OK folks. I don't want to pop the champagne just yet. But I believe I have made some progress worth reporting.
The summary:
Van was presenting a rattle sound from the engine, sounded at first like lifter noise, but thanks to input from members of this forum attention was focused on diesel knock. The symptoms of which were getting worse - louder clack sound, some rough running like a misfire occasionally.
Diagnosis:
Logging data was not conclusive (to me at least) to isolate the cause. I was looking at: Cylinder 1-4 fuel time deviation. Fuel pressure deviation. Fuel pressure nominal and actual values.
The resulting data was all over the place. This pointed towards a fuel pressure regulation issue - HPFP, N276 valve or pressure sensor.
Action:
First I replaced the injector in Cylinder 4 as this was over fuelling in a huge way. The new injector made no difference and still showed the same over-fuelling issue.
Next I wanted to replace the injector in Cylinder 1, plus the fuel pressure sensor and N276 regulator valve. But the ebay sensor and valve I ordered, despite claiming to be for my CXHA engine, were entirely wrong. So I just replaced the injector in Cylinder 1.
I also reset all learned values with VCDS.
Then took the van for a long relearning values drive. Low rpm, low load. Steady throttle for 20 mins. Then the occasional short and mild acceleration and back to coasting.
Result:
Near the end of the test drive the diesel knock was all but gone. All fuelling deviations are minor and within spec. However. towards the end of the drive Cylinder 2 was constantly under fuelling by -20 us. At first I thought I was in for another injector. However, after a bit more driving all 4 cylinders started to hover around 0 us.
Conclusion:
When one or more injectors are misbehaving the ECU learns how to trim the other cylinders to compensate. This can get to extreme levels and present as uncontrolled fuel pressure in the system - at the HP sensor for example. Changing the worst injectors, with the highest deviations, in my case, was the way to go. I should have just put the (apparently) good injector from cylinder 4 into cylinder 1 to test - but I'd already bought a new one. Once injectors are replaced, if things have been wildly out of spec, it is worth resetting learned values and giving the van a proper chance to relearn values.
The relearning process takes time. So after changing any injectors or sensors in the fuel system, then resetting learned values. You need to give the van a chance to relearn, and adjust. The first results might indicate a fault still exists. But after more driving the van will correct the fuelling - This presumes all faults are resolved.
Notes:
Pulling injectors in my van was really easy - well, it was with a modified Laser tool no. 7525. Out of the box the tool does not fit the injector well - it attaches to the high presure pipe thread. I cut about 8mm off the end of one part and it works perfectly well. Once attached to the injector its just a few light taps with the slide hammer and the injector pops out.
The replacement injectors I used were Delphi 2853147, about £260 or so each.
Getting the leak off/return hose off is a nightmare. There is a grey outer and a black inner. The grey outer should slide up - a little flat blade leverage in the notch might be needed. But it seems after years of heat cycles and crud the two parts seize together. The plastic is so brittle. I broke two getting the old connectors off.
A got a replacement hose off ebay for about £30 and it works fine - so far.
The summary:
Van was presenting a rattle sound from the engine, sounded at first like lifter noise, but thanks to input from members of this forum attention was focused on diesel knock. The symptoms of which were getting worse - louder clack sound, some rough running like a misfire occasionally.
Diagnosis:
Logging data was not conclusive (to me at least) to isolate the cause. I was looking at: Cylinder 1-4 fuel time deviation. Fuel pressure deviation. Fuel pressure nominal and actual values.
The resulting data was all over the place. This pointed towards a fuel pressure regulation issue - HPFP, N276 valve or pressure sensor.
Action:
First I replaced the injector in Cylinder 4 as this was over fuelling in a huge way. The new injector made no difference and still showed the same over-fuelling issue.
Next I wanted to replace the injector in Cylinder 1, plus the fuel pressure sensor and N276 regulator valve. But the ebay sensor and valve I ordered, despite claiming to be for my CXHA engine, were entirely wrong. So I just replaced the injector in Cylinder 1.
I also reset all learned values with VCDS.
Then took the van for a long relearning values drive. Low rpm, low load. Steady throttle for 20 mins. Then the occasional short and mild acceleration and back to coasting.
Result:
Near the end of the test drive the diesel knock was all but gone. All fuelling deviations are minor and within spec. However. towards the end of the drive Cylinder 2 was constantly under fuelling by -20 us. At first I thought I was in for another injector. However, after a bit more driving all 4 cylinders started to hover around 0 us.
Conclusion:
When one or more injectors are misbehaving the ECU learns how to trim the other cylinders to compensate. This can get to extreme levels and present as uncontrolled fuel pressure in the system - at the HP sensor for example. Changing the worst injectors, with the highest deviations, in my case, was the way to go. I should have just put the (apparently) good injector from cylinder 4 into cylinder 1 to test - but I'd already bought a new one. Once injectors are replaced, if things have been wildly out of spec, it is worth resetting learned values and giving the van a proper chance to relearn values.
The relearning process takes time. So after changing any injectors or sensors in the fuel system, then resetting learned values. You need to give the van a chance to relearn, and adjust. The first results might indicate a fault still exists. But after more driving the van will correct the fuelling - This presumes all faults are resolved.
Notes:
Pulling injectors in my van was really easy - well, it was with a modified Laser tool no. 7525. Out of the box the tool does not fit the injector well - it attaches to the high presure pipe thread. I cut about 8mm off the end of one part and it works perfectly well. Once attached to the injector its just a few light taps with the slide hammer and the injector pops out.
The replacement injectors I used were Delphi 2853147, about £260 or so each.
Getting the leak off/return hose off is a nightmare. There is a grey outer and a black inner. The grey outer should slide up - a little flat blade leverage in the notch might be needed. But it seems after years of heat cycles and crud the two parts seize together. The plastic is so brittle. I broke two getting the old connectors off.
A got a replacement hose off ebay for about £30 and it works fine - so far.
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