90 backfires

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HT4100 4.1, 4.5, 4.9 Discussion, 90 backfires in Cadillac Engine Discussion; I purchased a 1990 Cadillac Sedan DEville about 3 years ago. It has 112,000 good condition except it doesnt drive. ...
  1. #1
    korbkill is offline Cadillac Owners Member
    Join Date
    Mar 2004

    90 backfires

    I purchased a 1990 Cadillac Sedan DEville about 3 years ago. It has 112,000 good condition except it doesnt drive. After about six months of having the car it started to chug then after about a month or so it started to backfire bad. On the highway i blew my muffler. Took it to a caddy dealership and they did not want anything to do with it. Took it to a family mechanic and spent a lot of time on it and nothing. Put about 1000 dollars in parts trying to fix my baby and now finally wont start it cranks but nada

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  3. #2
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
    Join Date
    Dec 2002
    Fort Lauderdale, Florida

    Re: 90 backfires

    Turn on the key, simultaneously press and hold the OFF and WARMER buttons on the climate control panel until the onboard diagnostics activates. Read off the trouble codes displayed and post back. First step.... Any sensor or electronic problems with the system will set codes in the system.

    You spent $1000 throwing parts at a non-running car without knowing why it won't run??? Wow. You need to find a new mechanic that knows what they are doing. Or someone that has the factory service manuals and can read. All the diagnostic trouble shooting diagrams to solve something like this are in the manual. Just follow them.

    Basically....it has to be fuel, spark or air. Without either the engine will not run. Assume for a minute that it has "air" as about the only thing there that could fail to cause the engine to not pump air would be the timing chain and that is bulletproof on that engine.

    Get a can of starting fluid (ether) and shoot some into the throttle body and try starting it. If the engine starts on the supplemental fuel from the ether then you can guess that you are looking for a fuel problem. Fuel pressure regulator, fuel pump, etc....???

    If nothing happens with the extra fuel then pull a spark plug wire or two off , put a dummy plug in the wire and ground it and crank the engine and see if it has spark. Easy check. Could be a number of things in the ignition system but if it has spark then you can rule it out.

    One quick check for "too much fuel" is to go to the fuel rail that surrounds the top of the engine and connects all the injectors. Find the small canister shaped device on the rail where the fuel return line exits from the rail. It will have a vacuum line on it. Pull the vacuum line off and have someone crank the engine while you watch the vacuum nipple on the FPR for any fuel leaking from it. Crank and watch for 20 seconds. If you see fuel from the vac nipple then the FPR is leaking internally and has to be replaced.

    Get a fuel pressure gauge (garage, auto parts store, rental..) and screw it onto the fitting on the rail. Check the fuel pressure while cranking.

    Lots of basic simple things to check that any mechanic should be able to do....

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