No fuel to carbs, & relay identification 87 Atmo GTA

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No fuel to carbs, & relay identification 87 Atmo GTA

Postby Petehuws » Thu Jul 23, 2020 11:01 am

Hi folks,
Car is a October 1987 D500 Atmo. Had the car out for a short journey yesterday with no issues. And parked it on the drive at home.
As it was about to get dark I thought 'I'd better stick it in the garage' but would not start.
Did a little bit of fiddling in the waning light & detected that no fuel was being delivered to the carbs.
Removed the engine bay fuel hose from the steel delivery pipe, put a sealable bag over the end & cranked the car over a few times but was dry; that was enough for one night.

This morning, albeit in the rain but light I investigated further & suspected the pump, however when I manually, & directly applied 12VDC to the pump it started 'pumping' so my findings are the pump is not receiving 12V when ignition on or attempts to start.

I'll start by tracing the wiring back from the pump as best I can, however I'm suspicious of course of the fuel pump relay. Do any of you experts know which one is the relay for the fuel pump please? Or whether I can troubleshoot by moving them around? Not looked closely at the relays yet but keen to learn if there are several of the same type. :Douh

Here's some pictures, I know we all like pictures :super
Picture 1 - Shows the relays under the dash.
Picture 2 - Shows the pump and my my introduction of 12V that gets it spinning.
Picture 3 - Shows a clear filter in the engine bay I added to visually see the fuel after manually getting the pump spinning, (rules out a blockage).

So right now I'm left with wiring or a relay I'm thinking.

Many thanks to all you excellent folk. :up
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Re: No fuel to carbs, & relay identification 87 Atmo GTA

Postby mettersl » Thu Jul 23, 2020 12:02 pm

Hi Peter,
One more place to try.
When I had problems with my GTA Atmo post restoration there was an intermittent fault on the connector that joins the front loom to the core loom. The connector for this is under the front boot liner on the LHS suspension turret.
I had changed the pump (new one for another new one) before finding this. Its beside the brake fluid reservoir so the environment under there can be a bit corrosive. I bypassed the connector for just that one pin and everything has been fine since.
It taught me to start with the cheapest things and move up.
I have just checked and the pump relay is triggered by the feed from the ignition coil(nit the hall sensor in V1 of this post).Thanks John C for pointing that out.
I would start with a meter in the input side of the front connector, if that isn't showing any voltage as you crank the engine (then go back to the control relay, but you may be lucky like I was and find its "just" a dirty connector.
There is another set of relays behind the ones you can see, you need to unscrew the fuse box and lower dash to see them.
The wiring book is an excellent guide here, really comprehensive (and mainly accurate), sadly you just missed one on Ebay for an 1986 car. I only have later wiring books....you have my email address!!
Good luck
Lee
Last edited by mettersl on Thu Jul 23, 2020 4:00 pm, edited 2 times in total.
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Re: No fuel to carbs, & relay identification 87 Atmo GTA

Postby Petehuws » Thu Jul 23, 2020 12:14 pm

Hi Lee,
As always thanks a bunch.... I need to now send you a "Case of beer voucher", I'll go look at the wiring after my lunch, thank you..

I had my eye on that 86 wiring manual but totally forgot about it in the last few hours, was annoyed with myself.
I'll report back any findings & I thank you again
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Re: No fuel to carbs, & relay identification 87 Atmo GTA

Postby mettersl » Thu Jul 23, 2020 1:15 pm

Hi Pete,
I also notice that your car is an early one with the fuel metering unit in the front by the pump, my car is a later one where that is mounted at the rear near the fuel pressure regulator and the coil.
I'm sure that you'll let us know how you get on. :angel
Cheers
Lee
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Re: No fuel to carbs, & relay identification 87 Atmo GTA

Postby alpine744 » Thu Jul 23, 2020 7:53 pm

Petehuws wrote:Hi Lee,
As always thanks a bunch.... I need to now send you a "Case of beer voucher", I'll go look at the wiring after my lunch, thank you..

I had my eye on that 86 wiring manual but totally forgot about it in the last few hours, was annoyed with myself.
I'll report back any findings & I thank you again


Hi Pete

I have a wiring manual for your car. If you get stuck, I can copy any appropriate pages that you may need.

Craig
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Re: No fuel to carbs, & relay identification 87 Atmo GTA

Postby Petehuws » Thu Jul 23, 2020 10:04 pm

Hi Lee, & Craig
Thanks so much!

Well we have got the car running this evening, & now it's back in the garage - in short it was as suspected & assumed - electrics.
I can't confidently really say where the issue was but do have a suspicion it was around that front left strut connector & wiring loom connection next to the brake fluid reservoir. a

What is for sure was that engine cranking initially had no fuel flow & checking this morning only had ~800mV at the fuel pump, this is when I brought in an external 12VDC which got the pump running.
Using this external power I tried to fire up the car this way but would not ignite ; knowing we now had fuel flow I moved to the rear.
At the coil I was only seeing 3.8V so something was not right, it was at this point I suspected a high resistance somewhere in the wiring, as a look-see in the rear engine bay firewall the direct battery terminal was measuring 12.42V so all good with voltage capacity.

Moving back to the front connector I located the + feed yellow wire to the pump but again had no voltage on the terminal, (harness side) but in continuity was picking up connection with chassis ground & neighbouring wires?
At this point I undone the pump & flow meter wiring from their connections and separated all of the wiring loom back to the front connector,including the +/- to the pump.
With all wires hanging out and the pump disconnected I was surprised to now read 8.8V at the pump +/- wires.
Following this I then disconnected the front left wiring connector & sprayed some electrical contact cleaner & re-attached, I then did the same for the connector that connects at the rear to the Bosch ignition module & coil, together with the electrical connector right at the rear between the rear screen mechanical catches.
Returning to the front upon engine cranking I was now seeing 12.03V at the pump wires.
Following this I then returned the +/- wires back to the pump & redressed & returned all wires back to the conduit & tidied up.
Turning over the engine was now a success & the engine fired up & held.

I think all it turned out was poor wiring, high resistance and bad/dirty connections; ultimately nothing was replaced & all values now measure correct and strong.


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