Intermittent shutoff

[devildogcummins]

1987 r20 5.7 tbi 4speed. Driving down the road yesterday and truck shuts down. Radio, lights, gauges all still on. No CEL. Turns over fine. Cranked up drove 100’ shut off. Cranked up drove a mile. Let it idle might run 1 minute or 30. Did tune up a year ago, new tanks, pumps. Changed coil today. Fuel spray is constant until after shutdown and fuel stops. Truck runs great until it just shuts down. Anyone ever had similar issue?

 

[Ricko1966]

Start shaking wires with the engine running. Start near the tank working your way forward towards the fuel pump relay. If it's dual tank see if it does it on both tanks. There is a reason I'm following this path.It sounds electrical and if you are losing fuel spray you are either losing pressure from the pump or signal to the injectors. The pump has 2 power circuits. One is the relay,the second is from a redundant circuit powered by an oil pressure switch. To lose pump power on a running truck thecrelay and the oil pressure switch both would have to be bad,or the wire after they merge would have to be bad. The chances of both failing are not as great as just 1 wire loose or broken in the jacket. Not saying thats it for sure but it's where I'd start. Another common point would be the tank selector switch going bad because that is in that same circuit,after the merge.

 

[Ricko1966]

To add to this you can make a sweet diagnostic tool with a long run of thin 2 conductor speaker wire. Solder sewing pins, straight pin,Tee pin,whatever type you have to each of the conductors on one end. Take 2 x 12v LED lights twist the tails together. They will each have 1 long tail,1 short tail ,twist 1 long tail to 1 short tail,twist the other short tail to the other long tail. Solder 1 twisted pair to 1 conductor of the speaker wire the other to the other. Now you have a sweet led computer friendly test light . You stick the pins in the backside of one of the injector leads. The light will flash if the injector is getting signal. Put the light where you can see it driving. Move your connection pins to another junction in say power to the fuel pump,put your light where you can see it go for a ride. It's a handy long distance test light. A lot of times just I throw the leds up on the windshield,hold them in place with the wiper blade. Here's a pic of mine. I can trouble shoot electrical problems from my couch.

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[devildogcummins]

Ricko1966 I am not loosing fuel spray, spray is consistant until ecm shuts if off after truck dies, fuel sprays good while refiring also. I will
also be making a test light like you have, thank you for that idea

 

[Sad Sack]

Ignition module?

 

[gmbellew]

Ignition module?

Without a CEL to go by, that would also be my guess. Replace with an AC Delco part vs parts house.

 

[Ricko1966]

Hook a dwell meter to your tach lead and ground,watch your dwell readings,rev the motor watch the dwell rise and fall with engine rpm. If it doesn't move or move consistently replace the ignition module. Watch for glitches like signal going away.

 

[Sad Sack]

Hook a dwell meter to your tach lead and ground, watch your dwell readings, rev the motor watch the dwell rise and fall with engine rpm. If it doesn't move or move consistently replace the ignition module. Watch for glitches like signal going away.

Nice to know!

 

[YakkoWarner]

1987 r20 5.7 tbi 4speed. Driving down the road yesterday and truck shuts down. Radio, lights, gauges all still on. No CEL. Turns over fine. Cranked up drove 100’ shut off. Cranked up drove a mile. Let it idle might run 1 minute or 30. Did tune up a year ago, new tanks, pumps. Changed coil today. Fuel spray is constant until after shutdown and fuel stops. Truck runs great until it just shuts down. Anyone ever had similar issue?

I did have a similar issue a year or so ago. Would be driving along and it would just go dead - if I was going fast enough the transmission would still keep the engine turning, but zero power. Gauges and radio would still be on. Restart would not occur unless the key was rolled all the way back to OFF. Once I turned the key all the way to OFF it would restart perfectly, maybe do it again or maybe not. No error codes on the check engine light.

I never found an "answer" as such - I had so much other work done to solve other problems that it just kind of stopped happening but I still do this day do not know what caused it. I'm always afraid this ghost problem will return since there was never a found cause.

 

[pinballlarry1]

Just my 2 cents, many years ago our Chevy Venture van would die randomly for no obvious reason, a few times per year. Took a long time to find the problem. It was corrosion on the main battery cable ring terminal where it bolted to the starter. Looked good and felt tight, but when disassembled to replace the starter, the problem never returned!!

 

[75gmck25]

Just a guess, but it might be an issue with the toothed rack and rod on the ignition switch.

The end of the key switch is a gear, and it moves a toothed “rack”. The rack then pulls a rod up and down the column. Near the bottom of the column is the electrical ignition switch. The rack is made of cheap pot metal, and over time it can crack or break. If it is cracked then it may not move the rod correctly, and that screws up actuation of the ignition switch, and ignition-on power to the truck.

 

[devildogcummins]

update,
It was the ICM, good thing i saved the one a year ago when i did a tune up. $227 for gm module to last a little less than a year.

 

[Terlingueno]

update,
It was the ICM, good thing i saved the one a year ago when i did a tune up. $227 for gm module to last a little less than a year.

$227 ????

Rock Auto has two GM Genuine, $70 and $84 respectively

 

[Sad Sack]

 

[gmbellew]

that must have been the price for a full distributor. I like AC Delco modules and have been rocking one for several years