88 Coupe deVille backfire
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HT4100 4.1, 4.5, 4.9 Discussion, 88 Coupe deVille backfire in Cadillac Engine Technical Discussion; I own a 1988 Coupe deVille 4.5l, and I get a backfire or loud popping noise at a high rpm, ...
  1. #1
    88DeVille is offline Cadillac Owners Member
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    Question 88 Coupe deVille backfire

    I own a 1988 Coupe deVille 4.5l, and I get a backfire or loud popping noise at a high rpm, like when you mat the gas from a standstill or need to speed up to merge with freeway traffic. I'm also only getting about 11 mpg when I first got the car it was more like 18 mpg. I did run the car out of gas once and have changed the fuel filter, air filter, plugs. I also get my service engine soon light when I let the car idle on cool mornings for any period of time. any suggestions as to what the problems could be?

    I'm stumped so any suggestions are appreciated.

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    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
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    Re: 88 Coupe deVille backfire

    Quote Originally Posted by 88DeVille
    I own a 1988 Coupe deVille 4.5l, and I get a backfire or loud popping noise at a high rpm, like when you mat the gas from a standstill or need to speed up to merge with freeway traffic. I'm also only getting about 11 mpg when I first got the car it was more like 18 mpg. I did run the car out of gas once and have changed the fuel filter, air filter, plugs. I also get my service engine soon light when I let the car idle on cool mornings for any period of time. any suggestions as to what the problems could be?

    I'm stumped so any suggestions are appreciated.
    Possibly an ignition breakdown...???...plugs, wires, distributor cap...????

    Simultaneously press and hold the OFF and WARMER buttons on the climate control with the key on to activate the onboard diagnostics and read off the code that is turning on the SES light.

    Has the cooling sytem been service regularily with coolant replacment every 2-3 years/24-32K miles...??? If not , corrosion may have damage some internal engine gaskets causing internal coolant intrusion. Check the coolant level in the radiator (should stay full to the cap all the time cold) and the level in the coolant recovery bottle. If you have to add coolant frequently or the level drops over time then there may be some internal coolant intrusion causing a problem. If you suspect this, pulling the distributor would be a good preventive maintenance item to inspect the distributor gear for wear. If the gear is worn at all it is a sure sign of coolant intrusion depleteing the oil causing the wear (the distributor gear is the first thing to wear generally....and could cause an ignition misfire or popping like you describe.). If so, replace the intake gaskets, pressure check the head gaskets for leakage .

    In any case, the cooling system should be kept refreshed all the time with fresh coolant and the use of the GM coolant supplement pellets to seal the system is considered mandatory for that engine.

  4. #3
    JoeBleed is offline Cadillac Owners Member
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    Re: 88 Coupe deVille backfire

    Check codes yet? the ideling thing is likly the isc either messing up or posibly a sensor reporting bad info. as for the poping. i would defenatly check al of the above and i would also check the timing. if you can't do it have someone else do it. keep in mind it has electronic spark advancement and that needs to be disabled before checking timing.

    post back.

  5. #4
    88DeVille is offline Cadillac Owners Member
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    Re: 88 Coupe deVille backfire

    Thanx, it gives some things to check that I didn't think of, the waterpump was replaced last Sept and the rad was flushed then but I think it is time to do it again.

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