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Old 01-14-2005, 08:54 PM   #15
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Location: Newmarket, Ont
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<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Tom Norman:
No mention of a "fuel pressure sensor" in any of my Ford books. Only a "fuel pressure regulator" that I replaced about 5K miles ago. It checked out OK now though. <HR></BLOCKQUOTE>

I don't think you'll find any kind of fuel pressure sensor on any fuel injected engine. To my knowledge the last time any kind of pressure sensor/switch was used, was way back in the 50's on carbureted engines, in association with the new-fangled electric fuel pumps introduced in that era. In those days, fuel pumps would click on and off in response to fuel pressure.

With the introduction of high pressure fuel injection systems back in the mid seventies, fuel pumps have normally been constant-volume pumps which *never* shut off in response to excessive pressure. Instead, they incorporate two independent bypass safety systems:

1. The fuel-rail regulator, which maintains pressure at a maximum of 40 PSI. Once that criteria has been satisfied, the excess fuel is returned to the fuel tank;

2. The fuel-pump bypass, which serves to address anomalies such as a clogged fuel filter. The fuel-pump bypass kicks in at anywhere between 50 and 125 PSI.

Any extended key-on fuel pump activity, has to be in some way related to the PCM timing circuit that limits key-on fuel pump activity to a mere second or two. The two primary suspects in this case would suggest:

1. A munged PCM timing circuit;

2. Pinched wiring causing a random short circuit, leading the PCM to believe that the ignition switch is in "start" postition rather than in "run" position. In "run" position, the timing circuit will limit fuel pump activity to a second or two if engine rpm is less than 120; but if the PCM is being signalled that the ignition switch is in "start" position, then the fuel pump will run continuously. If that's the case, then compromised steering column wiring might be a primary suspect.

As for your fuel pressure tests, leakdown seems to be within acceptable limits.

You said that in response to key-on, "the gauge moved SLOWLY from 5 PSI up to about 30 PSI"; while that might be significant, I don't believe it's in any way related to the primary problem.

Ford fuel regulators are usually set at 40 PSI in preparation for start-up. This pressure should be achieved within about a second. If it takes longer, then a clogged filter or failing fuel pump might be primary suspects.

Prior to startup, the fuel rail should be charged to about 40 PSI. Once the engine starts, engine vacuum reduces fuel pressure to about 30 PSI at idle speed; increasing to around 40 PSI at modestly higher rpm.

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Old 01-16-2005, 12:32 PM   #16
Join Date: Nov 2003
Posts: 57
My fuel pump just barely gives me 30 PSI, with the engine on, or with the engine off and the fuel pump running.

I was finally able to contact the original owner of our rig and learned that I still have the OEM fuel pump---the one that has the extremely high failure rate. So I bought a new fuel pump and wire harness adaptor from a Ford dealer near here.

There's a guy who works on RVs near here and he said he's changed out several of these fuel pumps. So it looks like he and I will be getting under the rig to change out the fuel pump. I guess that at 58K miles, the OEM fuel pump was already running
on borrowed time, and was destined to fail at any time.

Thanks for all your help troubleshooting this problem, and I'll let you know the results of changing out the fuel pump.

Tom & Sallie Norman (And Our Lovable Dog Pepper)

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Old 04-10-2005, 06:02 AM   #17
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1. I maintain my motorhome meticulously. Here's a LONG list of maintenance items that have been replaced/work done that you'd think would at least partially resolve my cold-start problem. But it STILL runs like******after a cold-start, and the "Check Engine" light STILL comes on. (NO CODES were read at the Ford dealership. Just "1-1-1", meaning all systems OK.) And it STILL runs great after the engine has warmed up about 8-10 minutes or so.

Here's the long list of maintenance work that has been done:

Brand New/Less Than 50 Miles Ago:

spark plugs
spark plug wires
dist cap/rotor
PCV valve
fuel pump
fuel pump relay
radiator fan relay
idle air control valve
oxygen sensor
EGR valve position sensor
temperature sender
coolant temperature sensor
air charge temperature sensor

Brand New/Replaced Less Than 1,000 Miles Ago:

fuel filter
air filter
breather filter
oil/oil filter

Brand New/Replaced About 10,000 Miles Ago:

starter battery
radiator cap
fuel pressure regulator
EGR valve

Replaced By Ford About 10,000 Miles Ago Under Recall:

remanufactured PCM
idle air control valve
catalytic convertor

2. In short, I give up! I surrender! I have an appointment next Wednesday at the local Ford dealership. Actually my SECOND appointment, because the problem was not fixed the first time.

3. Thank you all for trying to help me, but my frustration level is maxed out. I'm burned out. My next vehicle will be a Dodge. We have three vehicles. Two are Fords and they are both basically crap, nothing but one problem after another. One is a Dodge, the engine has never given me a single problem, and it's still going strong at over 202,000 miles!
Tom & Sallie Norman (And Our Lovable Dog Pepper)

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Old 04-10-2005, 04:20 PM   #18
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Sorry to hear your problem was never solved. Somewhere there is a mechanic who will spot the problem, but I guess he isn't on this forum or at your local garage.

I think there are no fault codes becasue the problem occurs only in open loop mode. Few if any codes are generated until the engine warms and goes into closed loop mode.

I'm afraid you aren't going to find any Dodge chassis motorhomes, except perhaps for a Class B. Only Ford and Workhorse build gas Class A motorhome chassis in North America.

It's not much consolation, but your problem is a rare one. There are many, many solidly performing 460 Ford Class A's out there.
Gary Brinck
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL
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Old 04-14-2005, 10:59 PM   #19
Join Date: Nov 2003
Posts: 57

The verdict came in today, and it was a bad PCM. After a new PCM was installed it started immediately and ran like a top, just like it used to!

Thank you all for ALL your help on this!!!

Tom & Sallie Norman (And Our Lovable Dog Pepper)

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