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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old October 8th, 2006, 20:09   #1
Bear
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Default N108 from "Sheer Hell" to "Real Swell"

About a month ago, fivestring and I played around almost all weekend "fixing" a N108 valve to get rid of a 1269 code and restore his car's performance. This story is about the trials and tribulations of that fateful weekend. It was a wild ride to say the least. Unfortunately, there was little information available anywhere, including here or in the Bentley concerning the diagnosis of this particular problem. I am really surprised about Bentley, its the better part of $100 after all!
The moral of this story is: CHECK YOUR TIMING!
Here is how the weekend went. We confirmed that the car wasn't running right: not much power and the 1269 code. It seemed like it was making more of a diesel "rap" than normal but it was hard to tell for sure, especially at idle.
First, we spent an hour or so dinking around under the premise of getting the N108 out without taking the injection pump out. No way. There are two bolts holding it in. We decided the injection pump was coming out.
And out it came! Actually, it was not too bad taking it out. We did have the bent wrench and that helped a lot. It was a bit strange the way the bolts went through the pulley and the bolt holders, but it went really well. The pump needs to be "wiggled" just right and it comes right out. Wiggling it just right can take some patience though. Then we looked at the N108, took the bolts out, and then tried to get it out.
It wouldn't budge.
We looked it over and then decided to use a screwdriver and a hammer to tap on the "ears" of the N108. We did that and also sprayed penetrant liberally. After a while we could see that we were bending the ears on the N108, so we quit. This was after about a half hour of tapping. After a break, we resumed and kept it up. After about an hour we could see that we moved the N108 about 0.010". Success! Then we upped the ante a bit by putting some vise grips on the metal ears and rocking it. We could only turn it a few degrees with the vise grip. The routine was turn, turn, tap, tap for about another hour. Then we used one of my secret weapons for loosening stuff without a torch - we poured boiling water on it. That helped a good bit and we could then turn it at will and the taps became more productive. We had it out about fifteen minutes later. It was pretty ugly after being beat upon for over two hours.
Much to our surprise the N108 screen was clean, as was the orifice it sat in. We were pretty puzzled as we felt sure that it would have been plugged. At this point we decided to test the N108 to see if it would do anything.
Naturally, Bentley didn't tell us what voltage drove the thing. We were able to measure some resistance across the terminals but so what? We wanted to know if it actually worked. So we played around thinking that if we drove it with voltage, "something" would happen. A click, or something. Thinking that the N108 might be driven by 5 volts or so we rigged up some batteries and hooked them up but no response. We then tried 12V and voila! We were able to get an audible click. We then placed a small hose over the "tube" part of the N108 and we pumped it up to 25 psi with an air pump. We monitored the pressure gauge for a couple of minutes and guess what? It held gas pressure! BTW we were "driving" the gas flow the opposite way from how the fuel flows through the thing. No biggy. If the valve holds gas pressure it will sure as heck hold fuel back (remember liquids have viscosity values of about a million times more than gases). We then energized the valve and the gas pressure was relieved. We repeated this a number of times. We decided that the N108 was OK, so we put it back. BTW fivestring had new O-rings for the N108 and the inner one - having the correct p/n on the package - was in fact the wrong size so we reused the old one.
We then checked the timing using the normal method: put the pump pin in place, crank at TDC, etc., etc. We put the timing belt back on, hooked everything up and went for a ride and guess what?
It ran the same friggin' way as when we started! And threw the same code! Of course, this made sense as we didn't really CHANGE anything. We did waste about 30 man-hours though....
So, at 5PM on a Sunday... we looked at the VAG-com timing and sure enough, requested timing was 1.5 degrees BTDC and actual was 6.5 degrees BTDC. N108 duty cycle was about 70% (I believe... I am typing all this from memory). So, we figured that maybe the timing was off more than the N108 could compensate for. So much for it being a "cold start" injector. Its a timing device thats needed all the time, evidently.
Since the timing was more advanced than requested we loosened the pump bolts and pulled the pump housing in the direction of rotation (clock-wise looking at the engine from the passeneger side to the driver's side). Said another way, this was like pulling the top of the pump toward the front of the car. We were able to put a socket wrench through the pump pulley just by taking the TB cover off which saved time.
We started it up and whamo! Smoke all over the place and a horrible knock. Timing was now at something like 1.5 BTDC requested and 18.5 BTDC actual. So, we repeated the process and pushed the thing back the other way - toward the back of the car and guess what.... it now ran like a dream!!!!!
Timing requested and actual matched. N108 duty cycle percentage was down to around 40%. We went for a ride and it ran strong and quiet with no CEL.
Moral of the story. Check the timing. Lessons: BTDC to VAG-com must mean "beyond" TDC and not "before" TDC. Strange. The other thing I noticed is that the injection pump housing setting procedure is discussed in the injection pump part of the A3 Bentley and not in the timing belt section where it would seem to rightly belong.
Here is my take on what is going on with the N108 problems. Its a timing issue and related to timing belt replacement. The timing belt replacement procedure requires that the injection pump pulley and the crankshaft be locked down. The belt is then placed on and tightened. The problem is that there is no way to put tension on the timing belt in between the crank pulley and the injection pump pulley - they are fixed! So what happens is that all of the initial belt tension is around only a portion of the belt: from the crank pulley clockwise around to the injection pump pulley. When the car is started and the belt tension equalized then the injection pump timing naturally becomes slightly retarded from where it was (the distance along the belt path from the crank pulley to the injection pump pulley increases as the belt gets pulled harder).
I think that the timing belt procedure should be changed to incorporate injection pump setting. One way to do it would be to loosen the injection pump and move it forward to a retarded position before the belt is tightened at every timing belt replacement. That way, it would give you plenty of room on the slots to move the injection pump to the advanced direction (based on N108 duty and/or timing results from VAG-com).
Long one... sorry folks. Any comments???
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Old October 9th, 2006, 08:17   #2
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Interesting method of testing the N108 valve, did you notice the screen to be dirty at all?

All the timing checks were done with the VAG-COM "TDI Timing Graph" correct? Wouldn't you have just seen it to be visually off before the entire episode?

Was this job performed on an A3/B4 or the A4 03 I see in your sig? They do have very different ways of adjusting timing...
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Old October 9th, 2006, 09:17   #3
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Quote:
Originally Posted by Bear
About a month ago......

First, we spent an hour or so dinking around under the premise of getting the N108 out without taking the injection pump out. No way.....
At first, I thought this was another story about beer-swilling, driveway mechanics

Kudos on the reporting and getting it [belch!] back in shape.

hiccup
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Old October 9th, 2006, 10:39   #4
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JollyGreenGiant,
Bear and I (fivestring) were working on my 98 jetta. and yes we were using the timing graph setup in vag-com. I love this little gem of a jetta tdi. it only has 224,000 miles on it and still running strong. Fivestringcooper
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Old October 9th, 2006, 16:45   #5
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jollyGreenGiant: we didn't check the timing with VAG-com before we started. We did check it manually and noticed that the pump pin would not drop in until the crank was pushed about 3/4" or so past (retarded direction) from TDC. We felt that was close enough at that time to condemn the N108.

JettaJake: Hey wait a damn minute now.... don't throw out a compliment and retract it. It WAS a beer-drinking driveway thing.
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Old October 11th, 2006, 05:39   #6
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Good Morning,
I was wondering why this cold start injector valve (N108) is sticking. I did it to me on monday while i was going to lunch, and then it did it again coming to work on wednesday morning, I can clear it with vag-com and it will run great. Does any one have any suggestions? The code is 01269.
Thanks, Fivestringcooper
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Old October 11th, 2006, 07:03   #7
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There is a small screen that keeps debris out of the valve, it can plug up rendering the valve slow to respond or even useless. I'm guessing that the ECM sends the duty cycle to the valve and then looks for the timing to change respectively, if it doesn't within a certain % then you have a code. Either that or you can have a shorted winding or an open winding in which you would receive a different code thrown. I didn't look up your code but most likely it's one of the above situations that's causing the issue. The valve can be replaced when the pump is removed; however, it's a pricey little part ( ~$400 or so ). I remember reading that Herm was able to clean a screen with an ultrasonic jewelry cleaner...
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Old October 11th, 2006, 19:42   #8
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jollyGreenGiant, I agree with you 100% - that is what is going on. I wish we knew what the relationship was precisely. What fivestring and I are going to do next is reset everything again. The pump housing is pushed as far advanced as it will go now, i.e. its up tight against the end of the slots. So, we will push it back toward retarded almost the whole way and reset the timing belt. Fivestring also had a good idea to keep the cam pulley loose until the tensioner is set and tightened.

BTW the screen looked new when we took it out. The winding is fine, the valve worked great on the workbench and it had instantaneous response.
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Old October 12th, 2006, 07:49   #9
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Best of luck!

01269 is a Short to + code for the N108, Run the diagnostic test mode with the engine idling and listen for the timing change while the N108 cycles. If you don't hear it, try and backprobe the wires in the IP harness controlling the N108 ( Do you have the Bentley manual? ), see if the ECU signal is making it all the way to the IP connector. You may have an intermittent electrical connection somewhere between the ECU and the N108. You may have to trace the harness all the way back and do the wiggle test with a VOM meter connected looking for an anomoly. If It was determined that it was in fact a harness issue, I would probably remove the IP harness and connect my multimeter between both of the control wires to the N108 then I would remove the ECU connector and jump the two pins on that end. You should have .3 ohms resistance or thereabouts if it's open that's your problem, put your meter on min/max ( mine at least beeps when there is a change in resistance ) and then start wiggling that harness and plugging and unplugging any connectors on the path between the ECU end and the IP end... I recommend the Stabilant 22 stuff if you do find a non-corroded connector that seems to be the culprit.

Does anyone know what the default position of the N108 valve is? Does a high duty cycle retard advance or does a high duty cycle provide advance?

Does this help?
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Old November 5th, 2006, 12:17   #10
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Update on fivestring's car. It ran great for about two or three weeks and then the 01269 code came back again. We checked the physical timing and it was dead on. We also turned the engine over by hand to make sure that there wasn't more than one mark on the fllywheel - there wasn't (its a clutch car BTW). So, we turned on Vag-Com and tried timing it. The timing figure on block 2 group 000 was at about 175. We wanted to get it to about 70 or less (fuel temp was about 100). We pushed the IP as far retarded on the slots as we could and got the block 2 number down to about 100. It runs a lot better, but the 01269 code will not clear.

So, here we are in the strange predicament of having a car that is physically timed (cam, timing mark, and pump pin lined up beautifully) and the IP can't be put into a position to get the running timing set correctly. We know the N108 itself is OK, as we tested it per above and the car ran fine for a few weeks with no codes. We also know that when the N108 is energized it lets fuel through it to advance the timing. In basic settings the timing adjustments are all off (I think) so the only thing affecting the timing at that point is the physical pump location or a malfunction in the mechanism that the N108 activates.

The other thing is that while trying to set the timing the value in measuring block 004 for % cold start injector was 39.8% and fixed (did not budge from that number at all except when revving).

Here is my game plan. Since we did have the IP out at one point we should probably take the pulley off and make sure that the woodruff key is there. I am pretty sure it is as I saw fivestring put the pulley back on - but who knows maybe it fell off or something. If that doesn't work then new o-rings on the fuel shutoff valve. If that doesn't work take the IP apart enough to physically move the piston "thingy" that the N108 acts on to see if it is stuck. If we get no joy there then replace the IP.

What do you guys think?
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Old November 5th, 2006, 12:26   #11
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I'll go out on a limb a little bit and throw out a guess that it is a missing woodruff key. The reason being that the car run great for a few weeks and now the pump wants to be pushed retarded. If the pulley was moving on the pump shaft that's the direction it would tend to get pulled toward, i.e. the pulley is getting pulled past the pump shaft in the direcion of engine rotation.
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Old November 5th, 2006, 13:52   #12
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I just went through something similar, but I did not have that code, I had the 00550 code. My guess is someone adjusted the timing using the adaptation method. My take on what the N108 does is this, it actually controls the internal timing of the pump via the ECU. It ports fuel pressure to the piston that the cam plate sits on and pushes against a spring on the opposite end of the piston. That is how the computer changes the timing. If someone has changed the timing with the adaptation and moved it quite a bit then you can lose a lot of the range that the computer has to change the timing. I am NEVER going to change timing again without checking the adaptation first. The factory setting should be 32768. Login, 12233 go to channel 4 and make sure that is set to 32768. Then change the timing mechanically, by rotating the pump. Someone had run the adatptation all the way to the retarded side and my pump had no more range in that direction. I got some similar reading for the start of injection and actual, mine was 6.0 degrees apart.
Thats my guess.
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Old November 6th, 2006, 03:24   #13
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Ray, thanks a million! That's an excellent idea. We didn't check the adaptation.
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Old November 8th, 2006, 21:34   #14
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Quote:
Originally Posted by Bear
So, here we are in the strange predicament of having a car that is physically timed (cam, timing mark, and pump pin lined up beautifully) and the IP can't be put into a position to get the running timing set correctly.
I'm thinking one of two things happened here...
1- The keyway is missing....
2- The belt is a tooth off on the IP...

Try re-setting the belt again with the IP rotated about halfway (or a little more) through the adjustment range. I had to fiddle with our A3 for a little bit to get it to want to adjust the right way...

Kind of reminds me of a few gassers where I couldn't rotate the distrubutor enough to set the ignition timing.. Usually the distributor was dropped in a tooth off...

Just my .02, hope you get it all sorted out soon..
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Old November 9th, 2006, 03:56   #15
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Thanks!
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