Fuel Pump Diagnosis

[rob.043]

Ive had some fuel/running issues with the car recently (digi), the sequence of events is as follows:

Turned the car off after a short run, started it 10 minutes later and it died after running for 5 secs. Left it 20 mins and it was fine, started and drove me home. Had about a 3rd of a tank of fuel at the time I think

A Week later, drove 80 miles, Went around a large roundabout twice (bad navigation from co-driver), exited on slip road and engine then died, and would not start that evening. Less than a quarter in tank this time. Got it home, tried to start it a couple days later- no probs, ran up to temp in garage and turned off. Changed fuel filter, then would not start (despite much trying). Added 3 gallons to the tank, and it started and ran no bother.

I hear a pump priming when I turn the Ignition on, and from what I find in searches, this is the main pump out of the tank? So is this definately a lift pump problem, with enough fuel depth meaning it will run anyway?

[Ben Lessani]

You're going to need to do this next time it goes wrong ...

My bet is the heat of the engine + hall sender breaking up = engine dying randomly.

spark or fuel



this is just for a little guidance with those getting stuck at - my car doesn't start!

check for spark

1) remove fuel pump relay.
2) remove king lead - place near head and check for regular spark. if the king lead sparks evenly, go to 3, if not, go to 4.
3) re-connect the lead and remove a lead from cyl 1 and check for interval spark, if even, go to 5, if not, go to 6.
4) turn the ignition on, then off, there should be a single solitary spark, if there is, go to 7, if not, go to 8.
5) repeat step 3 with the next cylinder.
6) this is either a ht lead, rotor or distributor cap fault.
7) this is either a hall sender or wiring to coil fault.
8 ) this is either a coil pack, hall sender or wiring to coil fault.

coil pack, hall sender or wiring to coil fault
testing the hall sender requires pulling back the rubber boot on the wiring (ensuring it stays connected), connecting a voltmeter to the middle pin and the other end to ground. put the car in 5th gear and rock the car back and forth (around 1-2m) and watch for fluctuation on the voltmeter. if it doesn't change, then replace the hall sender/distributor.
testing the wiring/coil pack is using your voltmeter and common sense (wiggle wires, check for continuity etc.)

ht lead, rotor or distributor cap fault
to test the leads, swap the faulty lead with a known working lead and test again.
to check the distributor cap/rotor, remove and inspect for signs of arc'ing, ensure contacts are clean with plenty of material.

sometimes just replacing parts is the easiest way to test unknown parts (but not necessarily the cheapest).

checking for fuel

1) after testing the spark first, refit the fuel pump relay, crank the engine very briefly (or just flick the ign on/off) and release, you should hear the fuel pump(s) prime. this relies on all wires being connected to the coil pack - without the wiring connected, the fuel pump will not prime (on a k-jet). if it primes, go to 1a), if it doesn't prime, go to 3.
1a) Disconnect plug from main pump under car and repeat #1, you should hear the in-tank pump prime, if it does, go to 2, if not go to 6.
2) fuel flow needs to be tested.
3) remove the fuel relay and bridge the large pins with a suitably crimped piece of fused wire (rated 20a). if you hear the fuel pump running, go to 4, if not, go to 5.
4) your fuel relay is faulty.
5) replace the fuse for the fuel pump, then repeat step 1. if you have got here a second time, go to 6.
6) fuel pump(s) or wiring fault.

fuel flow needs to be tested
i can't be bothered writing fuel flow tests, check your haynes.

fuel pump(s) or wiring fault
you need to use a battery back and suitable wiring to connectors on the fuel pumps themselves to ensure they run. be extremely careful - any spark could start a fire. use your brain, be careful and figure this one out for yourself.

[rob.043]

Thanks ben, I may print a copy of that for the glove box!

I replaced the lift pump yesterday, as I spotted a genuine one on e-bay for a decent price, and figured it couldn't hurt. So with that on, I went for a spin and covered most bases (sitting idling in town for a bit, steady sustained cruise at 60, and spirited on the quiet twisty back roads). No problems.

I'll see how it goes. Will have a look at testing the hall sender, if this is possible....

fingers crossed it keeps going!