1986 Eldorado stalls under stress
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HT4100 4.1, 4.5, 4.9 Discussion, 1986 Eldorado stalls under stress in Cadillac Engine Technical Discussion; Need a few hints here... 1986 Eldorado, HT4100, bought it new, 178,000 miles. Ran relatively fine a few months ago, ...
  1. #1
    FrankC's Avatar
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    1986 Eldorado stalls under stress

    Need a few hints here...

    1986 Eldorado, HT4100, bought it new, 178,000 miles. Ran relatively fine a few months ago, then it began to struggle while climbing hills until I shift down so that the engine runs a little faster. Car runs fine on freeway going 75 mph. But it seems whenever the engine is stressed, say going 40 mph in high gear up a somewhat gentle slope, engine begins to "chug". If I attempt to give it more gas, it will stall and it has never stalled on these hills before. If I shift down, the engine will run faster and be "OK" but auto or manual shifting should not be necessary on these hills. Recently changed plugs, electronic ignition module, and fuel filter. I removed one plug wire at a time and each one affects engine idle. Car starts up immediately.

    On level highway, engine sounds OK and ride feels OK. Used to get around 19 mpg. Now it seems to be getting around 15.5. That is more freeway than city driving.

    Anyone have any hints? I do have the service manual. During the past 22 years I've replaced lots and lots of parts (camshaft and lifters at 98,000) on the car as any long time Eldorado owner would know. But I can't seem to figure out what else to do this time. I was thinking of buying a fuel pressure gauge to check that. My guess is that it is a fuel issue, but not even sure of that. (fuel pump? injectors? O2 sensor? valves?)

    Body is in perfect shape. I would like to make 200,000. (100,000 was my original goal)

    Thanks for your interest!

    Frank

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    ehall's Avatar
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    Re: 1986 Eldorado stalls under stress

    Do you have trouble keeping up with traffic at a light?

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    awadecki is offline Cadillac Owners Enthusiast
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    Re: 1986 Eldorado stalls under stress

    Probably a fuel issue. Check your fuel pressure first (very easy)--tape a gauge onto your windshield. Should read between 9-13 psi all the time.

    Sounds like it's just not getting enough fuel.

    Did you ever have intake gasket/head gasket issues? I had to replace the cam on my 85 Deville with only 38,000 miles on the clock because the previous owner drove it for a while after the intake gasket blew. Now, it runs just fine, although I had to use Seafoam about 6 times (no joke) to clean the antifreeze residue off of the exhaust valves which were sticking open.

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    ehall's Avatar
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    Re: 1986 Eldorado stalls under stress

    I had similar problems until I got the GM top-end cleaner treatment as well, which is why I asked about performance from a dead stop

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    FrankC's Avatar
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    Re: 1986 Eldorado stalls under stress

    Thank you for the replies folks!

    I do not have a problem keeping up with traffic at a light as long as it isn't heading uphill. If I tried, I believe I could keep up with them going up a low incline if I remained in a lower gear than normal. I did try one time to just let it shift normally from a light in traffic on a slight incline. Traffic ended up going around me and I had to pull off to the side of the road.

    I'll get hold of a gauge today. Need to buy some hose as well to get gauge to windshield. Perhaps 1/4" copper is the appropriate size and material (?) I will bring a fire extinguisher with me..... hmmm....

    It has never had intake manifold or head gasket problems. I replaced the cam because one lobe was completely gone. Never had water in oil. Car ran fine for 80,000 miles after cam replacement until now.

    I thought about replacing the two injectors until I discovered the price. If the pressure is OK, do the injectors somehow become clogged, or would the problem be much worse if that were to happen? And does the filter in the tank get clogged or would low pressure most likely be caused by a bad fuel pump? And how likely is it that the fuel pump could have gone bad? These are the issues that have been running around my head but I had no one with experience to ask.

    Another strange thing that happened was that just a couple of months ago, when I was working this "fuel" issue, the ignition module died. (It failed previously 2 years ago). I replaced it and figured, OK, this will fix the other problem. It didn't. But the bad module was tested - it failed perhaps 6 (all) tests. I've wondered whether the new module could cause this problem if it were to fail one of the tests (it wasn't tested).

    Again, thanks for the support!
    Frank

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    Re: 1986 Eldorado stalls under stress

    It's unlikely it's the injectors. But you can check it by visually checking the spray pattern with the engine idling and the air cleaner off.

    Like others have mentioned, do a pressure test. The fuel pump on my 88 Eldorado went out at 220k miles. I did not loose any power beforehand. It just suddenly died and the car was inoperable. Yes, the filter in your tank or your in line fuel filter could be clogged. The inline fuel filter is a $10 item so you might just want to change it out anyways and see if it fixes the problem.

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    Re: 1986 Eldorado stalls under stress

    Thanks!

    I replaced the in line fuel filter yesterday. I had big hopes. But car runs no differently. (and of course, that is good news too). It was a lot of work to replace that filter. I'm glad you agree that it was worth a shot.

    To check injectors, I suppose you look for a nice spray of fuel from the injectors as you mechanically work the accelerator. And I assume both injectors should spray equally. I'm dissapointed to hear that the fuel pump didn't slowly fade on your Eldorado. It sounds like the motor in yours just burnt out (?)

    I suppose it does seem reasonable that less fuel is needed to travel 70 mph on level freeway than what is required to travel 40 mph up an incline. I did notice that the instantaneous fuel consumption was around 10 mpg or less while going up the incline. And when doing 70, it may have indicated well into the 20's.

    Again, thanks for the support.
    Frank

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    Re: 1986 Eldorado stalls under stress

    The spray pattern should be even at idle and when you rev the engine up. When you turn off the engine, the injectors should not drip. Yes, both injectors should spray equally.

    My fuel pump completely died without warning.

    It takes a lot more power to go up inclines and to accelerate the car.

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    Re: 1986 Eldorado stalls under stress

    Thanks for the reply and the answers to my questions.

    I am just leaving to head to Advance Auto Parts to pick up a fuel pressure meter. In preparation for that trip, I took the brass cap off of the fuel line service fitting so that I would have some sort of idea of what fitting and tubing to buy. In the fitting, is what appears to be a small plastic plug. I don't know if perhaps it is a check valve of some sort. I hate to pull it out without knowing, because the cap does not appear to be of a type that would seal the fitting. Can you provide some advice as to what to do with that fitting?

    Thanks,
    Frank

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    Re: 1986 Eldorado stalls under stress

    Get a bottle of Lucas fuel treatment ("Tune-Up In A Bottle") and add that to a full tank. If you have injector problems, it will clean them out pretty good.

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    Re: 1986 Eldorado stalls under stress

    I'll pick up a bottle of the Lucas fuel treatment when I head back into town.

    I have a pressure gauge now, but not sure how to connect it to the fuel fitting on the gas line. The fuel pressure gauge kits had fittings to work with what must be a valve core similar to the type used for a tire or refrigerant system. But my fitting appears to have a plastic piece that doesn't appear to be set up to have something inserted into it. Is that normal?

    Also, the fellow at the auto parts place told me that he was surprised that all I needed was a gauge to measure up to 15 psi. He showed me that the pump was rated at 45 psi or something like that. I assume the reason you would have a 45 psi pump and a pressure of only 12 psi is because the return line allows the fuel to return back to the tank and therefore the line pressure is much less than the pump pressure. (?) I think the return line is a little smaller than the supply line and that is why there is some pressure in the system.

    Thanks,
    Frank

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    Re: 1986 Eldorado stalls under stress

    Another thought... Is it possible the "plastic piece" that is coming out of the main fuel line pressure fitting (shraeder valve type fitting) actually some hardened fuel residue that has oozed into the dust cap over the past 22 years? Is that something than anyone has seen happen? There is no way to check pressure unless I remove whatever that is.

    Thanks!

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    Re: 1986 Eldorado stalls under stress

    Don't these cars have a diagnostic mode? any codes? It's starting to sound like another catalytic problem but you should check that fuel pressure first. There shouldn't be anything plastic in the schraeder valve. It might be some rubber gasket from the cap; just guessing. I have to check my fuel pressure tomorrow so maybe I can clarify some more then if you haven't got it checked by then. Good luck

  15. #14
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    Re: 1986 Eldorado stalls under stress

    Hi there, thanks.

    Yes, it does have codes that can be read. I'll run through them to see if any help can be found there. When I was looking at the the fitting before, I didn't realize it was actually similar to a shraeder valve. So I didn't want to forceably remove the "plug" inside it. But now it seems I need to get that stuff out of there. It sticks out of the end of the fitting by about 1/8" and is quite hard and stuck pretty good. But I'll get some pliers and clean it up. Seems there is just one surprise after another when working on that engine.

    Thanks again.

  16. #15
    awadecki is offline Cadillac Owners Enthusiast
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    Re: 1986 Eldorado stalls under stress

    hmmm, the fuel pressure on any throttle body motor is always under 15 psi (at least, GM vehicles). the test fitting is on the driver's side of the engine. follow the fuel line from the throttle body down by the distributor. you can't miss it. you need to unscrew the cap. once you do so, you'll see the fitting and the nipple (looks like a tire valve stem). screw on your pressure gauge.

    i agree with the above post--it may also be a catalytic converter issue. in any case, the engine probably is fine, just something minor.

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