1979-1993 & 94 Conv [Subscribe to Daily Digest] |
t,
here goes the picture as I see it:
- on a cold engine you crank it up and it starts fine
- once it warms up you start getting bad timing for #3 cylinder
What happens when engine warms up?
- compression figures do change (cylinder bore is made of steel or cast iron while piston is made of aluminium; these metals have different thermal expansion)
- both fuel (bosch LH Jetronic) and ignition (bosch EZK) ECUs have different maps for cold and worm engine states. Moreover, they disable some inputs (e.g. Jetronic forgets about Labmda signal; and I believe, though not 100% sure, EZK goes the same way for knock sensor) when the engine is cold (engine temperature is observed by the input from water temperature sensor - this means that many bits are involved into this process: sensor to engine temperature connection, sensor to engine electrical connection, sensor to wire electrical connection, the wire all its length along, the wire to ECU connection - and it can fail at every step mentioned). They utilize different algorithms for cold and warmed up engines.
- other parts rather then already mentioned are also subject to thermal expansion; e.g. there's a gar between the rotor and the cap in the ignition distributor and it does change as it warms up or colds down
- electrical resistance is - tada! - also subject to temperature; also, the semiconductors have a certain temperature range within which they operate the way they are designed and this range varies with semiconductors' age - it goes down as they get older
I hope this moonspeak will help you a bit and you will understand why I advised you to carry a compression check out as well as inspect dizzy rotor and cap. Dizzy rotor play may not be that much subject of temperature expansion and usually it misbehaves right from the cold start in a case of excessive radial play, but there can be some 'transition' range when it goes good if cold and starts go bad when warmed up given the whole tolerances of shaft + rotor + cap.
Also, there is an extra fuel enrichment for cold start and if your 3rd injector is worn out, it can misbehave the following way:
- in a case of extra enrichment (read: increased duty cycle, the time when it's open per every cycle) it behave relatively good
- once the enrichment is cut off and duty cycle is decreased, the injector may start giving too bad flow and/or atomization
- the knock tendency is a function of many parameters and conditions like fuel octane, temperature, pressure, atomization - and air-fuel ratio: rich mixtures less tend to knocking while lean mixtures love to detonate
I hope this explains it more or less on how I see things happening: your EZK computer starts sensing some knock from #3 cylinder (well, it believes it does, but it is to be checked since a bad knock sensor or loose pistons/valves can fool EZK ECU) or the ignition discharge at #3 plug worsen upon the warm-up.
Good luck,
Zig
posted by 188.134.44...
, Mon, 19 Mar 2012 06:46:55
, Sun, 18 Mar 2012 09:08:38, Sat, 17 Mar 2012 18:23:05
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