2000 Cherokee 4WD 4.0 Backfiring through Intake

[Talyn]

Have you also pulled out the cam sensor drive and checked it as well?

 

[stonedv8]

Have you also pulled out the cam sensor drive and checked it as well?

No, I havent gone that far. Since that involves messing with the timing chain and pulling those covers, I wanted to try the sensors first.

 

[Talyn]

You don't have to pull the covers to check the drive and gears. Bring #1 up to TDC on the compression stroke then pull the drive. Check the gears and if good put the drive back in, alining the holes with a tooth pick.
Another way to check the sync w/o pulling the drive is to rotate the crank until the install holes in the drive line up (under the sensor). Check to see if the crank is at 0* on the timing cover.

 

[stonedv8]

Ok, got to do some more tests.

MAP and MAT both check out good by testing it the correct way.

Thanks again Talyn for pointing me in the right direction on the MAP.

Next on the agenda is the O2 sensor, Cam Drive gear and Crank Position Sensor.

Crank and O2 sensors are all $70-$80 at the local auto parts places. Can get them on Ebay for about $35 shipped for both of them brand new.

Think I will just go ahead and replaced those two as reading all over the O2 is probably due for it and while shipping from the same place go ahead and replace the Crank Position sensor as well.

I know the quality of these sensors are not up to snuff with OEM grade I am sure, but for piece of mind knowing they will do for now while I am still trying to diagnose a problem they should work. If one or the other fixes my problem, I can always go back and purchase OEM or better grade sensors for long term useability.

 

[Tim_MN]

There are numerous XJ threads about persistent CEL or driveability problems that were finally solved by using genuine Jeep sensors.

Cheap parts are cheap for a reason.

 

[Talyn]

Rock auto has NTK O2 sensors for $32 & $37.

 

[stonedv8]

There are numerous XJ threads about persistent CEL or driveability problems that were finally solved by using genuine Jeep sensors.

Cheap parts are cheap for a reason.

Well that sucks, dont want to buy new parts and continue having issues.

Looking through the search it seems you are more than correct as it seems that has caused numerous issues.

And thanks Talyn for the inexpensive O2 sensor links.

Will order one of those O2 sensors, and continue on in my diagnosis.

 

[stonedv8]

Well, small update of no help to me at the moment.

Bought a crank position switch. Replaced it and still does the same thing.

It may be in my head but it feels like it isnt as drastic, before it was like a gunshot now its slightly less pronounced and muffled. But still there and undriveable.

Waiting on the O2 sensor I ordered from the suggested place above.

 

[boncrshr]

This may or may not be helpful....but the only time my 2000 XJ has backfired through the intake it was the coil pack. It took me a long time to figure it out, as it intermittently threw a misfire code and the resistance on the coil pack was within specs. Just throwing it out there....

 

[stonedv8]

Another small update.

Got the O2 sensor in and installed just now.

Same symptoms. And still no codes popping.

Will be pulling the cam position drive gear out this weekend. I work Tuesday-Saturday.

So that will be my Sunday project. Then I am at a loss as to the next step.

 

[stonedv8]

This may or may not be helpful....but the only time my 2000 XJ has backfired through the intake it was the coil pack. It took me a long time to figure it out, as it intermittently threw a misfire code and the resistance on the coil pack was within specs. Just throwing it out there....

Thank You for your input. That does help as it gives me another direction to look at.

I am kind of in the same boat though, as no codes are popping and as you stated the coils are testing as correct. But again, I work in a motorcycle shop and have seen first hand coils that test out fine on the bikes and still be confirmed as being problematic.

Looking at some used ones at the moment, maybe I can find one cheap enough to throw on as another test.

 

[stonedv8]

Hmm,

Wife found a coil pack at a junkyard today, sent her as I work on Saturday and I knew everyone would be closed on Monday.

Got off work and was ready to swap it around but the parts jockey who pulled the coil pack broke off the connector end. So only thing I could do was compare ohm stats from one to the other. They both put out same stats.

I dunno.

Last step I figure I can perform would be the cam position gear timing as Talyn suggested previously. Will be doing that tomorrow.

And then if that doesnt work I guess its off to the shop. I just hate doing that because I have had an issue in the past where they couldnt figure out a problem on a Firebird, so they just kept on throwing parts at it. Cost me tons of money for them to do that.

 

[sidewaysstarion]

Do you have anyway to take video of it and upload it to youtube? Also how badly is the connector hosed, maybe you can halfway wire it in just to test?

 

[xjnco]

Had this problem on my '96 4.0 and it turned out to be a worn out distributor. Pull the cap off and see if the shaft has ANY play in it, if so replace entire distributor to correct the problem.
Good luck..

 

[stonedv8]

Do you have anyway to take video of it and upload it to youtube? Also how badly is the connector hosed, maybe you can halfway wire it in just to test?

Yeah, I thought about that and may just do it with some connector pins. I cant bring the coil pack back until next weekend anyways.

Had this problem on my '96 4.0 and it turned out to be a worn out distributor. Pull the cap off and see if the shaft has ANY play in it, if so replace entire distributor to correct the problem.
Good luck..

The 2000 and up model Cherokee's do not have a distributor, timing is based off of the PCM and the Cam position sensor and drive is located where the distributor normally would be.

 

[boncrshr]

Thank You for your input. That does help as it gives me another direction to look at.

I am kind of in the same boat though, as no codes are popping and as you stated the coils are testing as correct. But again, I work in a motorcycle shop and have seen first hand coils that test out fine on the bikes and still be confirmed as being problematic.

Looking at some used ones at the moment, maybe I can find one cheap enough to throw on as another test.

It took me about a week to figure it out...fortunately my Mom drives a 2000, so I just borrowed hers, and that turned out to be the problem,

 

[stonedv8]

Ok, tested quite a few more things now.

Did the test Talyn suggested by pulling the CMP sensor off of the drive and lining up the timing mark at 0* and seeing if I can put a pin inbetween the two holes. That tested out good.

Tried jumping the junk yard coil pack with the broken connector (no luck) so I reinstalled my coil pack and left it loose since I was still testing. Well I cranked the Jeep and it ran good with no backfire and a slight hesitation. So at this time I thought "ok" it is the coil pack.

Re-tightened everything and cranked it, backfire like crazy. Loosened the coil pack and crank the jeep. Backfire, so I move the coil pack around leaving it loose and it starts backfiring even worse. So I am thinking it is definitely the coil pack.

Go buy a new one from Autozone, install it and backfire. No luck, wasted money.

Well, at the same time I went ahead and bought a code reader because between swapping all of the sensors I did have a CEL pop finally.

Had 3 codes, cleared them and crank and ran it again to get an official one to pop. P1391 will not activate the CEL but I cleared it 4 times and each time it would pop but not CEL activated.

P1391 is intermittent loss of power to CMP and/or CKP. Since I replaced both of these and we had been messing with the CMP testing the drive gear making sure it was set right. I thought I had a bad one as I read numerous cases online of continual P1391 codes due to replacement of CMP and it being bad brand new as these were Autozone sensors. Went and swapped it out with another new one, installed and same thing.

Still getting a P1391 error, so this time I left it running for about 10 minutes as I check all of the connections again and wiring to see if it made a difference moving and re-arranging the wires. No luck, but it finally did have the CEL come on and still the P1391 error.

My dad came over to help as he is pretty mechanically inclined, he was scratching his head as well.

He did talk to an old man at Autozone who knew about these motors and he suggested maybe the CMP drive gear itself if stripping out.

Would the top of the CMP still line up with the crank at 0* and still cause this issue if it was stripping out on the bottom? Since I havent actually pulled it that is something I havent verified.

So, again, I am at a loss. Since it runs good at 2k RPM's I dont think its motor related, has to be the sensors or electrical. I dunno..

Guess its time to tow it to a shop. Kind of defeated at the moment, and it being Memorial Day weekend, probably wont be able to get it to a shop for a few days.

 

[Jnida63]

Did you ever test the fuel pressure? If it is low it will go extreme lean and cause what you are experiencing.
Also make sure the pins are tight on the coil pack plug and the cmp sensor, take a dental pick and tighten the plugs.
Also some newer jeep coil pack connectors are wired different, make sure your plug faces the same way as your old plug.
You will also need to set the cam crank correlation with a scan tool that shows that feature, i use a DRBII.
The pc sets the ignition timing but the cam sensor sets your injector timing

 

[stonedv8]

Did you ever test the fuel pressure? If it is low it will go extreme lean and cause what you are experiencing.
Also make sure the pins are tight on the coil pack plug and the cmp sensor, take a dental pick and tighten the plugs.
Also some newer jeep coil pack connectors are wired different, make sure your plug faces the same way as your old plug.
You will also need to set the cam crank correlation with a scan tool that shows that feature, i use a DRBII.
The pc sets the ignition timing but the cam sensor sets your injector timing

Yes, fuel pressure was at 49psi. One of the first things I tested.

New Coil pack connector is the same.

I read in the book about needing to reset the cam sensor with a scan tool, but it stated that was only if I removed the cam sensor drive gear and it may have gotten moved. Since it was never removed and I have had this problem from the beginning, would replacing just the sensor require having to reset it with a new scan tool?

 

[Jnida63]

If the camshaft unit is starting to sieze, it can move. look at the base where it mounts and try to see if there are any signs of it being moved.
It seems to be a common problem.
get access to a scan tool and check the readings on the coolant temp sensor, check it cold and cross check the reading with the ambient air temp sensor, both should be the same when your engine is dead cold.