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 Post subject: Fuel Pressure spec for B280F
PostPosted: Wed Nov 14, 2018 12:37 pm 
Cams + Headers

Joined: Wed Jun 07, 2017 6:59 pm
Posts: 60
Location: waterloo, ontario
What should be the PSI range of the fuel in the lines to the injectors?

I would like to stick a guage in to look at debugging hard warm start
issues. I think there check value may be acting up or intank fuel pump system
or something may be causing low pressure during warm start.

Anyone have the green book which covers the fuel system delivery for the B280F?


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 Post subject: Re: Fuel Pressure spec for B280F
PostPosted: Thu Nov 15, 2018 10:52 am 
Haha, I just built a W24 Octo-Turbo, now what?!
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Joined: Wed Dec 21, 2005 8:40 pm
Posts: 3482
Location: Calgary, Ab
Try here, if you don't find what you need let me know and I might have something:

http://www.volvotips.com/index.php/740- ... ir-manual/

That said, it's nothing unusual. Bosch EFI systems operate at either 2.5 or 3.0 BAR fuel pressure, with the pressure regulator dropping fuel pressure from there at a 1:1 rate relative to manifold pressure. When you shut the car off neither the fuel pressure regulator or the check valve at the fuel pump should leak, but if they do you'll potentially have the issue you're speaking of.

I've mentioned it to you before, but the valve lash settings are EXTREMELY tight for this engine, and there's almost zero margin for error when it comes to setting them up. I seem to remember that the factory settings were in the area of .004" clearance, and it's very difficult to hit that number without being .001" too tight or loose. Too loose is fine: I think I ran .006" or even .008", but .001" too tight is A LOT too tight, proportionally speaking. When things get hot, these clearances shrink and this drastically changes how long the valves are cracked open, which drastically changes how much compression the engine will build and how happy it is about starting.

My car was a lot happier with more intake valve lash. It ran the same when cold but it was FAR peppier just off idle when hot, and started easier. It gets a bit noisier but as long as you don't go too far above the factory settings, you won't damage anything. When I was building my engine I mapped out the camshaft and valve operation and the intakes didn't start really moving until about .012-.015" of lift (off the base circle) had been achieved. The approach ramps to this point are extremely gradual, so making the clearance a little tighter makes the valves stay cracked a WHOLE lot longer. You gain zero performance from this - the valves don't open appreciably further nor do they flow much when barely cracked - but they do bleed off low speed compression. It's a fine line and I'm not sure why the cams were ground like this or why the lash settings were chosen, but I felt comfortable enough to move away from the factory settings.


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 Post subject: Re: Fuel Pressure spec for B280F
PostPosted: Fri Nov 16, 2018 9:57 pm 
Cams + Headers

Joined: Wed Jun 07, 2017 6:59 pm
Posts: 60
Location: waterloo, ontario
2.5 - 3 bars is a lot of pressure. I plan to check both valves.

The car will start fine sometimes on the first crank when it is hot.
Not all the time. The last thing I will do is check the valve clearance.

I have a donor 780 PRV6 mostly intact to play with the engine. The body
looks beyond repair from rust. It needs a starter and a look over before
I attempt to start it. Mice chewed the return fuel line, so I have to patch that.
The rad is dry, but there is clean oil in the sump. Not sure how long it was
sitting in a field. Price was right $650. Demoused the inside and pushed
it into the shop just before the major snow last night.

I can mess with this engine without breaking my running mint 90.


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