
I do have them all separated except for the section close to the dist cap, i dont know that there is a way around that though.
Is there something i can do to datalog to help??
I did notice during one log that the rpm drop happened the same time that the SA spiked a little bit... did the advance cause this? or did the rpm drop cause the advance?? Also im' running 91 octane gas if that makes a difference...

I think i am going to try to load the bin on tonight with the following corrections:
Injector flow rate to 22.00lbs/hr
Cylinder displacement: 713.00cc/cyl

and we'll see what happens.
Thank you guys for the help.


PS I'll double check for touching wires..

Did you change the ign.module at the same time you changed dizzy?

My friends -88 IROC had similar issues a couple of years ago and in the logs the RPM signal spiked and the SA jumped the same time, making it idle wierd....

/N.

As the idle dropped the ECM added timing to increase the RPM. This is the idle compensation SA.

Back to the resetting of the distributor to 0* BTDC. When it was at 6* BTDC (stock setting) was there any knock retard? Try going the other way with the timing. Adding 6 degrees in. Move the distributor to 12* BTDC.

If that doesn't really make a change, as it should ping like crazy, then there is something else wrong. Be sure to put the timing back to where it should be. These changes are just to help figure out what is wrong.

Is this a stock L05 engine? Maybe used?

It seems as though there is a mechanical issue with the set up. I know you said that the injectors are fine. Although if they are stock style Multecs it would be worth replacing them anyway.

RBob.

The engine is believed to be mechanically sound. Vacuum test at idle showed steady 20inHg. Compression test showed 215PSI on all but #6 which was 210PSI. Fuel pressure: now that i think back i think the last guy who worked on it said it was around 35PSI. So if i was having a lean misfire, then the unburnbed fuel gets to the O2 sensor and the comp tries to lean it out even more... Ill check my fuel pressure. Injectors are Bosch design III 22 lb/hr.


Also i tried the calibration for the increased cyl vol. and inj flowrate and it seemed to idle real rough...

TPI fuel pressure should be 42 lbs with vacuum, and 48 with the vacuum disconnected

at least, thats how I have it set on my car

-jason

Attached is a picture of what i modified in the SA table of the bin. I kept the same curve but took out 8* from the whole thing. I also changed the injector constant to 19.7 ish since my fp is at 35psi vac off, and the inj are rated at 22# at 43.5... Also i took out some timing from the lower end (idle) of the closed throttle vs SA table.
top is mine, bottom is what it was stock.
check it out and lemme know what you guys think. I did also notice that the car ran smoother, but especially smoother with the heater blower motor on...?HUH???

any help is great! thanks again guys.

Anyone see the attachment??

So I have noticed that about a week after running this calibration code 42 pops up...HUH??? Is this common??

I have been running this bin for a while and it has seemed to help with the misfiring. Judging by the diagnosi (plural of diagnosis ) it is an ignition related misfire. I suppose it may be the balancer slipped like what dr. fiero suggested... Anything else you guys would do??

Thanks so much for all who contribute. I know this is a tougher one to help, but multiple inputs are better than one! thanks guys