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Re: How to tell if your fuel pressure regulator is (archive)

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Posted by Jeff Goss on April 02, 2000 at 13:36:17:

In Reply to: How to tell if your fuel pressure regulator is bad posted by Richard V on April 02, 2000 at 13:14:05:

: Does anyone know how to tell if the fuel regulator is bad? I realize the fuel economy has to be 1st sign, but I have a hesitation conditions on my '92 535I 5 speed, more noticeable when cold, but also noticeable (not as much) when warmed up, and I am suspecting the fuel pressure regulator. I can disconnect the 02 sensor, and the problem goes away. I have surmised, that I may have a rich fuel mixture and the 02 sensor is telling the system to "lean out" consequently, the hesitation.

: I have done all of the other stuff: new plugs, rotor & distributor cap, adjusted the valves, cleaned the ICV and TB & run fuel injector cleaners. The only fix was when I disconnected the 02 sensor one evening, when I went home from work. No hesitation…but had a smelly converter, (usually the sign of a rich mixture). Thinking the 02 sensor was possibly 'lazy', I replaced it, but had no improvement.

: My thinking is that if the fuel regulator is bad, it would allow the fuel pressure to increase, in turn, causing more fuel to flow through the injectors & making it run rich. The 02 sensor seeing this, gives a signal to "lean out" by retarding the timing momentary, then back to rich, then lean, then rich, etc. The shape of the plugs, with signs of carbon reinforces this when I replaced them.

: I wanted to do a fuel pressure test, but don't have a tester. Looking at the auto store, I found one for about $20-$25 bucks. That's about half the cost of a new regulator. I could just add another $25 & buy the darn regulator, but wanted some feed back before I did.

: Any insight from you Bimmer brains.

: TIA, Richard V.

I swapped mine with my 325's(m20) since they are the same regulator. If you don't have a friend with a 5er or older 3er, then you can try this to see if the regulator is having any affect on the fuel flow(working):
1. With the engine running, remove the vacuum line to the regulator and watch/listen for changes to engine speed etc.
2. " ", use regular pliers to clamp down on the fuel line into the regulator and " ".
If the engine remains constant no matter how you influence the regulator, then mabye the regualtor is not working. Other than this, I don't know of how to check it without a fuel gauge test. Hope this helps.

Jeff Goss
The 535i Website

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