Testing Fuel Pump Relay

[dan the man]

I'm looking at an 84 318i, the owner says it won't start due to a fuel problem. They've replaced both fuel pumps, and the car still won't start. They're saying it must be the fuel pump relay, though I have my doubts. So I'd like to test the relay when I look at the car tomorrow, how do I go about doing that? Thanks!

[thejlevie]

A bad relay or blown pump fuse are possibilities. A simple check, after verifying the fuse is to jumper the fuel pump relay socket If the pump runs and the engine starts, there's a problem with the relay. If the pump runs, but the engine still doesn't start, check for spark. No spark and no fuel pump operation could be:

No timing data to the DME
No power to the DME or a bad DME ground
A bad DME

[dan the man]

Jim, thanks for all the helpful info! How would one jumper the relay? Sorry if that's a stupid question, electrical problems are kind of my kryptonite.

[thejlevie]

Look at the relay and identify the contact pins from the diagram. I think it is #30 & #87, just from memory.

[ti36gold]

85 - 56 is control side (low power) and 30 - 87 is switched (high power)

85--~~~---86
30---/ ---87

Labels are also on the bottom of the relay

[dan the man]

So I just insert any wire in those pins and listen for it to make a noise/try to start it?

[ti36gold]

well you could jump 30 and 87 (car off), roll the key forward and listen for it. if it does make a noise then 30 and 87 are doing their job on the socket side... and your pump is working... assuming that it doesnt sound like some ungodly creation.

[Snou52]

What does it mean when I just 87 and 30 with the key off and the pump starts going? Sounds like its working, it's pretty loud when I just it with the key off. I have an 88 is

[richardodn]

Jumping 87 and 30 should power the pump regardless of the switch position. Power for the pump is hot at all times. Only relay control (pins 85 & 86) are switched.

[Snou52]

thanks for the help Rich

[Jcrunk]

Jumping 87 and 30 should power the pump regardless of the switch position. Power for the pump is hot at all times. Only relay control (pins 85 & 86) are switched.

so you are saying that even with nothing turned on just the battery charged up it should power the pump???

what if the ECU is unplugged? It will still power the pump up will it?

[richardodn]

so you are saying that even with nothing turned on just the battery charged up it should power the pump???

what if the ECU is unplugged? It will still power the pump up will it?

That's correct. Unswitched and unfused battery power is supplied on pin 30. Pin 87 connects to fuse 11 and from there to the fuel pumps. Jumping power across those 2 will power the circuit. I highly suggest using a fused (15A) jumper since you're connecting directly to battery power.

[Jcrunk]

That's correct. Unswitched and unfused battery power is supplied on pin 30. Pin 87 connects to fuse 11 and from there to the fuel pumps. Jumping power across those 2 will power the circuit. I highly suggest using a fused (15A) jumper since you're connecting directly to battery power.

Thanks man, im just reading things all over the place about this...

E30nostart.png

Is that correct what is said in that picture above?

My understanding is that the Mains/DME Relay has to work in order to get the Fuel Pump Relay to work...

So I have a 5 pin Fuel Pump Relay and my Mains/DME is a 4 pin also the 02 Sensor a 4pin... Everything I see are people with 5 Pin Mains/DME Relays...

I am in Australia its Euro Spec not sure if that has anything to do with it but they are the correct relays, nobody has switched them around they are actually original lol dated 1985...

What do I jump on the Mains/DME Relay box for the type I have???

Thankyou for your help

[82eye]

have you gone through the diagnostics check ? this is for m20b25 but is relevant:
Diagnostics, tips, & tricks by Jim Levie (E30 Jedi Master) (bimmerforums.com)

located in the faq.

edit : on an e you need to make sure the timing pin has not come off of the flywheel. if it has nothing you do will work until that is addressed. it's a fairly common occurrence.

[richardodn]

I am in Australia its Euro Spec not sure if that has anything to do with it but they are the correct relays, nobody has switched them around they are actually original lol dated 1985...

What do I jump on the Mains/DME Relay box for the type I have???

Thankyou for your help

What are the part numbers on your original relays? Is yours a Motronic (combined fuel injection and spark, distributor cap on front of camshaft) or Jetronic system (separate fi and spark, distributor on side of engine)? Can you post a picture of your relays?

[Jcrunk]

What are the part numbers on your original relays? Is yours a Motronic (combined fuel injection and spark, distributor cap on front of camshaft) or Jetronic system (separate fi and spark, distributor on side of engine)? Can you post a picture of your relays?

Hi there man, running a Motronic and ill post the ECU I have.... I actually bought a replacement as I thought maybe it was the ECU but seems possibly not...

Screenshot 2023-02-10 at 02-57-26 BMW E28 525e E30 325e Engine Computer ECU Bosch 0 261 200 027 .png

Thanks again guys!

[Jcrunk]

That's correct. Unswitched and unfused battery power is supplied on pin 30. Pin 87 connects to fuse 11 and from there to the fuel pumps. Jumping power across those 2 will power the circuit. I highly suggest using a fused (15A) jumper since you're connecting directly to battery power.

Ok lets put it this way,,, I did a 12v 5w test bulb on 85 on the fuel pump relay socket and got nothing!, I did 86 and got power, I did 30 and got power too... 87 and 85 no glow...

anyone know anything about this?

[82eye]

you jumper 30 and 87 to test the pumps. 30 has power.
87 and 85 have no power until the relay switches them on. that's what the relay does. 87 is connected to fuse 11.

maybe show some pics of what you are doing or working on as per richards request. we have no clear idea what you are up to.

[Jcrunk]

you jumper 30 and 87 to test the pumps. 30 has power.
87 and 85 have no power until the relay switches them on. that's what the relay does. 87 is connected to fuse 11.

maybe show some pics of what you are doing or working on as per richards request. we have no clear idea what you are up to.

What if I jumpered the wrong pins... Could I have damaged anything by doing that?

[82eye]

What if I jumpered the wrong pins... Could I have damaged anything by doing that?

it's possible but not very likely. at this point i'm not even sure what you are trying to do. car needs fuel / spark / air to fire. we're still at step 1, trying to determine if you have fuel. testing the pumps and jumping the relay is still the first thing. it's not hard.

[Jcrunk]

it's possible but not very likely. at this point i'm not even sure what you are trying to do. car needs fuel / spark / air to fire. we're still at step 1, trying to determine if you have fuel. testing the pumps and jumping the relay is still the first thing. it's not hard.

I know its not hard, but let me put this to you, jumping DME does nothing! jumping Fuel Pump does also nothing but makes the wire so hot its not normal to be that hot! Plus bits of spark from those Relay terminals!...

I stopped with that stuff because something isnt right... It shouldnt spark like that or get hot to the point of almost burning... and yes I know what I'm doing Pins 30 to 87... nothing just really hot!

[82eye]

I know its not hard, but let me put this to you, jumping DME does nothing! jumping Fuel Pump does also nothing but makes the wire so hot its not normal to be that hot! Plus bits of spark from those Relay terminals!...

I stopped with that stuff because something isnt right... It shouldnt spark like that or get hot to the point of almost burning... and yes I know what I'm doing Pins 30 to 87... nothing just really hot!

if you jumper the relay and don't hear the pumps or have another result then start with the pumps and tank. if the car sat long enough the fuel will have turned to varnish and would result in clogging the lines / pumps and possibly burning one or both. remove the in tank pump, and check both it and the condition of the fuel
left in the car.

[Jcrunk]

well I must say I never did that, and I actually put about 30 litres into it a couple of months ago now...

you really believe it could be that? I have read that some people just needed to unclogg the filter on the intank pump and that was it... However if no power gets to the pump that is basically pointless...

Today im going to test that the actual fuel pump wires are getting there with power... so Bulb Across Fuel Pump test I will do next...

[Jcrunk]

Something I want to also get to is the fact you say that everything could be clogged and bad and all that... Im trying to get the Fuel pump to start, that's all I really need to do. I know the car will start once I get fuel going...

There is spark on all... I have tested coils and everything,,, its either the Igniton Switch the Fuseable Link , Grounding Straps or the unknown...

So let me put this to you then... if the Fuel Lines and stuff are clogged could that possibly make the Pump not Engage? Could that be giving me back the sparks and hot wire when I try jump??? Because its clogged and built up its trying to really really push itself, causing some type of weird spike or overload.... Could that be the case???

[82eye]

Something I want to also get to is the fact you say that everything could be clogged and bad and all that... Im trying to get the Fuel pump to start, that's all I really need to do. I know the car will start once I get fuel going...

There is spark on all... I have tested coils and everything,,, its either the Igniton Switch the Fuseable Link , Grounding Straps or the unknown...

So let me put this to you then... if the Fuel Lines and stuff are clogged could that possibly make the Pump not Engage? Could that be giving me back the sparks and hot wire when I try jump??? Because its clogged and built up its trying to really really push itself, causing some type of weird spike or overload.... Could that be the case???

it'll burn the pumps out. i'd have a look at them.