GGXJ
09-19-2012, 11:21 PM
Ok, here's a little background... it's a 1990 4.0, 5 spd, 4wd. It's relatively stock with a few minor mods. The engine is all stock. At 210k miles, 90k of me beating on it like a red headed stepchild, I swapped the motor. It was complete block plus the head from a 1996 donor with 80k miles on it. So the intake, exhaust, accessories, transmission, etc was all from the original motor. Since the motor swap, it has been running REALLY rich. I'm getting less than 10 mpg. The only thing that's changed since the motor swap is the exhaust. I had been running with only a cat (ripped off the rest on a rock ledge). Since the swap, I cut out the cat and put on a glass pack. The only other thing that I can think of is that we had to use the temperature sensor from the 96 (located in the thermostat housing) as opposed to where it used to be located on the 90 (in the side of the block). I've double checked the vacuum system to make sure all hoses are where they're supposed to be and all looks well.
Another strange thing about this is that everytime I start it, it will just barely start and immediately die. Then the next time I start it, it starts and stays running. Rarely, I have to start it a third time but never more than 3 times. The idle is sometimes ok but usually surges. Also, when I'm driving, it accelerates fine and will cruise pretty smooth, but if I let off the gas for any amount of time and then push the clutch, it wants to die. If I release the gas and press the clutch at the same time, it's fine. It always starts back up though, if it dies.
I checked the plugs a while back and they were all pitch black, no sign of any single cylinder having more of an issue. Also, I noticed that my oil level actually ROSE. When I drained it, it smelled of gasoline and was very watery. I'm assuming it was running so rich that the gas leaked past the piston rings.
My first instinct is fuel pressure? Any ideals on what else could be causing this? The plugs were brand new after the motor swap, so them being black is just a symptom, not the cause of the problem. I'm not sure if there's maybe something else that I may have missed when doing the swap.
Another strange thing about this is that everytime I start it, it will just barely start and immediately die. Then the next time I start it, it starts and stays running. Rarely, I have to start it a third time but never more than 3 times. The idle is sometimes ok but usually surges. Also, when I'm driving, it accelerates fine and will cruise pretty smooth, but if I let off the gas for any amount of time and then push the clutch, it wants to die. If I release the gas and press the clutch at the same time, it's fine. It always starts back up though, if it dies.
I checked the plugs a while back and they were all pitch black, no sign of any single cylinder having more of an issue. Also, I noticed that my oil level actually ROSE. When I drained it, it smelled of gasoline and was very watery. I'm assuming it was running so rich that the gas leaked past the piston rings.
My first instinct is fuel pressure? Any ideals on what else could be causing this? The plugs were brand new after the motor swap, so them being black is just a symptom, not the cause of the problem. I'm not sure if there's maybe something else that I may have missed when doing the swap.