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Old 12-01-2013, 07:39 AM   #1
essiejacoby
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Default 1999 a4 1.8t cyl #3 no signal to coil

Hello,
this is my first post, but the forum has been very helpful. So on to the point.
I have a 1999 a4 1.8t mt avant with a constant misfire on Cyl #3. I have a ross-tech vag system and have checked thoroughly all known systems and here is what I have.

Codes -18010,17645-8,16684,16687,18014

The work I have done is as follows. Without the vag tool with me, I disconnected the coils one by one to identify the problem. Coil #3 when disconnected did not affect running condition. then I disconnected in sequence the fuel injectors and only injector #3 did not affect running condition. So I have pinpointed to cal #3. changed coil#3 to new one, no change, still running poorly. I had a new plug with me along with a grounding wire so I connected the harness to the new coil, added the plug and grounded the plug. No spark on coil#3, so I tried the other coils with same technique and had a spark on all three . Therefore I now know that coil # 3 is the problem and so onward...
Using my sensitive test light, I found that wire terminal 1 of each coil was receiving a signal except for coil #3. So I checked at the power output stage for signal and same result. I checked both incoming signals and outgoing signals at the power output stage and found that again #3(confirmed through testing each wire and verifying where it went) was getting no signal. I have since repeated this testing with vag in hand, factory manual wiring diagram, and test lights and meters. I am sorry to not have my notes right now, but i think it was T5c/2 at the inlet of the power output stage, and #78 at the edu. I then tested continuity on all four wires from ecu to power output stage as well as Power output stage to coil pack harness connections. ALL GOOD CONTINUITY! So, stumped, unfortunately It seems to me that all it could be is the ecu??? Sorry for the long post, but I have exhausted my options here as far as what to test and I am hesitant to spend the money for an ecu as I have falsely gone down that road on another vw golf. thanks for any input-
John-
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Old 12-01-2013, 07:41 AM   #2
4Driver4
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Change the POS unit.
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2005 A6 Sedan Q 3.2 (wife's whip)
2000 A4 Avant Q 2.8 (daily driver)
1980 VW Scirocco (mid-life crisis car)
1983 Mazda RX-7 (revolutionary sports car)
2003 Mini Cooper S (just because)
1995 Mazda Miata, Superdupercharged(anti-Audi)
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Old 12-01-2013, 08:04 AM   #3
essiejacoby
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but I have established there is no signal to the POS for cyl#3, both TO and from POS. Cyl 1,2,4 all show signals, but the signal wire from the ECU to the POS on #3 shows no signal, so to me the problem starts at the ECU. I am cautious to throw parts at the car.. curious on your reasons, not suspicious, just curious and thank you for responding so promptly!
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Old 12-01-2013, 01:50 PM   #4
essiejacoby
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Hi ,
thanks for your response to my post earlier. I would like to hear your reply to my followup post if you have any input.
It just seems like the lack of signal from ECU to POS on cylinder #3 wire only(cylinders 1,2,and4 all had signals) is the problem, but you obviously have an opinion on that that I value, so if you have any followup, I would really appreciate it. Thanks again for the response-
John
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Old 12-01-2013, 02:42 PM   #5
jseklund
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If you have established for certain that there is no signal to the POS then I would look for continuity in the wire that should be bringing signal to the POS next. How did you test for the signal...not doubting you...just curious as I've never heard of a test for this and it is a good point of info.
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Old 12-02-2013, 04:54 AM   #6
essiejacoby
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with everything hooked up and the car running(poorly), I use a very high resistance noid light(adds very little current carrying capability to the circuit) with the clip to the positive battery terminal. if i touch the probe to ground then obviously the light goes on. Using that info, you can probe different grounding situations and get either a pulsing light or a steady light in the noid tester and not screw up your ECU if it is a safe noid light. if I touch the head, steady light, if I touch a pulsing ground, the light pulses as is the case in terminal 1 at each of the coil connecting plug. If you clip to the positive battery and probe(or back pin really) the coil harness plugs at the wire that goes into 4a on the connector, you get a solid light. If you back pin the wire that goes to 1 on the coil connector then it pulses(car running). you can then probe that same wire at the POS and it pulses there, both before and after the POS. And yes I have checked for continuity on ALL wires from the ECU to the POS and ALL wires from the POS to the coil harness connectors and they ALL have continuity.
With the car running, I get pulses at each of those points EXCEPT coil #3 wire #1 in the connector, and as stated, yes the signal wire from the ECU to the POS is continuous.
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Old 12-03-2013, 09:09 AM   #7
essiejacoby
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anyone? really would like to get some more input in this or response to my posts.
thanks again-
john
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Old 12-03-2013, 09:09 AM
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