Installing a fuel pressure gauge

[Raider L]

Today is the beginning of the little build thread of how I'm replacing my Autometer fuel pressure gauge. This gauge is a "Sport Comp" series gauge just like the one that's in my dash I put in when I rebuilt my truck. For some reason it failed but it went through hell in the 25 years since it's been in my dash anyway. During the Summer months it was not steady at all. Sometimes it would fluctuate from 3 to 5 lbs, to sometimes 12 lbs. swinging wildly back and forth. Then it would steady out but would still be waving around wildly from 5 lbs. to 8 or 9 lbs.
Then during the Winter months it would be a srteady as a rock and would not swing between pounds hardly at all. Some of it's wild swinging could be blamed on engine compartment heat or something and then when it was cold I don't know why it would run more steady than not. There was not so much slack and vibration in the hose that it caused the wild swinging except in part of the hose coming from the fuel splitter on the manifold, that could be some of the cause of wild fluctuations just from engine vibration, but I don't believe it could have caused that much. My engine is balanced within a gram so I don't know where fluctuations like what I saw in the fuel pressure gauge could have come from. Here's the first thing to do is drain the hose from the gauge in the dash that goes to the back of the isolator in the engine compartment so as not to get a bunch of antifreeze on the back of the instrument cluster, and the floor inside the cab. So remove the connection first in the engine compartment so it's easier to clean up with water and soap later.

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First I had to break the union fitting from the gauge hose that goes to the gauge, from the extension I had to make.

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Then I removed the extension hose from the fitting at the back of the isolator.

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This is a cap for a AN-4 fitting that I will use to plug the back of the isolator in case I have to drive the truck tomorrow before I finish removing the gauge. The front of the isolator has fuel going into it, and any antifreeze still left in the back of the isolator would squirt out from pressure on the diaphram in the isolator. I'm replacing the antifreeze in the back of the isolator anyway but just want to limit the mess.

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Cap installed. Tomorrow I'll finish the reinstall. That little post sticking out the back of the cap is the flare part inside of the fitting of the cap that matches up with the male flare on the fitting in the isolator. That's what makes the sealing of the cap. I'm pretty sure most of you guys haven't ever seen anything like this, except for some of you retired Airforce guys who worked on planes. This is something any of you may want to use at one time so consider this thread part educational.

 

[Raider L]

Today I returned to the removal of my broke fuel pressure gauge and the install of a new gauge. On advice from Autometer they said since the isolator has been in the truck for so long, I needed to check the rubber diaphragm to see if it may have been damaged. And upon inspection, sure enough it had a split right in the middle of the diaphragm. Oh well. I'll need to see if I can get one from Autometer. They said I could, otherwise how can I restore my fuel pressure gauge to inside the cab?

So, here goes my little build.

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Remove dash panel and gain acces to gauge.

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Place rag under gauge to catch any anti-freeze that might be left in the hoise that didn't drip out. Remove gauge.

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Since I'm going to inspect the isolator remove it to. Place rags around and under the connection because I know there is still fuel left in this line at 7 lb. of pressure. Crack the hose nut (blue) loose at the fitting in the face of the isolator and let pressure bleed off. I have that cup under the rags (one is inside the cup) in case the rag gets soaked with gas and drips. I didn't want it getting to much on my wheel well. *That cup is an old icing container I kept, they're small and flexable and good for small amounts of fluids*

 

[Raider L]

Perform inspection of isolator.
But while I've got the gauge out let me see if the gauge is actually working and it was the isolator and not the gauge that was messed up.

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So, I hooked up the guage to the fuel line that goes to the isolator. I cranked the engine and here's what I found. The fuel pressure gauge is still working but is showing way to much "indicated" pressure.

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This is the pressure guage that comes off the fuel pump. The splitter, the thing that has the weird "W" on it, or "M" whichever, the hose connection to the right of the gauge is the fuel line that goes to the carb, at the bottom, out of the pic, is the line that goes to the isolator. You can see that the fuel pump is putting out 7.5 lbs. at idel. That's correct for this pump as it is rated at 6.5 to 8 lbs. pressure. I reved the engine several times to see if the gauge would return to normal and it did not. By the way the engine IS at operating temperature because I had to go get some meds a little bit before this pic was taken. I moved the hose around and bent it to see if the hose position was causing it to show higher and it made no difference. So, the gauge is malfunctioning. Good. At least that tells me I didn't waste my money buying a gauge that was okay.

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Remove isolator.

 

[Raider L]

Let's take the isolator apart and see if it's damaged.

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The screws were really tight and after I removed the nuts that held it to the bracket the screws seemed to be threaded into the back of the back half of the isolator.

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It didn't take a microscope to see the split right in the center of the diaphragm.

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And there it is! Also, look closely and you can see the circular imprint of the back of the fitting coming from the back half of the isolator housing. Fuel has been leaking into the hose that carries anti-freeze into the cab with me for no telling how long, since it's been in the truck for 25 years!! But more importantly it's been throwing the indicated pressure off to, possibly. Maybe that explains the irradict fluctuations I have been noticing for years, because it hasn't always been that way just here in the last ten years. So, I guess those diaphragms don't last that long, maybe ten or so years. You have to remember this type of equipment is supposed to be used for racing where it's not in the vehicle always on a daily basis before it's changed out or whatever, where it's removed and drained off and on, in and out of the race car.

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Here's the diaphragm in a resting state. It has extra material in the middle that bulges out towards the back half of the isolator. I don't know if this is normal or not. When I get the new one we'll see.

 

[Raider L]

The new fuel pressure gauge is somewhat not the same as my old one. What a difference a quarter century makes, ha, ha. From a '50's song titled "What a difference a day makes".

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Opp's! How'd that get in here? My wife surprised me with this one birthday, and I have no idea where she got it. Notice it's a Square to!

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My old one is on the left, metal body, an actual fitting in the middle, the new one is a fitting of a type which is a threaded nipple with wrench flats on each side of it, near the edge of the gauge which doesn't really matter. But what the deal is, the body of the new one, on the right is made of plastic. Yeah, lighter weight, you know for weight savings in racing. Yeah, sure. No, made cheaper but the price didn't go down. Modern business practices designed to get less and pay more. If the diaphragm doesn't fail again how long does anyone bet it lasts? Do you reckon it'll last another 25 years?

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This is the mounting bracket. It's some kind of palstic or composit. I won't be able to use it due to the space I have to place the gauge in the back of the dash panel. That's okay because the mounting screws on the new gauge are the same as the old gauge and are spaced the same, so it will work with what I used on the old one.

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The light hole is different in the new one. I'll just have to wire it in which is cool because I have to extend some of the ground wires on the other gauges lights on the side where this gauge goes anyway. The ground wires are not allowing me to pull the dash panel out as far as I would like, and I'll have to add some wire to them. I'll do a little build on doing that if anyone would be interested in seeing that.

 

[Raider L]

The metal housing of the old gauge, pic above on left, was made more for racing where the car would have a aluminum panel with the gauges installed. Also, the light bulb socket, above gauge on left with large hole for bulb, had only one white wire for power because the housing provided the ground for the light. So I had to scrape the sides of each bulb holder which is metal as well, and solder a black #20 wire to each bulb socket. When I was done with all the lights I drilled a hole in the dash support bracket, tap it for a small bolt and after soldering terminal ends on each wire bolted all the ground wires, i.e. gang ground to that spot instead of running ground wires every-which-a-way.

The new fuel pressure gauge housing is plastic so no more grounding through it. Instead the light is in a plastic socket with a white wire and a black wire coming out of the socket. So what I'll have to do is solder additional white wire to the new one and then to wherever the old one went, probably to the headlight switch. Then solder added black wire on the new sockets ground wire to the old existing ground since I can't get to that gang ground anymore, it's now behind the Autometer speedo and tach. in the factory plastic box, which used to hold the factory speedo and big gas gauge. And my new light will work that way. No problem because I've found I need to add a little extra black ground wire to the existing ones so I can get the dash out a little further. I didn't antisipate having to pull gauges out for a long time yet to come. As if 25 years isn't long enough.

 

[Raider L]

10-26-21 I have been trying to contact someone at Autometer for some time now. Today, see date, I called them for the third time and a guy picked up right off! I was caught off guard for a moment or two because I figured it was some recording, you know? Anyway, it was a human, and I explained my situation and sure enough he said, "Give me your name and address and I'll get one right out to you." I think I've talked to him before because he said, " I think I know who you are." Nice to be known at some place like that.
So, I've got a new diaphragm coming, no charge, no S & H, no tax, nothing, free. I hope it doesn't take long but in the meantime I've got plenty to do.
It's like, have you seen the cost of a new fuel pressure isolator, the hose kit, and the gauge? I have already bought the gauge and I have it, and I've bought the hose locally already, but I would have to go out to the shop and pull the receipts to see what I paid for all that back in 1995 but I'm sure it was a heck of a lot less, obviously, but I'd just like to see how much Autometer's prices have gone up since.
I made up a ring binder when I finished the truck and organized all the receipts into where the part came from, like Super Shops back then, Summit, etc., and then added up what I spent on rebuilding the truck. When I saw that number I had to look out the carport door at the truck because I didn't see parked there a truck that cost that much! Was it worth it? Well, now I see where the money could have been spent better that's for sure. It would have saved me a lot more money in the future, like now, 25 years later had I done what I had plenty of money to pay for it then. Even though I did do everything that was needed to do I left off a couple of important things but I was told by people who knew that "it would be okay". Well, no, I needed to have done those things then, to save me money now. Not ever have done those things before I didn't know, and didn't have a gut feeling about it either.

 

[Raider L]

PART 2 The rebuild of the Autometer Fuel Pressure Isolator

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I got the new fuel pressure isolator diaphragm in. (In the envelope)

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This is the old diaphragm (a little blurred but you can see a clear pic of it above).

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This is the new diaphragm. Nice a flat.

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First I cleaned the threads out with a 10-32 tap because there was somekind of residue left in the threads. It could have been some sort of "lock tight" but I don't know. I'll put some lock tight on the screws before I install the isolator. Only this half of the isolator had threads. The other half was just bored holes.

 

[Raider L]

Next pictures.

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Place new diaphragm onto back half of housing.

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There are three long screws and they go through in the mounting plate behind the isolator.

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Put in the short screws completing the assembly of the two halves.

 

[Raider L]

Next pictures.

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Apply mounting plate and put 10-32 lock washers and nuts on the three long screws.

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Secure with 3/8" socket to just snug. These nuts don't need to be torqued. They are just hand snugged. You can feel it when they are tight enough.

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And it's finished, ready to go back into the truck.