928 cold start and air/fuel mixture problems
01-09-2018, 01:02 PM
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928 cold start and air/fuel mixture problems
Alright so I've got several issues going right now. I suspect they might be all related.
The car in question is a 1980 Porsche 928 manual.
When I first got the car about three months ago the oxygen sensor was broken and the exhaust smelled very strong of gas. So the car sat for a little while until I got the oxygen sensor replaced figuring that would fix the smell because the car would be getting feedback on the amount of unburned gas. When I finally got the sensor replaced the weather had started to get cold and the car was impossible to get started when it was below 40 degrees also when I did get it started the exhaust stench persisted and I got no temperature readout on the dashboard. Is the temperature sensor bad and that's why the cold start injector is not injecting and I get no temperature readout. Or is the cold start injector not functioning properly and that's why when the car starts the exhaust smells because the injector keeps spraying fuel. Or is something still just messed up with the oxygen sensor?
The car in question is a 1980 Porsche 928 manual.
When I first got the car about three months ago the oxygen sensor was broken and the exhaust smelled very strong of gas. So the car sat for a little while until I got the oxygen sensor replaced figuring that would fix the smell because the car would be getting feedback on the amount of unburned gas. When I finally got the sensor replaced the weather had started to get cold and the car was impossible to get started when it was below 40 degrees also when I did get it started the exhaust stench persisted and I got no temperature readout on the dashboard. Is the temperature sensor bad and that's why the cold start injector is not injecting and I get no temperature readout. Or is the cold start injector not functioning properly and that's why when the car starts the exhaust smells because the injector keeps spraying fuel. Or is something still just messed up with the oxygen sensor?
01-09-2018, 02:38 PM
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Chapter 24 of the WSM has a testing procedure for the Temp II sensor, TTS, cold start valve, and Aux air regulator. Starts on page 17. Page 21 has a chart with potential no start causes.
01-09-2018, 03:57 PM
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Andrew --
The oxygen sensor varies the mixture in a pretty narrow range, "trimming" it rather than offering primary control. Further, actual fuel smell in the exhaust means you have cylinders that aren't firing. The mixture may be too rich, but more likely it is too lean. That causes lean misfire and the unburned fuel passing to the exhaust. For catalyst cars this is dangerous as it risks overheating the cats and a fire. Other ignition issues will offer unburned fuel to the exhaust, so it's probably a good idea to start at the spark plugs. Look for color, and wetness right after the engine has run. If you haven't done so already, carefully verify the integrity and routing of engine vacuum hoses plus any crankcase vent hoses, looking for damage and possible air leakage. If the ignition system components ar in less than great condition, now might be a good time to bring all that up to date.
You can buy a CD set of workshop manuals plus a collection of the tech publications from Roger at 928SRUS. There are free downloadable sets of just the scanned manuals, links show in the New Visitors thread at the top of the first forum page. The WSM's offer a lot of basic guidance on individual systems, and are essential for almost all work needed on the cars.
The oxygen sensor varies the mixture in a pretty narrow range, "trimming" it rather than offering primary control. Further, actual fuel smell in the exhaust means you have cylinders that aren't firing. The mixture may be too rich, but more likely it is too lean. That causes lean misfire and the unburned fuel passing to the exhaust. For catalyst cars this is dangerous as it risks overheating the cats and a fire. Other ignition issues will offer unburned fuel to the exhaust, so it's probably a good idea to start at the spark plugs. Look for color, and wetness right after the engine has run. If you haven't done so already, carefully verify the integrity and routing of engine vacuum hoses plus any crankcase vent hoses, looking for damage and possible air leakage. If the ignition system components ar in less than great condition, now might be a good time to bring all that up to date.
You can buy a CD set of workshop manuals plus a collection of the tech publications from Roger at 928SRUS. There are free downloadable sets of just the scanned manuals, links show in the New Visitors thread at the top of the first forum page. The WSM's offer a lot of basic guidance on individual systems, and are essential for almost all work needed on the cars.