thealmightyjohn

I'd like to keep a long story short.

'96 XJ 4.0

I'm getting a check engine light, and the code is missing on multiple cylinders.
This will stay lit 100% of the time for 3-4 weeks then go out.
When it goes out, the jeep then runs perfect for 3-4 weeks until the light comes back on.

I am now on a third cycle of "light on" running rough.

This is a daily driver. I commute apx 60 Miles per day 50/50 city/highway.

relevent parts changed over past 1-2 years
all ignition parts
o2 sensors
tps
iac
camshaft position sensor
crankshaft position sensor
ecu replaced with used part by a mechanic.

Any help is greatly appreciated.

BlueRidgeMark

When was the last time you checked your grounds?

thealmightyjohn

The large braided ground to the firewall is good.
Electrical is my weakness. I'm not sure where the others are.

tjwalker

*Post the exact codes that you are seeing, not just a description. With OBD codes, the devil is always in the details.

*When the misfire codes return, is it always the same cylinders? What cylinders are they? This is a very important distinction.

*What brand spark plugs do you have installed? Were they gapped to .035 prior to installation?

*Verifying fuel pressure would be high on my "to-do list". Not saying that is what it is, but it is something that you should verify that it is within spec.

*Below is more on grounds, as BlueRidge mentioned. Never a bad idea to refresh.
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Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.

thealmightyjohn

Thanks for the reply.
Unfortunately I don't have detailed code info. The first time this happened I had the parts store pull the code, and they told me "missing on multiple cylinders". I haven't had a code pulled each time, as the symptoms seemed identical. Would their be multiple codes to tell which cylinders? The first time there was only one code.

As to the grounds, I will double check both you mentioned ASAP. Likely this weekend.

thealmightyjohn

As to plugs, I'd have to pull one or pull receipts to be sure. I seem to recall forums mentioning sticking to oem with nothing fancy, so I imagine that's what I did. Gap would have been done according to Haynes manual info.

BlueRidgeMark

The one on the firewall is the least important, of course!

Battery to fenderwell. Just follow it from the battery ground terminal - it's less than a foot away.

Battery to coil mounting plate. This is the critical one. Your cornpoooter grounds there.

Take all of the grounds apart, make nice shiny metal on everything that contacts anything, slap some dielectric grease on there (prevents corrosion), and inspect the wires and connectors. Replace as needed. Be happy.



Consider investing in one of . I just got mine delivered, which replaced a $20 no-name unit that died after a year or so. Wish I had known about this one! It comes with the software to run on your PC and on your Android smartphone. Reads and resets codes, and better yet, will log information as you drive. Lots of information, not just codes.

Good stuff, Maynard!

LordLancifer

cornpooter? Is that a technical term? Isn't there a ground running to the alternator as well?

CCKen

Yes. Here's a pic of the two coil mount studs grounds for a '97 and '98, view looking up. The '96 may not have the TCM/PCM grounded here. I have no way of verifying (No FSM/No '96 XJ to look at)





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DO NOT use Dielectric Grease as suggested. Instead use Ox-Gard or NOALOX. Check Lowes and/or Home Depot for this stuff. Either one will do.

LordLancifer

Thanks for the image! I guess it's about time for me to check all my grounds and reapply ox-guard anyway lol

BlueRidgeMark

Us OxGard for all connections that are aluminum, especially if there is another metal involved. That's what it's made for.

If there's no aluminum, use dielectric grease. It's cleaner, and has exactly the same conductivity as OxGard. (Close to none, but don't worry about it.)

http://www.w8ji.com/dielectric_greas...ive_grease.htm

https://www.cherokeeforum.com/f2/ele...0/#post3279926