misfire in cyl 4

[jagboy96]

i have a 2000 jaguar s-type with the 4.0 engine with a misfire in cyl 4 now i have tested almost everything possible and have even put in a remanufactured injector and am still getting the misfire, i have done compression tests, taken the spark plug and coil pack out and had it sparking in my hand, then i thought it was an electrical problem i ran test on the coil wires and they were fine. i was wondering if the throttle plate was sticky or the PCM was bad/getting bad data

[SleepyHead98]

That car is getting up there in age. Have you check your fuel pressure? Injectors usually wont squirt unless they pressure is very close to specs. Not cursing you, but I would look to fuel next. Might be fuel pump/.

[jagboy96]

thanks for the idea ill have to check that tomorrow along with something else but that is a good idea, i have not checked it and just replaced the fuel filter a couple weeks ago and fuel went everywhere so its not the pump it might be the fuel pressure sensor for the injector

[SleepyHead98]

Sorry, I read through your post too fast, I forgot to mention as Im sure you already have gathered, give it a tune up. Or atleast plugs AND wires. Sometimes the core inside the wire will get pinched or crimped and the wire inside will break. Ive had that happen to my vehicle once.

[jagboy96]

its not the wires because i thought that too and i took the coil from cyl 4 and put it in cyl 1 and the miss stayed in cyl 4 and there isnt a problem with spark i had it sparking outside the engine block the other week

[SleepyHead98]

Have you changed the plugs yet? Thats what I would do. Changes plugs and if it has plug wires, change them. That way you KNOW with out a doubt that it is not the plugs or the wires. Like I said, if a plug wire has a bend in it, it may intermitently spark and miss. Thats where I would look first

[jagboy96]

ill try to do that sometime within the next week or so, is there anything else it could be though

[SleepyHead98]

Got a check engine light? If so whats the codes? If cam sensor comes up it could be timing chain (after you have changed cam sensor of course to verify), but Doubt it with so little miles. What does the plug look like in cylinder 4? Is it more corroded than the others? Does it have color on it, Such as the color of your coolant? Is it markedly more dirty than your other cyls? I still think its plugs, but cha know these are other ideas.

((Edit: You can always just buy one plug and drop it in just to be sure. Change the others out as soon as you can though))

[jagboy96]

the plugs are a blueish white like they should be so im not worried about those, the light is on but only for the miss, i was thinking of doing a cold computer restart? could that work?

[SleepyHead98]

Dunno, Doubt it. Worth a try I guess.

[jagboy96]

there are 2 methods i know of 1 is taking off the positive cable and touching it to the negative cable for 30 sec and the other one i take off the negative cable and touch it to the positive cable for 30 sec that 1 scares the hell out of me, which one is most likely to work?

[SleepyHead98]

Yeah those scare the hell out of me too. Dont do it, I have never heard it, so I cant recommend doing it. I always take off the neg for 20 mins. Take it off overnight if you want. I dont feel comfortable with touching pos to neg ever, thats just me.

[jagboy96]

i dont know what else it could be, i have tryed everything theres nothing left, i dont think its a valve because the compression is even in all 8 cyl

[SleepyHead98]

Any luck on this yet? I believe I asked if you had a check engine light on. Does it show a code for anything else other than missfire?

Other thoughts I have, Perhaps a cam position sensor/crank position sensor. My car has two crank position sensors, one controls RPMS on dash, other controls timing. Might start looking at those sensors.

Please don't take insult to this, but how do you know you have a misfire? based on what the computer says? Can you feel it while you are driving?

[jagboy96]

i now think its fuel pressure i did a pressure test and its at 35 psi which is not enough to get it from cyl 8 to cyl 4 the set up is
4 8
3 7
2 6
1 5 so the fuel comes in from 8 and around to 4 which is where i am getting a misfire so i did a little a research and at idle the psi should be 41.1 psi so its 6.1 psi off and i know it a misfire because its running rough and i can feel it especialy when i hold it at a steady speed but i do think its the fuel pressure