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Discussion Starter · #1 ·
I have a well maintained 89 RC 360 tbi 4x4 auto. I have changed the thermostat, O2 sensor, plugs, wires, cap & rotor, And The injectors (new). I still am only getting 7 mpg on the highway.
 

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How is your power? If your exhaust is restricted, it can cause problems like this. Check for plugged or crushed pipe.
 

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do you have emissions laws where you live? go to dual exhaust or at least get a high flow muffler i think flowmaster is the best. i put them on my motorhome and it made a huge difference.
 

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Coolant Temp sensor, the one for the computer, not the one for the gauge. Your RC is likely running in cold enrichment mode. If you have been driving like this for a while, your cat(s) may also be toast :(

-SM
 

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ok stupid question but any chance it's in 4 wheel? 7 mpg would break the bank real quick
 

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Discussion Starter · #6 ·
No its not in 4x4. I have changed the cat and put on a three chamber flowmaster. there are no kinks in the exhaust
power seems fine and its starts and runs great. The idol is a little high and its running so damn rich. I almost could watch the needle drop.I think i preety much covered everything i could think of.
 

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zapnca said:
No its not in 4x4. I have changed the cat and put on a three chamber flowmaster. there are no kinks in the exhaust
power seems fine and its starts and runs great. The idol is a little high and its running so damn rich. I almost could watch the needle drop.I think i preety much covered everything i could think of.
High idle, and running very rich---kinda sounds like the computer thinks the engine is always cold, and is therefore always running full enrichment & high idle!

>>>Replace the temp sensor<<<

-SM
 

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i agree 1000% with slanted mind. if ur running "so damn rich" as u put it, then its a 99.9999% chance its the coolant temp sensor. i had this same problem on my 90, changed the CTS, all was well again.

Duane
 

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Do you still have the standard size tires? If you have changed, the odometer may be off.
 

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You might also check for a vacuum leak. It would cause the map sensor to think the engine is under load and it would cause the rich condition. I had that problem for quite a while. You might also check your timing, if it's off you will have a weak vacuum signal and again, the rich condition.
 
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