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Topic
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2002 Mazda 626 2L 4 speed Winter Performance Issues.
Runs great in summer with no codes, no issues.
Last winter codes came on (p1516, p0303), car missed, ran rough, idled badly, sometimes stalling. The poor performance increased the colder the outside temp got. If left idling for a while the cel would blink.
Last spring codes disappeared and stayed off and car ran great
This winter when it got cold poor performance and codes came back (p1516, p0303). Car almost always starts on first try, in winter maybe second or third try. In cold weather, same conditions prevail even when the car engine temp warms.
I changed plugs. I think the coils are good (not many miles). Inspected air filter, PCV, coolant temp sensor, fluid levels and thermostat and all appear to look good or appeared to work properly. Inspected and cleaned MAF, it also appeared to be good. I think I have low compression in one cylinder, but still runs great and idles smoothly in summer. Codes now are P0303 and P0172. I suspected a bad coolant temp sensor, but after a cold start the high idling drops to normal rpm when it gets to operating temp, so I have ruled that out.
Can anyone provide any thoughts what the issues might be.
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P0172
Combustion engines run most efficiently when they maintain an air-fuel mixture ratio of 14.7 parts air to 1 part fuel. When the upstream oxygen sensor detects there are less than 14.7 parts air to 1 part fuel in the air-fuel mixture, a rich condition exists. To keep the engine running properly, the powertrain control module (PCM) tries to compensate for the rich condition by injecting less fuel to the mixture in an effort to maintain the proper 14.7:1 air-fuel ratio. When these adjustments become too large, code P0172 is triggered.Going by your description your miss-fire may well be dumping fuel causing the O2 to see a rich mixture.
You state you have low compression on one cylinder.
I would first do a compression test on all cylinders and see if your miss firing cylinder has a issue with compression.
Then suggest you hook up a scan tool and see what your fuel trims are doing.
Also might do a injector flow rate test to see if all the injectors are functioning equally.Thank nightflyr
I thank you for your reply. I understand your comments but I don’t have the tools or direct experience for this testing. I may study up on it and try my hand. However, wouldn’t the compression issue happen in the summer as well as the winter. How does the temp play a role in this. Thanks again
I may study up on it and try my hand.
That would be a good start.However, wouldn’t the compression issue happen in the summer as well as the winter.
Depends… how extreme the difference in compression / wear between cylinders.
There are many times when a vacuum leak will occur on a cold engine but seal itself once warmed up.How does the temp play a role in this.
When things are hot they tend to expand and when they get cold the tendency is to shrink.
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