Re: Fuel pressure regulator valves

[Carl Ratner <artdeco@bway.net>]

Jan Wikström wrote:

>Message text written by INTERNET:Juliansean@aol.com
>>Would it be correct to assume that if the fuel press. reg. went bad that
>>high
>>fuel press. could result, followed by running rich?<

>I would expect *low* fuel pressure to be a more common failure mode (tired
>spring, adjusting screw coming loose, gum in the works), especially as the
>valve spends most of the engine running time open. In normal cruising
>around speed-limited areas, I'd guess at least 4/5 of what the fuel pump
>delivers isn't used by the engine, so if the valve sticks, I'd expect
it to
>stick open.

Those fuel pressure regulator valves can cause some bizarre symptoms.
My '86 XJ-6 developed a strange, intermittent problem: it would
sometimes refuse to accelerate beyond 40 mph. This would usually
happen upon first starting out in the morning. At precisely 40 mph,
the engine would become very rough and would start "chugging" and
bucking, accompanied by some black smoke from the tailpipes. Usually I
could clear the problem by releasing the accelerator for a few seconds
and then depressing it again, but sometimes it would persist for
several minutes... very bad if one is trying to merge with fast-moving
traffic.

Several mechanics attempted to diagnose this problem, and, being a
Jaguar, the car would never misbehave while the mechanics were driving
it! Various sensors were blamed, and one mechanic was quite convinced
that the computer was at fault. (No, I didn't let him install a new
one, as the computers seldom give trouble. All other possibilities
should be eliminated first before changing a computer.)

Finally I found a man who knew exactly what was wrong the minute I
described the symptoms. He put in a new fuel pressure regulator and
the problem vanished immediately. In this case the pressure regulator
was sometimes delivering too much fuel, thus flooding the engine. 

--Carl Ratner

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