My cadillac is total Crap
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500, 472, 425, 368 Discussion, My cadillac is total Crap in Cadillac Engine Technical Discussion; Hi I posted this same thread in the Cadillac/Seville forum and someone told me to repost it over here. I ...
  1. #1
    bluecor is offline Cadillac Owners Member
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    My cadillac is total Crap

    Hi

    I posted this same thread in the Cadillac/Seville forum and someone told me to repost it over here.

    I own a 1981 cadillac seville V8/6/4
    The car only has 42520 miles on the clock.

    I recently replaced the ECM as it was internally burnt, and it made no difference.I used the proms from the old ECM.
    The engine harness wires appear to be in good shape .

    The engine still idles rough and the RPM is irratic.

    The check engine light flickers, but there are no trouble codes when i do an on board diagnostic with the engine running.

    I have replaced the O2 sensor, manifold temprature sensor and the water sensor, it has made no difference.
    When i disconect the sensor connector on the gearbox it doesn't make a difference.

    PLease help, i really wan't to drive the car again.

    Thank you

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  3. #2
    davesdeville's Avatar
    davesdeville is offline Banned
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    Re: My cadillac is total Crap

    I'd try getting a megasquirt FI control unit and ditch the 24 year old electronics. Or just stick a carb, FPR and carb manifold on there and drive it like that.

  4. #3
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: My cadillac is total Crap

    The electronics in these cars can be reliable but if stuff has been hacked then it will be a battle. What do I mean by hacked? Electrical work done by a body shop would be one example. Another would be aftermarket alarm installers. Add to the list of insults would be someone troubleshooting the electronic engine controls with a test light.
    You said the ECM was burnt inside but replacement made no difference. Where did you get the replacement ECM? Have you looked inside the new one to see if it isn't now burnt also? Toasted electronics is a symptom of other troubles as well as a problem itself.
    The ECM diagnostics are all too often consulted before basic engine mechanical/tune-up issues have been eliminated.
    Unless the ECM has smoke pouring out, was under water, was subjected to a runaway overcharging alternator or may have been hooked up while someone did some electric welding on the car, do not suspect it just yet. (This does not apply to your case as you found a physical defect) Always start with maintenance stuff first. Pull the spark plugs and compare their telltale signs. If one or more are really bad then maybe a compression check is in order. Used spark plug wires are usually junk after being unplugged at the spark plug end without a real careful twist. Someone could have replaced the plugs without replacing wires and they could have an internal open at the plug end. How about the distributor cap and rotor? It cost nothing but time to inspect these. The cap is not a common number anymore so may have not been available to someone doing a quick tune-up. Another potential problem can be crappy quality parts. Stay with original equipment manufacturer's or known quality brand parts. I know this sounds like sales talk but there are some auto parts stores that sell really poor quality ignition parts. Do not make the assumption that a part is good just because it is new. It could be defective, have been mis-handled and/or mis-installed.
    Another thing which can cause poor performance is low fuel pressure. Again, it cost nothing but time to check this if you have a gauge. Fuel pressure can be checked by cycling the ignition switch to run for a static reading. The pressure should also be checked under engine load conditions. This means hook up a gauge with a short hose. Put the gauge where you can see it on the windshield and take the car for a ride. Bring a large fire extinguisher.
    Another thing which is always suspect and is cheap to check is the catalytic converter. These sometimes need to be eliminated as a source of trouble. An engine vacuum gauge hooked to manifold vacuum will usually show up a clogged converter. Decreasing indication of vacuum with steady increase in engine speed is a good indication of exhaust restriction.
    The computer will not always set a code when something is out of range. Many set codes are the result of another problem. Don't install sensors or anything else pointed out in a diagnostic code without testing the component. This will keep you from spending hundreds before getting lucky hitting the problem. As an example: A TPS code can be set by mechanical binding of the throttle, bad electrical connection, poor ground, Mis adjustment, bad 5 Volt regulator in the ECM itself and probably another few things. So when the old display sez TPS it is not yet time to replace the thing unless you feel lucky. A bench test should always be done whenever possible.
    Another thing that can cause frustration are the helpful guys who will tell you that their car had the "same problem" and to change the framistat. Framistat and muffler bearing changers abound. I suppose they mean well.

  5. #4
    bluecor is offline Cadillac Owners Member
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    Re: My cadillac is total Crap

    Hi Ape Man,
    Thanks for your good advice.

    I have only used genuine Gm parts, except for the Ht leads wich i made up from copper spark plug wire about a year ago, it made no difference.
    I have also personally replaced the fuel pump with a genuine part.,no differnce.
    I had the catalytic converter removed so it only has a muffler.

    I agree with you about testing the parts before replacing, and i will do so in the future.

    this vehicle has been garage kept most of it's life and has not been started often.
    It has had no hacking done to it (electricaly and mechanically) as i do all the repairs.
    It only has 33000 miles.

    I disconected the NO.8 Ht lead lead and the check engine light stays permanently off and the MPG sentinel doesn't show weird numbers.
    The car misses a bit,"obviously".
    However with everything connected the car is slugish on take off, feels like it wants to cut out, then slowly it takes on.
    When i reach about 40MPH the car performs Ok and the check engine light is off,however when i give it gas the check engine light flickers or stays on till i release the pedal a bit.

    The engine runs better when it gets hot,it's only when you need to accelerate that it hesitates and gets slugish almost to a cut out.

    thank you

  6. #5
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: My cadillac is total Crap

    I'd stay away from solid core secondary plug wires with any electronic controlled engine. This just invites noise on the sensor wiring.

  7. #6
    bluecor is offline Cadillac Owners Member
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    Re: My cadillac is total Crap

    I,ve heard that faulty capacitors can cause alot of problems, could this be the cause?

    Thank you

  8. #7
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: My cadillac is total Crap

    Assuming that you are talking about the capacitors within the ECM, you really want another spare engine computer. Most capacitors age well unless they are exposed to heat. There are some elecrtolytic types which will dry out unless they get charged once in a while. It usually takes years of non-use for these to become defective. It would be easier to source another computer. Automotive electronics are not designed for service at component level.
    The part where you said that your spark plug wires are solid core types and removing one of them makes some of your symptoms go away could be a good clue. While they will work fine with a dumb carburetor and no ECM, there is no reason to have solid core wires in this application. These wires will act like a radio transmitter. Turn on your AM radio and listen for the noise. If you really want to keep them then they must be shielded coaxially from one end to the other with both ends grounded through short leads. Otherwise, they induce all kinds of noise and hash into the computer's sensor wiring. Resistance in spark plug wires is not a bad thing. Voltage drop is a function of current draw. Spark across a plug does not need much available current and will work fine with resistance in series as the resistance only limits the spark Voltage when excessive current is drawn.
    Another potential source of woe would be some kind of ground loop. Check anyhting that looks like a ground. At the age of this car it would be a good idea to remove any ground connections with lugs and clean them with a wire brush. Look at the wiring harness where it meets the firewall. You will see some coaxial lines which use aluminum foil as the shield. These are not servicable. All that shielding is pretty much at the same DC ground as the engine block. It is kept seperate to keep noise off the sensor inputs to the ECM.

  9. #8
    bobbyt's Avatar
    bobbyt is offline Cadillac Owners Member
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    Re: My cadillac is total Crap

    First of all, make sure that the engine is hitting on all 8 cylinders. The ECM cannot detect ignition problems, but a rough running engine can cause the check engine light to flicker due to the ECM seeing "weird" things.

    Second, Check that the vacuum port to the MAP sensor is not plugged. This is a rare but not uncommon problem on the older TBI units. The vacuum ports within the throttle body will eventually get plugged up and block the signal to the sensor. Pull tehlines off and see if you can blow (or suck) throughteh ports. If it is anything but completly free then pull the throttle body and clean out the ports.

    Good luck
    Bobby

  10. #9
    bluecor is offline Cadillac Owners Member
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    Re: My cadillac is total Crap

    I have fixed the car and it's back on the road,i't drives and runs like the day i bought it.

    After replacing two ECMS and all the sensors "nearly all of them"

    The problem was the spark plug wires.

    they had a resitance of 20 000 Ohms.

    It's unbelievable but true.

    Now i have one injector thats pissing a bit and it's causing a bit of black smoke.
    But man is this car going like a bomb.

    Thanks for all your help.

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