1998 S70 GLT Fuel pump cutting out

ferocity02 · Post by **ferocity02** » 25 Oct 2014, 14:15

The other day I went to drive my car and it started fine but after a few seconds it cut out and died. It did this a couple more times but once it was warmed up it seemed to behave better. When fully warm, it will only cut out every now and then. Sometimes it will almost die but then pick it self back up and continue at normal.

I put on a fuel pressure gauge and am getting 30-40psi at the rail depending on load. It's about 32psi at idle. When the engine dies, the fuel pressure is dropping very low, less than 10psi. Once it dies completely, the fuel pump re-primes back up to about 30psi where it will hold. I could be wrong, but I would expect fuel pressure to be in the 40's at idle.

Then I put a volt meter on the pump itself and it's getting about 13.1V at idle, but then it suddenly drops to 0V at which point the engine begins to die. When the pump voltage drops to 0V, I can also hear the fuel pump relay turn off. The pump sounds okay, it's making a faint whining sound which is normal.

When the pump cuts out, other electrical things stay working such as the radio, gauges, lights etc. I pulled out the fuel pump relay and took the cover off. It looks great inside, looks brand new.

It's almost like the computer is commanding the fuel pump to stop. Anyone know what could be the issue?

It's a 1998 S70 GLT 2.4L turbo, automatic tranny, 184K miles.\

Thanks!

Post by **erikv11** » 25 Oct 2014, 16:55

Great diagnostic work. Sounds like the fuel pump relay is cutting out. Very common problem, you can test it by jumpering the relay.

ferocity02 · Post by **ferocity02** » 25 Oct 2014, 17:26

Thanks for the reply. I bypassed the relay and didn't have any cutting out issues. So this means that either the relay is bad or the relay is getting intermittent signals.

The relay does get pretty warm. I wiggled it around while it was running and it didn't seem to cause the relay to switch off or on, it was very sporadic.

Post by **erikv11** » 25 Oct 2014, 18:07

It is a well known problem with the solder joints inside, I don't think jiggling it will simulate or trigger the problem. Eventually the relay will just stop working. I have never had it happen to my cars yet, but have a few junkyard units on hand for if it does.

ferocity02 · Post by **ferocity02** » 25 Oct 2014, 19:45

Ok thanks for the help. I bought a new relay, those suckers aren't cheap! It should be here in a few days. I'll install it and report back.

Post by **cn90** » 26 Oct 2014, 07:44

Jump 15 and 87 for now until you get the new relay.
Then keep the jumper wire in glove box just in case, don't forget the Torx keys in glove box.

ferocity02 · Post by **ferocity02** » 26 Oct 2014, 13:38

I did jump 15 to 87 to get the pump working continuously, but sometimes when I turned the ignition off and pulled out the key, the pump continued to run. I didn't wait to see if it eventually turned off, I just pulled the jumper out. Other times the pump would shut off right when I would turn the ignition off.

Anyone know what voltage the ECM it supposed to be sending to the fuel pump relay? I measured the voltage across 31(ground) and 31b(signal from ECM). Ignition on engine off is around 4.2V. Engine on is around 2.2V.

Also, is the fuel pressure I measured any cause for concern? 30-40psi seems low. Perhaps I need a new regulator. I believe it still has the original one.

Post by **cn90** » 26 Oct 2014, 15:03

- With key out, circuit #15 must be off. If fuel pump continues to run with key out, then you have problem with #15. How old is your ignition switch (the electrical part to the left of steering column)?

- Fuel pressure seems OK, how old is the fuel filter?

ferocity02 · Post by **ferocity02** » 26 Oct 2014, 19:16

cn90 wrote:- With key out, circuit #15 must be off. If fuel pump continues to run with key out, then you have problem with #15. How old is your ignition switch (the electrical part to the left of steering column)?

- Fuel pressure seems OK, how old is the fuel filter?

The electrical part of the ignition, the cylinder thing, is actually only a few months old. I replaced it because it was worn out. Very odd that the pump was still running with the ignition off.

I do not know when the fuel filter was last changed. It's probably due.

ferocity02 · Post by **ferocity02** » 29 Oct 2014, 22:52

Update: It was the fuel pump relay!

I got a replacement on eBay for $40 made by Kaehler. Threw it in and no more cutting out.

The relay that was in it looked brand new. I wonder what the issue was with it.