I have a 91 Chevy Astro van with 15x,xxx miles. It idles very rough and drives extremely poorly at around 40mph, and, overall, seems to lack a bit of power.

A compression test was performed on the vehicle. One of the cylinders read approximately 70psi, with another around 120psi. Obviously, these readings indicate a problem of some form.

However, my check engine light also comes on periodically. The van is throwing code 13 (open oxygen circuit) and code 45 (rich exhaust). I realize the O2 sensor itself could just be faulty, but this would not explain the low compression, nor, likely, the performance issues.

As such, I am curious if the reverse could be true; is there anything that results in low compression (burnt valve, head gasket problems) that would also result in these codes being thrown? Also, please note, the light only comes on sporadically; it is not consistent. In general, given this set of symptoms, what might be a likely cause of the van's performance problems?


  • 1
    I'd say you definitely have two issues. I doubt the O2 readings have anything to do with the low compression. Conversely, the low compression will have absolutely nothing to do with the O2 sensors. You could try and replace the O2 to see if there is any difference, but really you are most likely looking at major surgery on the engine (rebuild or rrplace). Commented Apr 29, 2017 at 16:08
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    I'm with Paul on this one. The low compression means the vehicle has 150K miles, missed an oil change or three and possibly had a coolant leak / engine overheat mishap once in its life. Or just prolonged running rich (no O2 sensor) with a hint of preignition knock for an extended period of time.
    – zipzit
    Commented Apr 29, 2017 at 17:47
  • Thanks much for the responses. I pretty much figured I would have to replace/repair the engine, but I would feel like a fool if I performed such an extensive repair unnecessarily. Thanks again.
    – KellyM
    Commented Apr 29, 2017 at 17:59
  • On the engine rebuild topic I always ask the $$ questions first. With a rebuilt engine you should easily get another 60k miles out of the car. Is the vehicle rust FREE? No accidents? No airbag deployments? If it's a rust bucket you may well be better off applying your scarce dollars to a new car, etc.
    – zipzit
    Commented Apr 29, 2017 at 20:32


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