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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 June 28th, 2020, 13:10   #1
ken.fresno-tdi
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Default No start AHU mystery after running great

back story: I did a AHU TDI transplant into Eurovan over a year ago. 150K on engine and professionally rebuilt 10mm injection pump. Great running; 4000 trip last summer and almost daily 150 mile r/t in past month to go from Fresno to Yosemite where I am helping build a cabin. Some problem with boost control (separate thread) but generally very nice running van. Three days ago started up fine but died after 5 or 6 seconds, still in driveway. No restart though seemed like it wanted to - engine would catch and stumble but not really go, and then just crank. First made sure 109 was good and that stop solenoid was clicking. Glow plug light works. I have a BEW in-tank fuel pump installed that pushes diesel through fuel filter but still bypassed any possible fuel filter clog or air leak by sticking both diesel lines into jar of diesel. Still no start- wants to and stumbles then dies. Looked for codes and found P1248 - timing issue? Checked to make sure timing was good - all checked out but IP was a bit off center so decided to retime the whole thing. Retimed using proper tools and made sure all was EXACTLY right - flywheel, camshaft, IP all on center and IP in middle of rotation. No sign of start at all after priming several times/cracking IP lines properly. Then I remembered when I first installed engine I had timing problem and had to advance IP sprocket one tooth to get engine running. Strange but apparently documented and true. Redid timing with IP sprocket advanced one tooth. Result is back to original condition - fires up for one or two seconds, stumbles, but not quite starting. Aaghh! Now thinking back to original issue three days ago where it started and then just stopped after running for a few seconds I wonder if some electrical issue in IP is the problem? fuel delivery seems fine. Air intake is fine. timing seems fine. N108 valve? never touched it before... Other things to check? I have VAGCOM and am not afraid to use it but without starting engine can't really check dynamic timing or other possible issues. Where do I go from here? Thanks for any thoughts!
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Old June 28th, 2020, 13:13   #2
Mozambiquer
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Quote:
Originally Posted by ken.fresno-tdi View Post
back story: I did a AHU TDI transplant into Eurovan over a year ago. 150K on engine and professionally rebuilt 10mm injection pump. Great running; 4000 trip last summer and almost daily 150 mile r/t in past month to go from Fresno to Yosemite where I am helping build a cabin. Some problem with boost control (separate thread) but generally very nice running van. Three days ago started up fine but died after 5 or 6 seconds, still in driveway. No restart though seemed like it wanted to - engine would catch and stumble but not really go, and then just crank. First made sure 109 was good and that stop solenoid was clicking. Glow plug light works. I have a BEW in-tank fuel pump installed that pushes diesel through fuel filter but still bypassed any possible fuel filter clog or air leak by sticking both diesel lines into jar of diesel. Still no start- wants to and stumbles then dies. Looked for codes and found P1248 - timing issue? Checked to make sure timing was good - all checked out but IP was a bit off center so decided to retime the whole thing. Retimed using proper tools and made sure all was EXACTLY right - flywheel, camshaft, IP all on center and IP in middle of rotation. No sign of start at all after priming several times/cracking IP lines properly. Then I remembered when I first installed engine I had timing problem and had to advance IP sprocket one tooth to get engine running. Strange but apparently documented and true. Redid timing with IP sprocket advanced one tooth. Result is back to original condition - fires up for one or two seconds, stumbles, but not quite starting. Aaghh! Now thinking back to original issue three days ago where it started and then just stopped after running for a few seconds I wonder if some electrical issue in IP is the problem? fuel delivery seems fine. Air intake is fine. timing seems fine. N108 valve? never touched it before... Other things to check? I have VAGCOM and am not afraid to use it but without starting engine can't really check dynamic timing or other possible issues. Where do I go from here? Thanks for any thoughts!
If you loosen the injector lines does it spray fuel out when you crank it?

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Old June 28th, 2020, 13:22   #3
ken.fresno-tdi
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definitely. each one loosened plus return line loosened at end of IP during each attempt to bleed fuel lines. evidence of sprayed fuel throughout engine bay : <
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Old June 28th, 2020, 13:32   #4
ken.fresno-tdi
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I should also add that during attempts at restarting I physically advanced IP to most advanced position (rotated toward engine) and most retarted (rotated toward radiator). When most advanced it definitely did not catch at all; when most retarted it comes closest to starting. This made sense to me since IP is advanced one tooth.... But when IP was on properly (not advanced one tooth) and physically rotated most advanced it still wouldn't start.... and battery and starter are almost new; good cranking speed with battery charger on overnight to ensure full amps.

Last edited by ken.fresno-tdi; June 28th, 2020 at 16:02. Reason: clarification
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Old June 28th, 2020, 19:52   #5
KLXD
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I wonder if the advance piston is stuck at full travel since it wants to start when you retard it. I didn't catch where you fully retarded it when you timed it straight up. Only when advanced a tooth.

I doubt it since rotation of the shaft would want to push it back to the normal retarded position. I think.

N108? Should be able to hear it clicking by applying 12V to it, not by turning on the key. Other clicks going on when you do that. Or remove the guts to be sure. Just a spring and plunger.

At this point I would try running it from a bottle to eliminate the possibility of a fuel line obstruction.

As far as timing it a tooth advanced is concerned, I've had to do it and not do it on the same engine. I think it has to do with how hard I want to try do get the slack out of the new stiff belt that has built in bends from shipping.
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Last edited by KLXD; June 28th, 2020 at 19:55.
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Old June 28th, 2020, 22:06   #6
ken.fresno-tdi
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thanks for the ideas. I'll work on them tomorrow, especially related to fuel. I just read through the post you and Mozambiquer and others helped diagnosing kurtzl's no start issue (AHU - Air in fuel system) and gave me some more ideas too. Yes, I too am wondering if there is some kind of fuel starvation/blockage issue - there is fuel coming out of loosened injector lines but perhaps not enough. I've dealt with hard start/no starts over the years (owned about 5 AHU engines since 06) but I can't recall one where I hadn't altered something on the car to cause the problem. Also, in rechecking VAGCOM codes it did throw a 01237 Fuel Shut Off N109 open or short to ground at one point while trying to start it but I've jumped the N109 solonoid straight to the battery several times to make sure it wasn't the issue with no difference, and the code didn't return after clearing. The 109 relay otherwise seems fine (looking for my spare to make sure).

Last edited by ken.fresno-tdi; June 28th, 2020 at 22:50. Reason: clarification
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Old June 29th, 2020, 12:58   #7
ken.fresno-tdi
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so I got a fuel container and hooked up a gravity flow fuel supply directly to the pump, with return line bypassing the fuel filter T. Tried starting and same issue - starts for a second or two and then dies, again and again... Decided to take out the N109 solenoid since I had the code and the clicking sound did not seem strong when hooked up directly to 12v. To do so I removed all the injector lines first to try to get access to the N109 without removing the top half of the IP. No luck - very tight and you can't get a 24mm socket or wrench on it. So I took off the top half of the IP, carefully making awl marks on top and bottom to match when I put it together again, and keeping everything very clean. I actually didn't have to take off the top half of the pump, just loosened all the bolts and pushed it as far to the left as possible to give access to a 24mm socket. Removed the N109 valve and tested it on the bench. I could not get any response from the solenoid with 12V on the wire end and a ground wrapped around the threads. Tried the same on two old spare solenoids I had laying around and same issue. I assume I should be able to get some kind of response from a working solenoid...?! Anyway, it kind of made me hopeful because if that is the problem I can temporarily make do by removing the spring and plunger and just kill the engine with 5th gear and clutch out. I removed spring and plunger and put N109 solenoid back, aligned and tightened all the IP bolts, and reinstalled the injector lines. Used a mityvac to fill the IP with fuel and pull fuel all the way through to the return line. Cracked the injector lines and cranked for a while to remove air and then tightened things up and cranked. Nothing. Not even a hint of wanting to start. checked codes in VAGCOM and got the following:

4 Faults Found:
00532 - Supply Voltage B+
27-00 - Implausible Signal
01237 - Fuel Shut-Off Valve (N109)
31-10 - Open or Short to Ground - Intermittent
00626 - Glow Plug Indicator Light (K29)
31-00 - Open or Short to Ground
00668 - Supply Voltage Terminal 30
27-00 - Implausible Signal

The N109 error makes sense since it wasn't even hooked up (since I took it off) but the others look like the 109 relay isn't working. But the glow plug light comes on for a second so I assumed it was. Or perhaps a bad ground? Now I'm thinking one of three things:
109 relay is bad and I'm being tricked into thinking it is good because it still mostly supplies power to glow plug light
or
I have a bad ground - since I put the whole engine together in the van I should remember where the grounds are, but I'm thinking the ones that come off the large circular connector are the ones I should be checking, since most all the engine wiring goes through there... correct??
or
when I carefully moved the top half of the IP over to the left to make way for the 24mm socket on the N109 I accidentally pulled it up to much and dislodged the IQ adjuster from the sliding mechanism below, or when I was realigning the top half of the pump I just lined up my scratch marks wrong (though they look exactly right). I've done the hammer mod several times and replaced seals on the top half of an IP so I know the basics of what to be careful for but I also know that is an extremely sensitive piece of machinery.

Thoughts? So frustrating!

Last edited by ken.fresno-tdi; June 29th, 2020 at 14:27. Reason: clarification
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Old June 29th, 2020, 14:20   #8
ken.fresno-tdi
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I went ahead and bought an new N109 solenoid ($35 from vwpartsplace.com)and a 109 relay (need one anyway as a backup) and will look for bad grounds while waiting for those to come...
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Old June 29th, 2020, 16:43   #9
ToddA1
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If the GP light works and you’re able to pull codes, I doubt it’s the 109. Jumping 12v to the stop solenoid should back feed the circuit, bypassing the 109.

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Old June 29th, 2020, 21:24   #10
Jetta SS
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I seem to recognize some of those codes from a no start I had. I had forgot to reconnect the IP electrical plug after doing some work. Maybe take a close look at the ip plug/wiring.
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Old June 29th, 2020, 21:49   #11
ken.fresno-tdi
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thanks. will do.
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Old June 30th, 2020, 03:51   #12
Mongler98
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Wireing harness. Sounds like something came unplugged or broken. Probably kn the ip harness. Mark6 has a similar issue. Turns out broken wire.
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Old June 30th, 2020, 20:06   #13
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Abacus, always finds broken wires, inside the loom. It’s worth investigating.

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