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A25c won't accelerate

funwithfuel

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That is a common problem. I asked early on about the fuel water separator. If it's the one with the glass bowl, they're prone to air intrusion. The rubber gets dry rot and cracks. The little plastic drain cock gets wonky too. And the seal for the screw that runs the center. The pressure sounds good. As long as its liquid fuel and not foamed.
Can you run an alternate fuel source to the lift pump?
 

Dakotab19

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Jun 9, 2019
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Michigan
That is a common problem. I asked early on about the fuel water separator. If it's the one with the glass bowl, they're prone to air intrusion. The rubber gets dry rot and cracks. The little plastic drain cock gets wonky too. And the seal for the screw that runs the center. The pressure sounds good. As long as its liquid fuel and not foamed.
Can you run an alternate fuel source to the lift pump?
Well this model has the plastic fuel water separator, and I checked it again today, but I couldn't find any cracks, it has a new O ring on it, and I couldn't find any leaks when I blew air into it. Is it normal for the primers on these pumps to have fuel leak out of them when you use them? Because it does that sometimes.
Is that really all the pressure you should get in the intake manifold?
Yes I should be able to hook up an aux line to the lift pump.
 

funwithfuel

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Can you post a pic of separator? Let's continue with other source of fuel in meantime.
Leaking fuel @ primer pump might need a new primer pump. They are prone to failure. The plunger does screw down tight though, right?
 

funwithfuel

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Pressure on intake sounds ok. Boost builds under load. So if you were in gear, you'd have been up near 25-30.if your fuel is up to task.
 

Se.la

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Qc Canada
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Do you lost the fuel pressure when the engine is loaded
when the problem of RPM on the engine has started ?
When the engine is hot the low idle spped showl be to (665 - 715) rpm
 

Dakotab19

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Do you lost the fuel pressure when the engine is loaded
when the problem of RPM on the engine has started ?
When the engine is hot the low idle spped showl be to (665 - 715) rpm
Well I can't really load the engine down, but when I just revved it up no load it got around 50 psi fuel pressure.
The idle speed seems about right I don't have the most accurate tachometer but the readings I got were real close to what you indicated.
 

Se.la

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Qc Canada
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The radiator fan should be at 700-900rpm when engine is at idle speed , when the engine exceeds 1500rpm , the fan motor speed will increase to 1400+ or - 50rpm
 

Se.la

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Qc Canada
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how did the engine problem happen ?, the machine working fine and the problem happen ? did you do some repair on the machine before the problem happen ?
 

Dakotab19

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Can you post a pic of separator? Let's continue with other source of fuel in meantime.
Leaking fuel @ primer pump might need a new primer pump. They are prone to failure. The plunger does screw down tight though, right?
I looked, the primer isn't one that can be screwed down ( I think I couldn't feel it engaging on any threads)
This is the seperatorIMG_20190614_112038664.jpg
 

funwithfuel

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The base of that sediment bowl looks like it has fuel/dirt accumulated. Find that source. Next the primer pump, if it leaks, change it. Because when it's not leaking fuel, its sucking air.
 

Dakotab19

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The base of that sediment bowl looks like it has fuel/dirt accumulated. Find that source. Next the primer pump, if it leaks, change it. Because when it's not leaking fuel, its sucking air.
So I did another few pressure tests and discovered that the fuel pressure is not consistant at all. So I've got the lift pump off trying to find a replacement and see if that helps.
As for the primer I was able to find one that was similar and screws down unlike the original. Hopefully the new lift pump will also come with a new water seperator so that can be ruled out.
Any other things to check right now for my problems, or just wait for the pump and see?
 

thepumpguysc

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The supply pumps can be rebuilt.. just take it/send it ,to your local fuel inj. shop..
& they'll put a new HP on it too..
The part # is etched into the hsg next to the HP.. so don't go thru a "middle man" to get/buy 1..
 

Dakotab19

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Location
Michigan
Quick update: found a new pump oe for a decent price should be here in about a week. I'll have to wait and see how it works out and tell you guys what happens. I will probably have more questions about this truck but for now ill just hold off to see what the pump does for it.
Thanks for everything so far everyone!!
 

Dakotab19

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Hi again everyone
Some news on the truck: I got the new pump and installed it today. The truck does seem to run better than before, but im still getting air in the fuel seperator bowl. The lines from the tank look good and the fittings are tight so I think it may be a suction problem in the tank. I will check the lines over more carefully, but does anyone know how the fuel suction is set up in the front tank, and how to remove the fitting, does it just screw out?
 

funwithfuel

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Yep, long stand pipe brazed in fitting iirc. Just make sure you have 2-3 feet clear directly above for removal. Could be a corroded pipe.?
Try alternative fuel source to see if it improves
 

Cmark

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Australia
I'm a bit late to this party but here goes.
I guess this truck has the butterfly style exhaust brake? If yes, read on.

Many years ago I got a call out to an old Volvo ADT (can't remember the exact model) with the same problem you're having. The story was that the turbo failed, someone replaced it and then the truck had no power. Long story short, I eventually found that the exhaust brake had been installed wrong and the valve was shut when in was supposed to be open. I suggest you give it a look.
 

Dakotab19

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Hi all,
I know it's been a long time since I posted, but I finally have some spare time to work on the truck again. Previously I'd been so busy that I had to put this project on the back burner.

Since the last time I posted I checked the fuel feed line from the tank (with a vacuum brake bleeder ) and it held good vacuum. I also checked the suction pipe inside the tank, it was good, but the return line was at the same level as the pick up. I shortened it up thinking that the pickup was just sucking airated return fuel, but then I started it a while later and I'm still getting air bubbles in the water seperator bowl, and my fuel pressure is all over the place.

So any ideas on what the problem could be? I'm going to hook up a separate can to run fuel from later today and see if that changes, but is there any other possible reason for this, especially with a brand new lift pump?
 

thepumpguysc

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Master Inj.Pump rebuilder
The "lift pump" supply fuel BUT the "Overflow valve" HOLDS the pressure to a preset limit & then lets it go..
So its a 2 fold system.. EVEN IF u put a guage on it.. if its low, u have to replace one or the other & then if that doesn't do it, u replace BOTH..
Hope that helps.
 
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