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Discussion Starter · #1 ·
My vacuum pump burned out.
So I replaced it and then I timed the duty cycle of how long the pump turned off before it turned on again.
This is all with the key in on position, motor off.

It was like 1 minute.

I then found that the hub lock relay thing was leaking a bit.
I pulled the vac line and held my finger on it. Pump down time improved to about 3.5 minutes.
So I plugged the holes with some JB weld epoxy since I now have manual hubs.

THen... I found that if I plugged the line that goes through the firewall to the heater controls the pump down time goes way up. I got tired of holding my finger on the vac line at about 7-8 minutes. So it seems there is a leak somewhere in the passenger compartment I think.

Any suggestions on what to do next?
 

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Discussion Starter · #8 ·
Im a little confused.
Behind the glove box i do see air lines.

I see a black and a white pair traveling through. They mate to a junction piece or maybe its an air connector. (Main vac supply traveling to hvac selector switch?)

There is a threesome as well. Looks traveling from hvac selector to above. These are red, blue, green. Also a junction/connector in line.
 

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Check the connector where several lines join each other, behind the glove box on the left

I would use a hand vac pump with a gauge -- the freight place has them pretty cheap
your electric pump should not run for a hour or more if the system is tight
start at the pump and test with a gauge -- it should pump up and hold
then work your way back to the cab and heater controls
that junction behind the glove box has the main line and most of the actuators in it
the hand pump is great there

I remember someone mentioning that the heater box on some models had a built in reservoir that would crack
 

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Discussion Starter · #12 ·
Well, seems the leak is in the white line behind the glove box.
I am sort of following the diagrams presented in this web page. No sure if the totally accurate, but they holding up for me so far..


So from my earlier post, there seems to be a black line traveling from engine to hvac controls? Think it is vacuum supply line?

Then i think, from the diagram, the white is traveling back from hvac controls to a recirculate door? It is paired with the black.

where is this recirculate door? I can’t see where the white goes. Seems to be traveling with the black towardsthe firewall again? Is the recirculate door in the engine compartment?
 

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I had the black line under the hood crack on my truck, the crack ran around the line and was still held on one side, so would only leak under certain temperature conditions. Was very difficult to find, but once I found the break was easy to see why. The line had hardened over time and would crack by bending. Replaced with a line I got from the big truck store and all is good now. They had line by the foot, I re-used the old rubber connectors
 

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Discussion Starter · #14 ·
Final Notes:
For anyone reading this later, I solved the problem.
Dave Ghost seems to have come in and erased his comments.

He had a good suggestion and that was to go in and change the settings on your HVAC control, then time how long it takes for the pump to have to turn back on and pump up.
THat way you can kind of see what function the leak is in.
My leak was in the MAX AC and OFF settings.

Using the schematic I reference above, It looked like the white line in the dash.

So basically how this is set up, the vac pump is in the engine compartment. The vac pressure is shipped out where it is needed in the engine compartment. Then, one (black) line is sent into the passenger area behind the dash and it goes to the HVAC control panel to open and close ducts for defrost, lower blower, upper blowers etc. But, one function, the fresh air or recirculate flap is back in the engine compartment. So one line (the white) is sent back out to the engine compartment. But... it turns grey when it passes from passenger area to engine area.
So when you go to the firewall, you will see a black and a white or grey, two lines.

ALso look up Diesel Tech Ron's video. He goes over how to trouble shoot the vac system.

During troubleshooting, after doing the HVAC panel switching tests.
THen I went into the engine compartmenbt. I disconnected each line and put my finger over it. When I did that to the grey line, cutting off all line circuits in the passenger compartmenbt, I saw the pump downtime go way up. So I knew the leak was toward the passenger area.

Then if you go behind the glove box, there is a group of three lines. From plugging them, I could tell it was in the white that was returning to the engine compartment.

Turns out it was in the grey line in the engine compartment.
I used epoxy glue to seal it.

I used bubble water in a spray bottle to discover the pinhole. I blew into the end of the grey line while spraying the bubble solution.
 

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One more thing to look into:
Max AC and Off sends vacuum to the water shut off valve on the heater hose -- pretty common for this line to get knocked off the valve fitting
 

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Discussion Starter · #16 ·
Thats what diesel tech ron called the grey line. I was thinkikg he miss spoke. Anyway, the grey line is the white line inside the cab.
the grey is where my leak was.

one more thing i learned. If you need to get to where the black and grey/wht go through the firewall.
From inside: the foot panel UNDER the glovebox exposes one side.
From outside: detach the plastic wheel well and you can see the grey black pair.

I have no idea what to pull on to detach the firewall pair. Get it straight cuz if you tug the wrong thing apart, its very very tight to get it back together. I guess unless you get full wheel well apart.
 

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How hard would it be to replace that side of the vacuum harness? Considering these trucks are ~20 years old now; My 99 had a rotted connector for the wastegate actuator, so (figuring the other fittings were similarly aged/bad) I replaced the whole engine vacuum harness... $38 OEM harness delivered from Tasca, or could be had for half that on ebay.
 

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Discussion Starter · #18 ·
I assume you are talking about replacing the passenger compartment side.
On my truck the passenger side looked in much better condition.
You can get a peak at some of your lines by simply looking behind the glovebox.
I think it would be a difficult job to replace all of it.
 

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You can get a roll of the little nylon line and re-use the fittings if you really want to do the work to replace all the lines
 

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I would guess that the connectors would be the first to rot/become porous (as I saw in the engine bay), but on seeing this thread, hardening and cracking of the lines could happen too apparently...
 
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