Fuel Accumulators?

Sharkey · Post by **Sharkey** » Thu Apr 05, 2001 2:37 am

I virtually destroyed a mechanical 100 psi VDO fuel pressure gauge due to fuel injector pulsation. The gauge was mounted in the dash using an isolator for safety purposes. During operation, the needle of the gauge flexed back and forth over a range of about 10 psi, buzzing like crazy until it finally let go after about 100 engine hours.

I am considering running a fuel accumulator from a late 80's watercooled VW to combat this issue. Anyone have any thoughts on this?

Veepster · Post by **Veepster** » Thu Apr 05, 2001 10:18 am

define fuel accumulator for me...

thanks!

------------------
Peace.............BartG www.teamgodspeed.com

Bruce · Post by **Bruce** » Thu Apr 05, 2001 11:08 am

The fuel acc. is a sealed unit with a diaphram and spring. when the pump is running it evens out pulses and when the pump stops (for CIS) it maintains about 2 bar of pressure for 30 mins approx to prevent fuel vapourisation due to a hot engine.
Very useful.

Post by **Tom Notch** » Thu Apr 05, 2001 11:22 am

It's a fluid shock absorber generally used in any pulseing fluid system. Really helps to keep the system intact. An electronic pressure gauge uses dampening built into its circutry. Use to deal with this stuff occasionally on the Big Ship's automation systems. Plus on the Big jets I work on now. Both of which have parts a bit Too Large for a car!

I will go back and re-visit your car on your site and see what all you used, I would think that it shouldn't do that. What pump? What regulator? Hmmmmm? Interesting.

------------------
Tom Notch
Tom's Old VW Home

[This message has been edited by Tom Notch (edited 04-05-2001).]

Veepster · Post by **Veepster** » Thu Apr 05, 2001 1:00 pm

thanks guys!!
Sharkey..
I can't see how injector pulsing would cause 10psi of variation in the fuel system(or any variation for that matter)....makes no sense to me....I would look elsewhere for a problem..

maybe I am missing sonmething.....

------------------
Peace.............BartG www.teamgodspeed.com

Sharkey · Post by **Sharkey** » Thu Apr 05, 2001 9:56 pm

That's what I am trying to do... narrow down the problem by installing a used fuel accumulator to see if that helps

If there is fuel pulsation existing in the system anywhere, the accumulator should be able to minimize it. I'm also replacing the POS CB Performance fuel pump (which is available at your local NAPA) with a quality Mallory one. Any pulsation left over will have to be sorted out afterwards.

My existing injectors are huge... 52 lb/hr. When these babies open and close, the sudden drop in pressure may cause the spike that I am experiencing. Perhaps the cheap CB pump is also at fault, but the accumulator is only costing me about $20 Cdn.

Post by **Tom Notch** » Thu Apr 05, 2001 10:17 pm

I'm running a Porsche 911 pump for an atmos. engine, unknown year or model, in my bug. I put the 944 one in my Notch, haven't lit it off yet but should be just fine. The 911 one is larger in diameter and heavier than the 944. The 944 fit in a coil bracket just fine and used a rabbit/golf rad. shock mounts, or maybe T3 fuel pump mounts. Have you looked at a possible regulator caused pulse? Wonder if that could even happen, maybe a weird vacumn signal to it? just a thought.

------------------
Tom Notch
Tom's Old VW Home

Sharkey · Post by **Sharkey** » Thu Apr 05, 2001 11:26 pm

Fuel pressure regulator? I'm running the Italian unit from CB Performance, and a fuel pressure of only 30 PSI at idle (to compensate for my overly large injectors). I felt that the addition of the accumulator would be the cheapest way of tinkering with my system, since adjustable fuel pressure regulators aren't cheap.

I'll know more in the next couple of weeks when my car is back on the road.

Post by **Tom Notch** » Fri Apr 06, 2001 6:37 am

I'm using a T2/T4/T3 fuel pressure regulator, used, and they are adjustable. Not sure of the full range of adjustment. And they are cheap at the local breakers, at least here they are cheap. I may even have another one laying around.

But I forgot that you are pressureized!!!

------------------
Tom Notch
Tom's Old VW Home

[This message has been edited by Tom Notch (edited 04-06-2001).]

Veepster · Post by **Veepster** » Tue Apr 10, 2001 12:35 am

this is what I use....3/8 line holley blue feeding a napa efi pump.....this flows into a one pint tank in the engine bay....my injector and NOS fuel lines come out of this tank...I then have a 3/8 line retuning to the main fuel tank with a poppet type relief valve in line(the old hilborn type).....I also run 55lb injectors......

to test fuel flow withengine off I removed my fuel lines that feed the NOS and ran them directly into a gas can.....turned pumps on and pushed NOS button.....I dumped about a gallon of fuel out of those lines in less than a minute and my pressure did not drop or pulsate at all.....I would let go of the button and then push it again with never more than a 1psi change in pressure.....

you can see my little fuel tank in the middle of the pic at http://www.teamgodspeed.com/engineout.jpg

I just can't see that being your problem...I would guess air in the lines...the only time I have seen fluctuations that big are due to air in the system..

good luck!

------------------
Peace.............BartG www.teamgodspeed.com