V8-6-4 Hesitation problem
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500, 472, 425, 368 Discussion, V8-6-4 Hesitation problem in Cadillac Engine Technical Discussion; Originally Posted by JJhomer83 Welcome to the forums the 864 you have is it still operational or did you disable ...
  1. #1
    damian's Avatar
    damian is offline Cadillac Owners Member
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    V8-6-4 Hesitation problem

    Quote Originally Posted by JJhomer83
    Welcome to the forums
    the 864 you have is it still operational or did you disable it so it runs on 8 all of the time.
    I have just got the car last week, and this is my second Cadillac. My first car was HT100 83'Eldorado. This one actually is in a very good shape and has only ca.50000 oryginal miles. The engine still runs in 864 mode, but I intend to disable MD (modulated dispatchment) and make it a normal v8.

    I am still going through "maintainance" stuff. The car hasn't been driven for 2 years, so I have decided to replace plugs, sparks plugs wires, fuel pump and filters.

    By the way... I do have a problem. The car sometimes have problems getting smoothly to higher RPM's, especially when I step on the accelerator and just floor it. It just doesn't respond fast enough and the engine stalls for a while and then slowly gets to highter RPM's. Maybe somebody knows what's going on. Anyway that's probably not a good subject to bring up in "New Members Forum " section. :-)

    Thanks for warm welcome!

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    elwesso's Avatar
    elwesso is offline Cadillac Owners Master
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    Re: V8-6-4 Hesitation problem

    Well Id say things are still recovering from the sitting for so long......

    Take it out and give it some WOT runs and then see what happens.... Also, try some fuel injector cleaner (techron is the best OTC stuff)......

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    damian's Avatar
    damian is offline Cadillac Owners Member
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    Re: V8-6-4 Hesitation problem

    You are probably right. This Saturady I'll do all repairs (plugs, wires, filters) and take a car for a ride. Then I'll see. Cleaning the injectors sounda smart too...thanks for a hint.

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    Cadillac Pat is offline Cadillac Owners Member
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    Re: V8-6-4 Hesitation problem

    Damian,
    Welcome to the board!
    Check the fuel pressure before and after replacing the fuel filter. It should be relatively steady and at least 10 psi. A bad filter puts an unecessary burden on the fuel pump and shorten it's life. Changing the fuel filter is a very good idea as it probaby has not been changed in a long time (or might be original).
    Next, check the TPS (Throttle Position Sensor). While many people think by it's name that it tells throttle positin, the TPS actually tells the computer the "rate of throttle opening" so it can determine fuel flow for it's "accelerater pump" function along with when the throttle is at WOT (wide open throttle). At idle, the "throttle switch" part of the ISC (Idle Speed Control) motor tells the computer the throttle is closed so that it may move to adjust idle correctly. WOT tells the computer to bypass the "closed-loop" O2 sensor readings and go to a "performance" fuel curve for more power. Of course, this is only under WOT throttle conditions, such as passing or accelerating quickly. The distributor, which tells the computer the engine speed, along with the BARO (Barometric Pressure Sensor) and MAP (Manifold Absolute Pressure, or intake manifold vacuum) determine fuel needs based programmed curves in the PROM (Programmed Read Only Memory) chip in the ECM (Electronic Control Module, or computer).
    Finally, replace the O2 sensor, even if it is good, because it is certainly "slow to respond, or "lazy". Being about $30 and fairly easy to replace, it is good insurance. It is recommended to replace it every 60,000 miles, and Bosch recommends every 30,000 miles (no, I don't work for Bosch, but I have noticed a difference).

    Pat
    Quote Originally Posted by damian
    I have just got the car last week, and this is my second Cadillac. My first car was HT100 83'Eldorado. This one actually is in a very good shape and has only ca.50000 oryginal miles. The engine still runs in 864 mode, but I intend to disable MD (modulated dispatchment) and make it a normal v8.

    I am still going through "maintainance" stuff. The car hasn't been driven for 2 years, so I have decided to replace plugs, sparks plugs wires, fuel pump and filters.

    By the way... I do have a problem. The car sometimes have problems getting smoothly to higher RPM's, especially when I step on the accelerator and just floor it. It just doesn't respond fast enough and the engine stalls for a while and then slowly gets to highter RPM's. Maybe somebody knows what's going on. Anyway that's probably not a good subject to bring up in "New Members Forum " section. :-)

    Thanks for warm welcome!

  6. #5
    damian's Avatar
    damian is offline Cadillac Owners Member
    Automobile(s): 2002 Deville DHS
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    Re: V8-6-4 Hesitation problem

    Quote Originally Posted by Cadillac Pat
    Damian,
    Welcome to the board!
    Check the fuel pressure before and after replacing the fuel filter. It should be relatively steady and at least 10 psi. A bad filter puts an unecessary burden on the fuel pump and shorten it's life. Changing the fuel filter is a very good idea as it probaby has not been changed in a long time (or might be original).
    Next, check the TPS (Throttle Position Sensor). While many people think by it's name that it tells throttle positin, the TPS actually tells the computer the "rate of throttle opening" so it can determine fuel flow for it's "accelerater pump" function along with when the throttle is at WOT (wide open throttle). At idle, the "throttle switch" part of the ISC (Idle Speed Control) motor tells the computer the throttle is closed so that it may move to adjust idle correctly. WOT tells the computer to bypass the "closed-loop" O2 sensor readings and go to a "performance" fuel curve for more power. Of course, this is only under WOT throttle conditions, such as passing or accelerating quickly. The distributor, which tells the computer the engine speed, along with the BARO (Barometric Pressure Sensor) and MAP (Manifold Absolute Pressure, or intake manifold vacuum) determine fuel needs based programmed curves in the PROM (Programmed Read Only Memory) chip in the ECM (Electronic Control Module, or computer).
    Finally, replace the O2 sensor, even if it is good, because it is certainly "slow to respond, or "lazy". Being about $30 and fairly easy to replace, it is good insurance. It is recommended to replace it every 60,000 miles, and Bosch recommends every 30,000 miles (no, I don't work for Bosch, but I have noticed a difference).

    Pat
    Thanks for a great post.
    As I've promiced a little follow up on the repairs today. I repalced plugs, wires and fuel filter, and guess what... things went worse. The engine runs like crap and I've noticed there is a lot of exessive fuel on the throttle body. It even ignites from time to time causing little "cough ups" and leaving a little cloud of smoke in an air filter compartment.Grrr... Not exactly what I was expecting today.
    I will probably go with the word of the wise (and my own intuition) and check the fuel pressure,fuel pressure regulator and see..
    Of course this is just a top of the iceberg. I figure I'll probably end up tuning up the whole fuel injection subsystem, I mean all the sensors,tps and probably ECM if nessessary. I already got a ISC. Well... that is not a bad idea. I'll end up at least with a reliable fuel injection for 368.

    I thing that we should actually write a FAQ or HOW TO on that and add it as a standard maintainance procedure. Most of 8-6-4 are least 20 years old by now and most of the Caddys will need a procedure like that before becoming a reliable transportation.

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