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[VT-VX] VT series 1 sedan fuel pump problem solved

Trevhead62

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Gudday peeps. I've used this forum to obtain heaps of great information on all sorts of Commodore related issues over the years so I thought I'd add a bit of my own experience for others to enjoy, particularly the VT series 1 fuel tank and pump.
Its a dual fuel model. Would not start in petrol mode and would only just start in LPG mode. When running in LPG mode and switched to petrol, it would stall.
The problem was that the fuel pump was not priming for the one second or so when turning the ignition on. I couldn't hear the whirr or buzz of the pump starting. Armed with a 6 to 12 volt test light I set out to diagnose the fuel pump problem.
Checked the fuse for the fuel pump - ok.
Checked for 12 volts at the fuse terminal - ok.
Checked the relay for the fuel pump by listening and feeling for a click when ignition turned on - ok. Swapped the relay for the air con relay which is identical. - no change.
Checked for 12 volts at the fuel pump connector on the chassis by the rear rh wheel. To do this I put the rear end up onto ramps, found the wiring harness connector to the fuel pump just near the fuel filter, uncoupled it and using my test light grounded to the skinny earth strap from tank filler neck, I had my assistant turn the ignition on and off whilst checking each of the wires for voltage. I checked the fatter ones first as I figured they would more likely to be the fuel pump wires and not the skinny ones which would be the fuel level gauge. As it turned out, I had 12 volts coming on for a second or so when the ignition was first tuned on. That narrowed it right down to the pump itself.
Time to drop the tank.
With the trolley jack holding the weight I removed the three straps holding the tank to the car and then slowly lowered it to the ground. The hoses were just long enough to allow this to happen without any problems. I also reached up and disconnected that little skinny earth wire from the filler neck just to get it out of the way.
Now that the top of the tank was accessable, I was able to disconnect the three hoses using the special removal tools and disconnect the wiring plug.
To get pump unit out of the tank, I used a hammer and punch to rotate the locking ring out of the tabs. The change- over was fairly simple but I found the replacement unit did not fit inside the locking ring as it should have. I had to file a good 2mm off the inside diameter of the ring so it would fit over the top section of the replacement unit. El-cheapo pump I guess.
Once in the tank, I reconnected the three hoses, refitted the wiring to the unit and to the harness connector and checked the new pump for operation and leaks. It primed up just fine. You beauty.
The tank was lifted back up into place using the trolley jack and all three straps bolted into place. Not forgetting the little skinny earth strap. The filler neck sat nicely back into the hole.
A new filter was installed. Then primed again and checked for leaks and the car started up first pop.
The photo shows what the top of the tank looks like with the original fuel pump unit still in it.
I hope some one finds this handy some day.
 

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outlander

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Helped me. Thanks

I measured the resistances on the old pump and the new one(terminals match diagonally)
The fuel sender goes from 50ohms (empty) to 300 ohms (full)
The new pump had a resistance of just under 3 ohms, while the old one was borked at 30ohms

There is a supercharge version of this pump that looks almost identical to the regular kind, and sells for $20 less on ebay. I wonder if OP used that by mistake?
 

Juice3

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I had this exact same problem, everything about new pump was identical and fit perfectly into the tank but the locking ring would just not fit over the new pump I thought about filing the ring but then decided not too. And my pump wasn't a cheap one either it was a goss pump and it said it fit my vin number
 
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