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Discussion Starter · #1 · (Edited)
2002 1.8T, AWM

Slightly rough idle after warm up.
VCDS shows faults/codes for multiple/random misfire and misfire cylinder 1.
The misfire only happens at idle. Short video of VCDS while running below. Look at the RPM and count misfires..


So far, I've -
Checked compression - all within 10%
Swapped coils. (misfire stays on cyl 1)
Ran NOID test on injector leads.
Replaced spark plugs - PFR6Q
Checked voltage at coils leads (per Bentley manual).
Checked cam speed sensor with VOM.
Pulled valve cover to check timing and condition of CCT (cam chain tensioner)

Gone through entire vacuum, EGR / PVC and secondary air systems -
Cleaned / Replaced hoses, "T's", elbows as needed.
Checked all one way check valves, venturi valve, replaced T" check valve, PCV valve.
Cleaned Puck valve - also removed it from intake and plugged it's intake hole while running - no change.
Checked N112 and N249 valves - applied 12v, valves open & shut without leaks.
Cleaned and checked operation of EGR valve.


About to install new injector o-rings and swap an injector.

Anyone have input on where to go next would be appreciated.

Ken

This is my third passat - others are a 98 AEB (daughter's) and 01 V6 (son's)
I perform all maintenance / repairs on them.
 

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Discussion Starter · #3 ·
Swap injectors from #1 to #4 . When did you take the compression ,hot or cold? and was it wet or dry?
#1 to #4... Will do.
Found a cracked o-ring retainer on the bottom of #3. May have cracked it when removing the rail.
Pretty sure my local Advance Auto has individual seal kit with the retainer. Will know for sure tomorrow.
image.jpg

Compression test performed after running the engine for a few minutes, so I'd say warm.
Didn't want any issues removing the spark plugs from aluminum head.

It was humid outside (if that's what your asking - wet/cold)

Thanks for your help so far, Ken
 

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Yes, try the injector swap next. My V6 developed a misfire on one cylinder, and I went through a lot of the same effort that you did. Then I swapped the injectors between two cylinders, and right away the misfire followed the injector, which had normal resistance and clicked like the others. I just ordered a whole refurb/flow matched set, which work great.
 

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Duh... The dome of piston #1 did look wet compared to the other three.
99vw might have been refering to the dry vs. oiled (wet) compression test. The idea is that you check compression dry, then introduce enough oil through the plug hole to coat the cylinder walls and re-check compression. Assuming that the compression pressure was below specs when dry- if the pressure goes up, then rings likely leaking. If no change, then valves are leaking.
 

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Discussion Starter · #7 ·
No luck on the injector swap.
Still random and multiple misfires and misfire cylinder 1.

While running the VCDS graph in various modes, I noticed engine timing varying quite a bit only at idle.
Checked the Bentley which says range should be 6 - 12 deg BTDC.
I'm getting a variance of 2.3 to a spike of 15 deg BTDC at idle only.
Bentley says resistance to engine speed sensor should be 400 to 1000 ohms.
Mine measured 1183 ohms.

New engine speed sensor time... I am going to figure this out eventually.. Thoughts?

Ken

1 1/2 minute video showing Timing variance, misfire count, etc..

 

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Discussion Starter · #8 ·
Update... Moving in the right direction...

Replaced engine speed sensor with one from a scrap yard. It measured in the low 900 ohm range.
As a side note, after removing my old one. I re-checked resistance. Off the car,it was measuring 980 (which was in the 400-1000 tolerance range). When I measured it at operating temp on the car, it was appx 1180. Knowing the misfires became more frequent as the engine warmed up, I held a flame near the end of the sensor. The resistance climbed on the OHM meter..
Enough to be an issue? Not sure..

Also checked the tension on the timing belt. The AWM has the push plunger type tensioner. 8mm is the adjustment setting. Mine was way above that and may have been at the the highest plunger position. Rotating the pulley, I collapsed the plunger and reset the tension.
Issue? Probably but not sure..

Also checked the MAF. Sensors looked a little corroded (not dirty but rusty).
At idle, it was measuring appx 3.7 cfpm on VCDS as I recall which was with-in range.
Checked the the part number (Bosch F 00C2G2040).
Don't think it's the correct. Searched and could only find one year that part number it was used on. Not my year (02)..
Issue? Not sure..

I had another MAF for an ATW engine (Bosch F 00C2G2040) on the shelf. From what I read, it's not correct either but would work temporarily.

Idle seems smoother now. Still getting a very occasional misfire on 1. Much better than it use to be and not enough to trigger a CEL.
Not sure which of the above helped the most.

Not knowing the age of the timing belt (it looked fine) or condition of the tensioner, I ordered complete timing belt kit.
Also ordered a new MAF (Bosch 0280218100).

Not really related to the issue's above but though I'd post.
Thought my alternator bearings were a bit noisey during start and warm up. The noise pretty much went away after 5 minutes or so. Was going to replace it after I got everything else figured out.
Last night, during warm up, I noticed the fan not spinning at full speed. Light bulb went off. Held the fan in place and the noise went away.
Ordered new fan clutch with the rest of the parts..
 

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Thought my alternator bearings were a bit noisey during start and warm up. The noise pretty much went away after 5 minutes or so. Was going to replace it after I got everything else figured out. Last night, during warm up, I noticed the fan not spinning at full speed. Light bulb went off. Held the fan in place and the noise went away. Ordered new fan clutch with the rest of the parts..
I was so sure that the chattering was the power steering pump on my V6, I ordered a new one. However, I next noticed the noise continued a little after the engine came to a stop, and the same light bulb went off.
 

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Discussion Starter · #10 ·
Updating the thread for anyone that has similar issues and might read this at a later date. Disappoints me when I read through an unresolved post.

It ended up being a small crack in an intake valve.
It's been running great for a while now (after I did a head swap).

Really took a while to figure this one out.
Back when I took the compression check, the crack must have been so small that all cylinders would check fine.
Only after a good warm up did the crack open up enough to reveal itself.
So glad I caught it before it dropped a valve.

Ken
 
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