rabjohns

So I took my 1990 C2 (race car) to the track (blackhawk,IL) yesterday for its second outing of the season.

The last time out it had performed flawlessly (12 x 30 min sessions) not a hiccup.

This time it started backfiring in the first session, my friends said they saw flames from the exhaust and puffs of smoke when changing gears from both pipes.

The onsite mechanic said that Cylyinder #1 was not working (tested by removing the injector).

It is currently in the shop being diagnosed. He said it could be a broken rocker or it could be "real bad".

Has anybody had this happen to them? Any ideas or thoughts? Also I would love to know what the list for "real bad" looks like

Thanks in advance

David

Colin 90 C2

did you mean he pulled the spark plug wires?

Sounds like you have unburned gas that is giving you the flames.
If it's only one cylinder, then I would look at the associated spark plugs, wires, distributor caps, and coils.
It seems we had a rash of coils going bad in the last couple years.

if the electrical and fuel systems are intact, then real bad things are possible.

gl with diagnosis. hope it's not too costly for you.

Oracle

Bad gas could've cause some detonation that could've damaged the rings in #1, maybe ignition wires or system.
I hope this is an easy one and not expensive.

rabjohns

He said he pulled the injectors (top or the engine on the left as you look in) he showed how if you pulled of #2 the engine spluttered byut when you pulled #1 nothing changed.

Thanks for the info, lets hope it is the distributor!

DR

rabjohns

I thought it could be bad gas, althought it was bought fresh in Indiana two weeks before. Good thought though thanks.

I will let you know what they find.

Colin 90 C2

Now I see. He pulled the electrical connector off the injector.

I would start with checking that specific injector first. Pretty easy to check the most obvious thing, but not likely the answer.

rabjohns

I think he was just using it as a shortcut to see what might be up.

DR

Geoffrey

Check the distributor belt. If you had a broken rocker it would be due to overrevving it or using a chip that exceeds the factory rev limit, or hitting the rev limit with weak stock springs. If the engine makes mechanical noise, I'd check for a broken retainer, broken spring, broken rocker arm.

Indycam

"Also I would love to know what the list for "real bad" looks like "

The backfire is caused by the charge not firing off inside the cylinder .
The charge is firing off inside the exhaust system .

If the charge is never given a spark , it will not burn until its in the exhaust system . IE , on the "blow" stroke , an unburnt charge is pumped out of the cylinder and that charge then is fired by the exhaust flame from another cylinder .

If an exhaust valve is not sealing , the charge on the compression stroke escapes past the exhaust valve and gets into the exhaust system where it "blows".

So you have a dead cylinder because of a lack of spark
or a leaky exhaust valve , imho .

As mentioned above , there is a possibility that the injector has gone bad and is making the mixture in that on cylinder so rich or lean that it does not fire well from just the spark .
If you suspect that is what is causing the problem , moving that one injector to another cylinder will cause the problem to move to that "new" cylinder .

rabjohns

So the mechanic (who I trust) called. He said they did a leakdown and there is leakage on cylynder one at the top. He said he won't know more till he gets the head off but things sound more "real bad" than "real good".

The engine was rebuilt, by Dan jacobs in conneticut, about 2,000 miles ago so he asked me to fax over the details so he can see what they did.

I will keep you all in the loop. Thanks for the input so far.

Indycam

Belt valve ?
My brother bought a zero mile rebuilt 356 motor that had an interference problem .
We could not rotate the motor without one valve hitting one piston .

rabjohns

For anybody interested here is the history of the car:
A quick summary:

Mileage 104,441 Dec 2004
- Complete case down rebuild and new rs clutch by Fairfield County motorsports

Mileage 106,387 (1,946 later) Mar 2006
- Service and valve job – same place

Mileage 108421 (3,980 later) July 2007
- Clutch master and slave – same place
Mileage 108,749 (4,308) Aug 2007
- New oil cooler

Mileage 109,057 (4,616) Feb 2008 (Tristan bought car)
- PPI/Leakdown all cylinders at 2% - Dan Jacobs (964 expert)
- Clean bill of health
Mileage 109,815 (5,374) Sep 2008 (David Bought car)
- PPI/Leakdown – Eurosport
- Cyl 1 – 10%
- Cyl 2 – 2%
- Cyl 3 – 4%
- Cyl 4 – 2%
- Cyl 5 – 5%
- Cyl 6 – 2%

Summary (from Carl) Told all within range, engine good just needs minor tune up and replace axles

Mileage 109,815 (5,374) Nov 2008 - Eurosport
- Replace axles
- Nut & bolt car
- Tune up
- Race prep

So it looks like this car has 5,374 miles since the rebuild.

Couple of questions:

1. Is 10% on a leakdown normal?
2. What would you guess the hours are on 5,000 track miles? Is it ready for another re-build?

Indycam

I don't think a 10% leakdown is going to get flames coming out your tailpipe .

race911

Gee, sounds just like what happened when the valve spring broke on the 3.8 in the yellow car! (AASE valve springs, for those keeping score............)

One bank of heads back to Steve to fix the one bent intake and make sure the surfaces on that bank are equal, a few odds and ends, and................well, it's been 8 months and I still haven't reassembled the damn thing. $2K out + how many hours of labor for defective aftermarket "performance" parts!

rabjohns

AASE valve springs? Do you think that is what they might have put in during the re-build?