LQ4 Cranks, Backfires, won't start. PLEASE HELP
Thread Starter
Teching In
Joined: Oct 2008
Posts: 23
Likes: 0
From: Syracuse, NY
LQ4 Cranks, Backfires, won't start. PLEASE HELP Okay, some background. Fox body Mustang with an LQ4 block, ported ls1 heads, decent size cam, all built by a pretty reputable machine shop. The owner had the engine installed and took it out for a drive. Ran pretty good for about 45 minutes, he drove it back to the shop parked it, and shut the engine off. That was the last time it ran.
He tried to start it again a few minutes later. No go. It cranks fine, but pops and backfires pretty violently, sometimes into the intake (blowing out valve cover gaskets etc).
This was a couple months ago. Since that time he has tried 2 new remanufactured PCMs 3 new crank sensors, 3 new cam sensors, fuel injectors, basically everything in the ignition system. He has checked, double checked, triple checked everything on the ignition side, all of the sensors work, no DTCs, has fuel, has spark, but the engine refuses to run.
Compression and leakdown tests appear to be well. The owner refuses to believe it's a Mechanical issue as its "a brand new motor". He's beat this car to death with diagnostics and can't figure it out.
Anyone have any idea what's going on?
Thanks in advance
He tried to start it again a few minutes later. No go. It cranks fine, but pops and backfires pretty violently, sometimes into the intake (blowing out valve cover gaskets etc).
This was a couple months ago. Since that time he has tried 2 new remanufactured PCMs 3 new crank sensors, 3 new cam sensors, fuel injectors, basically everything in the ignition system. He has checked, double checked, triple checked everything on the ignition side, all of the sensors work, no DTCs, has fuel, has spark, but the engine refuses to run.
Compression and leakdown tests appear to be well. The owner refuses to believe it's a Mechanical issue as its "a brand new motor". He's beat this car to death with diagnostics and can't figure it out.
Anyone have any idea what's going on?
Thanks in advance
Thread Starter
Teching In
Joined: Oct 2008
Posts: 23
Likes: 0
From: Syracuse, NY
He's got a double roller timing set, so he refuses to believe it's the cam, it's also an interference motor.
I need some sort of concrete evidence before he'll agree to pulling the timing cover to check the cam
I need some sort of concrete evidence before he'll agree to pulling the timing cover to check the cam
Thread Starter
Teching In
Joined: Oct 2008
Posts: 23
Likes: 0
From: Syracuse, NY
He does want help, I think he's just in denial.
Is it possible for the crank reluctor to spin on the crank? This was my thought to, because the ignition timing doesn't seem to be correct, but I'm not sure exactly how the reluctor is installed, so I want sure if it's possible for it to change orientation
Is it possible for the crank reluctor to spin on the crank? This was my thought to, because the ignition timing doesn't seem to be correct, but I'm not sure exactly how the reluctor is installed, so I want sure if it's possible for it to change orientation
Trending Topics
Thread Starter
Teching In
Joined: Oct 2008
Posts: 23
Likes: 0
From: Syracuse, NY
Just confirmed that he has a Callies Crankshaft, which I guess are notorious for having the reluctor wheel come loose. I'm headed over there in a couple hours to try fibbing the ignition timing in HPTuners to see if we can get it to run
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0
Brett Foote
TECH Addict
Joined: Mar 2013
Posts: 2,628
Likes: 30
You don't even want to know how many times I've seen new rebuilds go bad like this. I'd be looking at the cam timing 1st. I just seen the callies crank..........they have real issues, best to contact them.
pull the crank sensor off and see if the reluctor has moved.
If you are thinking you could use a inductive timing light to see when its firing number 1 cylinder.
If ALL ELSE FAILS I HOPE you don't need to use the HIENY LICK maneuver on this guy. LMAO
pull the crank sensor off and see if the reluctor has moved.
If you are thinking you could use a inductive timing light to see when its firing number 1 cylinder.
If ALL ELSE FAILS I HOPE you don't need to use the HIENY LICK maneuver on this guy. LMAO
Last edited by RockinWs6; Jan 29, 2014 at 01:56 PM.
Mine did this when we first got the swap going.
It was the coil pack harness on one side. Replaced the whole coil rail with one borrowed from a truck to confirm and it fired right back up and ran perfect.
It was the coil pack harness on one side. Replaced the whole coil rail with one borrowed from a truck to confirm and it fired right back up and ran perfect.
Thread Starter
Teching In
Joined: Oct 2008
Posts: 23
Likes: 0
From: Syracuse, NY
We used a timing light yesterday and it was definitely not firing at the right time, we didn't have time to figure out exactly how far off the spark was firing in relation to the stroke.
Tonight we'll roughly estimate how far off the timing is, and attempt to do some 'Kentucky windage' with hptuners to confirm
Tonight we'll roughly estimate how far off the timing is, and attempt to do some 'Kentucky windage' with hptuners to confirm
Thread Starter
Teching In
Joined: Oct 2008
Posts: 23
Likes: 0
From: Syracuse, NY
So tonight we hooked up the timing light, and basically cranked the hell out of the car.
When cranking, should the ignition timing be hunting around at all or should it be at a set value and stay there? The ignition timing varies by a few degrees every crank rotation, like the pcm is adding 3 degrees advance everytime the crank comes around.
When cranking, should the ignition timing be hunting around at all or should it be at a set value and stay there? The ignition timing varies by a few degrees every crank rotation, like the pcm is adding 3 degrees advance everytime the crank comes around.