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Need help, barely running ex...


February 29, 2004
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City, State
Halifax, NS, Canada
Year, Model & Trim Level
1991 XL
My 91 xl 4x4 is driving me nuts...

K, here's what's happening... About 2 months ago I blew a starter, which has since been replaced, next the fuse for the fuel pump went, there was only a hairline crack in the inside of the fuse and I wound up replacing the whole fuel pump cause I missed the crack, the truck wouldn't run with the new fuel pump which I later found out was defective, and replaced *again*. Now when I attempt to start her, it will occasionally frontfire into the intake (timing?) and when I do manage to get it started it will sputter and die after a few mins or will idle perfectly normally depending on it's mood. One thing remains consistant though, if I slowly bring the RPMs up I can rev it right to 4500 smoothly, however if I mash the pedal to the floor she bogs and sputters and tries to die. I'm suspecting the Throttle Position Sensor right now, but any insight would be appreciated. I have cleaned the IAC, MAF, replaced plugs, wires, fuel filter, fuel pump, battery terminals, etc, and I still don't trust it running long enough to make it around the block... I need her running soon, and I'm out of money and options. Would a crankshaft position sensor make this occur? Maybe it is TPS, or IAC, but I've been reading the site till my eyes burned out of my head and I'm no further along... Please help... :)

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Before I went about replacing any EEC-IV component, I would at least run the self-tests to see if the computer can see any problems.


Hehe, forgot to mention that, I did the diagnostic on the computer and it hasn't thrown any codes at all...

Now when you mash the gas it's bogging and almost dying and it frontfires two or three times before resuming idle... I'm stumped...

sounds like a bad fpr pull the vaccum line off and see if there is fuel in there. but some of the symptoms sound like crossed/bad plug wires

Checked FPR vacuum line, de nada... Dry as a bone, and the plug wires are new, put on according to diagrams I got from here actually... :) Normally I'd be able to fix this stuf myself but I'm not entirely familiar with computerized vehicles yet, I still like the old school v8's... Hrm, maybe time to swap to a 302...

you may have a pinhole leak in the fuel line did it run fine before the pump was changed i would pull a plug to see if it is running lean if it is then i would look at the leak if not than i would change the crank position sensor

You said you suspect the TPS... before you replace it you might want to check the voltage if you haven't already. All those 3-letters acronymed meters/sensors/valves/etc can be checked with a multimeter.

I checked the TPS and at idle I'm getting 0.93v which is about right, but when the gas is punched instead of rising smoothly it jumps to around 1.76v and bogs, then drops to about 1.43v before I let off the gas to drop it to idle again, I'm thinking the quick fluctuations of the readings might mean the TPS is toast, but like I said, I'm fairly new to anything with a computer in it... :)

I checked the ACT sensor as well, KOEO was around 2.25v, again right within range, I've been driving it without a thermostat for a couple of months so it doesn't warm up real quick but the voltage did decrease steadily as it warmed up, so I'm pretty sure it's O.k...

IAC and MAF were cleaned within the last 5000km, and it seems to idle fine so I'm ruling out IAC malfunction. When it gets hard to start if you tap the gas a couple of times and then crank it it'll kick, and if the TPS was bad the jostle of the butterfly moving may be enough to spark it to life for a few minutes at least... I'm pretty sure it's got to be something simple I'm overlooking but it's getting the three basics, fuel, air, and spark so aside from that I'm stumped...

my tps just bit the dust causing my transmission not to kick down

That does sound like a bad TPS, if I understood what you did.

if your tps reads .93 with the gas peddle up then that is in spec if it's not idleing right then then that would not be your problem i would be more inclined into the cps being the culprit then the tps but make sure you do not have any vacum leaks anywhere

Is there any way to check the CPS using a multimeter? I had her running today but the frontfiring when I crank her is getting worse. I'm running out of options methinks...

the 91 explorer uses a crank poisition sensor and that front firing is leading me to believe that your timing is way off the only real ways that could happen is the CPS goes out and the computer does not know when to send spark or the timeing chain has jumped but have you done anything with your spark plugs or plug wires latly?