92 Deville 4.9l backfire through carb after turning on a/c
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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; Hello all please help this car is driving me to drinking lol. OK so far replaced distributor plugs and wires ...
  1. #1
    xxfreeklingxx is offline Cadillac Owners Member
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    92 Deville 4.9l backfire through carb after turning on a/c

    Hello all please help this car is driving me to drinking lol. OK so far replaced distributor plugs and wires tps and isc motor on car. Set timing did minimum idle screw adjustment and adjusted isc just off of the throttle lever when I retracted it. OK so the car was Running like a dream after installing all that. Well after I got the car to run good enough I began tinkering with the a/c. I noticed any time I would hit auto on the ecc I would confirm compresor engagement. As soon as the compressor kicks on it began to stall out my engine. It starts sputtering and if I try to rev up the motor it would sputter and backfire with no power. Hit off on the a/c and the engine revs back up to normal and the car begins running great again. Well I wasn't happy with just accepting that the a/c was bad so I dug deeper. After turning the a/c off I figured my a/c compressor was freezing up or something causing serious resistance to the motor. So I figured I would try switching the a/c to just blow air and make sure compressor disengaged to see if I still had a problem without it engaged. I turned on just fan and the car still would sputter stall and backfire with no acceleration. Well I was switching back and forth at this time between auto and econ I did it about 3 times when I heard a pop under the hood and what seemed to be compression stroke or backfire through the carb. The car wouldn't start after that as well as the backfire. I pulled codes after that and got e22 e24 e31 and e70. All seem to be short related codes. So my question is how could a short because I was on fan mode when the engine blew could cause what I feel is a timing or valve problem any insight would be greatly appreciated.

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    onecool is offline Cadillac Owners Fanatic
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    Look up code definitions and postback then back.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 92 deville 4.9l backfire through carb after turning on a/c please help!!!!

    Car won't start now? Is it the battery?

  5. #4
    MoistCabbage's Avatar
    MoistCabbage is online now Cadillac Owners 10000+ Posts
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    Define "won't start".

    Does it crank?

    If not, does it make any noise?

    What's the battery voltage?

  6. #5
    xxfreeklingxx is offline Cadillac Owners Member
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    Re: 92 deville 4.9l backfire through carb after turning on a/c please help!!!!

    OK tried again today after work it does crank but no start batterys OK...I ran the battery down so I hooked up jumpers it continues to crank but no start. I checked and rotor is turning as I thought the missfire and backfire was due to the gear being sheared. It was OK and I loosened the distr. hold down and moved it around to see if I could get it to fire at least with no avail. I'm pretty sure the only reason that it would backfire out if carb seems like a timing or valve issue but like I said my codes tell me it must have been some kinda short.e22 is a tps circuit short e24 is a speed sensor circuit problem e31 map sensor circuit short e70 tps interimittent signal. Is it possible its not out of time and just the short is making it not start and backfire through carb.

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    MoistCabbage's Avatar
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    A faulty TPS and/or MAP sensor can definitely cause running/starting problems. You had the codes before the battery died, so I wouldn't expect them to be false.

    Also, you don't have a carburetor, the engine is fuel injected. You have a throttle body.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Carb ??? Isn't this engine a TBI unit ?

    Fuel pressure ............

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    xxfreeklingxx is offline Cadillac Owners Member
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Well ya my bad TBI and the fuel pressure when primed with the key jumps to 40 and stays

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    MoistCabbage's Avatar
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    Quote Originally Posted by Submariner409
    Carb ??? Isn't this engine a TBI unit ?

    Fuel pressure ............
    '90+ are port injected.

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    xxfreeklingxx is offline Cadillac Owners Member
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Right i got you I'm sorry I knew it was a throttle body idk y I said carb lol.

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    xxfreeklingxx is offline Cadillac Owners Member
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    .Got a new development need insight, with ignition on, the ground from battery to distributer ohms out at 50 k. Really high resistance. When I turn the key off resistance goes back down to normal. Grounded to body acts normal but with ignition on and grounded to engine gets high resistance. Chekced pcm, grounds, and pcm harnesses and grounds to harnesses... all checked out fine. I think I blew a relay was wondering if that would cause high resistance to ground with key on. Has anyone else had experience with this or any advice or insight would be appreciated. Later today I will start pulling relays to find the problem unless someone has a better idea

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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Perhaps someone with more electrical knowledge will chime in, but why are you measuring resistance with key on?

    Resistance is measured with power off (or disconnected)
    Voltage is measured in parallel with power on
    Current is measured in series with power on.

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    xxfreeklingxx is offline Cadillac Owners Member
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Let me clarify what I'm trying to do. With key off, connected DVM negative lead to battery ground put dvm in audible continuity check ( where you touch the leads and it beeps) touch positive lead to frame grounds behind battery and on right side. Then touched positive lead to distributer housing and all beeped the same and showed ground... is this correct? With the key on the frame beeps correctly but the distributer housing makes a different lower sound then when checking resistance from ground to distributer housing its extremely high. Am I correct in thinking it should be the same at the destributer housing as the frame with the key on or off?

  15. #14
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Bigm57ict gave you a clue - you DON'T check resistance when the circuit is energized. The way the DVMs work in Ohm metering mode is by running voltage through the circuit you're checking - the reason for the big 9V battery you have in the unit. And, as long as your Ohm meter (continuity checker) beeps the resistance is relatively low. Most DVM's will beep only if the reading went down to 0 or 1, which is a low resistance.

  16. #15
    aeronca36606 is offline Cadillac Owners Enthusiast
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    Re: 92 Deville 4.9l backfire through carb after turning on a/c

    Check the ground strap on the engine. there should be no resistance between the engine ground and the body ground. also check to see if there is any voltage measured between the engine block and the body ground and the battery negative. check this with the key on. If all the grounds check out i would suspect the ecm.

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