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Old 09-17-2016, 10:19 AM   #1
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Unhappy loss of power

Greetings. I have a 2004 W Brave with an 8.1. This past May we stopped at a turnpike rest area to get gas. I restarted the RV and it did not want to stay running or move. I had it towed to a truck repair and they diagnosed the problem as a bad throttle-body. They replaced it and it ran great that afternoon and evening. The next day it ran good for an hour or so and then started loosing power and backfiring.

The fuel filter has been changed 3 times since January. The fuel pressure measures out at 14psi.

Yesterday trying to come across 68 from Hancock, MD to Morgantown, WV it gave us tons of problems. It would lose power going up the hills and seemed like when our speed would drop to around 30 mph, all of a sudden there would be a surge and it would start pulling again.

This continued the whole 104 miles we had to travel. We also noticed if we stopped, when it got really bad and was backfiring, shut the motor off and sit for 10 or 15 minutes, it would restart and run like nothing was wrong until we got up to speed and had to back off on the accelerator pedal.

Can anyone shed some good techanical knowledge? Thank you.
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Old 09-17-2016, 12:29 PM   #2
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I'd temporarily install a fuel pressure gauge to monitor the fuel pump. It also could be a vapor lock problem from the fuel line passing close to a manifold or exhaust pipe. A pressure gauge should show when the fuel pressure is dropping, either from a failing fuel pump or vapor lock. The symptoms and the actions you've taken sound like a fuel delivery problem is suspected. Putting a pressure gauge on the line should reveal if the pump is failing. You could just put a new pump on, but I dislike throwing parts at a problem, I'd rather diagnose and replace what is necessary.

Have you cut open any of the replaced fuel filters to see if they were blocked with rust particles?

I don't think the replacement of the throttle body was necessary since the problem has continued.

Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 09-17-2016, 02:26 PM   #3
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Have not cut any filters apart but have blown through them and they have no back pressure. What should the fuel pressure be?

Alan Farley
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Old 09-17-2016, 02:33 PM   #4
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I could be wrong but I thought injectors needed more like 35 or 40 psi to spray properly. Bite the bullet and take it to a reputable shop. You could throw hundreds at it changing parts and not hit on the true cause.
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Old 09-17-2016, 02:36 PM   #5
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Vapor lock is a possibility with that year of GM 8.1. I have experienced that first hand a number of times. One way to tell, is while you are experiencing this problem and can get the engine to run, go to the back of the motorhome and listen. If you can hear the fuel pump and it sounds louder then normal it may be vapor locking.
Randy & Kathy
2004 Southwind 37A
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Old 09-17-2016, 02:50 PM   #6
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Fuel pressure in a 2004 8.1 should be 55-62 PSI, with key on and engine not running. When running, the pressure will drop 5-7 PSI.

Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
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Old 09-17-2016, 04:02 PM   #7
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I agree with all of the previous posts. No doubt was not the throttle body. I experienced a very similar problem this summer in my 2004 tiffin Allegro Bay with the 8.1 liter GM Vortec. Turned out to be low fuel pressure due to a bad fuel pump. These pumps are located in the fuel tank. 3 days and $1200.00 later I was on my way. $5.00 will get you $10.00 its your fuel pump.
Terrence D. Yount
2004 Tiffin Allegro Bay 36' LB
2008 Ford Fusion SE
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loss of power, power

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