Blue Pump NVH - some clues!

[BLKMGK]

Okay, today I decided to try and tackle the Holly Blue Pump noise. I hope to get my exhaust done soon and know that the buzz from that sucker will drive me nuts afterwards - it annoys me now!

 

After standing in my garage and pondering the piles of junk I began digging around. After I ran across the third set of sway bar end links from various cars I decided to try using them.

 

I put a bolt through the frame where the bracket is now and used the end links on either side. I also used a piece of rubber under one of the bolt heads on the pump bracket but was unable to do so on both sides. Cranked the car up all proud of myself and STILL had buzzing!

 

Puzzled I crawled under there with the car running. I found that the pump and the area around it didn't seem to be vibrating much at all?! Then I put my hand on the braided line - it was humming like a bass string! Looking along the line I found where I'd used a stock hose hanger to suspend a portion of the hose - temporarily removing this I found the noise GREATLY reduced!

 

I shut the car off and proceded to make some insulators from the high pressure rubber hose I'd used for my oil lines. I slit the hose to slide it over the hose wherever it contacted the body. I also suspended the hose where it used the old hanger using zip ties - it's now isolated from the body completely. The fact that I used adel clamps to mount the hose to the body helped too as I didn't have many places to insulate as I moved forward. Unfortunatly I mounted the regulator to my firewall sans rubber insulation, so now with everything insulated I have figured out what that strange background noise up front is - it's the regulator!

 

It still buzzes some in the back. My next step if I decide to do it will be to hang the pump from an aluminum plate and isolate it fully. However I have a feeling that the fuel cell mounting points could turn out to be the next area that's conducting the vibration

 

Hope this helps others since I know quite a few of us have bitched about this pump. It seems it's not completely the pumps fault!

[DavyZ]

Good information--I took note of your fix to isolate the lines too!

 

Eventually, you will discover that the biggest source of vibration is the thing called the motor

 

Davy

[Modern Motorsports Ltd]

Great you solved the rear noise Jim. Now you've noticed your FPR up front is buzzing/vibrating??? I have a hard time imagining why a fuel system part up front would create any noise in itself unless perhaps your return is too restrictive and it's at a pressure higher than desired??

 

any other ideers? I just can't see that vibrating/or buzzing when you're sitting their with only the fuel pump on and no engine harmonics etc to cause ONLY loose items to vibrate.

 

perhaps I misunderstood?

[BLKMGK]

Engine was running, regulator opens and closes to allow fuel through. It does this VERY rapidly and I've got no return line so it sends shock waves through the lines and into the firewall. It's not very noisy up front really but it has become more noticable since I quieted it down some in back. Still have a ways to go before I'm 100% happy and that probably won't happen until I'm running EFI with a return line to the back (shrug).

[TimZ]

My guess is that the vibration in the hose was from high frequency pressure spikes in the line itself. This could very easily get introduced by the pump, in fact this is precisely what the mysterious fuel damper was for in the FI Z's.

 

Since the fuel is not particularly compressible, the pressure spikes will travel right down the fuel line, and excite anything in their path (like the regulator). If you can feel the lines vibrating at the FPR, then this is probably the problem.

 

This shouldn't be much of a problem with carbs, but it can cause inconsistency in a FI system, since the pressure becomes unpredictable.

 

You might consider installing some kind of damper in the fuel line to help reduce the pressure spikes. I'm thinking maybe a T in the line, with a few inches of pipe or hose that is sealed on the end, and installed vertically. If you make sure that this section of hose has air in it, this should act as a filter for the pressure spikes. They do this in home plumbing all the time, and for much the same reason.

[BLKMGK]

Hrm, I agree and don't. I can hear and feel the regulator cycling - I think that it is what's sending pressure waves down the hose. You can put your hand on the pump and it barely vibrates but the hose feels like it's humming. The Blue pumps supposedly have a bypass in them but I'm pretty sure it's set for something like 14PSI. IF that's the case a lower pressure bypass would probably allow the regulator to stay open longer and not shock everything quite so frequently.

 

I may shock mount the regulator, I've not decided. I've got a bulkhead fitting that I cannot easily shock mount that I'm sure will be making noise too. I want to get to EFI anyway but if I end up with the carb for awhile longer I'll have to do something about the noise. Heh, after the exhaust that is. Right now the noise is finally bearable I think, when the exhaust is quieted it could be too loud again. Putting a stereo in the car is pointless right now unless I want to go deaf trying to hear it

 

P.S. The damper you're talking about - seen those in A/C systems too. Not sure how easy that would be to do effectively but it might be worth a shot if nothing else works. A regulator with a return line might also be a good way to reduce the vibration?

 

[ September 30, 2001: Message edited by: BLKMGK ]