Fuel Pulsation
 

OK... First, some background..... I've upgraded to a full -6an SS fuel system with billet primary and secondary fuel rails, 550 Primary's and 1600 secondaries, a billet filter, a Walbro 255 and an Aeromotove FPR.

I've been having a problem with the car leaning out and stumbling under light loads (it dues it under boost but its barely noticable when the 1600's are on) at and around 4K (never above 4k though) and can't get it figured out. Raising the fuel pressure helps, but raising the 4k fuel maps on the haltech does almost nothing (except make the car go rich right before and after 4k)

Now then... I have this knocking sound comming from the dash which is tied to RPM... thought it was in the tranny or rear of the motor... NOPE, its the pulsation from the Fuel Injectors reverberating through the filter, which is mounted on an old AC bracket like so:

http://mysite.verizon.net/res1f3en/s...nebay_0609.jpg

So we finally get to the point..... I HAVE NO PULSATION DAMPER...... ditched it with the stock system......

My question is....... could the hesitation and leaning problems around 4K i'm experiencing be tied into fuel pulsation somehow???? Like at certain rpm's the injectors pulse is matching the fuel pulsation and causing the fuel not to be shot from the injectors correctly. Data logs show that the injectors are operating normally and as expected when the stuttering and leaning out occurs, the old "ear on the vaccume tube" also says that the injectors do not miss a beat when the stuttering starts (it happens under no load when free revving the car as well). The guys at Haltech say it aint the ECU......

The fuel pulsation is no tippity tap tap... it feels like someone hammering on the fuel line with a rubber mallet!!!

Thoughts,,,,, experiences that might help me reason this thing out....

Does anybody make an aftermarket pulsation damper?????

yes yes yes! ive experienced this too. you have a couple ways to go here. marren injection i think offer a pulsation damper. or the 91ish mpv (its not the je27)has one like a stock s4 fc but with hose barbs. or you could plumb a stock fc damper in the system somewhere, all it needs is a tapped hole.

I don't know if this applies to you but I hope it helps. I have no PD and run a banjo bolt. I have no hesitation whatsoever.

David

A quick test:
Temporarily loop in about 2 ft or rubber fuel hose at the filter to crudely simulate a pulse damper.

OK..... I think some clarification is in order.... I'm not running the stock control system... Its a Haltech. The haltech fires the primaries in Batch fire mode... both of them at the same time. The stock system alternates them back and forth, this will lesson the pulsation, which, may be the reason you can run without it on a stock system.

I have no doubt i have pulsation, i can FEEL it!! I'm just wondering if my wierd leaning out problem is being cause by pulsation, which J9fd3s seems to think it is.

SureShot, thats a good idea... will have to get some -6an barb adapters and try that.

BTW, Marren Fuel Injection makes an aftermarket Fuel Pulsation Dampener. It's billet Aluminum, 3/8" NPT inlet with a 1/8" NPT scrader valve that can be replaced with a pressure gauge or sender.

Heck, if all else fails, use the design used in house plumbing- if the fuel line run is low enough, attach a "T" in the supply line, and attach a capped (or plugged) vertical section, maybe 6" long. This section will be filled with air at all times, and the air acts as the dampner...

decay, i notice that youre using uber cool ss fuel lines! that isnt going to help your problem. the best way to not use a fpd, would be to just use extra fuel hose, especially b/c right now your fuel filter is a weak point in your system, which is whats causing the chatter. now if you wanted to be really crafty, you could use 2 t fittings and make a loop in your fuel system that will help with harmonic fuel pulses. basically if you have the same pulse traveling through 2 different lengths of hose, itll offset any pulses that might occur, once again use rubber fuel hoses (or silicone? i forget..)

Well THe SS may not help the pulsations.

The normal rubber lines expand and flex a bit helping to absorb some of the pulses.

If it is as bad as you say then go get the Marren although I thought the FPR acted as a semi PD for the car as well.

That screams a warning to me...but on the ignition side instead of the fuel rails... Both low throttle Hesitation and stuttering are sometimes symptoms created with a ign problem.

1st, how close is the timing between the trailing and leading coils???

and

2nd, how are you triggering the ignitors for the coils??

The coils are firing Via the Hitmans directions. Haltech wiring into the neg wire on each coil pack (two on the trailing)... positive voltage supplied by factory harness to the coilpacks.


As for split.... above 2K RPM: at -15 Vac its at 5degrees, at -10 Vac its at 3 degrees, at 0psi its at 4, at 8psi it goes to 5, at 16PSI it goes to 6 and ramps up from there.


there is no low throttle hesitation (unless you happen to be right around 3950 RPM) There is a low throttle/ low pressure (IE 14"Hg Vac) hesitation/stutter/leaning blip right around 4K as you wind it out.

If the coils werent firing at 4k... it would go rich from unburnt fuel right???

If the trailing is too close to the leading... to much heat...lean??????

The Steel wrap on the hoses will make them more resistand to expansion, I new that going in... but i figured the fatty primary fuel rail would help with the pulsation even with its short length...... I neglected to think that the haltech fires the injectors in batch mode..... oops.

Well, I've decided to get the Marren Pulsation Damper... even if it doesn't fix the leaning out problem, it may stop the hammering sound on the dashbaord at idle which is driving me friggin NUTS. Hell, I might as well throw some MORE money at the car!!!

Waiting for advice on Trailing split.... will try that first as its free!!!!!

el bumpo

Ah... see the haltech split can be off as much as 5% in the real world (despite programming)... You probably want to make sure that it never drops under that, or it is possible for the trailings to fire before the leadings resulting in a major knock & could even sound like what you describe.

Just depends on how close the Haltech really is to spec.

I will make modifications to the split to esure that does not happen :)

I repeat post #4

A quick CHEAP test:
Temporarily loop in about 2 ft of rubber fuel hose at the filter to crudely simulate a pulse damper.

BING F'N GO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The Marren Pulsation Damper has freakin solved the problem!!!!!!!!!!!!!!!!!!!!

Now more leasning out at 3750...... but now i gotta re-map cause the non-boost maps are waay fat in some places and a litttle lean in others beacuse of the way i had it set to deal with the problem before..

BUT ITS FREAKIN FIXED!!!!!!!

thats it sticking out off the secondary rail
http://mysite.verizon.net/res1f3en/s...g.w560h420.jpg