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Fuel pressure regulators keep failing?

N

NLRegina

Member
Joined
Dec 7, 2023
I've been having some annoying repeated issues with my fuel pressure regulator(s) on my 1991 740 with regina/Rex. To my knowledge the smell of fuel inside the vacuum hose nipple indicates an internal diaphragm failure which would let unmetered fuel into the intake. I had some issues before with this which caused rough starts until I bought new FPRs. For awhile I bought the cheap ones off ebay for 10 bucks or so since its an easy part to replace. However after going through 3 or 4 of those, I figured I should stop buying low quality parts, and I bought a Delphi FPR from FCP euro. Figure I can't go wrong with the lifetime warranty. Fast forward a few months, and morning misfires seem to be starting again. Upon checking the nipple yesterday, I smelled fuel again. What could possibly be causing this issue? Is it just a series of bad luck/poor manufacturing? I buy gas pretty much always from Costco, unsure of the ethanol content, but I seriously doubt that a product that deteriorates on modern gasoline would still be manufactured and sold. So what is going on here?
 
Well the cheap ones may not be alcohol fuel rated. Even the Delphi unit is probably a reboxed chinese made unit. If you can find the original part that may be your best chance. That's the only thing I can think of unless there may be some kind of issue with the fuel flow. Like a clogged return line?
 
dl242gt said:
Well the cheap ones may not be alcohol fuel rated. Even the Delphi unit is probably a reboxed chinese made unit. If you can find the original part that may be your best chance. That's the only thing I can think of unless there may be some kind of issue with the fuel flow. Like a clogged return line?
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I suppose that's possible that it's a cheap unit, but I'll double check with FCP for ethanol compatability before I roll the dice with the warranty and get another. In terms of a return line clogging, wouldn't that cause leaks around the clamp connections on the lines before blowing out the diaphragm? Return hoses/connections are low pressure to my knowledge. I did recently swap out the two rubber return hoses in my engine bay since the outsides were cracked and old, but I didn't see any internal issues on them.
 
h20ham said:
that begs the question, how's your intake screen and fuel filter
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Air filter and fuel filter are both new as of ~6 months ago, neither seemed particularly worn out but were replaced due to a lack of service records as part of refreshing all the systems.
 
Does it just SMELL of fuel, or is there actually fuel in the line? Keep in mind that when you shut the car off, there's atomized fuel in the intake system, to which the fuel pressure regulator and corresponding hose are attached. Those vapors are going to go everywhere they can and leave their residue behind.

I'm not saying that you don't have an fpr problem, but I am saying that's not a bulletproof diagnostic solution.
 
shoestring said:
Does it just SMELL of fuel, or is there actually fuel in the line? Keep in mind that when you shut the car off, there's atomized fuel in the intake system, to which the fuel pressure regulator and corresponding hose are attached. Those vapors are going to go everywhere they can and leave their residue behind.

I'm not saying that you don't have an fpr problem, but I am saying that's not a bulletproof diagnostic solution.
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It smells of fuel at the FPR nipple end - I shoved the end up my nostril to be sure - no actual liquid. I was under the assumption that the vacuum pressure of the intake would not allow gas vapors to travel backwards up vacuum lines, and that the smell of gasoline near the diaphragm indicates a small leak where fuel is slipping by. Maybe I'm just being over cautious due to previous FPRs failing. I had one where I literally felt it go - idle in park went up from 750 to 1000 or so randomly, smelled of gas, when I replaced it it went right back to "normal".
 
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NLRegina said:
It smells of fuel at the FPR nipple end - I shoved the end up my nostril to be sure - no actual liquid. I was under the assumption that the vacuum pressure of the intake would not allow gas vapors to travel backwards up vacuum lines, and that the smell of gasoline near the diaphragm indicates a small leak where fuel is slipping by. Maybe I'm just being over cautious due to previous FPRs failing. I had one where I literally felt it go - idle in park went up from 750 to 1000 or so randomly, smelled of gas, when I replaced it it went right back to "normal".
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That is no way to diagnose the problem. You need to measure the fuel pressure. Test the regulator by applying vacuum to it and removing the vacuum line while the engine is running and observe what happens with the fuel pressure. And run the engine with the vacuum line disconnected to see if any fuel is actually getting past the diaphragm. Also, pinch off the return line and see if the fuel pressure shoots way up past the normal operating range. That will test your fuel pump condition. If the regulator diaphragm ruptures you don't just get the smell of fuel. You get a steady stream of fuel the diameter of the vacuum port running straight into the intake. It doesn't make your engine's idle go up. It nearly drowns the engine in fuel at idle.
 
2manyturbos said:
That is no way to diagnose the problem. You need to measure the fuel pressure. Test the regulator by applying vacuum to it and removing the vacuum line while the engine is running and observe what happens with the fuel pressure. And run the engine with the vacuum line disconnected to see if any fuel is actually getting past the diaphragm. Also, pinch off the return line and see if the fuel pressure shoots way up past the normal operating range. That will test your fuel pump condition. If the regulator diaphragm ruptures you don't just get the smell of fuel. You get a steady stream of fuel the diameter of the vacuum port running straight into the intake. It doesn't make your engine's idle go up. It nearly drowns the engine in fuel at idle.
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I guess I have a lot to learn - thanks for the diagnosis instructions. Does the fuel pressure gauge hook up to the same spot where my cold start injector line connects?
 
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