1979 Eldorado Hesitation/Stalling Problem
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Cadillac Seville / Cadillac Eldorado Forum Discussion, 1979 Eldorado Hesitation/Stalling Problem in Past Cadillac Vehicle Discussion; Hello everyone. I just bought a 1979 Cadillac Eldorado with fuel injection a few weeks ago and I have a ...
  1. #1
    bpmolder is offline Cadillac Owners Member
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    1979 Eldorado Hesitation/Stalling Problem

    Hello everyone. I just bought a 1979 Cadillac Eldorado with fuel injection a few weeks ago and I have a problem finding out why it is running funny. This is what I've got:

    The engine is hard to start when cold, but after a few tries, it will keep running without dying. Sometimes it tries to choke out and when I give it gas, it backfires through the throttle body. When I am at a stop, it will idle fine, but as soon as I step on the gas to start moving, it hesitates and acts like it wants to die until I get it to about 10 mph, at which time it smoothes out and surges forward as if suddenly empowered.

    I noticed that when I remove the air filter lid on the top of the throttle body, and run it open, it starts fine when cold and runs just fine.

    Does anyone have any ideas about what causes this condition and what may be faulty. I have done a complete tune-up, plugs, wires, distributor, new filters and oil, etc. and they were all carbon tracked (or clogged) and needed it. The car had been sitting for a few years in a garage before I bought it, so only God knows when the last maintenance was.

    All I know is that everything I have tried has not worked besides leaving the air filter lid off. I don't run it too much like this because I don't know what it would do to the emission system. Besides, the radiator started leaking as well, so that sucks too.

    Any help or advice would be greatly appreciated. Thank you.

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  3. #2
    FRANKO is offline Cadillac Owners Fanatic
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    This is a 350 gas, fuel injected? Check your Ohms readings for the water and air temp sensors. See similar post here.

    FRANKO

  4. #3
    carnut is offline Cadillac Owners Master
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    If this a 350 fuel injected car, then in the throttle body is an item called a choke heater. When the engine is cold, you should be able to press down on the heater and should feel spring tension. This item is located in the center of the throttle body beside the wing nut threaded shaft. Remove the threaded shaft, turn the choke heater counter clockwise about a quarter turn. It should pop up under spring tension. Clean the bore it sets in, clean the spring. Look closely at the black plastic heater, on the side you will see a small micro switch with a brass contact, clean that as well. After reinstallation verify 12 volts to the electrical plug to it with the ignit key in the on position. When the car is cold this heater is extended, after voltage warms up the spring, then it settles into the well it sits in, restricting air inside the throttle body, thereby lowering the idle. When its extended, it allows additional air into the body raising the idle so it doesn't hesitate or bog and die. Hard piece to buy new. Try gmpartsdirect.com Sometimes its all gummed up or has no voltage to it. Good luck!

  5. #4
    FRANKO is offline Cadillac Owners Fanatic
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    Quite often the little tin arm of the microswitch for this (Choke) heater is broken off.

    FRANKO

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    bpmolder is offline Cadillac Owners Member
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    Thanks for the tips and I apologize for responding so late. I have been seriously ill for the past 3 months.

    Is it possible that the fuel pump circuit could be faulty somewhere, such as the fuel pump relay? Today, I was out trying to drive it a bit and I noticed that the fuel pump under the driver's side door would not shut off, even after I cut the key completely off.

    It is getting harder and harder to start and keep running, even to the point where I had to have AAA tow it home this afternoon.

    If it could be the fuel pump relay or some related device, would anyone know where the location of the relay is?

    Thanks for your help and I apologize once again for the lapse in contact.

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    bpmolder is offline Cadillac Owners Member
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    I checked the fast idle valve this morning. I pulled the valve off of the throttle body and checked the resistance. I get about 24 ohms with the switch open and about 12 ohms with the switch closed. I was not able to verify if there was 12 volts to the connector because I was not able to keep the engine running at all. The condition is steadily growing worse.

    As far as the fuel pump thing goes, I still don't know how to explain how the in-line pump runs either constantly or just a couple seconds after the key is turned on as it should. I have been trying to research the fuel delivery circuit to no avail. I have a repair manual coming in the mail that will maybe shed some light on the fuel circuit as a whole. Everyone I talk to tells me that it is a relay and my own knowledge seems to agree with that (I am an electrical engineer by trade). If there is no external relay in the circuit, what is causing the pump to act like that? Could it be an internal relay inside of the pump housing, meaning that the whole pump needs to be relaced?

    Next I will check the resistance across the water and air temperature sensors.

    I appreciate everyone's help with this. This is a vehicle that I rely on for transportation right now and it really is a relief to have everyone here to ask about this problem. If there is anything else anyone can suggest, I would really appreciate it.

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    Re: 1979 Eldorado Hesitation/Stalling Problem

    Yes, there IS a fuel pump relay. If the engine is not cranked within 2-3 seconds the relay disconnects til it does crank. If the relay fails, then the pump will not turn on til a certain oil pressure is achieved ( I forget the exact figure) which will result in long crank times.

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    bpmolder is offline Cadillac Owners Member
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    Thanks, Ranger, for clearing that up for me. I received my repair manual in the mail today and discovered upon reading it that my particular car is multi-port injected. Since it is the type of fuel system where the injectors are in the manifold and not the throttle body, the system is controlled totally different electronically.

    There is indeed a relay, but it is in the ECM. Part of the circuit controlled by this relay is the oil pressure sesor, coolant temperature sensor, engine metal temperature sensor, TPS and fast idle valve. I went through the circuit, checking these things visually and with my meter, and found a wire coming off of the TPS with broken insulation and an exposed conductor. I snipped the section of broken wire and replaced it with another piece of wire of the same gauge.

    After this, the fuel pump stopped malfunctioning, which is a good thing. I got the car started and let it run for about 10 minutes so all the excess fuel would burn. After that, it smoothed right out, leaving just the original problem.

    The hesitation problem is still there, only when I first step on the gas to get moving from a stop. Imagine my relief as the problem reverts back to just a pain in the ass.....

    I checked the valve thoroughly, once again verifying resistance readings. This time, with the engine running, I also verified voltage to drive it as well. I checked the voltage at the air temperature and coolant sensors, as well as the TPS, metal temperature sensors, fuel injectors, fuel pump, the works. All showed around 12.8 to 13 volts.

    When I totally removed the fast idle valve from the throttle body, the spring jumped out on me. The little metal clips that are supposed to hold the assembly together are gone and the thing is in three pieces. This is the only thing I can find wrong with the whole picture. Could this be the cause of the problem? Is there some way that the condition of that spring assembly could be causing the air flow to be restricted?

    Any thoughts?

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    Re: 1979 Eldorado Hesitation/Stalling Problem

    It has been a long long time since I have even seen a '79 Eldo. I do know that a bad TPS will give the symptoms you are expiriencing, somewhat like a bad accelerator pump in a carburator, if that is of any help.

  11. #10
    carnut is offline Cadillac Owners Master
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    Without the benefit of seeing the fast idle valve, what you describe is normal. It is 3 pieces, the spring the valve itself and the piece that extends thru the spring. As I explained before, when the engines cold, the fast idle valve is extended causing a very fast idle approx 15 to 1800 rpm, after about 2 min. the rpm will slowly lower and the valve will no longer have spring tension. If I recall from memory, to test the TPS switch,turn the key to the run position, and by hand, you rotate the throttle slowly. You should hear a faint series of click noises inside the TPS as the throttle is rotated to wide open. If I recall there was a specific number of clicks that had to be verified to confirm normal operation and normal adjustment. The TPS is no more than a varible resistor. As the throttle moves from idle, the voltage is increased to keep the injector flow rate in time with engine rpm. Starts at about 1/2 volt and goes to 5 volts at wide open throttle. If you hear a static type noise rather than a distinct click while rotating the throttle, then theres a "dead" spot within the TPS. The cover is easily removed on the TPS and you will see the copper grid lines that the "fingers" follow. sometimes cleaning the grid with a pencil eraser will help. Please get a factory service manual. All other manuals will not be as in depth and will give you just enough info for you to be frustrated! The coolant temp sensor and the air temp sensor are the same part! We used to swap one for the other to help diagnose a cold start problem. If the air temp sensor reads incorrectly it will cause the car to run lean cold. If the coolant temp switch reads incorrectly, it will run too rich. These are 26 year old memories so be advised. Verify with the Factory service manual.

  12. #11
    carnut is offline Cadillac Owners Master
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    I just remembered something else. The piece that goes inside the fast idle valve spring has 3? little wires. These are what get hot from the 12 volts supplied and heat the spring causing it to shorten, lowering the idle. The car doesnt have to be running to verify 12 volts to the valve, just have the key on and ck with a test light. The TPS should be checked with a digital meter so as to not damage it. These pieces were BOSCH parts ie. injectors coolant and temp sensors, long since out of production. This era of Cadillac would also heat damage the fuel pump connector that plugs into the ECU under the center of the dash. Drop the ECU down, remove its multi wire connector and visually inspect for heat related melting and discolorization. Sometimes you can remove the spade from the connector and secure it tighter to the ECU fuel pump pin. Or----- remove it all and get an intake from a 350 Olds engine with carb and swap it out. Assuming smog compliance is not an issue? The carb would require a lower pressure fuel pump. There is a block off plate were the mechanical pump would go on the block, but no ecentric on the cam gear to make it function.

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    bpmolder is offline Cadillac Owners Member
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    I checked the TPS this morning and it is operating within specs. I followed the check procedure in my manual, both mechanically and electrically, and it was operating like the book said it should.

    When I went back out this afternoon to start her up, she was running fine again, except for that little bit of a hesitation when I first hit the gas, then when it opens up a few hundred more RPMs, it goes away and I get a sudden surge of power if I have stepped down on the gas too much.

    As far as the coolant and air sensors go, they are also within specs according to the book. I have even checked the warning bulbs on the dash for proper operation. Everything like that is working fine.

    I noticed that it also feels a little weak when I hit bumps in the road. If I am going at any speed and hit a bump, I feel a sudden engine hesitation like it is shutting off for a split second, then it runs again like normal. I wonder what can be causing that?

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    bpmolder is offline Cadillac Owners Member
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    Oops.....I forgot to address one more thing. I didn't notice any piece that goes inside of the spring. I have the valve, a spring with a plastic top that the valve touches, and a plastic ring on the bottom of the spring that fits in the throttle body hole on the bottom of the assembly. There is supposed to be something else in the middle? Wow....if this is so, I think I found the problem....please explain in more detail exactly what the valve and spring assembly consists of.

    Thanks a lot for your time. I appreciate all the knowledge you all are sharing with me. I am really learning a lot.

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    carnut is offline Cadillac Owners Master
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    The so called plastic top is what I'm referring to. You've got all the parts. Hitting a bump could be the connector I referred to at the back of the ECU. This era had some hesitation off idle. Some were worse than others. Sometimes by adjusting the TPS and the large air screw at the front center of the air horn, it can be better. Some air horns were just a screw, others were an allen wrench type screw with a jamb nut to lock it once curb idle was set. Maybe the warm curb idle is a little low? Turning that screw out should provide more air thus a higher curb idle which might cover up the bog off idle. Also confirm base timing is at spec and try 2 degrees more before top dead center. Dont do all of this at once. One thing at a time, then road test. Good luck. You've made no reference to having a fast idle cold? Does it? We used to shim the spring by placing a washer under the bottom plastic ring to allow the fast idle to last longer. This engine tended to be 'cold blooded" ie ran a little ragged cold. Not such an issue here in Calif.

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    bpmolder is offline Cadillac Owners Member
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    Re: 1979 Eldorado Hesitation/Stalling Problem

    This evening, I checked the connectors to the ECM and adjusted the TPS. I am getting the same thing. The symptoms seem to lead strongly towards the air intake system somewhere, especially since it doesn't stutter while hitting bumps if I have the cruise control set. It only stutters when I am pressing the gas, probably because of the sudden pedal jerk when hitting the bump. It seems that if I push the pedal too quickly, even at idle, it hiccups a little bit.

    As far as the air horn goes, I am not sure what you mean. Do you mean the air pump? I am a little confused here. The curb idle is slow at all times. There is no fast idle to begin with, even when it is dead cold and I first start it up. The idle remains the same. Do you think that shimming the valve with a washer could help any?

    Thanks!

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