soontobered84

I have determined that the ground for the relay is nonfunctional. I have traced the wire on the back of the fuse panel over to a connector on the front of the panel. Up throught the fuse panel continuty is good. My question is : Where does the fuel pump ground?

ROG100

As you know the 84 WD is about as useful as a *****
I looked at the 85 and it shows the ground point at MPIV which IIRC is under the instrument cluster.

Alan

John,

Good job narrowing it down - the ground for the relay coil comes from Pin 17 on the LH only - it exits on PLug X - Pin 4 of the CE panel...

See that Plug X.4 connects to pin 85 on the relay socket (seems maybe you did already) and that Plug X.4 connects to pin 17 on the LH. I think this is also connected to Ground Point VIII on later cars so may also be here - in any case it seems its supposed to be a fixed ground not a switched output from the LH.

Alan

soontobered84

Alan,
The plug X4 does connect to pink 85 on the relay socket, and the wire coming out of plug X4 is a red/brown. All the other wires at the relay are functional and if I put a ground to pin 85 of the relay or to the wire at X4, it works as it is supposed to. So it appears that the problem is the red/brown wire on the plug X4 not having continuity.

soontobered84

I am now going to check continuity on the wire at X4 to pin 17 of the LH. If I have no continuity, I will replace/fix the wire. But what if I have continuity? Does that mean my LH computer is bad?

soontobered84

The wire from X4 to pin 17 of the LH has continuity. Now what?

Jim M.

Sounds like that portion of the LH is fried. Time to try a different LH to see if it works.

Jim Mayzurk
93 GTS 5-spd

soontobered84

I was afraid that somebody would say that. I have an extra EZK but not an LH. I gues i'll pull the one out of the black car to try.

Alan

John,

I had originally thought that this pin was driven by the LH to shut off the fuel pump if the engine is not running (after an attemp to start say) - but I'm not entirely sure...

If it is than it certainly suggests the LH may have an issue.

The other option is that pin 17 on the LH car side of the plug should just be grounded and feeds the LH as far as I can see the LH has no other ground feeds (maybe pin 6 "ground from LH 2" so check that one too). It is possible the shielding and plug itself are the main ground connection though.

We need the LH experts to chime in on that one...

So anyway to debug look for a broken ground wire somewhere in the LH plug body qs a second connection to pin 17.

Failing that since its supposed to be grounded to run - just ground Pin X4 (very solidly - since if it fails - engine will stop). There are grounds to the back of the panel (long brown pigtails) you could use and there is a bolt on ground point right above the panel.

Nice to find the real cause - but you can get running again this way. Even if it is the fuel pump cut off - its not much different than other cars where the fuel pump runs whenever the ignition is on.

So - second if no joy with any of that - there are some LH rebuilders who will test the LH - and if its good - just return it to you for shipping costs.

I know of at least one who does - maybe they all do... PM me if you want more info on that.

Alan

Drewster67

On my Race car -

Hope this helps.

John Speake

The fuel pump relay is energised by one end being fed with 12v, and the other side is pulled to ground by pin 17 LH ECU.

It will only pull it to ground when the LH receives rpm pulses from the EZ-F ECU.

Check first that you have 12v on the one side of the relay coil.It is fed from ignition switched 12v.

Alan

John (S) - thanks that's what I thought it did - so either the LH is fried or its not seeing the required rpm pulses - so could be the EZK? or whatever sensor the EZK it uses to detect rotation?

Since it sounds like the car runs with this pin grounded - what might be the likely causes?

We know the power is OK to the relay and that jumpered everything runs - its the switched ground from the LH that is stopping the fuel pump from running - at least thats what I have gathered from John(C).

Alan

soontobered84

John Speake and Alan,
Thanks for chiming in. If i put a 253B relay in the socket and ground the top spade (87 ?) the relay works correctly and the fuel pump runs. Also, If I ground the wire at X4, the relay works correctly and so does the fuel pump. The wire has continuity to pin 17 of the LH.
Thanks for all your help.

John Speake

>>>>>>>>>>>>>>>>
Hi Alan/JohnC
It's not clear from what John says whether the car will start when the fuel pump is jumped to run....... ?

Anyway, if it does run, then the only thing can be wrong is a blown LH ECU. Probably done by fitting an incorrect relay, or jumping the wrong terminals of the fuel pump relay at some point. However it is easily repaired.

If the car doesn't run, then you need to check if there is a spark, this shows that the flywheel spped sensor, EZF ECU and its relay are OK. Until the EZF is working, there will be no rpm pulses to switch on the fuel pump drive from the LH.

The rev counter (tach) is also driven from the rpm feed from EZF to LH, so the tach should flicker when the engine is cranking. This will confirm that the LH fuel pump drive has failed.

soontobered84

John Speake,
The car starts right up when the fuel pump is jumpered to run.
If the tachometer bounces when cranking before starting, that would indicate the LH fuel pump drive has failed?