'01 250HP OX66 Surging at 3700RPM

[DennisG01]

Thanks, Zeno. Would you mind clarifying something for me? I wasn't familiar with the term hysteresis, so I googled it and came up with this definition:

Hysteresis is the time-based dependence of a system's output on present and past inputs. The dependence arises because the history affects the value of an internal state. To predict its future outputs, either its internal state or its history must be known.

Well... that confused me even more!

[zenoahphobic]

Thanks, Zeno. Would you mind clarifying something for me? I wasn't familiar with the term hysteresis, so I googled it and came up with this definition:

Hysteresis is the time-based dependence of a system's output on present and past inputs. The dependence arises because the history affects the value of an internal state. To predict its future outputs, either its internal state or its history must be known.

Well... that confused me even more!

Yeah that's why I did not add Google it!…

If we relate this to your gauge; your gauge is trying to constantly give you readings. Nothing in this world is stable, everything is constantly changing.

Your gauge in all likelihood has little mass in its internals so it can respond quickly. If you were to add weight to the pointer for example, it will respond slower giving you a much more stable impression. It is also to do with your eyes and brain interpretation. Animals vary but humans adapt many things to suit us. For instance incandescent bulbs don't flicker at mains AC frequency of 50/60 cycles per second etc. etc.

[zenoahphobic]

Another example of hysteresis is in the operation of a thermostat.
Say for example we wish the engine to be at 180 degrees, a thermostat cannot in it's design to precisely do that,
What does it responds when the temperature exceeds that, by say 10 degrees, then opens far more than it needs to to increase water flow until the temp is well below 180 degrees by 10 degrees and then closes.
The cycle continues over and over.
Another example of hysteresis is in cruise control. Your speed is regulated between a maximum and a minimum.
From an engineering or reliability point of view, we cannot have things changing at great rates. Your equipment will self destruct or you will (imagine con*****ing speed with cycles of idle to WOT every second - fly out the stern then forwards over the bow)

[rodbolt17]

to fix them? I typically trouble shoot them.

monitor rail pressures,ign timing, use of the diagnostic test lamp.
simple stuff that requires no training or equipment.

[99yam40]

Most fuel pressure gauges have a restriction or snubber in it to help reduce the flutter.
My guess is as long as the pump is running you would see the flutter if it was just the pump causing it, maybe something to do with once filled the check valve releasing pressure is what is causing the flutter, but I could be way off base.

Was this at idle or running at higher RPMs?

[DennisG01]

Hysteresis... OK, I got the jist of it. Not completely understanding the actual word in regards to it's definition, but I do understand your analogies.

The video (see the link in my post #32 above) was taken while running the engine at my "problem area" of 3,700RPM. The video is about 5 minutes long, but you really only need to watch for about a minute as nothing different happens throughout the 5 minutes that doesn't happen in 1 minute.

From what I understand, ~35psi is the proper pressure for (most) fuel injected engines of this design. But for some reason I thought that one would usually see 40-45psi? Am I wrong on that? I couldn't find a reference to this in the service manual. Or, would you say (based on what you see in the video, anyways) that the readings on the pressure gauge are fine?

Rodbolt - I am not opposed to taking it into my local shop at all. In fact, I've been in touch with them a few times already about this and inquired about bringing it in to them. It's actually been their recommendation to keep trying some things "at home". Their concern is that I'll bring it in and it won't act up for them, and they don't want to charge me for doing nothing.

Believe me, I know this is not easy for any of you when all you have to go on is what some guy is typing on a forum.

[zenoahphobic]

You have the added problem that the video we see also shows the needle bending; something to do with frame rates and synchro ( loved watching old cowboy ****** where the stage coach wheels appear to be going backwards - took awhile for someone (science teacher) to explain that one when I was a kid).

[DennisG01]

Yeah, it's an older, iPhone 4. Well, "old" as far as technology is concerned nowadays, anyways. The good thing is that it clearly shows the extent/travel of the flutter. Sort of like a strobe-light effect, I suppose.

Edit: Oh, you know what? I never even looked at the (posted) video that closely. You're right! The needle does appear to be bending! Could it REALLY be bending from the quick stop and start in a different direction? Or is it just an effect?

[zenoahphobic]

Yeah, it's an older, iPhone 4. Well, "old" as far as technology is concerned nowadays, anyways. The good thing is that it clearly shows the extent/travel of the flutter. Sort of like a strobe-light effect, I suppose.

Edit: Oh, you know what? I never even looked at the (posted) video that closely. You're right! The needle does appear to be bending! Could it REALLY be bending from the quick stop and start in a different direction? Or is it just an effect?

I've got an iPhone 4, it posts better than my new laptop .
The answer is the needle would bend but not to extent I see. It is a visual effect.
If the needle moves even more than it appears on the video it would be difficult to assess the real "average" pressure reading. Inertia will make the needle oscillate further than actual should be. Added to that it is a "spring" and therefore would assist in a lower inaccurate reading.
Try clamping it to restrict the flow and dampen the fluttering if you need a more accurate reading.

[DennisG01]

Ah, gotcha. Thanks. I think for my needs, it's accurate enough. I didn't have a pressure gauge before this weird issue that's going on so I figured this was as good of a reason as anything else to buy a new tool. As if there needs to be a "good" reason, right! Anyways, I'm only using it to try and narrow down the possibilities/variables of what could be wrong. Unfortunately, the engine didn't act up for me!

[Tucker]

Ok what are developments with this problem?? High speed surge is also a bad 02 sensor symptom. Has that been checked/cleaned?? I sprung for the test leads, about $40, and clean & check mine every year. The aftermarket 02 sensors are so cheap I just replace them every couple years.

[DennisG01]

Tucker, I'm so sorry I didn't respond. I totally missed your follow up question.

Are you referring to that "winky blinky" thing? Probably wouldn't be a bad idea to get that, anyways. I thought they were like a $100, though?

I do have a spare O2 sensor. But I would REALLY like to get this thing to act up when I have some type of diagnostic equipment hooked up to pinpoint what is going on. Problem is, it's so dang intermittent of an issue! Although, I suppose there's worse problems to have.

It definitely "feels" like something heat related - as in, the problem won't (possibly) show up until the engine gets good and hot.

Could a bad spark plug cause this issue?

Just to recap - so anyone reading this doesn't have to read back through the whole thing... At right around 3,700RPM, the RPM's will drop a few hundred for a about 10 to 20 seconds, then back up. This cycle will continue. Also, of note, is that the RPM's "roll" down and up - they don't "jump" down and up.