Fuel delivery issue when starting

E28 technical advice asked and given! Troubleshooting, modifications and more.
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Vladospetica
Posts: 11
Joined: May 24, 2012 4:40 PM
Location: Wakefield, MA

Fuel delivery issue when starting

Post by Vladospetica »

Hello everyone,
My name is Vladimir and I purchased a 1984 BMW 528e recently. It has a stock M20b27 eta engine but with 731 head (e2i swap), custom Megasquirt II unit and wideband O2 sensor. The car runs good but has an issue starting. The only way to start it is to turn the key on 5-6 times (I am guessing that that way pumps push enough fuel to the injectors ??) and than crank it over and only than it will start. Cold start valve has been deleated. I thought the problem was the in-tank fuel pump which looked really rough when I pulled it out so I replaced it with a used fuel pump that looks to be in great shape but that did not slove the problem. I checked the outside fuel pump and seems to be working good. I also changed the fuel filter and put in a new 2.5 bar fuel pressure regulator.
Any help would be really appreciated. Thank you very much.
Vladospetica
Posts: 11
Joined: May 24, 2012 4:40 PM
Location: Wakefield, MA

Re: Fuel delivery issue when starting

Post by Vladospetica »

demetk
Posts: 8431
Joined: Aug 09, 2007 8:58 AM
Location: CT, USA

Re: Fuel delivery issue when starting

Post by demetk »

Splice in a pressure gauge into the fuel line and check fuel pressure. Engine off, ignition on and at crank. Also check if the fuel line maintains pressure when the engine shuts off.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: Fuel delivery issue when starting

Post by Mike W. »

Adding to what demetk said, the system should remain pressurized when it's off. The fuel pump is supposed to have a check valve in it to hold pressure. I've cut into fuel lines in junkyard cars that clearly have not been running for some time and had it spraying everywhere. On the other hand, there were some problems where the check valve didn't hold and at one time BMW had a inline check valve, which I hear is long discontinued, though something similar might be available aftermarket.

Now I don't know what MSII does, but with motronic there is no prime function with the fuel pump so turning the ignition on and off might not be relevant, actually with a stock system it would not be relevant, but again, I don't know what MS does.
Vladospetica
Posts: 11
Joined: May 24, 2012 4:40 PM
Location: Wakefield, MA

Re: Fuel delivery issue when starting

Post by Vladospetica »

Thank you for your answers and sugestions. I will check the if the fuel pressure is maintained when the car is off.
Ju@n
Posts: 702
Joined: Apr 27, 2013 1:11 PM
Location: Uruguay

Re: Fuel delivery issue when starting

Post by Ju@n »

Stock Megasquirt behavior is a 2 second prime of the pump and a (VERY SMALL) injection event.
Check fuel pressure with the pump on (easy enough to turn on the pump on tunerstudio)
Check fuel pressure with pump off (after the test above)
If both ok, then you probably need to tune your starting priming pulse, cranking pulse, icv cranking setting.
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