Misfire again...please help!

wires/connectios/coilpack. start at wires pull one at a time to see which one is causing the problem. you may also use an indictive timing light on each wire to look for a dead hole. If everytjhing passes and you are truely getting a miss vs a dead hole then you will need to hook a cheap scopemeter to the car to look at output trace. Those devices can be had for a couple $100 and I think no doubt posed on a really cheap digital scopemeter about 1 month ago.

 

Try to pull the connectors to one lambda sensor at the time when the car is hot (water temp above 70 degrees celsius).
The lambda sensor will try to adjust the fuel mixture when the engine at idle up to 3000rpm, but only if the water temp is above 70.

If the misfire dissappears when the lambda sensor is diconnected, just get a new one.

mine did this the same day as my scheduled early inspection at the swedish (bilprovningen).

the car had high values of CO and HC, so i unplugged one sensor at the time and it was the R/H one that was unserviceable

 

Have you investigated the condition of the wiring to crankshaft position sensors?

 

Then I would try to pull one sensor at the time and drive the car,the fuel injection will use a backup law and will be a little richer but it´s not a problem.
The car will loose some performance when driving on the backup laws. So it´s normal if the car feels a little slow during this test, but the misfire should be fixed.

 

Here's a cheap oscope: http://www.ferrarichat.com/forum/showthread.php?p=137535152#post137535152


You've got some good suggestions above. I'd add to your suggestions so far above that a sticking fuel injector might start working enough above 3000 RPMs, but also, sometimes a bad plug wire will work at high rpms when it won't work at low ones.

Did you pull your spark plugs and see one that was gasoline or oil fouled? ... or really, really clean as if coolant was cleaning it?

 

Yes that's why you need to read the rest of the post. The unplug is to catch the obvious first. What happens if running on 7 and you have a miss? Keep going....What do you think happens if you unplug and at 3000rpms you are running on 7cyl but no miss?

 

Have you tried resetting the ECU codes?

I know my car occasionally acts up under 3K rpm, and idles at 1300... but after I clear the codes, the idle goes back to 1000 and thelow rpm problems go away... Mine is because for some reason the car gets a code that causes it to run rich, and that's when I have the problem.

Mike in Kuwait

 

To bad it wasn´t that easy.

A question is the misfire only present when engine is hot and during accelaration.

I know it´s hard to say but any idea how many cylinders fails to ignite.

I had a similar problem but the symptoms were misfire above 6000 rpm´s
it was only present when the engine was hot (oil temp at 100 degrees celcius).
but it happend with or without load.

My fix was to replace the ignition leads, tried first to replace to spark plugs but that didn´t fix it.

It seems like the insolation of the ignition leads can change due to high surrounding temp.

Do you have any one to change parts with?

I would try one thing at the time starting with the ignition leads then the coils and then even the ecu´s to rule out ignition problems.
If that don´t help check for fuel related problems ie injectors , fuel press.


I hope that I give you some ideas.

 

Does the misfire occur at different rpms if you turn your A/C off or headlights on?

 

Just a thought ,does it stumble alot when the fans kick in on idle.

thinking bad battery or bad grounding to the engine.

 

I had to go and measure my old leads and they where about 6 kohm all of them.

but the problem is to measure if the insulation is good, if its bad the current will jump to ground before to reach the sparkplug.

 

Again, I'll suggest that you check for problems with the wiring to the crankshaft position sensors. We've seen it a number of times.

 

These are the crankshaft position sensors, indicated by the pink arrows. The wiring seems to be very fragile. Peel back the rubber boots. Check for broken wires and loose pin connectors, and for oil contamination. The sensors themselves should be fine, but the wiring often has issues. It's worth a look.
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