I just finished putting in the new motor and after the first attempt at starting (didn't turn over) I went back and double checked the vacume lines(everything ok). I poured a little gas down the primaries and it started right up for about 3 seconds, then failed to start again. I have upgraded and rewired the fuel pump (walbro). When I disconect the return fuel line and run the fuel pump, I get no fuel coming out the return. I do get fuel flowing to the feed line. I also get fuel at the primary rail, where the feed comes from the secondary rail. It apears that fuel is not flowing all the way through the system.

What could be happening at the primary rail or further down the system that no fuel is reaching the return where the hard line exits to the rubber line?

90 S5 Turbo Jspec engine, Aspec fuel rails, injectors and vacume lines.

 

Did you run the lines from the filter to the fuel rails correctly? I'm not sure if fuel will flow backwards through the fuel pulsation damper so double check the way the lines are supposed to be connected in series.

 

I second the above. If it's a jspec engine the fuel rails are arranged different. On a normal USA engine the front pipe on the engine should go to the fuel filter. On a JSPEC its opposite that. This site is riddled with that scenario of no fuel flow due to JSPEC engines being involved in a new engine install.

 

The vacume spider is from the Aspec engine, and I'm 99% sure they are hooked up correctly. If you look at the hard lines, the main is the lower left, return is lower right, and the charcole canister is the upper one, correct? That how I read the vacume diagram, and thats how it's hooked up. I even switched the feed and return lines to see if I was losing my mind. That failed to put fuel all the way through the system too.

I think I'm going to pull the UIM and start pulling lines while running the fuel pump to see exactly where fule is not getting. I think this is going to turn into something bizare though.

 

Be careful and watch for sparks and put that doobie out first

 

What if the FPR was stuck closed? Where do you have it installed in the "scheme" of things?

 

Whatever engine you have, the return line must be connected to the FPR or no fuel will flow. Don't confuse the FPR with the pulsation damper on the other rail, they look very similar. The FPR is the one with the vac line connected to the manifold.

 

The problem seems to be coming from the preasure regulator. Fuel is reaching the upper(primary or secondary?) rail but not being returned. What preasure is the stock regulator set for? Shouldn't it allow SOME fuel through if the presure isn't high enough?
I was unable to blow any air through either direction of the rail.

My new theory is that my fuel pump isnt making enought pressure to pass the reg. One of the o-rings that goes where the output of the pump connects to the rigged stem in the pump assembly was lost when I swapped in the new pump. I think that flowing free, it would have no problem, that why when I tested it with an empty bottle it filled it up pretty quickly. But under restriction, it is going to by unable to make enough preasure to overcome the regulator.

Anyone have an idea if I'm close here? I'm going to buy a preassure guage and some o-rings today to see if that solves the problem, but I'm not clear on how the preasure reg works.

 

At atmospheric pressure it should regualte to approx 37psi. Anything coming in that is over the 37 will be by passed back into the tank. The fuel pump puts out somewhere around 70plus psi give or take.

Here's an example. I have a pressure transducer attatched to my fuel line. At idle the pressure is around 30/31 psi. If I shut the engine down...the pressure will drop down a couple of psi.....but as I sit there you will see the pressure slowly rise and acheive approx 37psi after about a minute, and stay there for the longest time at 37psi. It'll degrade over say an hour or so. I've never kept track of how long it takes to get back down to zip.

Oh, I saw 49.4 psi while going to the store a little while ago. So how much boost was I ...boosting to??? Heck, the fuel gauge is as accurate as the boost gauge.

 

If you're missing an o-ring in the supply circuit, that could explain your problems...The gap created there might be allowing enough pressure to "blow by" so that not enough rail pressure is created to crack the FPR open. It would seem you should be getting SOME fuel at the rails, though, just none past the FPR (which bypasses to the return line, if your setup is akin to the A-spec cars)...

 

I don't understand, the FPR should be the very last thing on the second fuel rail. It should output directly to the return line. That's the way it functions, it stays closed until all the fuel rails are at full pressure and then it bypasses any extra.

If something is preventing flow from the prmary to the secondary fuel rail then something is very wrong in the fuel routing order.

ed

 

We have a winner! Replacing the o-ring brought up the preasure and the fuel started out the return line. The car still won't start though. Damn. I was hoping a little oring would be my salvation and allow me to drive the car for the second time(the first was home from the guy I bought it from's house, the engine kind of shat itself on the freeway).

 

I thought the FPR was regulated by vacuum... Never was quite sure how that thing worked...

 

It's regulated by the manifold pressures (or vacuum, if you will), so that a semi-constant pressure can be achieved across the injectors throughout the engine's "breathing" range. Otherwise, the injector pressures would fluctuate depending on the manifold "pressures" on the other side of the injectors. Think I'm confusing you more, lol. NZ can describe it in layman's terms better than I can...

 

OK

The FRP is there to keep the injector flow rate constant. It does this by keeping the pressure differential between the fuel rail and the manifold constant. The FPR is basically a variable orifice that is opened and closed by manifold pressure. When manifold pressure is low (small throttle opening) the orifice is opened so more fuel is returned to the tank, which lowers rail pressure. When manifold pressure is high (large throttle opening and/or boost) the orifice is closed so less fuel is returned to the tank, which raises rail pressure.