LT-1 issue

[Alan Roehrich]

The check valve retains fuel pressure after the pump is turned off. For example, a stock or stock replacement pump will usually retain 90% or so pressure for several minutes. If your pump retained a significant amount of pressure last year, for a significant period of time, and this year it bleeds off a substantial amount of pressure fairly quickly, then something significant has changed. Since that change is accompanied by a performance/driveability problem, that is where you should look first.

I would think, and I may be wrong, that 45 psi is a little low. It would seem to me that you'd want to run closer to 55-60 psi if you can build that much pressure, and use a shorter duty cycle on the injector to maintain the A/F ratio the engine likes.

[Lee Valentine]

Every problem I had with my LT-1 was the opti spark

[John Nechiporchik]

Alan, Thanks for the info. I'll pull the fuel pump as soon as I finish my analysis on the Optispark question (below)
I tested the TPS with the following results:
Per the Accel manual, the input signal is 5V.

Input signal was 3.32 Volts (issue??)
.48 Volts at idle
1.74 at mid throttle
2.67 volts at WOT.

I tested a spare throttle body /TPS and got almost identical results.

Dyno/Lee: On the last pass I made last year, I destroyed the stock style rotor.It literally shattered in the shutdown area.
Over the winter, I replaced the cap and rotor with MSD parts.
Is it possible that the catastrophic failure caused some damage to the distributor itself that is resulting in this condition? All input appreciated.

[Alan Roehrich]

John,
Yes, reference voltage to the TPS being under 5.0 vdc is a serious problem, especially being almost 1.7 vdc low. When you are testing that voltage, is the connector disconnected and the battery voltage at 12.5 vdc or above? Is the battery input voltage at the ECU 12.5 vdc or above?

Yes, it is possible that a shattered rotor damaged the distributor.

[John Nechiporchik]

What about crank trigger sensor?

[John Nechiporchik]

Alan, When we re terminated the TPS connector, we added a testing port (connector) so I am able to test it with the harness connected to the TPS and the ECU harness. The battery is a 16 V that measured 16.85 volts with ignition on.

What do you think could have been damaged in the distributor housing itself?
Need to check voltage at ECU

[Alan Roehrich]

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]

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]

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

[Dave Edwards]

low voltage