P0300 Code & CC Runs Horrible*solved* (plug failure)

killian96ss · Post by **killian96ss** » Thu Sep 01, 2005 5:08 pm

My CC threw a P0300 code about 3 weeks ago, so I hooked up my scan tool and got a P0300 (Random Multiple Cylinder Misfire). This is not cylinder specific and I can't find anything wrong.

When I first noticed the code I just figured it just really needed a tune up which I did a week later, and it ran really good for the next week and a half, but 2-3 days ago it started idling rough again. This time around it's much worse, and almost dies when idling. It has been turning the SES light on and off randomly.

I have already replaced the cap, rotor, wires, plugs, and all three 02 sensors. There must be another sensor having problems, or maybe the distributor, or timing chain, etc. Does anybody have any ideas on this one?

Steve

Edited title-HJ

Post by **HenryJ** » Thu Sep 01, 2005 5:23 pm

Check the distributor to see if it is cracked.

Open the hood in the dark and look for spark leakage.

What about the ignition module? Take it off and have it tested?

Clean the throttle body.

How's that fuel filter?

Check the fuel pressure. Maybe a failing fuel pump or regulator?

Any chance it is your precat plugging?

When was the last maintence dose of injector cleaner?

Maybe try having the dealer do a nitrogen pressure cleaning of the injector system?

If all of that checks out look to the New design 96-up SFI injectors!

Just some ideas...

killian96ss · Post by **killian96ss** » Thu Sep 01, 2005 6:17 pm

Brule thanks for the quick reply. The distributor isn't cracked, and I did check the engine in the dark while it was running and no signs of arcing or spark leakage. I will have the dealer check the ignition module, unless you know the readings it should put out? I do have an nice Actron multimeter and scan tool. The throttle body is very clean, and the fuel filter was replaced less than 10k miles ago. I will check the fuel pressure with my test gauge. I don't think the pre-cat is plugged because I still have good power, but I will look into it anyway. I use injector cleaner every 2-3k miles, but that doesn't mean one or more may be plugging up, and I will mention to the dealer about the nitrogen pressure cleaning. I would really like to have the new injector design, but I'm sure that would be expensive unless I can talk the dealer into doing it under my 100k warranty if I have injector problems. Any other ideas? BTW thanks again for the fast response.

I was supposed to be going on a camping trip this weekend to Tahoe, and now it looks like I will be renting one of those newer Impalas to drive since that's all I could find.

Steve

Post by **HenryJ** » Thu Sep 01, 2005 6:44 pm

All the parts for the injector upgrade run about $200. I have every confidence that you can do the job if the warranty will not do it.
It might help to print out the TSB from that article to take with you in case they are not familiar with this.

My local NAPA can test the ignition modules, I have no idea of how accurate the test may be , or a way to do it yourself.

The system pressure cleaning may be a good way to go for a start.

24digger · Post by **24digger** » Sun Sep 04, 2005 1:46 pm

My 95 S-10 started running really rough on Friday. Mostly bad at idle, took off the egr valve and it had 2 small gravel sized pieces of carbon stuck in it. Cleaned it out a now runs fine. Maybe its your problem too.

killian96ss · Post by **killian96ss** » Sun Sep 04, 2005 2:27 pm

24digger wrote:My 95 S-10 started running really rough on Friday. Mostly bad at idle, took off the egr valve and it had 2 small gravel sized pieces of carbon stuck in it. Cleaned it out a now runs fine. Maybe its your problem too.

I will check that out also, especially since I have the EGR limiter which restricts EGR gases. Mine could plug up very easy because of the smaller passage. Thanks for the reply!

Steve

TheBigFitz · Post by **TheBigFitz** » Wed Sep 07, 2005 5:03 am

This sounds exactly like the problem that I had last month. My truck had the same code and was idling very rough and sputtered bad when you would take off from a stop. Changed the plugs, wires, distributer cap, cleaned the injectors, and it still ran bad. Finally determined the distributer was bad, had that changed, and it runs fine now.

killian96ss · Post by **killian96ss** » Wed Sep 07, 2005 4:45 pm

My CC is now at the dealer since I could not track down the problem. So far they have replaced the TPS sensor, with no luck, and now they are talking about the TSB which includes the newer injectors. I hope this is the problem.

They did find some other problems as well. I need new right side lower control arm bushings (mine are cracked and coming apart) and my 4wd is not working again

due to the 2nd encoder motor that has failed. I wish the Posi Lock was a more reliable option.

Steve

kf6kmx · Post by **kf6kmx** » Sat Sep 10, 2005 8:34 pm

killian96ss wrote:My CC is now at the dealer since I could not track down the problem. So far they have replaced the TPS sensor, with no luck, and now they are talking about the TSB which includes the newer injectors. I hope this is the problem. They did find some other problems as well. I need new right side lower control arm bushings (mine are cracked and coming apart) and my 4wd is not working again due to the 2nd encoder motor that has failed. I wish the Posi Lock was a more reliable option.

Steve

Ok, came into this late, been too busy at the air base to get online

Anyway... I know this probably sounds like a dumb suggestion

BUT, check your battery cables....

I use (used to use anyway, havent warrantied it out for another one yet) an offroad battery, similar to an Optima, but is an Exide I think.. The cables wont stay tight on it.. the screws apparently bottom out in the hole without really being tight on the cable.. we found this out after about 6 months on that battery, when the CC started running horrible.. stalling at idle, EXTREMELY rough idle when it would idle, surged taking off.. felt like an old points ignition system when the points are failing..
After checking about everything we could think of, while checking other things I happened to hit the ground cable with my arm and the person working on it with me said "hey! hold it, that moved!".
Tightened it up and it ran fine, for another week until it worked loose.. sooo.. I'm back on the Delco Heavy Duty battery, at least for now..

Might have nothing to do with yours, ut it might be worth a look.. the dealer/mechanic might miss it if they arent looking for it to be a power issue..

killian96ss · Post by **killian96ss** » Sat Sep 10, 2005 8:57 pm

Cables are tight.

Did your Crew set any codes when you had this problem? I'll bet Brule is right about the injectors being bad, or least I'm hoping that's what it is.

I want my Crew back!!!!!!!

Steve

kf6kmx · Post by **kf6kmx** » Sat Sep 10, 2005 9:14 pm

killian96ss wrote:Cables are tight. Did your Crew set any codes when you had this problem? I'll bet Brule is right about the injectors being bad, or least I'm hoping that's what it is. I want my Crew back!!!!!!!

Steve

Didnt appear to set any.. they probably cleared when the battery was unhooked to change it if they were there, so I didnt see them.
It was weird, they looked fine, and if you grabbed the cable end and wobbled it, it felt ok, but if the you the cable a little farther down the leverage would let it move easy.

killian96ss · Post by **killian96ss** » Wed Sep 14, 2005 12:38 pm

Dealer has now replaced the TPS and new injectors per the TSB, and still no luck.

I am now paying them extra to check the ignition module and distributor. They have had my CC now for 2 weeks! I really hope they can find the problem.

Steve

killian96ss · Post by **killian96ss** » Thu Sep 15, 2005 12:36 pm

Update! My GM dealership now says the only thing wrong with my truck is the NGK Iridiums???

All of their techs are saying that the NGK's are causing my PO300 code, and that these plugs are not designed for this engine???

They have tested evrything and can't find any other problems, so is it possible they're right???

I really don't understand how the plugs could be the problem.

Steve

Post by **HenryJ** » Fri Sep 16, 2005 4:18 am

Have you checked for a stuck EGR valve?

killian96ss · Post by **killian96ss** » Fri Sep 16, 2005 7:43 am

HenryJ wrote:Have you checked for a stuck EGR valve?

No, but I will now.

At this point I am willing to check anything, so if you have any other ideas, let me know. Thanks again for trying to help!

Steve

killian96ss · Post by **killian96ss** » Fri Sep 16, 2005 5:10 pm

Brule, do you remember what NGK part # you are using for the iridiums? I'm using the ones recommended by NGK's web site, iridium IX part # TR55IX, stock # 7164. Does this sound right? When I got my truck back today the tech who worked on the Crew said the NGK's didn't look like the right kind of plug. He said when he compared the NGK plug with a stock Delco they looked completely different and said they were fouled so bad he was surprised that they were even firing. I am going to pull a plug later and try to see what he's talking about. I also found out that the injector upgrade is fully covered by GM even if you no longer have a factory or extended warranty as long as you live in California. They will do this upgrade free of charge as long as your vehicle has 200,000 or less miles.

CONDITION

Some customers of 1996, 1997, 1998, 1999, 2000, 2001, 2002 model year S/T, M/L, C/K, G, P, W4/NPR trucks and 2003 NPR trucks, that are registered in California, equipped with 4.3L (RPO L35 and VIN Code W, or RPO LF6 and VIN Code X), 5.0L (RPO L30 and VIN Code M) or 5.7L (RPO L31 and VIN Code R) engine, and California emissions (RPO YF5), may experience a "Service Engine Soon" light, misfire, rough idle or hard start due to a deposit build-up on the Sequential Central Port Fuel Injector (SCPI) poppet valve(s). The deposit build-up may cause injector poppets to stick closed. Certain fuels have been found to interact with the SCPI system to cause the deposits.

SPECIAL POLICY ADJUSTMENT

This special policy covers the SCPI failure condition described above for a period of ten (10) years or 200,000 miles, whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership.

The repairs will be made at no charge to the owner. This special policy applies ONLY to repairs requiring SCPI system servicing, injector cleaning and/or MFI assembly replacement of the SCPI system. The customer should not be charged for performing a system check when it is determined that the SCPI system is not the cause of a customer complaint (labor operation T5532 is provided to submit claims for such system checks). Any additional necessary diagnosis and repairs that are not related to the SCPI condition are not covered by this special policy. The customer should be informed that any further service that is not covered by new vehicle warranty will not be covered by this policy.

VEHICLES INVOLVED

Involved are certain 1996,1997,1998,1999, 2000, 2001, 2002 S/T, M/L, C/K, G, P, W4/NPR and 2003 NPR model vehicles, registered in California, equipped with 4.3L (RPO L35 - VIN Code W, or RPO LF6 - VIN Code X), 5.0L (RPO L30 - VIN Code M) or 5.7L (RPO L31 - VIN Code R) engine; and California emissions (RPO YF5). This Special Policy covers all vehicles within these model years, with these engine and emissions RPO's.

Steve

Post by **HenryJ** » Fri Sep 16, 2005 5:40 pm

killian96ss wrote:Brule, do you remember what NGK part # you are using for the iridiums? I'm using the ones recommended by NGK's web site, iridium IX part # TR55IX, stock # 7164. Does this sound right?...

Yes , those are what I have been running.
Check that EGR valve too. A 10mm socket , extension ratchet and a few minutes is all that is needed.

killian96ss · Post by **killian96ss** » Fri Sep 16, 2005 6:16 pm

HenryJ wrote:Check that EGR valve too. A 10mm socket , extension ratchet and a few minutes is all that is needed.

Does it have a gasket that I'll ruin when taking it off, or is it just one of those foil gaskets that you can reuse?

Steve

killian96ss · Post by **killian96ss** » Fri Sep 16, 2005 7:17 pm

Ok, I just got a plug out and compared it to the stock Delco and I can't see anything wrong.

The part # on the plug is TR55IX and the gap is correct @ .060. The gap on the stock Delcos's with 58k miles were about .064. Both plugs also have the same light brown color. If anything the NGK's look like there in better shape than the old Delco's. I feel like it's just going to be a waste of time putting the Delco's back in, but I guess that's the only way to plead my case.

Steve

Post by **HenryJ** » Fri Sep 16, 2005 7:50 pm

You're right you might need a gasket afterward, although I have taken mine off a couple times and reused the gasket.

What was the deal about the plugs being fouled then?
Maybe this guy has never seen an Irridium plug before, and assumes the electrode is gone

Make the plug swap and swap back once they do find the problem.

killian96ss · Post by **killian96ss** » Fri Sep 16, 2005 8:04 pm

The stock plugs are supposed to be good for 100K right? I just want to make sure before I put them back in, because I don't want to hear them say that they should be changed @ 50k or something, and tell me that I have to have new ones before they can re-diagnose the misfire problem. With the EGR valve off, am I just checking for smooth operation, or is there something else i should be looking for also? I am starting to go

about all this BS with the plugs.

Steve

Post by **HenryJ** » Fri Sep 16, 2005 8:24 pm

Yes, they say 100k for the stock plugs. Check the service schedule in your owners manual just to be sure.

Just look for heavy carbon deposits, and make sure that the valve is closed so no gasses can pass.

killian96ss · Post by **killian96ss** » Fri Sep 16, 2005 8:50 pm

Just checked the EGR valve and everything seems ok. It was closed when I took it off, appears to seal nicely, and moves easily with no sticking, and has very light deposits. If you have any other ideas I will check them out also.

Steve

Post by **HenryJ** » Sat Sep 17, 2005 6:18 am

I guess, hope the plug swap helps.

F9K9 · Post by **F9K9** » Sat Sep 17, 2005 6:47 am

HenryJ wrote:I guess, hope the plug swap helps.

On a similar note and I am sure have but, just in case, have you looked at the cap and rotor to see if the corrosion came back?

killian96ss · Post by **killian96ss** » Sat Sep 17, 2005 8:23 am

f9k9 wrote:On a similar note and I am sure have but, just in case, have you looked at the cap and rotor to see if the corrosion came back?

The factory cap & rotor didn't have any corrosion, but the rotor contact ball did fall out when I took it off.

The new cap & rotor appear to be fine. For some reason I feel like it's the distributor, but the dealer said thay can't find anything wrong with it.

All I can really do at this point is put all the stock stuff back on and take it back again for diagnostics.

Steve

killian96ss · Post by **killian96ss** » Mon Sep 19, 2005 1:43 pm

Update

You guys are not going to believe this, but the NKG Iridiums were the problem. I decided to go buy a set of stock Delco platinums part # 41-932 and install them versus the used Delcos, and my problems immediately went away. My Crew is running great again!

After closer inspection of the NGK's, I found that all 6 plugs had really bad multiple carbon tracks or electrical path marks just below the iridium firing points.

If you are running these plugs I would highly suggest you check them immediately. Mine got so bad that my SES light began flashing which is a warning of impending catalyst damage. I think it is possible that the recommended plug is the wrong heat index. I have the same plugs in my SS and I'm not having the same problem, but I do have an MSD Digital 6 ignition firing those, but now I realize I need to check those plugs as well just in case.

Steve

F9K9 · Post by **F9K9** » Mon Sep 19, 2005 1:48 pm

killian96ss wrote: Update You guys are not going to believe this, but the NKG Iridiums were the problem. I decided to go buy a set of stock Delco platinums part # 41-932 and install them versus the used Delcos, and my problems immediately went away. My Crew is running great again! After closer inspection of the NGK's, I found that all 6 plugs had really bad multiple carbon tracks or electrical path marks just below the iridium firing points. If you are running these plugs I would highly suggest you check them immediately. Mine got so bad that my SES light began flashing which is a warning of impending catalyst damage. I think it is possible that the recommended plug is the wrong heat index. I have the same plugs in my SS and I'm not having the same problem, but I do have an MSD Digital 6 ignition firing those, but now I realize I need to check those plugs as well just in case.

Steve

uh-oh

Who else is running them without MSD ignition?

Post by **HenryJ** » Mon Sep 19, 2005 2:38 pm

I'll check them again ASAP. Thanks for the "heads up"

jeff024 · Post by **jeff024** » Mon Sep 19, 2005 3:11 pm

im running them and so far so good

killian96ss · Post by **killian96ss** » Mon Sep 19, 2005 4:14 pm

HenryJ wrote:I'll check them again ASAP. Thanks for the "heads up"

Brule yours might be ok because your MSD will make them fire no matter what. The NGK's in my SS (same part # as the CC) are doing great, but I have the MSD firing those. I would just say to anyone running these plugs without a CD ignition, you might just want to pull one plug and check it's coloring. The plug should should only have a very light discoloring to it. If it appears reddish or dark in any way then it's not burning the fuel completely and will most likely cause more problems.

Steve

F9K9 · Post by **F9K9** » Mon Sep 19, 2005 5:16 pm

OK, I probably have the newest set of NGKs w/o "after market" ignition. If we need to start a test or a search for different plugs I am willing to try another set at my expense or record what is going on with mine. Anyone have an idea on the parameters of what I should do or record?

killian96ss · Post by **killian96ss** » Mon Sep 19, 2005 6:53 pm

f9k9 wrote:Anyone have an idea on the parameters of what I should do or record?

How many miles have you got on them? Mine did not even make it to 2000 miles before they were failing, but to be fair I was also having the injector problem which I'm sure helped foul them out faster. If the NGK's were working correctly they should have started firing properly after my dealer fixed the injectors. I would say if you are running these, just check them every few thousand miles to make sure they look ok. I keep wondering if the set I got was somehow labeled wrong at the factory, but it seems highly unlikely that the plugs themselves had the wrong number printed on them.

Maybe I should call NGK and try to get some answers?

Steve

Post by **HenryJ** » Mon Sep 19, 2005 6:58 pm

killian96ss wrote:... Maybe I should call NGK and try to get some answers?

Absolutely! And if they are not going to work for you they should offer your money back.

killian96ss · Post by **killian96ss** » Mon Sep 19, 2005 7:10 pm

HenryJ wrote:they should offer your money back.

I got them from Summit, and they always give me my money back when I return something, probably because of the ridiculous amount of money I have spent there over the past 16 years.

Steve

F9K9 · Post by **F9K9** » Mon Sep 19, 2005 7:51 pm

This "mislabeling" thing is a possibility. I went through H_ll last week I had some mislabeled contacts from Bausch and Laumb and I thought the theory was ridiculous but, guess what? They were labeled wrong

Once I convinced my eye doctor I was seeing worse with them in she checked it out and they were wrong. Am only saying it is a possibility but, 24 hrs ago, I would have said "no way" the NGKs were the problem.

killian96ss · Post by **killian96ss** » Mon Sep 19, 2005 8:40 pm

I really hope my case is an isolated issue, because it would be pretty bad to have a product out there that can fail so miserably.

Another idea I had was maybe my injector failure was bad enough to foul these plugs to the point of no return.

Steve

jeff024 · Post by **jeff024** » Mon Sep 19, 2005 10:45 pm

I have around 10000-12000 miles on mine

killian96ss · Post by **killian96ss** » Tue Sep 20, 2005 7:22 am

jeff024 wrote:I have around 10000-12000 miles on mine

Do you have time to pull one plug and check its condition? If yours turn out to be ok, then I might try cleaning mine and putting them back in. I checked one of the NGK's in my SS, and it looked good, so I'm not giving up just yet on these plugs. My injector problem must have been really bad because even my stock Delcos looked horrible with only 58k miles on them.

Steve

jeff024 · Post by **jeff024** » Tue Sep 20, 2005 10:24 am

yeah I will pull 1 later on tonight

AZS10Crew · Post by **AZS10Crew** » Tue Sep 20, 2005 1:25 pm

I just put mine in a couple weeks ago and they're OK so far. <knock on wood>

Pauleo · Post by **Pauleo** » Wed Sep 21, 2005 5:57 am

Great! I just bought the NGK's. I sure hope this is an isolated case!

jeff024 · Post by **jeff024** » Wed Sep 21, 2005 1:25 pm

I pulled 2 and mine look almost new

killian96ss · Post by **killian96ss** » Wed Sep 21, 2005 4:22 pm

jeff024 wrote:I pulled 2 and mine look almost new

Thanks for doin that.

I'm going to try cleaning my NGK's and run em again and see if they are still good.

Steve

jeff024 · Post by **jeff024** » Wed Sep 21, 2005 4:25 pm

recheck your gap maybe something was off

killian96ss · Post by **killian96ss** » Wed Sep 21, 2005 4:32 pm

jeff024 wrote:recheck your gap maybe something was off

The gaps on all 6 of mine are .060, but they are heavily fouled. The color on mine is a very dark almost black red with obvious signs of carbon tracking. I hope a good clean up is all they need, or there going back to Summit.

Steve

jeff024 · Post by **jeff024** » Wed Sep 21, 2005 4:59 pm

wonder what fouled them so badly

killian96ss · Post by **killian96ss** » Wed Sep 21, 2005 5:21 pm

jeff024 wrote:wonder what fouled them so badly

My failing fuel injectors which were replaced under warranty and upgraded to multi port instead of the factory central port injection.

Steve

killian96ss · Post by **killian96ss** » Fri Sep 23, 2005 6:52 pm

Well, I cleaned the hell out of my NGK's to the point where they looked almost brand new and reinstalled them. Immediately after putting them back in my engine started to shake and set the P0300 random multiple misfire code again.

Now I'm convinced that these are either the wrong plug for the CC, or all 6 are defective.

After I put the stock Delco platinums back in everything was fine and the engine runs great again. I would still recommend to anyone running these plugs even if everything seems ok to just check them every once in a while just to be safe. If you ever notice a rough idle, even if it's slight, make sure you check your plugs, especially if you are running NGK's.

Steve

jeff024 · Post by **jeff024** » Tue Apr 25, 2006 3:31 pm

killian96ss wrote: Update You guys are not going to believe this, but the NKG Iridiums were the problem. I decided to go buy a set of stock Delco platinums part # 41-932 and install them versus the used Delcos, and my problems immediately went away. My Crew is running great again! After closer inspection of the NGK's, I found that all 6 plugs had really bad multiple carbon tracks or electrical path marks just below the iridium firing points. If you are running these plugs I would highly suggest you check them immediately. Mine got so bad that my SES light began flashing which is a warning of impending catalyst damage. I think it is possible that the recommended plug is the wrong heat index. I have the same plugs in my SS and I'm not having the same problem, but I do have an MSD Digital 6 ignition firing those, but now I realize I need to check those plugs as well just in case.

Steve

I threw the P0300 code sunday and it was my plugs the NGKs one of the electrodes were broken off I changed the plugs with new NGKs and all is fine

kwalsh · Post by **kwalsh** » Sat Nov 11, 2006 4:11 am

I'm having the exact problems with setting off the P0300 code. I changed the plugs to the NGK's, resulted in the throwing the code. I took the NGK's out and put in Bosch Platinum +2, same result...however it does idle a little smoother. I will check the EGR valve, change the fuel filter and give it another shot. This is frustrating.

Maybe I should just buy new Delco plugs..

Post by **HenryJ** » Sat Nov 11, 2006 4:55 am

kwalsh wrote:I'm having the exact problems with setting off the P0300 code...

How are your plug wires, cap , and rotor?
When you change that fuel filter be sure to add some injector cleaner. A sticky poppet can cause a misfire too.

GM data wrote:DTC P0300
System Description

The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and the camshaft (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause three-way catalytic converter damage. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present.
Conditions for Running the DTC

Important

If the start-up engine coolant temperature (ECT) is less than 7°C (20°F), misfire detection is delayed until ECT is more than 21°C (70°F). If the start-up ECT is more than 7°C (20°F), misfire detection begins after a 5 second delay.

* DTCs P0101, P0102, P0103, P0117, P0118, P0128, P0335, P0336, P0341, P0343, P0500, P0502, P0503, P1114, P1115, P1121, P1122, P1220, P1258, P1336, or P1345 are not set.
* The fuel level is more than 10 percent.
* Then engine speed is between 450-5,000 RPM.
* The system voltage is between 1-16 volts.
* The throttle position (TP) is steady within 2 percent for 100 ms.

Conditions for Setting the DTC

The powertrain control module (PCM) detects a deceleration in the crankshaft speed that is characteristic of either an emission type misfire, or of a catalyst-damaging type misfire.
Action Taken When the DTC Sets

* The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
* The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

* The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
* A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
* A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
* Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

The misfire index counts the number of misfires. The scan tool can monitor the misfire index. There is a current misfire counter and a history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring. Use the history misfire counter for misfires that are not currently present.

Many different conditions can cause an intermittent misfire. Check the following conditions:

* Check the ignition control (IC) circuit for an intermittent short to ground.
* Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.
* Ensure that the coil wire is securely attached to the distributor cap and the coil.
* Check the wire routing to ensure that cross-firing is not occurring.
* If the misfire occurs when the weather is damp, the problem could be due to worn plug wires.
* Check the fuel for the following conditions:
o Condition and quality--Dirty or contaminated fuel can cause a misfire condition.
o The fuel level--If the fuel level is low, the fuel pump can draw air into the fuel rail, causing a stumble and a possible misfire condition. Check the fuel trim number in the Freeze Frame in order to determine if this condition has occurred. This condition is likely if the short term fuel number was more than +20.
o Restrictions--A restricted fuel filter can also cause a misfire.
* Check for sticking intake or exhaust valves on engines which misfire when the engine is cold.
* Check the heated oxygen sensor (HO2S) for abnormal voltage readings.
* Check for a vacuum leak as a possible cause of the engine misfire.

An intermittent may be caused by any of the following conditions:

* A poor connection
* Rubbed through wire insulation
* A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent and Poor Connections in Wiring Systems. If a repair is necessary, refer to Wiring Repairs in Wiring Systems.
Test Description

The numbers below refer to the step numbers on the diagnostic table.

5.If the Misfire Current Counters are incrementing, but the engine is NOT misfiring, this indicates a mechanical condition. For example, an accessory drive belt could cause this condition.
7.The spark should be consistent when you test the spark at the spark plug wires. The presence of few sparks then nothing indicates no spark.

kwalsh · Post by **kwalsh** » Sat Nov 11, 2006 8:47 am

Yes, the first thing I did was install a new cap, rotor and wires; all Napa stuff, Echlin & Mileage Plus.

I put new AC Delco, 41-932 plugs in, (the OEM plugs). No Codes.

I have an MSD 6A sitting here, maybe I'll put that in and try the NGK's and/or Bosch and see if the MSD makes a difference....but that #3 plug is a major pain in the a$$. After changing the plugs 3 times, I'm pretty fast at it now.

F9K9 · Post by **F9K9** » Sat Nov 11, 2006 9:06 am

kwalsh wrote:....but that #3 plug is a major pain in the a$$. After changing the plugs 3 times, I'm pretty fast at it now.

killian96ss · Post by **killian96ss** » Sat Nov 11, 2006 9:19 am

kwalsh wrote:that #3 plug is a major pain in the a$$. After changing the plugs 3 times, I'm pretty fast at it now.

Unfortunately I know what you mean.

While trying to solve my P0300 problem I must have swapped plugs at least 4 times.

Each time I put the NGK's back in the P0300 code re-appeared.

Steve

S-10CREWCAB.NET

P0300 Code & CC Runs Horriblesolved (plug failure)

P0300 Code & CC Runs Horriblesolved (plug failure)