Fuel cutoff with hard bumps

[Bobkid]

Looking for ideas from some of y'all here. 2020 Rebel w/5.7 non-etorque, 16,000 miles.

I was on vacation driving on a remote fire road in the Colorado mountains when I hit a nasty patch of washboard road causing my truck's engine to stumble and stall like it was starving for fuel. Engine eventually died after 10-15 seconds and I had no CEL while it was running. Tried to restart, and it'd just crank away but never catch. Dug through my toolbox and got my scanner, which showed zero codes. Well I had lots of time to kill waiting for the tow truck, so I'd try to start it every now and then. After sitting about 20 minutes, truck started, ran smooth with no CEL, but I only made it about 1/2 mile down the road before the same issue appeared. Did this twice, if you let it sit for 15-20 minutes it'd start and run, just not long.

Finally got it towed to a local (100 miles away) dealer, but it was late on a saturday, so nobody touched it until mid-monday. Dealer started it, test drove twice, checked for codes, checked fuel pressure, and couldn't find a problem. Next day I picked it up and had my buddy drive it to pick me up when I drove the rental car back to the airport. Truck ran fine for him, but he thought he felt the engine stumble briefly when he went over some railroad tracks near the airport, but I dismissed his concern as being hyperaware after sitting on the side of the mountain road with me several days earlier. Turned in my rental car, went out to the parking lot, started the truck, and only made it 50' before the engine stumbled like it was starving for fuel and died. Another long tow truck ride back the dealer. Dealer drained the fuel (it looked and burned fine), replaced the fuel pump, flushed the fuel lines, insected all the wiring for rodent gnawing, and test drove it over the roughest road they could find with no issues.

I picked it up and made it almost all the way back to our mountain cabin when I hit another nasty patch of road and the same thing happened; engine stumbled like it was starving for fuel and died. Tried to restart and it'd just crank like it wasn't getting fuel, si I waited 15 minutes and it started fine and ran smooth. I ended up babying it the rest of the trip, driving like an old man to prevent large jolts and it ran fine and I completed the 750 mile drive home without any issues.

Dealers are clueless since it throws no codes and runs fine every time they drive it. Any ideas on what to check next? Is there any way the bumps might be jarring the fuel pump relay causing it to shut off the pump?

Thanks,

 

[Eighty]

Interesting puzzle, I'll be curious to see what comes of this. My first thought was that you were losing an electrical contact somewhere. But that doesn't explain why you have to wait for so long before it works again - I would think that it either works, or it doesn't. It seems like something is physically restricting the fuel flow, and it takes a while for enough fuel to "seep through" before it will fire back up.
I don't suppose there's something large in your fuel tank (e.g., a rock) that could get jiggled into a certain position that would block the flow of fuel?

 

[Bobkid]

They pulled the tank to replace the fuel pump, so anything foreign would've been found when they flushed it out.

I had the same idea on electrical, but can't think of anything other than fuel pump circuit that might open/short without throwing some type of code.

 

[834k3r]

Looking for ideas from some of y'all here. 2020 Rebel w/5.7 non-etorque, 16,000 miles.

I was on vacation driving on a remote fire road in the Colorado mountains when I hit a nasty patch of washboard road causing my truck's engine to stumble and stall like it was starving for fuel. Engine eventually died after 10-15 seconds and I had no CEL while it was running. Tried to restart, and it'd just crank away but never catch. Dug through my toolbox and got my scanner, which showed zero codes. Well I had lots of time to kill waiting for the tow truck, so I'd try to start it every now and then. After sitting about 20 minutes, truck started, ran smooth with no CEL, but I only made it about 1/2 mile down the road before the same issue appeared. Did this twice, if you let it sit for 15-20 minutes it'd start and run, just not long.

Finally got it towed to a local (100 miles away) dealer, but it was late on a saturday, so nobody touched it until mid-monday. Dealer started it, test drove twice, checked for codes, checked fuel pressure, and couldn't find a problem. Next day I picked it up and had my buddy drive it to pick me up when I drove the rental car back to the airport. Truck ran fine for him, but he thought he felt the engine stumble briefly when he went over some railroad tracks near the airport, but I dismissed his concern as being hyperaware after sitting on the side of the mountain road with me several days earlier. Turned in my rental car, went out to the parking lot, started the truck, and only made it 50' before the engine stumbled like it was starving for fuel and died. Another long tow truck ride back the dealer. Dealer drained the fuel (it looked and burned fine), replaced the fuel pump, flushed the fuel lines, insected all the wiring for rodent gnawing, and test drove it over the roughest road they could find with no issues.

I picked it up and made it almost all the way back to our mountain cabin when I hit another nasty patch of road and the same thing happened; engine stumbled like it was starving for fuel and died. Tried to restart and it'd just crank like it wasn't getting fuel, si I waited 15 minutes and it started fine and ran smooth. I ended up babying it the rest of the trip, driving like an old man to prevent large jolts and it ran fine and I completed the 750 mile drive home without any issues.

Dealers are clueless since it throws no codes and runs fine every time they drive it. Any ideas on what to check next? Is there any way the bumps might be jarring the fuel pump relay causing it to shut off the pump?

Thanks,

How fast were you going over the washboard? Just curious.

 

[Bobkid]

How fast were you going over the washboard? Just curious.

It varied. Some of it was light and would smooth out above 40, but other places were really washed out and I'd have to slow to 25 or so. My Rebel handled it all extremely well last year with the air suspension; it was actually the best vehicle I've had on that road in the last 25 years or so.

 

[Eighty]

Maybe with all the sloshing in the tank, you were sucking some air into the fuel line? That might explain the lag in being able to start back up successfully (basically repriming)? How low was your fuel level during these occasions?
I'm just throwing darts here, obviously.

 

[Bobkid]

Maybe with all the sloshing in the tank, you were sucking some air into the fuel line? That might explain the lag in being able to start back up successfully (basically repriming)? How low was your fuel level during these occasions?
I'm just throwing darts here, obviously.

Understand, unfortunately both times I'd just filled the tank and it was about 95% full.

Pretty much to the point that I can't trust the truck any more to go off pavement now (even with AAA, towing offroad costs $$s). Guess it's time to trade this one for a 2021/2022 if I can';t find the smoking gun to know it's fixed.

 

[Bobkid]

Did some more poking around and saw that the plastic molded case on my Pulsar programmer had separated on 2 corners, so I pulled it off and truck seems to run smoother and I can't get the stall to recur. Got my fingers crossed it was that simple.

Still can't figure out how that would induce fuel starvation without throwing some type of code, but removing it seems to have made a difference.