Help! '86 535is won't run after starting

E28 technical advice asked and given! Troubleshooting, modifications and more.
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knunger
Posts: 744
Joined: Feb 12, 2006 12:00 PM
Location: Tucson,AZ.

Help! '86 535is won't run after starting

Post by knunger »

Yep - it cranks, it fires up but dies as soon as I let go of the key. Sometimes, after 5-10 tries it will fire up and run perfect. Its getting worse - it was 2-3 tries before it would fire. When it does fire up it runs perfectly.

I replaced the main and fuel pump relays, tested the ICV, checked and cleaned the AFM flap, no help.TPS is right on.

Ideas??

Thanks
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: Help! '86 535is won't run after starting

Post by Aldo525 »

Hi, could be a lot of different issues but I'd look first:

- Fuel pump and fuel filter
- Temp sensor (ECU), connector
- Check all the electrical connections

Do you check the distributor cap and rotor??
1st 5er
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Location: Cypress
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Re: Help! '86 535is won't run after starting

Post by 1st 5er »

Crank sensors.
knunger
Posts: 744
Joined: Feb 12, 2006 12:00 PM
Location: Tucson,AZ.

Re: Help! '86 535is won't run after starting

Post by knunger »

Fuel supply is fine (I have a pressure gauge plumbed into the inlet hose). Distributor cap and rotor are fine.

The speed sensor tests fine per Bentley, but the reference sender gives 1300 ohms between terminals 1 and 2 vs. the recommended 960 ohms. Is that a big enough difference to cause my problem?

Again, I starts just fine but struggles and dies as soon as the key returns to the 'run' position.

Thanks guys!
danc
Posts: 205
Joined: Oct 08, 2010 10:39 AM
Location: Long Island, New York

Re: Help! '86 535is won't run after starting

Post by danc »

knunger wrote: Dec 02, 2022 1:14 PM The speed sensor tests fine per Bentley, but the reference sender gives 1300 ohms between terminals 1 and 2 vs. the recommended 960 ohms. Is that a big enough difference to cause my problem?
Check the crank sensors using AC on your DVM. Can't remember which is which, but there is roughly a 10-1 ratio of the voltage you should get on one sensor versus the other.
Not everyone agrees with this, but it's simple enough and it helped me find a problem.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Help! '86 535is won't run after starting

Post by Mike W. »

knunger wrote: Dec 02, 2022 1:14 PM Fuel supply is fine (I have a pressure gauge plumbed into the inlet hose). Distributor cap and rotor are fine.

The speed sensor tests fine per Bentley, but the reference sender gives 1300 ohms between terminals 1 and 2 vs. the recommended 960 ohms. Is that a big enough difference to cause my problem?

Again, I starts just fine but struggles and dies as soon as the key returns to the 'run' position.

Thanks guys!
I've found by just moving the connector end around I could get significantly different readings. And I had a bunch that tested good years ago, were put in a box and tested bad later. Try bending the cable back and forth a little bit and see what the readings are. Or swap in a spare, you've got a fleet down there in the desert, I'm guessing you have spares? :laugh:

I think the 1300 ohm reading should work, but I'm questioning/doubtful it stays at 1300.
1st 5er
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Re: Help! '86 535is won't run after starting

Post by 1st 5er »

Not sure how to test,
but ignition switch might be your huckleberry.
I've had more than one fail over the years.
chilone
Posts: 47
Joined: Jun 27, 2022 9:59 AM
Location: Colorado

Re: Help! '86 535is won't run after starting

Post by chilone »

I just got a 1984 533i for my daughter and we're experiencing the same issue. The shop we got it from said they replaced both fuel pumps, to no avail. Will be looking at sensors and ECU transistor solder joint soon.

We got it for the cost of paperwork, as they have had it for a couple of years and will be getting a mechanic's lean on it. Previous owner has reportedly passed away and they have been unsuccessful at trying to reach out to his family. They are friends of mine.
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