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Fuel Damper?


jayzrocket

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I google'd this for you to read:

 

http://forums.mbworld.org/forums/archive/index.php/t-119779.html

 

When a normally reliable component fails, it can put a 'damper' on a

quick diagnosis, especially if the symptoms are missed or misinterpreted.

 

Toyota has used dampers on its fuel injection systems for years. But if

you're like most technicians, you haven't looked twice at a damper

because it's normally very reliable. Trouble is, when a damper finally

does fail, it often confuses and frustrates uninformed technicians.

 

This month I'll explain how a fuel damper works and well as what can go

wrong with it. There are plenty of these dampers in service, and you

don't want a bad one fooling you!

 

At one time or another, eveiyone has heard a water pipe in a house begin

to bang after someone opens a faucet and closes it suddenly. If the

banging pipes bother you enough, you can source a little hydraulic

damper from a hardware store or home center and tee it into the noisy

pipe. Basically, this kit acts like a hydraulic shock absorber on the

water pipe, dampening the effects of the sudden pressure change inside

the pipe.

 

The fuel damper on an injector rail (photo 1 at left) also serves as a

hydraulic shock absorber of sorts. Electric fuel pumps don't produce a

totally smooth, seamless flow of fuel. To the contrary, fuel pump output

pulses, and ultimately this pulsing can cause noises downstream in the

fuel rail. Of course, the risk of hydraulic noise in the fuel system

varies from vehicle to vehicle and system to system.

 

On older Toyotas, you might see a fuel damper mounted right at the fuel

pump outlet. But the most common location for it is at the fuel rail

inlet. The damper contains a spring and diaphragm that absorb some of

the shock of the fuel pulsing into the fuel rail. When the system is

working correctly, fuel pressure lifts the diaphragm, pushing it up into

the damper housing. Pushing back this diaphragm allows the fuel to

continue flowing into the fuel rail.

 

If you pry off the plastic cover that's pressed onto the top of the fuel

damper, you'll find a factory-set adjustment screw (photo 2). This screw

limits the travel of the diaphragm inside the fuel damper. Ordinarily,

this adjustment is set for life and you certainly don't want to

experiment with it. This screw also provides a quick-and-dirty fuel

pressure check. When there's no pressure in the system, the screw sits

down against the recess in the damper cover. But when fuel pressure is

present, it lifts the damper's diaphragm enough to push the screw

noticeably outward.

 

Visually checking the position of this screw is no substitute for a

proper pressure/volume test. It's an all-ornothing proposition: When

there's no pressure, it's recessed; when there is pressure, it

protrudes. But it doesn't tell you how much pressure, or if the pressure

is stable under load.

 

Leaks are the most common Toyota fuel damper failures. When you

investigate a customer's complaint about a gasoline odor, you may find

fuel is seeping out of the fuel damper. Watch for gasoline stains on and

around the fuel damper. Replace it if it's seeping fuel.

 

Occasionally, the adjustment screw loosens up, allowing the diaphragm to

stroke too far downward. When this happens, the damper's diaphragm

restricts fuel flow, causing a severe lean condition during

acceleration. When the driver punches the gas pedal, the engine falls on

its face with a severe hesitation (sometimes almost stalling), bucking,

chugging or surging. When he backs off the throttle, the engine runs

better because enough fuel flows to satisfy it during light-throttle

driving.

 

Remember that fuel pressure has to push this diaphragm upward into the

damper assembly before gas will flow into the fuel rail. Rut when the

diaphragm has "overtraveled" due to a loose adjustment screw, fuel

pressure just can't push or lift it enough to provide normal volume to

the injectors. I'm not aware of any quick, reliable way to reset this

diaphragm travel adjustment back to original. Replacing the fuel damper

itself is the safest, surest fix.

 

An episode at Tom Dwyer Automotive Service in Portland, Oregon,

illustrates how potentially confusing symptoms can be when that

factory-adjusted fuel damper screw loosens up. Technician Steve Poole

wits troubleshooting a 1995 Toyota V6 truck with the same lean symptoms

I described earlier. The truck's fuel Eiter and fuel pump had already

been replaced.

 

Poole followed the fuel line up from the frame-mounted filter and found

a threaded junction in the fuel line down on the right inner fender

panel. He teed a pressure gauge into this junction, which happens to be

well upstream from the fuel rail inlet and the fuel damper. First, the

system passed a simple vacuum-applied/vacuum disconnected test of the

fuel pressure regulator.

 

Poole's experience taught him to verify that fuel pressure was stable

under load. Considering how severe the lean symptoms were, Poole

expected fuel pressure to drop like a stone during acceleration.

Surprise/ Fuel pressure didn't drop at alll Then, when Foole checked

fuel volume at the pressure regulator outlet port, the truck did more

than just iail the volume test miserably. He noticed there was hardly

any fuel flowing from the return side of the system.

 

A quick check of injector pulse width showed that the ECM was increasing

pulse width substantially when Poole snapped the throttle open.

Furthermore, feeding the engine some propane through a vacuum port

during acceleration perked the engine up considerably. So what the heck

ailed this engine? Dirty injector inlet screens might cause a severe

lean condition, but Poole wondered if all six injectors could be

restricted that badly. Plus, that still wouldn't explain the extremely

low fuel volume in spite of a new fuel pump and filter.

 

Poole studied the system a little longer and noticed the fuel damper on

the injector rail. He told me he had seen a number of these dampers seep

fuel, causing gasoline odor complaints. But he also wondered if

something was somehow hanging up the damper diaphragm, causing it to

malfunction when the system was under load.

 

He removed the truck's fuel damper and inspected it as well as the

opening into the fuel rail. Everything looked clean as a whistle, so he

tried a new fuel damper; that fixed the truck. Hindsight is always

20/20. Poole said that if ho had been thinking inoro clearly, he could

have compared the upstream fuel pressure reading to one taken downstream

of the fuel damper.

 

Poole's a good sport. I told him that the next time he encounters these

lean symptoms during acceleration on a Toyota or another similarly

equipped vehicle, he would be better prepared. When the driver asks what

might be wrong with his car, Poole could respond with a straight face:

"You may have a screw loose somewhere."

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Now I'm thinking I might need a damper on my fuel rail. The gauge on the end of my fuel rail definitely shakes the needle like it's trying to get the devil out. I run a return loop before the rail so the rail is dead-headed off the fuel loop. With batch injection and a dead headed rail, I am a prime candidate for a fuel damper. Maybe I'll try adding a length of hose to make an air chamber off of the fuel rail.

 

Or I could buy this...

http://www.injector.com/fueldampers.php

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Now I'm thinking I might need a damper on my fuel rail. The gauge on the end of my fuel rail definitely shakes the needle like it's trying to get the devil out. I run a return loop before the rail so the rail is dead-headed off the fuel loop. With batch injection and a dead headed rail, I am a prime candidate for a fuel damper. Maybe I'll try adding a length of hose to make an air chamber off of the fuel rail.

 

So I assume you took the stock damper (mounted near the pump) off?

 

I was debating this, because I'm installing a pump with a larger output line, and will probably run 3/8 all the way to the engine bay.

 

Any higher HP guys chunk the stock damper? Results?

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So I assume you took the stock damper (mounted near the pump) off?

 

I was debating this, because I'm installing a pump with a larger output line, and will probably run 3/8 all the way to the engine bay.

 

Any higher HP guys chunk the stock damper? Results?

 

 

I still use the stock damper but that was to dampen the pulse from the factory pump. Understand, I run a larger Walbro pump and large batch fired injectors which create large pressure fluctuations in the rail compared to the factory setup.

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I've built plenty of modern high specific output turbo cars without a damper. I think some of it depends on the size of your fuel rails, fuel lines and the quality of you fuel pump. Small fuel rails make it worse. Small fuel pump makes it worse.

 

Cygnus - Are you getting accurate and stable fuel pressure rise? You are feeding the rail off of the "dump" side of the regulator? Why?

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I am feeding the rail off of the pump side of the regulator, just like the factory setup. However, I am taking my return line off the regulator, straight to the tank. Two reasons...cleaner install of the rail plumbing and no heated fuel returning to the tank.

 

As a result, I get heavy pressure pulses in the rail when the injectors batch fire. The car runs fine but the pressure pulses could make the throttle response poor/intermittent, and mixture control erratic. I thought about adding a volume of air to the top of the rail via a small container Teed into the rail as a test.

 

To get an idea about the pressure pulses, I used to run a non-liquid filled gauge at the end of the fuel rail. Within a week, the needle tip snapped off inside the gauge.

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I am feeding the rail off of the pump side of the regulator, just like the factory setup. However, I am taking my return line off the regulator, straight to the tank. Two reasons...cleaner install of the rail plumbing and no heated fuel returning to the tank.

 

As a result, I get heavy pressure pulses in the rail when the injectors batch fire. The car runs fine but the pressure pulses could make the throttle response poor/intermittent, and mixture control erratic. I thought about adding a volume of air to the top of the rail via a small container Teed into the rail as a test.

 

To get an idea about the pressure pulses, I used to run a non-liquid filled gauge at the end of the fuel rail. Within a week, the needle tip snapped off inside the gauge.

 

 

You are taking your return line off the regulator straight to the tank versus what? That's standard method...

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My return line/regulator is not on the end of the fuel rail.

 

The pump supplies the high side of the regulator and the rail through the filter. The return line (not seen under the regulator) sends the rest back to the tank through the regulator. The end of the fuel rail near the firewall has a gauge on it that reads correct pressures. The only issue is that the needle vibrates with the injectors firing. This keeps the hose route nice and clean using the stock hard fuel lines, and keeps hot fuel from dumping back to the tank.

 

 

149043498_jgwJ4-L.jpg

 

OK?

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My return line/regulator is not on the end of the fuel rail.

 

The pump supplies the high side of the regulator and the rail through the filter. The return line (not seen under the regulator) sends the rest back to the tank through the regulator. The end of the fuel rail near the firewall has a gauge on it that reads correct pressures. The only issue is that the needle vibrates with the injectors firing. This keeps the hose route nice and clean using the stock hard fuel lines, and keeps hot fuel from dumping back to the tank.

 

 

149043498_jgwJ4-L.jpg

 

OK?

 

Ah, well, that's why you have pulsation issues. I know it's not as clean, but routing a line from the other end of the rail to your regulator would fix it. I am sure you know that, however. I think you're on the right track. A big pulsation damper would help the situation, but I don't know how big it'd have to be to avoid it altogether. You're turbo as well so that's not helping, obviously. I bet you've got a LARGE difference in A/F ratios from one combustion event to the next and one cylinder to the next. Especially bad since the hottest cylinders are the getting the most variation.

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I ordered a fuel damper. We shall see. I am going to try it at the gauge end of the rail first. If that doesn't help enough, I'll move it to the input side of the rail.

 

I also can feed the supply line to both side of the rail to help pressure distribution...

 

...or I could bite the bullet and run a return off the rail...

 

so many options.

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From the 280z Electronic Fuel Injection Theory/Troubleshooting book (page 3):

 

"From the fuel pump, fuel flows to a fuel "damper", mounted right next to the pump. The damper acts like a shock absorber. It has a diaphragm which is under spring pressure. If the fuel pump puts out pressure surges, then these surges push against the diaphragm and are absorbed by the spring instead of making themselves felt all the way to the injectors, and thus possibly affecting engine performance."

 

There's a lot of good info in this book pretty much anyone with a fuel injected L series. It can be viewed in PDF format here:

www.atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf

 

Val

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Yup, thanks Val, but I think that the pulse from large, batch fired, injectors is so far away from the fuel pump that the factory damper has little to no effect on the pressure wave resonances.

 

Paul (BRAAP) also has a dead head fuel rail as I recall. Paul, are your injectors batch or sequentially fired and do you see pressure "vibrations" at the rail?

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