cmaddox03

My father-in-law picked up a 1994 Camaro with 5.7 LT1. The car has full exhaust (long tube headers, off-road mid-pipe, and hooker cat-back), MSD opti-spark, Mallory ignition unit, and shift kit. The car runs good once it has started. He ran it at the track already and ran 13.9's.


The major problem is that it takes 7-8 seconds of cranking until it starts. The fuel gauge wasn't working so I replaced the pump & sending unit. This fixed the gauge but no help with the starting. I replaced the fuel pressure regulator but this didn't help with the starting. I check the fuel pressure and it has good pressure & does not lose pressure.


I've replaced the fuel filter & spark plugs. The fuel filter was ok but plugs were bad. I checked impedence of the injectors and they all measured the same.


I've removed the Mallory ignition unit to see if that would help but no change. I did notice that while the Mallory unit was still attached that the indicator light on the Mallory unit would blink for 6-7 seconds & then turn solid. Once the light went solid, the car would start. What would be causing signal to the ignition to be delayed?


It has the engine light on but cannot get it scanned yet. I'm dropping it off for alignment today and they're going to scan it.


Any ideas?

shoebox

Report back with the scan results. That will be the first step in diagnosis.

Injuneer

What "Mallory Ignition unit" are you using?

cmaddox03

It is a Mallory Hyfire VI unit.

Injuneer

But you got the same delayed start both with and without the Malloryunit installed? The engine can't start until the PCM gets the cam position signal from the Optical module in the Opti..

cmaddox03

That is correct. The delayed start was with and without the Mallory unit.

GaryDoug

My guess is that the code you see will be 36, loss of the high-resolution pulse from the Opti. The pcm uses the high-res pulses to determine which of the varying width slots (one for each cylinder) on the low-res ring of the timing disc is being read at the beginning of the cranking, so it can set the injector to fire first. Without the high res signal, it takes longer to compare the different low res pulses to make a determination of the timing. Once the engine is started, the high-res pulses are not used for much.

This is how it works: The pcm counts the number of high res pulses during the low res pulse. If there is just one, that is cylinder 1, 4, 6, or 7, and that is not definitive, so it waits till the next low res pulse. If there are 6 high-res pulses during the low res pulse, that is for cylinder 8. Likewise 11 means cylinder 3, 16 means cylinder 5, and 21 means cylinder 2.

Injuneer

The instructions for that unit indicate the LED will blink during cranking to indicate that the trigger signal is being received. Sounds like the ignition trigger must be reaching the unit.

cmaddox03

I've got cables on order so I can scan codes and read real-time data from the car. Besides the starting issue, the car is running rich. The plugs I replaced were dark. I can smell fuel from the exhaust while the car is running.

GaryDoug

For what it's worth, I just finished a test of the missing high res pulse at a low cranking speed (120 rpm). It took 6 seconds for the pcm to "figure out" the timing and start the ignition and injector pulses. But without any ICM pulses, the system wouldn't flash that Mallory LED evidently, so the code 36 may not be the case.

Injuneer

I wonder if - without the high res signal - the PCM picks an arbitrary first cylinder to fire (and hence the first injector to fire) based on the low res pulse, then starts changing to other cylinders until it hits the right one. That would meet the 6 second delay, while also explaining why the Mallory unit has a flashing LED.

Or it might just be a dumb thought. You are indicating it sends no pulses to the ICM until it figures it out.

GaryDoug

That is a reasonable guess. But I don't see (or hear) any pulses to the ICM during the 6 seconds. And I have an ICM, coil, and spark tester fastened to the pcm setup. So, I can see and hear the spark when it happens ;-)

The hi res pulses serve as the time base, since the cranking speed is indeterminate. Without it, I think the pcm "times" the signals over several revolutions and compares the real time pulse width of each slot before assigning slots to specific cylinders.

cmaddox03

I finally got everything together and scanned the car. The codes that it has are a #36 & #70.


With the #36 code, does that mean that I need to replace the optispark? That means replacing the entire distributor, cap, and rotor. What is the best replacement?


What does the #70 code indicate? It says "A/C clutch relay driver circuit", what does that mean?


I've got an excel file of data from a scan I ran. Is this the correct format for the scan data? I'll post it and let you guys dissect it.


Thanks for any help!!

shoebox

36 is either the opti, opti cable or electrical interference with the opti cable (like a plug wire). AC-Delco, Delphi, MSD (in that order) for an opti. Though,the MSD would add a venting function that you do not now have with a stock unit. Store brands and other aftermarket optis are very hit and miss on quality/reliability.

70 involves your a/c control circuit from PCM to the relay. Could be the relay or the wiring between the two.

cmaddox03

It is sad that it has a failed MSD opti-spark. It isn't the MSD's fault, it is vented but the previous owner never hooked up the vacuum ports. They re-routed some other vacuum lines. The PVC valve isn't hooked up to the port under the throttle body.