no start timing mess
Thread Starter
Teching In
Joined: Aug 2011
Posts: 6
Likes: 0
no start timing mess What I have:
Lq9 Gen III, stock bottom end, 24x and 1x mild bullet racing cam, morel lifters, AFR heads, fresh build by a respectable machinist. Reluctor on crank never came off. It was verified in correct position. Motor is NA. EFI is holley termX, brand new, with new harness. Cam sensor - new AC delco was used and tried the OEM one that came off the motor that worked for 70K miles. Cam sensor wiring was verified and it has 12V. Cam and crank pulses logging OK.
> verified No1 ignition timing with new timing light that works with DIS. Made a pointer and marked the balancer. Verified TDC on #1 compression stroke, making the mark on the balancer.
> If I crank the engine, it stalls the starter motor from having way too much advance.
> Ignition timing comes up as WAY off my TDC mark - 84 degrees retard. I offset it -84 degrees in the software and up loaded to my ECM. Verified at -84 it is spot on my TDC mark. I added 15 degrees advance for crank timing. Timing tappe says yes, it's cranking at 15 degrees. It will not start but it pulses like it would ++almost++ start.
> I then place the ECM in bank to bank mode which is crude, but ignores the cam sensor signal, and it ran briefly and rough. Would not stay running.
Mechanically and electronically everything checks out. If my cam gear was back 80 degrees, I am sure I would not build enough compression to run at all. Seems to me that the firing order is off by 1, then I would only have to offset by 6 degrees. The cam manufacturer verified it is not and the reluctor cast into the cam core is clocked right.
At this point I have exhausted mechanical, sensor, and electrical investigation. Holley tech is out of ideas too.
When in sequential mode, I get a cam error on the ECM. It goes red after 2 cranks and stays red until key cycle. I have a data log if anyone is interested.
Your thoughts please.
Lq9 Gen III, stock bottom end, 24x and 1x mild bullet racing cam, morel lifters, AFR heads, fresh build by a respectable machinist. Reluctor on crank never came off. It was verified in correct position. Motor is NA. EFI is holley termX, brand new, with new harness. Cam sensor - new AC delco was used and tried the OEM one that came off the motor that worked for 70K miles. Cam sensor wiring was verified and it has 12V. Cam and crank pulses logging OK.
> verified No1 ignition timing with new timing light that works with DIS. Made a pointer and marked the balancer. Verified TDC on #1 compression stroke, making the mark on the balancer.
> If I crank the engine, it stalls the starter motor from having way too much advance.
> Ignition timing comes up as WAY off my TDC mark - 84 degrees retard. I offset it -84 degrees in the software and up loaded to my ECM. Verified at -84 it is spot on my TDC mark. I added 15 degrees advance for crank timing. Timing tappe says yes, it's cranking at 15 degrees. It will not start but it pulses like it would ++almost++ start.
> I then place the ECM in bank to bank mode which is crude, but ignores the cam sensor signal, and it ran briefly and rough. Would not stay running.
Mechanically and electronically everything checks out. If my cam gear was back 80 degrees, I am sure I would not build enough compression to run at all. Seems to me that the firing order is off by 1, then I would only have to offset by 6 degrees. The cam manufacturer verified it is not and the reluctor cast into the cam core is clocked right.
At this point I have exhausted mechanical, sensor, and electrical investigation. Holley tech is out of ideas too.
When in sequential mode, I get a cam error on the ECM. It goes red after 2 cranks and stays red until key cycle. I have a data log if anyone is interested.
Your thoughts please.
Thread Starter
Teching In
Joined: Aug 2011
Posts: 6
Likes: 0
I used GM sub harness for coils.
That was verified with a timing light. We good on spark. It will briefly fire with a shot of starter fluid.
kinda seems like injector pulse is way wrong. It burps a lazy backfire through headers on crank. I got 60 PSI fuel and injectors are firing. Injector harness OK.
Im out of ideas.
That was verified with a timing light. We good on spark. It will briefly fire with a shot of starter fluid.
kinda seems like injector pulse is way wrong. It burps a lazy backfire through headers on crank. I got 60 PSI fuel and injectors are firing. Injector harness OK.
Im out of ideas.
He's over on the Holley forum, looking for answers. Looks like the GM harness was upside down. Still no happy ending.
https://forums.holley.com/showthread...55-Chevy/page2
https://forums.holley.com/showthread...55-Chevy/page2
I'm still confused on your timing situation, I've done a few of the Holley installs and never had to offset the timing, If I had a problem it was the cam sensor. I have a feeling you're chasing your tail by doing a timing offset and I would set it back where it normally is and double check that your coils harness are is connected to the coils in the correct order as in not only left bank and right bank but at each coil.
