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Discussion Starter · #1 ·
Greetings Forum! We have just completed an engine swap in our 2002 TDI Golf due to a runaway. The runaway engine was mated to a manual transmission we took from a donor 2003 complete car. Car ran well for an extended period after the transmission swap. ECU still thinks it is an automatic and throws a constant can't speak to the transmission brain error, which did not affect function. Before the swap, the engine in the 2003 donor did not make boost and threw a code P1556. It was partially rebuilt (head, rods bearings, and main bearings all for unknown reasons) by the previous owner (professional mechanic) but was in his boneyard because of non-payment of the bill (or perhaps he couldn't get it to make boost and gave up!). I replaced vacuum lines, swapped the N75 from my known good automatic, swapped known good MAF, cleaned the vanes, but never managed to get it to make boost and only got the P1556 code. Then came the runaway. In preparation for the swap we replaced the turbo on the donor with a rebuilt unit from idparts (old one had too much impeller play), checked the intake and EGR, which were quite clean, replaced lots of other maintenance issues. It fired right up (and started leaking profusely from the new rear oil seal but that's another matter). It still makes no boost and sends me a p1556. Not even for a short period after I reset the codes with my cheap xtool vag505. The only electric/vacuum parts that came over with the donor engine are the EGR, which tests fine and is very clean, the injection pump, and all of the various sensors attached to the engine. I've been all over the engine looking for boost and vacuum leaks and have found nothing. It makes no smoke and accelerates very weakly. I hear no turbo whir at all. I prelubed the turbo and have confirmed that the new actuator holds vacuum and moves the vane rod. Thoughts on where to begin?

Sincere thanks in advance for any and all advice. I am ready to buy a Ross-tech but am unclear where to start with diagnostics.

Best,
Rich
 

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From KeithUK's program P1556 gives that below. Maybe "Hoses/Pipes incorrectly connected, disconnected or leaking" or really your N75 doesn't work...?
Fault Location:
Charge Pressure Control - Negative Deviation

Possible Cause:
Reduced power output.
Limp mode.

Boost Pressure too Low.
Hoses/Pipes incorrectly connected, disconnected or leaking.
Charger Pressure Control defective.
Variable Nozzle Turbo (VNT) nozzles stuck.
Solenoid Valve for Boost Pressure Control (N75) defective.

Possible Solutions:
Check Hoses/Pipes to/between Components.
Check Solenoid Valve for Boost Pressure Control (N75).
Check/Clean/Replace Charge Pressure Control.
Check/Clean mechanism for variable nozzles.
 

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You don't mention troubleshooting the air pressure sensor. It's in a lousy spot behind the right headlight.

I bought/returned 2 new ones from an ebay vendor that were supposed to be vw oem that didn't work. Bought a Bosche sensor from a different ebay vendor that worked correctly.
 

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Discussion Starter · #5 ·
Thanks for the heads-up about the air pressure sensor Captain. I've ordered a new one along with a new N75. Between the two and all new vacuum hoses, I hope to have the issue resolved.
 

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Discussion Starter · #6 ·
Just wondering if vehicle had a runaway did you check intercooler for excess oil or blockage? Grasping at straws! Best of luck.
I have not checked for blockage. That is a good suggestion. Do you have a favorite technique for doing this? I did drain about three cups of oil out of it! I had no idea that these engines could run away. I stepped away from auto mechanics for too long! Thanks for the suggestions.
 

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Discussion Starter · #7 ·
Replaced N75 and MAP. Cleaned MAF. Ran better for a while but surging lightly like limp mode is clicking on and off. Got a new code related to EGR and then one related to ground fault or issue at pin 5. I've ordered a new MAF and will be replacing the EGR with another unit I have.
 

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Discussion Starter · #8 ·
We are getting closer. Got vcds and confirmed low fuel supplied. Hammer mod required to get fuel up but can’t seem to dial it in. Plan on switching in the 11mm pump from the runaway engine. Fingers crossed that will give us enough adjustment. Current symptoms are still low power and an intermittent limp mode that kicks in in 3rd gear on hills. MAF, MAP, and n75 are new. Vacuum lines replaced. No leaks anywhere that we can find. Could still need an intake clean, which we didn’t do while engine was out regretfully.
Thanks to all for your suggestions!
 
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