80 320i E21 Fuel Problems - think it might be fuel relay switch

[aflacsonke]

Good Afternoon:

I have a 320i that I gave to my sister. She has had the car for about 2 years now but doesn't drive it very much. I was having my car worked on and decided to borrow the 320i for a week or so. On day two of borrowing the car, I had some issues which are described as follows:
- On Monday, I drove to the gym. When I got in the car to come back home, it started a little rough but after reving the motor, it seemed fine, I went to back up and the car just died like someone turned off the ignition. When I went to restart the car, it wouldn't restart. I waited about an hour and the car started again. I was able to start the car and half way home the car just cut out again like the key was turned off. I waited another hour or so, got the car started and got it home. When I got home, I shut the car off and then tried starting it again. It started right up.
- Thinking that the car was alright and that maybe there was some sort of clog in the fuel system that worked its way out, I decided to take the car down to the post office but leave it running just in case. When I came out the car had died (within about 5 minutes) and would not restart. I didn't have time to deal with it any more so I parked it in a nearby parking lot and came back to it today (Thursday). It started right up and I drove it home. When I got home I turned it off and promptly restarted it. It started right up.
- I had to go back to where the car was originally parked as I left my other car there. I ran down there (about 20 minute run) and drove back (5 minutes). On my way back into the house, I tried to start the BMW again and this time it wouldn't start again. What was really wierd was that the other times after I would try to start it and backed off the key to turn it off, I would hear the fuel pump run for about 2 seconds. Now what seems to be happening is that the fuel pump keeps on running as soon as the key is engaged but before the car is started. It doesn't shut off after 2 seconds like normal but keeps on running. The car trys to start but has clearly flooded itself.

At first I thought maybe it was the warm up regulator. Now I am thinking it may be the fuel pump relay switch. Both fuel pumps were replaced about 3 years ago and the car has maybe 10K miles since. I checked the other fuses and they are all looking great. The cold start value and thermo switch have both been replaced in recent years. Also the ignition switch was replaced in recent years as well. Any ideas?

I really appreciate your help - sorry for the long thread but figured the additional information might help. - Marty

[cheap320i]

Marty, My daughters car had the exact same symptoms, turned out to be the pickup coil (pulse generator) inside the distributor.
Have you checked for spark?
Mike

[Zan320]

Definately check your fuel pump relay and make sure that it is making a good connection. I had a problem similar to this once where my car would just die when driving/ideling. Turned out it was a bad relay connection. Also make sure the fuel relay is not sticking on, that could keep the pump running.

[aflacsonke]

Is the fuel relay different than the fuel pump relay? - Marty

[aflacsonke]

I just got it started again and the fuel pump has stopped running continuously while the car is off. The car is running really rough most likely because of the excess fuel from earlier still in the system. I ordered two relays from Bavarian Autosport. I ordered a new fuel pump relay item number 1363827.2SHO or SK 6460 and I ordered a 5 prong 332204401 as that seemed bad as well. The 5 prong relay is the one right next to the fuel pump relay. Any idea what that one does? This particular relay is on the outside of the fuse box just like the fuel pump relay switch (not on the row of other relays with the fog light relay, high beam relay, relief relay, etc). I plugged this particular relay into the high beam relay and low and behold the high beams and low beams didn't work. It is the exact same relay switch so my conclusion is that this particular relay is bad.

I also noticed some other "relay" type devices about mid way down the firewall towards the rear of the engine compartment. Any idea what those are and what they do? Thanks - Marty

[Zan320]

Hey Marty, The fuel relay is the same thing as the fuel pump relay. That relay is #3 which is on the outside of the fusebox. The one right next to the fuel pump relay is either the "change over contact signal" or the diode relay- which protects transistors when a relay switches off. Your probably right about that relay being bad. Chances are there both bad.
The relays along the firewall are speed switch, relay starter motor,& hazard warning relay.

[aflacsonke]

Thank you for your help everyone. Hopefully the relays that I ordered will solve all the problems and the car will be operational again. I will find out within the next 5 days as the parts are on their way. Marty

[jrcook320]

The 5 prong relay is the one right next to the fuel pump relay. Any idea what that one does? This particular relay is on the outside of the fuse box just like the fuel pump relay switch (not on the row of other relays with the fog light relay, high beam relay, relief relay, etc). I plugged this particular relay into the high beam relay and low and behold the high beams and low beams didn't work. It is the exact same relay switch so my conclusion is that this particular relay is bad.

I also noticed some other "relay" type devices about mid way down the firewall towards the rear of the engine compartment. Any idea what those are and what they do? Thanks - Marty

Your fuel pump running constantly won't cause the car to flood itself. You can jumper the fuel pump so it runs whenever the ignition is on (motor not running) and try to start the car 20 minutes later with no problems, fuel is not injected unless the sensor plate moves which only happens if the motor is cranking or running.

Hey Marty, The fuel relay is the same thing as the fuel pump relay. That relay is #3 which is on the outside of the fusebox. The one right next to the fuel pump relay is either the "change over contact signal" or the diode relay- which protects transistors when a relay switches off. Your probably right about that relay being bad. Chances are there both bad.

The relay next to the fuel pump relay is the relief relay. It disconnects power to various hi amp electrical components while the starter is cranking. If it's not working it COULD be sapping the ignition system of the juice it needs to fire the motor while cranking, but I don't think this would make the car stall while running. I'd have to carefully study a wiring diagram to be sure. I've never seen a diode relay on an e21 wiring diagram.

When the car dies does the fuel pump run at all? If it's just the pump not running then it could be a bad connection/fuse box issue or a bad pump relay.

Do you lose your gages as well? If so I would be suspect of your ignition switch that was replaced recently. It's very difficult to replace the ignition and it's easy to damage the plug. If you have a damaged plug that loses contact then you'll loose ignition and the fuel pump at random.

The only relays on teh firewall I know of (on a post '80 320i) are the speed relay, which closes above 3500 rpm in series with the WOT switch to send the computer into open loop mode for max fuel enrichment, and a relay next to it which is part of the warm start recall.

[GDAus]

"I'd have to carefully study a wiring diagram to be sure. I've never seen a diode relay on an e21 ."

Hmmm .. it depends where you look .. by that I mean, not on US spec models .. and the relay refered to is on the outside of the fuse box towards the front ... so if it is a purely US spec car then it is probably the Lamba relay .... but maybe it is a Euro spec car ... I've seen a few reference here to euro models in the US .. if that is the case ..then it is a diode relay.

The main reason for the diode(s) .. yes there a few different types with 1 or more diodes ... is to provide a "latching" circuit to keep the relay coil energised after the ignition switch returns to the Run position after the relay coil is initially energised by the start circuit. Some diode relays have extra diodes to act as a "buffer" circuit to control switching transients (voltage spikes caused by the relay contacts opening).

In the case of Australian spec cars (which are basically RHDrive Swedish spec .. it's all about the anti-pollution stuff), the diode relay on start energises the Heat/Time Switch so the Cold Start valve works ..and the heating elements in the Aux Air slide and the WUR and also provides power to the Fuel Pumps until the ignition pulses are fed to the Fuel Pump Relay.

When the H/T switch opens ... the relay drops, out but there is another circuit with a temperature switch that senses the external engine temperature to keep the heaters going in the Aux Air Slide and the WUR until the outside engine temp is high enough to to keep these bits at their normal working temperature.

But I have noticed from stuff I have read ... there are a few different ways all this works depending on what market the car was originally sold in ... so first do a VIN number check to get info on the particular car ... then the fun starts to find the right info

Cheers

[aflacsonke]

This is a US based car. To answer jrcook320 question, when the first problems were noticed it didn't seem like the fuel pump was switching on. The most recent problems had the fuel pump not switching off at all but running continuously which seemed to flood out the motor. I never lost any of the gauges at all. The only thing that seemed to happen was that the motor just cut out while driving.

FYI to anyone that ordered a fuel pump relay or a 5 pronged relay from Bavarian Autosports, it is on severe back order right now. They said that I should not expect to see the parts for 2 weeks. Nice that they tell you that on their website when ordering. I checked with my BMW mechanic to see if I could get the parts from him. He quoted me $87 for the fuel pump relay, which I received a price of $37 through Bavarian and $15 for the 5 pronged relay which I received through Bavarian for $8.99. If all I needed was the 5 pronged relay I would have gladly paid the difference but for $50 more on a car on my sister's car, I figured she can wait a couple of weeks. The car is parked at her school most of the time anyhow. - Marty

[BruceH]

Call Harrison Motorsports in Atlanta. He'll get you the correct relay for much less. 678-879-1200

[Layne]

Did you try jumpering the relay? I don't think it is the problem, and this way you can find out for free.

[aflacsonke]

Hi Guys:

Well I was hopeful that the fuel pump relay was my problem. There is a mechanic in a local networking group that was able to order the relay for me and have it the same day for the same price as Bavarian charged. He showed me what the retail price was and gave me his wholesale price; very nice of him. Now I know that the BMW mechanic that I have, who is very good at what he does was charging me $50 profit on the part.

Well anyhow, I installed the fuel pump relay and figured I would take the car for a spin. Bad choice as the car just cut out about an .125 of a mile from my home. That is two hours of my life that I will never get back.

So here is the problem that I am noticing now. The problem that was happening before is happening again in that when you turn the key to the on position without starting the car, the fuel pump continuously runs. The car when cold starts up relatively well and stays running. However if you drive the car, when it gets warm, it cuts out and leaves you stranded until an hour or two later (once the car cools off it seems). When you try to restart the car while warm, it starts but the idle keeps dropping and it sounds like the motor is being flooded because it backfires and acts like it is getting choked. Eventually this causes the motor to die. Waiting 20 minutes or so will allow the car to start, then die a slow death as the motor gets flooded again, backfires and finally dies.

I am used to the fuel pump shutting off after about 1.5 seconds once you turn the key to the "on" position without actually cranking the motor. Now it seems to just stay on which I think is leading to the flooding problem. Additionally, the gauges are acting really weird when the key is turned to the "on" position without cranking over the motor. It seems that as the fuel pump keeps pumping, the tach in particular starts out showing 1000 RPMs then flutters down until it hits the bottom of the tach at 0 RPMs and continues to flutter down there.

My wife and I went back about 2-3 hours after the car died and was able to start it and drive it back the .125 mile home. What I noticed from driving it home was that it seemed the car was still getting flooded. I had to keep feathering the gas but the car ran really rich (gas smell was like driving a car from the 1950s with no tune up and a ton of unspent fuel being thrown into the air). Top speed was about 30-40 miles an hour.

At this point I have no idea what the cause of the problem is but have observed the car enough to know exactly what the results are. My guess is that some sort of sensor is telling the fuel pump to continuously run at the starting position (almost as if the car is already running) and once started telling the fuel pump to pump more gas than what is needed (almost like when you have the pedal floor boarded) causing too much fuel and not enough air to ignite the fuel being pushed into the motor. Any ideas what the cause may be?

[E21Adam]

Your fuel pump running constantly won't cause the car to flood itself. You can jumper the fuel pump so it runs whenever the ignition is on (motor not running) and try to start the car 20 minutes later with no problems, fuel is not injected unless the sensor plate moves which only happens if the motor is cranking or running.

Aflacsonke, Listen to what this man says. He knows his stuff. As do most of the other people here. If I were you, I would put the idea of a bad fuel system causing the problem aside. You may not be getting a proper signal coming from the distributor, causing incomplete combustion due to lack of spark. If you look on the back of the distributor, you should see a thick green wire. This is actually the wire that sends the signal to the fuel pump relay (among other things). It may be ripped up a bit, causing the signal to become erratic and eventually leading to the car dying. This is essentially what happened to me when I replaced my head gasket on my 83 a couple of years ago. I forgot to disconnect the wire and when I pulled the head off, it ripped the wire a bit. It could also be some other problem related to the impulse sender. Here, these should explain how the system is set up.

[aflacsonke]

So I started the car this afternoon, got it nice and hot so that eventually it would stall out and shut itself off like it has been doing in previous posts. After this occurred I had a friend listen under the hood as I turned the key. The same thing happens as before than when it is warm and you turn the key you can hear the fuel pump going non stop. One thing that I didn't realize as I was not able to turn the key and listen under the hood at the same time is that there is this constant clicking that starts fast and slows to a slower click under the hood at the same time that the fuel pump is continuing to run. Keep in mind that we just turned the key to the on position but did not try to start the car. The clicking noise is coming from the passenger side towards the firewall. It sounds like it may be coming from the distributor but it is inconclusive.

I checked all the wires leading off of the distributor and they all seem like they are intact. Of course with a car this old the wires don't seem new at all but there wasn't anything that was glaring at me.

Could this be the impulse sender that Adam mentioned in the last post? Do you know if the clicking is normal when the impulse sender goes out or could that be something else?

[Layne]

The clicking is the frequency valve. Nothing to worry about. It's not supposed to be running, but thats a side effect of the pump running. The fuel pump running all the time will not do any harm, but indicates that someone has messed with the wiring. Possibly jumping the relay under the relay socket, or powering it from another source. None of this has anything to do with your running problem.

[Layne]

My guess is that some sort of sensor is telling the fuel pump to continuously run at the starting position (almost as if the car is already running) and once started telling the fuel pump to pump more gas than what is needed (almost like when you have the pedal floor boarded) causing too much fuel and not enough air to ignite the fuel being pushed into the motor.

This is not at all the way the system works.
The pump runs at full capacity any time it is on. It is always on when the engine is turning. Fuel goes past a pressure relief valve and back to the tank. The fuel distributor then lets some fuel out of that system and into the engine. If the pump never shut off again for all time it would not flood the engine.

[unicyclemichael]

I am having this exact problem on my 1978 320i. So far I have replaced both fuel pumps, cleaned the spark plugs, I went through all the vacuum diagrams and put every thing back to where it should be (there were a few disconnected hoses). The car will run idling for a long time, but as soon as I drive it, I get about 1/8th mile and it loss all power and dies. I have checked the things mentioned here with no luck and a few questions:
- There are no green wires coming off the distributor, just 2 black wires going to the condenser (plus the 5 on top, of course)
- I cannot locate a fuel pump relay, does the '78 have one?
- There is a connector on the mixture regulator cover, under the intake cowl. Nothing is connected to it. Should there be?
- The baffle plate is about 1/32 - 1/16 inch below where the taper starts. Is this too low?
- The voltage across the ignition coil is 8 volts and the coil gets pretty warm. Is this normal?

These are things I am checking because I am out of ideas. Many thanks for any suggestions or information.

[GDAus]

I am having this exact problem on my 1978 320i. So far I have replaced both fuel pumps, cleaned the spark plugs, I went through all the vacuum diagrams and put every thing back to where it should be (there were a few disconnected hoses). The car will run idling for a long time, but as soon as I drive it, I get about 1/8th mile and it loss all power and dies. I have checked the things mentioned here with no luck and a few questions:
- There are no green wires coming off the distributor, just 2 black wires going to the condenser (plus the 5 on top, of course)
- I cannot locate a fuel pump relay, does the '78 have one?
- There is a connector on the mixture regulator cover, under the intake cowl. Nothing is connected to it. Should there be?
- The baffle plate is about 1/32 - 1/16 inch below where the taper starts. Is this too low?
- The voltage across the ignition coil is 8 volts and the coil gets pretty warm. Is this normal?

These are things I am checking because I am out of ideas. Many thanks for any suggestions or information.

Ok ... firstly .. this a link for electrical circuit diagrams on JT's website

http://www.jtresto.com/e21info.htm unfortunately there is a '77 and a '79 circuit but no '78 ... the difference i see first off is that the '77 has only one fuel pump ... by '79 there is the in-tank pump as well so use that one.

But on a '78 you would have a "points" type distributor unless someone has done an upgrade .. the posts before your's were refering to the transistorised ignition system on post '79 models and the wiring colour codes changed for the models from '80 onwards.

So .. your distributor should have 2 black wires from it.

Fuel pump relay should be a big one hanging off the engine side of the fuze box I think .. that is where it is on later models

Don't know

Yep .. the moving plate in the Air Flow Meter (AFM) should be aligned with the start of the taper.

8 volts is correct across the coil of a points type ignition system .. the coil is actually an 8 volt coil and uses an external ballast resistor to work with 12 volts ... however, the ballast resistor is a section of the wiring harness leading to the coil and isn't obvious


But .. what about your points gap and ignition timing ? and any indications from the spark plug's colour as to the rich or lean mixture problems ?

[pyeman]

i had the same issue with my 320 and turned out to be the rotar button and distributor cap worn..try getting someone to carefully wobble ur distributor cap as u try to start it..if it goes do it again while its going and see if it afects it at all..worked for me any way!

[Layne]

- There are no green wires coming off the distributor, just 2 black wires going to the condenser (plus the 5 on top, of course)

There are no green wires on the pre-80 models

- There is a connector on the mixture regulator cover, under the intake cowl. Nothing is connected to it. Should there be?

Nothing needs to go there.

[unicyclemichael]

Thanks for the link to JT's site. That was helpful. I adjusted the baffle plate, and then the mixture. It idles and runs better, but still dies after a little driving.

The spark plugs were, and are again after not very much running, shiny black. The Haynes book says it could be piston rings. I don't think that it is too rich because it still backfires when I give it 1/2 or more throttle (I thought that was an indication of too lean). The spark looks white when I crank the engine with the plug out.

I have not checked points gap or ignition timing, I need to educate myself on this. The rotor cap and button look good, in fact the whole distributor looks new inside.

I did identify the fuel pump relay from the wiring, the cover for the fuse box said timing switch, so that confused me. When I took it out and put it back in, the car would run again (and drive for another 1/8 mile), so maybe I should look into that...

[vazqued2]

Did you ever identify and correct the problem?

[unicyclemichael]

No, I am still having the same problem. I have replaced points, condenser, and spark plug wires. I have timed it, adjusted mixture and idle speed. I have reviewed vacuum diagrams and looked for leaks. I have cleaned the spark plugs again. All this since my last post, and no luck. I still lose all power (not starting with that much) after about 1/8 mile.

If anyone has insight or wants to buy the car for $750 PLEASE let me know. 1978 320i, 168,000 miles, new fuel pumps, new battery, new stuff listed above...

[rcavanau]

I'm having this problem too. Changed points, plugs, condenser, installed electronic ignition, changed relay. Nothing worked. Car runs fine with the relay jumpered. I'm wondering if the tachometer could be affecting the tach pulse and killing the send to the fuel pump relay. Anyone know?

ps - i MONITORED VOLTAGE TO THE FUEL PUMP FROM THE RELAY AND WHEN IT STALLS, THE VOLTAGE IS INTERUPTED.