Weird Misfire - no code but MIL set
 

Hi guys, newby here looking for some advice. I have recently acquired a 2005 4.2 SE S type, which is broadly speaking all fine and wonderful. However a couple of weeks back we went out on a fairly long run, after having stopped for a few minutes I restarted the car and got a fairly bad misfire for about 30 seconds, which then cleared. It did the same thing today but this time it put the MIL on, it did not come up with restricted performance, the misfire cleared a few seconds later. Got home and connected up my diag reader and it showed multiple miscellaneous misfires. I reset the MIL, it was running fine when I did so, there was no code set per se to give any clue as to why it happened.
Anybody got any ideas or thoughts? The common factor seems to be a restart from a full hot run but only if restarting within a few minutes:icon_confused:
Any input gratefully received.

1/2er.

Forgot to mention - the intake temperature was showing as 100 degrees - does this seem somewhat high?

The usual suspect for misfires in the 4.2 engine is the coils. Yours are pushing 10 years old if they have never been replaced. Misfire codes typically indicate the suspicious cylinder(s). Next time you experience misfires, pull the codes again and post them here. You will be rewarded with some expert advice on how to proceed....

Thanks Jon89, my reader did not show a code, it just showed "various random misfires on multiple cylinders". Don't know if that is a limitation of the reader or the on board diags. I started it again a couple of times this afternoon and it was perfect.

Keep an eye and an ear on it. It could be something as simple as a bad tank of fuel....

It didn't give a P0300 code the first time? The MIL wouldn't come on without some sort of fault code being set.

You did not mention the mileage. I had similar grief with a Ford 4.6 at 120k miles. Turns out that the coil on plug, which is a high failure item wasn't the culprit...but it turns out that the plugs in question had a wide gap, which did not fire on occasion, with the same intermittent readings. All of the plugs had same wear issues, but code reader only showed 2 misfiring. Check the plugs first. Much cheaper than replacement coils.

Symptom was weak spark, and on occasion no spark at all. I just replaced all 8 plugs, and not the coil packs. Big cost savings, and engine runs smoothly now.

Thanks for the responses, guys, much appreciated. The car has done 101K miles, it has a good service history, the plugs were replaced less than a year ago. While going through the paperwork I found a receipt that suggests this is not a new problem, it did the same thing a couple of months before I bought it. I still find it weird that it only does it on a restart on a full hot engine and that it sorts itself after a few seconds. It's also weird that there is no other fault to go along with it - I guess that does point more towards bad fuel or bad plugs / coils than any other problem. It's a shame it did not tel me which cylinders the fault applied to. Is there any diag equipment that will tell me which cylinder(s) are playing up?

1/2er

Bit of an update - having read the manual for my diagnostic reader (better late than never) I realise that the ecu had thrown a code which the reader translated for me in to the numerous misfires message. Stupid Arthur had cleared the code before looking further, which would probably have told me which cylinders were affected. I guess now I have to wait for it to happen again and read the codes properly. As I understand it I should see a p0300, with the last digit showing the cylinder number.
Now I have the cannot apply handbrake message to further spoil my day!! Will recalibrate it tomorrow and see what happens.

That may mean the battery is failing. If so, expect weird codes - which you're starting to see.

The good news is that a failing battery usually starts the car. The bad is all the weird codes till you get something worse.

There are hundreds of threads about this so read a few for tests & fixes.

^x2. Check your battery voltage. Car will start with as little as 10.8V (just barely)- but other things go haywire. Normal voltage should read in the 14.4 to 13.8 range. Even as "low" as 12.0 volts read at the terminals mean your battery is beginning to "go south."