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misfiring out of the blue.


rockfangd

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Hi all. My 2001 eldorado is acting up.

I was accelerating to highway speed and out of nowhere it just popped and started misfiring a bit. I carefully drove it the rest of the way home. It misfired all the way. SES light flashing.

I also hear a gurgling noise when I shut the engine off, Not alot but enough to notice.

Other than what has happened today it has been running normal. Gauges normal.

Has been using more gas than usual though over the past few months. about 16 mpg. Before it was getting 22 mpg. Travel has not changed, I assumed it was because of the winter months.

I wish it decided to do this next month when I have my Seville out and can afford to park it but it didn't.

Any opinions?

I will pull the cylinder codes tonight and post them. Thanks all

Update 3/6/2015.

unfortunately I had to drive the car a little bit more yesterday. problem did not go away

cylinder misfiring is 8. constant

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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The elements of healthy firing cylinders are gas, mixture, spark, and compression. Poor compression would mean a sticking valve, or carbon under a valve seat, which are rare on a Northstar so your reasonable choices are a vacuum hose coming off, fuel injector problems, or spark problems. Spark problems are the most common, particularly with a sudden onset. Bad recent gas mileage is a sign that it really isn't that sudden, though.

As a quick thing, smell the exhaust. If it smells like gas, you have a spark problem. If it doesn't, you have a fuel problem.

I would wait on the OBD codes for a diagnosis. It's tempting to go right to the crank sensors, the plug boots, or the plugs, but the OBD codes will tell the tale.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I have not done the rears yet.

I did the fronts about 8k miles ago when I changed the coil pack, The plugs I removed looked fairly new. I had planned to do the rears when I did the valve cover gaskets this spring, The AIR parts are in the way to remove the rear valve cover or coil module.

I have the plugs and boots already. Oe delco plugs

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Oil or water in the plug wells or arcing on the plug boots is more likely than bad plugs, if the rears are in the same shape that your front plugs were 8K miles back. That's small comfort because the air pump and coils have to be taken off to see the boots. But run the codes before you do anything.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Hi all. Sorry I thought I posted the code.

code is cylinder 8 misfire. that is the only code.

To update this.

cylinder 8 should be in the front bank by the waterpump.

Today I pulled the coil module and pulled the #8 plug. It was clean.

I swapped the #4 and #8 plug and wire. Did not change cylinder misfire, Still missing on 8.

I went and bought a used coil module and installed it. I swear it ran great for about a few minutes then it came right back worse.

I would think the chances of 2 of the same coils being bad on the same cylinder.

I used a screwdriver to listen to the injectors and they all sound the same.

I monitored misfire status of all cylinders and all were 0 but 8. constant miss

I am at a loss here. The weather has not been very forgiving.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Change the oil, and put an additive in for sticky valves - i know the purists who don't beliefe in the snake oil, but it just might be a gummed up lifter or something. Motor honey worked for my oil pressure flicker. It also is supposed to work on valves.

Also put some marvel mystery oil in the gas. The #8 injector might be binding. Im not sure how easy it is to swap in another injector.

You are correct going down the path of the spark first.

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The oil is new. I find it to be coincidental it occured shortly after I did the oil change.

I have chevron techron in the tank now, have about half a tank remaining.

The excessive oil consumption has bothered me with this car. I have never had one use so much oil.

I drive it hard and by now it should be better.

I worry because of the way it started. I dont hear any unnecessary noises, I also sprayed carb cleaner around the plenum and TB and rpms did not change.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Can you clean the injectors thru the Schrader valve? I know there are kits - possibly you can get your hands on one.

Also an additive to the oil might help with consumption.

I know its still cold up there, so i am thinking of quick fixes first.

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Update 3/10/2015

pulled coil module back off.

Checked compression on cylinder 8. 180 after 4 cranks warm.

So I reassembled and basically checked the wiring to the coil module and injectors, found nothing obvious.

Still missing.

I also sprayed carb cleaner around the intake and TB area again and nothing changed.

I do see minor wetness (looks oily) under the TB.

I may be mistaken but the end of the plug was a little wet and smelled like gas, It was hard to tell.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Good compression eliminates sticking valve.

If the plug smelled like gas, you almost certainly have a spark problem. I'll ignore "hard to tell."

Just one cylinder probably means that it's not the crank sensors or cam sensor.

If it was the throttle body, you would have mixture codes and such, and you don't. I'm wondering why you don't have a P0300, though; usually the only miss code displayed by the dash when you run the codes with the A/C buttons is P0300. The P030n codes are "hidden" and are found with a code reader, which can also look at the miss counts. If you can see a miss count incrementing, it is missing right then, so you can tell if it's missing at idle, under load, cold vs warm, etc.

Usually when you have a spark problem, it may fire at idle but misses under load.

You swapped the #4 and #8 plugs and boots and the miss stayed put. At this point, switch the coil modules and see if the miss moves to #1 (they are the same except for color). If it does, it's the coil.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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My scantool shows 0308. onboard shows 0300. misfire count is 0 for all other cylinders, 8 is constant

I will try another coil pack. I just find it coincidental that 2 in a row misfire on the same cylinder. I was wondering if it could be a wiring issue, to the coil module or something.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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You can swap the coil pack from front to rear. Does the exhaust smell rich like fuel? Us a long screwdriver and put it on #8 injector and listen to see if its clicking (operating)

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I cant tell with the exhaust. it seems almost normal.

I did use a screwdriver with the front bank of injectors and they all sound the same.

I can try to swap the coils this weekend. If it moves then that means 2 coil packs are bad on the same cylinder.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I cant tell with the exhaust. it seems almost normal.

I did use a screwdriver with the front bank of injectors and they all sound the same.

I can try to swap the coils this weekend. If it moves then that means 2 coil packs are bad on the same cylinder.

If the misfire moves to cylinder 1 and cylinder 8 begins to fire, the front coil pack (which would then be on the rear bank) is bad.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Don't know if you can do this or not with this engine, but here's an idea. Pull the plug wire from #8 cyl, (leave the spark plug in place in the engine) attach it to a known good plug grounded to the outside of the block. You can even duct tape it to the valve cover to hold it in place. Start the engine and observe the spark occurring at the electrodes. No spark, coil pack or bad wire would be suspected. You can also do this with a known good cyl in order to compare observations.

Never underestimate the amount of a persons greed.

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This engine has COP setup and the whole unit sits on top of the cam cover, so you cannot see anything.

Tomorrow I am going to try to figure it out. I am going to try to hook up spark plug wires to the coil and run them to the plugs.

I do have one question though.

The wires that go from the pcm to the ICM at each coil, I would like to know how to test for output to the ICM for cylinder 8.

I know the wire is dk blue/white but am not sure if it is a negatively pulsed, or positive, etc...

I see a coil pack harness is sold and it makes me wonder if that could possibly be my issue. By tomorrow I want to know for sure whether it is spark or fuel. I also plan to swap the coils around if I need to.

I hope it is just the coil so Ican get it ordered and be done with it. But dont want to rush to wasting money.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Ok so verified no spark.

I tried with both used coil packs and nothing.

It must be either both coils are bad or a bad wire to the pcm. I would rather not take apart the rear coil to swap them because I dont want to create more issues. I think I am just going to pick up a new coil.

In case it is a bad wire does anyone know how I can access the PCM to test continuity on the wire for that cylinder. Not sure how to test output on that wire hat fires the coil

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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Done. Runs like new.

It seems a bit of coincidence that I have had 3 coils that were bad on the same coil. I wonder if the ICM being right there over it has anything to do with the failures.

th_coil2_zpsyihtx9qe.jpg

look in the picture and the cylinder that failed is the one right below the ICM.

I am happy to have it running again. Maybe in the spring I will replace the other coil when I finnish the tuneup.

thanks all for the insight

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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