Slowly Losing Fuel Pressure

[MyTy]

I recently installed a Accufab AFPR and now I notice when I turn my key on to prime the fuel pump my fuel pressure goes to 42 and than steadily drops down to around 20 psi in the matter of like one minute.. I'm starting to think that this is why my truck is stalling when I come to a stop or when going in reverse.. at this point I'm pretty much having to give it gas when I'm at a stop so it wont die..

Could it be possible I have a bad AFPR? I really don't think I over tightened the fittings where the O rings are.. but I guess that could be a possibility.. Could it be the actual fuel pump?

Can someone with a lot of fuel system knowledge please help me out..

 

[Static]

Re: Slowly Losing Fuel Pressure

Make sure that there is no fuel coming out the vacuum line attached to the afpr. Could also be a loose hose clamp, split or delaminating hose in the tank. There is a special hose to be used for in tank pumps that can be submerged in fuel. The regular grade stuff comes apart after a few years.

 

[Quickstop [UK]]

Re: Slowly Losing Fuel Pressure

It should hold pressure for a few hours ar least once the key is turned and the pump primes. If it is dropping then you may have a faulty AFPR or you could have a leaking/stuck injector.

If you smell the vac hoses to the AFPR, do they smell like gas? Search on here for that symptom - usually means the diaphragm has gone or is faulty.

The fuel pump would be more likely if it struggled under load.

 

[Don W.]

Re: Slowly Losing Fuel Pressure

Since it started with this reg change back to your old reg and see it that fixes it. Then you'll know. First thing I'd do since all the other potential reasons are a lot more work.

 

[Ty1642]

Re: Slowly Losing Fuel Pressure

The Accufab AFPR doesn't hold pressure with the pump off very well. I think it is due to the shape of the sealing surface. I installed one and had the same behavior you are seeing. I exchanged it for another and it acted exactly the same way. I called Accufab tech support, and the person I spoke with said it didn't matter if it held pressure when the pump was off, as long as it regulated pressure with the pump running. Seems to make sense, although I'm not completely convinced. I swapped the old regulator back in after installing the two Accufab units, and the system held pressure again.

I also did some searching on the Turbobuick forums, and found several posts there saying that the Accufab units didn't hold pressure well.

 

[MyTy]

Re: Slowly Losing Fuel Pressure

Hmm I guess ill try going back to my old one, the reason I switched is when I try to adjust the pressure on the old AFPR something strange and kinda scary happened a lot of fine mist of gas shot out from what seemed to be the regulator but there was so much I couldn't see where it was coming from and rushed to turn the truck off,, my buddy said its probably a bad diaphragm on the old one. If so is that repairable?

There doesn't seem to be fuel in the vacuum line from the regulator.

 

[SEL777]

Re: Slowly Losing Fuel Pressure

Ok, so if the old one was leaking...do not reinstall it. Maybe someone has a cheap spare you can try to rule it out. And for $20 just get a fire extinguisher for your ride. Cheap insurance against a fire.

 

[MyTy]

Re: Slowly Losing Fuel Pressure

New question to add... So I have two typhoons and I cant figure out why this is happening on one of the Ty's and not both. When adjusting the fuel pressure on one, when I disconnect the vacuum line from the AFPR and plug the vacuum line the truck stalls out but on the other Ty it stays running. Both have brand new vacuum line kit from SportMachines and both hooked up the same.

Any advice would be much appreciated.

 

[Don W.]

Re: Slowly Losing Fuel Pressure

One if not both have incorrect fuel pres. Install your ga, run the pump using the test connection (empty female elec connector near the dist.) and see what your FP is. Should be near 40.

 

[MyTy]

Re: Slowly Losing Fuel Pressure

Ive never done that procedure and not sure exactly which connector you are speaking about. Do you happen to know the exact name of the connector? ill see if I can find it in the service manual.. the good ones for our trucks..

 

[MyTy]

Re: Slowly Losing Fuel Pressure

Also I'm thinking it is low but when I try to adjust the pressure the truck stalls when I plug up the vacuum line.. if I don't plug the vacuum line after removing it from the AFPR am I not properly adjusting the pressure? I can see the pressure drop and rase when the vacuum line isn't pluged but removed from the AFPR...

 

[MyTy]

Re: Slowly Losing Fuel Pressure

Ive been suspecting its the fuel pump that's the problem.. could it be a faulty fuel pump that is making the truck stall when I plug the vacuum line after removing it from the AFPR? Or possibly fuel filter?

 

[dgoodhue]

Re: Slowly Losing Fuel Pressure

The truck should run with vacuum line removed but if the fuel pressure is way off it may not. (Or you have other issues.) You can adjust the fuel pressure with the vacuum line on, you just have to compensate for the idle vacuum affect on the fuel pressure regulator. If the idle vacuum is 20"hg, that would equate to -10psi of fuel pressure. So if you trying to adjust for a base fuel pressure of 42psi, adjust it to 32psi with vacuum line connected.

 

[MyTy]

Re: Slowly Losing Fuel Pressure

The truck should run with vacuum line removed but if the fuel pressure is way off it may not. (Or you have other issues.) You can adjust the fuel pressure with the vacuum line on, you just have to compensate for the idle vacuum affect on the fuel pressure regulator. If the idle vacuum is 20"hg, that would equate to -10psi of fuel pressure. So if you trying to adjust for a base fuel pressure of 42psi, adjust it to 32psi with vacuum line connected.

Thanks, Do you know if DataMaster shows the Idle Vacuum?

After reading your post a few more times I'm now a little confused. I hope you can be patient with me.. So from what I understand when adjusting the fuel pressure the correct way by removing the vac line and plugging it, you than adjust 10lbs ahead of what your aiming for say you wanted 42lbs fuel pressure it should read 52lbs before reconnecting the vac line... so that's what I thought the procedure is.. but from what I'm getting that your saying is if I have the vac line connected than I want to go 10lbs below of what I'm aiming for? that's just confusing to me and it could be because I'm not an expert on vacuum lines and systems..

 

[dgoodhue]

Re: Slowly Losing Fuel Pressure

Thanks, Do you know if DataMaster shows the Idle Vacuum?

After reading your post a few more times I'm now a little confused. I hope you can be patient with me.. So from what I understand when adjusting the fuel pressure the correct way by removing the vac line and plugging it, you than adjust 10lbs ahead of what your aiming for say you wanted 42lbs fuel pressure it should read 52lbs before reconnecting the vac line... so that's what I thought the procedure is.. but from what I'm getting that your saying is if I have the vac line connected than I want to go 10lbs below of what I'm aiming for? that's just confusing to me and it could be because I'm not an expert on vacuum lines and systems..

I am confused by why you would adjust your fuel pressure 10psi higher than what you are aiming for. The base fuel pressure is the fuel pressure with the vacuum/boost source disconnected. (Plugging the vacuum line just plugs a vacuum leak) Most of us discuss the fuel pressure in terms of base fuel pressure. What are fuel pressure are you aiming for (or what chip do you have?)

I am not sure if Datamaster (I use tuner pro) gives the vacuum in "hg. If it is in kPA, you can calculate the vacuum in inches of hg. 100 minus the datamaster kpa x 0.147 x 2 will convert it to inches of hg. Typically I see about 35 kpa at idle, which calculates to 100 - 35 x 0.147 x 2 = 19.11" of Hg

 

[Don W.]

Re: Slowly Losing Fuel Pressure

DataMaster does read Vac. That connector is called something like fuel pump test term. It will be the only unconnected term near the dist.

The -correct- way to set fuel pressure is how everyone has described. Engine running, vac line off. What I suggested was a way to set a baseline of around 40 so that the engine would have a better chance of running so you could set FP correctly. NOT as a way to correctly set FP.

 

[MyTy]

Re: Slowly Losing Fuel Pressure

I am confused by why you would adjust your fuel pressure 10psi higher than what you are aiming for. The base fuel pressure is the fuel pressure with the vacuum/boost source disconnected. (Plugging the vacuum line just plugs a vacuum leak) Most of us discuss the fuel pressure in terms of base fuel pressure. What are fuel pressure are you aiming for (or what chip do you have?)

I am not sure if Datamaster (I use tuner pro) gives the vacuum in "hg. If it is in kPA, you can calculate the vacuum in inches of hg. 100 minus the datamaster kpa x 0.145 x 2 will convert it to inches of hg. Typically I see about 35 kpa at idle, which calculates to 100 - 35 x 0.145 x 2 = 18.85" of Hg

In the past when I was researching on setting fuel pressure I read on here that when you disconnect the vacuum line from the AFPR the fuel pressure goes up about 10lbs.. so when adjusting you have to go 10lbs above what your aiming for because when you put the vacuum back on it will go down 10lbs.. and from my experience that's exactly what happens when I disconnect the vacuum it goes up about 10lbs.. like I said I'm new to vacuum systems but I'm a novice at fuel pressure related problems as well. I'm a DIY kind of person so I always attempt stuff first before taking it in to people..

my DataMaster reads the vacuum KPg.. at Idle when warm its typically 67.4

To answer the question on what chip do I have.. its a Moates chip. It came with the truck and I know absolutely nothing about the chip. I recently emailed a person that works for Moates and was the goto guy.. at least that's what the post said. I didn't happen to look at the post date because its been about a week now and ive got no response yet.. I'm starting to think the guy don't work there anymore.. I want to learn more about the chip but don't know how.. was going to start a post soon about it but trying to get other things figured first.. I'm a lil worried the chip has something to do with this and that is really out of my realm.. heres a pic of the chip..

 

[Don W.]

Re: Slowly Losing Fuel Pressure

In DataMaster, Setup, Display Units and switch it over. Switch everything else over to English while you're there. I don't know where you're getting all your info but...with all due respect, dgoodhue is mistaken. Per the manual:

Install fuel pressure gauge
disconnect vac hose
ign off for min 10 secs and AC off
ign on. Fuel pump should run for 2 secs.
Note pres after pump stops.
Pressure should be 35-38 psi and holding steady

If all the above happens then:

Start engine (normal operating temp)
Reconnect vac line
pressure should drop slightly

If yes to all of this then the problem is somewhere else.

 

[MyTy]

Re: Slowly Losing Fuel Pressure

In DataMaster, Setup, Display Units and switch it over. Switch everything else over to English while you're there. I don't know where you're getting all your info but...with all due respect, dgoodhue is mistaken. Per the manual:

Install fuel pressure gauge
disconnect vac hose
ign off for min 10 secs and AC off
ign on. Fuel pump should run for 2 secs.
Note pres after pump stops.
Pressure should be 35-38 psi and holding steady

If all the above happens then:

Start engine (normal operating temp)
Reconnect vac line
pressure should drop slightly

If yes to all of this then the problem is somewhere else.

The problem with my situation is I have a brand new Accufab AFPR and when I put the key in on position the fuel pump does prim and goes to the desired level immediately starts dropping in fuel pressure down to about 20lbs than stops.. Its the reason I started this post. someone resonded saying that they had the same exact problem with there new Accufab AFPR and had a new one sent to them and it did the same exact thing again. apparently that's what Accufab regulators are prone to do. when the truck is runnin it holds pressure though..

 

[dgoodhue]

Re: Slowly Losing Fuel Pressure

In the past when I was researching on setting fuel pressure I read on here that when you disconnect the vacuum line from the AFPR the fuel pressure goes up about 10lbs.. so when adjusting you have to go 10lbs above what your aiming for because when you put the vacuum back on it will go down 10lbs.. and from my experience that's exactly what happens when I disconnect the vacuum it goes up about 10lbs.. like I said I'm new to vacuum systems but I'm a novice at fuel pressure related problems as well. I'm a DIY kind of person so I always attempt stuff first before taking it in to people..

my DataMaster reads the vacuum KPg.. at Idle when warm its typically 67.4

To answer the question on what chip do I have.. its a Moates chip. It came with the truck and I know absolutely nothing about the chip. I recently emailed a person that works for Moates and was the goto guy.. at least that's what the post said. I didn't happen to look at the post date because its been about a week now and ive got no response yet.. I'm starting to think the guy don't work there anymore.. I want to learn more about the chip but don't know how.. was going to start a post soon about it but trying to get other things figured first.. I'm a lil worried the chip has something to do with this and that is really out of my realm.. heres a pic of the chip..

Of the commercially available chips, they ranged from a base fuel pressure of 40 to 50psi and it does make a huge difference. A 50# ultimate had a base FP of 40psi, with a 50# fp it is eye watering pig rich.

If you have a moates chip, it could be any chip program or a custom tune. The person at moats isn't goig to know what your tune is inside of programable chip. You either need to ask the previous owner to find out what it is or chip a burner to upload and determine it that way. You would probably be better off starting over with a new chip (turbo tweak) or putting back the stock one that is piggy back to the carrier. The injectors and (2 or 3 bar) map sensor need to match the chip.

From reading your posts, if it was me I would go back to the basics. Try to determine what mods your truck has. Figure out the chip/injector/sensor combo. Then get your basics straightened out -change the fuel pump, fuel filter, verifying the timing (remembering that the balancer can slip), make sure it has the correct spark plugs, new cap/rotors/wires, check the IC pump operation, and change the vacuum lines. From other post on the adjusting the TPS and throttle stop, you make also want to clean out the throttle body and replace the gaskets.