Sluggish Misfiring TDI

Catnip64

A2OC Donor
United-Kingdom
Need to some help to fix our 2004 TDI 75 (AMF with 180k miles).

The car seemed to lose power and felt a little slow to respond to the accelerator, then it became very difficult to pull away and eventually started to misfire with smoke from exhaust at moderate revs (2-3k).
No EML or fault codes using full-fat VCDS.
Runs poorly and sometimes difficult to start (coughs/splutters with white/grey smoke), then idles okay, but response to accelerator is very slow, ie foot to floor and hits 3k in about 3 seconds!
Here's what I've checked so far to assist with diagnosis:
  • Turbo - I was convinced that it was broken! But no, it spins okay and there is no play or contact. With the engine running at idle it spins fine. Boost is happening, but because the power is so low, it only builds a little. I also checked waste gate and it's closed, the control pipes are all connected with no leaks.
  • Car has no EGR valve so this can be ruled out. The anti-shudder valve is operating correctly and open when running.
  • Intercooler is fine and there's no excessive oil build-up.
  • The cambelt was changed about 4 years ago, condition is fine and timing has been checked and is spot on. Torsion value fluctuates a little but is around 0.0.
  • Injector impedances are all the same at 0.9 Ohms Edit: 0.4 Ohms (corrected for lead resistance), the loom was replaced a few years ago.
  • Injection Quantity Deviation from VCDS is within range (+/- 2.5 mg/str), the largest value being +0.71.
  • Injection timing looks fine at around 5deg BTDC.
  • Coolant and fuel temperature values are correct.
  • MAF gives sensible values, disconnecting this does not improve running at all.
  • The glow plugs are all switched off.
  • Last fuel was a few weeks ago, tank is 1/3 full. Fuel filter replaced 2-3 years ago.
  • No fuel/air leaks from tandem pump.
I've not driven it since we limped home the other day, only started it on the drive to take measurements etc. I could venture out to do some logs, but suspect that it will be a pig to drive!

I'm leaning towards injector issues as one of the VCDS parameters for Switch Time Deviation looks different from the others (Group 23 if anyone wants to check :)), cylinder 1 is consistently higher than the other two with a figure at idle of 35-38 whereas the others are 12-17 (not sure of units, guessing they are ms). Being higher this would suggest that cylinder 1 injector is slower than the others at responding meaning that cylinder is firing later and causing smoke/power loss.
However, I've not found any details of other tests that could be carried out to confirm this. I could whip them out and send off for testing/calibration, or maybe take a punt and replace all three with a second-hand set.

Has anyone has similar issues or have any ideas for further testing.
Any input would be greatly appreciated.
 
Last edited:
Not saying it is not the injectors, but a cheap and easy thing to do is run a GOOD fuel system and injector cleaner through the system paying attention to how it is added to the fuel. Also replace the fuel filter as 2-3 years can be getting dirty and clogged. Is there a chance you have water in the fuel? How old / clean / dry is your air filter?

Unfortunately the A2 is too old to report all items back to VCDS so tandem pump injector loom and to an extent even the injectors are not well if at all monitored by the fault recording process.

As for the EML pretty sure the AMF does not have an EML light but the BHC and ATL does - emissions standard related.


The small plastic /rubber hoses to and from the turbo to N75 valve only take a VERY small leak to cause havok. Check the joins between the plastic and rubbers are really tight and the other place I have found them to fail is the right angle rubber coupling onto the back of the N75 valve going porous and cracking - just replace with a short straight section of rubber pipe that is a nice tight fit onto the valve and the small plastic pipe.
 
Need to some help to fix our 2004 TDI 75 (AMF with 180k miles).

The car seemed to lose power and felt a little slow to respond to the accelerator, then it became very difficult to pull away and eventually started to misfire with smoke from exhaust at moderate revs (2-3k).
No EML or fault codes using full-fat VCDS.
Runs poorly and sometimes difficult to start (coughs/splutters with white/grey smoke), then idles okay, but response to accelerator is very slow, ie foot to floor and hits 3k in about 3 seconds!
Here's what I've checked so far to assist with diagnosis:
  • Turbo - I was convinced that it was broken! But no, it spins okay and there is no play or contact. With the engine running at idle it spins fine. Boost is happening, but because the power is so low, it only builds a little. I also checked waste gate and it's closed, the control pipes are all connected with no leaks.
  • Car has no EGR valve so this can be ruled out. The anti-shudder valve is operating correctly and open when running.
  • Intercooler is fine and there's no excessive oil build-up.
  • The cambelt was changed about 4 years ago, condition is fine and timing has been checked and is spot on. Torsion value fluctuates a little but is around 0.0.
  • Injector impedances are all the same at 0.9 Ohms, the loom was replaced a few years ago.
  • Injection Quantity Deviation from VCDS is within range (+/- 2.5 mg/str), the largest value being +0.71.
  • Injection timing looks fine at around 5deg BTDC.
  • Coolant and fuel temperature values are correct.
  • MAF gives sensible values, disconnecting this does not improve running at all.
  • The glow plugs are all switched off.
  • Last fuel was a few weeks ago, tank is 1/3 full. Fuel filter replaced 2-3 years ago.
  • No fuel/air leaks from tandem pump.
I've not driven it since we limped home the other day, only started it on the drive to take measurements etc. I could venture out to do some logs, but suspect that it will be a pig to drive!

I'm leaning towards injector issues as one of the VCDS parameters for Switch Time Deviation looks different from the others (Group 23 if anyone wants to check :)), cylinder 1 is consistently higher than the other two with a figure at idle of 35-38 whereas the others are 12-17 (not sure of units, guessing they are ms). Being higher this would suggest that cylinder 1 injector is slower than the others at responding meaning that cylinder is firing later and causing smoke/power loss.
However, I've not found any details of other tests that could be carried out to confirm this. I could whip them out and send off for testing/calibration, or maybe take a punt and replace all three with a second-hand set.

Has anyone has similar issues or have any ideas for further testing.
Any input would be greatly appreciated.
Cam sensor on way out maybe, I’d also check the entire cam belt as I lost 32 teeth on my tdi with same powerloss issue.
 
Thanks for the responses chaps.
@audifan I'll check the air filter but I've removed the intake hose from the manifold and it's still very slow to rev so don't think that's causing a restriction.
Possibly the fuel filter though, but I'll run some injector cleaner into the pump using this technique to see if there's any improvement and to rule out the filter causing a restriction or any water contamination.
Just tried the engine again and definitely very rich with a 'catalyst' type smell to the smoke and a black patch on the drive!
I'll check the N75 pipes at the valve to ensure there are no leaks.

@kp 115 Good shout with the cam sensor, but would this not flag up a code in VCDS? I checked the belt and it looks like new.
 
You can check that your getting a signal from the cam sensor by checking the Torion value in the engine meauring blocks using VCDS, (I thinks its in block 4 or 5) this figure tells you the relationship between the crank and cam sensor signals (and from that if your cam timing is advanced or retarded the tolerance is +-5) if your cam timing is spot on the torsion value would be 0, if the cam timing was way off you will get a fault code saying something like crank/cam corrolation, a dodgy cam signal usually gives a longer than normal cranking time but once started they tend to run fine
 
You can check that your getting a signal from the cam sensor by checking the Torion value in the engine meauring blocks using VCDS, (I thinks its in block 4 or 5) this figure tells you the relationship between the crank and cam sensor signals (and from that if your cam timing is advanced or retarded the tolerance is +-5) if your cam timing is spot on the torsion value would be 0, if the cam timing was way off you will get a fault code saying something like crank/cam corrolation, a dodgy cam signal usually gives a longer than normal cranking time but once started they tend to run fine
Thanks.
I checked the Torsion value and it's hovering around 0.0, it was a touch higher but I tweaked the adjustment back to neutral position to see if this had any affect. There was no change at all.
The engine fires up straight away and takes a few seconds before it settles down to a steady rough idle.
 
Although your mileage is about 100k short of my AMF - fitting refurbished injectors at the very least (and doing the calibration as part of the refit) probably wouldn't harm. For the sake of about 150 quid for 3 it seems a bit of a no-brainer.
 
Thanks for the responses chaps.
@audifan I'll check the air filter but I've removed the intake hose from the manifold and it's still very slow to rev so don't think that's causing a restriction.
Possibly the fuel filter though, but I'll run some injector cleaner into the pump using this technique to see if there's any improvement and to rule out the filter causing a restriction or any water contamination.
Just tried the engine again and definitely very rich with a 'catalyst' type smell to the smoke and a black patch on the drive!
I'll check the N75 pipes at the valve to ensure there are no leaks.

@kp 115 Good shout with the cam sensor, but would this not flag up a code in VCDS? I checked the belt and it looks like new.
Fully rotated ?
 
Have you tried disconneting the MAF and driving it
I've not driven it, but disconnecting the MAF didn't change how it started and ran at all. It still misfired and smoked.
The airflow values for the MAF in VCDS change when the engine speed is altered, not sure what it should be, but at idle I recall figures of around 220.
 
If its running super rich could it be the car thinks it's really cold? Any way you can see the live mpg on the dis?
 
Any chance the anti shudder butterfly is not fully open and severely restricting intake air flow

Cheers Spike
 
If its running super rich could it be the car thinks it's really cold? Any way you can see the live mpg on the dis?
The ECU temperature data is reading correctly and the dashboard is normal, but I will try disconnecting the sensor to see if this has any effect on the running.
I’ll need to drive it to see any mpg figures, so not keen on doing that at the moment.
 
Any chance the anti shudder butterfly is not fully open and severely restricting intake air flow

Cheers Spike
I did think that could be the cause initially, but the actuator is working fine and is moving correctly. I ran the engine with the inlet disconnected and checked that the valve was open and then closed when shutting off.
 
Today's activities:
  • Disconnected each injector wire in turn to see if running was any different, not conclusive as struggles to start and run on any two cylinders.
  • Disconnected temperature sensor, much more difficult to start and smokes (white) really badly.
  • Checked hoses/pipes on N75, no issues found. Disconnected electrical connector and started engine, no difference noted.
  • Went for a short drive, still down on power and smoking.
I'm going to run some Diesel Purge through the injectors to see if this has any affect.

@Robin_Cox Was it Darwen Diesels that you used for your injector service? Did you change the seals and mounting bolts at the same time?
 
Today's activities:
  • Disconnected each injector wire in turn to see if running was any different, not conclusive as struggles to start and run on any two cylinders.
  • Disconnected temperature sensor, much more difficult to start and smokes (white) really badly.
  • Checked hoses/pipes on N75, no issues found. Disconnected electrical connector and started engine, no difference noted.
  • Went for a short drive, still down on power and smoking.
I'm going to run some Diesel Purge through the injectors to see if this has any affect.

@Robin_Cox Was it Darwen Diesels that you used for your injector service? Did you change the seals and mounting bolts at the same time?
yes, it was Darwen on @depronman 's recommedation and they were great - good price, good communication, and did refurb ; cleaned, replaced all the seals and wee filtery things and tested. Injectors came back looking brand new - I got two sets done, one for the AMF and a set of ASZ (Fabia vRS?) ones for the build engine. I followed general advice on here and bought entire set of authentic correct bolts both for retaining the injectors and the other ones that are taken off as part of the disassembly process, a new loom and a new rocker cover. The mechanic also followed the workshop manual instructions on setting the injectors using the adjusters and it's running beautifully - much better than before.
 
Today's activities:
  • Disconnected each injector wire in turn to see if running was any different, not conclusive as struggles to start and run on any two cylinders.
  • Disconnected temperature sensor, much more difficult to start and smokes (white) really badly.
  • Checked hoses/pipes on N75, no issues found. Disconnected electrical connector and started engine, no difference noted.
  • Went for a short drive, still down on power and smoking.
I'm going to run some Diesel Purge through the injectors to see if this has any affect.
I used 1/2 lire of LiquiMoly Diesel Purge and it ran much smoother but it's still very slow to pick up. I did note that there was no pinking whilst it was being used up, but once I re-connected the tank, it was noticeably rougher and did pink at higher speed when revved. I'm thinking this is due to the improved cetane level of the Diesel Purge making combustion smoother.
Smoke is now less, so maybe some overall improvement, but still nowhere near what it should be.

I might try a replacement set of injectors to see if there's any change and if there is then I'll send them away to be refurbished.
The only other potential cause I can think of would be the tandem pump, is there a recognised test procedure for this?
 
I used 1/2 lire of LiquiMoly Diesel Purge and it ran much smoother but it's still very slow to pick up. I did note that there was no pinking whilst it was being used up, but once I re-connected the tank, it was noticeably rougher and did pink at higher speed when revved. I'm thinking this is due to the improved cetane level of the Diesel Purge making combustion smoother.
Smoke is now less, so maybe some overall improvement, but still nowhere near what it should be.

I might try a replacement set of injectors to see if there's any change and if there is then I'll send them away to be refurbished.
The only other potential cause I can think of would be the tandem pump, is there a recognised test procedure for this?
Is there anything (filter) in the tank sender which could be causing your issue??
 
Back
Top