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Discussion Starter #1
Hiya, I have a 2001 2.5 TDI Caravelle with the AJT engine.

It's had a new fuel pump and EGR delete. I have also cleaned the EGR assembly and put everything back as it was. I have a big flat spot between 2000 and 2700 rpm in third and fourth and the turbo seems to bang in at 2800 rpm in a big lump. In fifth the bus gets no where near 3000 rpm very often.

When we plugged my mates diagnostic kit into the OBD port the only fault it found was the water temperature sensor. That will be sorted in the next few days.

I have a couple of questions, shouldn't the boost be progressive as you accelerate? Can the boost be adjusted at all and can it be made to boost at lower revs?
Could a faulty water temperature sensor affect the fueling in any way?

Any advice at all would be most appreciated

Cheers
;)
 

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Literally, white van man
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4,071 Posts
Hi,
Was the van running correctly before you had the work done?
If it was take it back and ask them to sort it.
It's possible that the temp sensor could have an effect, however I cant imagine that the water temp would make that much difference.
When you had the Fuel pump replaced was the pump timing set up with VCDS?
Can your mates diagnostics check the pump timing? (VCDS or some other OBD2 scanner)
When you had the EGR delete was that electronic, a change in the inlet pipe (EG Allard EGR delete pipe?) or a blanking plate.
Have any of the Vacuum pipes been disturbed whilst the work was carried out and you havent noticed?

My pump timing was out and the van seemed sluggish but would pull up to about 3500rpm, but I never got the turbo boost come on strong at any particular rpm.
Now the pump timing is correct it pulls strongly from about 1400 all the way to 4000+

I have a 2002 2.5Tdi AJT and the pull is good throughout the range, a remap can change when the boost comes in and adjust the fuellling accordingly.
If you go down the remap route ensure the engine is running correctly before the map

Let us know how you get on.

Chris
 

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Discussion Starter #3
Hi,
Was the van running correctly before you had the work done?
If it was take it back and ask them to sort it.
It's possible that the temp sensor could have an effect, however I cant imagine that the water temp would make that much difference.
When you had the Fuel pump replaced was the pump timing set up with VCDS?
Can your mates diagnostics check the pump timing? (VCDS or some other OBD2 scanner)
When you had the EGR delete was that electronic, a change in the inlet pipe (EG Allard EGR delete pipe?) or a blanking plate.
Have any of the Vacuum pipes been disturbed whilst the work was carried out and you havent noticed?

My pump timing was out and the van seemed sluggish but would pull up to about 3500rpm, but I never got the turbo boost come on strong at any particular rpm.
Now the pump timing is correct it pulls strongly from about 1400 all the way to 4000+

I have a 2002 2.5Tdi AJT and the pull is good throughout the range, a remap can change when the boost comes in and adjust the fuellling accordingly.
If you go down the remap route ensure the engine is running correctly before the map

Let us know how you get on.

Chris
Thanks for the advice, I'll have it looked at as soon as I can. The EGR was blanked with a plate. between the link pipe and EGR valve housing. I'm not sure if the butterfly is supposed to be open or closed though. I'm sorting the temperature sensor this week and then look into getting it mapped by someone who knows T4's. Sadly I have no history with the bus so have no idea if anyone has messed with it.

Cheers again for the reply.
 

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Literally, white van man
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The blanking plate should cause no problems, if any of the vacuum pipes were disturbed during the plate fitting that could cause problems.
The butterfly valve is the anti shudder valve I believe, used when you turn off the engine only.
Was it the injection pump (front of engine) or the booster pump (in the fuel tank) that was changed?
If the injection pump timing is out it can cause various problems, bad starting, bad running, excessive smoke, it may well still start and run but the timing needs to be checked with VCDS ( the fuel pump is mechanically timed, and electronically trimmed for fine adjustment, as far as I'm aware you need VCDS to get the electronic trim readout so you can adjust it correctly)
I believe part of the turbo control is the vacuum system (along with other inputs) you can check that the actuator on the aft upper bit of the turbo to see if it moves freely, it will require moderate force to move it but it should be smooth throughout. its range, if its sticking just manually moving it may free it up.
Any good remapper should ensure the van is running correctly before attempting to change the map.

Chris
 

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I'd go with the above on the turbo itself. These are pretty basic turbos unless you have the 150 bhp fitted which is variable vane.
The only control on the turbo is the vacuum on the dump/wastegate valve on over-boost.
Your turbo speed is driven by the exhaust gasses so should be turning constantly & consistently on an exponential curve. The more exhaust gasses the faster it turns.
Your problem sounds like something is sticking inside the turbo, either the vanes are fouling or the dump valve might be sticking open.
Check for movement side to side & up/down on the cold vanes (Inlet) there should be none or very little.
Then spin it with your fingers to see if it runs freely without any catching or noises.
The faulty temp sensor will effect fuelling but not in the way you describe. There is also no lift pump to the injector pump the pump merely sucks from the tank & squirts into the injectors.
If your engine has had a previous catastrophic timing belt snap there could also be metal in the hot side vanes causing your problem.
Hopefully this will help you diagnose.
 

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Discussion Starter #6
Thanks for the replies. I'll start by making sure everything is clean and working as it should.

I did notice a burp or fart from the solenoid area yesterday when my mate turned the engine off while I went to disconnect the battery. We were doing a bit of welding. Not only has it got engine issues but rust in all of the usual spots too. ;-)
 
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