Juddidiah

'92 LT1 383
juddidiah.com (for vehicle specifics)

Engine backfires, misfires, hard to start, will not idle, won't run over 3000rpm.

Spark at all 8 cylinders, double checked sparkplug wires. New sparkplugs gapped ~.049", ~43psi Fuel pressure.

Datamaster Scans; (Save As)
Scan 1
Scan 2
Scan 3
Scan 4

As you can tell from the scans, it doesn't respond to TPS at all. Unplugging the MAP doesn't change it. The O2's values don't seem to fluctuate as they should. You can see the computer go to closed loop after only a few seconds running. The LT's and ST's only move once in ~45 seconds of running.


My questions are;
Potential for a bad computer?
Anyone with clogged injectors ever seen the same?
Any other suggestions?

Thanks for your time!
juddclot@hotmail.com

Z95m6

i'm far from an expert but with backfires. It sounds like a timing issue. Did it run good before? is it a fresh rebuild? and this is the first fire up?

Juddidiah

Excellent point. Fresh Rebuild, just firing it up.

Made Triple sure that the opti went on right.

Z95m6

did you cut down the cam dowel pin? that might of messed up the opti. Have you pulled the opti off to actually check it. I put mine in one hole off when i rebuilt my motor. I couldn't even get mine to run and it would back fire. I trouble shooted everything and it ended up being the opti one hole off. I don't know anything about the PCM stuff i leave that up to my buddy.

Juddidiah

Didn't cut down the dowl pin at all. had the engine out of the car when I installed the opti. Was dead on. I even tried to see what it would feel like if I put it in a hole off. Totally different feel.

shoebox

Valves too tight or timing gears incorrectly indexed? Was the MAP unplugged during the logs?

Juddidiah

Valves shimmed to ~120psi installed pressure, ~330psi @ .575 lift. Had the motor out of the car, to install everything.



MAP was plugged in during the runs

Spinner

Crossed any wires (Doh)
Fuel pressure okay? Fuel injector fuses ok?

shoebox

If the MAP sensor was plugged in, it's hardly seeing any vacuum. Of course, if you are holding the throttle open, there won't be a lot, but the MAP and BARO are almost the same all the time. You usually only see that at WOT.

If your valve timing is off, you won't get much vacuum. Stick a vacuum gauge on it to see what you have, in case the MAP is lying.

Juddidiah

Actually triple checked the wiring, and re-ran them
Fuel Pressure ~43psi, but i've tried from 38-46psi.
All Fuses intact

I'll stick a vacuum gauge on it, but I'm pretty sure the reason that the MAP always shows near Atmospheric is because the throttle is wide open & has to stay that way to keep the engine running. You can see it dip a little bit when the TPS goes down.

Really Thanks for all the input everyone! I do appreciate it!

shoebox

You might be right about the MAP, with the low RPM and open throttle, but it's just a thought. I hardly ever see a scan that looks like that.

Z95m6

If you didn't cut down the dowel pin (Assuming you have a new cam) you could of ruined the opti.

Juddidiah

Differences in the 92-94 and 95-97 opti setups. If you look at the picture up above you'll notice a much different setup that you might be used to with a '95. The dowel pin from the cam to the gear is flush, and the driver that goes from cam gear to opti is sized just right.

Perhaps you're refering to something different.

Same cam & opti that worked before. Has spark in all 8 cylinders.

Z95m6

sorry, nm. I'm just so use to everyone having a 95+ or converting to the 95+ setup. I still think it has to do with timing. Goodluck. I'm chasing down a problem on my car too. TTT for you.

Juddidiah

It was opti