Engine load with AC on.....'96 LT1
Thread Starter
Safety Car
Joined: Dec 2007
Posts: 3,616
Likes: 5
From: Sandhills of North Carolina
Engine load with AC on.....'96 LT1
What controls the engine load when the AC compressor comes on? I get a very distinct hesitation when is cycles on and off. It's almost like a skip or miss. Engine seems to run fine with AC off although gas mileage seems to have fallen off a tad. I had a DTC 122/TPS low voltage but I cleared it and it hasn't come back. I had this condition before and new injectors seemed to have fixed the problem but now it's back. Hand held scanner says everything is in order. -Mike
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
A/c request is from the Programmer or Processor. Assuming the PCM is getting a good voltage signal from the Pressure Sensor (usually about .8 volts), it bumps idle - increases IAC counts - a nano second before the PCM grounds the compressor relay. When the a/c request is funky, it usually stalls or surges. I'd suspect that your throttle body might need cleaning, but your compressor could also be getting tired. You could confirm the PCM part with the right scanning equipment (not your hand held) - fairly expensive for the DIY'r so you might let a qualified Dealer hook up his stuff and if they're using Mitchell or some of the better software, they should be able to pinpoint it in 5 minutes or less (of course you'll have to pay for an hour). Otherwise, you can do some preliminary checks on the compressor. Remove the belt and turn the outer hub by hand. It should turn the compressor shaft with some resistance, but not so much that you can't turn it by hand. Check the air gap between the outer hub and the pulley. It should .020 inch and if it's too wide, you can re-shim it, though it may need a new assembly (you won't know until you take it off and look at the surfaces).
Thread Starter
Safety Car
Joined: Dec 2007
Posts: 3,616
Likes: 5
From: Sandhills of North Carolina
Thanks for the reply. I cleaned the TB a few months ago and that made a world of difference in the idle and throttle response. Cool then no AC running. I just used a TB spray cleaner though. Might be time for a thorough cleaning or maybe just a new TB. That might be the reason for the slight drop in gas mileage also. I hope it's something as simple as that. If that gets no results I'll try the stealership for a scan.
Before I changed the injectors a few weeks ago the car was running very rich. Can O2 sensors get dirty and not throw a code? The previous owner replaced one a few months before I got the car in NOV. to pass inspection. The other one is OE as far as I know with 86K on it. Didn't know if that might have some bearing on the hesitation or not. Probably should just change it for general principles anyway.
Thanks again, -Mike
Before I changed the injectors a few weeks ago the car was running very rich. Can O2 sensors get dirty and not throw a code? The previous owner replaced one a few months before I got the car in NOV. to pass inspection. The other one is OE as far as I know with 86K on it. Didn't know if that might have some bearing on the hesitation or not. Probably should just change it for general principles anyway.
Thanks again, -Mike
