fuel pressure guage install
 

I just installed a fuel pressure gauge in my 300D and I thought I'd post pictures here to help anyone who wants to do the same. I bought a small pressure gauge on Ebay and bought the other fittings and hose at an auto parts store. The fittings, hose, clamps and 1/8 NPT tap cost me about 18 dollars. I got 8 feet of hose; 7 would have been plenty. I removed the banjo bolt on the out line on the filter and drilled and tapped this bolt to install a hose fitting. Measure carefully to make sure you drill exactly in the center of this bolt. If you're off center you'll cut through the side. I found a rubber grommet in the firewall with extra space to run the hose through. I cut off a rubber nub to make a hole in it. The pictures should be pretty self-explanitory.

Better hope it doesn't leak or you'll have diesel all over under the dash.

Why did you install it?

That looks like a high pressure gauge, 0-100psi. Those kinds of gauges are designed for fuel injection systems that put out 40-60 psi. or more. As I understand it, our pumps are more like 5-10 psi and the purpose is to just get the fuel out of the tank and keep the injector pump supplied. It would seem to be a mismatch for the intended purpose.

I could be wrong, I'm only going by what I've picked up here. What are you showing on your gauge?

Regardless, nice installation.

Interersting mounting position. A first I believe. What type of pressures are you seeing?

For those interested harbour freight has a fluid dampened gauge that is 0-30 lbs in range. The gauge has to be liquid filled to dampen oscillations of the needle.

I personally would like to know the fuel pressure you are seeing at about 60 mph. May as well post what you are seeing at idle as well.

The whys for installing a gauge are many. The nice part is on average it will save its cost in my opinion. Excellent early warning of fuel supply issues. Or if one crops up suddenly it helps you establish what it might be easier. Or can eliminate it as a possibilty usually.

Little more complicated than just getting the fuel into the pump.Manufactures specification is about fifteen pounds in the base of the injector pump. Nineteen pounds is even better.

Lift pump should put out about thirty pounds with the return clamped or closed off on the injection pump.

For our purposes the 0-30 pound gauge is almost ideal. He will just have a lesser range of needle movement to interpret with a 0-100 lb gauge. This is still a lot better than no gauge.

How do you save the initial cost? It informs you of the sagging pressure as the fuel filters load up. A restricted fuel filter contrary to what one might think hurts milage far before any physical sensation is known. You just change the fuel filters when the need is indicated..There are not a lot of things that pay for themselves out there. Installation of a gauge does have a chance though.

Beats driving around not having a clue about the condition of your filters alone. Or changing them just because you think you should.Or waiting for the car to quit.

Now if you do not have fifteen pounds pressure in the base of the injection pump find out why. Mechanical reasons may be an underporforming lift pump or a tired relief valve on the injection pump. You get more power in the seat of the pants feeling with good fuel pressure. Everything really in good condition and cold starts should be better as well. There is a chance the engine may be quieter on the highway with good pressure . The idle is smoother compared to a system running very low pressure.

Thanks for the explanation; I stand corrected. And I agree having a fuel pressure gauge would be a good addition to systems monitoring.

No correction just information. To me it still is a good ideal for so little money involved. On the 616 four bangers you really should have one in my opinion.

Most of these fuel systems are twenty five years old now and it is safe to say less than a very nominal percentage have ever had their fuel pressure checked.

Lift pumps get tired over the years. You can usually recondition them for ten dollars or so in parts. Thats if the need is indicated. Relief springs get tired over the years as well. Tank screens partially obstruct too..

Are you driving around with partially obtructed fuel filters? Is the injection pump still getting good fuel pressure at highway speeds? We get threads all the time that involve cleaning the tank filter,changing the fuel filters etc. Then posting that it was not the issue. If they had a fuel pressure gauge may have saved them that effort.

A fuel filter can take on enough dirt etc. in one filling to make the pressure sag. It can remain in that condition for a very long time. This is going to be one unknown without a gauge and will cost you.

Since the 616s in europe apparently do not suffer the first rod bearing failures like the ones in north america do with their different injection pump. You want to make sure that your 616 is not operating on low fuel supply pressure in my opinion.

The only other variable that I have considered between the two different versions is that their fuel is better than ours. I do not think this makes the difference though. Long term running on the 616 with substandard fuel pressure is a far more likely culprit in my opinion.

When I first joined the site. It was felt that it was a rod oiling issue. If so the five cylinders should have suffered the problem even worse. Logically the oiling passage was longer to reach the first rod bearing on them.

The standard 616 lift pump develops less output pressure than the later turbo five cylinder engines.So perhaps a design error was introduced as they were not aware the fuel filters may not be getting changed out as often as they should be.

So it is logical any restriction in the 616 fuel system and some defects are going to have a much greater effect in lowering the available fuel pressure. The main pressure regulating spring in the 616 lift pump should possibly be exchanged for a stronger one out of a five cylinder lift pump as well. Used is fine.

There is very little cheap out there these days. Yet this is one area tha can be restored if required for peanuts in comparison to almost anything. An added benifit is you get to know your fuel supply system much better. Your cars reliability is vastly improved as the main failure of diesel engines is their fuel supply. The gauge will generally give an early warning something is occuring well in advance.

Different application but serves the same purpose - I installed a fuel vacuum gage on my Rabbit truck diesel. The Mk1 VE pump draws fuel from the tank via suction. The vacuum gage is a very good indicator of the state of the filter, and can even predict gelling fuel and ultimately the health of the vane lift pump integral on the VE IP.

But then again I like instrumentation so I also monitor the VE internal pump pressure which controls dynamic advance among other things.

Eric

That's usually what folks here have done, a vac gauge to tell how their filters are doing.

The Caddys are cool little truck. Great for running around town.

A vacuum gauge will not work to monitor secondary fuel filter in a 617.xxx because the lift pump pressurizes it. You have to use a pressure gauge.

If you put it before the lift pump it will read vac. But I can't say if the vac will increase as the filters clog.

Most aircraft have fuel pressure gauges... and fuel boost pumps. Part of the takeoff and landing checklist is check fuel pressure and turn on boost pumps.

If it wasn't critical, they probably wouldn't go to the time and expense to include these components in their systems. Our cars are not so critical as a fuel failure is generally an inconvenience rather than an emergency, but as has been pointed out, gauges can provide a wealth of information that can help identify problems before they strand us.

I'm not sure I'll install a dash gauge, but I probably will install a diagnostics port or a gauge in the engine bay.

Since you do not have to examine it all the time . Hidden in the back of the glove compartment is one option.

You want to see what the pressure is at highway speed with the engine under load. You also lose the ability for early detection of an issue by just having a random temporary hookup under the hood.

Either way basically costs the same other than a little time. If a non smoker the ashtray area may be another position to consider. A fuel system issue can be a major inconvienience and cost something if out of town especially. When away from major cities every town no longer has a garage that repairs cars. Even if they do there is usually a waiting list. The old days are history.

Doing what you say, the vacuum gauge reading will decrease as the filter clog. It will measure how clogged the in-tank strainer is though. ;)