Fuel pump question for dual fuel 96 auto disco

**markyc** · 11th September 2006, 08:23 PM

Hi Guys,
This one raises its ugly head again (question, not me!!): In general, the bad/non existent idle on ULP but OK on LPG.

I raised this back in April but have been a bit slack (and broke) so sorry to go over part of this again...

I can hear my fuel pump; it's pretty loud. I wonder if this is because of the small rear sill tank and its location, or it's semi-stuffed.

When the crap idle starts (it's intermittent) I can hear the pump noise going up and down in pitch, in perfect sync with the 0-1500 rpm idle. So I'd like to know this: Should the pump run at a constant speed or is there some electronic thingy further up the line which controls it?

If it should be constant then I'll do the Holden thing and be done with it. If not, well I don't want to waste cash and still have a crocked car!

I'd like to run it for a week or so on petrol but the way it behaves at a standstill is a bit of a pain. Other drivers think I'm gunning the motor or else it stalls (even in 'drive')...By the way, driving at any speed is fine; only at standstill does it misbehave.

I'd like to eliminate the pump before looking at the MAF and such.

If Rovernaut's around, I think we have the same conversion and I wonder how he's getting on?

Ta!

**matbor** · 11th September 2006, 10:04 PM

I believe the fuel pump runs at one constant speed.

someone else might know.

matt.

tombraider · 12th September 2006, 12:27 AM

Sounds more like fuel load making the pump noise vary...

Ideas would be:

1 attach guage to fuel rail and check pressures
2 remove and clean IAS
3 replace pump

Cheers
Tombraider

**PhilipA** · 12th September 2006, 09:31 AM

I recommend that You check and clean your stepper motor before anything else. If you can borrow a good one it would be good.

The fuel pump may be fluctuating because of the different voltages being applied 12-14.1 from stopped to 1500RPM, or this may indicate a poor connection somewhere. Usually if the pump goes it pumps. Its when it is quiet you worry. Also relplace the fuel filter. But if it goes above idle then I am pretty confident that the stepper is more likely than the fuel pump.
Regards Philip A

**markyc** · 12th September 2006, 10:18 AM

Thanks guys.
Tombraider, what's IAS?
Phillip, I've got access to all manner of testing gear here at work. How do I test the stepper?

Ta
Mark

**markyc** · 13th September 2006, 06:52 PM

I pulled what my Haynes manual calls the 'By-pass air valve' from rear left of the Plenum (looking into engine, radiator in my gut). Is this the stepper? It has a spring-loaded plunger but I couldn't depress it by hand. Anyway I cleaned and replaced it.
Ditto the Airflow sensor, although this was spotless inside. I couldn't see any wires poking out in it; is this normal?

**Blknight.aus** · 13th September 2006, 07:50 PM

If you can (easy in the original tank) hook up your volt meter to the pump while the engine is running watch the voltage.. if its stable turn it all off hook up the amps meter in series with the pump and go it again.

if you have no fluctuations on the voltage (say less than .5v ) then the problem is more than likely in the pump or the delivery system. If its not stable flog the battery from your partners car and hook the fuel pump and amps meter to that.

If you have minor fluctuations in the amps (less than say 20% of the nominal draw) then the pump is ok and you are getting air or internal leakage in the lines inside the tank (more than likely if this is your second or third pump in the same filter)

If the fluctuations are significant (more than 50% of the nominal draw) then either the pump is faulty or you have an intermittant blockage somewhere in the system.

to prove this couple the output line of the tank to the return line and restest.

Not guarenteed but its usually pretty close.

**markyc** · 14th September 2006, 07:34 PM

Thanks Dave,
Off to Adelaide for the weekend so I'll give it a crack next week...

Mark

**markyc** · 23rd September 2006, 07:27 PM

Ok, maybe the cleaning did the trick; much better now with just a bit of idle wander but no stalling!
Today I fitted a new fuel filter (petrol in my armpit, nice!), a new set of leads and manifold gaskets so I think a long blast tomorrow is in order to see what's what...
Thanks for the tips guys.

Mark

**4bee** · 23rd September 2006, 07:59 PM

It has a spring-loaded plunger but I couldn't depress it by hand.

You won't, as it's a motor driven plunger.

You might like to recheck it again though.
At rest, the pintle length must be no longer than 28mm from the gasket sealing face to the end of the cone.

To achieve that adjustment, take the tension off the spring & rotate the pintle to get that dimension. A couple of drops of sewing machine oil doesn't hurt.

If it's too long when you screw it into the throttle body, you can damage the internals of the valve as it comes up to the seat.

If you need to replace it, GM P/N 25527077 fits as does AC-Delco 217-437. Apx. 50% of LR's price for the same thing.

The best way to clean it is soak it in Throttle Body/Carby Cleaner for an hour or so & then give it a careful blow out with air or a small brush, lubricate it & replace it after adjusting as above.

You may also want to clean the air on side & around the butterfly as that may not be closing off as it should because of crap buildup.

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