03 Alh losing prime

[coffeehouse]

2003 alh jetta hard starting in any weather and airlocking. The problem seems to progressively be getting worse and i cannot find where it is getting the air. As just a little background info here is all of what I have changed/tested trying to rectify this.
I've installed all new lines with gates fuel line including the small ones at the injectors. New fuel filter, new T at the top with o rings. New pump seals, added mini lift in the engine bay to help it if it was draining back. Did injector seat washers incase one was leaking cold. New connectors for the fuel lines. For the past 2 months the car has been long cranking on the first start but would eventually start. Yesterday I replaced the timing kit and put the car all back together fired up checked timing through obd eleven pump was at 55/123 which is right where it was before. everything was good and it was running fine drove home from the shop and parked overnight. I come out this morning and the car took way longer than it ever does. So I stopped and tried again. Still no start. This time I cracked cyl 1 injector and it slowly started to pressurize up and about 5 cranks later started and sprayed. Went out and closed it car ran fine. And is now starting 2 cranks every time after the initial cold start. It's only after sitting until stone cold that it gives me issues. Everything I see says pump seals but my pump is dry as a bone. None of the fuel system was disconnected last night as I was just doing a belt and component kit. I'm kinda baffled on why it would be airlocking so badly over about 10 hours.

 

[BobnOH]

Thermostatic tee seals? Pull it out, if the orings look good put a bit of grease on them to help them seal.
If all else fails try testing the fuel supply in sections.
Remote possibles include debris in the tank interfering with fuel pickup.

 

[IndigoBlueWagon]

I wonder if your injection pump is near end of life.

 

[coffeehouse]

Thermostatic tee seals? Pull it out, if the orings look good put a bit of grease on them to help them seal.
If all else fails try testing the fuel supply in sections.
Remote possibles include debris in the tank interfering with fuel pickup.

I have changed out the Thermo T for an oem with new seals originally thinking that was an issue. Still continued to happen.

I wonder if your injection pump is near end of life.

No shavings inside, iq is static at 3.5 and it's got loads of pressure when you crack the line. From what I've seen usually a loss of pressure at injectors comes first and everyone sees the dreaded dribble not spray. So I don't really think my pump itself is the issue.

 

[coffeehouse]

Was going to give it a shot later just stuffing the hose into a gallon of fuel and see if it still does it after a few hours.Just kind of at a loss where the air could be entering

 

[IndigoBlueWagon]

The pump may do fine in providing fuel at pressure once it's available to the pump, but it may be struggling to pull it from the tank. And I also wonder if your small inline pump is creating vs solving a problem in some way.

 

[coffeehouse]

The small pump was suggested to try to see if that was the issue but adding that made no change in how it started cold. Even if I leave it unplugged and try without it it's the exact same. This problem started long before adding the small pump.

 

[coffeehouse]

The pump may do fine in providing fuel at pressure once it's available to the pump, but it may be struggling to pull it from the tank. And I also wonder if your small inline pump is creating vs solving a problem in some way.

I will hook a gauge up later on and post the results of how much suction the pump has off cranking

 

[Brett San Diego]

Did you change the injection pump head O-ring? If not, do it. I've had a hard start/no start be caused by losing prime from air getting past that O-ring on more than one ALH.

Here's the first video of a 3 video series:

Brett

 

[ranagon]

I'm fighting with basically the same problem on an '03 ALH. Since the innards of the IP operate under pressure from the VE lift pump, you'd expect a fuel leak out if it's also leaking air in. Apparently, that's not always the case. I least I don't see any leaks on mine, but it's still loosing prime. I suspect it might be the input shaft seal on the IP. It operates under the same vacuum that pulls fuel from the tank. It might not leak fuel. But if it's leaking air into the pump under static conditions, that leak is above the tank and could siphon the IP and fuel filter dry through the suction line. The tank pickup on earlier ALH's had an internal check valve. Those are available. In 2003 they got rid of the in-tank check valve and installed a (1-year only) check valve in the hard line between the fuel pick-up and the under-chassis hard line. (That 2003 item is NLA and later PD engines had an in-tank lift pump.) The only function I see for the check valve is as a back-stop to prevent drain-back resulting from a vacuum leak. A leaking input shaft seal coupled with a check valve that isn't sealing tight would do exactly what you're describing. Or, the vacuum leak(s) might also be at the little return hoses between the injectors, again coupled with a dysfunctional check valve. Those hoses are hydraulically connected through the IP to the suction line, and operate under very little pressure. Incidentally, I've had Mercedes and Isuzu diesels that had hand pumps mounted on the IP to allow manually priming the system.

 

[Brett San Diego]

I'm fighting with basically the same problem on an '03 ALH. Since the innards of the IP operate under pressure from the VE lift pump, you'd expect a fuel leak out if it's also leaking air in. Apparently, that's not always the case. I least I don't see any leaks on mine, but it's still loosing prime. I suspect it might be the input shaft seal on the IP. It operates under the same vacuum that pulls fuel from the tank. It might not leak fuel. But if it's leaking air into the pump under static conditions, that leak is above the tank and could siphon the IP and fuel filter dry through the suction line. The tank pickup on earlier ALH's had an internal check valve. Those are available. In 2003 they got rid of the in-tank check valve and installed a (1-year only) check valve in the hard line between the fuel pick-up and the under-chassis hard line. (That 2003 item is NLA and later PD engines had an in-tank lift pump.) The only function I see for the check valve is as a back-stop to prevent drain-back resulting from a vacuum leak. A leaking input shaft seal coupled with a check valve that isn't sealing tight would do exactly what you're describing. Or, the vacuum leak(s) might also be at the little return hoses between the injectors, again coupled with a dysfunctional check valve. Those hoses are hydraulically connected through the IP to the suction line, and operate under very little pressure. Incidentally, I've had Mercedes and Isuzu diesels that had hand pumps mounted on the IP to allow manually priming the system.

Or, it's the pump head seal, a very well-known and thoroughly documented source of fuel leaks and/or air leaks causing loss of prime at the IP. I've never heard of the shaft seal being an issue. Another documented cause for loss of prime is the "thermo-T" connector at the fuel filter.

VE system doesn't have a lift pump.

Brett

 

[coffeehouse]

I'm fighting with basically the same problem on an '03 ALH. Since the innards of the IP operate under pressure from the VE lift pump, you'd expect a fuel leak out if it's also leaking air in. Apparently, that's not always the case. I least I don't see any leaks on mine, but it's still loosing prime. I suspect it might be the input shaft seal on the IP. It operates under the same vacuum that pulls fuel from the tank. It might not leak fuel. But if it's leaking air into the pump under static conditions, that leak is above the tank and could siphon the IP and fuel filter dry through the suction line. The tank pickup on earlier ALH's had an internal check valve. Those are available. In 2003 they got rid of the in-tank check valve and installed a (1-year only) check valve in the hard line between the fuel pick-up and the under-chassis hard line. (That 2003 item is NLA and later PD engines had an in-tank lift pump.) The only function I see for the check valve is as a back-stop to prevent drain-back resulting from a vacuum leak. A leaking input shaft seal coupled with a check valve that isn't sealing tight would do exactly what you're describing. Or, the vacuum leak(s) might also be at the little return hoses between the injectors, again coupled with a dysfunctional check valve. Those hoses are hydraulically connected through the IP to the suction line, and operate under very little pressure. Incidentally, I've had Mercedes and Isuzu diesels that had hand pumps mounted on the IP to allow manually priming the system.

I apologize for not updating I've been really busy switching jobs. So I've actually gotten this sorted out recently and the car starting normal again. It was none of the issues mentioned rather it was a air leak at the tube nut on inj #1 , again there was no diesel leaking out of it but upon spraying it with cleaner ( was cleaning off from cracking lines) I got it to stumble, sprayed the hell out of it again and it stumbled again! After pulling the line it had a ridge on the edge of the sealing surface so I cleaned it with a small file and it has been completely fine starts second crank even when it was below 50 the other morning. But you are correct there are known issues with the check valve and pump. I did what was mentioned above and put the fuel lines to a gallon container to isolate the pump and injectors from the rest of the car and still had this issue which pointed me to it being after the filter. This sounds like it may be a good test for you too if you believe the pump is shot. I've already done all my seals,and distribution head was swapped along with camplate well before this issue arose and ran fine so I did not suspect my pump to be an issue.

Or, it's the pump head seal, a very well-known and thoroughly documented source of fuel leaks and/or air leaks causing loss of prime at the IP. I've never heard of the shaft seal being an issue. Another documented cause for loss of prime is the "thermo-T" connector at the fuel filter.

VE system doesn't have a lift pump.

Brett

He's referencing the front seal on the pump which absolutely is a known problem on these pumps from the research I've done trying to remedy this it is a big concern aswell as the pump shaft itself getting "out of spec" and not pulling hard enough to get fuel through. I spent a long while trying to find this before posting here and I know it's groundhog day on this forum but it isn't always the pump head and Thermo T. There's so many references to these being issues if I skipped right over that and asked anyway I'd be a smoothbrain idiot. I came to get the answers from outside the box, and if you look at my original post it even says pump seals were done.

 

[coffeehouse]

A side note for anyone dealing with something like this. Make sure you ENTIRELY degrease the engine bay and under side of the car. This will greatly increase your chances of seeing small leaks especially if it's hiding behind oil sludge. My engine bay along with my underside are clean as a whistle and it made it alot easier to be positive I didn't have any fuel leaking. Plus it's nice to have a clean Shiny engine.

 

[coffeehouse]

I'm fighting with basically the same problem on an '03 ALH. Since the innards of the IP operate under pressure from the VE lift pump, you'd expect a fuel leak out if it's also leaking air in. Apparently, that's not always the case. I least I don't see any leaks on mine, but it's still loosing prime. I suspect it might be the input shaft seal on the IP. It operates under the same vacuum that pulls fuel from the tank. It might not leak fuel. But if it's leaking air into the pump under static conditions, that leak is above the tank and could siphon the IP and fuel filter dry through the suction line. The tank pickup on earlier ALH's had an internal check valve. Those are available. In 2003 they got rid of the in-tank check valve and installed a (1-year only) check valve in the hard line between the fuel pick-up and the under-chassis hard line. (That 2003 item is NLA and later PD engines had an in-tank lift pump.) The only function I see for the check valve is as a back-stop to prevent drain-back resulting from a vacuum leak. A leaking input shaft seal coupled with a check valve that isn't sealing tight would do exactly what you're describing. Or, the vacuum leak(s) might also be at the little return hoses between the injectors, again coupled with a dysfunctional check valve. Those hoses are hydraulically connected through the IP to the suction line, and operate under very little pressure. Incidentally, I've had Mercedes and Isuzu diesels that had hand pumps mounted on the IP to allow manually priming the system.

Brett is correct in saying there is no lift pump in the tank. There are only the 2 wires for the level sensor . So it will bleed back to tank and have trouble pulling it back up if that check valve is failed and it is drawing fuel back but there would need to be a reason for it sucking back to tank they don't just bleed back for no reason as there's also the 90 degree upward to the tank so gravity will only take it so far. I have installed a small 5psi inline pump after the filter but it did not solve the issue nor did it make the leak any easier to find but it did slightly raise iq so keep that in mind.

 

[Brett San Diego]

I've seen plenty of people say the injection pump seals were replaced, when only the quantity adjuster seals were done, including on a 2003 wagon I just bought. The owner said a reputable shop resealed the pump, but it started losing prime again. I dug into the pump head O-ring after purchasing the car for a song, and it was brittle and came out in pieces. Hadn't been touched in a millenium. After pump head O-ring replacement, it will start after sitting for a couple of months.

Brett

 

[icesimpson]

Experiencing the same problem and having replaced and reprimed lines between filter and pump… but still getting air, I’m planning to replace filter and rubber chassis lines on the right fender… are those rubber lines custom or generic cut to fit? I can’t seem to find them anywhere

 

[STDOUBT]

The right fender hoses are custom formed, but it's possible to replace them with off the shelf hose.
Thing is, the most common areas of air intrusion are the seals in the injection pump and the little plastic "thermo-tee" in the filter. I would rule all that out before getting into hose replacement.
And, yes, air intrusion into the pump itself will present as bubbles in the clear line. Don't throw out the line you replaced. They're harder to find every year.
Oh, and Welcome to the Club!!!

 

[AndyBees]

I apologize for not updating I've been really busy switching jobs. So I've actually gotten this sorted out recently and the car starting normal again. It was none of the issues mentioned rather it was a air leak at the tube nut on inj #1 , again there was no diesel leaking out of it but upon spraying it with cleaner ( was cleaning off from cracking lines) I got it to stumble, sprayed the hell out of it again and it stumbled again! After pulling the line it had a ridge on the edge of the sealing surface so I cleaned it with a small file and it has been completely fine starts second crank even when it was below 50 the other morning. But you are correct there are known issues with the check valve and pump. I did what was mentioned above and put the fuel lines to a gallon container to isolate the pump and injectors from the rest of the car and still had this issue which pointed me to it being after the filter. This sounds like it may be a good test for you too if you believe the pump is shot. I've already done all my seals,and distribution head was swapped along with camplate well before this issue arose and ran fine so I did not suspect my pump to be an issue.

I realize that the Original Poster to this Thread has not re-visited the TDI Club since May, 2024. My hat is off to him and all his work and basically thoroughly explaining what he did in his introductory post.

That said, I really find it hard to believe that an Injector Hard Line not sealing at the Injector was allowing siphoning of fuel out of the Injector Pump (replaced by air).

Unless I totally do not comprehend his explanation, there is no way in *ell that spraying anything on a loose or defective sealing hard line at the Injector is going to cause a running engine to stumble. Prove it! The Fuel Pressure is outward and zero suction.

Next, there is no way in *ell that a non-sealing hard line at the Injector will allow fuel to siphon out of the Injector Pump. Think... think! At the pump head the hard lines are secured to the Delivery Valves with the same size nut that's on the Injectors. Those Delivery Valves also serve as "check-valves" preventing back-flow out of the hard lines back into the Injector Pump.

A simple Internet search (and my own knowledge) >>>> "A VE injection pump delivery valve's primary function is to control the precise timing and amount of fuel delivered to the injectors by acting as pressure-regulating valves, preventing backflow from the injector line while ensuring a consistent supply to the injectors during the injection cycle, thereby maintaining the optimal engine performance. Backflow prevention: This is the main function of the delivery valve, ensuring that fuel doesn't flow back from the injection line to the pump when the plunger retracts, which could disrupt the injection timing."

Lastly, if there was, in fact, a defect in the sealing surface of the hard line at the injector, well, it would leak like crazy with the engine running. And, I am surprised that filing on it didn't make it worse ......... the sealing surface on the Injector and Hard Line is extremely precise.

So, my guess is, the OP accidentally "fixed" something during more searching for the problem.

Someone, please tell me what I've missed.

 

[BobnOH]

my guess is, the OP accidentally "fixed" something during more searching for the problem.

Happens a lot, especially with wire/connects.