1998 v70 No start, no pressure at fuel rail, wiring at fuel pump Topic is solved

Post by **benpineapple** » 27 Sep 2016, 22:01

Howdy all. I have an odd no-start issue happening right now.

Car wouldn't start the other day, cranks just fine. No pressure at fuel rail, no fuel priming sound audible. I check fuses, they're all good. I plug in my spare fuel pump relay, no change. I plug in my fuel pump relay jumper wire, no change. I plug in my multimeter at the relay to check for impedance, nothing. With the key in the II position I check voltage, nothing. Everything seems to point to fuel pump being bad at this point.

I didn't have a whole lot of time to diagnose more in-depth, so I go pick up a new pump for the car, and install it. Car is originally an AWD, so it was a bit of a process installing the new pump. I took the route involving cutting an access panel.

Anyways, fuel pump system is still non-functional. What else could it be? I'm thinking of running some wires straight from the relay to the pump itself, potentially a short in the wiring somewhere? Let me know what you think. I'm out of ideas.

Post by **abscate** » 28 Sep 2016, 02:16

If you have no voltage at the pump, but voltage on the output of the fuel pump relay, it's wiring or connectors.

Where were you checking for voltage after the impedance measurement !

Post by **benpineapple** » 28 Sep 2016, 07:45

I was checking for voltage between pins 31 and 31b of where the relay plugs in to, using this thread as a guide: https://www.matthewsvolvosite.com/forums ... hp?t=52252

If I want to run new wires straight to the pump, would I run them from the fuel pump fuse directly to the pump?

Post by **abscate** » 28 Sep 2016, 08:48

You want to look for 12V at terminal 15 (one lead to pin 1, the other to ground) first.

If that is ok, look for voltage at terminal 87 (one lead to pin 3, the other to ground) as you turn the key from off to POS II. You need to set this up so you can see it as you turn the key, as I think the ECU only burps the fuel pump to get pressure, then shuts it off.

If you jump pin 1 and 3 and the fuel pump doesn't run you have a voltage supply issue.

Post by **benpineapple** » 28 Sep 2016, 10:53

Alright, I'll check for voltage at terminals 15 and 87 later. When I initially tried jumping the relay, I plugged my jump wire into pins 1 and 3 (15 and 87), and the pump still didn't run. I'll check for voltage, but I'm assuming it will show nothing based on the jumper failure.

So, if I have a voltage supply issue, where should I check? Wiring diagrams show current flows as such: Battery -> 11A big fuses -> Main relay 2/32 -> Fuse #3 ->Fuel Pump relay -> Fuel pump

I'm assuming I should be looking at power in the big fuse, and in the main relay?

Post by **abscate** » 28 Sep 2016, 11:46

You trouble shoot voltage like Salmon - you swim upstream. If you don't have 12V at Terminal 15, the jumper doesn't tell you anything. You have to find where that 12V is missing/stopped/grounded.

Post by **benpineapple** » 29 Sep 2016, 07:06

abscate wrote:You trouble shoot voltage like Salmon - you swim upstream. If you don't have 12V at Terminal 15, the jumper doesn't tell you anything. You have to find where that 12V is missing/stopped/grounded.

Well, double-checked both fuses and voltage at the main relay, with good readings. I am also reading 12V at terminal 15, but the jumper cable doesn't work. I'm thinking there is a break in the wire somewhere between pin 87 (current flows: pin 15 -> through fuel pump relay -> out pin 87 to fuel pump) and the pump. I'm going to run a wire directly from 87 to the +pos wire on the pump. If I do that, where should I run the -neg/ground wire? Should I just run it to the body (there's a grounding point on the body quite close to the access hole I cut to get at the pump)?

Thanks for all the help abscate.

Post by **abscate** » 29 Sep 2016, 07:14

You don't need to run a ground wire - just get 12V to the right place on the fuel pump.

But....first....look for 12 VDC at the pump + with the jumper wire in.

Post by **benpineapple** » 30 Sep 2016, 16:43

Alright, issue resolved. Let's tag this one solved. Ended up being the +pos wire was bad between the fuel pump and the tank insert thingy that holds the pump and the fuel level sensor. Impedance test revealed the fault. I replaced the wire, soldered it to its post, and used heat shrink wrap to coat it. Impedance tested nominal, reinstalled everything, and the car fired right up.

Thanks abscate for pointing me in the right direction. My V70 is once again roaming the streets.

b

Post by **abscate** » 30 Sep 2016, 18:11

Bravo Zulu!