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

[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]

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.

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