Problems with the engine

[RvRev2]

In another post on "So What Did You Do To Your GMC Today?" I shared some engine problems I was having on the way down to the Spring Rally. Someone suggested that it would probably be better to make this topic its own post. So, I have attached the history on this topic from the other post in a PDF below.

In a nutshell, I traveled down to Vidalia for the Spring Rally. I took 3 days to get there. After driving more than 4 hours, when I would slow down or come to a stop, and then started to accelerate, the engine would shut down. This happened on the first two days getting down there. The third day was a short trip, just 2 or 3 hours long, and I had no issues. Each time I had this issue, it would not restart for between 10 minutes and 30 minutes.

This happened on the way back home as well. However, on the way back home, once I got past Dallas, it started to cool down outside, and was getting dark. I reasoned that I wouldn't have vapor lock running at night, so I drove all the way home non-stop except to refuel. No vapor lock troubles after dark.

I have since replaced my fan clutch, as well as the thermostat. I disconnected an electric fan I had purchased on the way down to the Rally. I had also replaced the Ignition Module in the distributor cap before I returned home. I have also replaced the carburetor fuel filter.

I have purchased an electric fuel pump to install near the fuel tank, but have not installed it yet.

I was thinking of installing a 3 port mechanical fuel pump to replace the 2 port pumps our rigs come with, and then run a return line back to the tank as I had heard that was helpful. Others thought it not a good idea because of potential fire hazards.

A new issue has since arisen. I drove the GMC to the gas station to put non-ethanol fuel in it. As I pulled out of my drive way, and onto the street, as I attempted to accelerate, it died. While rolling, I put it in Neutral and it fired right up. I made it to the gas station and back, and it stumbled a few times. It wasn't even warmed up yet. I didn't have much power as well.

Today I was tracing out the fuel lines to see if there was another fuel filter I didn't know about. I didn't find an inline fuel filter, but I discovered I have a 3 port mechanical fuel pump with line running back to the tanks.

I'm thinking I have a fuel delivery issue. Would a worn out or close to failing mechanical fuel pump cause my issues? Could something with the fuel return line be causing my issues? I'm in over my head here.

 

[Carl Stouffer]

A cracked or deteriorated fuel hose, somewhere in the system, could be sucking air. Keep looking for an additional in-line filter somewhere. That's what it sounds like.

 

[RF_Burns]

Did you put thermal compound (heat sink grease) on the back of the ignition module before installing?

The wires on the distributor pickup fatigue and break from the vacuum advance moving them back and forth continuously causing intermittent ignition.

My coach would stumble, die or not start intermittently. I finally found an OEM crimp connector that was fully crimped on the insulation but the conductor itself was loose in the connector. Once I found that and re-crimped the wire tight it has run great ever since!

 

[RvRev2]

Did you put thermal compound (heat sink grease) on the back of the ignition module before installing?

Yes I did.

The wires on the distributor pickup fatigue and break from the vacuum advance moving them back and forth continuously causing intermittent ignition.

My coach would stumble, die or not start intermittently. I finally found an OEM crimp connector that was fully crimped on the insulation but the conductor itself was loose in the connector. Once I found that and re-crimped the wire tight it has run great ever since!

I'll look into that. Thanks!

 

[mech0001]

Get yourself a can of starter fluid.
When you encounter the no start condition, see if engine will start with a shot of starter fluid. This will help to isolate the problem to fuel or ignition related.
If it's fuel, you could install the electric pump temporarily to see if that solves the problem. My system is a FiTech injection setup and I have a feed pump installed underneath at about the middle of my coach. Pretty easy to do and nearby the fuel lines. Add a metal shield underneath for added protection.
If it's ignition, verify ignition isn't "sloppy". Some coils can fail when hot, though not something I've seen much with HEI coils. Also, replacing your ignition module isn't the guarantee it used to be. I bought a new NAPA module as a backup. Replaced it at last tuneup and it didn't work. OE part back in their. Electronic module parts aren't what they used to be. Or maybe I'm using the wrong sources.

 

[RvRev2]

Purchased the Carter fuel pump. Looking at installing it before the fuel tank selector valve. Wiring is not a problem. I just don't have a lot of room under there. Here are photos of my current set up. Where/how would you install the pump? I know people like to install on the outside of the frame rail, but I have the emergency brake cable running there. There is no room on the inside of the frame rail, as you can see in the pictures below. If I were to install it near the selector valve on the crossbeam, I would need to manufacture something to make the pump sit proud of the "C" channel as the pump is too tall to fit inside the "C" channel (assuming you can't lay the pump on its side). Plus I got the last of the fuel hose from the parts store, and that is only 3 feet.

 

[Carl Stouffer]

Purchased the Carter fuel pump. Looking at installing it before the fuel tank selector valve. Wiring is not a problem. I just don't have a lot of room under there. Here are photos of my current set up. Where/how would you install the pump? I know people like to install on the outside of the frame rail, but I have the emergency brake cable running there. There is no room on the inside of the frame rail, as you can see in the pictures below. If I were to install it near the selector valve on the crossbeam, I would need to manufacture something to make the pump sit proud of the "C" channel as the pump is too tall to fit inside the "C" channel (assuming you can't lay the pump on its side). Plus I got the last of the fuel hose from the parts store, and that is only 3 feet. View attachment 18527View attachment 18528

I have mine mounted on the outside of the frame:

One moment, please...

But I've seen them mounted to the cross-member. The only issue I can see with that is there is a lot of heat under there, but probably no more than the spot on the inside of the frame rail.

 

[RF_Burns]

I have mine mounted on the outside of the frame:

One moment, please...

But I've seen them mounted to the cross-member. The only issue I can see with that is there is a lot of heat under there, but probably no more than the spot on the inside of the frame rail.

I can see the point of having the pump, filters etc on the outside of the frame for serviceability.

But at the same time I think its an accident waiting to happen. Road trash thrown up by the front wheels, damaged in case of an accident etc. Need some protection around that stuff.

 

[Carl Stouffer]

I can see the point of having the pump, filters etc on the outside of the frame for serviceability.

But at the same time I think its an accident waiting to happen. Road trash thrown up by the front wheels, damaged in case of an accident etc. Need some protection around that stuff.

Your concern is noted.

 

[RvRev2]

I took the GMC for a drive today. Got out of town just fine, as I'm only a few blocks from the outskirts. Drove 65 mph for 15 minutes, and everything was just fine. Went through a small town to turn back towards home, and at a stop sign, it stalled within 2 or 3 seconds of starting off from the dead stop. I was able to put it in Neutral and restart, and tried to accelerate, and it stalled again. Neutral and restart, and took it easy on the gas until I was rolling above 40 mph, and all was well again.

Came to another stop sign. Died as I started off again. This time it did not restart easily. It would crank, fire, and die before I could accelerate. Then it wouldn't even crank. I rolled to a stop and put it in Park, and then it restarted.

I drove back in to my town, and came to a 4 way stop. I topped and waited for 2 cars, and then on my turn I accelerated through the intersection very slowly. I made it to my driveway. At one point in backing in my driveway, it stalled again, and would not restart. It would crank, but not start/run.

I drove to the auto parts store and purchased some starter fluid. Drove back home and tried that. It started with the starter fluid, but would soon die. Then, all of a sudden, it started and ran just fine again.

The engine temps were good, running between 180 and 200. It may have reached 205 at one point. It was in the 90's for ambient temperature today.

I am not a mechanic, but am not afraid to get my hands dirty.

I don't know if this is fuel related, electrical related, or carburetor related, or something else.

 

[Bhart]

Two things to do to determine if it is gas or electrical.

#1 When engine has stalled open hatch, remove air cleaner, and cycle throttle cable on side of carb. Look down the throat of the smaller bore and see if you have a steady stream of gas.

#2 Purchase an in-line spark tester to check for spark.

https://www.harborfreight.com/in-line-spark-checker-63590.html?hftm_sc=3017&hftm_source=google&campaignid=22887599467&adsetid=187591848190&product=63590

Or disconnect sparkplug wire from one of the cylinders and hold it away from a ground source and check for spark.

My thoughts are you have a bad fuel pump.

 

[RvRev2]

Two things to do to determine if it is gas or electrical.

#1 When engine has stalled open hatch, remove air cleaner, and cycle throttle cable on side of carb. Look down the throat of the smaller bore and see if you have a steady stream of gas.

#2 Purchase an in-line spark tester to check for spark.

https://www.harborfreight.com/in-line-spark-checker-63590.html?hftm_sc=3017&hftm_source=google&campaignid=22887599467&adsetid=187591848190&product=63590

Or disconnect sparkplug wire from one of the cylinders and hold it away from a ground source and check for spark.

My thoughts are you have a bad fuel pump.

I have a mechanical fuel pump, and have not yet installed the auxiliary electric fuel pump. I was thinking that mechanical fuel pumps worked, or they didn't. Am I wrong in that? Replacing the mechanical fuel pump would be straight forward.

 

[mech0001]

I took the GMC for a drive today. Got out of town just fine, as I'm only a few blocks from the outskirts. Drove 65 mph for 15 minutes, and everything was just fine. Went through a small town to turn back towards home, and at a stop sign, it stalled within 2 or 3 seconds of starting off from the dead stop. I was able to put it in Neutral and restart, and tried to accelerate, and it stalled again. Neutral and restart, and took it easy on the gas until I was rolling above 40 mph, and all was well again.

Came to another stop sign. Died as I started off again. This time it did not restart easily. It would crank, fire, and die before I could accelerate. Then it wouldn't even crank. I rolled to a stop and put it in Park, and then it restarted.

I drove back in to my town, and came to a 4 way stop. I topped and waited for 2 cars, and then on my turn I accelerated through the intersection very slowly. I made it to my driveway. At one point in backing in my driveway, it stalled again, and would not restart. It would crank, but not start/run.

I drove to the auto parts store and purchased some starter fluid. Drove back home and tried that. It started with the starter fluid, but would soon die. Then, all of a sudden, it started and ran just fine again.

The engine temps were good, running between 180 and 200. It may have reached 205 at one point. It was in the 90's for ambient temperature today.

I am not a mechanic, but am not afraid to get my hands dirty.

I don't know if this is fuel related, electrical related, or carburetor related, or something else.

Definitely sounds like a fuel delivery problem. I am assuming you did replace the fuel filter in the carburetor? You are pretty much right about a mechanical either working or not, but if it's original, replacing would be advised.
The thing that concerns me is the relation to engine temperature. Any fuel lines near exhaust lines, somehow, or physical damage causing a restriction? Some hose leak on the inlet side?
I would definitely try the electric to see if it changes the symptoms. Do you have to drive it to get it to fail?

 

[RvRev2]

Definitely sounds like a fuel delivery problem. I am assuming you did replace the fuel filter in the carburetor? You are pretty much right about a mechanical either working or not, but if it's original, replacing would be advised.
The thing that concerns me is the relation to engine temperature. Any fuel lines near exhaust lines, somehow, or physical damage causing a restriction? Some hose leak on the inlet side?
I would definitely try the electric to see if it changes the symptoms. Do you have to drive it to get it to fail?

I have replaced the filter at the carb.

I don't think it is the original mechanical pump. I have discovered that my mechanical pump has 3 ports, the third port being a return line to the tanks.

In regards to temperature, last summer I drove from Kansas to Oklahoma to travel Route 66. There were days of triple digit temps, but I never had a single problem like this.

I have replaced the fan clutch, and the thermostat. The engine was rebuilt about 3,000 miles ago by the previous owner. The engine does appear to be running cooling after the new parts.

Yes I do have to drive it to get it to fail. It appears to idle just fine. It also appears to go forever as long as you are driving at highway speeds. Slow way down, or stop, and the problem rears its ugly head. In fact, I feel like it is getting worse. It just appears to not like to accelerate after slow or stop.

I'll get creative with the auxiliary electric fuel pump to see if it solves the problem.