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 Misfire at 1800 RPM and AC compressor wont engage 
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Joined: April 16 2012, 9:55 PM
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Post Misfire at 1800 RPM and AC compressor wont engage

My '94 (manual) is misfiring between 1500 and 1800 RPM. It doesn't happen unless the engine is warm and seems to get worse in hot weather and after idling at a stoplight. The car drives fine above 1800 so I just accelerate through it but I don't want to let it get worse. I am trying to avoid the old "replace everything ignition related" because it seems to be so systematic I hope I can narrow it down. The plugs are new and the wires are good. I am thinking it could be a distributor advance issue but it doesn't ping and like I said it goes back to normal above 1800. I am used to working on carbureted dinosaur cars (LOL my MX-3 is almost 20 years old but it is ultra-modern to me). I just ordered a code reader so I can't give you that info yet but anybody else had a similar problem?

An unrelated issue- the AC compressor won't kick on. I checked the fuses (and the circuit breaker under the dash) this morning and they are all fine. Can I manually hook a positive lead up to the compressor clutch to kick it on without damaging anything? It's getting hot... My crappy mechanic wants to recharge the system. That ain't going to help one bit if it leaks to begin with right? Regardless of the whether it's holding freon, the compressor should engage when I push the AC button, fan on, slider on cold, right???

Thanks for your help,

April 16 2012, 10:31 PM
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Joined: July 27 2006, 8:09 PM
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Location: Chattanooga, TN
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Post Re: Misfire at 1800 RPM and AC compressor wont engage
to your ac question, no. there is a pressure switch that will engage the compressor clutch IF there is pressure in the system. Which means you'll need to charge it. Which means that if it leaks then it leaks. You can hook up a positive wire to engage the clutch, it'll click on and off, to test the clutch but it don't mean it's going to get cold.

I would get a pressure gauge and test the pressure. then run a wire to the compressor and test the clutch. no pressure and clutch engages, hten charge. may need a little oil in it if you ahven't ran it in a while.

If your system during charging, won't engage the clutch no matter how much freon you try to shove, then you're prolly looking at the switch underneath the dash next to the evaporator housing.

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April 16 2012, 11:09 PM
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