LT-1 issue

[Ed Wright]

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]

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]

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.

[John Nechiporchik]

Will do. Flushed fuel system prior to start-up.
May be good idea to do it again and check volume after the regulator.
What is the process to inspect individual injectors once removed from fuel rail?

Thanks,
John

[Ed Wright]

Look for debris in the screen in the top of the injectors.

[buzzinhalfdozen]

John, not sure on your system but most I've seen have 5 volt reference to TPS as someone stated earlier not having the 5v volts would be a problem. Can you not view live data with a laptop on your system? If so use that to look at what the ECU is seeing in relationship to any and all sensors. I had this very thing on my set up a few years ago and it was a loose terminal in my TPS plug, it would read at times then drop out and the engine would hardly move the car. Also not sure but some systems you can calibrate most of the sensors including the TPS. Since the main inputs used for timing and fuel are the MAP and TPS, (there are others but less important as to throttle responce) I'd look closely at both those. BTW engine off does the MAP and BARO sensors read the same, and what is MAP reading with engine running?

[John Nechiporchik]

After thrashing on this beast all day, checking all the items that were suggested, it appears that going thru the valve train and re-lashing the valves was the primary contributor.
I installed a new cam this winter with the "shimmed" lifters and appears I adjusted them too snug...and 4 valves (2 Ex and 2 In) were extremely over adjusted. So I went thru the system and re- set them all until "0" lash.
Fired it up and idled like a dream....revved it up slowly and with the exception of a slight flat spot around 3000RPM, it revved right up to 7000. I'm thinking (Ed, the tune up)needs to be tweeked for the new components. Tomorrow we'll hook the lap top up and see if we can work on the flat spot.
I'm thinking it's time to make an appointment with the chassis dyno guy to see if we can fine tune this thing.

I hope I'm done on this issue. Thanks to all of you for your ideas and support.

Special thanks to Russ Abrams for the all day text message and phone call support.

John

[Rob Petrie E395]

mind if I ask what brand lifter you used?
Thanks

[John Nechiporchik]

Stock GM lifters modified by Tom Russell.

[Alan Roehrich]

Glad to hear you're making progress John. Be sure and fix your voltage problem before you spend dyno time and money, you don't want to spend time and money on a system that is not working correctly. Make it all work correctly first, then hit the dyno. Good luck.