MK5 GTI Intermittent Faults/Misfires

I bet the issue is high resistance / intermittent brake on the 5v supply

Can you verify cam correlation on vcds again cold and hot idle and 2500 rpm and report back if you can post the data. If you clear the code how fast does it come back. I have seen oil pressure good when cold then that goes away after driving at 10 miles on the freeway at 75 miles an hour. When you did your oil pressure check did you Drive 10 miles on the freeway and then check it out at idle again.

I did verify cold then hot oil pressure by letting the car warm up in my driveway. That's why it went from 66 to 34 psi at idle and 69 to 66 psi at 2K rpm. I'm pretty sure it was warmed up to normal operating temperature. It was 70F outside at the time. If driving it at freeway speed is critical to the test, let me know.

The code typically comes back between 1 to 10 miles of driving. I thought I had fixed it one time after driving across town and back (5mi each way) with no code. I drove it the next day and the code popped up within a mile. More recently, after clearing codes, it came back just driving around my neighborhood.

I looked at the WD and saw the black and gray wire that feeds voltage to the cam position sensor, and joins the wires to the fuel pressure sensor. Physically, I can see them under the fuel rail, but where do they join at what is described as "connector 1, engine wiring harness" in the WD? Is that within the black friction tape wrapped around the wires, or somewhere else? Do I need to cut the bundle open to inspect or is there a terminal block where they connect further up the line? The book wasn't clear on connector 1 location.

Run a temporary over lay from ECU to components isolated to test.

Jack@European_Parts said:

Run a temporary over lay from ECU to components isolated to test.

Click to expand...

I'm sorry but I don't know what that means. Can someone explain?

Run temporary wires that are in question and isolate them from the existing harness.

There are many cases where you need to "back probe" for testing.... this is a short (but blurry) video showing the basic concept:


I use "T-pins" and soldier a wire onto them as needed. I like the T-Pins because they are dirt cheap (100 for maybe $5) and the "T" on them makes them easier to grip/handle when trying to insert them for back probing.





When doing this kind of testing, I tell people it doesn't have to be pretty, but it does need to be safe... so make sure you don't have things shorting out where they shouldn't be.

ShaneOF said:

I bet the issue is high resistance / intermittent brake on the 5v supply

Click to expand...

If 5V is the correct voltage to this sensor, where can I pick that up? Will I kill it if I connect to a 12V source?

Thanks Jef, for the backprobe info. I'll have to get some of those handy T pins.

If 5V is the correct voltage to this sensor, where can I pick that up? Will I kill it if I connect to a 12V source?

Thanks Jef, for the backprobe info. I'll have to get some of those handy T pins.

Click to expand...

You better RTFB!

You will kill ECU or part supplementing 12 V for 5 V when needing 5 V ref.

I couldn't find anything in the Bentley manual that said 5 V. I didn't get a chance to try it before I sold the car. But I told the new owner what to do and directed him to this thread. Hopefully that does it. Thanks for all the help.

Last Post on this. I hate when a thread like this has no conclusion, so here it is. The new owner is better at diagnosis than I am and he traced the wiring, finding no fault. He said he replaced the ECU with one from a 2.0T in a wrecking yard and said the intake cam timing was off by one tooth and he corrected it. He told me it's now the fastest car he's ever driven and he loves it. No more codes...well, except that airbag code. He's working on that now. Then his wife gets the car so he doesn't get tickets.