92 Deville 4.9l backfire through carb after turning on a/c - Page 2
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, 92 Deville 4.9l backfire through carb after turning on a/c in Past Cadillac Vehicle Discussion; OK I'm away from the vehicle at the moment but I feel like you kinda understand what I'm talking about ...
  1. #16
    xxfreeklingxx is offline Cadillac Owners Member
    Automobile(s): 92 cadillac deville
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    OK I'm away from the vehicle at the moment but I feel like you kinda understand what I'm talking about finally. Now that you mention it I never have checked for volts to the engine block to grounds I should have...but earlier today I was pulling fuses and when I pull the ignition switch maxi fuse the resistance reads good and when I plug it in it reads high again. I'm thinking possibly pass key module or my ignition switch is to blame not sure still looking for the pass key module to check it as I have a service manual and I see how to check and that I need to check the ckt from the pass key to pcm. Also is there a way to check the ignition switch itself also how would I remove it been lookin in the book but haven't come on how to remove it.

  2. #17
    aeronca36606 is offline Cadillac Owners Enthusiast
    Automobile(s): 85 Coupe Deville 4.1 V8 & 4.3 V6 Deisel & 1970 Eldorado
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Using resistance measurements for diagnostic purposes while useful in many situations can be problematic. A circuit can show no resistance while checking it with a meter and actually have a lot of resistance when put under load. This is especially true when you are dealing with corroded connections. The other problem you can encounter with your measurements can result from stray voltages present in the circuit being tested. Resistance measurements should be made with the battery disconnected for best accuracy. Voltage across the circuit being tested will cause false resistance readings. This is the nature of all but the most sophisticated Ohm meters.

    I find it best to look for bad grounds by looking for voltage readings where there should be none. This should be done with the circuit in question fully loaded. For instance a bad engine ground strap will show up best when the alternator is working hardest or the starter is engaged. You will see a significant voltage reading between the block and the frame of battery negative.

    Here is a decent article on circuit diagnosis. There are many more on the Inet.
    http://www.popularmechanics.com/cars...enance/4314662

  3. #18
    Slipgate is offline Cadillac Owners Enthusiast
    Automobile(s): 1998 Deville
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    I would also confirm the firing order and make sure you didn't hook up your plugs wrong. Back-firing out the TB is either plugs hooked up wrong, really bad timing or a vacuum leak.

  4. #19
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    I also remember that some of this series of deville had a TSB indicating trouble with the A/C blower module interfering with the proper operation of the ECM.

  5. #20
    xxfreeklingxx is offline Cadillac Owners Member
    Automobile(s): 92 cadillac deville
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    OK with ignition I have set DVM to measure volts measured 12.2 across battery and .02 from engine block to battery ground when pulling the maxi fuses I found that pulling the ignition switch fuse is the only fuse to make any dif in situation. Also when probing the top terminal from where the maxi fuse came out is the same as battery which is good but when probing the bottom terminal from where the ignition fuses came out of is a ground? I knw this can't be right with key off no more ground to fuse terminal.i checked the other fuse terminals and the dnt show ground which is correct im sure. pulled pass key module and no difference also disconnected ecc and blower control module. Is it possible I have some sort of short in the steering column I'm stumped...thanks for all the input guys really helps a ton and thanks for that article still reading and re redeadin to try and understand it fully.

  6. #21
    aeronca36606 is offline Cadillac Owners Enthusiast
    Automobile(s): 85 Coupe Deville 4.1 V8 & 4.3 V6 Deisel & 1970 Eldorado
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    With the fuse removed you very well may read a ground on the load side. This is because what ever is on this circuit has a path to ground. This is normal. If you where to check the headlight positive terminal you would read 12 volts when the lights are on but would drop to zero when the headlight switch is off. If you took a resistance measurement at that point it would show almost a dead short. (actually it would read about 1.3 ohms if you have 2 55 watt bulbs in the circuit)

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