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How to tell if there is a misfire?


bigfoo

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I feel something that seems like a misfire, or a non firing of a plug but I can't tell. I always used to check on my older cars simply by putting it in 4th or 5th gear at low rpms say 1000 rpm or under and then smashing the pedal.. if it was misfiring the whole engine/car would vibrate, if it wasn't it was real smooth. I can't do that on this car because it's an automatic and every time i even barely touch the gas it upshifts or the tcc comes off so .. how to tell.. how to tell :> (I checked the plugs/wires and they are fine, wires give off some lightshow at night but nothing major, although there was a lot of redness(ozone i think) around the wires and on the plugs themselves, but i changed the plugs). All the plugs are definitely firing because I checked, but one or two of them may be firing 90% of the time which is very difficult to check.

Is there a way to force the TCC to engage and not disengage unless you hit the brakes? :)

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Pull your codes and look for a P0300 to P0312 DTC. P0300 is a generic "engine misfire detected" code and P0301 to P0312 codes identify specific cylinders.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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The smoke and mirrors of electronics and sufficient computing power.

Crankshaft position sensors are the basis of a calculation that measures the rate of change of crankshaft speed on the power stroke. If the rate of change differs from what is expected under given conditions, something is not happening on schedule and the computer makes a note and sets a code.

Jim

Drive your car.

Use your cell phone.

CHOOSE ONE !

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The following procedure might be a bit tricky, certainly not any kind of approved diagnositic or even be what you're looking for...but then again WTF. :rolleyes:

If you pull the fuse (for testing purposes only) for the traction control components, I believe the DIC will state "traction control disabled" and the tranny will default to start in second gear (instead of first). This low torque and stall-sensitive condition might "force" the weakest plug (if any) to misfire. <_<

No, I don't know what fuse it might be and I only theorized this possibility from previous posts - so please be carefull. :huh:

As you noted, the TCC "Torque Convertor Clutch" disengages from "lock-up", if the brake pedal is touched a bit, or any downshift perhaps. This masks any misfire that might be transmitted to the cabin itself via the locked up mode.

I would guess that if the suspected misfire condition is serious enough, a code would be set as JimD duefully noted.

This sounds like a good BS-excuse to "benchmark" the car every now and then with timed WOT's to 60 (and flat-out, top-end if you have enough road). ;)

But Officer, I was only.... :lol:

Add power to leave problems behind. Most braking is just - poor planning.
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ahah yea.. You know the 99's do have a traction control BUTTON :) If i press it, it disables traction control and forces 2nd, which annoys me because i'd rather have it disabled and start in 1st :> I don't like traction control. I'm old school :>

ABS I can deal with though. I don't think it's misfiring enough to cause it to set a code. I have a VERY picky ear and sensitivity to vibrations and such. I can hear all the fuel injectors ticking if i stand next to the car. Exhaust leaks REALLY bother me. The fuel injector ticking bothers me too but there's nothing I can do about clicking solenoids :> I really don't care how loud a car is from the exhaust, in fact I like it. It's the small things that bother me. Like the chirping noise when the a/c kicks on (i got a new belt and i'm going to try that) and the fact that one of my tie rod ends is bad and it ever so slightly clunks when i pass center(got a new one and going to replace that soon), and that one of my tires or rims or SOMETHING is still causing vibrations even though I just had all the tires balanced. So maybe i'm just being overly picky..or maybe not.. I've heard piston slaps, bad lifters, slightly bent valves, ticking rockers, rod bearings, unbalanced crank, etc.. way before anything happened to a car and even after taking cars in 5 times to mechanics and dealers that couldn't hear anything I could still hear it (or sense it). I also have this uncanny ability to count things.. like if i hear a ticking noise, i can count the TPS (ticks per second) of the noise.. I even told one mechanic that this noise was occuring at 600 rpm when the engine was at 1200 rpm (i think it was a piston slap on the power stroke). My version of my OCD is things like that, ticks, noises, dust, etc.. :)

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Soooo,

You're the kind of computer nerd (a compliment) that could:

Discern the diverse digits a dot-matrix printer punches without looking ?

Hear the hard drive's servos scouting sectors ?

Feel the floppies floundering furtively ?

Enough alliteration already ?

Sound like you might need a few hours of the kids' headphones. The resulting tinnitus, just might just cure the Caddy's vibration problem ! :D

Actually, you might want to test drive a similar used Caddy or even a new one, just to have a comparison.

Good luck :)

Add power to leave problems behind. Most braking is just - poor planning.
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I feel something that seems like a misfire, or a non firing of a plug but I can't tell. I always used to check on my older cars simply by putting it in 4th or 5th gear at low rpms say 1000 rpm or under and then smashing the pedal.. if it was misfiring the whole engine/car would vibrate, if it wasn't it was real smooth. I can't do that on this car because it's an automatic and every time i even barely touch the gas it upshifts or the tcc comes off so .. how to tell.. how to tell :> (I checked the plugs/wires and they are fine, wires give off some lightshow at night but nothing major, although there was a lot of redness(ozone i think) around the wires and on the plugs themselves, but i changed the plugs). All the plugs are definitely firing because I checked, but one or two of them may be firing 90% of the time which is very difficult to check.

Is there a way to force the TCC to engage and not disengage unless you hit the brakes? :)

Didnt you change your plugs or am I mistaken? If you did what did you use? Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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bigfoo, you posted this a while back "Anyway i replaced them all with the DENSO IT16 plug"

The misfire that you are having could easily be traced to the aftermarket plugs no matter how good they are or how expensive they are. My lifetime experience has been that GM cars run best on OEM AC DELCO plugs. They have never run good on Champion or Autolite. I personally used BOSCH in an 86 Corvette and had all kinds of idle troubles. Given the tight combustion chambers on the NS, I strongly feel that what you are feeling is the aftermarket plugs. Everyone here has recommended the AC DELCO and Guru has gone into the reasons why. If your idle still is misfiring... look to the plugs... Go to the AC DELCO site and look the plugs over they are quite impressive. Good Luck, Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Yes Scotty I replaced the plugs BECAUSE of this :) I had Ac delcos in it. It helped a little and got rid of some of the vibration but I still notice it. There's just SOMETHING that isn't quite right and I can't put a finger on it. I'd try swapping coil packs and wires but they are freggin expensive. I did the 'misting' of the wires and they show little 'dots' of light (and so does one of the coil packs) no major arcs or anything but that doesn't mean they aren't bad. I had lots of red ozonish stuff (dust) on the outside ceramic of the plugs and in the wire boots when I took them off. I reused the same wires so maybe the wires are blogging up. I just hate to spend $100 on a set of wires if that's not it.

You should see me with diesels. I can't stand listening to a diesel. It makes so much 'normal' ticking and knocking and rattling noise that it drives me nuts :> Now my weed eater, it's just SO LOUD that you can't hear anything anyway so I don't even notice ehehe.

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Just don't overlook the plugs because they are new! LOL... Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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I'm a technology nerd.. not just computers :>

If i could tell which cylinder it was i'd definitely pull the plug, but it's not like it's every time.. It on'y does it at certain times and not for any type of length.. so it's quite impossible to track it down :>

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Those DENSO plugs look pretty impressive I must say, I reading up on them. If you are feeling a misfire maybe it is your ignition wires leaking or arching. You did say that you saw arching. I would think that any arching on the wire would potentially cause a rough idle as the electric charge would be lessened that was suppose to arrive at the plug, causing a weaker or slower spark. So I would look at that for sure.

But I want to tell you a story. My neighbor is about 80 and he is a Cadillac nut, he has 4 in his driveway including a 67 Eldorado with 55,000 miles on it plus extra parts in his garage. He told me that when he bought his 77 coupe, he visited the lot and saw a green one he liked with 40,000 miles on it. I think he told me the car was $5,000 at the time. Starting it up, the engine was rough, he lifted the hood and looked at the plugs. The salesman said, yea, we just can't seem to get it running smooth we even "changed the plugs". My friend offered him $4,000 to "take it off his hands in that condition" and the salesman took it. He told me he brought it home took out the CHAMPIONS and put in AC DELCO, and she purred..... he said when he saw the CHAMPIONS, he knew what the problem was! Now I know that the 77 engine is not the Northstar, but I have heard this story repeatedly over the years. And as I mentioned previously, i had a rough idle experience with BOSCH in an 86 Corvette. Which my neighbor quickly rubbed in my face and said use AC DELCO :lol: .... Maybe my neighbor is lucky that he didnt have a burned or valve hanging up or maybe the ignition wire connection was loose at the plug or cap and he inadvertantly tightened it as I routinely used to do. We have had lots of discussions here regarding the use of aftermarket plugs. Keep on this until you find out what it is, your experience will add to our collective experience (im sounding like the BORG now)... Relax and Enjoy, Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Alright.. I might just try changing the wires.. but they aren't cheap :)

Misting the wires at night produces 'stars' .. not arcs, just little dots of light on the wires themselves and occasioanlly a small arc off to a bolt or something nearby but not much. I'm guessing the wires are shot because of the red ozonish stuff more so than the lightshow. The only wires the local shop carries that are already pre-cut are umm.. can't remember, it's like purolator is to filters this is to plug wires and stuff.. i think it starts with an M. I could go to the dealer but I really want even more shielding on the wires than the stock ones have because I plan on keeping the car for a long time and the more shielding on the wires the less damage it could do to the electronics. Why can't they make stock 8.5mm wires or something ugh..

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Call me MR. SAFETY, but I would go with the OEM wires also. Remember that besides the fact that the OEM wires are very high quality they are the proper resistence and length for your engine. With all of the sensors and the sensitivity of the blower, I would stick with the OEM. Do a search of the archives there has been much discussion. Whatever you decide, I would make sure that they are routed and protected properly near metal with that high-temp covering that comes stock. Lots of times when you replace wires, that flexible covering is dryrotted and breaks off its not easy to find replacements for it, as I dont think the dealer sells it but I think its important to promote the longevity of the wires. Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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What flexible covering ar you talking about? My wires go Right over the top of the plastic intake (under the beauty cover). The back ones just go right to the plug hole from the coil pack. I don't see any coatings or coverings?

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What flexible covering ar you talking about? My wires go Right over the top of the plastic intake (under the beauty cover). The back ones just go right to the plug hole from the coil pack. I don't see any coatings or coverings?

Maybe its possible that they do not use the plastic loom anymore. It does not cover the wires 100% only where it hits or touches metal. Maybe its not used anymore. Good Luck I am off on vacation talk to you all next Saturday, Mike

Early on sailors navigated by the stars at night and the North star became the symbol for finding ones way home. Once you know where the Northstar is you can point your ship in the right direction to get home. So the star became a symbol for finding ones way home or more symbolically even finding ones path in life.

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Have a good vacation..... no they don't use it any more, but I Have a ton of it sitting around.. guess I could use some :>

Will keep everyone posted.

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Bigfoo,

I second what Mike said. I have read several threads where someone had nothing but trouble with aftermarket wires. If your gonna replace them, go OEM. I'm surprised Guru hasn't chimed in. I remember him once giving an explanation of exactly what the misting should look like. Search the archives for misting, maybe you'll find it. Might have even been on the old board for all I can remember but it was a pretty good discription.

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Alright.. I'm used to misting on super high power ignitions. like I said before, i've built hotrods and such and this caddy is the newest car I have. next car is 98 expedition which I don't do anything on except normal maintenance. All the other cars i've had/worked on are 85 or older, carbuerated, and mostly swamped with aftermarket parts :) So misting on a hi-po msd ignition looks a lot different than it does on this caddy.. I decided to 'mess with' the caddy because it's out of warranty now and also I wanted to learn all the computerized crap the newer cars have on them...... Heck maybe ill dive into the PCM one day and see if I can figure out how to reprogram it, probaly not hard, just very tedious.

I'll check the dealer for the wires and some local stores for them also and see what I come up with. I've tested a lot of wires and the stock one are always worse than the other ones (like msd, jacobs, etc.). Really has nothing to do with resistance, just mainly containing the electricity in the wire and not letting it get out (which u can see during misting). I want to mist and see NOTHING :) That's my goal :> (well except a slight glow but no twinkling stars or arcs)

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