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Re: Warm starting problem (look for fuel pump check valve failure)

>>From: Joon Kim <joon@domain.elided>
>>Date: Mon, 26 Aug 1996 22:29:52 -0400
>>Subject: <e28> Warm starting problem update
>>
>>Ughh, again.  The car gods are angry with me.  I had my '86 535i towed to
>>the mechanic only to receive a call from the mechanic the next day saying it
>>started fine.  Now it starts fine again so my update is it has become
>>dormant no doubt to return whenever Murphy's Law says it must.  Any further
>>suggestions from digesters?  Main and fuel relays are new.
...clip
>>Joon
>>- - '86 BMW 535i, '85 Yamaha FJ1100, '74 Alfa Spider, '84 Chevy Blazer

My '84 E23 acted like this:

- - when cold it started on the first turn

- - when hot it would start immediately after being shut off

but....

- - if it had soaked for 1/2 hour or more when hot it would
require 4 to 8 seconds of cranking... but would always start,
eventually

Diagnosis:

The check valve in the main fuel pump was leaking allowing the
fuel injector rail residual pressure to bleed off resulting in formation
of a huge fuel vapour bubble in the fuel rail and back down the
fuel line toward the pump. The extra cranking time was needed
by the fuel pump to recompress and eliminate the fuel vapour bubble
in the line and repressurize the fuel injector rail.

I could have replaced the fuel pump for $200 but I fixed the
problem by putting a $10 brass check valve (3/8") in the fuel line
near the pump. I bought the check valve from a Dayton Electric
outlet. I can get the part number if you're interested.
I also bought a pair of small brass hose barbs, some teflon
joint tape and two small stainless hose clamps to complete the
installation. Total cost was about $15 and 1/2 hour of my labor.

Now the engine starts on first turn, hot or cold, overnight or
after standing for a while ....ie it always starts easily
and immediately, even after soaking in Houston sunshine while hot.

Regards