'86 528e Not Starting

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Boz Scaggs
Posts: 8
Joined: Feb 19, 2023 10:09 PM
Location: America

'86 528e Not Starting

Post by Boz Scaggs »

Have a 1986 528e that has been sitting for five years and currently will not start. It turns over fine, but for some (as of yet) unidentifiable reason it won't run as is. Here is what's been done to it (in order) since it's been worked on over the past few months:

-Old gas siphoned out, new gas put in with stabilizer
-Motor oil changed along with new oil filter
-Main electrical relay tested and replaced
-Main fuel relay tested and working
-Fuel regulator replaced
-Fuel filter replaced
-Main fuel pump (under the car, near back right tire) replaced
-Spark plugs cleaned and tested
-Fuel rail taken out, all injectors cleaned and tested, replaced with new o-rings and caps

The main issue seems to be the fuel system, as the car will run on starting fluid but sputters out once it has to run on its own. The pump runs on ignition, the injectors are getting electrical signals, the spark plugs are sparking, and fuel is coming into the fuel rail and out through the regulator; yet there seems to be something preventing the engine from getting gas. Any suggestions would be appreciated.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: '86 528e Not Starting

Post by Mike W. »

Welcome to the group Boz, I liked some of your music way back when.

I would first hook up a fuel pressure gauge, either a regular automotive one of a cheapie for a ten spot from a hardware store water gauge and a couple of fittings. Assuming you have pressure I would look at the main relay. It's an unusual and unique on the car relay, often mistaken for other 5 pin relays and could cause your very problem. If it has an 87a designation on it it's the wrong relay.
Boz Scaggs
Posts: 8
Joined: Feb 19, 2023 10:09 PM
Location: America

Re: '86 528e Not Starting

Post by Boz Scaggs »

Ran a new set of tests on it today: Hooked up a fuel pressure gauge to the cold start valve just to make sure the pressure was alright (even though fuel was running through the regulator) and it consistently measured at 40 p.s.i, so that seemed to be working fine. The main relay works and gets power to everything as well.
One potential issue lay with the idle control valve, as it was difficult to tell if it was actually working and could have prevented the engine from starting. However, it worked perfectly after hooking it up correctly and spraying some carburetor cleaner through it.
The next thing to do seems to be getting a new Motronic unit in order to see if that's what's causing the starting issue. If anyone has any other ideas for why it won't start (even though it has spark and fuel), please let me know.
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: '86 528e Not Starting

Post by Aldo525 »

Have you checked the AFM??...signal/connector???

And check also temp sensor or sensor wiring to motronic....In my case (euro 525i) if you disconnect that sensor the engine shut off inmediately.
Boz Scaggs
Posts: 8
Joined: Feb 19, 2023 10:09 PM
Location: America

Re: '86 528e Not Starting

Post by Boz Scaggs »

AFM works fine, temp. sensor also within the acceptable range. I'll post an update when the new Motronic comes in and we'll see how it does.
BMWCCA2
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Joined: Feb 12, 2006 12:00 PM
Location: Central Virginia

Re: '86 528e Not Starting

Post by BMWCCA2 »

I know you think it's fuel-related but humor me and test the position sensors. Easy check with a VOM at the cable connector.
Mike W.
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Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: '86 528e Not Starting

Post by Mike W. »

Boz Scaggs wrote: Feb 21, 2023 11:16 AM AFM works fine, temp. sensor also within the acceptable range. I'll post an update when the new Motronic comes in and we'll see how it does.
I'm not saying it is the AFM, but without a test lab you can't definitively say it's good.
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: '86 528e Not Starting

Post by Aldo525 »

I know you check the injector signal (..."the injectors are getting electrical signals..")...but, are you sure they are not fully clogged???...the car was sitting for 5 years....Maybe you can ear them "clicking" but without spraying fuel to the chambers.
Boz Scaggs
Posts: 8
Joined: Feb 19, 2023 10:09 PM
Location: America

Re: '86 528e Not Starting

Post by Boz Scaggs »

We figured they might be clogged after sitting for so long, so we managed to extract the entire fuel rail and clean each injector out with carburetor cleaner. Injectors 1 through 6 all ended up working after a day of being cleaned and got new o-rings and caps. It was after we cleaned them out that we tested them to see if they were getting signal.
Boz Scaggs
Posts: 8
Joined: Feb 19, 2023 10:09 PM
Location: America

Re: '86 528e Not Starting

Post by Boz Scaggs »

BMWCCA2 wrote: Feb 21, 2023 3:04 PM I know you think it's fuel-related but humor me and test the position sensors. Easy check with a VOM at the cable connector.
Which position sensors specifically?
Mike W.
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Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: '86 528e Not Starting

Post by Mike W. »

Boz Scaggs wrote: Feb 24, 2023 10:43 AM
BMWCCA2 wrote: Feb 21, 2023 3:04 PM I know you think it's fuel-related but humor me and test the position sensors. Easy check with a VOM at the cable connector.
Which position sensors specifically?
I'm fairly sure he's referring to the speed and reference sensors, which I refer to as the flywheel sensors mounted in the bellhousing.
Sh00bs
Posts: 31
Joined: Aug 01, 2022 9:42 AM
Location: Pasadena, MD

Re: '86 528e Not Starting

Post by Sh00bs »

Boz Scaggs wrote: Feb 23, 2023 9:06 PM We figured they might be clogged after sitting for so long, so we managed to extract the entire fuel rail and clean each injector out with carburetor cleaner. Injectors 1 through 6 all ended up working after a day of being cleaned and got new o-rings and caps. It was after we cleaned them out that we tested them to see if they were getting signal.
hey man. this part right here. "working" is different from working at 100%. see if you can find someone in your area that can clean and flow test your injectors. i was just in the same boat as you and the injectors were my issue
i also replaced my plugs, wires, both fuel pumps and fuel filter.
Remember, just bc your fuel pump is getting signal and "working" doesnt mean its working correctly. you can take your fuse out of the panel and using a jump box, send 12v directly to your inline pump - that way you can take that out of the equation and confirm you're getting 12v to that new pump and "should" have plenty of fuel at the rail
after getting your injectors flow tested/cleaned, i'd do that. 2 of mine were completely clogged, 2 were firing at about 80% and the other two were around 40-50%
my cold start valve was also stuck open so i bypassed that in the fuel line

Good luck!
Arktis_Conviction
Posts: 8
Joined: Aug 21, 2014 4:55 PM
Location: New Jersey

Re: '86 528e Not Starting

Post by Arktis_Conviction »

Sh00bs wrote: Mar 07, 2023 6:12 AM hey man. this part right here. "working" is different from working at 100%. see if you can find someone in your area that can clean and flow test your injectors. i was just in the same boat as you and the injectors were my issue
i also replaced my plugs, wires, both fuel pumps and fuel filter.
Remember, just bc your fuel pump is getting signal and "working" doesnt mean its working correctly. you can take your fuse out of the panel and using a jump box, send 12v directly to your inline pump - that way you can take that out of the equation and confirm you're getting 12v to that new pump and "should" have plenty of fuel at the rail
after getting your injectors flow tested/cleaned, i'd do that. 2 of mine were completely clogged, 2 were firing at about 80% and the other two were around 40-50%
my cold start valve was also stuck open so i bypassed that in the fuel line

Good luck!
Wow! I bet it felt good getting those injectors cleaned up/replaced.
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