Something a-miss?
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  1. #1
    Member
    Join Date
    Sep 2003
    Location
    Boolarra Vic
    Posts
    95

    Default Something a-miss?

    I am lookin for some advice on a miss in a recently acquired '89 405 auto.

    I purchased the car for my daughter to drive to uni. Looked and drove reasonably well, only 172000Km on the clock and not much to do for the roadworthy.

    It went well for the 250 Km drive home and for the following couple of weeks as we drove it round to get roadworthy etc. Then I decided to try to clean up the engine bay with the pressure cleaner. Got a little water in the distributor cap which was easily dried out but since then the car has developed a miss.

    It only happens once the engine is well warmed up and is most noticeable at 2-3000 rpm under light to medium throttle - IE cruising along at around 100 Km/h . It does not happen when the engine is cold or warming up and I have the impressoiin that it is less noticeable at full throttle and higher revs. I am not sure it is just one cylinder missing because it creates quite a jerk in the power delivery where i suspect a single piston not firing would have less effect at these revs.

    I guess the possibilties are electrical or Fuel injection.

    I have changed the plugs today with no effect and checked and cleaned the distributor cap again. I have had a bit of a read of the haynes manual but there does not seem to be much that can be done to check or adjust the bosch Motronic1.3 ignition/fuel injection system without plugging into an engine analyser. I have seen a list of diagnostic codes for early Mi16s where you count the flashes of a LED and have used a simmilar system to effectively trouble shoot a Nissan Pintara about the same vintage as the pug. Is there any simmilar or do I just have to trust the local Pug dealer? We do now have one locally here in gippsland but I am a bit of a DIYer if I can...

    The other option is the FI system. I tried to get the electircal connectors off the injectors to make sure they were dry but found it very difficilt to unlock the bloody things Is there a trick to it? I plan to replace the fuel filter this week but what else if anything can I do?

    Thanks in advance for any assistance

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    Cheers
    Last edited by trevh; 13th February 2005 at 11:03 PM. Reason: proof read
    Trevor Hoare
    Boolarra Vic

    '95 405Mi16 - what a great car! ; 89 405 ( for my daughter )
    previously 205Si, 504Ti, HR wagon with R16 seats, R16, R10, VW kombi, VW passat, HQ panel van, FB panelvan, Rover'49 P3 4-light

  2. #2
    Fellow Frogger!
    Join Date
    Feb 2002
    Location
    Tamworth NSW
    Posts
    496

    Icon7

    Hi there,
    If the engine "miss" is occuring after reaching operating temperature, the cause will almost certainly be electrical.

    The usual scenario is that a small amount of water is sitting somewhere that turns to steam with heat, and then provides an electrical path to earth. This usually happens on the HT (High Tension) side of the circuit, where insulation requirements are high.

    If you are really certain about the distributor cap, what about the HT leads, particularly around the dust / water covers at both ends? Any moisture / cracking of the material etc will cause a short to earth. Remove them one at a time and check carefully.

    The reason that it will be noticeable at light throttle (cruising) power is that lean mixtures are more difficult to combust than richer mixtures. Thus, the demands on the ignition system (particularly the spark plug) are greatest under those conditions. Fouled spark plugs on the other hand tend to break down under high engine / RPM load.

    The electrical connectors for the FI system usually have a wire band (clip) surrounding them that needs to be expanded at both ends. A small screwdriver, scriber etc can be used for this. During replacement, just push the connector back onto the terminal until it clicks.

    Good luck,

    Kim.

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