XJ XJ6 / XJ8 / XJR ( X350 & X358 ) 2003 - 2009

2004 XJ8 N/A 88k Miles - High RPM Misfire

 
  #1  
Old 07-02-2019, 09:13 AM
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Default 2004 XJ8 N/A 88k Miles - High RPM Misfire

I'll go ahead and start a thread for the last nagging problem with my 2004 XJ8 "mystery car" that I purchased for 1,400 bucks a few months ago. Hopefully the diagnostic approach will help someone else struggling with the same frustrating issue. I've got everything sorted out, no trouble codes, no idle stumble, the car seems to run fine, engine feels great... except when I put my foot to the mat, at about 5k+ rpm under full load, she trips a cylinder #3 misfire.

Last night I replaced the plug and coil to rule out those issues quickly. No change in behavior, drives great until I dig my foot into it. No overheating issues, no idle stumble, no hesitation below 5k. Transmission seems fine, catches the shifts, I seem to have all six gears. When I pulled the spark plug out last night it looked oddly clean. I'm not really great at "reading" plugs but I'm sort of concerned that it kind of looks like it took a steam bath. Hopefully I'm not uncovering a head gasket issue, I'm hoping it just looks clean because it is running really lean in that cylinder. I think the computer is shutting off fuel when it hits a certain misfire threshold because it flashes the SES and you can feel it fuel cut as revs fall back below ~3k.

I've ordered a new set of fuel injector o-rings and one reman. GB injector. I've also sourced two brand new Jaguar OE knock sensors. When I bought the car, the knock sensors were reversed and disconnected. I repaired the wire harness and got them properly seated on the correct side of the motor but they didn't look to be in great shape.

This weekend (4th of July) I'm going to pull the intake, replace a few gaskets, install a factory valley hose (vs aftermarket), install two factory knock sensors, restore the foam sound insulation, re-seat the intake, install new injector o-rings and replace the injector on #3. I'm also going to install eight NGK IFR5N10. If the aforementioned (which needs to be done anyway) doesn't sort it out I'll try to get it out for a drive on the scantool and investigate further. With a new injector, new plug, new coil, new knock sensors... the best I can hope for is that the ECM is flagging the wrong cylinder.

Any thoughts? I'm sort of stumped with this one.
 
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Old 07-02-2019, 09:56 AM
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After replacing the coil pack and spark plug, I also would be in suspecting a problem with the injector on that cylinder.
 
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Old 07-02-2019, 11:33 AM
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Yeah fuel injector is sort of where I'm headed. I'm going to be surprised if this is something more serious because the engine feels great otherwise.

If memory serves... in the course of diagnosing other issues with this car I had the intake off and I seem to remember one of the injector o-rings looked cracked. I remember the o-ring issue being on bank 2 though.

I wish cars could talk because mine would have a lot of stories to tell... how a dealer serviced / one owner 04 with 88k original documented miles ended up being totaled in the hands of a crappy indy mechanic I have no idea. I wish the guy I bought it from would just tell me the real story, I'm not upset at all, I just want to know.
 
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Old 07-02-2019, 12:38 PM
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I have found over the years so many people just can't tell you the truth.

About what happened to their broken whatever.

Buddy bought over his mower for me to look at couple days ago.

Said he had adjusted the carb, to improve the way it ran.

Then next time he went to use it, said it would not start.

Also it also now backfires, and jerks out of your hand.

Did you hit something, and stop the mower?

NO

Pulled the top off the motor, the shear pin was torn in half, crank was bent.

Asked how the F--- did this happen,if you didn't hit anything?

Well i'm always running over, or hitting something, don't remember if i did.

Reading things you find, can tell you a lot more about the previous owner.

Than his story's as to what happened, or his reason for selling the vehicle.

Two, or four wheels, or anything else, that's for sale.
 
  #5  
Old 07-02-2019, 02:26 PM
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I bent a crankshaft on an old mower once when I was a teenager, thought it was going to clear the rock ... you really can't mistake that bone jarring jolt through the handle and the sinking feeling when the motor locks up.

This car is insane. If you stand back and look at it on paper or in person it seems like an amazing deal, CarFax looks awesome, private owner, dealer serviced, full service history up to 2015ish. Changed hands in Jan 2015 and only accumulated ~2k miles after that. I purchased from an older gentleman who told me that it went into limp mode and he didn't have time / money to have it serviced. He and his wife only drove it around town on weekends, etc etc. His neighbor friend offered to take a look, he had it towed to the guy's indy shop yard, but decided it wasn't worth fixing. Let it sit with a for sale sign in Timbuktu NY in a storage yard for a year and a half. Body looks perfect, inside and out. Clean CarFax, clean title, symptoms consistent with the story.

In reality I get it home and discover that the engine was removed and / or replaced. Nearly every electrical connector under the hood was destroyed. Whoever attempted the engine removal completely screwed it up, stripped bolts, literally bent the transmission cooler lines into a new route, left half of the intake components off. Screwed up the AC compressor connections. One of the knock sensor connectors was jammed into the harness plug for the fuel rail temp sensor, the other knock sensor pigtail was pinched between the engine and transmission bell housing with the plastic connector ground up by the flywheel. Transmission lines were cut in half by the serpentine belt spewing transmission fluid all over the engine bay. Insanity. Literally everything touched was destroyed. Missing the whole boot on the passenger side rack inner tie rod with about 1/4" play in the exposed joint and fluid gushing out of the rack seal. Someone literally totaled the car with the worst workmanship I've ever seen. You couldn't make this story up if you tried. I'm so glad I bought this car because it would have soaked some unsuspecting buyer.

Right now I'm just hoping that the engine actually was a drop in replacement, that the same crazy mechanical work doesn't extend into the motor. I'm holding out hope because it looks likes the engine was spray painted silver with a rattle can... which seems like the sort of nonsense that a salvage yard might pull when selling a used motor online.

Gentlemen I bought it from claims he bought / financed it at a local defunct used car lot for 10k in 2015 and immediately had problems with it. Essentially parked it because he couldn't afford to repair and pay the loan at the same time. Sounds reasonable except that in the condition it was in when I got it home... it would have NEVER run. No way he could have even got it home from the used car lot five miles down the road. So what did he do, blow up the motor and attempt to replace it himself? I'd love to know, I'm not upset, I actually respect that he tried to bail himself out of a crappy situation. Lien sacked car with a dead motor is everyone's worst nightmare, so maybe he tried to get himself dug out but ended up defeated. Just wish he would tell me because I'm dying to know.

I'm perfectly at peace with the idea that I might need to drop a motor into it. That's why I only paid 1,400. Worst case scenario is it's a rolling chassis for 1,400 bucks... I'm still happy because the body is flawless, interior flawless, it's in great cosmetic shape.
 
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Old 07-02-2019, 03:32 PM
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When & if you get to know the seller, you find out just what's wrong with this car.

Fix it, then ask, hey did you have this problem when it was yours?

After they find out you have sorted things out, and are fine about it.

They open up a bit, & often wind up bringing their stuff for you to look at.

An old riding buddy of mine died a while back, bought a motorcycle from him.

Then we rode together for years, didn't talk much just rode the back roads of southern Ohio.

Showed him the modifications made to my bikes, which he then did to his.
 
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Old 07-08-2019, 09:13 AM
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Quick update... I pulled the intake last night (for the second time.) Took a little more time to clean it out and noticed a bunch of RTV squished around the front seal that I didn't see the first time. Pulled the front / back covers. Silicone gaskets looked fine maybe even new, someone just squished RTV in there as a "precaution," totally unnecessary. I cleaned everything up, rubbed a little clear silicone grease on the seals and put the manifold back together.

I scrubbed out the valley, replaced the valley hose with an OEM part, replaced both knock sensors with OEM parts, torqued to spec. 15 ft-lb. I also installed some high temp silicone foam to emulate the factory sound insulation foam. I cut and carved the foam around the knock sensors on both sides to make sure they are isolated from outside noise.

Haven't had a chance to drive the car yet. I'm going to get more Mercon SP transmission fluid and do my absolute best to raise the car flat and level to check the fill.
 
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Old 07-09-2019, 09:28 AM
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Drove the car last night... no luck, engine running much better overall but I'm still stuck with this stupid high RPM intermittent misfire. I added about 1 quart of fluid to the trans. Car was as level as possible without being on a lift.

I've got three codes related to the transmission that are "sticky" in that they never clear. Even if I leave the car in park, command a reset with the scantool and cycle the ignition key. The following three codes come back immediately and / or never clear in the first place:

P1798 - CAN TCM/IC network malfunction
P0730 - Gear ratio fault - Transmission mechanical failure
P0706 - Gear selector position plausibility fault - TCM/J-Gate module CAN fault

Of the three codes reported, my greatest concern lies with P0730 because I believe that the ratio fault follows a calculation of actual gear ratio tracked by the TCM's comparison of input speed vs. output speed. Theoretically it is possible that my high RPM restricted performance event occurs as a result of the TCM faulting out, misfires might be a symptom of the restricted performance mode triggered by the TCM. Normal messages related to the transmission may not be coming through on the instrument cluster display due to the condition causing P1798. If the CAN link isn't working, I might not be getting the usual "Gearbox Fault" message on the dash.

Hopefully my Autoenginuity scantool will report the calculated "effective" gear ratio that underpins the P0730 fault. If so, I can drive with the scantool connected to see if the value falls out of range immediately before a restricted performance / misfire fault occurs.

I wish there were a way to place the TCM in a diagnostic mode (as with some other makes) to block a fault trigger on a diagnostic test drive. I wouldn't mind letting the clutches slip a little if I could prove that the misfire condition is solely caused by a TCM fault.

Sunroof rain water leaks may have soaked a couple of inline harness connectors carrying the transmission CAN signal. I need to dig through the wiring diagrams some more.
 
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Old 07-12-2019, 01:53 PM
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Hello Weekend, Hello Jag... Heading into another fun filled weekend of trying to figure out why she wants to misfire. I suppose it's time to figure out why I've got three trouble codes for the transmission. Will post an update with my findings.
 
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Old 07-12-2019, 02:48 PM
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A misfire often upsets a trans so it's often worth fixing misfires or other engine issues first. High RPM and/or misfire - often an air leak. Look at fuel trims and see.
 
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Old Yesterday, 07:27 AM
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I really want to resolve the P1798 TCM to Instrument Cluster CAN fault. I really don't want to have a CAN network fault lingering in the background when I'm trying to diagnose actual problems. To that end I've virtually gutted the interior because I need to figure out how I'm getting ~1 gallon of rain water in the cabin every time it rains and I want to trace the entire CAN network to figure out why the trans isn't speaking to the instrument cluster. I'm not getting any transmission messages on the cluster display now.

I'm going to pull the front seats and the carpet tonight. Tomorrow after work I'll ask my wife to hose down the car while I sit inside and watch for leaks.
 
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Old Yesterday, 07:29 AM
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I agree that the high RPM misfire could be causing the trans fault or vice versa. I've replaced virtually everything that could be causing an ignition or fuel misfire. I've lifted and fully sealed the intake. Fuel trims look great, all of the intake duct work is literally brand new. There's no good explanation for the misfire. It jumps all over the place, sometimes bank 1 sometimes bank 2. Just doesn't make any sense.
 
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Old Yesterday, 11:09 AM
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For the water leak, here are some TSBs which might help:

JagRepair.com - Jaguar Repair Information Resource

Look for XJ501-07 and XJ501-07a - Entry Of Water Into Vehicle –Possible Sources

Dave
 
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Old Yesterday, 11:44 AM
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Thanks! Yeah XJ501-07 is an interesting read. I'm going to strip down the interior anyway because I need to detail, dry out the carpet and replace the headliner. I'll grab a tube of body panel adhesive and go to work. Surprisingly the trunk seems okay. Sunroof is leaky but the drains seem to flow alright, I'll install a new Jaguar seal on the sunroof glass panel.

On first blush it seems like the issue is concentrated around the passenger side doors. Interestingly I've noted some paint work on that side of the car... maybe minor body damage that never made it onto the CarFAX report.

With so many things wrong with this car I'm trying to make broad sweeps, correcting as many items on the punch list as possible at one time. I was hoping to get her through inspection next weekend but that's going to have to wait. I'm going to tear down the interior tonight, test out the entire CAN circuit and try to narrow down the source of the TCM / J-Gate CAN faults. Then I'll target all areas identified for water intrusion by the TSB and do a full detail / resto on the interior. I'm going to strip down the front passenger door to replace the power mirror, and strip down / replace the headliner, pillar fabric.
 

Last edited by pcmos; Yesterday at 11:55 AM.
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Old Yesterday, 12:16 PM
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You can replace the power mirror w/o stripping down the door assembly. Also use marine grade clear sealant.

Do each of the ingress areas outlined in the TSB, especially the trunk and rear door suggestions. You'll be surprised how much water collects on the rear carpets due to these areas alone.
 
 
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