Mk4 Jetta ALH Fuel Issues

[Brandiianderson]

Just reaching out to see if anyone has some advice for my tdi, I’ll start from the beginning to give some background information.

So when I bought the car it was having underboost issues, I eventually replaced the turbo because it was going bad, I now have overboost issues. I’ve replaced a few parts with no luck, but the car was still running and driving just throwing into limp mode if it overboosted. Over the winter I had been starting the car about once a week but not driving it due to the overboost issues. I had let the car go about 2-3 weeks without starting it and eventually it wouldn’t start anymore. I assumed the battery needed jumping but needed to replace my coolant thermostat so I replaced that part and then attempted to jump the car. Car won’t jump, motor shakes furiously, oil light flashes when cranking. I had autozone test the battery and it wasn’t holding a charge so I bought a new battery and the car still cranks but won’t start. So I know most likely the car is not getting fuel. I loosened the bolts on the fuel lines to the motor and had someone try to crank the car a few times. I see fuel at the lines but there isn’t any fuel spurting when it’s being cranked. About 8 months ago I replaced two gaskets on the fuel injection pump but did not replace the one on the right side, I lined everything up, afterwards the car seemed to be running much better, and has been running since with no issues starting until about a month ago. When I tried jumping the car I did notice a single drop of fuel at the bottom of the fuel pump injector drip off but hard to tell where it was actually coming from. Since then I haven’t seen any other drop of fuel and no pooling of fuel anywhere around it.

I’m kind of stuck on what to do next as I don’t have access to vagcom right now. I was planning to check the fuel pump and the fuel filter check valve to see if maybe the pumps not working or maybe the valve is clogged. I’ve also read the possibility of the crank shaft position sensor going bad. Advice on maybe that single drop of fuel could be a sign that 3rd gasket on the fuel pump injector is a full on leak? I’m just writing on here to see if anyone has had similar issues or has recommendations on where to start. Thanks

 

[STDOUBT]

Scanning the car could really help point to the problem.
How did you know the new condition was overboost vs. underboost w/o a scanner?
The car's shaking is probably a worn out dogbone mount
(pendulum mount between the bottom of the tranny and the front edge of the subframe)
and that would smooth out once the engine is running. Very much worth it to replace. Pretty easy job too.
The Thermo-Tee at the return side of the fuel filter will sometimes crack and allow air into the system. I've never heard of clogging to be a problem there. If your car is a manual there's a clear portion of the fuel sending line - how much air is in there?
Also, I never opened my injector top nuts enough to spray - mine just dribbled, and it's all good.
You might need to crank a bit longer though, to purge all the air if your car's sitting spell caused it to lose prime.

oil light flashes when cranking

Not sure what to say about that. Someone else will comment, I'm sure. Doesn't seem right.
Crank Position Sensor - do you see RPMs on your tach when cranking?
These might help:
This is the go-to Limp Mode thread. Much good info.
This is the go-to Car Won't Start thread.

 

[STDOUBT]

Oh, another question since I saw your prior thread just now.
Did you let WVO sit inside the fuel lines when you let her sit for the 2-3 weeks?
You did run out whatever fuel the prior owner had in there, and you've been using
regular old Diesel #2 right? When it was running well, that was all normal Diesel, right?
(or B20... or B50... or B99...?)

 

[P2B]

Brandiianderson said:
oil light flashes when cranking

Not sure what to say about that. Someone else will comment, I'm sure. Doesn't seem right.

That is normal after 20 or so seconds of cranking without starting. It means give the poor starter a rest to cool down

 

[Vince Waldon]

Oil light will flash if the engine is cranked longer that 10-15 seconds.

The sensor is ignored initially but will wake up, see low oil pressure (due to cranking RPM) and complain if cranking continues.

Safe to ignore.

 

[Brandiianderson]

Scanning the car could really help point to the problem.
How did you know the new condition was overboost vs. underboost w/o a scanner?
The car's shaking is probably a worn out dogbone mount
(pendulum mount between the bottom of the tranny and the front edge of the subframe)
and that would smooth out once the engine is running. Very much worth it to replace. Pretty easy job too.
The Thermo-Tee at the return side of the fuel filter will sometimes crack and allow air into the system. I've never heard of clogging to be a problem there. If your car is a manual there's a clear portion of the fuel sending line - how much air is in there?
Also, I never opened my injector top nuts enough to spray - mine just dribbled, and it's all good.
You might need to crank a bit longer though, to purge all the air if your car's sitting spell caused it to lose prime.

Not sure what to say about that. Someone else will comment, I'm sure. Doesn't seem right.
Crank Position Sensor - do you see RPMs on your tach when cranking?
These might help:
This is the go-to Limp Mode thread. Much good info.
This is the go-to Car Won't Start thread.

I meant to mention I do have a basic scanner so I can scan codes on that but not as detailed as vagcom. I only mentioned vagcom because every forum I’ve read I know everyone immediately mentions connecting to vagcom to diagnose. So with my basic scanner it was scanning for underboost when I found oil sitting in the intercooler tubing. Then after replacing the turbo it began coding for overboost. The actuator was moving good but I was going to check it again but that issue was put on the back burner because of all of this now. I feel like that’s most likely not connected to my issue but I know it could be array of possibilities. I did also replace all the motor mounts last year so it’s not that. I had read up on a couple forums where the motor shaking and the oil light flashing without the car starting is often a fuel issue and I do feel like the cars wanting to start but it’s just not getting fuel so that’s where I’m stuck.

I am getting over 2k rpm’s but I’ve heard of people still being able to drive with a bad crank shaft position sensor so I’m confused on that part. Different car but my boyfriend’s car had a bad crank shaft but he wasn’t getting any rpm’s so I’m not sure how that works.

My car was manual swapped by the previous owner so I will absolutely check the line, I appreciate that recommendation.

I mentioned the spraying because I watched a Kerma video of them priming the fuel system and he undid all the bolts, had someone crank until 1 and 4 sprayed quite a bit, tightened those down, and then repeated 2 and 3. I’m worried about cranking it too much, do you think I could cause any issues by cranking it a bunch? If not I’ll go back out there and try some more.

Also the previous owner was running biodiesel through the wvo system for some reason. He’s unfortunately passed away so I can’t ask him anything but tank was empty and cleared out and I’ve been running regular diesel in it for over a year with no issue

I appreciate all the responses!

 

[Brandiianderson]

I posted this because after reading what feels like a million forums, there are so many different parts recommended to replace and I don’t want to keep throwing parts at it hoping it’ll work. I wish this car was easier but I feel like I have a lemon at this point because one thing after another breaks lol

 

[csstevej]

Just out of curiosity……where did you get the turbo and what brand was it?

Are you getting the Glow Plug light for a second or two when you first turn the key on? If yes continue…if no then you have a bad 109 relay and that is located under the steering column in the relay panel.

On the clear section of hose that goes from the fuel filter to the injection pump….is there a large air bubble there?

Try hanging a container of fuel off the hood with a hose to the injection pump like an IV bottle . I suspect you may have air in the pump , this will help with a little head pressure to the IP.

Don’t give up on the car…..you don’t have a lemon…..but there are some nuances that a lot of people don’t know about , but you are at the right place to get help .

The people here will help you get it sorted out….. be patient.

There is a learning curve with these cars but once figured out they are very reliable. I’ve got 5 in the family with the oldest being a 2000 to the “newest “ being my youngest daughter’s “ 2003 NB and she been driving it for 10 years now doing 115 miles a day with it.

 

[Brandiianderson]

Just out of curiosity……where did you get the turbo and what brand was it?

Are you getting the Glow Plug light for a second or two when you first turn the key on? If yes continue…if no then you have a bad 109 relay and that is located under the steering column in the relay panel.

On the clear section of hose that goes from the fuel filter to the injection pump….is there a large air bubble there?

Try hanging a container of fuel off the hood with a hose to the injection pump like an IV bottle . I suspect you may have air in the pump , this will help with a little head pressure to the IP.

Don’t give up on the car…..you don’t have a lemon…..but there are some nuances that a lot of people don’t know about , but you are at the right place to get help .

The people here will help you get it sorted out….. be patient.

There is a learning curve with these cars but once figured out they are very reliable. I’ve got 5 in the family with the oldest being a 2000 to the “newest “ being my youngest daughter’s “ 2003 NB and she been driving it for 10 years now doing 115 miles a day with it.

The turbo was a used oem turbo in great shape that came off another mk4, Garrett.

Yes glow plug lights for about a second, I did replace the 109 relay just in case because I had one in my parts car but obviously didn’t solve the problem.

I don’t think I have a clear hose lined up from the fuel filter, if I don’t is there a specific way I should check it for air?

For hanging the fuel do you have anymore details on doing that or anything to avoid when doing it? I just want to make sure I’m doing it correctly without breaking anything else

I’ve been told over and over again to sell the car but I’m being stubborn and refusing to let it win, I’m determined to get it back to running and driving

 

[shoebear]

You've mentioned several issues, not just fuel. Let me address the over/underboost issues.

First, some general background... Diesels have no throttle plate, so they do not generate vacuum as gas engines do. So we have a vacuum pump which supports the power brake booster, EGR valve, anti-shudder valve, and the turbo boost. All of these except brake boost are controlled by vacuum valves which are, in turn, controlled by the engine computer. The valve that controls turbo boost is called the N75. There are many things that can go wrong with the vacuum system, and unless it's in good shape, you will probably have turbo boost issues. The most common vacuum issue is old hoses that get brittle, crack, and leak.

Assuming the vacuum system in in good shape -- the N75 valve sends variable amounts of vacuum to the boost actuator (a linear diaphragm motor) mounted on the turbocharger. This operates a push rod that alters the angle of the vanes inside the turbine (exhaust) side of the turbo. The diaphragm can go bad and leak, and the turbine vanes can get clogged with carbon and not want to move easily.

So you can see that effective control of the turbo boost pressure requires a chain of things to be all working correctly.

Here are steps to find and isolate problems in this system (hat tip to burpod). You will need

• A hand vacuum pump (e.g. mityvac) with various adapters that comes with the pump
• Some extra vacuum hose
• A tee
• Something thin and flexible -- a thin feeler gauge, a piece of Scotch Tape folded over stuck to itself, etc.
• VCDS for step 3.

The process:

1. Test for overall vacuum leaks.
   1. You can do a "quick and dirty" test by holding your foot on the brake and shutting off the car. If you have a major leak, after 5-30 secs, you will feel the brake pedal rise, and if you are on a hill, you will have to push hard on the brake to keep the car from rolling.
   2. For a more precision: The vacuum pump is located on the driver side of the head. There is a thick rubber hose that connects to the rear of the pump. After a couple of inches, it transitions to a plastic hose which attaches to the brake booster, and at the transition, there is a tee with a thinner hose attached.
      
      
      1. Disconnect the thinner hose from the tee.
      2. Disconnect the brake booster hose from the pump and from the brake booster. You will have to pry the brake booster end loose; it's not easy.
      3. Plug the brake booster end of the hose and also the tee (I can use my fingers for this). Use the mityvac to apply vacuum to the pump end. If you can't create and hold a vacuum, the booster hose has a leak -- probably cracks in the plastic section. This is very common. You can fix temporarily with electrical tape until you get a new hose.
      4. Next connect the mityvac to the thinner hose you disconnected from the tee, and pump. If you can't create and hold a vacuum, there's a leak somewhere between the test point, the control valves, or vacuum reservoir. Detailed troubleshooting is beyond the scope of my instructions, but I have two suggestions:
         1. Feel and wiggle all vacuum hoses. If you find hard, stiff, or cracked, replace.
         2. Test downstream of the control valves: get a vacuum diagram and use mityvac tests at appropriate points to find/isolate any further leaks. Start by testing the output vacuum hose for each of the three vacuum valves.
2. Test the turbocharge and vane actuator
   1. Under the car, find the vacuum line to the turbocharger and disconnect it.
   2. Attach a hand vacuum pump (e.g. mityvac), put your fingers on the vane actuator rod, and start pumping. You should feel the rod pull back away from the turbo smoothly, with no catches or bumps. If it won't move properly, it probably has carbon chunks fouling the vane mechanism that will need to be cleaned. The quick way to do this is with oven cleaner (search for that), the most thorough way is to pull the turbocharger, disassemble the turbine side, and clean by hand.
   3. (You can alternatively do this test while testing the N75, Option 1). There is a set screw that limits the movement of the actuator; the actuator should hit the screw at about 18hg. If not, note where it does hit. You can detect when it hits by putting a feeler in front of the screw and wiggling it. When the actuator hits the screw, it will grab the feeler and hold it so you can't wiggle.
   4. Reconnect the vacuum hose to the turbocharger
3. Test operation of the N75 valve (two options)
   
   
   1. Option 1, with a tee
      1. Install a tee between the N75 and turbo control line, and connect your mityvac to the tee. It's helpful to have a vacuum hose connected to the tee that will reach back into the driver seat of the car.
      2. Start the engine and connect your VCDS.
      3. Run the VCDS N75 test and use the vacuum gauge on the mityvac to monitor vacuum as the VCDS runs up and down the duty cycle.
         1. At 0% duty cycle, the vacuum should be 24-25hg, and at 100% DC, vacuum should be 0hg.
         2. Optional: you can also double-check with your feeler gauge that the turbo vane actuator is hitting the set screw with each test cycle.
      4. Exit VCDS and shut off the car.
      5. Disconnect the tee and plug the turbo vacuum line back into the N75.
   2. Option 2, without a tee
      1. Disconnect the vacuum line from the turbocharger and connect it to your mityvac.
      2. Start the engine and connect your VCDS.
      3. Run the VCDS N75 test and use the vacuum gauge on the mityvac to monitor vacuum as the VCDS runs up and down the duty cycle. At 0% duty cycle, the vacuum should be 24-25hg, and at 100% DC, vacuum should be 0hg.
      4. Exit VCDS and shut off the car.
      5. Disconnect your mityvac and connect the turbo vacuum hose back to the turbo.
   3. If you don't have access to VCDS, you can hook up your vacuum gauge as described in option 1 or 2 above with the engine off, then have someone start the engine while you monitor vacuum. As soon as the engine starts, you should see vacuum increase to 24-25hg and stay there (engine idling).
   4. If the vacuum doesn't behave as expected, you could have a bad N75, a leak in one of the vacuum hoses having to do with the N75, or a wiring problem (unlikely).

I hope this is helpful. This should nail down the boost problem as long as the basic turbo is good. If you get stuck, ask us.

 

[Brandiianderson]

You've mentioned several issues, not just fuel. Let me address the over/underboost issues.

First, some general background... Diesels have no throttle plate, so they do not generate vacuum as gas engines do. So we have a vacuum pump which supports the power brake booster, EGR valve, anti-shudder valve, and the turbo boost. All of these except brake boost are controlled by vacuum valves which are, in turn, controlled by the engine computer. The valve that controls turbo boost is called the N75. There are many things that can go wrong with the vacuum system, and unless it's in good shape, you will probably have turbo boost issues. The most common vacuum issue is old hoses that get brittle, crack, and leak.

Assuming the vacuum system in in good shape -- the N75 valve sends variable amounts of vacuum to the boost actuator (a linear diaphragm motor) mounted on the turbocharger. This operates a push rod that alters the angle of the vanes inside the turbine (exhaust) side of the turbo. The diaphragm can go bad and leak, and the turbine vanes can get clogged with carbon and not want to move easily.

So you can see that effective control of the turbo boost pressure requires a chain of things to be all working correctly.

Here are steps to find and isolate problems in this system (hat tip to burpod). You will need

• A hand vacuum pump (e.g. mityvac) with various adapters that comes with the pump
• Some extra vacuum hose
• A tee
• Something thin and flexible -- a thin feeler gauge, a piece of Scotch Tape folded over stuck to itself, etc.
• VCDS for step 3.

The process:

1. Test for overall vacuum leaks.
   1. You can do a "quick and dirty" test by holding your foot on the brake and shutting off the car. If you have a major leak, after 5-30 secs, you will feel the brake pedal rise, and if you are on a hill, you will have to push hard on the brake to keep the car from rolling.
   2. For a more precision: The vacuum pump is located on the driver side of the head. There is a thick rubber hose that connects to the rear of the pump. After a couple of inches, it transitions to a plastic hose which attaches to the brake booster, and at the transition, there is a tee with a thinner hose attached.
      
      
      1. Disconnect the thinner hose from the tee.
      2. Disconnect the brake booster hose from the pump and from the brake booster. You will have to pry the brake booster end loose; it's not easy.
      3. Plug the brake booster end of the hose and also the tee (I can use my fingers for this). Use the mityvac to apply vacuum to the pump end. If you can't create and hold a vacuum, the booster hose has a leak -- probably cracks in the plastic section. This is very common. You can fix temporarily with electrical tape until you get a new hose.
      4. Next connect the mityvac to the thinner hose you disconnected from the tee, and pump. If you can't create and hold a vacuum, there's a leak somewhere between the test point, the control valves, or vacuum reservoir. Detailed troubleshooting is beyond the scope of my instructions, but I have two suggestions:
         1. Feel and wiggle all vacuum hoses. If you find hard, stiff, or cracked, replace.
         2. Test downstream of the control valves: get a vacuum diagram and use mityvac tests at appropriate points to find/isolate any further leaks. Start by testing the output vacuum hose for each of the three vacuum valves.
2. Test the turbocharge and vane actuator
   1. Under the car, find the vacuum line to the turbocharger and disconnect it.
   2. Attach a hand vacuum pump (e.g. mityvac), put your fingers on the vane actuator rod, and start pumping. You should feel the rod pull back away from the turbo smoothly, with no catches or bumps. If it won't move properly, it probably has carbon chunks fouling the vane mechanism that will need to be cleaned. The quick way to do this is with oven cleaner (search for that), the most thorough way is to pull the turbocharger, disassemble the turbine side, and clean by hand.
   3. (You can alternatively do this test while testing the N75, Option 1). There is a set screw that limits the movement of the actuator; the actuator should hit the screw at about 18hg. If not, note where it does hit. You can detect when it hits by putting a feeler in front of the screw and wiggling it. When the actuator hits the screw, it will grab the feeler and hold it so you can't wiggle.
   4. Reconnect the vacuum hose to the turbocharger
3. Test operation of the N75 valve (two options)
   
   
   1. Option 1, with a tee
      1. Install a tee between the N75 and turbo control line, and connect your mityvac to the tee. It's helpful to have a vacuum hose connected to the tee that will reach back into the driver seat of the car.
      2. Start the engine and connect your VCDS.
      3. Run the VCDS N75 test and use the vacuum gauge on the mityvac to monitor vacuum as the VCDS runs up and down the duty cycle.
         1. At 0% duty cycle, the vacuum should be 24-25hg, and at 100% DC, vacuum should be 0hg.
         2. Optional: you can also double-check with your feeler gauge that the turbo vane actuator is hitting the set screw with each test cycle.
      4. Exit VCDS and shut off the car.
      5. Disconnect the tee and plug the turbo vacuum line back into the N75.
   2. Option 2, without a tee
      1. Disconnect the vacuum line from the turbocharger and connect it to your mityvac.
      2. Start the engine and connect your VCDS.
      3. Run the VCDS N75 test and use the vacuum gauge on the mityvac to monitor vacuum as the VCDS runs up and down the duty cycle. At 0% duty cycle, the vacuum should be 24-25hg, and at 100% DC, vacuum should be 0hg.
      4. Exit VCDS and shut off the car.
      5. Disconnect your mityvac and connect the turbo vacuum hose back to the turbo.
   3. If you don't have access to VCDS, you can hook up your vacuum gauge as described in option 1 or 2 above with the engine off, then have someone start the engine while you monitor vacuum. As soon as the engine starts, you should see vacuum increase to 24-25hg and stay there (engine idling).
   4. If the vacuum doesn't behave as expected, you could have a bad N75, a leak in one of the vacuum hoses having to do with the N75, or a wiring problem (unlikely).

I hope this is helpful. This should nail down the boost problem as long as the basic turbo is good. If you get stuck, ask us.

Hi there,

So I had replaced both the maf and n75 with no resolution. I then did an egr delete and nothing was clogged up in the piping. I’ve also vacuum tested it and replaced a couple lines. When I installed the newer turbo I hand tested the actuator and it was moving good. The turbo sounds great now but the car doesn’t seem to have that omf except for every so often, so for the most part it’s not getting power. I’ve had checking the pin on my to-do list but haven’t gotten that far with the new issues.

Other issue I forgot to mention is my ecu is locked so I can’t run any diagnostics on it but I can see codes. I’m buying a new plug and play ecu today and hopefully that’ll fix that issue. I don’t know if maybe the underlying issue is just the ecu not reading properly? I’m not sure if that could be a culprit for my boost and fuel issues but again I haven’t been able to run an actual test on it to know. Only other issues I know on the car that I haven’t gotten around to fixing yet is my clutch master cyclinder behind the brake pedal is leaking brake fluid. And then my ac compressor isn’t getting power right now, the only thing I could read was my switch wasn’t getting power but I tried replacing a couple parts from my parts car and still haven’t solved that issue.

I’m going to try to get under the car Sunday and test the actuator and check all the fuel lines for air again. I feel like replacing my coolant thermostat couldn’t have caused any of these issues, any opinions on that?

 

[csstevej]

When you said new turbo I thought it was brand new…. Not a used good turbo .
Yes do as shoe bear suggested , hook a mity vac or equivalent and check that the arm hits its max stop by 18” of vac and starts to move by 5” and the movement is smooth both ways.

What do you mean that your ECU is locked? If you get a new ecu you will need the secret key ( SKC ) code to program it , unless you got an IMMO delete done on the ECU.
You will need VcDS to program it.

No replacing the coolant thermostat wont cause your issue.

 

[Brandiianderson]

When you said new turbo I thought it was brand new…. Not a used good turbo .
Yes do as shoe bear suggested , hook a mity vac or equivalent and check that the arm hits its max stop by 18” of vac and starts to move by 5” and the movement is smooth both ways.

What do you mean that your ECU is locked? If you get a new ecu you will need the secret key ( SKC ) code to program it , unless you got an IMMO delete done on the ECU.
You will need VcDS to program it.

No replacing the coolant thermostat wont cause your issue.

My boyfriend recently started working at a Vw dealer (doesn’t know much about VWs though) and took it up there. One of the mechanics tried to run testing for the boost issue a few months back and they said the ecu was showing blocked or locked. They weren’t able to run any test on it just read the codes. I bought one with immo defeat plug and play so I won’t need to program it thankfully!

 

[csstevej]

That’s good that it’s immo deleted.
I don’t believe though that you have a problem with the ECU.
You may have a connection issue.
I highly recommend that you find someone who has VCDS or purchase one yourself.