Does a normally operating Fuel Pressure Regulator make any noise or can you feel it "pulse" a few times per second during idle?
I've had some periodic "hot soak hard starts" and just trying to chase down anything obvious. I can't say I have ever put my hands on the FPR during idle, but I was not expecting to feel it pulsing like this. I expected whatever regulating it was doing would be more of a smooth adjustment. This feels like it is cycling several times per second. Is that normal? I don't have a gauge to put on the fuel system yet.
This is on a rebuilt 3.0 and it idles like a dream and runs really smooth for the most part. Only issues I've had are some sluggishness until 2,700 RPMs (at which point it feels like I cut off the AC compressor or hit the nitrous) and it takes 3-4 seconds for it to start if it is warm and sits for an hour. Not sure how the FPR would affect either, but just starting to look into it and it seemed odd.

 

It will make a "whining" noise when pushing air through it (e.g., after changing the Fuel filter), but in normal operation mine is silent. So "pulsing" does sound odd to me.

But before you starting thinking about addressing the FPR, you need to get a pressure gauge. If you get this gauge it comes with the 12mm banjo-schraeder fitting you need for the 3VZE. You can save money (probably) buy building up a gauge from scratch; your choice.

 

Thanks for that. Yeah, I'm planning to grab the loaner from AutoZone when I get a chance. It is supposed to have the M12x1.25 banjo adapter in it. Once I go through all the tests I will know more, just thought it odd how much pulsation there was in that fuel system. Putting my fingers on the FPR I feel a pretty hard bump about 4-5 times per second at idle. I do have a brand new Toyota pulsation dampener on it. Have no idea if it behaved this way with the old one. That was several months ago and I don't guess I've ever put my hands on the FPR at idle until now. Maybe that dampener is doing its job and it would be much worse without it

 

Hmmm. All 6 injectors open at the same time. At spec idle speed (850 rpm) that would be 7 openings per second. Maybe I should put my finger on my FPR to see if I can feel the same thing.

"Damper." It doesn't "dampen" (make wet) anything. (Though the English anti-police will get after me for that correction.)

 

I didn't think to do the math, but based on 850 rpm, or 14 rps, all 6 injectors cycle through 7 times per second. That does seem to be about the frequency of this "bump" in the fuel damper. My idle feels super steady to me. No misses that I can detect. But for argument's sake let's say that one of the injectors failed to open every cycle. That would give a bump in the fuel rail 7 times per second, would it not? Check my math on that. Gives me something to go looking for anyway. When I put this engine together after rebuild I put in freshly cleaned injectors and it ran like crap, missing on #5. Pulled plenum and sure enough, #5 injector was not opening at all. Took it out and doused it in TB cleaner, rapped it a couple times with a hammer, and hit it with 9V until it opened reliably. Put it all back together and it has idled and run really well ever since, albeit a bit sluggish under load with light pedal usage (something I don't THINK is related to this, but who knows!).

Haha. I did notice the different verbiage used all over the innerwebs on this. Toyota uses the word "damper" so I will go with that. Although Webster and many other dictionaries have a definition for "dampener" that seems synonymous with "damper", so I see the confusion.
https://grammarist.com/usage/dampen-damper-dampener/

 

I misunderstood your statement here, Scope. I thought you were suggesting that my particular issue could be because all 6 opened together for some strange reason. I now realize it was a statement...all 6 injectors open at the exact same time on this particular engine. I did not know that until reading something else today. So a bump in the fuel pressure every 7 seconds is to be expected and the damper probably smooths this out a little bit. The reason I never notice it when cold starting is just the higher RPMs means higher pulse rate and so that "hammer" is just not as noticeable.

 

I finally located a loaner fuel pressure test kit at OReilly and put it on the rail near the regulator. I get about 46psi with just fuel pump running, about 38psi on a cold start at idle (1200 RPM this time), and 47psi on same cold start idle with the regulator vacuum crimped. Warm engine (800 RPM was almost identical numbers, 38psi or 46psi with regulator crimped). These values are just a tad higher than the FSM says, but I don't think the FPR is bad, do you? And to my original question on the pulsing of the FPR, the gauge barely showed this. Maybe one psi back and forth. So I don't think there is cause for concern, but curious what you guys think.
I also noticed that when I shut off the engine it went from 38 up to about 42 very slowly (took about a minute, assume this was fuel warming up in the rail now that it was just sitting there on a hot intake?) and held that pressure extremely well. It took an hour for it to drop below the 21psi the FSM says is the threshold for the 5 minute test. So I think my 29 year old Toyota fuel pump and FPR are working just fine! I'm kind of surprised, to be honest, because I've had some "hot soak" or "warm start" issues with this vehicle (may start a different thread if I need more help) and going through the usual suspects. I was convinced I had low fuel pressure causing vapor lock or some of the hesitation at low RPMs, but that does not seem to be the case. Guess I'm glad I don't have to replace the fuel pump (yet)!

 

IIRC, that exact situation is what the vacuum line on the top of the FPR is for. It comes from a VSV, that applies vacuum which changes the pressure the FPR holds when the engine is started hot. I'm not certain of the exact functioning of the system, but with hot start/heat soak problems it can be the VSV, the ECT sensor, or the signal from the ECU to the VSV. Or, of course, the vacuum lines between the VSV and the FPR, or the TB and the VSV.
I believe that the VSV is switched off during a start cycle with the coolant temp above a certain point, causing a higher pressure in the fuel rail. I believe this will help prevent the vapor lock situation. More pressure, it reduces the chances of bubbles forming in the fuel rail. Once the engine starts, the VSV is switched on, which applies vacuum to the FPR, lowering the pressure in the fuel rail.

I may have it all bass-ackwards, but I believe that's how it all works. With the vacuum line removed from the FPR, it should maintain 38-44 PSI in the fuel rail, with the vacuum line ON the FPR, 33-37 PSI. See what I mean?

Does this help any?
​​​​​​​Pat☺

 

Yes, thank you! It does make sense and that is my understanding as well. I was kind of expecting to see lower overall fuel pressure on both sets of readings from maybe a faulty fuel pump or restriction or electrical gremlin, which could have caused vapor lock on hot starts. But all my pressures were very high and also passes the leak down with flying colors. So I’m looking in other directions for my hot start now, but my original question was in regard to the pulsing in the fuel rail so I wanted to pass along my findings. Seems to be normal and not fluctuating too much on the gauge that I used.