Craig Duren

So I just bought this Cherokee, it's the Sport model 4x4 with a 4.0 and it ran great. I bought a Rough Country 3" lift and new wheels and tires. Drove it for 98 miles since doing the lift, then it starts surging going down the road. This gets progressively worse as days go by. Then it starts blowing black smoke and of course stinking really bad out the exhaust. I could rev it up and that would clear it up as long as I didn't let it idle much. Then I went to move it around in the yard and it just blowed black smoke and ran really bad and wouldn't clear up so I parked it for a couple of days. Now it won't start at all, so I pull it in the shop and it has no fuel pressure, so I put a new pump from O'reilly's in it, still wont start. SO I have since then put a Crank Position Sensor, Pickup in the Dist, and an Oxygen Sensor by the engine. Still wont start, HOWEVER I can spray either in it and it'll crank and run as long as you spray it? I checked the power at the fuel pump and it is not getting anything at the pump, so I put an ECM in it yesterday, and still no power? WHAT AM I MISSING???

CCKen

Shotgun enough parts?

Check fuel pump fuse in the PDC. Mini fuse, 15 Amp, bottom row, second from the left, as you look at the fuses from the radiator.

Swap the fuel pump relay with the radiator electric fan relay and see if the pump primes. Both marked on the lid of the PDC.

Craig Duren

Sorry, should mentioned that, all fuses and relays are good, even the fues in the pass side kick panel inside, I'm at a loss, and about outa money!!!!

Roler

Wow. May I suggest you just take a step back from the whole situation and look at what you are actually doing. I mean this in a good way.

Example: after replacing the fuelpump (...), did you even verify you had fuel pressure again?

I think you have several issues to sort (the surging, the black smoke and now the non start), which can be related (like TPS gone out) or can be separate issues. Unless you are planning on replacing virtually ALL parts involved, I'd recommend you do some diagnostics first.

The fuelpump fuse/relay Ken mentioned, is a start.

Craig Duren

According to the scanner I have tps readings. It's at like 14% with foot off the pedal, then it goes to 70% at floor. I know I shoulda checked for power going to the pump before replacing it, but the jeep has sat for 6 to 8 months before I bought it so I figured the fuel had eat it up. The rest is what all I read on line at different places. I agree 100% on taking a step back and looking at it from a different angle, that's why I'm on here BEGGING for ya'll's help!!! LOL I'm kinda at a loss here. I had a friend bring his Cherokee over yesterday and that's where the ecm came from I didn't buy one of them, I'm just tired of throwing parts at it! And what we did with the ecm was put mine on his and it started his right up?

Roler

The TPS was an example of things being related, it's not stated as being the culprit.
Do the suggestion of Ken first.

Your no start is usually a no-spark, no-fuel, or both scenario. With no volts at the pump, you will at least have a no fuel. Sort that first before moving on. Don't expect a "once solution fits all" answer on the forum, you will have to put some time in diagnosing first.

Craig Duren

OK Sounds like a god idea, start with the pump having no power. From what I can tell on Mitchell on demand, the power leaves the relay and goes into the ecm, is that right? If so I wonder what tells the ecm to power up the pump?

Roler

Those kind of questions are right in CCKen's backyard comfort zone. I'd have to look up info/wiring diagrams to help you with that, if you want more than " ASD and NSS circuits are involved in that" answers

CCKen

Sorta...

The power/PCM relationship is the relay control coil circuit. When the ignition key is turned to RUN/ON, before cranking the engine, power from fuse F11 in the PDC is made available to the control coil (pin cav D4, see PDC pic). When the key is turned to RUN the PCM also provides a ground to the fuel pump relay control coil (pin cav D6) and the relay power contacts are pulled in, powering the fuel pump. The pump will run momentarily to prime the fuel rail, then shut down. The pump won't run again until the PCM sees the engine rotating (CPS), then it will pull in the relay to continuiopusly run the pump.

You can check the PCM/relay control coil circuit with a digital voltmeter.

Refer to the PDC pic and fuel pump diagram below, specifially the Fuel Pump Relay pin cavity layout. Look for D4 and D6.

Remove the fuel pump relay and inspect the relay pin cavities in the PDC for corrosion (Gray/Black apperance) and for a pin cavity being shoved down inside the PDC.

Voltmeter to 20 VDC scale. Next, using the voltmeter, (+) probe to pin cavity D4, and (-) probe to the battery negative post, key OFF, you should see 0.00 volts. Turn key to RUN, you should see battery voltage. If you don't see battery voltage withkey to RUN, there's an open in that wire from fuse F11 in the JB to pin cav D4. F11 also powers the ASD relay, so if you are getting spark the ASD relay is working.

Note here: The fuel pump relay is totally independant from the ASD relay.

For this check you may want to turn your meter to the 2 VDC scale. Key OFF, (+) to pin cavity D6, (-) to batt negative post. You may see around .02 volts. If not the CCD Bus + and - circuits are matched. Normally there is a .02 volt differential. Turn key to RUN, now you should see around .03 volts. If you do see any low voltages like these it means the fuel pump relay control circuit from the PCM to the PDC is good. If there is no voltages at all, there's a chance that wire is open.

Do these checks and get back.

The fuel pump is grounded behind the spare tire mount in the cargo bay.

BTW, does your gas gauge register when you turn the key to RUN?

CCKen

You can test the fuel pump power circuit from the PDC.

Fab up toggle switch (see pic) using a 12 VDC, 15 Amp rated, on/off switch, with some 18 or 16 gauge wires and two .250" spade connectors. My switch already had wires factory installed.

Turn the switch to OFF, insert the switch in the fuel pump relay pin cavities D2 and D8. Turn switch ON and the pump should run continuously until the switch is turned off. It runs off the battery.

Pic shows a 10 amp fuse in place of the normal 15 amp fuse because I was testing my fuel pump max amp draw of 10 amps (FSM type procedure).

Craig Duren

WOW OK Thanks a lot for that info, I'll get to checking everything. And yes the fuel gauge does work.

Roler

Told you so, lol.

Craig Duren

Yes you did! Now I gotta get off my butt and try and figure this thing out! And I was ready to part the thing out! THANKS GUYS!!! I'm gonna get on it as soon as work allows it!!!!

Craig Duren

Got It! Bad Ground, THANKS ALL FOR THE HELP, You guy's ROCK

Roler

Bad grounds.....the nails to many Xj-coffin-of-despairs, sneaky hidden-agenda-items and tried-everything-but-the-free-stuff-which-eventually-fixed-it sagas
Thanks for letting us know. Happy travels.