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1985 745t
I posted a while back with a wierd problem in my brick. Basically it would stumble slightly upon first acceleration in the morning or after it had sat for awhile. Symptoms were slight gas smell at start up, stumble on initial acceleration (but never a stall), and no difficulyt tunring over in the morning.
Car had a new FPR and no leaking injectors. Fuel lines looked solid to the rail and it would always start without a pause or a problem on likme the first or second crank in the morning. Fuel Filter and pump checked out, car was kept well tuned, AMM, o2 sensor, and ECU all checked out. No hose leaks in the turbo plumbing, new plugs, etc.
Now to the solution. I was under the rear end working on the diff the other day, smelled some stronger fuel odors than usual, and decided to poke around quick while teh rear was up. Discovered that the fuel pipe (actual metal, not the hose) was rusting through on the blind side and had started leaking. The rust had gotten progressively worse to the point where it was a fairly profound smell and would leak fairly quickly (for a pin hole rust leak).
So it turns out that the reason I could start the car without issue was that the fuel pressure in front of the pump to the rail was fine, but teh pressure BEHIND the filter was down. This was likely causing the filter and line to empty slightly, providing enough fuel for idle but not enough to get going. The reason it was on cold start was the fact that it was a small leak and would drain very slowly.
Cut the rusted metal section out, removed the fuel hose that was there, and replaced the entire thing with a brand new fuel hose. Problem solved, no more stumble on initial acceleration.
So if you have a similar problem check the fuel lines beetween the tank and the main pump/filter assembly for pinhole leaks or rusting.
-rt
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