Intermittent ignition issue

I believe that there were reports about early ignition switch failures caused by the excessive amount of current that runs through the switch for the headlights. Some have added a headlight relay to minimize the ignition switch current/heat.

For starters the distributor only has 1 ignition module. Not 2. Th ignition switch will be on the backside lower end of the steering column. I'd replace it (I did on mine). Use Delco parts whenever possible.

Thermal grease must be used on the bottom-side of the ICM not dielectric grease.

The pick up coil can only be replaced by removing the distributor from the engine. Then the distributor shaft must be removed from the distributor body.

I'm willing to bet that the (pick up coil) is what is causing your sudden engine off scenario. I just replaced both my ICM and pick up coil in my RV myself. The following pic is of the original pick up coil after having been in my RV since new 1994 with 58,301 miles on it....

https://www.dropbox.com/s/7v3r2hi4q0ckdef/20190515_220427%5B1%5D.jpg?dl=0

Changed that too

JNW57 wrote:
FUEL PUMP RELAY

Thanks...just to be clear, this last hiccup was while the engine was running, 3 hours into the trip. When I changed the module my jobber didn't have proper heat sink compound so I used silicone under it. Could have been the problem, will correct with right stuff. What would you suggest for plug gap?

Matt_Colie wrote:
Seann,

Your coach has GM-HEI. This is a known issue in our community of older GMC coaches. While at passcar loads, HEI cn be reliable, at the loads a motorhome sees it is problematic. The people that do not have problems are all careful to acquire an install genuine Delco modules and coils. If you have to change out the module, there has to be heat-sink compound under it so it can use the distributor to cool it.

It is also advised to keep the plug gap short. While HEI was introduced (40+ years ago) with huge gaps, that was soon discovered to be more than the hardware could actually handle long term.

Your coach is also old enough to have many other issues.
First thing to check always (because it is easy) is fuel at the injectors. Just pop the air filter housing open and look in at the fuel spray.
Next, put your meter on the power terminal of the HEI. Unplug it if you have to. But if there is good power there, go on to the last check.
Third check, do you have spark. This can be both harmful to the hardware and painful for you if done wrong. Pull off a spark plug boot (pull the boot, not the wire), put a screw driver in there and hold it close to metal. Crank the engine. Do you see/hear good hot spark?

Well, there you go. If you have fuel and spark, it should run.

Matt

If you are not carrying a test light or meter. Get one and have some friend teach you how to do the essential checks.

FUEL PUMP RELAY

On my 1990 the ignition switch had to be changed because of bad contacts. Not sure where yours is located but mine is in the dash. I noticed that the metal bezel around the key would get very warm. When i pulled the switch the back end of it had burnt wires on it and was slightly melted.

Seann,

Your coach has GM-HEI. This is a known issue in our community of older GMC coaches. While at passcar loads, HEI cn be reliable, at the loads a motorhome sees it is problematic. The people that do not have problems are all careful to acquire an install genuine Delco modules and coils. If you have to change out the module, there has to be heat-sink compound under it so it can use the distributor to cool it.

It is also advised to keep the plug gap short. While HEI was introduced (40+ years ago) with huge gaps, that was soon discovered to be more than the hardware could actually handle long term.

Your coach is also old enough to have many other issues.
First thing to check always (because it is easy) is fuel at the injectors. Just pop the air filter housing open and look in at the fuel spray.
Next, put your meter on the power terminal of the HEI. Unplug it if you have to. But if there is good power there, go on to the last check.
Third check, do you have spark. This can be both harmful to the hardware and painful for you if done wrong. Pull off a spark plug boot (pull the boot, not the wire), put a screw driver in there and hold it close to metal. Crank the engine. Do you see/hear good hot spark?

Well, there you go. If you have fuel and spark, it should run.

Matt

If you are not carrying a test light or meter. Get one and have some friend teach you how to do the essential checks.