There is nothing regular about this problem. It happens at random moments, however mostly at idle. When idling, the Jeep starts to sputter and almost cuts off. If I put it in nuetral and give it a little gas, to keep from cutting off, the throttle seems very touchy (I barely touch it and it revs up to 2500 RPM's). If it starts sputtering and I start accelerating it continues to sputter until it goes back to normal. If I give it a bit of gas it sounds like it's not getting enough air through the intake then it backfires through the intake. I've checked the throttle body and air filter and there is nothing onstructing air flow. It seems to help if I turn off the Jeep and turn it back on. Someone suggested replacing the MAP sensor, so I tried that with no success. Do you guys have any suggestions/ideas of what might be happening?
Sputtering and Backfiring
- Thread starter Wanker
- Start date
birchlakeXJ
NAXJA Forum User
- Location
- Melrose, MN
What year/engine? Any check engine light? If so, pull codes.
I would start with verifying proper fuel delivery as backfiring in the intake can be indicative of a lean condition.
Verify it with a fuel pressure gauge at the schrader valve on the fuel rail. Compare what you get to factory spec.
There are certainly other possibilities but proper fuel delivery should be ruled in or out early in the process.
I would start with verifying proper fuel delivery as backfiring in the intake can be indicative of a lean condition.
Verify it with a fuel pressure gauge at the schrader valve on the fuel rail. Compare what you get to factory spec.
There are certainly other possibilities but proper fuel delivery should be ruled in or out early in the process.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
In his profile it says 2000.
Would this be happening after hot restarts?
Would this be happening after hot restarts?
Sorry for not including that info. It's a 2000 Cherokee, 4.0L. No check engine light. I did check my fuel pressue at the rail and it was around 45 psi. Is that high or low? It doesn't happen right after I start the engine. It happens after the engine is warm and has been running for a while. If I shut the engine off and restart it usually acts normal.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
49 psi + - 5 psi so your pressure is fine.
There is an issue with heat soak on the 99-01 XJs but that doesn't appear to be your problem.
Not all codes result in a CEL, so have the codes pulled if you don't have a scanner/reader.
If it was mine I would do the following:
Test the TPS
Clean the throttle body and IAC port
Clean the IAC pintle--be careful, they can break
The backfiring concerns me. Backfiring is ignition of unburned HC in the exhaust due to the introduction of o2. Any exhaust header leaks? Do you have the 50-state emissions with the two mini-CATs in the header?
Any recent work--mods or repairs? Last time the plugs were changed--should use NGK V-Fire with the distributorless ignition. Last o2 sensor change for the upstream sensor?
There is an issue with heat soak on the 99-01 XJs but that doesn't appear to be your problem.
Not all codes result in a CEL, so have the codes pulled if you don't have a scanner/reader.
If it was mine I would do the following:
Test the TPS
Clean the throttle body and IAC port
Clean the IAC pintle--be careful, they can break
The backfiring concerns me. Backfiring is ignition of unburned HC in the exhaust due to the introduction of o2. Any exhaust header leaks? Do you have the 50-state emissions with the two mini-CATs in the header?
Any recent work--mods or repairs? Last time the plugs were changed--should use NGK V-Fire with the distributorless ignition. Last o2 sensor change for the upstream sensor?
No header leaks. I'm not sure what the 50 state emissions is, but in Alabama we have no emissions testing, if that makes a difference. As for recent repairs, when this all started it did throw PO138 and PO135 codes, so I replaced both o2 sensors, and I've replaced my MAP sensor. During this same time I did put a Borla cat back system on. I bought the Jeep with a hair over 114k, it's now at 120k, and I haven't changed the plugs.
joe_peters
NAXJA Forum User
- Location
- Grants Pass, OryGun
There are 49-state emissions equipped vehicles--they can't be sold in California, and 50-state emissions equipped vehicles--CA legal. Excess production of 50-state emissions vehicles get dumped all over the country, so you could be in NY and have a CA emissions equipped vehicle.
Take a look at the fuse/relay for the HEGO--heated o2 sensor--circuit, see if its working.
Take a look at the fuse/relay for the HEGO--heated o2 sensor--circuit, see if its working.
birchlakeXJ
NAXJA Forum User
- Location
- Melrose, MN
For a 2000, the fuse for the heaters for the oxygen circuit is under the hood in the PDC (power distribution center), the black box. I believe it is in the area of 15-17
mrfreakinwhite
NAXJA Forum User
- Location
- MASS
Related problem here. (Thanks for the new to me searching tips!)
*My friend's 1999, 4.0L AW4, 49 state XJ*
I am getting codes for (one is PO138) both of the O2 sensors and their heating circuits on this and I'm trying to help her out.
She had the down stream o2 sensor replaced. Wires look good. Install looks clean, harness connector looks good. - CHECK
I replaced the upstream o2 sensor. - CHECK
It seems there is a problem blowing the o2 sensor heater fuse.
I am trying to diagnose the cause of the fuse popping.
Making sense?
I have replaced the the fuse and turned off the CEL light with my scanner, which worked for a couple days. Then she called again about the Change Engine Soon light. Same thing - fuse for 'heater.'
(This also makes both sensors appear to be non-functioning.)
*My friend's 1999, 4.0L AW4, 49 state XJ*
I am getting codes for (one is PO138) both of the O2 sensors and their heating circuits on this and I'm trying to help her out.
She had the down stream o2 sensor replaced. Wires look good. Install looks clean, harness connector looks good. - CHECK
I replaced the upstream o2 sensor. - CHECK
It seems there is a problem blowing the o2 sensor heater fuse.
I am trying to diagnose the cause of the fuse popping.
Making sense?
I have replaced the the fuse and turned off the CEL light with my scanner, which worked for a couple days. Then she called again about the Change Engine Soon light. Same thing - fuse for 'heater.'
(This also makes both sensors appear to be non-functioning.)
