Random power loss to engine and accessories

[CmuCmu]

Hey guys as title says, I'm getting a random power loss to engine and accessories while driving; it lasts maybe for a second or two and both the engine and accessories restart on their own. Granted, I was doing 40mph more or less whenever this happened so the engine restarting on its own by inertia isn't out of the question.
Headlights are unaffected since they use the battery circuit.
I'm suspecting either switch or master relay.
Has anyone else had this issue?
I don't thing it's coil or distribution since accessories turn off as well.
Please help

 

[Scott91370]

Check the bulkhead fitting under the hood and make sure it is tight.

 

[Sad Sack]

...anything electrical I always confirm state of charge in the battery and if the alt is performing as expected, before going any deeper. Free bench testing at any auto parts store is always handy.

 

[CalSgt]

Hey guys as title says, I'm getting a random power loss to engine and accessories while driving; it lasts maybe for a second or two and both the engine and accessories restart on their own. Granted, I was doing 40mph more or less whenever this happened so the engine restarting on its own by inertia isn't out of the question.
Headlights are unaffected since they use the battery circuit.
I'm suspecting either switch or master relay.
Has anyone else had this issue?
I don't thing it's coil or distribution since accessories turn off as well.
Please help

I'm leaning towards ignition switch since it controls power to the accessories and engine.

Ignition switches can wear out right in the spot where the contacts always ride, sometimes a minor adjustment to the ignition switch on the column can buy some time or cure issues. The adjustment may make the contacts in the switch ride in a fresh spot that isn't worn/burnt out. If you remove the switch from the column visually inspect for heat damage from the contacts burning up, discoloration Etc. They're fairly inexpensive and kind of a pain to get to and adjust, if you go through the trouble to remove and inspect it you might as well just replace.

Wouldnt hurt to check your grounds and fusible links for damage. IIRC there are two main power feeds into the bulkhead on the firewall that supply power to two main circuits in the cab. One circuit supplies the headlights and anything that maintains power while cranking, the other circuit supplies the accessory circuits through the ignition switch.


This one is a long shot... and kind of a funny story

Had a customer come through the shop years ago with intermittent engine dying and accessory loss. After numerous shop visits, tons of trouble shooting with no success and no one was able to recreate the issue. Finally, the mechanic had her take him on a drive. Every time she hit a small bump the car died, he eventually noticed the weight of her massive key ring had turned the ignition cylinder when she hit the bump just far enough to kill it. All of the times she dropped the car off the key ring she left the shop to work on it was just an ignition and door key, that's why we could never recreate the issue.

 

[Broken85]

This sounds like a ground issue somewhere but, I think we can solve this. Can you tell us a little bit about your powertrain set up? Is this a stock engine or is this a redo?

 

[CmuCmu]

Check the bulkhead fitting under the hood and make sure it is tight.

Done, all are tight and with good continuity. Hit with rubber mallet to simulate road bumps and they're all good.

...anything electrical I always confirm state of charge in the battery and if the alt is performing as expected, before going any deeper. Free bench testing at any auto parts store is always handy.

Battery is charged and alternator is sending between 14.1 and 14.7 depending on rpms and load. No problems there.

This sounds like a ground issue somewhere but, I think we can solve this. Can you tell us a little bit about your powertrain set up? Is this a stock engine or is this a redo?

Stock 292. Checked all grounds are all good.

I'm leaning towards ignition switch since it controls power to the accessories and engine.

Ignition switches can wear out right in the spot where the contacts always ride, sometimes a minor adjustment to the ignition switch on the column can buy some time or cure issues. The adjustment may make the contacts in the switch ride in a fresh spot that isn't worn/burnt out. If you remove the switch from the column visually inspect for heat damage from the contacts burning up, discoloration Etc. They're fairly inexpensive and kind of a pain to get to and adjust, if you go through the trouble to remove and inspect it you might as well just replace.

Wouldnt hurt to check your grounds and fusible links for damage. IIRC there are two main power feeds into the bulkhead on the firewall that supply power to two main circuits in the cab. One circuit supplies the headlights and anything that maintains power while cranking, the other circuit supplies the accessory circuits through the ignition switch.


This one is a long shot... and kind of a funny story

Had a customer come through the shop years ago with intermittent engine dying and accessory loss. After numerous shop visits, tons of trouble shooting with no success and no one was able to recreate the issue. Finally, the mechanic had her take him on a drive. Every time she hit a small bump the car died, he eventually noticed the weight of her massive key ring had turned the ignition cylinder when she hit the bump just far enough to kill it. All of the times she dropped the car off the key ring she left the shop to work on it was just an ignition and door key, that's why we could never recreate the issue.

I did remove the whole key the second time it failed just in case it was that, but still failed later without the key inserted. Tried to diagnose it with the rubber mallet against the steering wheel, the column casing, and even the switch itself but couldn't get it to fail as it did on the road.
Also, the failure happens at random on flat or bumps, no difference there.
So I'm leaning towards the master relay now; anyone know how to diagnose it? By omhs maybe? Like "should be X omhs but because it's old it reads Y omhs"?

 

[CalSgt]

Done, all are tight and with good continuity. Hit with rubber mallet to simulate road bumps and they're all good.



Battery is charged and alternator is sending between 14.1 and 14.7 depending on rpms and load. No problems there.



Stock 292. Checked all grounds are all good.



I did remove the whole key the second time it failed just in case it was that, but still failed later without the key inserted. Tried to diagnose it with the rubber mallet against the steering wheel, the column casing, and even the switch itself but couldn't get it to fail as it did on the road.
Also, the failure happens at random on flat or bumps, no difference there.
So I'm leaning towards the master relay now; anyone know how to diagnose it? By omhs maybe? Like "should be X omhs but because it's old it reads Y omhs"?

IDK how to test a relay other than they seem to either work or not. I’ve seen a piece of debris or bug get between the contacts and stop them from working. I’ve seen some types of relays wear out and get stuck open or closed regardless of signal from the switch….

My truck is a little older but I don’t think my truck has any relays other than one for the horn and ones I’ve added for aftermarket stuff like remote power windows and locks.

AFAIK The ignition switch itself is fairly heavy duty and carries the load for the whole system without the need for relays

ETA: Just to be sure… when you say switch you are not talking about the ignition cylinder where the key goes right? The switch is on the top side of the column under the dash

 

[H2OnSnow]

So I'm leaning towards the master relay now; anyone know how to diagnose it? By omhs maybe? Like "should be X omhs but because it's old it reads Y omhs"?

Specifically, what relay are you talking about? What does it feed from, and what does it feed?

 

[CmuCmu]

IDK how to test a relay other than they seem to either work or not. I’ve seen a piece of debris or bug get between the contacts and stop them from working. I’ve seen some types of relays wear out and get stuck open or closed regardless of signal from the switch….

My truck is a little older but I don’t think my truck has any relays other than one for the horn and ones I’ve added for aftermarket stuff like remote power windows and locks.

AFAIK The ignition switch itself is fairly heavy duty and carries the load for the whole system without the need for relays

ETA: Just to be sure… when you say switch you are not talking about the ignition cylinder where the key goes right? The switch is on the top side of the column under the dash

Specifically, what relay are you talking about? What does it feed from, and what does it feed?

I think I'm referring to the same thing: It's a huge relay behind (? It should be bolted somewhere but it's hanging) the dash. When the switch is on, it powers the accessories circuit, drawing power from the battery. By "huge" I mean its the size of four normal Bosch type relays.

 

[Ricko1966]

If you are referring to the fuel pump relay as the master relay. As long as your secondary oil pressure switch is good the relay isn't going to shut the car off. The second oil pressure switch is a redundant circuit so the car will not die and leave you stranded if the relay goes bad. A symptom of a bad GM FP relay is an extended crank time to start. Oil pressure has to build to power the pump if the relay isn't powering the pump. And just to make it clear the oil pressure switch will not cause an extended crank and is not there to shut the pump off if you are low on oil. I have no idea why so many people think that.

 

[BadBowtie]

Check all of the fuseable links- Firewall & down by starter.