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Severe loss of power


Jan Olsson

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Hi all!

My STS with 180k miles is not new anymore. There has been all the usual stuff with cars coming to age and mileage like oil-cooler lines but nothing too severe until now. This morning my car started to act funny. I noticed a decrease in power and drove on a couple of miles to get to a freeway exit. The car lost almost all power and about 55 mph was about all it was able to keep. I tried to resume the set cruise speed (75 mph) but to do that the car had to go into second gear and the SES light started to blink. I also heard some knocking noises and thought "this is it, the car will break down". I pulled over, car idles beautifully, no codes at all, no leaks, smoke or any signs at all to give me a clue.

I managed to get the car home and when I got home from work I tried it cold. It seems to behave the same, cold or warm. I did however seem to notice a slight improvement after disconnecting and connecting the various connectors for the MAP, TPS and MAF sensors. Finally it threw a code, P0101. Tomorrow I'll check if the connectors seem ok in the engine bay. I recently replaced the cats on my Jaguar and so far this seems quite like it....

Hopefully it is just a bad connector but I noticed a rattle when revving the engine and it seems to come from the cat area. Will have to jack the car to confirm that.

It is ironic that i purchased the Jag to have a new daily driver and use the STS as a second, back-up car. I have used the STS as a daily driver like I always have anyway, because the Jag has proven to be really unreliable.

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A maf trouble code.  Have you tried to listen for a hiss? Maybe a plenum blew apart and you have a vacume leak? Only other thing I can think of is that your fuel pump is failing.  do you have a gauge to connect up and check the fuel line psi? Yes, when a fuel pump is not operating to spec, it can throw a bunch of other codes that are unrelated to the root cause.

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catalytic converter might be clogged. Disconnect the converter from the down pipe and drive it. Remove the 4 flange nuts from the converter and separate it there. 

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Hi all.

 

I checked the obvious first. No vacuum leaks, sprayed over all sensor connectors with WD-40 to be sure there are no contact problems, no FPR leak.

According to the FSM there aren't a lot of options left if the only code you get is P0101. The rattle is from the cat. Sounds a bit dangerous to let the hot exhausts out from right under my butt ;)

Since the cat is rattling I'll replace it because it is bound to go south anyway. The OEM is discontinued. Does anyone know about a good replacement alternative?

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I had that rattle in a 91 Seville CAT, your exhaust is probably restricted also. 

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Thanks guys for all the input!

I'll let you know about the progress. I'm keeping my fingers crossed that the weather will keep above freezing temperatures the next week or so because I don't have winter tires to my Jaguar. Didn't want to spend money on "new" rims or tires because it is for sale. Replaced the cats on my Jaguar just a couple of months ago. VERY expensive to say the least...

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12 minutes ago, Jan Olsson said:

Do you have any personal experience with this cat? It doesn't seem to have an O2-connection.

Sorry. I had a blonde moment there. The sensor on the STS is located near the resonator so the new cat does not need one. Was thinking Jaguar where the two cats had 2 sensors on them. Of course they where impossible to remove.

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Its not a big deal to unbolt that flange and drive a mile or less. You will know instantly if it's clogged. The first time you give it any gas, it will actually accelerate :) Plan on new bolts though. You wont need to drive long enough to get anything hot.

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19 hours ago, Jan Olsson said:

Sorry. I had a blonde moment there. The sensor on the STS is located near the resonator so the new cat does not need one. Was thinking Jaguar where the two cats had 2 sensors on them. Of course they where impossible to remove.

Jan you may be aware of this but wet them down with a good penetrating solvent and then warm the engine up to about 125 degrees, it will help you to remove O2 sensors.  Trying to remove O2 sensors on a cold engine is much harder.  

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 3 weeks later...

Hi all!

I'm happy to report that a catalytic converter solved all of my issues. I ordered an aftermarket one from Eastern Catalytic via Rock-Auto and it worked like a charm. Since I cant raise my vehicle AND have the garage door shut at the same time I let a local shop do the work. To cut a pipe and replace the old cat with a new one shouldn't cause any other problems but to be sure I'll hoist it and check thoroughly if the missed a bolt or a exhaust system hanger etc. The engine runs better than ever, the exhaust note is quiet, better mpg, even smoother shifts and the power is back.

A happy new year to all of you!

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Glad to hear it Jan!

Happy New Year

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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  • 5 weeks later...

An update. Not surprisingly my gas mileage has increased from about 18 mpg to 20 mpg. I´m pretty sure that it is just not my imagination. It also seems that my oil consumption has decreased but I'll have to get back on that when I have confirmed the mileage between two consecutive "check oil message" warnings. I replaced the valve cover gaskets because of a leak but there has to be a massive external leak in order to amount to any significant oil consumption so my theory is that the clogged catalytic converter caused more back pressure and more oil burning than normal. Oh well, now it seems in order for another 180 k miles ;)

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