Engine would not start 2011 Tiffin Allegro Red Open Road 36’ Isb6.7 CM2250We had drove for about 6 hours stopped twice at rest stops about every two hours no problem starting. Third stop for fuel after fueling motor would not fire up motor turned over but would not start up. Let set for three 30 min intervals tried to start each interval and still would not start. Then waited for another 60min and engine started.So after engine set for 2.5-3 hours it started.This is second time this happened last year it did the same thing except we were at a location we could let it set overnight and it started right up next morning. Took into mechanics after first event and they could find nothing wrong.Any ideas. Vapor lock-fuel pump-on????

It could be an electrical item that when it heats up it goes open. First thing to check is connections on fuel cut off valve.

Were you really low on fuel? Does that engine have a lift pump? ( fuel ) Can youhear it run when turning the key on? How old are your fuel filters?I suppose it could but I never heard of diesel vapor lock.

When an engine is shut down it gets hotter due to lack of cooling and then cools down, could be related. I'd check/clean all electrical connections. A good Cummins mechanic will know the most likey suspects but shotgun repairs can get expensive. Have you checked for codes if any?

Did you let the engine idle for awhile when you pulled into the station? It takes a few minutes of idle to let the engine (and turbo assuming it has one) cool down properly.

Ready set go wrote:Any ideas. Vapor lock-fuel pump-on????No idea at all... Vapor lock.This was a think 50 or 60 years ago but modern gas engines have the fuel pump in the tank. not mounted on the side of the engine (Vapor lock is when the gasoline in the pump vaporizes and the pump can not push vapor like it pushes liquid).So in theory vapor lock is a thing from history.Does not mean other things can not cause the heat related issues however.. Some electronics are heat senistive.If the rig is a gasser it should have an OBD II port under the dash (most likely) and there are adapters you can plug in and then use the TORQUE app (Or rather have your co-pilot use it) on a phone to read error codes Live. (NOTE: one of many programs and some of them have their own OBD-Blue tooth. devices)

Won’t start | Good Sam Community

enblethen
Nomad
Jul 01, 2023
It could be an electrical item that when it heats up it goes open. First thing to check is connections on fuel cut off valve.
oldave
Explorer
Jul 01, 2023
Were you really low on fuel? Does that engine have a lift pump? ( fuel ) Can you
hear it run when turning the key on? How old are your fuel filters?

I suppose it could but I never heard of diesel vapor lock.
CA_Traveler
Explorer III
Jul 01, 2023
When an engine is shut down it gets hotter due to lack of cooling and then cools down, could be related. I'd check/clean all electrical connections. A good Cummins mechanic will know the most likey suspects but shotgun repairs can get expensive. Have you checked for codes if any?
LouLawrence
Explorer
Jul 01, 2023
Did you let the engine idle for awhile when you pulled into the station? It takes a few minutes of idle to let the engine (and turbo assuming it has one) cool down properly.
wa8yxm
Explorer III
Jul 01, 2023
Ready set go wrote:

Any ideas. Vapor lock-fuel pump-on????

No idea at all... Vapor lock.
This was a think 50 or 60 years ago but modern gas engines have the fuel pump in the tank. not mounted on the side of the engine (Vapor lock is when the gasoline in the pump vaporizes and the pump can not push vapor like it pushes liquid).

So in theory vapor lock is a thing from history.

Does not mean other things can not cause the heat related issues however.. Some electronics are heat senistive.

If the rig is a gasser it should have an OBD II port under the dash (most likely) and there are adapters you can plug in and then use the TORQUE app (Or rather have your co-pilot use it) on a phone to read error codes Live. (NOTE: one of many programs and some of them have their own OBD-Blue tooth. devices)
enblethen
Nomad
Jul 01, 2023
OP says it is an ISB 6.7. That should make it a diesel!
Stim
Explorer
Jul 04, 2023
Possibly fuel shutoff solenoid.
They get weak over time and back pressure will keep them from opening until pressure is relieved. (over time/cool down)
I had a CAT that would do it on a Boom Truck. If I came in from a run and shut it off it would not start after a short time.
If I loosened a fuel line and the pressure then it would start right up.
I was too poor at the time to buy the solenoid so I would just shut it off, then turn the key back on to keep the solenoid open so it would restart.
bigred1cav
Explorer
Jul 05, 2023
Alternator ran on battery until batt was drained..
grldst
Explorer
Jul 05, 2023
Leave it idle while fueling…leave it idle at rest stops unless you’re going to be there for more than 15 minutes. Shutting down diesels without a 5-10 minute idle is not good.

HOWEVER…I do not think this is your issue. You have something else going on. Check on a forum like Cummins engines on IRV2.
wolfe10
Explorer
Jul 05, 2023
grldst wrote:
Leave it idle while fueling…leave it idle at rest stops unless you’re going to be there for more than 15 minutes. Shutting down diesels without a 5-10 minute idle is not good.

Please post a link to that advice from Cummins!

And, with the newer emission controlled engines long idle time has more significant negative effects.

Totally agree on a "let it idle until the turbo is cool" (ranges from 1 minute if you have been on slow city streets/CG/etc to perhaps 4 minutes of just pulling off the highway.