twigger

So I have already done many hours of research and I am still stumped on what my problem may be.

I was driving down the highway and the car started missing, similer to when the ICM went out twice but this time the tachometer was not flickering with the drop in rpms. So after work I figured I would just limp it home but it was hard to start and when it started it ran like garbage for 10 seconds and then it died. Fired right back up and ran crappy for a while and smoothed out. Took off down the road driving it really easy, got on it a bit and soon as I did it died for about thirty seconds. Got it going again and drove it home keeping it below 10 percent throttle, any more than that and it would start missing.

So a few days went by and I got a fuel pressure tester, key on and not running it would pull 42 psi. Took a good minute of cranking and it finally caught and ran for 10 seconds with tons of black smoke and died, started right back up and ran with a consistant 36psi with no more smoke.

Now a few day later I have a scan tool, no codes, but I cant get it started to get some live data out of it. Used my spark tester and it has spark, took my noid lights and the fuel injectors are getting power. Tried squirting fuel through the manifold and no change. Tried adjusting the distributor timing and I got it to pop a little.

Relevent stuff that has been replaced in the last 2 years is,
Complete distributor X2
Cap rotor plugs wires
Set of Bosch 3 injectors
Oem EGR valve
Fuel filter
All intake gaskets
Idle Air Control valve


Only thing I have done recently is switch to a 0W-30 synthetic oil and from what I understand is there is a oil pressure switch that if it doesnt see 4 psi of oil pressure it will kill the motor. But from all the driving I have done it rarely dropped below 30psi. Could a faulty switch cause these problems?

Any help or advice on what I should check next would be greatly appreciated thanks in advance!

vetteoz

iTrader: (13)

The ECM needs to see the input from the OP switch when cranking to pulse the injectors
but you say you have injector pulse

The OP switch is not a kill / safety switch;
over 4 psi the switch runs the fuel pump as a backup should the pump relay fail
and it indicates to the ECM (only while cranking ) that the engine has oil pressure so the ECM can allow engine to fire.
Under normal cond if you were to lose oil pressure the fuel pump would still be run from the pump relay so engine would continue to turn regardless of what OP is

Definitely looking like a spark /timing problem
How "strong " a spark are you seeing
What do the plugs look like ; have they been firing or are they wet with fuel indicating no / weak spark?

twigger

With my spark gauge it was jumping .060 so its a decent spark. With an oscilloscope when I was cranking it looked like an erratic spark so I tested the coil and the distributor pickup and figured it was the igntion control moduleagain. Swapped distributors with a new unit and it fired right up got it timed but it kept having a complete miss where the whole screen lit up on the scope. Finally smoothed out but the timing sounded off, then after 5 mins of running it just died. Started up and died two more times and now it wont run again. I am stumped and ready to give up.

twigger

I check all the rest of the sensors and all were good. I have been using a MSD coil for not even two years and it turns out that it was the culprit. Still jumping a .060 gap but it was no good, probably the reason I fried 2 ignition control modules.

ASE doc

Ive had this problem with MSD coils. They are sodl as bolt ons but are actually intended for use with MSD ignition controllers, which have a much higher current capacity. If you test the coil primary resistance, you'll likely find it's under .5ohms. Too low for the OE ignition module.

Vetteoz, are you sure that the OP switch prevents injector pulse while cranking? I'm fairly sure that the OP switch runs parallel to the FP relay and has no effect on Injector function. I'm also fairly sure that it will shut off the fuel pump at under 5psi.

vetteoz

iTrader: (13)

I'm only going by the commonly referenced L98 startup procedure
Example here
http://www.corvettebuyers.com/c4vettes/l98.htm

The most common explanation I have seen is that signal into the ECM tells the ECM that the engine has oil pressure and it can fire it up. That input is only referenced while cranking

Common misconception that switch is a low oil pressure cut off switch
You can see from the circuit diagram ;should the OP switch go open ( loss of oil pressure) while engine is running, power would still go to ECM pump signal input ( terminal B2 ) from the pump relay side of the circuit so the engine would continue to get fuel

ASE doc

The fuel pump relay is powered up when cranking, providiing power to the same ECM fuel pump signal circuit the OP switch powers. So it doesn't seem that the OP switch would affect injector pulse. I do see though how it appears the OP switch will not kill power to the fuel pump. I have the factory manual for the 87 and I'm referring to those diagrams. It would be interesting to test this on a subject car.

vetteoz

iTrader: (13)

Not the way I read it,
if the OP switch signal is not seen 1st , then the ECM won't pulse the inj and then operate the pump relay
( also know not to believe everything posted online )

From the L98 start up procedure

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor, it will energize the injector drivers .The ECM will also pull in the fuel pump relay