Topic: Cherokee 4L misfire (Read 3712 times)

James · « **on:** June 17, 2010, 11:24:37 AM »

Hi, don't know if anyone can offer any suggestions to help me on this one but its driving me bonkers!!

My Cherokee 4L started to misfire on one cylinder about a month ago, So far I have

1, replaced the Rotor, Cap, Leads and Plugs.
2, downstream O2 sensor,
3, Had diagnostic done, this pointed to closed circuit on injector 4,
4, replaced all injectors with new.

Still got misfire on Cyl 4. The only clue seems to be that the No.4 injector is receiving a constant un-pulsed 12-13 volts where all the others seem to be getting around 6volts ( I assume this is because they are pulsing).

So any suggestions anyone ............. Please!!!!!

wildwood · « **Reply #1 on:** June 17, 2010, 01:42:41 PM »

Had this and loss of power on the GC
Also had it on the YJ which was more intermittant.....

Code showed up on the YJ

No code showed on the GC

Both cases it was the TPS....... (throttle position sensor....... ) £25 from lightys £100 with the drink from a stealer

James · « **Reply #2 on:** June 17, 2010, 02:04:14 PM »

Hi Wildwood
Thanks for that. I don't understand why a tps would create a missfire on one cylinder. What is lightys? is there a way of checking the tps?

Tank · « **Reply #3 on:** June 17, 2010, 02:26:24 PM »

Ligthys is lighthouse,they sell jeep stuff.Im sure someone will be along to give you the full details soon.They might be in the suppliers section too

wildwood · « **Reply #4 on:** June 17, 2010, 02:39:55 PM »

Lighthouse Jeep parts........ Crown Jeep parts for the UK 01953681237 Andrew or Julian.

They didn't have any TPS parts when I called last month so got the dealer price......(stealers)

Then called Charlton Breakers 01223832656 who sent me the complete throttle body WITH TPS MAF and IAC attached for £65 Was easier to undo 4 proper bolts and spring 3 cables to replace the Throttle body than to tart around with the cheesy little rusted torx bolts that hold the TPS on

As to why?......... Really not sure...... not being the sharpest blade in the drawer when it comes to lekertrickery........

Not sure why the GC didn't display TPS prob code either........

I ended up asking here then googled the prob and read reams of stuff stateside....... and it all pointed to TPS.......

Like others, prob now solved and smoothest changing gearbox and performance that its ever been.....

Not really any help but ....... my initial probs felt like gearbox probs so just goes to show..... how a little plastic cigar stub thing makes such a difference

James · « **Reply #5 on:** July 01, 2010, 04:46:45 PM »

Bit more news on my 97 4L Cherry misfire. I had an auto electrician in to really check out the problem. I have been informed its the ECU.
I have looked into a repair but nobody seems to offer that service for this ecu. I am seriously at the point of getting rid although it is a shame to break a 4L sequential lpg injected cherokee with only 60k on the clock, but at the same time I must have thrown over 600 quid at the problem already and dont want to gamble any more.
The fault seems to be that the ECU is not pulsing No.4 injector. Any ideas anyone? when this started hapening I was just taking the car for an MOT and it was my wifes daily drive, its been off the road now so long that its had to go onto a SORN. Help!!!

Panic mechanic! · « **Reply #6 on:** July 01, 2010, 04:48:34 PM »

take a pic of the ecm and post it up as I am sure there will be someone with a spare kicking about on here,

James · « **Reply #7 on:** July 01, 2010, 05:12:48 PM »

Cool Idea[attachment=1][attachment=2]

James · « **Reply #8 on:** July 01, 2010, 05:15:21 PM »

Oops! Lets try that again......

Panic mechanic! · « **Reply #9 on:** July 01, 2010, 05:20:29 PM »

ok where are you?

James · « **Reply #10 on:** July 01, 2010, 06:58:38 PM »

Good Point Panic.
I am in south London/Kent.

Panic mechanic! · « **Reply #11 on:** July 02, 2010, 02:34:40 AM »

been thinking about this,I don't think its your ecu,I think you need your lpg emulator replaced,unplug the injectors and plug in the original injector loom and see if it runs ok then.

Mike Pavelin · « **Reply #12 on:** July 02, 2010, 08:05:34 AM »

Jeep PCMs are ultra reliable. reinstate the original wiring first.

James · « **Reply #13 on:** July 02, 2010, 10:09:50 AM »

Yes. You could be right, but I have tried unplugging the emulator but of course that does not work. I actually don't know how to knock the lpg system out of the system. Apart from turning it off of course and that does not change anything. There is no separate loom to bypass the emulator as far as I can see. but there are a lot of cables under the bonnet!

James · « **Reply #14 on:** July 02, 2010, 11:57:01 AM »

Hi Mike & Panic
Ok, after a bit of research on the web I have managed to figure out that you are(once again) correct and there is still the original loom for the injectors in place so I disconnected the LPG ECM from each injector, therefore cutting out the the LPG system from controlling the injectors. Started her up, but she still has the same old misfire. So I am going to go and put it all back again. But this does at least isolate the problem a bit and still makes me think a bit more that the Jeeps ECM is at fault. Great idea of yours though, I would never have thought it was that easy to disconnect the injectors from the LPG system!

Panic mechanic! · « **Reply #15 on:** July 02, 2010, 01:10:45 PM »

You should be able to get hold of a replacement second hand ecm, I have one here you could try but I am in birmingham and I will need it when I put the 4.0 I have here into one of the jeeps.

James · « **Reply #16 on:** July 02, 2010, 02:28:41 PM »

Yep. I think thats the next step. I will keep my eye out for one. But that brings up another issue. do you think I should just try and get one the same year and shape or try to match up numbers? The problem is when I have investigated companies to repair mine they dont seem to recognise the part number. how important do you think the numbers are or do you think for the most part thee ECMs are interchangeable?

Panic mechanic! · « **Reply #17 on:** July 02, 2010, 02:37:46 PM »

there are 2 types of cherokee ecm i beleive, there is an early type and a later type available, ideally you want one from the same year as the connectors are different.There are usually someone breaking one on here or ebay so I would look there for someone close to you.

Mike Pavelin · « **Reply #18 on:** July 02, 2010, 03:16:36 PM »

Assuming yours is a 1997 model year car (black key, no SKIS, immobiliser turned off by square remote) Any 1998 onward XJ or TJ module won't work because they are all SKIS mmobiliser enabled. If you get a used 1997 module will still have to go to a dealer because the VIN numbers in the PCM and immobiliser module have to match and only they have the software and (possibly) the knowledge to relearn the vin. You could try to get a 1997 US spec module that hasn't been SKIS or VTSS enabled, it will then run without the pesky May and Schofield immobiliser. There is a possibility that a 1996 (last of the pre facelift XJs like mine) will work but the instrument cluster drivers may not be compatible with the newer dash.

MOCAJ · « **Reply #19 on:** July 02, 2010, 06:30:49 PM »

i have been down this replacement pcm route and it isnt as easy as it seems

my recent 97TJ problem was cured by replacing the upstream oxygen sensor. Problem was when warm and under load, eg up a long hill, jeep lost power and backfired, could hear it through the snorkel.

new sensor cured it

Bubba · « **Reply #20 on:** July 02, 2010, 07:43:26 PM »

this last two years have seen a few leky problems on later jeeps

James · « **Reply #21 on:** July 04, 2010, 09:30:39 PM »

Well People. I have taken a punt. and am getting another 97 cherry ECM. I think you are right about all the re-coding and stuff but this cherry is pre-digital dash, It has that really quaint infra-red remote that unlocks it but no immobiliser or anything like that. I am hoping that re programming won't be an issue. If it doesn't work I am sending my ECM to the states for an exchange unit (still a fraction of the cost of a main stealer here). Will keep you informed as to how I get on ....... not really holding out too much hope though. This is a real nightmare fault.

Mike Pavelin · « **Reply #22 on:** July 04, 2010, 09:57:03 PM »

It ain't a 97 then. Must be a 96, in which case a used '97 PCM definitely won't work and there is no chance of making it work as the anti theft can't be deactivated. You need one for a '96.

Bubba · « **Reply #23 on:** July 04, 2010, 09:58:56 PM »

o crap

James · « **Reply #24 on:** July 05, 2010, 11:04:07 PM »

Well, It started! and ran really sweet, so nice to here a smooth straight six again............ then it stopped ........... then I started it again .......... it ran for about 10 sec....... then stopped. So there you have it, I put the old ECM back in to check all was how it was before and it is. I now have a spare 97 ECM and a spare 8 injectors. I am going to order a new ECM from the states, I will tell you how I get on ............ unless of course you have any other great ideas?

Author Topic: Cherokee 4L misfire (Read 3712 times)

James

James

Tank

James

Panic mechanic!

James

James

Panic mechanic!

James

Panic mechanic!

Mike Pavelin

James

James

Panic mechanic!

James

Panic mechanic!

Mike Pavelin

James

Mike Pavelin

James