While mine car, 95 VDP, is in full stop - idle mode, it missfire randomly.
If that is resoult of vacoum leak.
Where to look for resolution?

Thanks,

 

This might be difficult to diagnose unless you have trouble codes to help you along and/or live data from a scan tool showing a fueling problem. Such is the nature of random faults. Sometimes you have to wait for the problem to become worse before a decent diagnosis can be made.

I've had several problems with "misfire at idle" in the past and, actually, right at the very present as well.

On a couple occassions the misfire was constant and replacing a coil fixed the problem. Much easier to diagnose a constant misfire than a random misfire. :-)

Another time the miss was very severe but random. I took a wild guess and replaced the crank position sensor. Fixed.

Yet another time a random misfire was caused by two faulty injectors. I had suspected an injector problem and sent all six of 'em off to a specialist who was able to identify the two duds....which were just barely out-of-spec. In this case the misfire only seemed to occur with the transmission in "P".

Presently the idle misfire is random but doesn't occur at all until a fair amount of heat has built up. I haven't confirmed a diagnosis but suspect another coil is failing. Coils have been the bane of my existence on this car. Never buy cheapies!

Through all this I've never had a trouble code or check engine light.

I've had one sort of idle problem or another on all three of my Jags. This car is by far the worst of the three.

Cheers
DD

 

Doug thanks a lot!
I will check for trouble codes and live data from a scan tool showing a fueling problem, an d than come back later.

Loui,

 

recently my car has become hesitant while driving. first noticed it as a slight misfire at idle then a hard misfire while driving causing the cel to flash when the event occurred, this happened twice. Now the car just runs very hesitant. I checked all my coils, all are good, went back to champion plugs and now have moved on to the crank position sensor. my question is what is the proper ohm reading that i should get on the sensor on a bench test? It starts off as 1350 and slowly drops to 1230 over a minute or two. Thanks for all input on the issue.

 

How did you confirm the coils were all OK?




Did it make any difference?

My recent misfire problem, which was fairly severe, "appears" to have been fixed by replacing the plugs. I say "appears" becuase, in battling this problem, I done of few things that seemed to fix the problem but were only temporary.

I went from Champions to NGK but am having a hard time determining why brand name should make any difference....although I have some speculations on the subject


Cheers
DD

 

I checked each coil individually with a HEI Ignition Spark Tester, all passed when put to the test. I use to check ohm readings on the coils but that way is not very accurate. How do you check your coils? And by taking off the Iridium NGK and placing the Champions made no difference. Only the cel flashed when this event occurred very hard while on the fwy, no codes no cel light now.

 

I've tested mine either by checking resistance (which isn't conclusive, as you say) or by substitution. I don't have a tester as you describe.

What concerns me with any test of these coils is one that hasn't outright failed but that might simply be sub-par/borderline in performance.






I went from NGK iridium to standard Champions a few months ago. All seemed well but a misfire eventually developed. Just recently I changed from the standard Champions to standard type NGK and the misfire went away....at least for the time being.

I can't confirm that the *brand* of spark plug was significant here.

I'm happy the engine is running well but am waiting for "further developments" as I'm not quite convinced that I've reached (or even understand) the root of the problem.

I'm wondering about coil-vs-spark plug compatabilty issues....aftermarket (or age/heat degraded OEM) coils versus different types of spark plugs. I don't have the knowledge to do more than wonder and speculate, though.

Or...perhaps one of the Champions I installed a few months ago was simply faulty in some way and I'm over-thinking the entire matter.

I dunno!

Cheers
DD

 

Doug, back about 40-50 years ago when I was racing and doing tuneups on a lot of Lucas ignition cars I noticed that a couple of days after installing new plugs in an engine I could often detect a slight misfire at idle. Swapping out the plugs for another new set would take care of it. Sounds similar to what you are writing about.

 

crank sensor is within ohm limits on bench test, but engine cranks a few times before sensor responds and rpm reads 200. only when rpms read 200 then the motor will start, before that 3 or 4 cranks no signal then it kicks in. What do you think? then i tried to bypass the ecu temp sender with a paper clip and I couldnt get the engine to start this way. wanted to run it and see if any difference in performance, shouldnt the paper clip bypass get the engine to start?

 

was able to check ecu temp sensor with my scanner and it would change back and forth, open loop to close loop, placed a new sensor and now the car is back on the road. thinking about putting ngk iridium back in because the car idles lumpy with the champions, smoother idle with ngk and they werent the cause of my problems. Im glad it was a inexpensive fix.