engine missing/backfire
Thread Starter
Racer
Joined: Feb 2006
Posts: 304
Likes: 0
engine missing/backfire
98 c5 m6 243 heads and a aftermarket cam install, had frost tune the ecu. went through the relearn procedure car now idles however the driver side of the engine has a bad miss/backfire, how I was able to determine its the driver side was by standing behind the car I could hear it on that side of the exhaust. checked all coils by unplugging one at a time and starting the engine, engines condition didn't change, each coil was hot enough that it would arc out of the coil to the coil housing. all new plugs and new gm red wires. only code is p0500 current. I started the car before I sent the ecu to frost and it had backfired and busted a catalytic converter as well as ran extremely rich to the point everything smelled like gasoline., ive yet to replace the cat. could that be the problem? or p0500? help guys=\
Instructor
Joined: May 2013
Posts: 249
Likes: 1
From: Denver North Carolina
St Jude Donor '15
Are you getting a constant backfire out the exhaust ?
If you are I woud pull the valve covers and check for a broken valve spring pay special attention to the exhaust valves. If not a continous backfire you need to look somewhere else for the cause
If you are I woud pull the valve covers and check for a broken valve spring pay special attention to the exhaust valves. If not a continous backfire you need to look somewhere else for the cause
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
P0500 is NOT your issue. Its a sVehicle Speed Sensor VSS issue..
If you know that you have a BAD cat, you should fix that.
I agree! Look for a valve train issue. Broken springs are very common..
Pull the cover and visually inspect each spring and then crank the engine over and make sure that you have proper rocker and spring action on all the valves.
Bill
If you know that you have a BAD cat, you should fix that.
I agree! Look for a valve train issue. Broken springs are very common..
Pull the cover and visually inspect each spring and then crank the engine over and make sure that you have proper rocker and spring action on all the valves.
Bill
Thread Starter
Racer
Joined: Feb 2006
Posts: 304
Likes: 0
There brand new brian tooley dual springs. I pulled the cover and rotated the engine by hand. All seem to rise and close. I pulled a plug, they were new tr55 plugs. There now very black from starting the car before tune. However I did find that the rubber boot attached to the drivers side valve cover has a 3/8th size hole in it. This is the same side as the backfire. Ill replace the boot tomorrow. Think this could bethe culprit?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Misfires on a SINGLE cylinder makes our engines run like crap! The damn engine runs better if you kill an entire bank of FOUR cylinders...
I drove 12 miles with one bank out of commission!!
I drove 12 miles with one bank out of commission!!
Melting Slicks
Joined: Jun 2005
Posts: 3,088
Likes: 61
From: NY- 2013 Corvette Challenge Champion-2013 Index Combo Champion 2015 CC/MM Champion
St. Jude Donor '07
I had a backfiring/popping out of the exhaust when I pressed on the throttle,Had a broken spark plug.
Thread Starter
Racer
Joined: Feb 2006
Posts: 304
Likes: 0
just pulled all the plugs, all looked good but cylinder 3 & 7 which were very black from running rich it appears. replaced with new plugs and same outcome, come one guys
has to be something im over looking. 
has to be something im over looking.
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Instructor
Joined: Jan 2012
Posts: 249
Likes: 11
From: Montgomery Co. PA
Pour a little oil into the low cylinder, recheck compression. If it comes up, rings, cracked ring gland etc etc. If number stays the same possible valve issue. A leak down tester would be next step, but fix that bad convertor.
Thread Starter
Racer
Joined: Feb 2006
Posts: 304
Likes: 0
Verter will be fixed this week. I need to get the car home to replace it. Ill try to do a leakdown test on it this week. Im suspecting its a valve issue. Car ran great before the head/cam swap. Always something; )
Thread Starter
Racer
Joined: Feb 2006
Posts: 304
Likes: 0
had a few minutes today, I took a fiber optic camera I had and stuck it in the sparkplug hole, I could see the piston going up and down, I couldn't make out any places in the piston were a valve had hit... ill try to do a wet compression test tomorrow if I can find the time... is it possible to overtighten stock rockers on these motors? would that be a option to why im losing compression?
Burning Brakes
Joined: Dec 2003
Posts: 1,243
Likes: 5
From: Loveland CO
Id pull the valve cover and look at the rocker, springs and pushrods. it only takes a few min to look. I dont think Pedistal mounted rockers like we have will be effected by overtightening the rockers.. but its allways good to set the TQ on the bolts correct.
I agree also with the "DRY" and "WET" comp test. doesnt take much to make it bump put.. I used a long straw from starbucks and a filled it with oil, Finger over the end to hold it... straw in cyl hole and remove my finger.. walla oil in cyl.. and good for a test.
S
I agree also with the "DRY" and "WET" comp test. doesnt take much to make it bump put.. I used a long straw from starbucks and a filled it with oil, Finger over the end to hold it... straw in cyl hole and remove my finger.. walla oil in cyl.. and good for a test.
S
Last edited by RedZMonte; Dec 23, 2013 at 07:39 PM.
Drifting
Joined: Sep 2009
Posts: 1,719
Likes: 4
From: cinnaminson n.j.
St. Jude Donor '14
Do NOT replace the converter until the misfire is corrected! You will just ruin the new one. Pull it off and gut it, then reuse it until the car is running right. If it's restricted it will lower your compression readings.
With the key off, remove the rockers from #3 cylinder. Remove the shrader valve from your compression gauge, thread the gauge hose into #3 and attach the shop air hose to it (Make sure everything is clear from the serpent belt because the engine will turn). Then listen at the t body and exhaust. If you hear and/or feel air you just confirmed a leaking valve.
Did you measure for the correct pushrods when you did the heads/cam job?
With the key off, remove the rockers from #3 cylinder. Remove the shrader valve from your compression gauge, thread the gauge hose into #3 and attach the shop air hose to it (Make sure everything is clear from the serpent belt because the engine will turn). Then listen at the t body and exhaust. If you hear and/or feel air you just confirmed a leaking valve.
Did you measure for the correct pushrods when you did the heads/cam job?