'91 explorer acting funny

[predator86]

ok i dont know what is really going on with my explorer so i will start from the very beginning of when i bought it 2 years ago....it is a '91 explorer with a 4.0 and a 5 spd. the tranny has 12,000 miles on and the motor has 30k. the motor is out of a '96 ford explorer, the guy i bought it from told me that he just bolted on the '91 upper motor parts to get the wiring right. but after he did that the fuel pump would run when the vehicle is turned off so he told me just to lift the fuel pump fuse out and it would stop, so i did this until the vehicle started to run like crap and then it wouldn't start. so me and a good friend of mine spent 6 days with a meter and we tested every connection in the vehicle and after we ran a wire from the ground on the maf sensor it started and got back to normal.


fast forward 10 months- when i was coming home from work it seemed like the vehicle was losing power when the cruise was on, when i tried to give it some gas it acted like it was flooding out, the only way i could get it home was downshifting into 4th and alternating pressure on the clutch pedal and the gas pedal. i recently put in a junkyard maf sensor and it seemed to fix the problem for a week or two but now it is happening again, and not every time i drive it either, if i let it sit for a while and take it for a drive then nothing happens, it only happens once in a while when i am driving it.....does anyone know what is going on or happening here?? cuz i really have no clue...

 

[bluesman2333]

Sounds like you still have wiring trouble. You really need to fix the fuel pump circuit too. When I was troubleshooting my MAF problems, I ran 4 wires into the cab from the MAF so I could see meter readings in real time while driving. I hooked up two meters to the four wires coming out of the plug on the MAF. Checking codes is helpful too. Also, check for vacuum leaks.

 

[predator86]

so what do i need to do in order to repair this? what wires do i start looking at? where do i have the codes read? this is my first vehicle without a carb so i really dont know what im doing...

 

[bluesman2333]

Since knowledge is power, I'd say start with reading through this forum's threads. The wiring harness is pretty simple as you don't have EGR, ABS or some other things. You can go to autozone.com to printt a basic wiring diagram and start checking things with a meter. When things don't make sense, post back and someone will try to help you. One thing you can do right now is check for vacuum leaks and do a compression test and fuel pressure test. I still think you probably have some wiring problem, but these things are easy to check and they will eliminate many reasons your engine could be running poorly.

 

[BrooklynBay]

Try a new MAF sensor, not a junkyard one. You might either have one from the wrong year, or it could be defective.

 

[bluesman2333]

I tried a new MAF from AZ and that turned out to be my problem! I would go over the wiring and fix/eliminate simple/cheap things before spending large amounts of cash on maybe's. Being it's an old X, you know that there is a high probability that the FPR is bad, it has vac leaks and the IAC and MAF are dirty. It also will have bad plug wires and other tune up items if they haven't been changed by now. Throw in some wiring problems and you have a real mixed bag of nuts. Eliminate some things and the problem will become obvious most of the time.

 

[predator86]

I tried a new MAF from AZ and that turned out to be my problem! I would go over the wiring and fix/eliminate simple/cheap things before spending large amounts of cash on maybe's. Being it's an old X, you know that there is a high probability that the FPR is bad, it has vac leaks and the IAC and MAF are dirty. It also will have bad plug wires and other tune up items if they haven't been changed by now. Throw in some wiring problems and you have a real mixed bag of nuts. Eliminate some things and the problem will become obvious most of the time.

what and where is the IAC and the FPR?? will give it tuneup after paycheck, thanks guys!!

 

[bluesman2333]

The IAC is on the upper intake, you can go here for cleaning: http://www.explorer4x4.com/iac.htm for the FPR, it's just behind the upper radiator inlet on top of the engine. You can put a fuel pressure guage (about $40.00 from an auto parts store) on the fuel rail shrader and test for pressure. It should be about 32-35 PSI and if you pull the vac line off it should jump up to 40 or a little more. There shouldn't be any fuel in the vac line, if there is then it's bad too.