LT-1 issue

Alan Roehrich · 04-12-2015, 04:28 PM

John,
Right now, what is important is the voltage on the battery supply terminal at the ECU? Especially with the engine started and running.

There could be any number of problems caused by binding, flying debris, etc, inside your distributor.

Lee Valentine · 04-12-2015, 04:53 PM

If you never welded the shaft in the opti spark it may have moved making the phasing wrong for the crank trigger,try another distributor

John Nechiporchik · 04-12-2015, 05:46 PM

Thanks for all the info. Will continue the investigation tomorrow.

Dave Edwards · 04-12-2015, 08:34 PM

low voltage

Ed Wright · 04-12-2015, 09:47 PM

You would be extremely lucky to find a dead spot on the TPS wiper with a volt/ohm meter. They are too slow. What you see on a digital meter is not real time. It is data frames, like frames on a movie film. The update rate with a meter is so slow, sweeping the TPS usually falls between data frames. You would have to move the throttle lever VERY slow to catch it with a meter. Thing to use is a fast digital lab 'scope. I always used a Fluke 98A. Very fast. Still need to sweep the TPS 15 or 20 times to be sure there is no issue there.

Stock fuel systems will hold fuel pressure a long time after the key is shut off. Factory fuel pumps have check valves. Not so aftermarket race pumps. My Aeromotive system drops pressure quickly. I wait a couple seconds after turning it on to crank the starter. Much shorter crank times if I wait for fuel pump to get the pressure up.

Problem is likely TPS, MAP related, or a tuning issue.

Mike Taylor 3601 · 04-13-2015, 07:38 AM

Once a LT-1 I had built was acting weird backfire some would'nt idle, long story short,
found rotor out of phase was almost half way between cylinders and optical sensor showed out of range,probably had slipped on shaft,I slotted the wheel and got the opti sensor in range and slotted rotor and phased it ran good then.
When rotor etc exploded could have knocked out of phase,I used a small degree wheel to turn engine to where ignition timing was so I could check phasing of rotor
Mike Taylor 3601

Ed Wright · 04-13-2015, 10:16 AM

Sheep Boy can't post here, but thinks you may have a rubber fuel line deteriorating inside, putting crap in your injectors. If you have old stuff on your car, it sure would be worth checking.

04-12-2015, 04:28 PM	#1
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,115 Likes: 1,572 Liked 1,829 Times in 414 Posts	Re: LT-1 issue John, Right now, what is important is the voltage on the battery supply terminal at the ECU? Especially with the engine started and running. There could be any number of problems caused by binding, flying debris, etc, inside your distributor. __________________ Alan Roehrich 212A G/S

04-12-2015, 04:53 PM	#2
Lee Valentine Senior Member Join Date: May 2004 Location: Brookfield, CT Posts: 708 Likes: 13 Liked 319 Times in 68 Posts	Re: LT-1 issue If you never welded the shaft in the opti spark it may have moved making the phasing wrong for the crank trigger,try another distributor __________________ Lee Valentine 1661 STK

04-12-2015, 05:46 PM	#3
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 316 Likes: 84 Liked 13 Times in 7 Posts	Re: LT-1 issue Thanks for all the info. Will continue the investigation tomorrow.

04-12-2015, 08:34 PM	#4
Dave Edwards Junior Member Join Date: Oct 2004 Location: Washington C H, Ohio Posts: 90 Likes: 28 Liked 13 Times in 4 Posts	Re: LT-1 issue low voltage __________________ Dave Edwards 3852 STK

04-12-2015, 09:47 PM	#5
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: LT-1 issue You would be extremely lucky to find a dead spot on the TPS wiper with a volt/ohm meter. They are too slow. What you see on a digital meter is not real time. It is data frames, like frames on a movie film. The update rate with a meter is so slow, sweeping the TPS usually falls between data frames. You would have to move the throttle lever VERY slow to catch it with a meter. Thing to use is a fast digital lab 'scope. I always used a Fluke 98A. Very fast. Still need to sweep the TPS 15 or 20 times to be sure there is no issue there. Stock fuel systems will hold fuel pressure a long time after the key is shut off. Factory fuel pumps have check valves. Not so aftermarket race pumps. My Aeromotive system drops pressure quickly. I wait a couple seconds after turning it on to crank the starter. Much shorter crank times if I wait for fuel pump to get the pressure up. Problem is likely TPS, MAP related, or a tuning issue. __________________ Ed Wright 4156 SS/JA

04-13-2015, 07:38 AM	#6
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,372 Likes: 354 Liked 307 Times in 103 Posts	Re: LT-1 issue Once a LT-1 I had built was acting weird backfire some would'nt idle, long story short, found rotor out of phase was almost half way between cylinders and optical sensor showed out of range,probably had slipped on shaft,I slotted the wheel and got the opti sensor in range and slotted rotor and phased it ran good then. When rotor etc exploded could have knocked out of phase,I used a small degree wheel to turn engine to where ignition timing was so I could check phasing of rotor Mike Taylor 3601

04-13-2015, 10:16 AM	#7
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: LT-1 issue Sheep Boy can't post here, but thinks you may have a rubber fuel line deteriorating inside, putting crap in your injectors. If you have old stuff on your car, it sure would be worth checking. __________________ Ed Wright 4156 SS/JA