Testing/Experimenting with Fuel Pump Relays

Post by **SonicAdventure** » 31 Dec 2019, 08:53

I have several fuel pump relays for 850/x70 vehicles and I'd like to know how I can bench test them.

I have two red OEM 9434225 models, one is made in Germany, one is made in Hungary. The Hungary-made one came out of a '99 non-turbo V70. I believe the German-made one came out of my old '98 non-turbo V70 but I'm not 100% sure.

The yellow relay, part number 9434013, made in Germany, appears to be OEM, and came out of a '95 non-turbo 850 sedan.

I believe my cold weather 850 non-start fails are due to the fuel pump relay. When the ambient temp raises into the mid 30's, the car will finally start and stay running, usually after a semi-loud whirring or clicking sound from the area of the relay. The sound lasts about 5-8 seconds and does not reoccur until after it fails to start again another time. Then, reliably, the buzzing will happen again when it finally stays running.

I know the preferred method is to just plug in a new relay and if it runs it works, but I'd like to know how to bench test these outside of the car. As the P80 chassis is starting to dry up at the junkyards around here, I am usually now collecting these working or not whenever I come across them.

All this aside, what is the optimal relay to use in a '96 non-turbo 850?

Post by **SonicAdventure** » 31 Dec 2019, 08:55

Here are the relays I have:

Post by **misha** » 31 Dec 2019, 09:49

Yellow one is used in '95 & some '96 850 with Jetronic and M4.3 managements.

Red ones are used in some '96 and ALL '97 850 with M4.4....should also be used in '97 & '98 s,v,c,xc70 .
I don't know if yellow and red ones are interchangeable.

Post by **SonicAdventure** » 31 Dec 2019, 11:26

What about the '99 and '00 models? Are they their own thing too because of the ignition differences?

Post by **abscate** » 31 Dec 2019, 12:44

SonicAdventure wrote: ↑31 Dec 2019, 11:26 What about the '99 and '00 models? Are they their own thing too because of the ignition differences?

The 9434225 relay will fit the “ bastard “1999 and 2000 models, too.

Post by **abscate** » 31 Dec 2019, 14:58

On the bench testing, have you tried cold soaking it in the freezer for an hour?

By saying” cold soaking it on the electrical bench” you can charge $200/ hour for using engineer-speak

“ put i n freezer” is a mere $15/hour phrase

Post by **erikv11** » 31 Dec 2019, 18:32

Definitely OK to swap the relays around from newer to older P80 cars. There is nothing special about the ones in 99 and 00 cars.

Post by **SonicAdventure** » 01 Jan 2020, 18:34

Setting the multimeter to 2k ohms, red to terminal 15 and black to terminal 31, both of these red relays read ~1.75 at ambient room temp.

Removing the red covers, on the same multimeter setting, the silver caps in each relay are reading ~.44 and the brown caps in each relay are reading ~.55.

Do these sound like “in-spec” readings? I admit to being pretty new at using multimeters. I’m trying to use these as a control against what I think is a failing relay in my car, which I am about to pull and do similar tests with...

I’m also including photos of the yellow and red relays without their caps for those who might like to see what they look like on the inside.

Post by **abscate** » 01 Jan 2020, 18:39

You can test for an open relay, but evaluation the coil and pull in isn’t really possible with a VOM

You can find a really dead one, but not one that is failing on hot/ cold

Post by **SonicAdventure** » 01 Jan 2020, 20:05

abscate wrote: ↑01 Jan 2020, 18:39 You can test for an open relay, but evaluation the coil and pull in isn’t really possible with a VOM

You can find a really dead one, but not one that is failing on hot/ cold

Ok. Assuming my fail to start issues are caused by freezing temps affecting an iffy relay, if I removed the suspect relay and kept it cold, what would be the tell-tale sign, a certain meter reading in one of the caps?