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

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    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 02:35 PM.

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    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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    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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    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.
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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

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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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    Freeman LibertyAddict's Avatar
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    Quote Originally Posted by IPreferDIY View Post
    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.


    The tranny wasn't the issue, but I still want to add the ATF protectant. I won't for now, and who knows if ever. Going to be reading about it in depth.

    Drove the car twice since I changed the plugs. The shaking went away, all of it.

    The spacing? I don't know. They're the SP-493 from Motorcraft. I just went to Advance Auto Parts, both times(3 yrs ago and recently), different branches, and they both gave me those.

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    Freeman LibertyAddict's Avatar
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    Quote Originally Posted by EaOutlaw1969 View Post
    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.
    Never knew those existed! They look like a good option if things start to go bad faster than before. If not I'll remove and clean twice a year, or replace every two yrs.
    I'll be changing the ignition coils soon, so I'll probably drop one of those non-fouling things in that odd plug hole.

    Quote Originally Posted by EaOutlaw1969 View Post
    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.
    Oil is fine, losing one drop a day, or less. Could be from the valve cover on the driver's side.
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    If you notice, to the right of the cover you can see the oil spreading.

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    Freeman LibertyAddict's Avatar
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    Quote Originally Posted by 87GrandMarq View Post
    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.
    People talk very well of many brands. I have to read more about it.
    I have no problem with the tranny, I thought I did. If anything, overheating is the worse that it should have gone through.
    I remember this time I drove for hour to get to a place and when I got there I turned the car off and immediately tried to turn it back on to move it to a better spot. It wouldn't start. I let it rest for hour and a half and then it started like nothing. I don't know what could have been but that day I know for sure it shifted like crazy going up and down all those roads.

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    Was the "going over rumble strips" feeling only when you pressed on the accelerator? Like if you let off it quit? Then it could be bad U-joints on the driveshaft. When I had torque converter shudder, it was only for a few seconds while it was trying to lock up or unlock or whatever. It was like duh-duh-duh-duh-duh (about as long as it takes to say that out loud or adding two duhs) with a noticible vibration and then everything was smooth. It didn't constantly rumble strip/shake. So the problem could be a bad u-joint could be binding and causing driveshaft vibration, and it can be an intermittent thing, but when it does it, it's only when you're on the gas. The torque converter shudder went away for awhile when my mechanic put in some 'shudder fix' goop, and when it came back I just had the fluid changed/trans serviced and never had a problem again. IIRC when my torque converter was shuddering it would do it EVERY time you were in cruise control and started up a slight hill, like it started to give it just a liiiiiitle bit more gas to maintain speed. I've had bad u-joints act up more intermittently. Good luck.
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    Quote Originally Posted by sxcpotatoes View Post
    Was the "going over rumble strips" feeling only when you pressed on the accelerator? Like if you let off it quit? Then it could be bad U-joints on the driveshaft. When I had torque converter shudder, it was only for a few seconds while it was trying to lock up or unlock or whatever. It was like duh-duh-duh-duh-duh (about as long as it takes to say that out loud or adding two duhs) with a noticible vibration and then everything was smooth. It didn't constantly rumble strip/shake. So the problem could be a bad u-joint could be binding and causing driveshaft vibration, and it can be an intermittent thing, but when it does it, it's only when you're on the gas. The torque converter shudder went away for awhile when my mechanic put in some 'shudder fix' goop, and when it came back I just had the fluid changed/trans serviced and never had a problem again. IIRC when my torque converter was shuddering it would do it EVERY time you were in cruise control and started up a slight hill, like it started to give it just a liiiiiitle bit more gas to maintain speed. I've had bad u-joints act up more intermittently. Good luck.
    As I said before, the shudder stopped since the spark plug change, but now that you bring this up I have to say the U-joints are suspects for other issues. I do get the clunk noise when shifting from D to R and vice versa. Sometimes it clunks more than other times. I can barely hear it with windows up.
    Also, there is this metal to metal noise I get when I go over the slightest bump or even a small imperfection on the road while I'm on the gas pedal. When I'm not on the gas pedal it almost never happens. The noise comes from the back and could very well be a suspension issue but I'm not 100% sure due to the fact that when I'm not on the gas pedal it is almost never there and if it does happen it's very low and short and it had to have been cause by a considerably big bump.



    The rocking, shaking, sensation happens when in idle, or at a stop while on Drive. This also stopped, BUT, I did feel just a slight rocking/shaking when the car was cold, at the first traffic lights stops, then it was fine.
    So, if non-fouling plugs do not hurt a thing I might just add one on that plug hole that had the dirtiest plug of all.

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    Freeman LibertyAddict's Avatar
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    So I bought a couple of these spark plug non-foulers and tried to install them.

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    All goes well until you try to seat the ignition coil boot. It's too long. The spark plug ends up being raised too much for the boot to seal the hole. Even without a seal, I don't see why it shouldn't work(I didn't try it, I'm concerned with debris falling into the port).

    So the solution could be using a different ignition coil.
    Here I joined images of the bent one, which is the type that the 4.6L SOHC takes, and the straight one which works on engines for cars like Explorer, Expedition, F-150/250, to name a few.

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    It seems shorter. Could give it a try...
    What do you guys think?
    Am I better off modifying one of the old coils when I replace them all?


    (BTW, I know I'm diverting from the topic of this thread, but if all works out I'll be making a separate thread on this separate issue)

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    I would fix whatever the problem actually is. Those non-foulers really don't work well, and modifying the coil sounds like a good way to cause problems.

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    Ditto
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