My 95 TA shut down unexpectedly while driving at a leisurely pace. (I replaced the OEM Optispark with an MSD unit about a year ago after the OEM unit granaded during a 1/4 mile pass. I also have an MSD coil and routed the ignition wires over the valve covers to prevent header-burn damage.) I don't have a Scan Tool to read PCM codes. There's spark from the coil and there's spark at different spark plugs. The fuel pressure is 45 psig, bled fuel looks and smells normal, fuel pump sounds healthy. I used starter fluid to assist the start but the engine won't start. I suspect the crank sensor. How can I test the optical crank sensor without a scan tool (I will read the manual tonight but would also like to hear from you). Any other suggestions?

 

The optical module in the Opti is a cam position sensor. By inference, it serves the same purpose as a crank sensor.

Shoebox has a test procedure.:

4th Gen LT1 F-body Tech Articles

But if you have spark, the PCM is receiving the signals from the Opti. Sounds like it may be more of a fuel problem. Is the SECURITY light on? Does it sputter or backfire when cranking (without the starter fluid)? If so, could be the rotor screws have backed out. MSD had major problems with their Opti about 3 years ago, with the high voltage in the cap causing interference with the pulse signals from the optical cam position sensor. I was able to show them with data logs from several vehicles, where the problem showed up, and they indicated they revised the design. You may have received a unit from tha period I’d time. I strongly recommend against using the MSD.

You are really limiting your diagnostic capabilities without a scanner. Why not try Scan9495, free scanning/data logging software, written by a member here, GaryDoug:

https://www.camaroz28.com/forums/com...95-lt1-874306/

You run a data log, post it here in .csv format, and I can take a look at it.

 

Hi Fred

Thanks for your prompt response. I checked the fuel pressure with ignition on and also while cranking and it holds at 45 psig. The fuel pump comes on and off normally when the ignition is on prior to cranking. There is no pressure bleed when the pump stops, with a residual pressure of 30 psig (engine not running).

There was some backfire but not much when cranking.

Everything points to the MSD Opti, and I bought it 2-3 years ago. I'm running out of options.

Let's see what I can do to procure a scanner. If someone lives near Robinson Township and has a scanner I can borrow send me a PM.

 

The PASS-Key (VATS) system controls the fuel system, via the PCM. It allows the pump to prime for 2 seconds when the key is turned to "run", but it prevents the PCM from turning on the pump again unless the PCM receives the "fuel enable signal" from the theft deterrent module, part of VATS. You can have 45 PSI/no leakdown, but pump/injectors aren't doing anything. Use a stethoscope of a 'noid light to see if the injectors are pulsing when the starter is cranking the engine.

 

I'll check that as well. If the PCM is not sending a signal to the pump during cranking, the pressure would not go up to 45 psig during cranking correct?

 

Would prime to 45, but would not hold if an injector is opened. With the faulty fuel enable signal, the engine will often run for a couple seconds on the fuel reserve in the rails, then stall.

I read your PM. You indicate you have spark. That means the PCM is receiving the low resolution cam position signal from the Opti. I wouldn’t jump to the conclusion that the current problem is the MSD Opti. But my philosophy is to do the requisite diagnostic work to determine the actual cause, rather than just start replacing parts.

 

wouldn't the starter not work too if vats was the problem?

 

Depends what part of "VATS" is not working. If the key resistor read fails, no starter, no fuel enable signal. But a second failure mode is the fuel enable 50 Hz signal generator in the theft deterrent module (TDM). If that fails, starter cranks the engine, but the PCM will not turn on the fuel pump after the initial prime. There are "bypass" chips available for the 50 Hz signal.

Not saying that's his problem, but it could seem to be a possibility. The PCM actually sets a code (DTC 46) if it does not receive the fuel enable signal, and when the code sets, it does NOT turn on the SES light. That's why a scan can be valuable. DTC 16 for failure of the low resolution pulse from the Opti also does NOT turn on the SES light. Ditto with DTC 41 and DTC 42 for the ICM..... no SES light.

Read the Shoebox write up..... very educational.

4th Gen LT1 F-Body Tech-PassKey/VATS

 

Pump continues to run during cranking. All voltages and grounds from the ICM and the Optispark harness read correctly. Security system checks ok. Everything points to the Opti but before I start disassembly let me know if there’s something else I should check (and yes the fuel tank is 3/4 full)

 

Update on Optispark issues: removed the MSD Optispark and sure enough, it rattles when shaken, something is loose in there. Will not open it until I talk to MSD Customer Service. Let's see how they react, as this Optispark had less than 1500 miles driven!!

Decided to never again go the Optispark way, as this is the third one gone bad.

In the process of installing a Torqhead 24xLink LS PCM conversion kit.

 

But you bought the MSD, which is a known problem. I tell anyone who asks for a recommendation not to buy it.

If you actually had spark as you indicated, could be the rotor came loose and the spark isn’t going to the right cylinder at the right time. But that should have produced sputtering and backfiring, which you never indicated.

Please follow up with feedback on what MSD says.

 

I did not know about the MSD problem until recently. BTW, I installed an ACCEL Opti prior to the MSD and it didn't work from the getgo, replaced it with the MSD!! I find out later ACCEL and MSD are all owned by Holley.

Definitely the rotor is loose but most probably attached. The OEM Optispark (second one installed) grenaded the rotor completely.

MSD will repair it free of charge once I ship it to them. They will not send a new one. I wonder if it's worth the shipping cost and effort to get it repaired and then put it up for sale in eBay!! Who would buy this POS??

 

I identified three different MSD units with the erratic low res pulse pattern problem, causing erratic/spiking idle and roughness. Two of the three people sent their units back to MSD, and both of those returned/rebuilt units were dead-on-arrival when MSD sent them back. Of those two, one guy had it rebuilt a second time (all these were totally free shipping/rebuilds, because MSD admitted the unit had a specific problem), so what was essentially his third MSD was finally OK.

People buy it because MSD has a reputation for building quality ignition products. Go to the NHRA events, and all the top fuel cars have those two giant MSD magnetos sticking out of their engines. But for some reason, MSD has never fully solved the art of building a quality Optispark. They fix one problem, another appears. Again, not saying they all fail, but when you are paying their premium price, the failure rate should be much lower.

In a way, it's like Aeromotive. They are known for killer fuel systems. Yet their LT1 adjustable fuel pressure regulator has been failing for 20 years, and they still haven't managed to get it right. The first question I ask when someone has a fuel system , and indicates they have an "AFPR".... is it an Aeromotive????

Accel.... another known problem. Not saying they all fail, but the failure rate is higher than it should be.

The current best feedback seems to be the unit from Petris:

https://petrisenterprises.com/collec...rk-distributor

The Corvette forums seem to find it OK, and a couple people here have bought the Petris.

There are often references here to someone who rebuilds the optical module, and so far nothing negative or positive.

 

I'm done with the Optispark system, enough is enough.

 

Bit the bullet, ordered and I'm in the process of installing a Torqhead multi-coil system. Lots of interferences encountered with the multi-coil bracket install (I bought the option that bolts to the valve covers). Several observations:

1) The AIR system will interfere on both sides, requiring either relocation/bending of tubing and hoses or elimination of the AIR system. I have decided to eliminate the AIR system but will still need to bend tubing connected to the headers out of the way and plugging them. I decided to eliminate the AIR system because the passenger side has very little space for rerouting, not worth the trouble for a system that is used for a few minutes during cold start.

2) The heater line (passenger side) interferes with the third coil (#6 cylinder). Will need to reroute this hose (new hose will be needed).

3) Bolting the multi-coil brackets to the valve covers requires removing very small allen bolts holding the coils to the bracket, one bolt per coil for the two coils on top of the bracket flanges. These two coils need to be rotated in order to insert and tighten the valve cover fastener. Obviously installation of the small allen coil fastener is very difficult and prone to drop the small bolt. Torquehead should re-design the multi-coil bracket to allow installation without messing with the coil fasteners.

4) The LT1 PCM needs to be replaced with an LS PCM, which is included in the kit. What's not included is the PCM bracket, I bought one used from Hawks, but I could have saved a few bucks by pulling one out of a salvaged car. The LS PCM installs "upside down" compared to the LT, so all the connectors are facing out instead of tucked behind the PCM. The wire harness needs to be rerouted but it just takes minor effort.

5) I have an ATI SuperDamper, so Torqhead provided an ATI compatible hub, nice piece, all important dimensions are identical. Now I have to find the right damper installation tool, as my Proform tool's shaft is too short (don't laugh). I sent them an eMail but have not received a response yet.