Engine/Transmission (1994 - 1998) How to build a Fuel Pressure test gauge for a 12 Valve.

[Signal73]

After experiencing lower then usual power levels on my 95 12V, and researching the forums for a cause, It seems the starting point for checking the fuel system is being able to know your fuel pressure. I have seen partial posts and some pictures about how to do a FP gauge for a 12V, but never a detailed write up. Below I'm listing the tools and materials I used to make a homemade fuel pressure gauge for less then $30 in parts. The Ideas for most of this write-up was from Forum member Joe G which without some of his ideas and posts I wouldn't have went through this project with such ease.

With all that said, Well start off with the Parts I bought.



Here is a Picture of the gauge I bought. I got it from Grainger who has locations throughout the country and also has an online catalog. The P/N for this gauge is 5WZ35. It has a 1/4" thread outlet:



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Here is a grease gun hose I bought from Pep Boys. Ill use this between the pump and the gauge:



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Here are the parts laid out in assembly order:



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[Signal73]

Part A+C. Its a 1/4" Female tube thread to 1/8" NPT male.



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Here's Part B. Its a 1/4" tube to 1/4" tube male threaded needle valve. If you can find one in 1/8th NPT instead of 1/4" tube, it will save you a few parts. The valve can then be threaded directly into the banjo bolt:



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Here's part D. Its a 1/8" X 1/8" NPT coupler.



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[Signal73]

Part F is a 1/4" female X 1/8" NPT Female reducer coupling.



Here is where the banjo bolt is located:



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Picture of the Banjo Bolt removed:



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1/8" NPT tap and drill bit:



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[Signal73]

Banjo in vise ready to tap:



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Here is the banjo after being drilled:



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Here is the tap in place:



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[Signal73]

Finished Product:



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Yellow Fuel rated thread sealant used. Wrap clockwise onto threads:



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Assembled banjo bolt end:



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[Signal73]

Assembled gauge end:



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Overview:



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Reassembled banjo:



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[Signal73]

gauge reinstalled:



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FP reading at Idle. 10 PSI. As suspected bad overflow valve. I clamped off the return line and the gauge pegged at 60. Idle PSI should be 20-25 and @ 2000rpms, should be 35-45:



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I hope this is helpful in building a gauge and diagnosing a fuel pressure problem. I ordered a new overflow valve. After removing the old one, I found the spring which holds the check ball in place was in 2 pieces. 108 K on the original overflow valve.

 

[Signal73]

Just wanted to condense these into one thread for easier viewing.

Thanks, Jim

 

[The patriot]

Very nice!

Look in my redaers rigs to see how I went about it.

My truck is an 1998, so I just tapped the fuel filter housing. It had bosses pre cast right into it just for that purpose. I now have instantanious readouts of pre, and post filter ctg.

Mine's electric. I dont really like the electric gauge, but I put a switch on it so that I can go from pre to post at any given moment.

The senders are always off a few lbs of each other, even with a new filter. Other than that it's OK.

Eric

 

[94ram]

Hi, just a question on reading fuel pressure,

How about the bleed screw hole on top of the fuel filter?



I had a cheap Harbor Freight FP gauge with an adapter that threaded right in to the bleed screw hole.



I believe this will give accurate fuel pressure to the injection pump, Right?



Thanks,

KB

 

[mmeersman]

man, new to the forum and found exactly what I needed in this thread. Nice looking home made gauge. Question is - where do you pinch off the return line since most of the line is rigid? The only place I see soft rubber line is behind the pump and it looks so tight I don't know where to get to it from to pinch it off.



I'm also having FP problems,just replaced the lift pump and ran new marine rubber grade lines from the tank to just behind/below the fuel filter on my 98 12V. When I did this, I primed the lines with the bleeder bolt open until all the air bubbles evacuated and only fuel came out, tightened the bleeder bolt and continued priming until I heard the overflow valve release.



I replaced the overflow valve last year but could it be bad already?

Both before and after the new fuel line and lift pump my fuel pressure readings are about 12 at idle and 20 cruising at 70 mph.



Any chance this is my IP? This is my first diesel, almost had it a year and not too familiar with IP going out.



Any help or advice would be appreciated. Thanks.

 

[PToombs]

Grainger part # for 1/8th male/ female thread needle valve, 6MN31.

Grainger Industrial Supply: Valve,Needle,1/8 In 6MN31

 

[JIM BOB]

I read this, and tried the Harbor Freight cheap gauge, it did have an adapter in it that fits the bleed hole in top of filter. (It looks like the same adapter for a early fuel injected Honda)

In my opinion it's worth it to buy th HF just for the adapter, and then use a liquid filled gauge to dampen vibrations.

The HF gauge will work but hard to read.

James

 

[JGranberry]

Before and after benefits on power while towing? I need about 50torque BADLY while towing. I'm fully sock, 96 2500 12v and towing a 10,000 lb gooseneck. THANX!

-JT

 

[BGuilty]

what would happen if you leave the pressure guage on with a 90 degree coming off the pump instead of a valve and a plug?

 

[Axtell3]

I squoze my return line below the filter area just after it switches to rubber... New overflow valve for me too.

 

[Crazy Horse]

This is the guage I got from Geno's when I put my Walbro pump in. I decided to mount it under the dash viewing convienence. #ad
It's been working perfect for a few years now. The only thing is you have to watch the liquid doesn't freeze. Luckily I'm in SC now so that's not a worry in the garage. This is the hookup on the side of the VP:#ad




This is another shot under the dash. #ad
The entire fuel line from the pump to the guage is run inside split loom to protect it through the firewall. Well I guess it's been in for 6 years now looking at the photo date. All the photos can be seen here in the "Old Readers Rigs".