knock sensor/bad M/P/G need to fix

[tomjanovich]

so here it is.
My brothers car, a 87 grand am 4 cylinder. a few months ago he went from 36-38 mpg to 25 mpg. big drop. We did not know why, changed and cleaned everything we could think of(mechanical dad, not professionsl mechanic though). He bought a new car recently. I was thinking of buying it for school since my car(toyota supra) does not go well in snow, and has never been in snow.

My father was talking to a friend the other day, and he discovered that grand ams are natorious for knocking, which this engine does enough of, not bad knocks, but lifter knock/valve niose, etc. This guy is an extremely good mechanic, he said that the knock sensor is prob sending off signals which would cause retarding in the timing, and inriching the fuel mixture, making bad gas milieage. The car only has 98k on it, so the eningine isnt shot.

When i was fixing this same problem on my supra, it was bad wiring, not knocking that wassetting the sensor off.

My question is what can I do to fix this.

Is there an easy solution?
can I just bypass the sensor?
Need help and fast, leave for school in 2 weeks.
any input would be great.

also, with my supra, the knock sensor was not to detect knocking of the engine, it was for detecting detonation, which could be knocking also in a way, but it is not the same, it is the same case here?

thanks for any help
Joe

[GTP Dad]

The knock sensor is located on the engine block and is relatively easy to change. The knock sensor cannot be removed or you will get a constant check engine light. Detonation is knock caused by low octane fuel and various other problems. As for your car, replace the knock sensor and also replace the O2 sensor. It may also be going bad and sending more fuel to the engine than is necessary. This should improve your fuel mileage.

The engine in your car, if properly maintained has a lot of miles left in it so don't discount it yet.

[tomjanovich]

thanks,
I figured as much, but is it common for the wiring to go bad on these
thanks
Joe

[GTP Dad]

It isn't common for the wires to go bad but depending on the environment, ie heat, cold, oil, general road crap can cause the wires to go bad. They will also break down over time.

[tomjanovich]

ok
so ive just found out that the car doesnt have a knock sensor. or so they say. I called autozone to find out how much, and they said the 88 4 cyl engine wasnt equipped with the knock sensor.

He said to change the pcv valve, o2 sensor, and breather filter and see if there was better mileage, any thoughts on this.
thanks
joe

[GTP Dad]

He is correct about the 2.5 but the 2.3 has one. If you have the 2.5 then change the O2 sensor and PCV as recommended along with a new air filter. If you have a 2.3 changing the knock sensor may help greatly.

[tomjanovich]

ok sounds good ill try that,
and thanks for working with me on this one, I dont know much about this particular car, but I guess im gonna learn, been obsessed with my supra, but Im movin on to my winter car.

so anyways, thanks a lot and I hope it works.

Joe