VR V8 wont start when hot...??

[bandit10]

Hi guys ive got a VR 5.0 V8 and when it gets hot it wont start, the fuel pump wont prime if i sit there 15 mins and let it cool down it will prime and the car will start.. im lost as to what is causing this..

So far ive replaced the following with brand new parts..

Fuel pump
temp sender
oil pressure switch
ignition module
oxygen sensor
fuel pump relay
efi relay

What would cause the fuel pump to not prime?? as soon as it primes it starts and drives fine
any ideas???

Thanks

[bandit10]

Should also add ive checked for error codes and nothing comes up.

[88GreenVN]

most common issue is the starter motor not wanting to turn the motor over when hot.

Fuel pump should not be a problem if you have replaced it.

[bandit10]

it turns over fine but wont start until the fuel pump primes which only happens when its cooled down for 15 mins, this one has got me stumped

[88GreenVN]

it turns over fine but wont start until the fuel pump primes which only happens when its cooled down for 15 mins, this one has got me stumped

may well be a fualty pump - or was it doing the same thing before replacing it?

[bandit10]

was doing the exact same thing with the old pump so cant be the fuel pump.

Is there some sensor that cuts off the fuel pump if it thinks somethings wrong..??!?!

I would of thought it would log a fault code but nothing comes up just 12 12 12 repeated

[Vee-ard]

Low oil pressure will cut the fuel pump off, as a safety precaution. oil light not on/disconnected? Oil flows easier when hot = less pressure. Also check wires around oil pressure switch.

[bandit10]

Low oil pressure will cut the fuel pump off, as a safety precaution. oil light not on/disconnected? Oil flows easier when hot = less pressure. Also check wires around oil pressure switch.

ive replaced the oil pressure switch with a new one and its still doing the same, oil light is not on.
It will run fine once the fuel pump primes but then if you turn it off it wont start again until its cooled down.

Is there anyway to check the oil pressure is correct?? no dash warning light is coming on, globe not blown as it lights up when engine not running and key in acc position

[westbad]

you can rule out the EFI relay, if the EFI relay fails the fuel pump takes power direct from the oil pressure switch which you say you have replaced as well. The car will crank over for longer until the oil pressure is up before it will start if this happens.
The temp sensor is part of the fuel system wiring also, did you replace the sender or the sensor? theres 2 temp probes in the inlet manifold next to each other.

[hako]

Must be the ECU. You could trick it by wiring a switch into the oilpump circuit to make it seem as though oil pressure is up.

[VrWagz1]

You need to find out if the fuel pump is getting power. If it isnt go back to the relay and see if it is coming in. If not you need to find out why. First test would be the ecu output for that relay. Then see if that is making all the way to the pin connector(edit: if the ecu sinks the voltage then it may appear to be on all the time with a test light, which happens somtimes but cant be sure).

[bubba2pac]

hi guys i have a vr wich was doing the same thing i was told two chaNG THE CRANK ANGALL SENSORRS WICH NEAR THE LEFT HAND SIDE BEHIND HARMOMNIC BALINCER I REPLACE IT ON MINE NO MOORE PROBLAM

[westbad]

hi guys i have a vr wich was doing the same thing i was told two chaNG THE CRANK ANGALL SENSORRS WICH NEAR THE LEFT HAND SIDE BEHIND HARMOMNIC BALINCER I REPLACE IT ON MINE NO MOORE PROBLAM

V8's dont have a crank angle sensor

[Helicopter]

Crank angle sensor on a V8.........I like that.

Anyway down to business. I guess you have seen the circuit diagram of a VR V8?
see this link:

http://memcals.com/pdf/VRV8%20Wiring%20Diagram.pdf

The signal to prime the fuel pump comes from the ECU [pin A1] and goes to one side of the coil on the fuel pump relay. Initialy, as there is no oil pressure to begin with, the oil pressure switch contacts ar open. The fuel pump relay must get its power via fuse 21 to prime.

If as you say you don't hear the fuel pump prime when turning the ignition to on, I would be first looking for the ECU signal [+12v] appearing on one side of the relay coil for a couple of seconds. If that's OK, then checking the relay and its connections perhaps.

Anyway, hopefully the diagram will help you.

Cheers

[bandit10]

thanks for the advice so far guys, The problem seems to be getting worse its now cutting out whilst im driving and even after a short trip less than 10km it cut out and wouldnt restart for 5-10mins.
i disconnected the battery for 5 mins to reset the ecu and it still wouldnt start, no fuel pump priming.
Im running out of ideas, i will try a new ecu lets hope this will fix it.

thanks

[delcowizzid]

check fuse 10 under the stearing colomn its oil light fuse and efi relay control may not be making good contact

[bandit10]

check fuse 10 under the stearing colomn its oil light fuse and efi relay control may not be making good contact

i checked out fuse number 10 and its not blown and has good contact. I started another thread about changing the ecu and memcal as a fault finding elimination process, could you ckeck it out and give me your opinion please.
Thanks

[sus steven]

hey mate is it an auto or manual this is just a blow in the wind but if it's and auto sometimes the neutel swicth in the shifter plays up an that and makes it think its in gear when it's not but the motor will turn over but will not have spark or won't let the fuel pump run might be worth changing and cheap to v8 and v6 swicthes are the same

[Helicopter]

hey mate is it an auto or manual this is just a blow in the wind but if it's and auto sometimes the neutel swicth in the shifter plays up an that and makes it think its in gear when it's not but the motor will turn over but will not have spark or won't let the fuel pump run might be worth changing and cheap to v8 and v6 swicthes are the same

I don't think that is correct, and if my memory serves me, the motor will not even turn over if the neutral switch is the culprit.

cheers

[Helicopter]

thanks for the advice so far guys, The problem seems to be getting worse its now cutting out whilst im driving and even after a short trip less than 10km it cut out and wouldnt restart for 5-10mins.
i disconnected the battery for 5 mins to reset the ecu and it still wouldnt start, no fuel pump priming.
Im running out of ideas, i will try a new ecu lets hope this will fix it.

thanks

You said the fuel pump was replaced so I can only assume that the 12V power to the pump is somewhat intermittent. I think this is becoming obvious when you say that you cannot hear it prime again. Did you check with a multimeter as per the circuit diagram I linked to you. When the problem occurs it should be relatively easy to check if the correct voltages are present on or around the fuel pump relay circuit.

In fact I had a similar intermittent problem that I could not hear the fuel pump being primed. It turned out to be the fuel pump..........BUT to get to that conclusion I first checked that I could see the 12V from the ECU being applied to one side of the the relay coil during the priming cycle.

Do do this I removed the relay, pushed a small wire into the coil position "G/W" [check the diagram] then pushed the relay back in ontop of the wire so it was held in by the relay. Connected the multimeter between the wire and earth and checked for the 12V appearing for a few seconds after turning the ignition on. Alternativelly just get someone to put their finger on the fuel pump relay and when you turn the ignition on to check if its clicks and stays on for about 3 seconds.

Satisfied that the fuel pump relay was working I then simply removed the relay, and using a wire shorted out points "V" and "O" in the connector, and presto the fuel pump still didn't work.

Only thing left was the wire to the fuel pump but it was the pump anyway.

You should be able to fault find the issue because as you say it stays faulty for a while giving you enough time to investigate.

cheers

[Dr.304]

i found that if you give the car a bit of gas while starting, she starts right up.

I only tried it like twice, but it seemed like it worked.