Injector voltage cutting out on one cylinder

[98XJblack]

So the story begins, been awhile since I've posted here, been caught up in a world of s#*t with my newest XJ, a 2000 XJ Sport, 4.0.

Anyways coolant was horrifically bad and overheated and head gasket blew and cracked the head. Ok pretty bad yes took care of all that business, new machined head put it all back together, sweet! Cylinder 6 was missing and there was a slightly ticking from the rocker arms like you may here from se of those ford engines which I thought was strange so did the guys from the shop in doing this at. Anyways we checked the voltage at the injectors because all other possible misfire scenarios were debunked. On start up we had voltage but once the rpms hit somewhere around 3000, out it went no spark at the injector and never would come back unless restarted. We found a pcm and it seemed to fix the issue however a few days later I started to experience backfiring at the intake manifold! Yes I am in the process of removing and replacing the camshaft. Lifted on cylinder 6 was torn up and valves weren't closing (hence the backfiring issue). Now here's the big question,

Is it just pure outrageous coincidence that the cam was banged up and not lifting the valves on cylinder 6 and voltage is getting cut from the cylinder 6 injector? Or did the pcm see an issue with the cam, or camshaft position sensor tell the pcm not to send fuel to that cylinder?

Thoughts or ideas on why I am losing voltage only on that cylinder would be greatly appreciated. I should have things back together on Friday and we'll see how she runs but if I can find the issue of resolve it during this reassembly that would be ideal. (If there is one)http://tapatalk.imageshack.com/v2/14/10/29/0b22030ebafa7e4364a345d2ea6e6bf2.jpghttp://tapatalk.imageshack.com/v2/14/10/29/99e05c3f4ed1b60c2cdd03d69ce188dc.jpg


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[98XJblack]

I also want to add that the misfire/lack of voltage at the injector was post head gasket blowout disaster and replacement.


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[4.3LXJ]

Voltage drop is a product of resistance. I don't think the cam situation could affect that. I think it is just coincidence.

[98XJblack]

I'm an electrician I understand voltage drop (not trying to sound like an ass) however this is a complete shutdown/stoppage/controlled removal of voltage from the circuit. It was there and then no more. Wiring is good from the injectors to pcm. They do share ground amongst all the injectors, maybe I'll have to investigate that a little bit. I just find it extremely coincidental that it's all happening together at the same time on the same cylinder.


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[4.3LXJ]

I don't think the PCM is capable of doing that for one cylinder. In 98 they were not that sophisticated. At that point in time, all injectors receive the same signal. At this point in time, they are moving towards individual signals for each injector. But in 98 that was not the level they were at.

[slvmart]

Sounds like a "hot" short with a electrical component or wiring. Based on what you wrote, it might be possible that there is a wiring harness problem to the #6 injector. I had a similar problem with a '94 Dodge Durango. It would run fine until it warmed up. Then it would die and wouldn't start. Eventually, after having to wait for the underhood temps to drop, countless times, the problem was determined to be a bad wire in the harness going to the ECM.

[98XJblack]

Just so we're all on the same page don't let my profile name fool you this is a 2000 xj but I doubt it's any different tech wise for the pcm. Now in regards to the "hot" short scenario because the harness wires seem to be semi molded together would anyone see running a new wire from the pcm to the injector a good idea or should I risk going through the harness and potentially damaging other wires in the process? I know the wire has continuity from the injector to the pcm but I what I don't know is if the insulation opened up in the harness to the point where it could short out.

Curious question but for the injectors does voltage stay constant or does it stay at an idle voltage and rise/pulse out to the injector to tell it to dispense fuel?


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[4.3LXJ]

New wire is fine. The 200 is a step up. It splits the cylinders into two groups, 1-3 and 4-6 for signals and mixture from the injectors. But still, 4&5 receive the same voltage. The difference in signal is duration, not voltage to the injectors

[98XJblack]

Ok we'll see how things go tomorrow I'll keep everyone posted


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[slvmart]

Sort of a side note. I don't think my issue, with the Dodge, should had said Dakota not Durango, was related to insulation break down as much as that the wire may have partially sheared. I remember that the problem originally surfaced after doing a tune up. I may have inadvertently leaned on the wiring harness and fractured the wire. The wire does get pretty brittle with age.

[98XJblack]

Yea understood man didn't get to dive into the issue just yet. Still have to install a few pieces fill the coolant do and oil change and break in the new cam probably Monday. Till then...


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[98XJblack]

Also I've been instructed to use on oil with zinc additive or racing oil with zinc because the 4.0 doesn't have rolling lifters. The cam showed wear starting on more than just the 6th cylinder but in 2 others as well, apparently due to the lack of proper lubrication. Anyone else have this issue with their 4.0? Never did this in my 98 xj and didn't see any issues in this department.

[slvmart]

I didn't notice how many miles you have on the 2000. I only have about 118k on mine, and so far no signs of any engine issues. I use full synthetic, and so did the previous owner.

For break in purposes, most recommendations I have heard or read, indicate high zinc, phosphorous, and moly.

Here is Comp Cams, site : http://www.compcams.com/Products/CC-%27Lubricants%27-0.aspx

I'm sure there are other similar alternative available. Lucas even sells a additive : Amazon.com: Lucas Oil 10063 Engine Break-In Oil Additive - 16 oz.: Automotive@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41dmlTVTMIL.@@AMEPARAM@@41dmlTVTMIL

[4.3LXJ]

Also I've been instructed to use on oil with zinc additive or racing oil with zinc because the 4.0 doesn't have rolling lifters. The cam showed wear starting on more than just the 6th cylinder but in 2 others as well, apparently due to the lack of proper lubrication. Anyone else have this issue with their 4.0? Never did this in my 98 xj and didn't see any issues in this department.

I use Valvoline Racing oil in my rigs. It has the most zinc of any oil and is made for flat tappet racing engines. Also will not foul your plugs if you burn a little.

[98XJblack]

Yea I guess that's what I'll be doing from now on. And the 2000 xj has 63000 miles on it. One owner before me, not beat on from what I can see just I don't know, so many major things from stupid undone maintenance. And my ownership of the jeep has only been since mid August!


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[98XJblack]

Ok so broke in the camshaft and lifters everything's running great and no more loss of voltage at the 6th cylinder. Looks like the pcm is a little smarter than we all thought. I did nothing to the wiring before start up.


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[4.3LXJ]

Probably just shot the gremlin