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Varments or Gremlins?

BrokenSockets

NAXJA Forum User
Location
Ayr, Ontario
96 XJ country 4.0 AW4 242 3" lift, 350K

Started up the XJ this morning and headed in to work, had a bad miss. Drove it the two miles to work and opened the hood, found a nest of grass and pink insulation on top of the intake manifold and the wires to one of the injectors chewed clean through right to the stub of the connector. It was only parked for about 6 hours!

Rats! I said (among other things.)

I have taken the connector apart and soldered two short leads to the pins and then soldered and taped to the wires at the harness leads but it made no difference. Still not running on that cylinder. Could the wires shorting have damaged the injector? or the computer? What should I be looking at to verify that there is a pulse at the connector for the injector? I have a DVM and electronics repair gear here but not my XJ manuals or service book.

I also have a parts '95 XJ 4.0 that I can pull parts from. I know they are the same body style but what about the same injectors or wire harness if needed.

Thanks in advance for any assistance, I'm hoping that I'll be able to drive home from work today without limping along at 25 and sounding like crap.
 
Injector plugs are the same ... injector style didn't change until 2000 (but possibly late 99)
 
I had a bad miss on my '95, and ended up replacing all 6 injector plugs, pigtails and the wiring back to almost the firewall. Getting the wire bundle apart was the worst problem.

Rock Auto sells new connectors from Dorman for $5.44 US each. They come with a 6 inch pigtail of high temp wire.

The ground wire for each injector is common, and spliced inside the wire bundle. Because I knew my bad connection was in the wire, and not the connector, I spliced in extra wire to go all the way back nearly to the firewall. In your case, you could just splice as it left the bundle. And yes, the connectors from your '95 should work fine.

I did notice the new connectors fit in far more snugly than the old ones. The XJ also now runs better than it has in several years, even when it wasn't misfiring.

David Bricker / SYR
 
Thanks.

Do you know what should I be reading from the injector connector lead with a dvm while running to verify I have a good signal? (and impedance on the injector?)
 
OK, so I am reading battery volts at the pwr wire at the injector lead while running, good continuity from the neg side of the lead to the corresponding pin for injector 4 at the PCM connector block. This tells me my re-wire was OK.

I can make the injector click with a 12 volt battery, connected pos to the pos injector terminal and gave the Neg terminal a few quick taps with the black lead from the second injector pin. Click, click, click.

I think I have power and a working injector but no PCM switching the negative. Blown driver in the PCM because of the wires being shorted out by my friendly mouse?

If I take the PCM apart will it be possible to trace and replace the problem component, which I assume is most likely to be a shorted mosfet?

(I have my scope today to check the driver response before pulling the computer.)
 
Some guy in East Europe did that on a Renix ECU about 3 years ago, he posted the details here. If you know what you are doing, it sounds like it is worth a try.
 
The ground wire for each injector is common, and spliced inside the wire bundle.

David Bricker / SYR

Are you sure about that, David? I am currently troubleshooting my 2000 XJ injector harness. The POSITIVE wire is common across all injectors. The GROUND wire from each injector goes to the pcm. The injectors see a constant voltage and the pcm controls the firing of the injectors through the negative ground signal.
 
Are you sure about that, David? I am currently troubleshooting my 2000 XJ injector harness. The POSITIVE wire is common across all injectors. The GROUND wire from each injector goes to the pcm. The injectors see a constant voltage and the pcm controls the firing of the injectors through the negative ground signal.

Thats the way the 99XJ FSM shows it. Also it make a lot of sense to do it that way, it's way easier for the PCM to sink the current flowing through the injectors than to source it. I haven't looked inside a PCM but I wouldn't be surprised if they are just using some mosfets in order to pull the injector down to ground and turn it on.
 
Well, computer is toast. Burnt traces. Not going to get a reliable fix in that condition.

Anyone know if the 251 computer is swappable with the 296 I have? I can find several 251 versions local to me but not the 296. What's the difference? they both say 96, 4.0, auto, all models and a couple of postings on ebay indicate that a 296 is a match for the 251.

Just want to get some verification from someone who isn't trying to sell it to me.
 
New Computer did the trick. Injectors now A-OK

Regarding computer part numbers - I think the 199 and 251 would have worked. 296 seems to be a software update. The computer I got from the JY was listed as a 251, but when I picked it up I noticed a Chryco sticker indicating dealership number that said it was upgraded to revision 296. I have also seen that 199, 251, and 296 versions are all cross referenced as working for any 96 4.0 auto.

Since I rolled it into the garage, I thought I would changed the shocks and put on a new cat and muffler. Now it's quiet, doesn't bounce, and doesn't miss. Good weekend's work.
 
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