Not the AFM but what?

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Hefeweizen
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Not the AFM but what?

Post by Hefeweizen » Thu Apr 19, 2018 9:44 am

I thought that my AFM (Part #13621359641 -Bosch #0280203002) died since it looked like it no longer sends a signal to the double relay (1979 M90 L Jet engine) and hence the car does not run anymore.

I do have continuity from the battery to the fuse box and again to the double relay and continued from the double relay to the fuel pump. If I jump the two connections by the double relay I get a humming from the fuel pump. I understand that the AFM is supposed to send a signal to the double relay which kicks on the power that gets the engine going when the flap opens in the AFM and it's also supposed to click. Well, it does click but still no power to the pump. The thought that the DME is busted, since it smelled burned had crossed my mind but according to the diagram the DME has no say in this.

Had the AFM open. Everything looked OK. With the ignition on I got power to port 39 and when I open the flap power goes over to 36. So the micro switch seems to work. I checked continuity from both wires to the double relay and we have continuity. I have an old double relay in and also connected the new relay and still nothing. Lack of ground on 6 maybe? Is there any other item that would enable the power to the pump?

So from the way it looks the AFM is good. I get 12V to the AFM and when the flap is opened 12V go out. I measured at the connector by the relay. I can also hear the click at the relay. There is ground at #6 at the AFM but only when the ignition is on. So from the way it looks the circuit is good there. Does the DME provide input to the fuel pump power cicruit?

I ordered a DME, it arrived and I could not wait to plug it in. Plugged it in and measured for voltage at the pump. YES!!!! I had what it takes! I put the thermostat housing back in (had to change the thermostat since it was stuck in the open position due to the PO sticking a screw in there). Had some complications since some of the screws broke due to old age and me beasting around (unrelated issue). Strange thing is that for a while I have power at the pump regardless of ignition on or off and flap at AFM open or closed. Did not last long though).

The car sat there for a while and when I tried it would not start anymore nor did I have current going to the pump. If I apply 12V at the pump (bypassing everything going straight from the battery to the pump), the car runs fine and as soon as I disconnect the power.

Harness in itself?
Rainer

1980 633 CSi Project car
1985 635 CSi Daily driver

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maybeillbuyit
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Re: Not the AFM but what?

Post by maybeillbuyit » Fri Apr 20, 2018 1:49 pm

OK I'm going to offer my advise even though you obviously are way ahead of me in technical diagnosis skills. It sounds to me like your problem is intermittent. IE power to pump sometimes. Could it me the combination relay? I have taken the older style combo relay apart on my 79 e24. Its the old metal style. Inside are the two switches that provide power to fuel pump and ( can't remember exactly off the top of my head) Anyways I pried the relay apart and it was quite dirty with lots of carbon dust all built up everywhere. All the contacts were very dirty. I cleaned it all and the car started up much more quickly than it had before. Mind you I never had an actual problem starting it. I was just curious what was going on inside the relay. I also have a spare. My .02 cents good luck with it.
Edit, So as usual I reread your post and I see you have tried a new relay so I guess my idea doesn't do much good
1977 530i another project
1979 635csi Euro "project"
1987 635csi

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10ringarcher
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Re: Not the AFM but what?

Post by 10ringarcher » Fri Apr 20, 2018 8:39 pm

I had a similar issue. I remember getting stuck on the side of the highway and crawling underneath the car to run a wire from the fuel pump to the battery. The car started and I made my way home. Check the connections and contacts at the ignition control module. Mine was not plugged in all the way. It took me forever to find the problem. Hope this helps.

01 CONTROL UNIT TRANSITORIZED IGNITION 1 08/1978 12141267415 $1199.70 ENDED

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Hefeweizen
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Re: Not the AFM but what?

Post by Hefeweizen » Sat Apr 21, 2018 9:06 am

Thank you all for your input. I have to admit that I have not checked the red cable going directly (well, via the ignition switch) to the double relay (http://www.house-calls.us/images/1980_633_EL123.jpg). This is after all where the power comes from. I'll check that and report my findings later.
Rainer

1980 633 CSi Project car
1985 635 CSi Daily driver

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Hefeweizen
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Re: Not the AFM but what?

Post by Hefeweizen » Sat Apr 21, 2018 1:05 pm

Red cable has power :( Would have been too easy!
Rainer

1980 633 CSi Project car
1985 635 CSi Daily driver

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528i-1981
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Re: Not the AFM but what?

Post by 528i-1981 » Wed Apr 25, 2018 4:38 am

I had some very strange electrical behaviors and had overlooked that the charge indicator light was dark when the key was in the ON position before starting. It turned out to be the voltage regulator. Once I figured that out and thought to check the voltage from the system while the car was running, I saw it was at 12V not 14.4V. She was very unhappy running at 12V. The fact that the pump was getting voltage all the time after you plugged in the new combo relay makes me think it's not the harness. God luck!
(oo=00=oo) Eric
1981 528i Manual

PatinaBeforePolish
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Re: Not the AFM but what?

Post by PatinaBeforePolish » Mon May 14, 2018 2:04 pm

Hefeweizen,

I posed this question in another thread but haven't seen any replies so sorry for slightly changing the subject on this one. Are you able to determine from the wiring diagram the routing of the 7 wires in the plug at the MAF? I see some go to the ECU and some to the multi-relay but am not knowledgeable enough with wiring diagrams to determine the exact routing. I replaced the plug and rubber housing on MAF connector and mixed 2 or more of the pins. My car runs great until I plug in the MAF connector. And it ran perfectly before. Any help is greatly appreciated!
78 F150
79 528i
81 528i parts car
01 540i
86 944
08 X3 don’t judge me it’s there to preserve the others

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