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Discussion Starter · #1 · (Edited)
Guys any one had similar problems. my 2000 Audi A4 1.8 T has developed a missfire #3 cyl. ive done all the common checks compression 165 across the board ,replaced plugs switched coilpack(no different) cat converter was glowing which tells me lots of unburnt fuel in exhaust ive swapped over injectors still # 3 not firing, so my guess is wiring?? anyone came across anything similar before i start to tear things apart

thanx in advance
 

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ya it could be the wiring, i was thinking coilpack but us switched them, and its ok to have a glowing cat though

i had the same problem as u and it was cause i hat 3 bad coilpacks, it might be the sprak plug wires
 

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Discussion Starter · #3 ·
missfire

thats originally whay i thought but ive switched coils, injectors wires, plugs and #3 icylinder is still not firing i thought i read somewhere Audi has problems with the wiring harnesses??i also tried 4 new coil packs no different
 

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Your best bet now would to be to plug the car into VAG COM and see what fault code is logged, should indicate where the problem is hopefully ..
 

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Swap the injectors over
 

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A28-0005.png sorry,check the ignition coil output n122 on the air boxTesting ignition system
Testing power output stages for ignition coils
Testing actuation of power output stages

  • ‒ Pull the connectors off all four injectors.
Note:
It is important to ensure that no fuel is injected during the test, as this would damage the catalytic converter. Therefore, the connectors must be withdrawn from the injectors.
  • ‒ Remove the 5-pin connector from the power output stage
  • Connect diode test lamp to the following contacts on the connector:
  • ‒ Operate the starter for a few seconds.
5-pin connector on the wiring harness, contact.
Specified result
1 + earth
Diode test lamp should
2 + earth
flash (short pulse)
4 + earth

5 + earth

If the specified results are not obtained:
  • Switch off ignition.
  • ‒ Connect the V.A.G 1598/22 test box to the wiring harness for the engine control unit.
The following wiring connections should be checked for open circuits and/or short to positive or negative.
5-pin connector on the wiring harness, contact.
Test box V.A.G 1598/22, socket.


e wiring harness, contact.
Test box V.A.G 1598/22, socket.
1
70
2
78
3
2
4
77
5
71


  • ‒ Rectify short circuit or open circuit if necessary.
If no fault is detected in the wiring:
‒ Connect the 5-pin connector to the power output stage.
  • ‒ Pull the 4-pin connector off the power output stage.Connect the V.A.G 1527 diode test lamp to battery positive (+) and to one of the contacts on the 4-pin connector on the power output stage.
  • ‒ Operate the starter for a few seconds.
  • Diode test lamp should flash.
  • ‒ Carry out the test with all 4 contacts on the power output stage.
  • The diode test lamp should flash each time.
If the diode test lamp does not flash when testing one or more of the contacts:
  • ‒ Renew power output stage.
 

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Discussion Starter · #8 ·
Im going to be working on it tonight i may open up the wiring harness check grounds, also am i correct in thinking each injector is grounded inside the ecm computor?

jimmy
 

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Jimmy i would suspect that your fault lies at the coil output unit on top of the airbox,if the pulse is lost on cylinder three it will be that.Trace via continuity the signal wire from the output unit to the coil pack so you have the correct one and follow the instruction towards the bottom of the workshop document i attatched.I would have to look at the wiring diagram for the injector earth
 

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Sorry to come in so late on this, but I had the same problem with a 1998 A4 1.8T.
It turned out to be the ICM (Ignition Control Module). I had gone the route of swapping coils, plugs etc and it still kept missing on plug 3.

You can do a quick test with a digital meter on the ICM (housed on top of the air intake, front left hand side of engine bay). It has 5 pins on the incoming side and 4 on the outgoing. All it really does is switch, via some transistors, the feed to each coil.

Set the meter to Diode test.
On the 5 pin side of the unit the middle pin is the common emitter for all 4 transistors. Each one of the other pins is the base for of each corresponding transistor - you should get around 0.6 - 0.8v between each base and ground & also between each base and collector (the output pins). Use the negative lead of the meter on the middle pin.

If its the ICM that's gone you will see a reading on 3 of the 4 output pins (this is what causes it to miss on one plug.

Part numbers are:
Bosch 4D0905351 ICM
OEM F2045=-86642

Do a search as there is a big difference in price, real part can cost a few hundred, unknown make around one hundred.
 

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Posted some under other heading for you.

By the way the reason they blow is that they overheat, thats why they are positioned on top of the air intake, the air flowing by helps to cool it. I was often thinking of putting a small fan above it just like in a PC where you have a fan over the main chip to keep it cool, might get around to it some day.

decarman
 
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