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[Victor]

Hi, I've been having a weird problem with my truck. The fuel pump will
turn on and off at random times with the ignition off. Most often, it
is after I have just turned off the truck. Once in a while I am in
the vicinity of the truck and hear the fuel pump just turn on. The
span that it is on is usually about 10 to 30 seconds. The truck runs
great and I've never had a problem with it not starting, or stalling,
or running rough. However, my fuel mileage is crap. I get
18.5L/100km or less than 13MPG right now and it seems to be a little
short on power.

To give some background... I had the check engine light come on,
checked the codes, got the code for the oxygen sensor and replaced the
oxygen sensor, which fixed the check engine light. I recognized that
the sensor was just a symptom. I had a manifold leak, which I got
fixed and thought that was the cause of the oxygen sensor misreading.
There was a lot of carbon on the sensor and in my exhaust, probably
cause I ran it for about a year before deciding to shell out and fix
the manifold and oxygen sensor. I thought that fixing the manifold
and oxygen sensor would fix my rich running problem. It didn't. Now
I suspect that maybe my fuel pressure regulator is broken causing too
high of fuel pressure and therefore causing a rich mixture, which will
eventually lead to the oxygen sensor going again. So, I'm going to
check the fuel pressure, and also the catalytic converter backpressure
so make sure it's not plugged with carbon a little (exhaust does kind
of smell worse than it should).

However, I want to know if the fuel pump going off at random times
could be a factor in this. As I understand, the fuel system stays
pressurized even with the vehicle off. If the pressure regulator is
broken and the pressure drops with the truck off, is there a sensor
that will turn the fuel pump on to bring the pressure back up to par?
Will the fuel relay be a problem in this case, or is it maybe a short
somewhere? Maybe the fuel pump going on with the truck off is normal.

Anyways, any insight into why my fuel pump has a mind of its own and
if this could in any way be a cause of my bad fuel mileage would be
greatly appreciated.

Thanks in advance,
Victor

[Rob Munach]

Victor wrote:

[Victor]

Ok, as a follow-up, I checked the fuel pressure which I thought was
the problem. It's supposed to be 43psi without vacuum attached to the
pressure regulator and 34psi with vacuum attached. Instead it was 46
and 36psi respectively. I don't think this is enough of a problem to
be resulting in my 150km less per tank than I should be getting. I
checked the ECU in mode 1 and the exhaust gas sensor was alternating
between lean and rich like it's supposed to. In mode II red and green
lights flashed simultaneously like they should indicating the mixture
is being regulated fine. No error codes... no nothing.
When the fuel pump turns on while the ignition is off, the fuel
pressure goes up to 10psi, but this is no problem I don't think.

It runs fine, but seems to be lacking a bit of power.

I guess next thing is checking to make sure all my cylinders are
actually firing, although I would think that a cylinder not firing
would result in a rich reading somewhere.

Thanks for the comments so far, Victor

meamsosmart@gmail.com (Victor) wrote in message news:<f0ccb75a.0411171141.4abadf62@posting.google.com>...