Dictys

The PO made a permanent ground from pin 85 on the XXV relay rather thru terminal W21 (brown/white wire) to terminal 21 on the LH Control Unit.

I understand that normally this is a switched ground when the engine is running or starting (ignition in 2 or 3).

I have now restored this to the factory configaration.

There was also a mass of relays in the spare wheel which were connected directly to the "+" on the main fuel pump.

The intank fuel pump was connected as normal but no "+" wire to the main fuel pump.

The grounds at both pumps are connected to the rear ground pump.

The car was working with this weird set up, but I have had other issues with electrical drains etc which I have suspected are the mass of relays connected in the rear trunk which have now been removed.

I will connect up the correct connections on both pumps this weekend and I haven't started the car since restoring the electrics back to normal as I need to refill the tranny with fluid and I am waiting for a part. So I am unsure whether the will start in factory spec or not at present.

My questions is really, why would this be done?

I can only think it was the LH going bad and not sending the grounded signal to the LH relay.

However, the LH was replaced by the PO, but I do not know whether this was before or after this new homebrew wiring mess. I suppose if replace after the wiring had been change, as the car ran the PO didn't return everthing to spec.

Landseer

You should if you haven't already, ensure clean grounds and good ring terminals at each side of rear of V at engine/bell housing area. And polish CE panel, new fuses, and especially check the back side for any wire anomolies. These are areas I've found problems.

Also, Rich Andrade found that a MAF circuit flaw, when MAF got hot, would somehow result in deenergizing the LH circuit. Just some thoughts-he said that was unusual for an early MAF like mine, but has seen it with later ones.. You might ask him about it.

Could also be simply a bad fuel pump or ground, but misdiagnosed?

Just speculating with / for you.

Though I can't imagine in Dubai climate that corrosion would be a big issue.

Dictys

Thanks Chris,

"polish CE panel, new fuses, and especially check the back side for any wire anomolies" ,new 53 relays, clean grounds have been done. Also new MAF

I don't think all the PO mechanics had the workshop manuals as most things seems to have been done as a quick fix

Corrosion is not too bad but it is very humid here as we are just a few miles from the sea, myself and another 928 rennlister were working on the car for seven hours in the 115f heat last weekend. Lucky we had beer.

Mrmerlin

since you mention you have an intank pump if it has not been recently replaced or inspected for a failed transfer hose then the intank pump could cause the engine to not run,
you might consider replacing the intank pump with the fuel strainer

Landseer

I totally missed the dual pump ref.

Dictys

"replacing the intank pump with the fuel strainer", Roger sent the strainer etc last week so have that covered, hopefully be here this week.

I'll have to check but i think the in tank pump is still connected to the original wiring, only the main fuel pump was on a seperate home made ciruit. I'll have to see whether the in tank pump is still getting current.

If the in tank pump does not work would the main pump work despite this. I am assuming it must work this way if the in tank pump had failed otherwise the car would have never run.

Mrmerlin

the intank pump should be connected to the main pump feed wires

dr bob

Dubai is probably one of the places where the second in-tank pump is actually needed. Purpose is to avoid inlet boiling in the main pump in hot weather with high fuel temps. It may be that modern fuel mixes there are blended to reduce the vapor pressure, but you can't depend on every batch of fuel being "just right". My vote would be to maintain the intank pump if at all practical. Else risk sitting on the side of a very hot highway with no-start.

Alan

I suspect the mass of relays were a previous attempt to resolve a parasitic current draw - quite possibly non-effective even then - and from what you say certianly not effective now...

Its possible there was an ECU failure on the fuel pump enable circuit that prompted this also - have you got it running with the stock config yet?

Alan

Dictys

Alan, not yet, but I can only work on the car at weekend, so I'll report back then. I'll test all the wires before connecting it all up and see where we are.

Rich9928p

Just a point of clarification about this statement. Some of the early MAFs have a thermal run-away failure in the MAF control circuit. They may work at start-up but heat-up, go out of calibration and the engine will stall. The LH just sees the incorrect voltage from the MAF, the engine will not run with this incorrect voltage.

Dictys

Thanks for everyone replies.

All is now connected back as stock now and as I suspected no start.

Jump the fuel pump relay and both fuel pumps work.

However, it seems the LH is not drawing down the voltage on pins to 20 &21 to close the fuel pump and LH relay. I checked and found 12v at W15 & W21 should these not be 0v when ignition is position 2?

I assume this indicates a bad LH unit? Looking through the PO invoices it seems the LH was rebuilt in August 2005.

To me it seems that the PO had connected W21 to give a permanent ground to shut the LH Relay (would this be a current draw even if ignition switched off as it connects directly to battery?).

Then the mass of relays installed in the trunk then connected to the "+" on the fuel pump direct was to replace the fuel pump relay and give power once the ignition was on, as I assume with my very limited knowledge if you grounded W15 the fuel pump would run all the time.

Next steps I assume is to get the LH checked and replace or rebuilt again, unless there is another way?

I have a diagnostic computer, is there any way to check this problem further using this?

Alan

I belive the LH only activates the fuel pump when the engine is spinning - even at startup - so then if the engine stalls the fuel pumps don't run.

So your testing shhould evaluate the relay enable during cranking.

But it did seem likely to me that this was related to an LH failure so I think you are on the right track

Easier path would have been to enable the FP & LH relays via an ignition switched line -- not sure why they went so elaborate...

Alan

Dictys

Thanks Alan,

I'm going to give the LH to John Speake to test and rebuild.

I'll work on some other issues in the meanwhile.

Regards
Mark

TheoJ

yes, sounds like a LH hybrid circuit that is toast. The LH energizes the fuel pump relay when the EZK is on, speed signal is there so the engine is turning over. If it fails to activate you'd probably best swap with a known good one to make sure, and go for a repair if it is defective.
It should be on everyone's agenda to have the LH rebuilt as these circuits in the LH will break. Just a matter of time. A quick and easy way to get home is this:
http://jenniskens.livedsl.nl/Technic...8/MyTip809.htm
http://928gts.jenniskens.eu
Regards,