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1991 engine runs fine, not when driving.

J

jimk403

NAXJA Forum User
Location
Campo, Ca.
Just picked up a 91, 4.0, AW4, small lift but engine is stock. Got about half way home running fine, then it just stops accelerating and starts backfiring, no power, gets hot (but not into the red). In park or neutral the engine seems fine. Not sure where to look first?
 
Might want to jump the ballast resistor, because it is easy and will do what you describe. It would be neat if it was that easy :).
 
I would get yourself a fuel pressure tester, pretty inexpensive as far as tools go. Otherwise its a total guessing game with fuel. Probably a dying fuel pump, leaning out under throttle and possibly heating up due to being lean.

I have cat still going over 300k miles. IF it is your cat, it is usually caused by something. Physical damage happens, but it usually over rich fuel related which can be a number of things. Blowing any black smoke gettin on throttle ?
 
I was told the cat is new and it looks it. The fuel pump on my 90 can be heard when the key is first turned on, but this one is loud all the time. Is that a symptom of bad pump? Would your average Autozone or O'Reillys type store have the fuel pressure gauge?
 
Loaner tool is a good option, I don't buy expensive Snapon or OTC tools that are not used often. I have a crap load of HF tools I only used once.

Warning...If it is a pump, don't go cheap. Get a bosch and do it once.

Pump getting louder is a good sign of failure.
 
I measured the voltage at the fuel pump connector and only get 5.9 volts, both with or without the ballast resistor jumped. Should this not be 12v?
 
How many volts do you get to the ballast resistor connectors? This is pretty much in the center of the circuit.

Which ground did you use? The one in the connector or a ground on the chassis some place.

Are you sure you weren't testing the fuel gauge an not the pump? Power to the pump is only there when you first turn the key to run (prime).

While your cranking. And while the motor is running.
 
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