fuel pump

[Chimp871]

gremlins time.

New alarm/immobiliser from abacus installed.

Ignition on, both relays click, no pump prime but engine cranks over. Check pump +ve wire volts at B pillar behind passenger seat and at cranking it's ~10v, stop cranking it goes to ~12v before pump relay switches it off (normal) - pump does not prime.

Stick direct 12v feed to pump and it primes. Car starts. Switch engine off and try as normal and of course if works, several times.

Are these typical signs of a pump being knacked (no weird noises at the moment), just wondering if these things can jam and bar a technical tap or a good battery boost, gets them going again.

[Belle427]

I go for a poor connection somewhere, the post below is a similar problem.
https://www.pistonheads.com/gassing/topic.asp?h=0&...

[blitzracing]

Sounds unlikely that a 2v drop would stop the pump from running at all. Whats to voltage pulse on the pump during the pulse when you first turn on the ignition?

[Oldred_V8S]

Chimp871 said:

gremlins time.

New alarm/immobiliser from abacus installed.

Ignition on, both relays click, no pump prime but engine cranks over. Check pump +ve wire volts at B pillar behind passenger seat and at cranking it's ~10v, stop cranking it goes to ~12v before pump relay switches it off (normal) - pump does not prime.

Stick direct 12v feed to pump and it primes. Car starts. Switch engine off and try as normal and of course if works, several times.

Are these typical signs of a pump being knacked (no weird noises at the moment), just wondering if these things can jam and bar a technical tap or a good battery boost, gets them going again.

When you say you apply 12v directly to the pump, is this just the positive side or ground and +12?

You might have a voltage drop on both the +12 side and the ground. Poor connections matter as much on the ground side as well as the positive side.

[Steve_D]

Does your meter do amps? If so put it in line at the B post and see if the pump is getting/pulling any amps.
Poor connections can sometimes fool a digital meter showing reasonable volts but will not pass a current.

Alternatively bypass various parts of the circuit with a long (heavyish) wire i.e. Supply pin on relay to pump, pump to battery negative, output of relay to pump etc.

Steve

[Chimp871]

Probe kit: 12v direct to +ve on pump with negative connector on chassis where suppressor is.

So I've a voltage drop between pump relay and connector in B pillar. How many connectors are there upto the pillar?

Alarm (black plug under dash)
Intertia

Anything else? I'll check for resistance between points.

Blitz - can't measure pulse..

Edited by Chimp871 on Monday 17th September 13:02

[Chimp871]

Update : so checked Volts between fuel pump +ve in B pillar connector and battery - ve and its gone from 10 to 12v and of course working fine.

Same question as above, what connectors are there between b pillar and relay?

[SwanJack]

From memory there's the cut off switch and a big brown block connector in the lower dash, accessed through the stereo 'hole'. There is a wiring sketch diagram of the circuit on a old thread IIRCr

[SwanJack]

http://www.bertram-hill.com/fuel-pump-schematic.ht...

There you go

[blitzracing]

Chimp871 said:

Probe kit: 12v direct to +ve on pump with negative connector on chassis where suppressor is.

So I've a voltage drop between pump relay and connector in B pillar. How many connectors are there upto the pillar?

Alarm (black plug under dash)
Intertia

Anything else? I'll check for resistance between points.

Blitz - can't measure pulse..

Edited by Chimp871 on Monday 17th September 13:02

You have enough time to get a DVM reading when you first turn on the ignition as the fuel pump gets about a 3 second burst even if you dont try starting. Sounds odd after an immobilisers been fitted??

[Chimp871]

SwanJack said:

http://www.bertram-hill.com/fuel-pump-schematic.ht...

There you go

Thnx for that. So the plug with just black wires is near the alarm and goes off to the immobiliser but the other one, to right of picture with brown/blue socket is where?

[Belle427]

I seem to remember seeing it in the passenger footwell area, above battery but under dash.

[Chimp871]

found the brown connector, it was hidden well. It is in the stereo slot but behind a flap that you can only see if you look through the passenger 'glovebox' sideways. Sprayed contact cleaner and checked connections, nothing obvious. Working now, fingers crossed.

[Belle427]

Did you manage to pull it apart and inspect the connections or was it too tight in there?

[Chimp871]

Yes pulled apart and nothing obvious. It's going to be a case of if it repeats then I can check the connector. Been looking a while for it

Meanwhile, my o/s wheel bearing went today so the gremlins have been busy, little bds!