Slight stumble under light load - 1995 ETC
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Slight stumble under light load - 1995 ETC in Past Cadillac Vehicle Discussion; Last week I bought my first American car, a 1995 Eldorado with the 4.6 300hp engine. On the test drive ...
  1. #1
    jonkheer is offline Cadillac Owners Member
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    Slight stumble under light load - 1995 ETC

    Last week I bought my first American car, a 1995 Eldorado with the 4.6 300hp engine. On the test drive before buying the car ran very good, but now i'm experiencing a stumble in the engine when cruising. The car idles good (600 rpm), but when driving with slight throttle or on cruising speed, the engine stumbles slightly. It's not bad but noticeable. When i press the throttle more than 20% open, the car runs good and quick. The MPG is normal.

    I already searched the forums, and learnt to pull the codes. But there's no engine error code at all.. only for the rear right suspension solenoid (S027). I cleaned the coil pack connectors, the throttle body and the coil pack ground cable. Didn't help. The spark plug wires look pretty new, but the plugs didnt so I replaced them today, but that didnt fix the problem.

    The old spark plugs all had the same color, so I don't think it's a bad injector. Those engines are new for me, so I don't really know what to do now. Does somebody have a idea or suggestion to solve my problem?

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    SliceOfLife is offline Cadillac Owners Enthusiast
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    Re: Slight stumble under light load

    Welcome, jonkheer. How dirty was the throttle body? I know my car is a little different and a little later than yours, but I got significant improvement when mine exhibited such stumbling by cleaning a rather filthy TB.

    Also, I've read that you can't really tell for sure how old plug wires are just by looking at them.

    I've also heard that some of these cars can be pretty picky about the spark plugs, insisting on the correct delco part number--no substitutions tolerated! Try a search here on "correct spark plug", or some such. But, again, I'm not sure this applies to your eldo.

    Sorry I can't be much help. Smarter people are likely making their way to your post as we speak. I just thought I might help get the ball rolling.

  4. #3
    97PearlEldorado is offline Cadillac Owners Member
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    I have been having the same issue kind of relieved its not looking like a bigger issue. I bought some throttle body cleaner will post results...

    ----------

    Post results if possible I've been having the same issue plan on cleaning the TB

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    I agree with Slice. Looks are no indication of how good the wires are. When I had a slight misfire on my '97, a new set of wires cured it. They looked good too.

    Here's the (lengthy) thread if you care to read it.
    http://www.cadillacforums.com/forums...ine-trans.html

  6. #5
    jonkheer is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    The throttle body was not very dirty. There was some carbon buildup inside, but not bad. I only cleaned it to be sure.

    But.. er... i'm afraid that my local car parts shop sold me the wrong spark plugs. I got a set of Bosch HR8DCX's from them.. and after reading the suggested spark plug topics here, I understand this is possibly the most wrong choice of all the available brands? Oh well. Lets hope i can return them and get the money back :P

    I totally agree about the wires- they look fabulous but I don't know how old they are. I've decided to buy 8 new AC Delco 41-950 spark plugs and a fresh set of AC Delco wires. Is 748J the correct part number for those wires? (found at the Rockauto site). There are some American car specialists nearby, so i'm gonna contact them for those parts, instead of the local car store.
    Finding those parts can be difficult in Holland.. most of the USA car garages are specialised in older pre-1980 cars so they don't have many stock for modern Yank tanks.

    Thanks for the advice so far, I'll keep you updated!

  7. #6
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    Yes, 748J are the correct wires. 9748J will work too. They are cheaper, but not custom cut to length.

  8. #7
    jonkheer is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    Well, i spent my last weekend troubleshooting the Eldorado.. I bought new spark plugs and wires, and swapped them. I also cleaned the coil pack connectors during this job.
    And.. the car drives a lot better now! But the stumble is still there, now only sometimes and less noticeable...

    During last Friday night I drived the car for the first time in the dark, and i noticed something strange; ALL the lights are flashing! Not on-off, but from normal to bright and back, with a frequency of 2 times a second. This frequency doesnt change, it stays the same in the entire rpm range. When the engine is shut off, everything works in good order without flashing.
    When I start the engine again, everything starts to flash and it doesn't stop doing that.. only when I shut the engine down.

    Pretty weird.. so i went to investigate the problem today. I pulled the codes, and got a 'battery voltage too high' error. But the voltage always floats around 14.2-14.8 volts while driving, sometimes it spikes above 15v for a few seconds, thus generating the error. I thought the problem was lying in the voltage regulator, but the alternator with built-in regulator (i think) is brand new..
    So I cleaned all the battery cables, ground connections and negative engine connection. I even made a additional negative earth cable on the inner wing. That didn't help. I also looked under the dash for faulty wires, but found nothing special.

    But i noticed that the fuel pump speed also fluctuates simultaneously with the flashing of the lights, it's pretty noticeable when I keep my head around the fuel tank. Because of this reason, I think the flashing light problem is also the culprit of the stumbling engine, because the fluctuating fuel pump generates pressure spikes in the fuel lines, which makes the engine stumble under light load. Am I correct with this idea?

    I'd love to hear a possible solution for this flashing problem.. since I cleaned all the connectors and the fact that the alternator is new, i don't have any ideas anymore for fixing this. I'd like to repair the flashing problem first, to see if the stumbling engine problem disappears simultaneously.

  9. #8
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: Slight stumble under light load

    Relatively rapid rises and falls in the indicated battery voltage are usually the fault of the alternator (actually, voltage regulator, built-in), a bad wiring circuit: fluctuating excitation or field voltage, or a bad/intermittent wire/connector/battery cable.

    Rising and falling voltage affects EVERY electrical part of the car - from light bulbs to sensors to the PCM/ECM.

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    Ranger's Avatar
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    Re: Slight stumble under light load

    perhaps a ground?

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    apachedawg is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    If it were my car I would take it to an auto parts store and get the alternator tested in the car. Then pull it and have it tested again.

  12. #11
    SliceOfLife is offline Cadillac Owners Enthusiast
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    Re: Slight stumble under light load

    Quote Originally Posted by jonkheer View Post
    But i noticed that the fuel pump speed also fluctuates simultaneously with the flashing of the lights, it's pretty noticeable when I keep my head around the fuel tank. Because of this reason, I think the flashing light problem is also the culprit of the stumbling engine, because the fluctuating fuel pump generates pressure spikes in the fuel lines, which makes the engine stumble under light load. Am I correct with this idea?
    While it sounds like a plausible explanation, I tend to doubt it, because of the function of the fuel pressure regulator. The FPR should have the effect of smoothing out the "spikes" you mentioned. As Submariner has said, voltage variations at the source will affect ALL the car's electrical systems, including ignition. I like this as a better explanation of the stumble.

    As Ranger has said, though, a loose ground could be the cause of these voltage variations.

    I don't know if I can go along with the idea of the alternator/voltage regulator being responsible, though. I'm not all that familiar with that part's failure modes, but my sense is that they would be more catastrophic. I may check the FSM's diagnostic chart for your "battery voltage too high" code (exactly what code was that?) for some clues.

  13. #12
    jonkheer is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    I think I cleaned all the grounds and wires in the engine bay. Are there more grounds in the car to look out for?

    The error code is I052 / Battery voltage too high (also pops up sometimes on the dash while driving). The voltage is always around 14-14.6, but occassionaly spikes to 15.5 for a few seconds. This happens sometimes.. i think about 1 time per 2 hours? Not very often.
    But where can i find the FSM diagnostic chart? Is 'FSM' the service manual? (which i don't have :P)

  14. #13
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    Re: Slight stumble under light load

    FSM = Factory Service Manual (by Helm Inc. NOT Chiltons or Haynes). Ebay is your friend.

  15. #14
    jonkheer is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    Well.... I fiddled around with the wires yesterday. I tried to measure resistance in the engine bay main wires, to locate a possibly bad ground or wire. I didn't found any.. but there were some non original wires (somebody had bypassed the starter solenoid wires for no apparent reason), so i removed that rubbish. And I discovered that the + lead on the alternator connection had a spring washer underneath it, instead of on top of the cable connector, so I swapped it over. Nothing too special, and I didn't expect those 'solutions' to actually fix the blinking light problem.

    But.. after those jobs.. the lights didn't flash anymore! I was really surprised with that, but also very confident! And the car drove like new again, no stuttering problems anymore!

    When driving to work today, there was a small stutter again.. meh. I didn't look out for any flashing lights.. I thought, because I 'fixed' the flashing problem, that the solution laid somewhere else, so i decided to clean up the EGR system. I cleaned all EGR pipes, passages, the valve, and looked under the inlet manifold for small EGR passages. Didn't find them. The starter cable washer on the motor was slightly loose, so I tightened it. When everything was putted back together.. i discovered that my lights were flashing again! AAAARG!

    But even when I disconnect the starter motor cable from the battery, the lights keep flashing. When I remove ALL cables from the positive pole of the battery, the lights stop flashing... so I tried another battery, without success. Using jump start cables between engine block and chassis to make good earth also didn't help.
    I think I'm gonna pull my alternator out of the car and get the damn thing tested. I don't know another possible solution anymore..

  16. #15
    jonkheer is offline Cadillac Owners Member
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    Re: Slight stumble under light load

    OK, i pulled out the alternator last week and brought it to a specialized shop to test it. Turns out the alternator is good, so that's one point tracked down.

    After putting the alternator back in the car, I tried to test the L circuit on the alternator. If the car runs, and the L circuit is off, the lights don't flicker. The L wire puts a voltage of ~10V on the alternator, which gives ~14,4 volts at the battery. Then I hooked a external power supply on the L pin of the alternator, so I could adjust the input voltage myself. 12 volts on the L gives 16+ volts on the battery (and flickering lights), but when I turn the input voltage to around 3-4V, when the alternator just starts charging (measured 13V at the battery), the lights still flicker..
    So I think the L circuit is doing its job as it should.

    I also tried two different batteries, without any positive result..

    Today I checked the whole engine bay for earth points, found some more at the gearbox, and cleaned everything up. Still no result. The thing what intrigues me is that you clearly hear the alternator working hard when the engine is running, even at stationary rpm with NO accessoires on! The alternator gets pretty hot too. I think the thing is outputting at it's max amps, but why is it doing that..?

    Finally, I tried to determine which accessory circuit could be the culprit by pulling out those big 50A fuses out one by one, with the engine running. (well, all except for the ignition fuses of course). That didn't make any difference, so I think the problem must be in the wiring before the fuse box..
    Tomorrow I'm gonna look under the inlet manifold again, but the last time i did this, i din't find anything wrong there.. i'm starting to get crazy! HELP!

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