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FBH start sequence:
- glow plug pre-heats ~45 sec
- fuel pump starts (audible ticking under rear seat) ~5-10 sec
- combustion air blower starts (whine)
- burn must start (audible change in sound - small jet  ) w/in ~15-20 sec or the fuel is shut off. Combustion air blower runs for a while to clear the FBH and sequence starts over
If your FBH is firing and then cutting out, there are numerous possible causes but I would start by checking the amount of fuel being delivered. The pump is a metering pump and delivers an exact amount of fuel to the FBH. Specs can be found online. After that R&R the FBH. If the combustion chamber is ok, the combustion air blower will need replacing as a matter of course.
Disclaimer: This info is based on my experience servicing FBH in the early 90s and mainly on the previous gen of FBH. While the theory is surely still accurate, weaknesses and common faults in this gen of FBH are obviously not reflected.
Cheers,
Steve 
RRC 2Dr, RRC 4Dr,
P38, and 2 L322s
(wife thinks I'm nuts - prob right, too)
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26th Nov 2013 7:39am
