: Replaced plug wires and plugs still misfire code



ronstoney
08-20-05, 02:29 PM
I have a 96 Concours, that was throwing a PC0300 code (misfire). I replaced the spark plug wires with AC Delco OEM ones, and replaced the plugs with the OEM plugs.

I cleared out the codes, and I am still getting a misfire. Any suggestions? A history of PC01380 also came up.

Ron

Ranger
08-20-05, 05:37 PM
ICM or bad coil?

ronstoney
08-20-05, 08:22 PM
ICM or bad coil?

Are there any steps I can take to determine if ICM or bad coil?

What are the short/long term effects of misfire, besides running rough? It's my daily driver, and if I can get along until I resolve, that would be comforting to know.

tks

Ranger
08-20-05, 09:01 PM
A minor misfire is not too bad but a severe misfire (flashing check engine light) can cause damage.

If you have a stethescope, it can be a big help in listining to the coils to see if you hear one arcing. That would be a sign of a bad coil. You could also get a known good coil (buy one, borrow one from a wifes, friends, neighbors car and swap one at a time and see if that cures the problem.

Not sure about the ICM. I think that is more invovled.

ronstoney
08-21-05, 09:15 PM
A minor misfire is not too bad but a severe misfire (flashing check engine light) can cause damage.

Not sure about the ICM. I think that is more invovled.

Unfortunately, no avail coils. Read a post earlier that you could perhaps take the coils off and take them into a parts store to check? If so, that would certainly be very helpful!

Ranger
08-22-05, 01:21 PM
I suppose you could test the resistance but I am not familiar with that proceedure or what the resistance should be. Maybe someone else more knowledgable will chime in .

mcowden
08-22-05, 03:11 PM
Unfortunately, no avail coils. Read a post earlier that you could perhaps take the coils off and take them into a parts store to check? If so, that would certainly be very helpful!

I can't imagine how a parts store would test them. Without the ICM, they won't be able to trigger the coil to fire. I'm not an expert, but AFAIK, the best way to test them is to either CAREFULLY ground a plug and watch for spark or hook up a light to the coil. I've seen the lights before but never used one. You might be able to hear a bad coil with a stethoscope or a hose, but I've never tried that. You could also swap coils around and see if it changes. If the misfire is different, get one new OEM (AC-Delco) coil and swap them one at a time until you get it. If it doesn't change, and you're absolutely sure the wires, plugs, and gaps are good, the ICM is next in the chain. Have you checked to be sure all of the wires into the ICM are tight and in good condition? The ICM is what the plugs are sitting on. With newer models, there is no ICM and that functionality is built into the PCM.

Some scanners can tell you which cylinder is not firing. I think the codes are P0301 through P0308 to indicate the cylinder number, but they may go off of CKP and tachometer data instead of the DTC. I'm not sure if the DTC will set for the cylinder number or not. I've never seen one. The AutoTap tool might show you if you get the extended data package. Other scan tools probably have similar functions, but I've used the AutoTap. Thankfully my misfire problem went away by replacing the old wires and crappy Bosch plugs with the AC-Delco stuff.

Res STS
08-24-05, 01:14 AM
Nobody mentioned sticking fuel injectors. I've had two stick on my STS (one triggered a MIL lamp and info panel message. A number of coworkers have had them stick on their Pontiacs and Chevys too. Fuels vary in detergent content and can cause the pintle (needle) in the injector body tostick and stop moving. In some cases this is transient; a heavy application made mine go away, for awhile anyway.

Check out toptier.com for brands of fuel that prevent injector sticking, intake valve fouling/sticking.

Eldyfig
08-24-05, 10:31 AM
A little help with that website, please. I am interested, but the web address doesn't seem right.

Ranger
08-24-05, 03:23 PM
http://www.toptiergas.com/index.html
Take it with a grain of salt. You'll notice that nowhere does it say who is behind this site. Any guesses?

Res STS
08-26-05, 11:36 PM
Ranger, you are smart to be skeptical about Top Tier. But are you saying the major automakers are in cahoots with some of the major oil companies? Sounds like that would be a pretty big conspiracy to keep secrret. I think the story that automakers are for approved fuels is plausible because it can reduce warranty costs and keep them out of trouble with the EPA on the 100K mile emissions requirements.

I can truthfully say since I no longer frequent the cheapest gas stations, I have had no further problems with misfires in about 1 1/2 years. My misfires were cured with new injectors/pressure clean under warranty, not new wires, though I agree that wires can be at fault. Further, by me, Phillips 66, a Top Tier approved fuel is nearly as cheap as the Costco in town, which seems to leverage the local stations lower than prices in surrounding towns.

kaps52
08-29-05, 11:50 PM
i really dont think that it is a ecm i dont rec. using a stethescope to check ignition system unless u want to get shocked in there ear there is as much as 50,000 volts and you are providing a path to your ear plus if there is an acr youl hear it. there is a few things you need to do first what cylinder does the miss specify? inspect the plug for closed gap then stick a screw driver in wire at plug end start vehicle check for spark if no spark check coil for that plug check for corrosion or rust, and spark. if still no spark remove other wire on coil if there is spark on other end of coiil replace coil. if still no spark take off coil pack and get test light hook up to the two pins crank or start engine to see if it blinks no blink replace that coil and and ignition module. if it blinks replace coil.

kaps52
08-29-05, 11:53 PM
DONT DRIVE WITH MISS FIRE miss fires are bad first they damage very expensive converters. also the un burned gas washes away oil from cylinder walls and may and sometimes damages cylinder and pistin rings which leads to no compression it is common

Ranger
08-30-05, 12:04 AM
i dont rec. using a stethescope to check ignition system unless u want to get shocked in there ear there is as much as 50,000 volts and you are providing a path to your ear plus if there is an acr youl hear it.
How are you providing a path to your ear? There is a non-conductive rubber hose between the probe and the ear piece. What do I not understand? Can you elaborate?

EcSTSatic
08-30-05, 09:24 AM
I use a timing light to find misses. Just put it on every plug wire and watch the show. There should be a steady cycle of flashes. A miss will show up as a missing pulse.

There's nothing wrong with using the stethoscope method. Anything solid will transmit sound. I've put my ear to the handle of a long screwdriver, a wooden 3/4" or larger dowel works well too. There's no chance of getting shocked unless you use something entirely conductive.

Eldyfig
08-30-05, 10:14 AM
I use a timing light to find misses. Just put it on every plug wire and watch the show. There should be a steady cycle of flashes. A miss will show up as a missing pulse.


A timing light works good. That is one of the methods I use. Another, is to use an inline test light put between the wire and the plug.

T93Eldo
08-30-05, 03:02 PM
Has anyone checked the fuel line pressue, if it is below spec , it could be that the fuel pressure regulator could be bad and that could cause a misfire, if yours has been starting really hard after it is warm, it can leak from the fuel pressure regulator and cause low fuel pressure and hard start when warm, which can cause a misfire code. Been there, done that. changed the fuel pressure regulator and solved our misfire code after we spent the $$ on wires, plugs, etc. Its worth a check.

Ranger
08-30-05, 07:37 PM
Ranger, you are smart to be skeptical about Top Tier. But are you saying the major automakers are in cahoots with some of the major oil companies? Sounds like that would be a pretty big conspiracy to keep secrret. I think the story that automakers are for approved fuels is plausible because it can reduce warranty costs and keep them out of trouble with the EPA on the 100K mile emissions requirements.

I can truthfully say since I no longer frequent the cheapest gas stations, I have had no further problems with misfires in about 1 1/2 years. My misfires were cured with new injectors/pressure clean under warranty, not new wires, though I agree that wires can be at fault. Further, by me, Phillips 66, a Top Tier approved fuel is nearly as cheap as the Costco in town, which seems to leverage the local stations lower than prices in surrounding towns.
I think it just might be cleaver marketing. I have always bought gas form whoever has the best price. I have no allegiance to any brand and have NEVER had a problem. I have 105K on the clock now and had 125 on my '92 when I traded it.

kaps52
08-31-05, 12:21 AM
how does the car run do you notice a miss at idle, under load, only when warm, cold, while starting, after driving for a while, do you even notice a miss? more info would be needed to pinpoint. there are many thing that can cause miss fires most common on n* primary/secondary ign (mod, coil, wires, plugs etc) fuel delivery (leaky pressure reg, low fuel pressure, injector problems) mechanical (vacuum leaks around manifold, valve train problems. plus many more possible causes possibly the cheapest way is to take it to a qualified tech with ignition scope rather than process of elimination which may cost hundreds and hundreds just to still have same problem.

kaps52
08-31-05, 12:24 AM
i am always real carefull when checking secondary ignition system while car is running and arc can jump 3 inches ive been shocked tryn to do a cylinder dropage test on a car that the injector were un exsessable and got shock even though i had insulated plug boot pliers it would hurt you the current is low but it is not fun

powerglide
08-31-05, 12:53 PM
could be the coils.....I had the same problem

http://www.cadillacforums.com/forums/showthread.php?t=36384&page=2&pp=20&highlight=misfire

that thread shows what I did to disagnose it. It turned out to be a bad coil pack. Top of page 2 of that thread describes how to check the packs and how much the new part costs etc

good luck

cadillacgirl
09-01-05, 12:11 AM
ranger i had this problem a few months ago check your gap on the plugs make sure they are set correctly also check your o2 senor that could be a problem also..