2nd Gen Non-Engine/Transmission Fuel Filter

[Don Bellamy]

I changed my fuel filter today, now I start the truck it runs at 450-500 rpm no throttle response and the idle is rough as a cobb. Any thoughts?

Don

 

[JLandry]

Don,



Unless there's something wrong with your new filter, it sounds like you probably just have air trapped in the fuel injection system... or you may have an leak at the fuel filter canister lid.



How's the fuel pressure at the VP44 inlet while this is happening?



You might want to unscrew the fuel canister lid and check to see that the o-ring seal isn't deformed and is still seated correctly in its groove. While open, be sure the filter canister is full of fuel. Lubricate the o-ring seal on the lid with a thin coating of silicone grease (or motor oil if you don't have that) to prevent it from deforming when installing the lid. Reinstall the lid and tighten to the proper torque.



After doing the above, turn the ignition key to the run position and then bump the starter BUT DO NOT START the engine. With the ignition key still in the run position, you should hear the lift pump run for about 25 seconds. When it stops running, turn the ignition key off. Repeat this procedure 3 times to completely fill the fuel filter canister and pressurize the VP44 fuel injection pump.



Start the engine and hold a high idle while you watch for the fuel pressure to increase and stabilizes to its normal range after a few minutes running.



Let us know how that works out.



Best regards,



John L.

 

[Don Bellamy]

John

When I bump the starter my pump runs and the gage in the cab reads 14psi and the gage under the hood at the fuel filter housing reads 15psi. I get no response from the throttle. Is it possible to suck air account of a cracked cap or a twisted o ring but not leak fuel? When the thing is at idle I do see that the fuel pressure drops to 2-3 psi? Thank you for your time.



Don

 

[JLandry]

John

When I bump the starter my pump runs and the gage in the cab reads 14psi and the gage under the hood at the fuel filter housing reads 15psi. I get no response from the throttle. Is it possible to suck air account of a cracked cap or a twisted o ring but not leak fuel? When the thing is at idle I do see that the fuel pressure drops to 2-3 psi? Thank you for your time.



Don

Don,



OK... with that 15 psi engine off and 2-3 psi at idle it sounds like you either have:



1. A severe restriction in the new filter.

2. A lot of air in the system.

3. A failing lift pump.



Did you remove the fuel filter canister cap, check the o-ring seal, and verify the filter canister is completely full of fuel? If it's not completely full, pour in CLEAN diesel to top it off before closing it again.



Are you sure you have the correct fuel filter installed? Pull it out and examine it to make sure it's not somehow contaminated. Could you possibly have gotten a bad tank of fuel that just happens to coincides with replacing the fuel filter?



If the lift pump is failing, it's possible it can't supply the necessary fuel volume to keep the VP44 injection pump adequately supplied when the engine is running. Another thing you can try is to disconnect the fuel line at the VP44 inlet, place the end in a container (coffee can, etc. ) and then bump the starter to activate the lift pump. You'll be able to observe the volume and quality of fuel being pumped into the container. Look for bubbles.



Please keep us posted.



John L.

 

[Don Bellamy]

John

I took the new filter out, the canister was half fuel of fuel, I replaced that filter with another new filter which I get from Geno's put the cap on but not tight, bumped the starter til fuel ran out then tighten to specs. This lift pump would push 14psi when the starter was bumped but while cranking the pressure went to 0. I installed another new lift pump bumped the starter and pressure went to 14psi, would start and idle at 300-400 rpm, very very rough, never heard so much noise. I did not check the pressure while cranking though, will do in the morning.

Don

 

[JLandry]

I installed another new lift pump bumped the starter and pressure went to 14psi, would start and idle at 300-400 rpm, very very rough, never heard so much noise. I did not check the pressure while cranking though, will do in the morning.

Don,



Assuming you have god fuel pressure when the engine is running now, the low rpm, rough running, and excessive noise is very likely just caused by air trapped in one or more of the high pressure fuel injection lines between the VP44 and the fuel injectors. This is normal when a bunch of air has made its way into the VP44 and should start to clear itself up after several minutes of running. While idling you can try gradually increasing the throttle to a higher idle to help the process along. The engine may not completely smooth out until you get the rpms up and a load on the engine.



Now on the other hand if the condition doesn't clear up, something else could be wrong and we'll have to continue trouble shooting.



Let us know.



Best regards,



John L.

 

[Wyomingcowboy]

You can try cracking the lines at the head, also. It makes a bit of a mess but it will help you purge any air that might be trapped between the VP and the tubes. You can get to a few of them easily and that should help it smooth out some and the others that you can't reach will purge themselves. I had a similar problem when I fired mine up after the rebuild and all lines were totally empty. I bumped the starter several times and cracked all lines loose and still had the extremely rough idle for a minute or two until I could crack all the easy to reach lines again.

 

[Don Bellamy]

When cranking the pressure gages go to O, I now have 2 codes, p0253 and p1688.

 

[Wyomingcowboy]

P0253 - FUEL INJECTION PUMP FUEL VALVE OPEN CIRCUIT



P1688 - INTERNAL FUEL INJECTION PUMP FAILURE



Where is your fuel press. gauge located?

 

[JLandry]

When cranking the pressure gages go to O, I now have 2 codes, p0253 and p1688.

Don,

Those DTC's normally would indicate a failed VP44 fuel injection pump, but because you've been having problems with air in the fuel system, and you've undoubtedly run your batteries down by now, hang in there and try a few things before coming to any conclusions. The P0253 can be triggered by less than 12 volts being supplied to the VP44, which of course could easily be happening if you've been cranking a lot and the batteries haven't had a chance to be recharged.

First off, low fuel pressure during cranking is normal... even more so when the battery has been run down... so you can effectively ignore that. I was hoping you'd tell us what the fuel pressure is when idling. It should be about 14-15 psi.

Here's what I would recommend next...

1. FULLY recharge the batteries.

2. Disconnect the fuel line at the VP44 inlet. Place the end of this fuel line in a suitable container then turn the ignition switch to RUN and bump the starter. As you well know by now, the lift pump will cycle for 25 seconds (if you let it). The goal here is to verify the fuel supply system is completely purged of air and pumping fuel appropriately. Once you've verified this, reconnect the fuel line to the VP44.

3. Start the engine and no matter how awful it sounds, LET IT RUN. Don't be afraid to gradually raise the rpm to a high idle if you can. The VP44 needs time to push all the air out of the high pressure lines and injectors... and it's not very good at doing it. IF the engine won't start after cranking for 30 seconds or so, then you'll have to first crack open a few of the high pressure lines where they go into the side of the cylinder head as Wyomingcowboy said. This allows air to escape the lines and fuel to reach the injectors. BTW, I like to place shop towels around the loosened fittings because I hate soaking my engine with diesel. As soon as the engine starts, close the fittings and let the engine run no matter how bad it sounds. If the injection pump is working properly, the engine WILL smooth out eventually... it just takes time.

If you succeed in getting the engine to run and the fuel pressure (while idling) indeed shows low pressure, then you may have a problem with the lift pump not getting adequate power. We can deal with that if needed.

Please try the above steps and report back.

Hang in there!

John L.

 

[Don Bellamy]

John

When I bump the starter my pump runs and the gage in the cab reads 14psi and the gage under the hood at the fuel filter housing reads 15psi. I get no response from the throttle. Is it possible to suck air account of a cracked cap or a twisted o ring but not leak fuel? When the thing is at idle I do see that the fuel pressure drops to 2-3 psi? Thank you for your time.



Don

In the cab and on the out side of the filter.

 

[Don Bellamy]

John

Just what you explained is what I was told today by a fellow that does nothing but work on these engines. He also said not to worry about those 2 codes, but had it been a p216 in his experience the game is over, he claims he has installed 344 of these pumps. I have recharged my batteries and in the morning I will go thru the process, thanks for all your time.



Don

 

[JLandry]

I have recharged my batteries and in the morning I will go thru the process, thanks for all your time.

Don,



Dumb question...



You DO have plenty of fuel in the tank... right?



I ask because there have been guys here on the TDR forums that have gone through nightmares trying to troubleshoot perplexing fuel supply problems and it turned out to be a faulty fuel level reading with the lift pump sucking air from the tank.



Thought I'd mention this just-in-case.



Best regards,



John L.

 

[Don Bellamy]

John,

I have a full tank of fuel, after going thru what you explained the truck now idles at 750 rmp, still on the rough side, 14 psi at idle. When I give it throttle the rpm's flutter a little but still no throttle?



Don

 

[HBarlow]

As I quickly scanned the posts I see some excellent detailed advice from knowledgeable members but I didn't see any discussion of the method used for replacing the fuel filter or the possibility that changing the filter introduced foreign particles into the system downstream of the filter.

When I owned an earlier truck with a screw-off cap and drop in filter I changed the filters according to schedule but rarely dumped or wiped out the cannister when the filter was out. I have forgotten the details of discussions and warnings I've read years ago but it is possible to introduce particles into the cannister downstream of the new filter element when changing it.

Has that possiblity been considered? My old '01 would stumble and run rough for a minute or two but quickly purge air itself and smooth out when I dumped the fuel cannister.

 

[JLandry]

John,
I have a full tank of fuel, after going thru what you explained the truck now idles at 750 rmp, still on the rough side, 14 psi at idle. When I give it throttle the rpm's flutter a little but still no throttle?

Don,

With that fuel pressure you're seeing, you've pretty much eliminated everything up to the VP44. It's sounding more like your VP44 has died and gone into the dreaded "dead pedal" mode.

Ya know it's interesting... I've lost track of how many times I've read here about someone just changing their fuel filter and then all of a sudden they find the VP44 has died. If I had to guess I'd say the VP44 was on the verge of failing already, and temporary low fuel pressure (due to air being introduced in the fuel filter canister) pushes it over the edge.

Do you have a code scanner so you can clear those trouble codes you saw before? After you clear the codes, you'd want to start the engine, shut it back down, then check for trouble codes again with ignition in the RUN position (engine not started). That might reveal something. But keep in mind some VP44's die without ever throwing a trouble code.

Since a replacement VP44 is so expensive, there's something else I'd want to eliminate first before deciding the VP44 is toast (unless new trouble codes indicate it is). You may want to verify the APPS (Accelerator Pedal Position Sensor) is working properly. My thinking behind this is maybe the VP44 isn't being told to increase engine rpm because there's something wrong with the Throttle Position Sensor (TPS). It's a long shot, but not much trouble to check.

To do this, remove the big APPS assembly from the front driver side of the engine. BTW, the accelerator pedal cable pops straight off a ball on the bell crank assembly... don't try twisting it off or prying on one side of the cable end only. When you get the APPS assembly off, on the backside you'll find the black plastic TPS. Disconnect the wiring harness connector and you'll see 6 pins coming out of the TPS. Using an ANALOG multimeter, check the resistance between pins 5 and 6 as you slowly open the bell crank (just like if the accelerator pedal cable were opening it). The resistance isn't important. You're simply looking for a smooth sweep of the multimeter needle from the TPS fully closed to fully open. The TPS is basically a giant rheostat and any jumping around or dead spots mean it's got problems.

Next, using either a digital or analog multimeter, check for continuity (a closed circuit) between pins 1 and 6 when the bell crank is closed (like it would be at idle). When you open the bell crank (coming off idle), at some point this circuit will open and have no continuity.

Lastly, check for an OPEN circuit (no continuity) between pins 1 and 2 when the bell crank is closed, and for continuity (a closed circuit) when the bell crank is opened (off idle). This is exactly opposite of the last test.

If all this checks out, then I don't know what else it could be but that the VP44 suddenly failed after changing the fuel filter. Maybe someone else will chime in with other ideas.

Regards,

John L.

 

[JLandry]

Has that possiblity been considered? My old '01 would stumble and run rough for a minute or two but quickly purge air itself and smooth out when I dumped the fuel cannister.

Same here, but maybe if the VP44 was on the ragged edge, the lack of fuel pressure could rupture the already weak accumulator diaphragm.

I guess the proper thing to do when changing the fuel filter and you have an old VP44 might be to loosen the fuel line at the VP44's fuel inlet and activate the lift pump to purge all the air from the low pressure side of the fuel system prior to starting the engine.

Just an idea.

John L.

 

[fmj]

John, I've often wondered if we don't hurt the VP when we change filters. Since its so critical to have fuel to lub it, is it scored when air enters line during filter change, and over time the pump fails? My VP failed at about 160k and had always seen 12# or more for the first 30k miles, and then I installed a pusher pump and it was never under 16#. The only exception to this is when fuel filter was changed. I'm sure this wouldn't account for all the failures, but ???? Just wondering. Good thread.

 

[JLandry]

Just wondering.

You've got to figure the VP44's wear internally over time even when supplied with plenty of fuel. I guess there just comes a point when they give out and maybe we do help them along a little by allowing a bunch of air through them. Hopefully they give some fair warning first by throwing a trouble code... or at least having the courtesy of failing when the truck is in your driveway.



The VP44 on my own truck recently started throwing an occasional P0216 DTC right after I changed the fuel filter and apparently didn't get all the air out of the fuel filter canister. Maybe just coincidence, but from my reading here on the TDR forums this pattern seems to happen pretty often. I already have a replacement VP44 standing by just waiting to go in. I'll probably install it when I get a nice dry sunny weekend (a rare commodity in Seattle in the fall).



Best regards,



John L.

 

[fmj]

Hopefully they give some fair warning first by throwing a trouble code... or at least having the courtesy of failing when the truck is in your driveway.

oh ya. mine gave me no code either on dash or my code reader until it crapped out in east nowhere, on a 115 degree day, after everything closed on a friday, towing 5er. yep, what could go wrong.