"Sort-of" Limp mode problem- serious

[gozierdt]

Vehicle is a 2004 Holiday Rambler Admiral SE 31'. 26,000 miles. P32 chassis, 8.1 engine, GM transmission, 18,000 lb GVWR. Ultra RV Iridum plugs and UltraPower 8.1L Extreme Magnum Spark Plug Wires August 2018, 1500 miles ago.


Problem:

Twice now- a year apart, I have had this problem. I will have been climbing 6-8% grades- one was the pass on CA Hwy 5 just before descending into Ashland, OR. The one today was CA Hwy 80, heading east, just around Blue Canyon, both 4000 to 5000 ft elevation. The engine is not overheating on my Scan Guage. All of a sudden, while still pulling the hill, the engine goes into a sort-of limp mode, losing power and speed, and within 5 seconds or so barely able to run. If I hit the accelerator at this time I get some "woomph" sounds from low on the engine, but not hard knocks (low fuel cylinder charges igniting in the exhaust manifolds?). In Oregon, I was just at the top of the pass, and after about 20 minutes I was able to start down the grade, and had no further problems. Today on the 80, I still had 5 miles of climbing. After 10 minutes of sitting, I started the MH, and still had the symptoms. Waited another 25 minutes and the engine would run well enough that I was able to crawl the last 5 miles. Then we had to check into the campground, and again after 5 minutes the symptoms occured-barely running, woomphs, and all. Waited 1/2 hour and finally made it the last mile to our campsite. No codes thrown on the scan guage either time. I'm looking for suggestions. My best thought so far is vapor lock or weak fuel pressure leading to vapor lock. The problem is definitely related to pulling long grades and altitude. Sitting until the engine and engine compartment cool down some seems to temporary fix the problem. I'm supposed to pull on up to 7000ft on the 80 to get to Reno next week, but that's an optional part of the trip, and I'm afraid I'll have to skip seeing my sister and brother-in-law there.


I'd appreciate any suggestions on fixes.
TIA,
Gene

[gozierdt]

I couldn't do an edit since more than 1 hour has passed. I wanted to add that this issue is more serious than normal "limp" mode, because the vehicle won't move. Wherever it is at the end of the 5-8 second beginning of the problem is where it is stuck for the next 20-30 minutes. So far I've had a shoulder to pull off on, but the situation would be much more serious if I was stuck in a freeway traffic lane... And no OBD II codes gives me no clues...


PS: MAF sensor was also replaced 1500 miles ago...

[akpd]

Originally Posted by gozierdt

Vehicle is a 2004 Holiday Rambler Admiral SE 31'. 26,000 miles. P32 chassis, 8.1 engine, GM transmission, 18,000 lb GVWR. Ultra RV Iridum plugs and UltraPower 8.1L Extreme Magnum Spark Plug Wires August 2018, 1500 miles ago.


Problem:

Twice now- a year apart, I have had this problem. I will have been climbing 6-8% grades- one was the pass on CA Hwy 5 just before descending into Ashland, OR. The one today was CA Hwy 80, heading east, just around Blue Canyon, both 4000 to 5000 ft elevation. The engine is not overheating on my Scan Guage. All of a sudden, while still pulling the hill, the engine goes into a sort-of limp mode, losing power and speed, and within 5 seconds or so barely able to run. If I hit the accelerator at this time I get some "woomph" sounds from low on the engine, but not hard knocks (low fuel cylinder charges igniting in the exhaust manifolds?). In Oregon, I was just at the top of the pass, and after about 20 minutes I was able to start down the grade, and had no further problems. Today on the 80, I still had 5 miles of climbing. After 10 minutes of sitting, I started the MH, and still had the symptoms. Waited another 25 minutes and the engine would run well enough that I was able to crawl the last 5 miles. Then we had to check into the campground, and again after 5 minutes the symptoms occured-barely running, woomphs, and all. Waited 1/2 hour and finally made it the last mile to our campsite. No codes thrown on the scan guage either time. I'm looking for suggestions. My best thought so far is vapor lock or weak fuel pressure leading to vapor lock. The problem is definitely related to pulling long grades and altitude. Sitting until the engine and engine compartment cool down some seems to temporary fix the problem. I'm supposed to pull on up to 7000ft on the 80 to get to Reno next week, but that's an optional part of the trip, and I'm afraid I'll have to skip seeing my sister and brother-in-law there.


I'd appreciate any suggestions on fixes.
TIA,
Gene

Just a thought here, I wonder if it might be an internal muffler baffle warping (closing off the exhaust)?


Timing retarding, (crankshaft position sensor)?

[vettenuts]

There have been others with the exact same problem that were posted some time ago. As I recall it was due to the fuel return and heated fuel. Look at post #44 in the link below, hopefully this helps resolve your issue. The second link is actually one provided in post #44 that provides a detailed explanation of how someone fixed this issue. Please post any follow-ups if you get it fixed.

Good luck, hope you get it resolved.

http://www.irv2.com/forums/f22/2003-...-254153-4.html

http://www.irv2.com/forums/f22/workh...em-222658.html

[zorro2kita]

I've had similar issues - limp mode or stalling climbing grades - Stalled on I-95 several summers ago - very scary. Vapor lock is the culprit !! Wrapped the fuel line with reflective tape, never ran below 1/2 tank. Finally decided it was time to fix for good - had fuel pump located in fuel tank replaced - problem solved. Fuel pump had new design to overcome flaw of original.


L & M to have a truck repair shop in Great Falls MT was about $1500. Not cheap but necessary. Let me know if you need more details --

[LETMGROW]

If your scan gauge doesn't have the ability to display data or record freeze frame you need to take it to a shop where they do.
You will have to do a road test with the scan tool hooked up to the coach and watch for variations in data. Hopefully you can duplicate the running issue during the road test.
If the engine acts up you can trigger the freeze frame mode and scroll through the data to see what changed at the point the engine started acting up. The freeze frame mode will record several frames before, during and after the event.
I had a similar problem with my '02 P 32. It turned out to be the throttle position sensor on the throttle body. I used my Snap-On scan tool to find the culprit. The freeze frame showed where the TPS had dropped out while running steady at 55 MPH.
Intermittent runability problems can be frustrating. Having the right equipment to diagnose them is imperative. Running a fuel pressure test while road testing is also recommended. If the scan tool data shows the computer is adding fuel (ST fuel trims going plus) to overcome a lean condition and the fuel pressure has dropped off there is no doubt the pump is faulty, a hose is pinched or deteriorated internally causing a restriction or the fuel filter is partially plugged.
Lynn

[gozierdt]

Just got back home to Santa Rosa from the Sierras. Had no problems at all (well, terrible traffic, but that’s another story). After reading the reply’s above, I didn’t expect any problems going down from altitude. Thank you to VetteNuts and zorro2kita for the most helpful references and experiences. I’m sure the culprit is vapor lock at the pump causing loss of fuel to the engine. And I’m on a 2003 P32 chassis, which is the last one before GM changed the fuel system because owners were having this exact problem. I’m investigating potential fixes, but in the meantime I’ll take it easy on long uphill climbs and keep the tank above 3/4 while I’m doing this climbing.

I looked at my fuel tank, and I don’t have an extra fuel filler inlet on the opposite side from the one that is used for filling the tank. So I can’t do the fairly simple fix suggested in the reference from vettenuts. But I was wondering, could I reroute the return line from the engine into the vapor line coming up from the tank on the active fuel filling hoses?

Alternatively, could I purchase the 2004 fuel filter system that allows excess fuel to be rerouted just before the fuel filter and put it on my rig (I know about the problems with obtaining those filters, and I would use the adapter available from UltraRV). The biggest question I have is this fix would involve cutting and blocking the existing excess fuel return line from the engine. Would this interfere with the emissions system on the 2003 engine?- I’m thinking of the little green tire stem cap that sits in the fuel rail system at the front of the engine. I saw a thread that said that green cap covers a test port for the emissions system?

I’ll reply more as I work on the problem.
Thanks All

[vettenuts]

Might be worth a call to Jon Brazil, he might have some ideas.

Not sure where the fuel pressure regulator is located on your coach vs. later coaches but that might give you some insight on how to reroute the return.

There are fuel cooling devices available, primarily used for racing, but not sure how well they could be adapted to a motorhome application. They also make a diesel fuel cooling radiator but not sure if it can be used for gasoline. If these methods could be adapted, then you might be able to install in the existing fuel return.

[LETMGROW]

DO NOT USE THE TEST PORT WITH THE GREEN CAP! This port is for smoke and pressure testing the Evaporative Emission Control System. You will destroy the EVAP purge valve, the charcoal cannister, the vent valve and all the vapor lines as well as stuff the intake manifold with raw fuel. If you don't blow yourself up first.
Lynn

[Arch Hoagland]

Gene...when climbing mountains how high are your RPM's?

[zorro2kita]

I'll repeat again - drop the tank and replace the fuel pump for the correct and proven fix - all the previous suggestions are band aids in my opinion -

[Full.Monte]

Find your answers here:
http://www.irv2.com/forums/f22/workh...em-222658.html

You don't have to do all the work...the answers are right here on IRV2. It is a vapor-lock problem caused by hot fuel being returned into the fuel pump canister where it eventually gets too hot and provides a gas bubble to the pump instead of liquid gasoline. I did replace my fuel pump, but it may have not been immediately necessary. What was immediately necessary was to provide cool gasoline to the fuel pump. I did this be re-routing the fuel return from the fuel injection system to the fuel tank at the alternate air vent on the opposite side of the tank from the fuel filler. The manufacturer puts fillers and vents on both sides of the tank to accommodate the needs of various coach manufacturers. By dumping the return there, it forces the pump to pick up fuel from the main tank....cooler by definition than the hot fuel returned from the injection system. I spent months figuring all this out with the help of some smart people here on IRV2.
Since I made the changes, all my problems have gone away. The original posts now show up without photos. I don't know what happened to them in the system.
You are correct...it is a serious problem...possibly life and death. I had two episodes of vapor lock that caused me to be stopped in very dangerous locations. Good luck on your fix.

[Full.Monte]

I forgot to mention....two of my vapor lock episodes happened east of Fresno on the 11 mile long grade going from Millerton to Shaver Lake. Uphill, of course. It's a good test for your fix. Good luck!

[vettenuts]

Originally Posted by Full.Monte

Find your answers here:

http://www.irv2.com/forums/f22/workh...em-222658.html



You don't have to do all the work...the answers are right here on IRV2. It is a vapor-lock problem caused by hot fuel being returned into the fuel pump canister where it eventually gets too hot and provides a gas bubble to the pump instead of liquid gasoline. I did replace my fuel pump, but it may have not been immediately necessary. What was immediately necessary was to provide cool gasoline to the fuel pump. I did this be re-routing the fuel return from the fuel injection system to the fuel tank at the alternate air vent on the opposite side of the tank from the fuel filler. The manufacturer puts fillers and vents on both sides of the tank to accommodate the needs of various coach manufacturers. By dumping the return there, it forces the pump to pick up fuel from the main tank....cooler by definition than the hot fuel returned from the injection system. I spent months figuring all this out with the help of some smart people here on IRV2.

Since I made the changes, all my problems have gone away. The original posts now show up without photos. I don't know what happened to them in the system.

You are correct...it is a serious problem...possibly life and death. I had two episodes of vapor lock that caused me to be stopped in very dangerous locations. Good luck on your fix.

See post #4. I remember when you originally posted this issue.