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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, Prom needed/High speed great, mid to idle speeds terrible. in Past Cadillac Vehicle Discussion; Carnut, Please if you would, let me know what you typed in for finding the shop manual. I just came ...
  1. #16
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Carnut,

    Please if you would, let me know what you typed in for finding the shop manual. I just came up with a big zero for cadillac factory repair manual.

    Gerry

  2. #17
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Carnut,

    I found the page after all in books. THere were 367 books and none for an '84 DeVille. Will keep a lookout for one though. If you ever spot one, just shoot me the link. You can do a direct shot to gsim@tds.net if you want to.

    Thank you again.

    Gerry

  3. #18
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Carnut,

    I will have to read fuel pressure via a Schrade valve type fitting. Will have to buy a gauge for that. Looks like an old freon charging valve.

    Seems odd to me that fuel pressure would fail at idle to low-medium , yet would not fail for hundreds of miles at 70 MPH or above. Can that even happen? Almost more like a faulty pressure bypass valve. At the higher speeds all of the fuel goes into the engine and none goes back to the tank. Any possibilities there?

    Kindest regards,

    Gerry

  4. #19
    dennis93coupe's Avatar
    dennis93coupe is offline Cadillac Owners Connoisseur
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  5. #20
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thanks Dennis 93coupe.

    gerry

  6. #21
    carnut is online now Cadillac Owners Master
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    Re: Prom needed

    Again there is no low speed or hi speed injector. The left one feeds the right bank, the right one feeds the left bank. Re read my explanation on holding off and hi. Holding those IN DIAGNOSTICS will erase codes after a 0.0 is displayed. Its not used to enter diagnostics but to erase old soft codes. Loosing voltage is a good clue. Did you check for bare wiring under the adapter? I agree, there should be voltage at both injectors. if the car stalls while running and voltage quits as well there is a problem in the harness to that injector.

  7. #22
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    I did check the wiring and there are no bared wires shorts, etc. The voltage stays steady even while the thing is stuttering and stumbling down and when it is revving up a bit. The thing that was weird was that when the engine died, one had the voltage die too even tho the key was on. However the other had the voltage stay even tho the engine had died with the key on. That was what made me think that one might be for start/slow and the other for high speeds. However both stayed at a steady 2 v while the engine was running no matter the speed. The voltage did not vary even though the engine did vary a real lot in speed and smoothness. The fuel does sporadically stop when the thing is stumbling down even tho the voltage is steady. I can see that with a flashlight very easily. Made me wonder about the fuel pressure regulator.

    I just cannot imagine the fuel pump or filter being bad if it will run flat out 70 mph and up to 85 mph with no problem at all. The slower you drive the worse it gets. I will check at an auto parts store the next time I am out to see if I can buy a gauge that will fit the schrader valve in my car. I want to watch that gauge while that thing is stumbling and stuttering and also when it is smooth and picks up rpm's. Is the regulator in the center between the two injectors or is it mounted elsewhere? I have seen them mounted on the fuel rail in most cases, but seems I was looking at a Pic in the Haynes manual that showed it to be in the throttle body itself, feeding the two injectors. There should be a line from it returning to the fuel tank.

  8. #23
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Prom needed

    I'd look around for a dirty connection in a weatherpak connector somewhere. The pins to the intake manifold temp sensor can get a little grunge and make things act wierd. The sensor itself is a known problem with 4.1 RWD cars.

    Many short or on edge sensor readings will not always show up as a code.

    The factory manual's trouble trees are excellent. Do not try to out think them. Been there done that.

  9. #24
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thanks, Ape Man. I will pull those apart and take a look around the vicinity of the Intake manifold. I did run a test on the fuel line and I saw a steady 5 or 6 lbs the whole time it ran. It alternately ran at a fast idle to stumbling down and almost dying. When it stumbled down and ran rough, I could actually see the gas vapor coming and going off an on, even tho the voltage and the pressure were steady the whole time. I have a steady 2 VDC and a steady 5 or 6# fuel pressure and neither wavers. I am wondering about the fuel regulator adjacent to the injectors. It is mechanical tho, no wires. Does anyone know what the three wire gadget on the passenger side of the throttle body housing is? A sensor of some sort?

    Gerry

  10. #25
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Carnut,
    I just did look again at the codes. It definitely has to be the 'OFF' button and the red 'Warmer' button pressed simultaneously. No other combo will even produce a code reading of any kind or even a starting number. I am seeing 1.8.8 52 1.8.8 52 1.8.8 7.0


    And I did succeed in getting readings with the key in 'Run' position without starting the engine. IT just takes a bit longer to start. Also I have both the 'service engine soon' and the 'service engine now' lights on the whole time the codes are flashing. My book (Haynes) says that means ECM or P R O M are bad. (a new ECM did not help)

    I have not found a DeVille manual, but I did find a electrical manual on the Deville. I bought a 1984 final repair manual for supposedly all caddy models, but it has the Fleetwood symbol on it, so I am thinking that there will be little there to help me. It was only around $10 or so. Maybe $7 for the wiring book, factory also.

    Both fuel pressure and voltage are steady even tho fuel flow is not.

    Gerry

  11. #26
    The Ape Man's Avatar
    The Ape Man is offline Cadillac Owners Connoisseur
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    Re: Prom needed

    Quote Originally Posted by gsim View Post
    Thanks, Ape Man. I will pull those apart and take a look around the vicinity of the Intake manifold. I did run a test on the fuel line and I saw a steady 5 or 6 lbs the whole time it ran. It alternately ran at a fast idle to stumbling down and almost dying. When it stumbled down and ran rough, I could actually see the gas vapor coming and going off an on, even tho the voltage and the pressure were steady the whole time. I have a steady 2 VDC and a steady 5 or 6# fuel pressure and neither wavers. I am wondering about the fuel regulator adjacent to the injectors. It is mechanical tho, no wires. Does anyone know what the three wire gadget on the passenger side of the throttle body housing is? A sensor of some sort?

    Gerry
    That's the TPS throttle position sensor. It's the same thing as a 3 terminal potentiometer. You can check it with a VOM. One wire on the center terminal, one on an end terminal. Run the throttle through it's range slowly and see the reading change on the ohms scale.

    Those get flaky usually just off idle position first. I doubt it is causing your problem.

    Remember voltage readings taken with a modern meter may be bogus. Modern meters don't put any load on a circuit. You can read 12 volts through dirt but not have 12 volts available to light up a tiny light bulb.

    You can look at the spray from your throttle body injectors with a timing light for a good stop action view.

    The fuel pressure regulators built into GM throttle bodies of that era were very reliable and trouble free unless tampered with.

    The injectors are controlled through the ECM which is looking at distributor pulses from the pickup and module. They have 12 volts hot on one side through IIRC 3 amp fuses and the ECM completes ground for a pulse.

    A good factory service manual describes all this stuff. I'm doing it from memory. Distant memory. I have not touched an HT-4100 for a long time.

    My experience is make sure all ignition components are in top condition before chasing DEFI problems. Your engine has the cap buried where it isn't easy to check.

    Spark plug boots on these era cars can break the wire internally if not given a half twist before removing from the plug. That internal break can cause a mis-fire under conditions of higher required firing voltage like climbing a hill.

    Always check the easy and cheap stuff first. Good luck.

    Off to diagnose a high voltage power supply on my ham transmitter....................................... ..Wish me luck.

  12. #27
    gsim is offline Cadillac Owners Member
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    Re: Prom needed

    Thanks ape man. Thing is this car will run flat out smooth as silk at 70 MPH and above all day long. I drove it some 500 miles with this trouble in order to get home. it does not act like an ignition trouble, AND I can actually see the fuel being interrupted while both the voltage at the injectors is steady and the fuel pressure is steady too. So I am puzzled. I am going to check that TPS thing though. It could be that it is cruddy internally at the lower end position and is reading correctly at the higher speed end. Will be easy to test using an Ohm meter and it should be a steady constant and predictable slope to the readings. If dirty/burnt in one position but ok in the higher ranges, it could explain what is happening maybe.

    Gerry

  13. #28
    gsim is offline Cadillac Owners Member
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    High speed great, mid to idle speeds terrible.

    I have a 1984 DeVille sedan with the 4100 engine. It runs well at 70 mph and above, but seems to be sometimes starving for fuel at lower speeds. Will really not idle at all. Needs starter fluid to restart once has warmed up. Drove it this way 500 miles to make it home. Have repl O2 sensor, MAT sensor, and finallly, ECM due to codes read. Still have code 52. Have steady voltage on both injectors of 2 VDC and have steady fuel pressure of around 6# (Low) Am wondering if fuel pump needs to be replaced, but cannot understand why it will run for hundreds of miles at 70 MPH and up with a weak fuel pump??? Am also wondering about TPS potentiometer being dirty/burnt maybe internally at the lower speed positions and not at the higher speed position?

    Gerry

  14. #29
    carnut is online now Cadillac Owners Master
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Hold the OFF and Hi buttons after you are in diagnostics! Once you see 7.0 displayed, press them and hold them until .0.0 displays. I'll say again, both service lights WILL be on while in diagnostics. Its the car's way of confirming the bulbs illuminate. Once you see the zeros, press any other button to exit diagnostics. Then re enter diagnostics to confirm 52 is gone. You will see both engine lights come on, a 18.8 display then a 7.0. and NO 52. Try swapping the injector connectors left to right. Pinch the white connector on the top of the injector and lift up gently. If the sputtering injector switches to the other one, you have a wiring issue, if the same injector sputters, you have a partially plugged injector.

  15. #30
    gsim is offline Cadillac Owners Member
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    Re: Prom needed/High speed great, mid to idle speeds terrible.

    Thank you, Carnut. I am going to revisit the code thing again based on what you say. I was not able to do anything with the car yesterday. I did discover that I had left a valve open while using my manifold AC gauges to read fuel pressure, so likely that is how it read low but steady @ 6#. I will re-read that today and will get a really good light so I can watch the fuel spray better on both injectors.

    One thing I did notice on the voltage test three days ago was that both did remain steady @ 2 VDC while engine was stumbling. Here is the funny thing tho: Driver's side voltage remained @2 VDC after engine died and Passenger side injector voltage died when engine died even tho the key was still 'RUN'. I thought that was pretty strange and am going to confirm that today as well.

    Gerry

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