Need help..engine won't idle after motor/cam install
#1
Launching!
Thread Starter
iTrader: (7)
Join Date: Mar 2005
Location: Florida
Posts: 235
Likes: 0
Received 0 Likes
on
0 Posts
Need help..engine won't idle after motor/cam install
I have stock LS1 engine with stock 241 heads not ported/milled with PAC 1518 springs, stock rockers, TSP 7.4 push rods, and a TSP 233/239 cam on a 112 lsa. I installed the cam dot to dot (checked it 10x), re-installed the heads with GM MLS gaskets, all torqued to spec, and a LS6 intake and stock 98 injectors. Here is my problem...the engine will fire and run with your foot on the gas, BUT when you let off the gas the engine idles for a few seconds then there is a loud POP/backfire from the exhaust and we shut it down. There are no engine codes, I have spark, and coils are working, ruled out the MAF, and all sensor appear to be working when hooked up to the computer.
I've looked up the issue and can't pin this one down. Anyone ever had this issue? or any suggestions? The car has been at a LSx local shop right now and we are kinda stumped at this point.
I've looked up the issue and can't pin this one down. Anyone ever had this issue? or any suggestions? The car has been at a LSx local shop right now and we are kinda stumped at this point.
#4
Dot to Dot does NOT necessarily mean the cam is installed correctly, that's why there are degree wheels out there. You need to check it correctly. The back fire could be timing or a lean condition.
As for it not idling, probably a lack of air to stay running and that's in the tune.
#6
Launching!
Thread Starter
iTrader: (7)
Join Date: Mar 2005
Location: Florida
Posts: 235
Likes: 0
Received 0 Likes
on
0 Posts
How loud was the POP on yours? Mine sounds like a shot gun in a metal barrel. The shop said it's not a tuning issue, and are pointing at the cam as the problem. I didn't think the cam is the issue, if it runs above 1,000rpm it will not back fire, but let it idle and backfires. There is a basic tune on it that I am told should allow the car to at least idle properly without the backfire.
Trending Topics
#8
TECH Junkie
iTrader: (5)
It has a tune on it already for the mods,
The shop that it is at is well known on here, and they kinda feel it may be the cam,
Either way, I would take it to an actual capable tuner and watch your car idle and drive almost as well as stock. That cam isn't that big that it cannot be tuned. People have much bigger cams in their cars and theirs idles and drives.
#9
I have same cam and my car idled bad after install. Had lmr work out the tune and runs like a champ! I suggest get a new shop imo
Last edited by sscamaroburn02; 08-17-2013 at 09:09 PM.
#10
Launching!
Thread Starter
iTrader: (7)
Join Date: Mar 2005
Location: Florida
Posts: 235
Likes: 0
Received 0 Likes
on
0 Posts
I'm hoping that's all it needs is a tune. I have been working on cars for over 12 years and have had this one for over 10. I strongly feel that it is nothing mechanical/electrical or it would throw a code or not even start. I put the cam in the car when it was the stock short block with the stock cam, I put it TDC, the cam gear dot was at 6 o'clock and the crank dot was at 12, pulled the stock gear then cam, put in the new one in, EXACTLY as the stock cam came out, and the cam gear lined up perfectly with the crank. All this with a new LS2 timing chain, so I know if the cam is ground correctly then all is good.
Would an improper tune really make the car backfire so loud at idle? I'm very frustrated at this point as to the time I have put into the motor build and money spent into having someone swap out motors (if I had a lift I'd do it myself).
Would an improper tune really make the car backfire so loud at idle? I'm very frustrated at this point as to the time I have put into the motor build and money spent into having someone swap out motors (if I had a lift I'd do it myself).
#12
TECH Enthusiast
iTrader: (25)
Join Date: Nov 2011
Location: Milwaukee, WI
Posts: 547
Likes: 0
Received 0 Likes
on
0 Posts
I'm hoping that's all it needs is a tune. I have been working on cars for over 12 years and have had this one for over 10. I strongly feel that it is nothing mechanical/electrical or it would throw a code or not even start. I put the cam in the car when it was the stock short block with the stock cam, I put it TDC, the cam gear dot was at 6 o'clock and the crank dot was at 12, pulled the stock gear then cam, put in the new one in, EXACTLY as the stock cam came out, and the cam gear lined up perfectly with the crank. All this with a new LS2 timing chain, so I know if the cam is ground correctly then all is good.
Would an improper tune really make the car backfire so loud at idle? I'm very frustrated at this point as to the time I have put into the motor build and money spent into having someone swap out motors (if I had a lift I'd do it myself).
Would an improper tune really make the car backfire so loud at idle? I'm very frustrated at this point as to the time I have put into the motor build and money spent into having someone swap out motors (if I had a lift I'd do it myself).
Have you checked your spark plugs to see if they are clean and good? You may have spark but you could've killed them.
Personally I would go to another shop or find someone around that has HP tuners. I know it's a simple question but did they open the small hole in the throttle blade up at all? You're IAC could be bad and the hole could be too small so the engine can't get enough air. Just a thought.
#14
Launching!
Thread Starter
iTrader: (7)
Join Date: Mar 2005
Location: Florida
Posts: 235
Likes: 0
Received 0 Likes
on
0 Posts
Checked it out today, turned out to be the coil packs, the shop put on a set of coils from another car and she is running PERFECT! Thanks to all that replied, it is a huge relief. I am going to check the coil wiring, because i think the wire harness was flipped resulting in the firing order to be reversed on one side. If that is the case that may have been an error on my part not theirs.
#17
Launching!
Thread Starter
iTrader: (7)
Join Date: Mar 2005
Location: Florida
Posts: 235
Likes: 0
Received 0 Likes
on
0 Posts
Can't wait to get it back. The cam sounds SICK, and the dyno yielded 374hp and 361 torq. If I had the extra money I would have bought some ported heads, but the car is only driven about 1,500 miles a year and I do not race it. After owning it for over 12 years I have come to just enjoy having the car instead of beating the crap out of it. Don't get me wrong their will be the occasional itch in my right foot, but I'm gonna love the choppy cam notes from the exhaust.