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Fuel Pump And Starting Gremlin

JZP

By JZP,
in Motorsport Discussion & Builds

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JZP Proficient

JZP

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Hi all, given my problem exists in my track car and Ive exhausted the general maintenance search/diagnosis I thought I'd post this in the Motorsport section.

Basically I've had a intermittent problem where my r33 gtst track car won't start. It turns over easily, but won't start. You can tell that the fuel lines don't seem to be filling, and you can't hear the pump going.

Racepace replaced the fuel pump with a new high flow and got the car working temporarily, only for the gremlin to come back intermittently again.

I've installed a relay to ensure adequate power directly from the battery but it is still being triggered via the standard wiring, but the intermittent problem remains..

Question is, to eliminate all the electronics between the power FC and the pump, would it be sensible to run a wire directly from the pump relay trigger wire to the power FC fuel signal connector?

I'm hoping some of you Motorsport guys who have experience in this field could impart your expertise.

This is really frustrating and preventing me from getting back on the track.

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https://www.sau.com.au/forums/topic/418061-fuel-pump-and-starting-gremlin/
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Risking Grand Master

Risking

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Posted

Do away with the power FC ground trigger all together if you suspect it could be a problem.

You can get a timed, rpm triggered relay from any LPG installer.

When ignition is supplied the relay activates, it runs for 5 seconds if no RPM signal is received it turns back off.

When it receives an RPM signal turns the relay back on and pumps run again.

Engine stalls pump will run for 5 seconds more then turn off.

We use them to run fuel pumps all the time when the ecu doesn't have enough outputs to run everything. Saves one output when a relay can do the job.

JZP Proficient

JZP

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  • Author
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Do away with the power FC ground trigger all together if you suspect it could be a problem.

You can get a timed, rpm triggered relay from any LPG installer.

When ignition is supplied the relay activates, it runs for 5 seconds if no RPM signal is received it turns back off.

When it receives an RPM signal turns the relay back on and pumps run again.

Engine stalls pump will run for 5 seconds more then turn off.

We use them to run fuel pumps all the time when the ecu doesn't have enough outputs to run everything. Saves one output when a relay can do the job.

Hey Brad, had to read it a couple of times to digest what you were saying. The current trigger wire runs via the standard Electronics and loom that eventually gets to the PFC. Are you saying that the PFC trigger may not work? I was hoping to eliminate all the old stuff in between assuming something was broken.

I know you are the expert, so not questioning your expertise. What you suggested is seems to definitely be the next step, I was just hoping to eliminate the old stuff first.

Duncan Grand Master

Duncan

Posted
Posted

Brad's way sounds like the easy way to get to the root of the issue.

but if you want to troubleshoot first you need to work out:

Does the pump have power and earth when it is not running (probably not, but if it does the pump is the issue).

One side of the pump is relay switched. Does the other side have constant power or earth (earth I think but I can't check right now)

On the relay side- does it have constant input (earth or 12v, probably 12v)? Does one side of the relay input have constant 12v (or earth)? Is it the other side that is loosing it's earth (or power)? If they are OK it is a faulty relay.

If the signal is faulty check for the same condition at the PFC output, that will rule out a wiring issue.

If the PFC signal is not there....is it meant to be? the fuel pump should turn off after 3-5 seconds of priming with the key on (makes troubleshooting hard, especially with 1 person!). If it is missing can you swap to another PFC or a standard computer to see if it gives fuel pressure.

BTW, a mechanical fuel t'ed into the fuel feed line is really cheap (under $20) and makes troubleshooting starting isssues so much easier. Electric in cabin gauge is an ever better idea but costs about 10x

JZP Proficient

JZP

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Hey Duncan, had an auto elec check all the connections and make sure the relay wiring was earthed and powered correctly.

I just haven't done the validation of the signal at the PFC when the gremlin is around. Sounds obvious now! Thanks.

I'm almost tempted to do what Brad suggested cos I'm sick of rooting around with it. See how I feel about it tomorrow morning!

Not sure what you mean by the mechanical fuel t'ed into the fuel line though...

Risking Grand Master

Risking

Posted
Posted

If the problem is intermittent I'd be inclined to get a noid light or simple globe and bridge it across the ECU's main relay power supply and use the pump trigger output to ground the light.

Obviously if the ecu drops the ground trigger the light will turn off.

DJRIFT Veteran

DJRIFT

Posted
Posted

Up untill recently I would have ruled the ecu out as a fault but with the age of the power fc I'm seeing more and more silly faults.

My own power fc has has the tacho output drop out. So I got it repaired then almost 12 months later it got an internal idle switch fault. There was no reason for it to stuff up it just did.

New ecu is in the cards.

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