Club 80-90 Forums

Hello i have a vw t25 1.6 turbo JX westfalia, i recently performed a leak off test from the Bosch injectors to measure how much diesel is being returned to tank. After making a simple kit and piping from the injectors to bottles i found that no diesel was being return (bottles and pipes completely empty), ran the engine from cold for about 5 mins occasionally revving to about 3000 rpm.
I have a big problem with smoke do you think the injectors are over fueling hence smoke.
I have recently replaced the nozzles within the injectors.

If you’re not getting returned fuel you likely don’t have enough fuel getting to the injectors, has any work been carried out in the fuel system? The

no work has been done on the fuel system apart from new fuel line from tank to pump, new filter and injector nozzles.
If there is lack of fuel being pumped to injectors why is it smoking so much?

Mick.source wrote: ↑11 Jun 2023, 17:07 no work has been done on the fuel system apart from new fuel line from tank to pump, new filter and injector nozzles.
If there is lack of fuel being pumped to injectors why is it smoking so much?

Because of incorrect fuel air ratio

Who and why were new nozzles fitted

Touched any filter to pump fuel lines ?

I have replace the fuel line from filter to pump.
The nozzles were changed to try and stop smoke, old ones tips had gone black.
i have also played with the mixture screw, retarded that much had a job to drive it, but still smoked.
Do you think it might be the pump??

i fitted nozzles, i didn't set up with pop tester

Mick.source wrote: ↑11 Jun 2023, 18:30 I have replace the fuel line from filter to pump.
The nozzles were changed to try and stop smoke, old ones tips had gone black.
i have also played with the mixture screw, retarded that much had a job to drive it, but still smoked.
Do you think it might be the pump??

The only method really is removal and testing, guessing and moving stuff isn’t the way to fault find, pull the fuel inlet union off the pump and check it’s clean and clear , check the filter in
The return union on the fuel pump , check the union is clear too

davidoft1 wrote: ↑11 Jun 2023, 12:48 If you’re not getting returned fuel you likely don’t have enough fuel getting to the injectors, has any work been carried out in the fuel system?

The purpose of the " Back leakage" pipes is just to return any fuel which leaks back out of the injectors to the tank, although it is connected to the return pipe it is not part of the fuel flow and return system. The amount of fuel from the back leakage pipes should be minuscule, just a few drops here and there, so lack of fuel from them is not an indication of fuel starvation.

Black smoke is an indication of poor combustion due to.....

• Lack of air, but right amount of fuel. Look for blocked air filter, or other blockage in the inlet tract. The air pipe that drops from the rear vent down to the engine can rot, and collapse in on itself restricting airflow. Check this first. Could be the turbo, but I know nothing about these turbos so can't help with that.
  
• Too much fuel, but right amount of air. Injection pump fault. Unlikely. Once again I know nothing about the injection pumps on JXs, specifically the LDAs.
  
• Poor atomisation of fuel at the injectors. If you've fitted new nozzles, but not pop-tested them, one or more may be operating at reduced pressure due to a bad spring causing poor atomisation and smoke. Or they could be dribbling or hosing fuel due to dirt.
  
• Injection too far retarded. By the time the fuel is injected, the piston is going down the bore and the air charge is cooling so the fuel wont burn so well.
  

colinthefox wrote: ↑12 Jun 2023, 18:15

davidoft1 wrote: ↑11 Jun 2023, 12:48 If you’re not getting returned fuel you likely don’t have enough fuel getting to the injectors, has any work been carried out in the fuel system?

The purpose of the " Back leakage" pipes is just to return any fuel which leaks back out of the injectors to the tank, although it is connected to the return pipe it is not part of the fuel flow and return system. The amount of fuel from the back leakage pipes should be minuscule, just a few drops here and there, so lack of fuel from them is not an indication of fuel starvation.

Black smoke is an indication of poor combustion due to.....

• Lack of air, but right amount of fuel. Look for blocked air filter, or other blockage in the inlet tract. The air pipe that drops from the rear vent down to the engine can rot, and collapse in on itself restricting airflow. Check this first. Could be the turbo, but I know nothing about these turbos so can't help with that.
  
• Too much fuel, but right amount of air. Injection pump fault. Unlikely. Once again I know nothing about the injection pumps on JXs, specifically the LDAs.
  
• Poor atomisation of fuel at the injectors. If you've fitted new nozzles, but not pop-tested them, one or more may be operating at reduced pressure due to a bad spring causing poor atomisation and smoke. Or they could be dribbling or hosing fuel due to dirt.
  
• Injection too far retarded. By the time the fuel is injected, the piston is going down the bore and the air charge is cooling so the fuel wont burn so well.
  

Why when a return pipe is split does it pi$$ fuel out ? Because it’s excess, if there’s not enough to begin with there will be no excess, the pump is restricted to create pump
Pressure, change the pressure change the fuel delivery

I have triple checked the pump timing it is now set to 1.00mm it was 9.4mm
It Starts on the button, slightly rough tick over until warm
No smoke on tick over, when i rev i get lots of smoke, unburnt fuel.
My next step is to buy a pop tester and check it pops at 155 bar and not dribbling or hosing.
If that ok, the only thing i haven't changed is the pump, but if it was worn i would have thought it would be hard to start. 

The OP specifically said he tested back leakage from the injectors. If he had said he tested the return pipe to see how much fuel was being returned from the injection pump I would agree with you. Perhaps the OP would clarify with some more details.

Sorry.OP posted in between. My last was a reply to Davidoft1 .

Mick.source wrote: ↑12 Jun 2023, 20:03 No smoke on tick over, when i rev i get lots of smoke, unburnt fuel.

I would check that inlet air pipe for restriction. Or disconnect it temporarily at the inlet to the air filter and see if that makes a difference.

Check the fuel unions are correct

I'm no expert but might be worth checking the banjo bolts to and from fuel pump as one is marked with "out" I remember reading they need to be the correct way round or can cause issues. Might also be talking out my ar*e but thought it could help