VN firing problems

[timmy01]

i have a 1990 VN wagon (manual) with a vp motor & i am having some extremly bad firing issues.
after about 5 mins of driving the motor will start running rough & jolting while accelerating, sometimes jolts on decel (foot off accelerator), when idling in neutral with clutch engaged it sounds like it is miss firing & runs rough, sometimes it will sort itself out & fire normally but idle will start high then drop down & continues to run in that up/down pattern.
As soon as i touch the clutch to disengage the car will completly drop in revs, sound like its running on 1 cyl, back fire continue to run like this for up to 3 min then cut out, half the time it just stops dead & takes about 3 attempts to re start (will not start with clutch in).
i have been chasing down this problem for about a month.

i have replaced : coil pack
crank sensor
ECU (2nd hand)
fuel injectors (2nd hand)
fuel filter

Hoping that someone may have experianced the same kind of issues & will be able to help me out on this one.
Any type of advice will be greatly appreciated in trying to sort out this problem.

[SBM]

Have you checked your throttle body? Give it a good clean out they often make your engine run rough. Also check the IAC motor it could be dirty give that a clean while you have the throttle body off.

[vk.jonno]

U got the right firing order

[timmy01]

hey mate thanks for the input......already done all that it didnt seem to change a thing........yer the firing order is right

[ybl8te]

M.A.P - manifold absolute pressure, the thing bolted to the fire wall.

the pcm uses the map sensor to control fuel delivery and ignition timing - i think vacuum hose attached (make sure) - car should run rich if pulled off, and if tapped with handle screw drive and the engine miss fires there maybe your problem - maybe-ish thinking like

[david dubbo]

mybe dfi plate as well (wrong one)under coil packs

[timmy01]

yer m8 already checked the map sensor everythin seems to be doin what its meant to.......& already replaced the dfi plate.....thanks for the input....

[david dubbo]

check the pressure output of fuel pump and that fuel tank is clean

[timmy01]

yer cheers mate i think ill be doin that next week also will do a compression test & make sure evrythin is right......ill let u kno how it goes

[ybl8te]

if after five minutes it starts - seems then a sensor picking up the car is heated up and maybe then the sensor sends some faulty readings to the computer............engine coolant sensor ???/

[mcqunt]

check the pins on the coil pack plug,
male can brake off if loom is a bit short or female can
get a bit flogged out from vibration

[potshots007]

i would think a sensor issue as said before....coolant temp sensor or something along those lines.....or yes check fuel pressure from the pump

[timmy01]

yer thanks guys......i will be changing the coolant sensor this week......i just did a compression check they are all reading good in the 130-140 psi range so not much happenin there.......& i will also be replacing the fuel pump......thanks for the input guys cheers