Fuel Pump Grounding/Earthing

[toggyvet]

Hi folks,

Still trying to get to the bottom of my 1988 failing to start.

Does anyone out there know the best way of checking the fuel pump grounding/earthing, i.e. where the connection from the fuel pump is likely to be grounded/earthed. I'm assuming that there will be a connection somewhere on the chassis.

All I know so far from the wiring diagrams is that I'm looking for a black wire - so that should narrow it down to a few thousand!

Cheers,

Chris.

 

[vigman]

Some reading

http://corvetteactioncenter.com/forums/showthread.php?s=&threadid=7501&highlight=Getting+Grounded

Vig!

 

[vigman]

To answer your question more directly on grounding

The fuel pump ground comes from the frame
( Body sheet metal)
Interior.. top of drivers side rear wheel well under carpet. Top of door pillar.

( G-401 )

Goes into the rear harness

( *S-400 )

a 14 wire splice in the harness about 4 inches back from the ground lug

( It also has S-401 & 404 in that splice zone )

And it runs up to the fuel pump connector!

( According to the shop manual )

Additional notes
Have you checked the fuel pump fuse?

Vig!

 

[vigman]

Faded memory/ Tank grounding

There MIGHT be a ground LUG on the top where the fuel pump bolts into the tank... you might want to remove the cover plate around the filler neck and inspect.....

Also try powering the pump directly to make sure it works (tan white wire).... has the car been sitting for a bit?


Just a thought!


Vig!

 

[toggyvet]

More info

Thanks for the posts Vig,

I'm working through the postings - just a couple of comments at this stage:

- you may have seen from my original posting on the problem, that the engine cut out occurred directly after a rear end wheel 'tap' against a kerb - this has led me to believe that the power loss must be connected in some way (e.g. the fuel pump grounding coming lose / fuel pump damage) - although if the grounding point is protected in some way this is unlikely.

- I can definitely NOT hear any whirring when the ignition is turned to the ON position (faulty fuel pump, fuel pump relay, fuel pump fuse / fuel pump circuit)

- the AA chap who came out to the car reckoned he could smell fuel when the system primed (this contradicts a fault with the fuel pump though)

- your post to Ken solved the mystery of the 5th pin on the fuel pump relay (i.e. the ALDL connection)

- can you post more info about the wire needed to connect the battery to the ALDL 'G' pin - is there a minimum wire size that I should be using (don't understand enough about wire guages yet)

- the frame grounding points and references - do they refer to some sort of diagram

Thanks again - the car being stationary in the garage is annoying, but I've learnt a hell of a lot about the car in the past 5 days and its all very interesting.

Probably have more questions when I've gone through the rest of your posting to Ken (by the way, I assume the diagrams posted there are NOT for a 1988)

Cheers,

Chris.

 

[toggyvet]

Fuse check

Oh and I forgot to mention that I checked the Fuel Pump fuse and fuel pump relay fuse - both OK.

Do you know what sort of sound etc I should expect from turning the engine if the fuel pump is not working (probably a stupid question - but I'm still learning)

 

[vigman]

Gauge of wire

A paper clip should do nicely..

The bigger the wire.. the larger the number the more current it can carry SAFELY! ( measured in amps)

So a standard table lamp should be 18 gauge ( in american ) I'm sure there is a metric cross reference..

The sound of the car... just cranking with no attempt to fire.

The ground point's are related to the frame & the service schematic.. I have tried to give accurate physical descriptions where the actual lug nails ( screws ) down to the bare metal of the frame ( or body ) as the case may be.

Ken's schematic should be fine for you as well!

Go to the local auto depot.. and get a spray can of "Quick Start" or ether.. and spray it down the intake of the air cleaner.. if the car lights off ( vroom ) then it's fuel!

 

[toggyvet]

Making progress!

Things are improving a little! - I used the ALDL 'G' connection direct from the battery and the fuel pump burst into life, hence proving the circuit, the fuel pump, the pump fuse and the grounding.

A few more queries at this stage folks:

- if I keep running the fuel pump (even though its only for a second at a time), is this going to cause a problem - where does the fuel go that is being pumped???

- I measured the voltage to the relay from the battery and it read at 0.96 V - I reckon this could well be the problem, everything is working OK, except there isn't enough juice to run the pump - could this be caused by the fusible link between the battery and the fuel pump relay being virtually blown? If so, does anyone know where the fusible links are?

- when using the ALDL connection, I again measured the voltage into the relay (this time though the ALDL input) and it read 11.86V, exactly the same as a direct reading from the battery

- I thought I might prove that the relay is OK by switching it with another - can anyone recommend which one would be OK to use (I thought the horn relay, but I don't know where it is.

Thanks

 

[vigman]

Making progress! GOOD NEWS

Things are improving a little! - I used the ALDL 'G' connection direct from the battery and the fuel pump burst into life, hence proving the circuit, the fuel pump, the pump fuse and the grounding.
WILL THE CAR START NOW WITH THE PUMP IN MANUAL MODE?

A few more queries at this stage folks:

- if I keep running the fuel pump (even though its only for a second at a time), is this going to cause a problem - where does the fuel go that is being pumped???
IT RECIRCULATES BACK TO THE TANK

- I measured the voltage to the relay from the battery and it read at 0.96 V - I reckon this could well be the problem, everything is working OK, except there isn't enough juice to run the pump - could this be caused by the fusible link between the battery and the fuel pump relay being virtually blown? If so, does anyone know where the fusible links are?
I WILL HAVE TO CHECK ON THIS TOMORROW... SHOP MANUAL @ HOME

- when using the ALDL connection, I again measured the voltage into the relay (this time though the ALDL input) and it read 11.86V, exactly the same as a direct reading from the battery

- I thought I might prove that the relay is OK by switching it with another - can anyone recommend which one would be OK to use (I thought the horn relay, but I don't know where it is.

BUY A NEW ONE... THEY ARE REALY CHEAP.. NO SENCE MUCKING ABOUT WITH ANOTHER ONE.

GOOD LUCK
VIG( sorry about the caps...not shouting!)

 

[vigman]

The fuel pump relay

- I measured the voltage to the relay from the battery and it read at 0.96 V - I reckon this could well be the problem, everything is working OK, except there isn't enough juice to run the pump - could this be caused by the fusible link between the battery and the fuel pump relay being virtually blown? If so, does anyone know where the fusible links are?
I WILL HAVE TO CHECK ON THIS TOMORROW... SHOP MANUAL @ HOME

Ok yes there is a fusible link for the relay/pump

BUT FIRST

Measure pin A on the fuel pump relay
(+12 batt HOT all the time)
Orange wire

Along with pin C ( Orange )
of the oil pressure switch
the mass burn off relay
Pins A & C ( Orange )
and the ECM pins B-1 & C 16 ( Orange )

If this is Hot skip the next paragraph

If this is NOT HOT the you need to locate fusible link H

Under the hood... drivers side ( assuming right hand drive)

Taped to the Positive main batt terminal should be a single wire going to the link.

Careful here... there are 2 others lurking in the same area ( E & D... E is a 2 pin connector).

The link has a red wire coming into a round tubular black moulded bit of hard rubber.. then a short bit of wire ( the actual "link")... and a splice, which on the otherside should be orange.


Get a test light with a sharp pointy bit on the end ( make sure you have a good ground) and check that BOTH sides of the actual wire ( Red & Orange) are HOT by jabbing through the insulation of the wire itself.

Noodle Doodle yet?


Vig!

 

[vigman]

Oh and if you jumped on the ALDL

and the pump "burst to life" this assumes that all wiring going back to the pump is OK!

And

Since you have no check engine light
& no fuel pump power... link H is the prime suspect...


Espically if you got the fuel up to pressure and the car would not start.....

Have you tried this yet?


Vig!