View Full Version : My '90 SC

08-18-2005, 10:41 PM
I finally got mine running to perfection tonight!! I thought I made a big mistake when I first purchased this one. I just wanted to share some information that might help others here who may be having the same problems I did.

I have a '90 SC aod, with a few mods, a brand new ford longblock and aod. It was running sort of ok when i first purchased it, then the next day something happened.

it would not hold an idle, it would barely turn over when starting it, but if i revved the engine above 2,500 rpms it would stay on. i drove it like this for a day, then it got worse- the thing wouldn't run at all. The first thing i did was unplug the MAF to get it into limp mode. I did make it home that way.

Pulled the codes, came up with 66 (maf signal too low). luckily i had 3 maf's laying around, and swapped them all in after clearing the codes for each one, got the same code 66. that didn't make sense to me, so i started the engine with the maf unplugged, and then swapped and plugged in each maf, measuring output voltage for each. They all read the same at idle (about 1.04 volts) which told me all the mafs are working. Then i measured the maf voltage on a friend's SC that was running fine, got the same reading.

i then decided to check for vacuum leaks (re-sealed all IC tubes, clamped all loose vacuum hoses i found). I traced all wire looms in the harness for shorts and exposed/frayed wires (only found one which was a ground leading to nothing). Traced/back probed for shorts on the maf wires (found nothing wrong). Checked fuel pressure at idle, was getting 39 psi which was ok (and it did not leak down either). Probed for possible shorted fuel injectors- all measured about 16 ohms (no problems here). Measured input voltages at the maf, and tps, those were ok. checked the ircm relay power output to the eec- that was ok. swapped a DIS and a coil pack- no improvement. Traced the crank sensor wiring- nothing found. The harmonic balancer did not wobble so no troubles here (i think).
the last thing i checked were the pins at the EEC connector- i probed all the relative pins to ground (pin 20, 40, and 60) for shorts between the maf sensor input pins and return signal pins (no problems found). Then i realized that in all this time the EEC was refusing to clear the bad maf code regardless of what i did. all the maf's were good (i verified this on another SC), so plugging them in while the car was running would have cleared the CEL.
I was convinced to purchase a new EEC.
I installed the new EEC, and all of my prior running troubles just dissappeared. i mean this car is running to absolute perfection now. i know alot of times guys say that the eec doesn't usually go bad, but consider this: i think an eec can have a partial circuit failure especially if it's 15 years old that won't necessarily trigger a code or if it does, it's a code that's totally invalid as in my case. if the SC is doing weird things, and you have ruled out the basics, then it's worth it to replace the EEC. But don't replace it if it was replaced with a remanufactured unit, because it's probably no where near as old. Mine happened to be the original one which made sense as to why it crapped out.