Fuel pressure problem

TXredfish · 12-01-2010, 07:03 PM

My motorhome after sitting runs for awhile, after warming up, it misses very bad, has little power and backfires. I replaced the fuel filter which was clogged but this did not help. I have in a repair shop. The mechanic said that the gasoline is running too rich. The plugs were very black and sooty and would need to be replaced. He checked the fuel pressure on the fuel rail at the engine. The fuel pressure was 95 to 100 PSI. His conclusion was that the fuel pump regulator was faulty and I would need a new fuel pump. Does this make sense? Anyone else have this problem of the fuel pump putting out too much pressure and causing the fuel to run too rich?

RVhauler · 12-01-2010, 08:17 PM

normally in general the regulator is seperate from the pump tho I don;t know about your engine. never heard of a fuel pump putting out too much pressure always been the other way. Believe would obtain a second opinion

DriVer · 12-01-2010, 10:51 PM

Quote:

Originally Posted by TXredfish

Does this make sense? Anyone else have this problem of the fuel pump putting out too much pressure and causing the fuel to run too rich?

The regulator is up on the rail. It handles the fuel pressure that the pump delivers. If the pump is not delivering the fuel, that would be a problem.

Midniteoyl · 12-01-2010, 11:25 PM

Whats the engine? Some actually do have a internal regulator at the pump. Most of the time, however, it is on the fuel rail, either before or after depending on design. If it did fail open, the fuel pressure would be whatever the pump is supplying. If your injectors are designed to use 45psi and now you have 95pst, you will be pumping close to 1.5x the normal fuel into the cylinders making it rich.

But, this should have set some codes and flashed the CEL. Did your Engine Light come on and were there codes? if so, what were they?

oemtech · 12-02-2010, 03:39 PM

The fuel pressure from the pump TO the fuel rail is about 90 psi. But, the pressure AT the fuel rail schrader valve should be between 55 & 62 psi.

TXredfish · 12-02-2010, 04:14 PM

The engine is the 8.1L. The pressure at the Schrader valve is 95-100 lbs.
It is causing the gas to be too rich. No lights come on. No error codes using a Tech II.

Midniteoyl · 12-02-2010, 06:42 PM

No code is weird, but I would say the tech is correct. The regulator failed Open (full pressure).

TXredfish · 12-20-2010, 06:13 PM

My MH is finally fixed. The problem was the fuel regulator located inside the fuel pump which is located in the fuel tank. The fuel regulator was stuck. Workhorse would not sell just the regulator. I had to purchase the complete fuel pump assembly from WH. The fuel was running so rich that it carboned my plugs which was replaced. I also had my mechanic replace the plug wires. My MH feels like it runs the best since I have owned it. Thanks for everyone's help .............

Full-Timers · 12-20-2010, 09:25 PM

I know there is a regulator on the fuel rail at the engine but didn’t know there was one in the fuel pump. It doesn’t really make sense to me that there would be 2 regulators.

DriVer · 12-20-2010, 09:32 PM

Quote:

Originally Posted by Full-Timers

I know there is a regulator on the fuel rail at the engine but didn’t know there was one in the fuel pump. It doesn’t really make sense to me that there would be 2 regulators.

Let's chalk it up as a bad pump!

Just had mine replaced so that's the end result regardless of what's found in or on the pump.

I had "No" pressure.

JonBrazel · 12-21-2010, 10:16 AM

On 04+ chassis the fuel pressure is regulated by the fuel pump and in place of the regulator on the fuel rail is a "fuel dampner" that absorbs the pulses of the fuel pump. On the 01-03 they use an adjustable fuel pressure regulator on the fuel rail. A restriction in the fuel return line could also cause the problems TXredfish had.