Fixing a Misfire .... The Fun Way

[cegerer]

What is with these cars???? It seems like the harder you run them, the better they run. I've been chasing after a 3500 RPM misfire for several months, to no avail. So I've learned to live with it because my 2.5 runs perfectly otherwise. Well, Saturday I ran the car harder than it has probably ever been run. 2 hours plus with the tach rarely lower than 5000 RPMs. Lot's of tight 2nd gear corners. Banged it off the 7300K rev limiter numerous times. It's amazing that these motors can take that kind of abuse without hand-grenading.

Well guess what? No more misfire. It's gone completely. Drove it 300 miles this morning and not even a hiccup. WTF? What would some of you suspect could explain this? -- Curt

[Eric M@ Ashers]

SEE they love it.. it's a SPORTS CAR Curt.. not an estate wagen. drive it hard!!!!

Eric

[nhromyak]

MY dad has been telling me this for years about his '80.

Whenever he drives for a long time (i.e. to Laughlin NV or Las Vegas - from Bakersfield) he swears his car runs better.

I can only think moving more fuel (and good fuel - like Chevron) will clean the carbon off the valves and spark plugs etc.

Have FUN!

[Eric M@ Ashers]

well if anyone has a missfire come to next years Taj Kruzers fun drive and we'll clear it up for ya! hahah right Curt!

[724doorE]

The plugs get dirty when you drive like grandma.
They get clean when you get serious

[cegerer]

Don't get me wrong ... I don't baby this car at all! It regularly sees the redline and just returned from a 2600 mile trip with plenty of triple digit speeds. The only real difference this weekend was the repeated hard cornering and lots of 2nd gear full on/full off throttle.

[724doorE]

Thats just it, you can drive 90 miles an hour but your at a steady rpm say 3600, and that'll get those plugs dirty, at least thats the way mine usually went. But then I have a slightly worn MFI and you have webers. so who knows. Its the hard pulls that clean it up though.

Maybe you just drive it harder now that your use to the Uber UTE

You going to Indy for the F1?

[cegerer]

Can't make Indy F1 this year

I've put brand new plugs in during my quest to cure the misfire and it did nothing. I'm guessing maybe it was/is some kind of carb problem (sticking float?????) that got jarred free????

[gerry100]

It's called a german tune up.

My car runs best after a two day DE.

[jester911]

I totally agree. Last fall after having a track day with a lot of high revs in 2nd the car ran better than ever.

They really should be driven

[azasadny]

Curt,
Something very similar just happened to me the other day. I drove the car all weekend, then on Monday, the car was missing from low RPM up to 3400, then no miss at higher RPMs. As soon as the RPMs dropped to 3400, the miss would come back, almost like a plug was loose or disconnected. I drove the ca home (8 miles) and after 6 miles the miss stopped and the car has run perfect since. I think Helga is "self-healing" which is OK by me!

[RoninLB]

Originally posted by azasadny
Something very similar just happened to me the other day.

missing from low RPM up to 3400, then no miss at higher RPMs.

after 6 miles the miss stopped

if the subject is still carbs ?

The idle jet orifice got clogged and it eventually blew clean. Sometimes it happens within a few miles.. and I guess a stiff clog could take thousands of miles.

So you didn't have a misfire that spiked your EGT at that cylinder.. actually the EGT crashed due to no fuel below rpms when your "mains" came on. So some of our mains come on around 3-3.2k rpm.. I guess some come on at 3.4 .

An EGT probe in each exhaust tube would have instantly diagnosed the clogged cylinder. A good EGT probe will last about 50-75k miles.

[azasadny]

Oops, I forgot to mention that I have a 2.7 CIS engine, no carbs. The car has run great for the past week, this happened a week ago and hasn't happened since...

[cegerer]

In my case, it was carbs. I had cleaned the idles, mains and passages until I was blue in the face, to no avail. The hard driving cured it. For awhile. The miss eventually returned and is still there - although it occasionally goes away at random - at right around 3200 - 3800 RPMS. Doesn't matter now, engine and carbs are going to be rebuilt this winter ......

[RoninLB]

Originally posted by azasadny

Oops, I forgot to mention that I have a 2.7 CIS engine,

ok..

CIS is a great system imo. Although it's very dirt and varnish sensitive I never had a prob with it. I would do the Techron act a couple of full tanks before every oil change. The second tank was to flush out the Techron in the first tank. I still do the Techron and continue using Redline gas treatment at every gas fill. A Redline bottle costs about $7. A dose from the bottle makes it last for 100 gal of fuel as per directions.

[RoninLB]

Originally posted by cegerer

around 3200 - 3800 RPMS. Doesn't matter now, engine and carbs are going to be rebuilt this winter ......

3200 is transistion territory. I'm curious on this one. It sounds like a cylinder was going lean from a vac leak of dirt somewhere IF it was carb related.

fwiw going lean raises the EGT