W124 '88 300TE fuel pump relay failure? - PeachParts Mercedes-Benz Forum

pifcat2 · #1 05-19-2009, 07:36 PM

To verify the pump works, I disconnected the fuel line to the distributor and jumpered sockets 87 & 30 and got gas flow into a container. When I installed both relays, no gas flow.

Background: I replaced the engine in the TE and it ran fine for a couple of days before suddenly turning over but not starting. I replaced the aftermarket KAE with a relay I purchased from the dealer 3-4 years ago for the donor car which ran fine up until I removed the engine a few months ago. Both of these relays do not trigger the pump.

Is there a way to test the relay? What can cause a relay to fail? I don't want to put in a new one and have it short or burn out. Replacement OEM costs $270 at the dealer or $120 aftermarket KAE)

Additionally the aux fan comes on when I turn the ignition key.

ps2cho · #2 05-19-2009, 08:00 PM

You can get them on ebay for under $40 and I may actually have a spare one that works if you are interested that I'd give away real cheap.
Obviously I can promise you the one works as I swapped it into my 88 300TE in a cheap attempt to rule it off the rough idle list.

If you are electrically-inclined...you can always pull it apart and check to see if there are any cracked points and just touch them up with solder to see if that fixes it. I have done that with both the electrical relays for the wipers + multipurpose and it fixed most of the problems I was having.

pifcat2 · #3 05-19-2009, 08:53 PM

Quote:

Originally Posted by ps2cho

You can get them on ebay for under $40 and I may actually have a spare one that works if you are interested that I'd give away real cheap.
Obviously I can promise you the one works as I swapped it into my 88 300TE in a cheap attempt to rule it off the rough idle list.

If you are electrically-inclined...you can always pull it apart and check to see if there are any cracked points and just touch them up with solder to see if that fixes it. I have done that with both the electrical relays for the wipers + multipurpose and it fixed most of the problems I was having.

I found another spare relay that didn't work so I suspect it's in the wiring. I don't have other pre-90 W124s to confirm these relays are good. For a relay to switch, the low voltage circuit from the ignition must work. I need to find the schematic...

Arthur Dalton · #4 05-19-2009, 09:11 PM

Your Jumper 30/87 is only jumping the load contactor set in the relay and that test only verifies FP....the relay circuit needs the coil to pull in the contactor, which is the relays sensor/low amp side.

So, what you want to be checking is if you have 12v at pins 15+ and 31 neg . w/key in RUN position.
If NO, then check fuse # 7 ...........

Check the plug on the blu 2 wire sensor..if that is a poor connection, high aux fan will default to RUN.

pifcat2 · #5 05-19-2009, 11:05 PM

Quote:

Originally Posted by Arthur Dalton

Your Jumper 30/87 is only jumping the load contactor set in the relay and that test only verifies FP....the relay circuit needs the coil to pull in the contactor, which is the relays sensor/low amp side.

So, what you want to be checking is if you have 12v at pins 15+ and 31 neg . w/key in RUN position.
If NO, then check fuse # 7 ...........

Check the plug on the blu 2 wire sensor..if that is a poor connection, high aux fan will default to RUN.

Thanks Arthur, I have 12V at 15+ and 31-. I also have 12V at fuse 7. Maybe it is failed relay(s)...

Ivanerrol · #6 05-19-2009, 11:50 PM

Could be a bad earth also.
There is an earthing point close to the IACV valve on the manifold.
Make sure that this earth is free from corrosion - includes the bolt and screw in hole.

pifcat2 · #7 05-20-2009, 10:02 PM

Quote:

Originally Posted by Ivanerrol

Could be a bad earth also.
There is an earthing point close to the IACV valve on the manifold.
Make sure that this earth is free from corrosion - includes the bolt and screw in hole.

I found that ground not connected to the chassis and when connected, it started and ran for about 15 minutes then died!

pifcat2 · #8 05-20-2009, 10:04 PM

I replaced the ignition control module with one from my donor car and it ran for 20 minutes so I drove it to my mechanics shop to get it smogged. Their machine was down so when I drove it home it died. I called a tow company and before they showed the car started and I drove it home. I'm still perplexed...

Arthur Dalton · #9 05-20-2009, 10:08 PM

If you have a set of jumper cables , run one cable from the battery Neg with the other end on a good solid ground on the engine and retry.

pifcat2 · #10 05-21-2009, 03:34 AM

Quote:

Originally Posted by Arthur Dalton

If you have a set of jumper cables , run one cable from the battery Neg with the other end on a good solid ground on the engine and retry.

Ok, I'll have to scrounge for some since I haven't needed any since buying a porta-battery. I'll recheck the engine ground too. Can a bad ground heat up and make a poor connection worse?

Since I brought my car home (and the evening was cooler) I can start it every time and it turns over immediately. Prior to that the engine died after 20 & 45 minutes of running. The last time the engine cut off while I was turning and luckily I avoided head on traffic and cranking the powerless steering before coasting to a stop...