1997 Volvo 855 GLT Misfires (P0300, P0301,... ) at hot start

Post by **jreed** » 02 Apr 2014, 18:53

Today after a hot restart I noticed the car idle dipping from 800-1000 rpm down to about 500rpm and the engine nearly stalling. I could hear sound from the fuel pump changing pitch and getting slightly quieter and lower pitch.
I pulled the codes and got: P0300 (multiple misfires), P0301, P0302, P0303, P0304 and P0305.

I'm suspecting the problem could be the fuel pump relay or the fuel pump. I did replace the capacitors in the fuel pump relay a couple years ago with some 105C rated ones.

My next plan of attack is the use a jumper on the fuel pump relay socket to bypass the relay, in case the relay is bad. Does this seem like the best thing to do next?

Post by **cn90** » 02 Apr 2014, 19:08

Sure, good method.

BTW, I made a jumper wire with in-line fuse. I posted photo in that Fuel System Troubleshooting DIY.

Post by **mecheng** » 03 Apr 2014, 11:48

Yes and check the solder points on the relay. Honda's had the same issue as Volvo, the solder points for the coils did not have enough solder and cracked. It is easy to fix yourself; melt more solder.

Post by **jreed** » 03 Apr 2014, 12:03

Thanks. I will check out the solder joints.
This morning I took out the relay and made a little jumper wire to connect 87 and 15. Now the fuel pump comes on and stays on when the key is in position II, rather than running for a few seconds and then turning off. I haven't had a chance yet to get the car really warmed up and then test to see if it still misfires during a hot restart -- hopefully later this afternoon. Thanks again!

Post by **jreed** » 04 Apr 2014, 04:49

With fuel pump relay jumper wire installed, I got the car nice and warmed up yesterday afternoon. I stopped it and let it soak in the heat for about half an hour and then tried to restart... it ran totally smoothly with no misfires and no idle fluctuations. I repeated the test yesterday evening and it was the same: no problem. So, I think the fuel pump relay must have failed. I'm going to order a replacement. Thanks again for your advice!

Post by **jreed** » 04 Apr 2014, 05:44

I opened up the fuel pump relay and inspected the solder joints... One of the joints has a crack. This joint had a crack in it the last time I opened up the relay a couple years ago. At that time I added some fresh PbSn solder and reflowed the joint to repair the crack, but it didn't make for a lasting repair.

: Solder joint for the coil actuation wire -- cracked again!; Fuel Pump Relay Volvo 850 crack.jpg (133.6 KiB) Viewed 1285 times

Post by **mecheng** » 04 Apr 2014, 07:15

Its usually the coils because they are relatively heavy so they have a lot of momentum and force applied to the joints. If it failed again, I would suck up the old solder, clean with a bit of rubbing alcohol and re-solder

Post by **cn90** » 04 Apr 2014, 09:08

The relay is expensive, about $50 at dealer.
Best is to get some old relay from junk yard for cheap, and yes keep the jumper wire in the glovebox.
This jumper wire will get you home if you are stuck in the middle of nowhere with a bad relay.

Post by **jreed** » 05 Apr 2014, 15:29

I removed the solder from the cracked joint, applied some fresh solder and then glued the relay frame to the circuit board using glue. Hopefully this will make for a more lasting repair.

: Solder removed with 'solder wick'; Solder Removed.jpg (177.31 KiB) Viewed 1276 times

: New solder applied to joint; New Solder.jpg (214.66 KiB) Viewed 1276 times

: Hot glue applied between the relay frame and the circuit board; Hot Glue applied.jpg (202.38 KiB) Viewed 1276 times

Post by **jreed** » 09 Apr 2014, 17:40

Yesterday the new fuel pump relay arrived. I took it apart today to see what was inside. The case has a clip on each side that you spread and then you can slide off the case.

: Opening up for inspection; Taking apart new relay.jpg (197.23 KiB) Viewed 1271 times

One of the capacitors has a 105C rating. I'm not sure about the "K" and "M" markings but they may be the tolerance of the capacitance value, K being 10% and M being 20% according to Wikipedia:
http://en.wikipedia.org/wiki/Capacitor# ... r_markings

: Relay capacitor rated for 105C.; New Relay 105C rated cap.jpg (191.35 KiB) Viewed 1271 times

I took a look at the solder joints on the relay frame. These were the joints that on the original relay developed cracks after ~15 years (the first time) and after ~2 years (the second time after an ineffective repair that I attempted)

: Solder joints on relay frame; Joint inspection.jpg (183.46 KiB) Viewed 1271 times

I inspected the back of the board and saw three red dots. They didn't appear to have an electrical function. Then I noticed that the IC and the resistors, chip caps and diodes on the board also have the red material underneath them. I think the red material is a type of adhesive used to hold the components in place to improve their ability to withstand shock and vibration. Or maybe to hold them in place during the solder reflow process. The red adhesive is not visible on the front of the board. On the old board it was the relay solder joints that failed -- maybe they should be applying the adhesive to the relay frame as well to prevent fatigue of the solder joints.

: Three dots on the back of the board -- mystery indicator; Three red dots.jpg (158.63 KiB) Viewed 1271 times

Finally I checked out the relay contacts. I haven't seen brand new relay contacts in a while. These looked silvery and smooth.

: Brand new relay contacts; New Relay contacts.jpg (221.17 KiB) Viewed 1271 times

I'm going to install the relay tomorrow or the day after... hopefully I'll get the same ~15 year lifetime out of this one as the first one!