I just finished a cam install on my 95 LT1 Firebird. The car started, ran, idled fine. No leaks at all. Everything was PERFECT. I took the car for a drive and it drove well (like stock!) Excellent oil pressure, temp was normal, new gas in the car.

While driving the car a short while later, it backfired, shot flames out the exhaust pipes, and backfired hardcore till it died. The car wouldnt idle at all. There are still no leaks, all new plugs, plug wires, new Optispark. Cant figure it out? What is causing the massive backfire when it ran so perfectly before?


Here's what was done, and the parts used.
- Pulled motor and replaced every gasket on it.
-New Optispark, NGK TR55 plugs, Taylor wires.
-Comp 224/236 cam, 1.6rr, springs, pushrods. All new equip.

Cant think of anything else that might help here... it back fires like nothing I have ever heard before. Oil pressure still good. So no bearing issues...

HELP

-Cam

 

I would start off simple and pull your plugs to make sure they are not fouled. Then check your wires to make sure you didnt burn through any of them.

 

A Tune might help

 

Check 02's

 

rockers too tight??

 

I was driving it around before all this happened, it drove, and idled absolutely perfect. It drove like stock. Then when I was cruising down the highway at 100km/h in 5th (2100rpm) it backfired and wouldnt idle anymore, so I shut it down. I cant get it to stay running. It's not the plug wires, they all seem fine. I havent pulled a plug yet tho. I cant see it being a plug. But i'll check them anyways first thing in the morning.

The tune isnt the problem at all. Car WAS great, something went wrong, or has changed while cruising.

-Cam

 

I think i've got it.... the dowel pin on the cam. Might it be too long? What is the correct length? I never measured it after installing the cam/opti. Seems like it would cause the symptoms that I have had.... Anyone know the correct length?

-Cam

 

Here are the wise words from Shoebox....and i quote,

Before you install the cam, it is a good idea to check the dowel pin length. Compare the new length to the old and make any adjustments if needed. If the dowel pin is too long, it can ruin the optispark in a short time. GM specs indicate that the dowel should be .620" long (protrusion from the front face of the cam) for the vented optispark. Some people have said it is supposed to be .685". Mine was actually .650" and still was in no danger of bottoming out in the optispark drive (I'm thinking .685" might be the max it could be). Here you can see the difference in the Comp Cams dowel (right) to the original. The CC pin was .840". That would put pressure on the back of the optispark and destroy it in a short time. If you have any doubts about the length, use some modeling clay (even PlayDoh :-) ) to test fit the opti and check the clearance.

remember you have a 95, therefore vented opti. you should be using the longer dowel anyway, which makes me wonder what your problem is. however it might be too long even for a 95...check it out, meausre it see what you get.

 

Problem solved... my new opti blew up in less then 30min run time. I put my old one on and its back to normal again. The dowel pin is the exact same length as the stock cam as well. So that isnt the reason it went out...

But im happy now, the car sounds mean as hell! To the dyno I go!

-Cam

 

Umbrae I plan on installing the same exact cam as you on my 94 formula in a few weeks....any tips? i am even doing the same plugs, etc as you....i wonder if ill like the ngk's everyone else seems to be raving. also how is driveability with this? you getting a retune?

how does it sound? PM me back or post it up on here...thanks a lot!