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360 fuel pump ground location?

aussyvolvo

Will stalk for money
Joined
Jul 12, 2007
Location
South Australia
so my trouble shooting has this on my 1986 LH volvo 360. the relay is working, there is voltage getting through the fuse behind the (about 11.5v), but the fuel pump is getting 0v, this is going by the terminals on the plugs at the fuel pump (tested with multimeter).

I can't seem to find where the wires go from the pump, they just go up into an impossible to reach place. If anyone could inform me where the grounding location is, I'd be able to do more diagnostics. (the fuel pump pumps when directly connected to a battery)

Further information, the car ran when parked a few months ago, just an intermittent misfire. And at some point, people siphoned the petrol out (I forgot to lock the cover).
 
This is an LH injected car? Then the ground for the relay is provided by the ecu. At least that is how the ones work that we got over here. is it a white six pin relay? the fuel ecu has to see an engine rpm signal from cranking and then it will ground and turn on the fuel pump relay.
 
so I found that the fuel pump doesn't go through the ecu (I think they share a relay though), when cranking, under the rear seat I get 8-9v only, and when testing resistance from the car's side, I get this reading (pictured), can anyone else please take a quick reading at let me know if this is good? (I don't know how to read this multimeter either, there's no labeling)

BEtPFT3.jpg
 
The fuel ceu provides a ground for the fuel pump relay in the LH cars we have over here. The power does not pass through the ecu. It provides the turn on ground after it sees the ignition system is making spark.

For a basic spark check you can put a test light on the coil terminal 1 and see if it switches the coil. The light should flash if it is. Then you can use the meter to see if the signal for engine speed is being sent to the fuel ecu. If it is and you get no ground on the fuel pump relay then it may be the fuel pump ground circuit has failed in the fuel ecu.
 
The fuel ceu provides a ground for the fuel pump relay in the LH cars we have over here. The power does not pass through the ecu. It provides the turn on ground after it sees the ignition system is making spark.

For a basic spark check you can put a test light on the coil terminal 1 and see if it switches the coil. The light should flash if it is. Then you can use the meter to see if the signal for engine speed is being sent to the fuel ecu. If it is and you get no ground on the fuel pump relay then it may be the fuel pump ground circuit has failed in the fuel ecu.

I know I get spark, and when cranking I get about 11v at the fuse behind the battery, and about 8v by the time it makes it to the place shown, and 0v by the time I check at the pump (I'm going to re-check at the pump when I get help later).

Front probing is bad!!!!!

why? because it stretches out the plug? it was a nice fit, and I have no trouble bending them back down.
 
That ground could be bad and cause a low voltage reading. Try another ground. Like the ring on the cig lighter.

Use a test lamp also. A meter won't show if there is inadequate CURRENT but may show 12v.
 
yeah. So the fuel pump wasn't working, but the pump I put in was completely broken, this is where I was up to. But putting in the old one suddenly worked. There was also a fuel pressure regulator issue too that may have made me think something was wrong with the original.
 
Great. Thanks for the update. Sounds like the electrical test method was incorrect if your pump indeed runs. Another good ground I use all the time is the tailpipe. I connect one end of my 10ft retractable leads to it for electrical tests in the rear.
 
okay, the long version, the relay was dead, but I've only had experience with cars where the fuel pump fails, so I did what I knew, which was to replace the pump. But I put in a bad pump. I did some testing, and there was no voltage, so I replaced the relay after looking into it.

So we had a new relay, bur no fuel, so I assumed I was still getting no voltage. This is around the time I wrote this. My error wasn't testing, it was me making assumptions. I found out after re-testing the voltage at the pump, and plugging in the old pump, and changing the regulator it runs nice.
 
Got it. Yeah I always put a test lamp between the power and ground wire and crank the engine before replacing a "dead pump". I skipped this step recently (being lazy) and later found rodent damage to the wiring.
 
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