Questions and Answers

Mustang DTC 181 And 189 Q. Hi Vince, I have a 1995 Ford Mustang GT convertible, with a 5.0 liter SFI, automatic transmission, ABS, P/S, P//B, A/C, cruise control, with 58,000 miles.

I have lately been getting a check engine light periodically, but frequently. I had the OBD-I codes pulled. I was advised that the test showed a Code 10, #1 cylinder low power, and codes 181 and 189, left and right O2 sensors at rich limit.

I replaced the spark plug in the number 1 cylinder (it had a light whitish powder). I checked the #1 plug wire. It is getting spark. Next, I was going to attempt to check the #1 fuel injector.

However, I was wondering do I have two separate problems here? I don't see how a #1 cylinder problem could cause excessive richness in both exhausts. But, could there be a Mass Air Flow sensor problem that would impact only one cylinder?

Any suggestions on how to attack the problem, after the spark plug and plug wire?

Thanks for any help you may offer.
Mike H.

A. I'm glad to see that both the HO2S sensors weren't replaced. In this case they are a symptom, not the problem. What the code 181 and 189 are telling you is that the fuel mixture is too lean and the HO2S are at the limit of their enriching capabilities. Not that the mixture is too rich.

There are a few reasons the fuel mixture is too lean. The fuel pressure could be too low. A fuel injector may not be working due to a bad injector or a problem in the wiring. There may be a bad Manifold Absolute Pressure (MAP) sensor. Or it could ba as simple as a vacuum leak.

With only 58,000 miles, I would think the two most likely possibilities are the MAP sensor or fuel injector.

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