LT1 Gurus, I need you!

[choco]

Hi gang. It's been a while since I was here. Isn't it a true test of friendship when you only here from someone when they want something?
Anyway, I am in Fall City, Wa, for a month visiting friends and going to the Portland swap meet next week. Anyway, my buddy here has a 55 F100 with a 92/93 LT1 and TH350. It's a nice car, well built but the wiring is pretty bad. I have sorted it all out, and it's all back together, but the engine isn't playing properly. It seems to die when you pump the gas pedal. If you keep tickling the gas it will run, and that lets us move it around the yard, but there's a fundamental problem that I need to fix and I am not a mechanic. We are getting a new cap and rotor for the optispark, but I'm not sure if that will fix it. The TPS looks OK, not slipping around at all. I think there is a MAF and MAP, but I have no idea what I'm looking at. I have zero experience with GM engines.
Any ideas?

[kb426]

I found this: https://shop.advanceautoparts.com/r/advice/car-technology/the-big-problem-with-chevys-57-lt1-v8
and this:

I'm not much help.

[jaybee]

Nice to see you stop by, Choco!

[wayne petty]

Hi gang. It's been a while since I was here. Isn't it a true test of friendship when you only here from someone when they want something?
Anyway, I am in Fall City, Wa, for a month visiting friends and going to the Portland swap meet next week. Anyway, my buddy here has a 55 F100 with a 92/93 LT1 and TH350. It's a nice car, well built but the wiring is pretty bad. I have sorted it all out, and it's all back together, but the engine isn't playing properly. It seems to die when you pump the gas pedal. If you keep tickling the gas it will run, and that lets us move it around the yard, but there's a fundamental problem that I need to fix and I am not a mechanic. We are getting a new cap and rotor for the optispark, but I'm not sure if that will fix it. The TPS looks OK, not slipping around at all. I think there is a MAF and MAP, but I have no idea what I'm looking at. I have zero experience with GM engines.
Any ideas?

change the ignition coil first..  its right up on the front of the head...  put new thermal grease under the module..

there are 4 or 5 ground wires on a stud directly above the coil bracket.  wire brush both sides of those ring terminals. the studs and reinstall.. counting..  that is the G111 location for the PCM. and a bunch of sensors.

many years ago.. an LT1 camaro came in the shop.. it was misfiring.   i said change the coil.. the owners said.. we are going to work on it..   must be the cap and rotor.. 2 days later. it was still misfiring.. i said.. change the coil.. .. nope.. it must be the spark plugs and wires..    3 days later its still misfiring.  the dynamic pair are now deep into the repair info computer in the office.. i took the brand new coil i always kept on top of my tool box and installed it.. reached thru the open window and fired it up.. no misfiring. .

as they walked up.. i tossed the coil at them.. it had massive signs of external high voltage leakage.. where the highest part of the spark voltage build up leaks to ground and there is not enough to complete the spark on that cylinder.

i am NOT saying your optispark is not screwed up.. i am saying put a coil on it first..  and NOT a race coil.  just a stocker.. MSD and other coils have lower resistance on the primary as MSD and others use up to 400 Volts on the primary instead of 14 volts.. this causes the coil to never fully saturate at 14 volts as its pulling 1/3 more current thru the same circuit..  give or take..

here is an LT1 coil that is leaking high voltage out the sides..

https://i.imgur.com/vRpsytK.jpg

https://i.imgur.com/wOEaDoA.jpg

https://i.imgur.com/MprpXAn.jpg

G111 ground location.. https://i.imgur.com/qHXeSor.jpg  

PS... if you have an autozone nearby.. order an SU102 by part number .. its the Engine coolant temp sensor screwed into the water pump.. the sensors go bad.. the pigtails go bad..  change both. https://i.imgur.com/pPbhmKY.jpg  

you don't want to know how bad your engine runs when it thinks the temp is -40C

[wayne petty]

also..

learn how to pull codes from gm cars..

http://www.tomco-inc.com/Tech_Tips/ttt2.pdf  

use the right hand half of the code page. the left is for dodge..

please also check the boot between the air flow meter and the front of the throttle body..

those tend to tear on the bottom and leak unmetered air into the throttle body..

just for kicks.. while you have the throttle body boot off.. and you are looking down the throttle body bores..  engine off.. grab the throttle lever... open slightly.. wiggle.. in and out of the shaft play is expected.. but play from throttle shaft bore wear causes issues..

this confuses the computer as the Throttle position sensor voltage really needs to be at 0.53 volts every time the throttle is closed on L98 TPI and LT1 TPI engines..  

what happens.. the TPS voltage with the throttle closed change with the wear.. if it does not close to the exact minimum voltage the computer does not let the fuel trim fall into idle fuel calculation..

so instead of iding at 1.2 to 1.4MS of injector pulse width.. it will stay at 2.4 to 2.6MS like you were staged on a drag strip waiting for the tree to come down..

if your throttle body shaft bore is worn.. ask for instructions before tearing the throttle body apart. there are procedures to take it apart without breaking the screws off in the shaft.  the exposed end of the threads have to be ground down.

[enjenjo]

In damp climates there was a problem with the early optisparks retaining moisture. GM updated it in 96 to cure that problem, they pulled filtered air through it with manifold vacuum to  pull the moisture out. If your cap and rotor are corroded inside that would be the cause. Summit has an updated replacement. Listen to Wayne on the TPS. Also the throttle body to plenum gasket can blow out on the bottom with no sign at the top.Spray some carb cleaner under the throttle body while running to find it.

[choco]

Wow, great advice, thanks guys. I only have a couple of days left, and I'm frantically trying to finish wiring on a 60 Starliner pro-street car. I put the F100 to the side for now, but will print out your advice and go through it with my buddy with all the cars. Apart from the F100 and the Starliner, he has a very quick 428 Cobra, a 69 BB Chevelle, a 70 Cutlass with 350 crate motor, a 65 Mustang, a Viper, all of which are good, working cars. Unfortunately they never get driven until I come to visit! Our daily driver while we are here is a 96 Crown Vic Police Pursuit black and white with only 30k miles on it. Great car! Hopefully I can return to Australia knowing I got at least one busted F100 back on the road.
Thanks again guys, I knew you'd come through for me!