If that doesn't work, check the TPS again. I just fixed a problem with identical symptoms on an 87 GXL. It suddenly died on the highway and then wouldn't start. It would act like it was going to start and then died. I checked the ECU codes, nothing. So I used my little lights to set the TPS. I was was off. The TPS was fine but I'm guessing the screw backed out or something. Anyway, i set it cold and the car started up. Warmed up the engine then reset the TPS, idle and checked the timing. It ran fine! It's not my car so I assume that it's still fine. I haven't heard otherwise.

 

Aight, it WAS the coolant sensor wires!!

Only problem now is that the timing is way off for some reason. It's running uber-retarted. I wonder why that changed . . . :p

 

Apparently the S4 ECU doesn't default to a "warmed-up" coolant temperature when you disconnect the sensor either... it just keeps dumping fuel in the engine like it's running super cold.

 

Ok, so I've fixed the coolant sensor issue, now the car runs like garbage

The timing is set dead on, I pulled everything apart to make sure that there are NO vac leaks, but for some reason I still get the following problems:

1) Car surges like crazy (Worse when the engine is cold)
2) When the engine is cold, it absalutely will not idle without my foot on the gas holding it at 2.5K. The car does not make enough power move forward untill about 30 seconds after it started.
3) Accelerates from 4KRPM to 7KRPM fine, though it _feels_ a little more sluggish then usual (Butt Dyno = Unreliable though!).

Anyone have any ideas?

 

Did you check the TPS again? Put an ohm meter on it and make sure it's smooth from about 0 to 5K ohms. Then adjust it and recheck the timing.

 

Yep, I checked it.

Timing is still dead on. The way it drives, you'd be SURE the timing was off, but when I hit it with a timing light, it's dead on the line!

 

Aw man, I put some additional grounds into the car and it preforms MUCH better (Still not fixed)

But the grounds made a HUGE difference.

 

so how exactly did you determine the sensor was reading -80 degrees? and what did you do to fix it?

 

We mesured the resistance of the sensor at the wires going into the ECU to determine the tempreture reading.

To fix it, I repaired the wire that had broken.

 

OK! The major problem has been discovered! The negitive ground for the ECU is totally toasted. 2Kohms on every single ground for the ECU.

Nasty. Well, it runs great now.

Time to MegaSquirt this car!