Misfire after warm up

Hi All,

Troubleshooting a weird problem with my 8KM XJ220. I get the impression I’m the first person to drive this car, I mean actually drive it. Belt service, fuel cell, etc all up to date and a significant amount of maintenance ($100k+) performed by the prior owner. I’ve driven this one about 100 miles or so and started to have unusual performance problems.

Now, 5-6 minutes after start whether it’s driven or not, idling from start, it will repeat this behavior. The idle RPM drops, it begins misfiring and light throttle input results in amplification of the misfire - the engine revs slowly.

This is not correlating to boost, the engine has had none or little boost when it begins (this example in video is from start, idle, not moving the car or touching the accelerator). Note the tachometer swings around oddly with throttle input too - something funky here.

The car goes from idling smooth to a reduced idle that’s rough with some minor to major popping out of the exhaust. The mixture out of the pipes smells rich when this behavior occurs.

Here’s today’s example in video form showing the behavior at the dash and then with no throttle input from the rear of the car.

It starts, runs, idles and revs normally prior to 5-6 minutes of warm up time now. (For good measure I’ve turned my aftermarket boost controller down to 0 and 5% and see no variance.)

Video here: Misfire - YouTube

Anyone have any tips tricks or ideas on what might be driving this behavior?

Thanks in advance!

Check the coolant temperature sensor. If faulty it will create the issue you are experiencing.

Luke, When was the last full service done, blatter and all?
mminch is right as well.
What country is the car dialed into ? Do you have cats and stock exhaust?
GTJOEY1314

Less than 2 years. Have run 2 or 3 tanks of fuel through it since received, behavior started after a leisurely cruise, park for lunch and restart. Lived its life on the west coast, now in North Carolina. Exhaust is modified - has cats but the rest is custom.

Got it, Ill make a call, hope to help.

@mminnich interesting. The behavior, if on a modern car, I would call “limp home mode”. It runs fine, then suddenly begins behaving this way.

Also, JUST ASKING,What kind of gas? High octane, Ethanol, NON Ethanol?

@j_limongelli thanks much! Check out the video for the behavior. I shut it down and restart briefly, and it idles and revs OK for a very short time. Does fine cold, if very briefly.

@j_limongelli 93 octane gas station petrol I’d run in any normal high performance car, at least for the last 2-3 tanks.

I bought the car in late last year. It had odd behavior prior to this where, under power and boost, it would begin popping and stuttering but only occasionally - chalked it up to cold temperatures and boost reaching different levels than it did in sunny warm California. Has an aftermarket boost controller, pulling the boost back seemed to remedy this behavior.

Well try this…
Check fuel pressure and fuel filters as there are 2 sets…
I get leary with ethanol gas and it sitting in a rubber blatter.
Pray it didnt eat through it…
Check pressure, if low then filters if clogged,
If filters clean and pressure is low or dropping.
Go to the fuel pumps…
Its a good guess, hope im wrong.
Ill post pictures in a second.
Just get a read on the pressure …
Good luck.
gtjoey1314


Been there done that​:rofl::flushed::roll_eyes:

Luke, ALMOST forgot…If the filters are clogged and BLACK.
Its an engine out, new blatter again, fuel lines and runners.
Then YOU MUST check the injectors, if it went that far, make sure you have a credit line of 85 to 130 grand for the repairs…The black is rubber eaten away, all those filters are to protect the particles getting to the injectors.
This is extreme but if so , its washing onto the valve and then boom.
PM any time
gtjoey1314

Thanks. Do you have a shop, and work on these things “regularly”?

Im just an old man, who ate, drinks and sleeps this…I have guys, near you, I have another here on Long Island and of course you can go all out and mail the car to Don Law…but thats a 200,000 bill!
I do it for get this…FUN on my own cars and help out at the shops who need a little guidence.
PM your phone, ill try to help.
You have a local guy to check the pressures and all?
gtjoey1314