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Jeep has no power And backfiring

We just disconnected the cat and muffler. No change.
 
Just listened to your motor (youtube), you got to get back to basics. Make sure your basic setup is right then move on from there. Read Cruisers writeup on how to find number 1 TDC, recheck your firing order.

Have you had the timing chain off for any reason?

Could be something else, but it sure sounds like your initial setup is wrong. My best guess is back to basics and move on from there.

Where is your Rotor pointing when the motor is on the compression stroke, cylinder one and the timing marks are aligned? Some of the distributor caps actually have a "1" molded in the top, many of the newer ones don't.
 
8Mud said:
Just listened to your motor (youtube), you got to get back to basics. Make sure your basic setup is right then move on from there. Read Cruisers writeup on how to find number 1 TDC, recheck your firing order.

Have you had the timing chain off for any reason?

Could be something else, but it sure sounds like your initial setup is wrong. My best guess is back to basics and move on from there.

Where is your Rotor pointing when the motor is on the compression stroke, cylinder one and the timing marks are aligned? Some of the distributor caps actually have a "1" molded in the top, many of the newer ones don't.
Click to expand...

We just double checked that. Rotor is in the correct location. Timing chain hasn't been messed with.
 
SPECFab said:
clogged injectors have bit me in the past with the same symptoms
Click to expand...

We just swapped rails and injectors. No change.

By the way, my MJ has 27 missing parts now.
 
Drill a hole in the pipe on both sides of the Cat, to look for pressure differences. A rich fuel rate can burn up a CAT very fast!!!

You might try a vacuum gauge but not sure they are much help for your problem. They would show up a clogged exhaust!!!!!

Edit, never mind. In your case I would go back to square one, start over you missed something. You even swapped out the ECU right?

Try another TPS and MAP, or check and verify their action with an ohm meter and vacuum pump versus the FSM

Gold Cobra said:
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.
Click to expand...
 
Last edited:
One more wild ass guess, alternator?

Put a volt meter on stuff one at a time, sensors TPS, MAP, alternator.... and look for a spike when you goose the gas peddle, a spike that is way off,. or a missing spike that should be there. Try moving the harness like it would move when you goose the engine see if that make it miss.
 
SPECFab said:
you have to be missing something stupid simple
Click to expand...
I'm with you, I've had my share of brain farts, but even getting one tooth off on the distributor, or a couple of spark plug cables crossed didn't make it run that bad.

Do a voltage test on the green and orange wire (with the engine running or cranking), you can pick it up at the ignition coil. This is your ASD main out circuit and supplies voltage to the coil, the injectors and alternator. Does the alternator charge when it's running? You get way low voltage or fluctuating voltage in this circuit and you have issues. You might try swapping out the ASD relay and take a look at the pins and see if they are discolored. If the relay is chattering you can see it better with a analog (needle) volt tester at the green and orange wire.

I'd also do a volt test at the sync sensor voltage feed, either 7 volts or 5 volts, I think it is 7 volts on the 91. Possible you have a short someplace in the sensor feed. This can suck down the voltage and affect numerous sensors (garbage in garbage out).
 
Ecomike said:
One more wild ass guess, alternator?

Put a volt meter on stuff one at a time, sensors TPS, MAP, alternator.... and look for a spike when you goose the gas peddle, a spike that is way off,. or a missing spike that should be there. Try moving the harness like it would move when you goose the engine see if that make it miss.
Click to expand...

I was having the same thoughts actually, thinking the alternator is shorting out the ASD circuit or maybe even a bad diode is scrambling things up some. Try switching your meter over to AC and test at the battery poles with the motor running and see what kind of voltage you are getting. Sometimes a bad diode shows up as AC current (depends on the meter).
 
We didn't meter meter anything while running because we couldn't keep it running long enough. When idling, it idles awesome, for about 20-30 seconds then will die. We swapped the ASD relay and the gauge on the dash is showing correct alt output.

Between the 5 people that have tinkered with this we have like 50 years experience with 4 liters. Not that that makes us experts, but it doesn't hurt. We just gave up and he's dropping it off at the night drop of a local shop right now.
 
looks like a couple things....timing is a bit off. but i believe the pressure return hose from hardline to pump in tank may be cracked. causing it to idle okay but have other issues. I will know more tonight
 
More data BINGO!!!!!!

When idling, it idles awesome, for about 20-30 seconds then will die

:)

Amazing how much a little bid of missing trivial data can mean:

I would bet real money the O2 sensor DATA to the ECU is bad as it tries to go closed loop!!! Get an analog meter on it. Read my old thread here about the heater in the O2 sensor, the wiring etc and how to test step by step!!!

Check the O2 sensor wiring for a short damage..

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen



Gold Cobra said:
We didn't meter meter anything while running because we couldn't keep it running long enough. When idling, it idles awesome, for about 20-30 seconds then will die. We swapped the ASD relay and the gauge on the dash is showing correct alt output.

Between the 5 people that have tinkered with this we have like 50 years experience with 4 liters. Not that that makes us experts, but it doesn't hurt. We just gave up and he's dropping it off at the night drop of a local shop right now.
Click to expand...
 
Last edited:
I just tested resistance on both grounds on the O2 plug. Both are good. O2 sensor is getting proper voltage. I couldn't test it while it was running because I don't have an analog meter. We also replaced the O2 sensor.

We also just replaced the rubber line in the tank, someone else recommended that. Our fuel pressure gauge from o'reilleys just quit so we can't get that reading anymore.

The Jeep is running right now, but sounds like there might be a slight and random misfire, but its hard to tell because we could be over critical at this point. Not sure if its resolved or not because this problem quit once before.
 
Disconnect the O2 sensor and see if the problem is still there or gone. Drive it, give it the full test. The ECU will default open loop and if it runs great it is a problem in the O2 sensor system. Test the 12 volt supply wire to the O2 sensor heater. Test the continuity from the O2 sensor to the ECU on the 2 ECU-O2 sensor wires. Look for chaft wires on the O2 sensor line from exhaust or driveshaft encounters. A loose random contact wire short in the O2 wires will do it!!!!
 
We just took it for a 20 mile drive. No issues. We just got back to my place to see if we can get the problem to return. It did disappear once before.
 
Stealth mode Jeep Gremlins no doubt with a cloaking device.
 
Ecomike said:
Disconnect the O2 sensor and see if the problem is still there or gone. Drive it, give it the full test. The ECU will default open loop and if it runs great it is a problem in the O2 sensor system. Test the 12 volt supply wire to the O2 sensor heater. Test the continuity from the O2 sensor to the ECU on the 2 ECU-O2 sensor wires. Look for chaft wires on the O2 sensor line from exhaust or driveshaft encounters. A loose random contact wire short in the O2 wires will do it!!!!
Click to expand...

We just tried running it with and without the O2 sensor plugged it. It's running fine today, but with the sensor unplugged the idle is noticeably smoother. We inspected the wiring and went through your write up and everything looks/tests fine. Idle is a little rough but it stays running.
 
An intermittant problem probably eliminates initial setup issues. Next best guess would be a wiggle factor problem (connector or harness) or a harness cooking on the exhaust problem in the sensor circuit someplace.

Just a wild arsed guess, go look at the the rear O2 sensor pigtail and see if it is cooking on the exhaust.

Where the harness makes the bend at the rear of the fuel injector harness. Feel each individual wire between your fingers, they can break under the insulation. You'll see the likely spot if you look closely.

You really have to spray out all the connector with a good contact spray. A little oil or coolant in there can cause all kinds of grief. Oil is an insulator and cuts off low voltage, coolant is a conductor and shorts things out.
 
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