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Jeep has no power And backfiring

dellstopjeep

dellstopjeep

NAXJA Forum User
Location
KUNA, ID
91 jeep Cherokee 4.0. Auto Basically jeep has no power When I press pedal. Motor will rev but then basically cut out with no power And backfire. I can slowly accelerate and it wont happen but the minute i give it any really throttle it cita out And backfires. I swapped a tps And it wasnt the problem. Any ideas?
 
Check your fuel pressure. A problem with that can cause both of the symptoms you describe. A fuel pressure gauge can be rented from many parts stores inexpensively; call around for availability.

For a 91, you should have approximately 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be sure that the vacuum line to the FPR is not wet with raw fuel which would indicate a ruptured fuel pressure regulator.
 
Vacuum leak from the throttle body to the MAP sensor will cause that.


Clogged Cat converter too. Low fuel supply volume, pump, filter or pres reg. CHeck the ballast resistor to fuel pump and the battery ground clamp.

Spark plugs been inspected?
 
souske said:
An itteermittent cps failure manifested itself the same way on mine
Click to expand...

Mine also, a CPS going out caused those symptoms on mine. Actually both my Renix and my HO. My guess was sometimes I got an intermittent pulse out of the CPS that was too weak for the ECU for the PCM to read.

Check your CPS pigtail and make sure it isn't cooking on the rear of the exhaust manifold. Also have a look at the CPS and see if it isn't covered in oil from a leaky valve cover gasket. I don't know why or how, but the CPS on my HO acted up once when it was covered in hot oil.

But like Mike said, many things can cause the same symptoms. My anti theft module was failing and had trouble keeping the ASD relay energized. The motor would periodically buck and snort, run really bad if at all. Sometimes I could coax it into running, feathering the gas pedal. Much the same as a failing CPS.

Can you retrieve the MIL codes using the key methode in a 91?
 
So we swapped the distributor from my running 92 to his 91. As well as The ECU, O2 sensor and TPS. CPS and MAP sensors all tested fine.

Nothing has changed. Idles fine most of the time then when throttled up it bogs down and sputters.

This thing has to run perfect by Thursday. Please help.
 
Also brand new fuel pump and filter.
 
Ecomike said:
Vacuum leak from the throttle body to the MAP sensor will cause that.


Clogged Cat converter too. Low fuel supply volume, pump, filter or pres reg. CHeck the ballast resistor to fuel pump and the battery ground clamp.

Spark plugs been inspected?
Click to expand...
 
cruiser54 said:
Can you SEE electricity, other than lightning? Make sure it, and both ends of the strap between the firewall and rear of the head are immaculate. No paint. clean and shiny. Connectors must be removed and refreshed.
Click to expand...

He cleaned all grounds and replaced several in the troubleshooting process.
 
Ecomike said:
Vacuum leak from the throttle body to the MAP sensor will cause that.


Clogged Cat converter too. Low fuel supply volume, pump, filter or pres reg. CHeck the ballast resistor to fuel pump and the battery ground clamp.

Spark plugs been inspected?
Click to expand...


Plug have been inspected and there's no vacuum leak at the map. We checked the ballast resister by trying to bypass it.
 
Clogged up exhaust? Cat, pipe or muffler? Is the exhaust stock?

Spark problem? Cross fire, HV coil?
 
Gold Cobra said:
So we swapped the distributor from my running 92 to his 91. As well as The ECU, O2 sensor and TPS. CPS and MAP sensors all tested fine.

Nothing has changed. Idles fine most of the time then when throttled up it bogs down and sputters.

This thing has to run perfect by Thursday. Please help.
Click to expand...

The dizzy swap may be not be index right!!!!! Check the 1-1 plug to cap match ups too. Maybe two got flip flopped.
 
We indexed the dizzy like 3 times and also swapped coils.

I'd there anyway to check for a clogged cat? He's running a flowmaster so I'm sure that isn't clogged.
 
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