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Thread: Unknown Problem Getting Worse

  1. #1

    Default Unknown Problem Getting Worse

    I got a 1990 Grand Marquis a couple years ago, so I'm still relatively new to it.

    Back in December, it was flashing the Check Engine light on the highway, so I took it in and they replaced the TPS. After I picked it back up, it began to give me hesitation when accelerating from a stop. In the following weeks, that began to get a bit better until one day when I come back I notice a sulfur smell coming from the left rear of the car (probably the catalytic converter's done).

    When the catalytic converter started doing that, there was also a rattling coming from the front of the car (kind of like when shifting gears on a bike) when accelerating to highway speeds. It would stop after a few seconds of getting up to speed, but every drive I've taken on, it has gotten worse. Now, it rattles pretty loudly when going from 55-60 mph, and 35-40 mph. It stops after it shifts usually, but now it's happening whenever accelerating up hills or on the highway. Keep in mind that this is only over about 5-8 drives.

    The mechanic told me that the transmission might need to be rebuilt, but I'm not sure if the rattling is related to the catalytic converter in any way, since they both started happening at the same time. Back in November when I took it in for another issue, the transmission was in decent shape.

    None of these issues were happening until I picked it up from the mechanic after the TPS was replaced.

    Extra info: It's consistently below freezing this time of year around here, and last winter I hardly took it out because it wasn't inspected.
    Last edited by 1990grandmarquis; 01-23-2021 at 02:02 PM.

  2. #2
    Member of the Orb Alliance packman's Avatar
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    I am by far not an expert on this; and I hope the more knowledgeable members chime in with this. I would scan the ECM for codes to see what symptoms it's seeing. Then go from there.

  3. #3
    I'm an air-conditioned gypsy gadget73's Avatar
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    Without hearing exactly the sort of rattle you're talking about its hard to say.

    agree on scanning it for codes though if all of this started after the TPS got changed. The only thing I can imagine being computer-related and rattle-sounding is detonation which is a timing problem or running very lean. Broken cats or some other loose parts sort of noise would still be loose even with a bad TPS and I don't see the noise changing unless the exhaust or whatever got damaged while it was in the shop.

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    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  4. #4
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    The flashing check engine light is indicating one (or more) cylinders are misfiring and causing damage to the cat (which sounds like it's already done). Sulfur smell is a dead giveaway. Do not drive it until you can sort this out. If it hasn't had new plugs and wires then I would start there. Once that is done then move on to the cat replacement.
    These are highly engineered precision vehicles, the first step in diagnosing the problem is to strike the suspected offending part sharply and repeatedly with a blunt object, then re-test.

  5. #5
    I'm an air-conditioned gypsy gadget73's Avatar
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    these actually don't have any way to ID a cylinder misfire. The ECM just isn't that smart. There are no misfire codes in the EEC-IV of this generation.

    A handful of things trip that light, the TPS is one of them. The intermittent light is exactly what I got from my Mark VII when the TPS failed. Error code was something about TPS out of range. When the throttle was closed on decel it hit a dead spot and the voltage went stupid, causing the light to come on only when it was in that spot. It also had a weird hitching thing going on when coasting and a hesitation off-idle. Replacing the TPS fixed all that. The other common thing that makes the CEL come on are EGR related problems. Loads of other codes will set without the light. I actually wish I had a chart of exactly what does cause the light to come on but its definitely not all of the codes.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  6. #6
    Road Warrior Kodachrome Wolf's Avatar
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    Just my on the TPS: If the shop replaced it and didn’t verify if it was in range, it’ll drive funny.

    IIRC, closed throttle should be 0.5-1.25v (usually the I’ll aim for 0.95v when setting) and wide open should be 4.2-4.6v+. You can check output with a multimeter with the key on and engine off. I had a bad one where closed throttle ranged out fine, but at wide open it would only read 3.4v, so it never “knew” it was actually floored.

    I’ve also found sometimes you have to widen the mounting ear holes a bit to get enough adjustment out of the sensor.

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  7. #7

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    Quote Originally Posted by FordMan77 View Post
    The flashing check engine light is indicating one (or more) cylinders are misfiring and causing damage to the cat (which sounds like it's already done). Sulfur smell is a dead giveaway. Do not drive it until you can sort this out. If it hasn't had new plugs and wires then I would start there. Once that is done then move on to the cat replacement.
    I didn't notice anything in the engine. I may be wrong, I'm pretty sure it's the transmission (the Check Engine light went away after the TPS was replaced, hasn't come on since). There was no evident bucking that would give away a misfire. It got new spark plugs / wires in late 2019, so those should still be good.

  8. #8
    2 decades of DDing Box Panthers, now in a Whale VicCrownVic's Avatar
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    Symptoms don't seem familiar to me. The only rattling I've experienced with both of my '91s is loose cat heatshields, but that's only noticeable while standing still not while driving.
    Spark plugs can foul quickly depending on how well previous owners may have cared for the car and/or how many miles are on the engine.
    The Scab can foul #8 in weeks to months timeframe. #8 tends to foul first on any SEFI 302 that I've worked with. #4 and #7 next. I long ago learned the hard way after checking #6 which looked perfect only to find, when I convinced myself to check again, that #8 was super fouled.
    Fouled sparkplug doesn't seem like it would cause rattling.

    How about the smog pump? Could it perhaps be it going out that you're hearing? Take the belt off that side and see if the rattling goes away. That belt only runs the AC compressor and the smog pump, so it's not essential. (I ran my '89 and fist '91 without that belt for more than a decade combined.)
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  9. #9
    GMN Regular DerekTheGreat's Avatar
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    Quote Originally Posted by VicCrownVic View Post
    ...Spark plugs can foul quickly depending on how well previous owners may have cared for the car and/or how many miles are on the engine.
    The Scab can foul #8 in weeks to months timeframe. #8 tends to foul first on any SEFI 302 that I've worked with. #4 and #7 next. I long ago learned the hard way after checking #6 which looked perfect only to find, when I convinced myself to check again, that #8 was super fouled...
    Can confirm. Years ago my wife had an '89 Town Car. Ran fine for years and then started fouling #8 once the valve seals went bad. Would foul that plug within 230 miles.
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  10. #10

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    Update: Turns out, it was the heat shield that was rusting out and making the rattling noise. Got one taken out, but I found out immediately after that the other heat shield was rattling as well. Both seem to have gone at the same time. They checked the catalytic converter and said it was looking alright, so the fuel was likely running rich. Car still hesitates when going from a stop, but it's likely due to the cold.

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