hey guys, hope someone can help me. Im new here. Just bought a 98 xjr superchared. love the car...I think lol

One of the reasons I came on here and started looking was because the XJR that I bought last week has had a couple of issues. One of which is fixed, I kept getting a trans fault message. I got the code and it was a shift selector error. I took out the shift selector sensor, cleaned it up and adjusted the cable and it seems to be good now. It also has a misfire under a moderate to heavy load. Its totally fine with normal acceleration and crusing but if you get into the trottle much more i get an intermittent misfire. the car will miss a few then not miss for a spit secone then miss...surging like that right up through the rpm range until i let out of the trottle. It idles perfect and doesn't miss a beat till I am probably about half throttle then it starts to miss fire..if i had to guess its at least 2, maybe 3 cylinders missfiring. Im judging that by the amount of power loss during the missfire situation, and during the missfire situation there are times that it pulls like it should but its only for a split second then it misses again. No cel,, could there be a code present without the cel coming on...I have a snap-on modis diagnostic scan tool... just so ya know. right now Im kinda thinking the coil packs?? Is there anway to test them?? the car was fine when i test drove it before i bought..figures right lol it always works out like that haha

thanks in advance!!!!

 

Id check the fuel filter. When I bought mine and would get on it there would be some timing pulled after 3000 RPM. Figuring it was the knock sensors pulling timing I went ahead and checked the filter. It was so clogged I couldnt blow through it at all. Suprised the car ran at all! LOL. New filter cured the issue and the car is much quicker now.

Usually a missfire on any OBDII based vehicle will result in a CEL. Problems like MAF, TPS, coil, crank angle sensor, cam angle sensor etc etc will throw a code.

Problems that will make it kinda feel like a missfire would be poor compression (bad rings or valves) but if the car dont smoke or clatter then they are usually ok. Blown head gasket but if you dont loose coolant and it dont smoke you can rule that out.
OR there isnt enough fuel in which case the car gets detonation or knock from being too lean and the knock sensors hear this so they pull timing from the ignition untill the knock goes away. As soon as the knock goes away they stop commanding a timing retard and the car surges forward again and yet again has knock so the knock sensors do their job yet again. It happens quick so it would feel like a missfire under load.

Hope it helps.

 

Pull the coil pack covers and check for oil down the plug wells - you might need new seals if there's oil.

 

hey Sean, I actually did that today. There was a small amount of oil in a few of them. I cleaned it all up and changed the fuel filter...still no different. I also put a can of fuel injector cleaner in the tank with some fresh 93 octane fuel. Took it for a nice long ride and still the same. I also would say the longer i drive it the worse it gets. When its cold its not as bad, its more intermittent and has some microbursts of good power but only for a split second then missfire the a burt of good power over and over but as I drive it and gets to full operating temp it is more like a constant missfire under a load..... I hooked up the scan tool and no codes present. Im baffled. You would think with such a recuring missfire that something would be giving a code. Im not that lucky lol. not sure what else to do at this point..oh ya. i also pulled all the plugs and they look spot on...a nice chocolate brown and dry. fuel filter was pretty bad..had to blow pretty hard into it to push air through it and there was some yucky sh*&% coming out when i did blow throught it. but new fuel filter didn't help... I have read in another post on here that someone had a missfire with no codes and it ended up being a coil pack... I thought that a bad coil pack would shoot out a code???? If anybody has any other ideas id love to hear them

 

Hey laser forgot to mention this, I also did a compression test..the lowest cylinder was like 130 and the highest was like 145...i will also say that the supercharger seem kinda noisy..not sure what they should sound like but at idle it sounds very metal on metal ish if that makes any sense. but as soon as it comes off idle it quiets down quite a bit and sounds good under load..just at idle it sounds kinda crappy and loud. the supercharger is new..prob like 1000 miles or so on it and my boss (the guy i bought it off) said that it sounded like that when he first put it in...long story as to why he had to replace it lol. ill share if your interested in knowing thanks for your help btw and read my other post as to what else i did today to try and solve the missfire issue

 

SOOOOOO happy!!! I put a new set of bosch platinum plugs in and cleaned out the spark plug wells again and holy crap....runs so good now. a subaru wrx sti pulled up next to me at a light and gave me a smile and the head nod lol so i nodded back with confidence ...ya you can fig out the rest haha...I soooo pulled on that thing it was silly!!!! happy guy now....I finally get to enjoy the car.

thanks for all your help guys...very much appreciated!!!!!

now i just gotta fix the small kinda annoying exhaust leak somewhere on the drivers side by the cat..its not leaking between the head and the manifold, its somewhere after that and its not after the cat...its gotta be somewhere under the sheilds cuz i cant see it...is there a tube that comes off the manifold on the drivers side..the passenger side tube that goes to the egr is fine but there is so much crap in the way on the drivers side i cant see down or up in there lol..is there a common spot back there where it will devleop a leak???

thanks in advance

Seth