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2003 dhs 75000 mi. was running fine and all of a sudden started to stumble. rough and low idle and stalled. pulled over got out and had a strong smell of rotten eggs. started car back up ran fine. couple hrs later went to pick wife up from work started fine about 2 miles out did the same. shut off, let sit a minute. started and ran fine again. went to Sunoco filled up with premium gas drove home told wife to take the bus. (didn't go over well). went to store later and happened again. seems to be doing this when on the accelerator. limped a block to my house, this time service engine light came on as i was pulling into garage. was flashing. stunk up garage like rotten eggs. this time got a code of p0300. misfire. only code in system. light did not come on previous "attacks", just ran like crap and smelled worse. go out there now. starts fine. any ideas would be greatly appreciated. thanks

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Is the P0300 the only code you are getting? Did you retrieve this code or did it show on your DIC? The P0300 is a misfire code, it can be caused by igntion or fuel, but its basically a cylinder not carrying its weight, there is a misfire and the PCM senses the mis. This is an undefined misfire code as opposed to a P0301 which would be a specific cylinder #1.

If you have not checked your codes check them and post them all.

This sounds like a couple of things but the rotten egg smell means to me that its running rich. That it has happened intermittantly and as you rev/labor your engine makes me think its your FPR. Check your FPR for fuel at the vacuum port, both with the engine off and while you rev the engine, any spitting of fuel out of the FPR vacuum port replace it. If it has not been replaced in this mileage its probably due anyway.

Check your fuel filter also but that won't set a P0300 code

Check your ignition wires and plugs also as possible source of P0300

Also, if you keep going nuts trying to figure this out, keep clogged CAT in the back of your mind, but that won't set an 0300 code

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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Is the P0300 the only code you are getting? Did you retrieve this code or did it show on your DIC?

If you have not checked your codes check them and post them all.

This sounds like a couple of things but the rotten egg smell means to me that its running rich. That it has happened intermittantly and as you rev/labor your engine makes me think its your FPR. Check your FPR for fuel at the vacuum port, both with the engine off and while you rev the engine, any spitting of fuel out of the FPR vacuum port replace it. If it has not been replaced in this mileage its probably due anyway.

Check your fuel filter also.

Check your ignition wires and plugs also

Also, if you keep going nuts trying to figure this out, keep clogged CAT in the back of your mind

yes only code that came up other than u1713 history. pulled from DIC. have had car for a couple of months and no problems until today. was just out in garage looking around and scratching my head started up no sevice engine light on. no new codes. hope its that easy. go to store grab a six pack and check FPR and thow a fuel filter in there. can i get FPR at auto parts store or dealer only like the license plate light? (go figure). thanks for the help. how would i know if it is clogged cat? start cheap and work my way up?

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....this time got a code of p0300. misfire. only code in system. light did not come on previous "attacks", just ran like crap and smelled worse. go out there now. starts fine. any ideas would be greatly appreciated. thanks

The P0300 code might seem to sort of non-informative but it really is pointing you at the problem. Which is - one or more spark plugs are not firing.

Your challenge is to diagnose the why. The least expensive possiblity is one or more broken spark plug porcelain insulators. Have you had any spark plugs replaced lately?

Otherwise, the likely suspect would be the ignition coil cassette that sits on top of the spark plugs. The challenge will be to diagnose which bank coil cassette is causing the problem. Coil cassette failure is not uncommon.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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I agree with Jim, its a cylinder misfiring for some reason. The more I think about it the FPR would not set a P0300 code, the rotten egg smell made me think in that direction.

Check plugs and wires as Jim noted. A vacuum leak can also cause P0300 but that is unlikely since no work was done to engine and you are not getting a lean code.

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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I agree with Jim, its a cylinder misfiring for some reason. The more I think about it the FPR would not set a P0300 code, the rotten egg smell made me think in that direction.

Check plugs and wires as Jim noted. A vacuum leak can also cause P0300 but that is unlikely since no work was done to engine and you are not getting a lean code.

Thanks for the responses

Could not look at anything last night however i did start it up this morning and problem did not occur until it reached operating temperature. code popped p0300 again.. Only other codes were irc u1016 history and pdm u1713.

I have autozone 2 blocks away so i got a obd II AUOTO SCANNER made by actron, model cp9176l on loan. could this scanner help in any way? just waiting for it to cool down so i can go try a few things.

Hooked up the scanner and pulled freeze frame result. dont know what they mean but may shed some light. here we go.

THROTTLE POSITION 0.7%

ENGINE RPM 476

LOAD VALUE 2.35

MAP SENSOR 54 KPA

IGNITION TIMING 20.0 DEG

COMMANDED SECONDARY AIR STATUS ATMOS

SHORT TERM FUEL TRIM 1 3.1%

LONG TERM TRIM 1 3.1%

SHORT TERM 2 34.3%

LONG TERM 2 19.5%

SHORT TERM 3 40.6%

LONG TERM 3 -54.6%

LONG TERM 4 -1%

SHORT TERM 4 64%

VEHICLE SPEED 0MPH

FUEL SYSTEM 1 CLSD

FUEL SYSTEM 2 CLSD

DTC CODE P0300 PENDING

ALL I/M MONITORS EITHER OK OR N/A EXCEPT EVAP INC

Do you still no longer think FPR? Prob will check anyway. Car is still under warranty from when bought. Only the basic lemon law 60 days. i believe the ignition system is covered as is under 80000 miles.

Should i just leave it and let them worry about it? also to far to drive it in this condition unless i keep stopping and letting cool down. about 20 miles. flat bead if necessary.

ALSO LOOKING FOR GOOD PLACE TO GET WARRANTY.

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Check the plenum for a vacuum leak. On the 2000+ Northstar, the plenum is the rubber coupler between the TB and the manifold. They tend to split on the bottom side where is cannot be seen and cause a vacuum leak. Spray some Brakleen around it and listen for an RPM increase.

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Read this article

http://www.autotap.com/Articles/Analyzing_...n_Misfires.html

Do you have any other symptoms? Racing idle?

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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Read this article

http://www.autotap.com/Articles/Analyzing_...n_Misfires.html

Do you have any other symptoms? Racing idle?

idle actually drops when this occurs. almost cannot get it up the driveway, and my driveway is only as long as the car but uphill into garage, and seems to happen at operating temp. if i go start it cold seems to be fine but once it reaches norm temp on gauge it starts and is very rough.

the more i think about it car was fine on the way to work to drop wif off. happened on the way back. twice since then. every time i drove it.

i do have a noisy secondary air pump when started cold but that stops after about 30 seconds

renting car tomorrow and flat bedding back to mom and pop dealer i bought it from to have their mechanic look at it as i dont want to hurt anything or work out in the cold if i dont have to.

hopefully covered or at least a good deal

also do not want to throw the sink at it to find out it something stupid. i appreciate your efforts and responses. hopefully covered or at least a good deal.

these forums are very informative also overwhelming.

thanks

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could this have been just possibly bad gas??? maybe water in gas?? went to store all is well no lights. no misses. drove around a while.

1hr later....

spoke too soon.. on a flatbed to the shop. almost a shame to see it go like that. will post what they come up with.

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From what I have gathered from your posts... it is running rich...but ONLY after it warms up and reaches normal operating temps.

It would seem to me that it has to be something that changes when it switches from closed loop to open loop.

Not sure what... maybe an O2 sensor?

Strange that there were no other codes except the misfire code.

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all figured out now. or at least we hope. rear valve cover leaking filled spark plug wells causing the misfire. so new gaskets and a tune up and what the heck throw in a fuel filter. will get back on friday. cant wait to have it back as everything else i drive in feels like a go cart. dealer covering most. so thats cool. hopefully no more problems for a while.

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