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1994 Suburban Intermittent Ignition & Electrical Failure

FALCON2

By FALCON2
in Ask A GM Technician

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FALCON2 Enthusiast

FALCON2

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1994 C1500 5.7 Suburban automatic. Problem is intermittent and occurs occasionally while driving under normal conditions. What happens is that the ignition system will completely cut out. When this occurs the instrument panel gauges (Oil & Temp) freeze at whatever condition the engine was operating at, and the Volt meter drops to zero. I may even recall the speedometer freezing in place. When attempting to restart, the engine will turn over. but the first attempts to restart usually fail due to no spark. One thing to note is that the gauges will not reset (oil press to 0 and temp to current engine temp) and the voltmeter still registers 0 volts when the ignition key is turned to on. The first indication I get that the the engine will restart is that the gauges all reset when I turn the key on. When this problem first started, the engine would usually restart after several attempts, now the time between the failure and a successful restart could take more then a day. The other thing to note is that, in most cases when I finally get the engine to start, as soon as the transmission is taken out of PARK and placed into gear the fault immediately occurs along with the gauges freezing again, and then I have to sit and wait from anywhere from a couple of minutes up to hours before it may start again.

The truck has a new ignition system including distributor and new coil, and a new ignition switch, all of which had no effect on the problem. I swapped the ECM from the Suburban into my my 94 Silvarado PU, and the ECM tested good, so the ECM itself appears not to be the problem.

FALCON2 Enthusiast

FALCON2

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They are. I don't loose any of the other electrical systems when this occurs and the starter turns the engine over without any problems.

Because of the way it instantly fails when the transmission is taken out of PARK I'm thinking that this might be caused by something inputting to the ECM from the transmission. The only problem is that this doesn't occur all the time. sometimes I do get into gear and the engine will run fine. The last time this happened I ran the truck for a day with no problem until the very end of the day when I had to stop, put the trans in PARK, and then when I put it back in gear it stopped. I ended up having to get it towed home after trying for several hours to get it started. The next day it started without any problem, although as soon as I took it out PARK it stalled again. It also doesn't matter whether the engine & trans is hot or cold.

bobcat5544 Enthusiast

bobcat5544

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Your problem has the characteristic of a bad PCM ground. Pull of the ground wire on the back side of the passenger side head. Clean it up and tighten it down. Also there is a ground with by the thermostat clean that up and retighten down.

See if this takes care of your problem if not then we will try something else.

FALCON2 Enthusiast

FALCON2

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  • Author
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Your problem has the characteristic of a bad PCM ground. Pull of the ground wire on the back side of the passenger side head. Clean it up and tighten it down. Also there is a ground with by the thermostat clean that up and retighten down.

See if this takes care of your problem if not then we will try something else.

 

So far no luck on the connections. All are clean and tight. I think my next step might be to disconnect the ECM and with the ignition switch off compare resistance readings on all of the inputs to the readings on the ECM inputs on my 94 chevy P/U. Then perhaps with the key sw in the ON position compare voltage readings on all of the inputs . They should all read the same.

FALCON2 Enthusiast

FALCON2

Posted
  • Author
Posted
Your problem has the characteristic of a bad PCM ground. Pull of the ground wire on the back side of the passenger side head. Clean it up and tighten it down. Also there is a ground with by the thermostat clean that up and retighten down.

See if this takes care of your problem if not then we will try something else.

 

 

The problem appears to be in a bad hot feed to the fuse panel. I have no power to just the left side of the fuse panel that contains the fuses for the ECM, Gauges, & Turn/Backup Lights. Now I have to figure out why.

FALCON2 Enthusiast

FALCON2

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Keep in mind the power feed wire to the fuse will only have power when the key is turned to the on/run position.

 

Yep, I'm aware of that. The circuit is dead in both the on/run and start postions. It looks like the fault is some where in the wire that runs from the fusible link locate under the hood, through the ignition switch, and then to the fuse panel.

Hopefully I'm getting closer to the problem.

 

Thanks

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