Misses with AC On
Burning Brakes
Joined: Feb 1999
Posts: 1,157
Likes: 3
From: Encino CA
Originally Posted by dan6712cc
My 94 misses at idle when the AC is on, it misses once or twice a minute. If I turn the AC off or Im driving it won't miss. Any ideas why this is happening?
Welcome to the missing/stumbling/hesitation club chronic to LT-1. When my 95 did this a few years ago, it progressively got worse and was also quite noticeable going up a grade in overdrive gear. The dealer changed the opti and plugs but it came back after a few months. Dealer changed the opti again plus plug wires and it was okay for almost 2 years which brings me to a few months ago when the miss came back. I cleaned a bunch of corrosion off the wire that goes to the coil and it ran fine for a couple of days but the miss/stumble/hesitation has come back with a vengeance as now I have a backfire on hard acceleration from stop.
If you search the threads, you can find almost any explanation you can think of from opti (the most common guess but not necessarily right), to bad wires, bad coil, bad coil module, bad egr, bad O2 sensor, bad catalytic converter, miscellaneous bad or loose other connections, etc.
I have given up with mine and will be bringing it in to someone else to find the problem. Like I said in another post, I would love to have a nickel for anyone with an LT-1 that has complained about missing, hesitiation, or stumbling--you have joined a populous club.
Last edited by DougSilver; Apr 21, 2005 at 07:36 PM.
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,455
Likes: 2
From: East TN
I dont thin its the AC compressor cycling, this just started happening recently.. it jolts the car pretty bad when it misses. My first guess would be the wires as they're about 4-5 years old.
I was wondering if turning on the AC, having a higher load on the electrical system, could cause the car to miss with faulty spark plug wires? Could bad wires deliver less spark because of this?
The other thing I noticed today is at idle with AC on, the battery voltage dropped from 14.1 to under 13 volts. After that I turned the AC off since I was driving in town and didnt want to get stranded if it fell too low and it went back to 14.1. The battery is about 2-3 years old so I dont think thats the problem. It has new O2 sensors and bullet cats... Opti is going to get replaced soon but I dont see how that ties into the AC issue.
Finally made the club!
I was wondering if turning on the AC, having a higher load on the electrical system, could cause the car to miss with faulty spark plug wires? Could bad wires deliver less spark because of this?
The other thing I noticed today is at idle with AC on, the battery voltage dropped from 14.1 to under 13 volts. After that I turned the AC off since I was driving in town and didnt want to get stranded if it fell too low and it went back to 14.1. The battery is about 2-3 years old so I dont think thats the problem. It has new O2 sensors and bullet cats... Opti is going to get replaced soon but I dont see how that ties into the AC issue.
Finally made the club!
Burning Brakes
Joined: Feb 1999
Posts: 1,157
Likes: 3
From: Encino CA
The a/c is merely putting more of a load on the engine in the low-rpm range. These types of misses are most noticeable under high load/low rev condition like idling with the a/c or going up a grade in overdrive. It is normal for the volts to drop a bit when the a/c kicks in.
Burning Brakes
Joined: Aug 2001
Posts: 1,238
Likes: 0
From: walled lake MI
are you sure it's a miss, and not a flutter in idle speed? when the A/C compressor kicks in, the IAC opens up to adjust for the added load to the engine at idle. if the IAC is sticky i can see the engine can stumble intermittently, every time the compressor kicks in. note the compressor does not constantly run, but is switched on and off by the ECM depending on the A/C pressure.
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,455
Likes: 2
From: East TN
Originally Posted by tempest
are you sure it's a miss, and not a flutter in idle speed? when the A/C compressor kicks in, the IAC opens up to adjust for the added load to the engine at idle. if the IAC is sticky i can see the engine can stumble intermittently, every time the compressor kicks in. note the compressor does not constantly run, but is switched on and off by the ECM depending on the A/C pressure.
Burning Brakes
Joined: Jul 2003
Posts: 922
Likes: 1
From: Brisbane Queensland, Australia
Originally Posted by dan6712cc
My 94 misses at idle when the AC is on, it misses once or twice a minute. If I turn the AC off or Im driving it won't miss. Any ideas why this is happening?
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Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
I would very thorougly check the grounds to the engine, frame, and battery ground terminal.
The easiest way to check these is with an accurate digital voltmeter: put the negative lead of the voltmeter DIRECTLY on the negative post on the battery and leave it there.
Then, with the engine running and the AC clutch engaged, take the positive lead of the voltmeter and measure the voltage to the frame of the vehicle and to the block of the engine (make sure you don't get the voltmeter leads near any moving parts). These two measurments will tell you the qualitiy of the grounds on the frame and engine block.
This reading should be below half a volt, and probably less.
If not, start checking ALL ground cables and connections.
Tom Piper
The easiest way to check these is with an accurate digital voltmeter: put the negative lead of the voltmeter DIRECTLY on the negative post on the battery and leave it there.
Then, with the engine running and the AC clutch engaged, take the positive lead of the voltmeter and measure the voltage to the frame of the vehicle and to the block of the engine (make sure you don't get the voltmeter leads near any moving parts). These two measurments will tell you the qualitiy of the grounds on the frame and engine block.
This reading should be below half a volt, and probably less.
If not, start checking ALL ground cables and connections.
Tom Piper
Racer
Joined: Jun 2002
Posts: 278
Likes: 0
From: Perry Ga
Originally Posted by smacko
Alternator?
