New to BMW with an 88 535is

General conversations about BMW E28s and the people who own them.
Blue Shadow
Posts: 9294
Joined: Feb 12, 2006 1:00 PM
Location: SE PA

Re: New to BMW with an 88 535is

Post by Blue Shadow »

2 pumps. In tank low pressure feed to external high pressure pump. If in tank is dead car doesn't like running with less than 1/4 tank. Pump relay is about the most common 12v relay. Triggered it us on and that comes from the computer because of the disabling feature built into the OBC. Probably not the issue.

You do have the ETM and Bentley for you car?

Other ptojects with free dead links: www.e38.org/e28.
tn535i
Posts: 5357
Joined: Jul 14, 2006 1:30 PM
Location: Middle Tennessee

Re: New to BMW with an 88 535is

Post by tn535i »

The firs thing I posted was to get a DMM and the ETM... Hah. Now he needs that.

As stated the fuel pump ONLY runs once the DMM see the engine turning. I would not say fuel pumps and relays are big problems just known ones that are easy to diagnose. Simplest thing to do is put you meter on Fuse #1 for the pump and see if it gets 12v once cranking over. If not trace back. You can even jump 12v to that fuse and hear the pumps runs and try to start then when you have a no start.

Fuel relays do go bad, fuses also have poor connections that need cleaning. The In tank pumps are almost always kaput unless they've been replaced (thus the <1/4 tank thing). The main relay can also give fits but then you would have no spark. The check valve in the main pump is also known to leak back and you loose rail pressure making the first start more difficult than subsequent starts.

One more time >> ETM + DMM ;)
cek
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Re: New to BMW with an 88 535is

Post by cek »

Blue Shadow wrote: Sep 20, 2020 4:32 PM No that doesn't sound right The fuel pump does not operate before the car cranks so you don't hear the pump.
This is not true, at least on am M30B35 with 179 ECU. I just tested this. The fuel pump runs when the ignition is in Start or Run. If I stall the car by unplugging the MAF, the fuel pump continues to run.
Blue Shadow
Posts: 9294
Joined: Feb 12, 2006 1:00 PM
Location: SE PA

Re: New to BMW with an 88 535is

Post by Blue Shadow »

Not something I know anything about a later motor in these cars. I was speaking to the stock situation. Fuel pump will run in start and run but can't hear it while the car cranks or while it is running. Could easily meter it for voltage.
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