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Thread: Loss Of Power - Intermittent Loss Of Power - 1998 GM LS

  1. #1
    Freeman LibertyAddict's Avatar
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    Question Loss Of Power - Intermittent Loss Of Power - 1998 GM LS

    Greetings! Haven't posted in a while!
    My 1998 GM LS has been good to me, but this year on its 20th anniversary and its achievement of 100k miles, it has manifested some issues that I'm yet to fully diagnose and treat.

    I'm getting a loss of power, mainly when going uphill, in an intermittent manner, sort of like how I heard some people describe it: "Going over rumble strips".
    Most of those people spoke of the transmission being the suspect.
    For the record, I changed the transmission oil 3 years ago.

    For the moment, I will follow a sort of standard procedure, which to my understanding starts with spark plugs, coils, fuel filter, fuel pump, and then the more serious stuff.

    Right now I'm a few hours away from changing the spark plugs(I had changed them 3 years ago, the previous ones where the originals). I'll update you all on this later.


    In the mean time, I would like to share pictures of something that caught my attention.

    Looks like that fuel injector caught some damage from the coolant that was leaking when the intake manifold was cracked(replaced IM 3 years ago). The IM was cracked just next to that FI.
    Could the damage be more than cosmetic/external?
    Is the O-ring seated between hole and FI enough protection from fluids falling into that space?

    More general questions:
    How weak are fuel injectors?
    How often should they be replaced?
    Can they be checked for failure with a volt meter?

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  2. #2
    No mean-spiritedness here. IPreferDIY's Avatar
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    I can only offer some basic things. First, the "going over rumble strips" effect typically describes the torque converter lockup not locking up properly, and this is sometimes corrected with changing the fluid. I presume the requirement for Mercon V rather than regular Mercon goes back to at least 1998. Did you use Mercon V?

    If the spark plugs were changed properly, I can't imagine an issue developing except for the possibility of coming loose, which is known to happen. There is not much thread in the holes, so it's a relatively fine line between getting them tight enough and overdoing it. I would recommend use of a proper torque wrench. Not sure of the torque value off the top of my head.

    A weak coil could cause misfires, and that can result in a curious intermittent loss of power. A scan tool rather than a mere code reader is great for tracking down misfires if no code is set.

    Fuel filter is a good idea if it might be due, though I doubt it's the culprit.

    I'm curious as to why the injector was not cleaned up at least a bit when the IM was changed. (One reason I like doing stuff myself is knowing things like that will be addressed.) In any event, I'm guessing the body is plastic, so the rusty stuff shouldn't be an issue. The o-ring should provide protection against stuff falling in, considering that it's main job is to keep the high-pressure fuel from getting out. You might want to consider cleaning what you can (e.g. use compressed air to blow off loose crap, spray on some lube, and use more compressed air to blow it off) to prevent the rusty stuff from having a further chance to deteriorate the o-ring from above. You would definitely want to do such cleaning if you ever decide to take it out, since you don't want crap falling into the hole.
    Last edited by IPreferDIY; 12-06-2018 at 03:35 PM.

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

  3. #3
    Beater gonna beat sly's Avatar
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    Injectors will trigger a code if they are electrically bad. If they're just clogged or open, they won't code.

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  4. #4
    Freeman LibertyAddict's Avatar
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    Yes, we used Mercon V.
    I checked the dipstick and it's completely fine, both in quantity and appearance.
    I did buy some ATF treatment fluid from LUBEGARD the other day. I'm thinking of pouring some into the system just to improve performance. And I say "improve performance" because so far it looks like the trans wasn't the issue. I just changed the spark plugs and the shaking and loss of power went completely away! (None of them were loose)
    I didn't think it was going to be that simple because the spark plugs where only 3 years old. Apparently they deteriorated faster than they should have. Specially the one on the passenger side, nearest to the front of the car. That one was nasty. Check the pictures out. The picture with one plug corresponds to the odd one, the dirtiest. The other picture shows the type of wear found on all the other seven.
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    It looks like there's oil on the threading. Is that normal? What could be causing it?



    BTW, fuel filter change is coming soon, regardless having fixed the loss of power and stuttering.

    Thanks for the tip on the FI.
    The injector piece should be plastic, but doesn't look like so. It's dusty and gives the impression of being metal. I'll have to check that out later.

  5. #5
    No mean-spiritedness here. IPreferDIY's Avatar
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    Personally, I wouldn't add stuff to the tranny. The Mercon V has everything the tranny needs.

    I forgot to mention fuel injector cleaner. It might not be absolutely necessary considering that gas has some cleaning stuff in it, but every once in awhile can't hurt.

    Can you measure the spark plug gap? It does seem very surprising that they would go that quick if they were the right ones. Dunno about the oil on the threads. I don't have much experience with spark plug issues.

    2000 Grand Marquis LS HPP, a hand-me-down in 2008 with 128,000 km; 175,000 km as of July 2014
    mods: air filter box "tuba" (in place of the "trumpet"), headlight relay harness, J-mod (around 186,350 km), 70mm throttle body, NKL4 PCM (from a 2000 CVPI, nothing great there apart from highway cruising), KYB Gas-A-Just shocks (after >202,000 km on originals)

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    Member EaOutlaw1969's Avatar
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    It looks like that cylinder with the coated electrodes and oil on the threads has been burning oil. Could be worn rings and or leaking valve seals-guides ( maybe even a leaking head gasket )
    You could do a compression and leak down test on the entire engine to get a idea of the overall health of your engine or just plan on replacing that plug more often and keep a closer eye on the oil and coolant levels.
    2000 MGM LS Palm Beach Edition a work in progress

  7. #7
    Member EaOutlaw1969's Avatar
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    I forgot to mention you could use a Aldor non oil fouling spark plug for the cylinder giving you short plug life. I am not sure if they make one to fit your engine but it is worth looking into.
    I would not put them in each cylinder just the one known to consume oil.
    2000 MGM LS Palm Beach Edition a work in progress

  8. #8

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    The only trans additive Ive used and can recommend is seafoam trans tune. When I bought my 98 p71 there was no 2nd gear. If I drove it enough it would shift momentarily then upshift. So as a last ditch effort I poured the bottle in and like a miracle the next time I drove it 2nd gear was back and it stayed that way until I sold it 2 years later.

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