Misfire on all cylinders above 2,000 rpm

[DeathtoRice]

My truck is misfiring on all cylinders when i hold a gear too long, according to my buddies scanner. Any ideas what could be causing this? I just had it tuned up 2 months ago. Also, how many o2 sensors are these trucks supposed to have? Mine has 4...2 in each manifold pipe, 1 before the cat, and 1 after the cat, but everywhere i go to buy them says only 2 are required. Is my truck just weird? Thanks

[OBI WAN]

Nope not weird. There are 4 02's, 2 for the tune on the down pipes, one before cat to take a precat and final tune reading and one after which is there just to see if the cat is functioning. OK, at nite open the hood and look to the sides of the coil. You see blue flames, you got a side burnt through coil which is kinda par for these trucks!!

[OBI WAN]

Also within the aritcles section of the site, link is right under the main headers you'll find a article about dealing and troubleshooting P0300 misfires.

http://www.sicgmtrucks.com/forum/article.php?a=71

[firehawkclone]

If it aint what MASTER says go get you a cap and rotor,my truck burns them up all the time!it doesn't matter if thier the good ones or the cheap one's.hell i just burnt one up coming back from VEGAS and had to change it out in the autozone parking lot in the rain.

[DeathtoRice]

hmm, well there is no code, according to the scanner, and the check engine light is not on. (it does come on when i turn the key to acc, so I know its working) I will look into the things that the article brought to light. Thanks for the help.

[DeathtoRice]

I took it to a shop today, and they said that my de screened maf was being damaged by sucking in fibers from my k&n filter. That doesn't sound legit to me, because no aftermarket maf comes w/ a screen. Are they trying to rip me off?

[OBI WAN]

No, but dont exactly know what there talking about it sounds like to me!!!
Fibers, I never have ever heard that one in the least. Besides the screen wouldnt stop minute fibers from passing through and I'd like to know what those fibers could even do.
Now with the K&N filter on there, the #1 problem running them and problems with the MAF is its oil. The oil coats the MAF and insulates its reading properly and can cuase a misfire. If there is no physical damage to the MAF wires and or resistors going between the wires, like no connection, then you simply use electrical cleaner, or even throttle body cleaner and spray the wires down a few times. This will clean the oil off and usually fixes this problem. Still say check the coil!! MAF would cause misfires accross the RPM USUALLY instead of just holding a gear!

[DeathtoRice]

Well, i went out and cranked it up tonight but did not see any blue flame.

[bvr775]

I took it to a shop today, and they said that my de screened maf was being damaged by sucking in fibers from my k&n filter. That doesn't sound legit to me, because no aftermarket maf comes w/ a screen. Are they trying to rip me off?
they'er right and wrong. yes a an oiled cotton filter isn't great for a maf but most of the oil sticks to the screen instead of the maf sensors. Yes if your getting oil on the wires it will cause a misfire, but don't buy a new one. Carefully clean the maf with some electical parts cleaner. you can find it at radio-shak.
You need to look at your filter I've seen them dry rott from being under oiled or not cared for at all and clog up the screen. This will cause it not to run well at high rpms. K&N gives you that million mile warrenty, but look real closely at the care instuctions than came with the filter. It dose need regular maintenace just like paper. Try running a paper filter for a few days after you clean your maf.

Here's a tip: Low quality paper filters flow better than cotton oiled filters.
A foam filter will out-flow a cotton oiled filter and low quality paper filter.
oil will cling to vital parts.


get a super charger it's safer

[DeathtoRice]

Well, the filter has only been on there for 2 months, and not even 1,000 miles But I do have a cleaning & oil kit left over from my POS monte carlo. I usually clean it every 6 months weather it needs it or not. I will try the electric parts cleaner. Thanks

[OBI WAN]

Water, moisture and rain passing around the headlight area can cause the oil to release from the filter.

[firehawkclone]

i bet its the cap,but maybe its my JACOBS ign that does mine in all the time!

[DeathtoRice]

Replaced the cap and checked the filter...filter looked fine, but still misfire. Now my buddies scanner says its #3&4 that are misfiring, and not all 6. I hate cars.

[OBI WAN]

Its getting better though. Now its narrowed down to 2 which then leads to maybe a bad wire, plug or maybe what you dont want to hear. Injector issues!! Injectors can be cleaned by the dealer or trying touse multiple cans of Sea Foam in the tank to clean them from inside which will take a tank run!!

[firehawkclone]

Did you change the rotor to,or just the cap?And tonight set the parking brake(than start it) so the headlights won't come on,and really check for some arching on them plugwires!

[DeathtoRice]

Well, I took a known good set of wires off my buddies truck and used them on mine, and replaced the rotor w/ his known good one too, so I guess it must be injectors. I have used seafoam before, but I also know that injectors are problematic on these trucks, so I may as well start saving for a shop to replace all 6 of them...All that stuff goes over my head, especially on modern cars. Thanks for the help, guys.

[firehawkclone]

what year is this truck?I've allways had great luck with the techron cleaner,A couple cans of whatever cleaner you like may just do the trick!

[DeathtoRice]

it's a '97

[firehawkclone]

I have this letter that GM sent me,saying that the poppet vavles(injector kinda)can get deposits built up on them.and the dealer will fix it for free.but my letter say in CA so i don't know if it will work were you live.it cover just about all vans/trucks from 96/01 with 4.3 all the way up to the 5.7..you have 10yrs or 200,000 mile the get this done.the letter has a number on it G99066E

Maybe MASTER knows more

[OBI WAN]

I have this letter that GM sent me,saying that the poppet vavles(injector kinda)can get deposits built up on them.and the dealer will fix it for free.but my letter say in CA so i don't know if it will work were you live.it cover just about all vans/trucks from 96/01 with 4.3 all the way up to the 5.7..you have 10yrs or 200,000 mile the get this done.the letter has a number on it G99066E

Maybe MASTER knows more

I applies to California " ONLY"if 2 cleanings dont solve the problem, injectors are replaced for free.
California uses alot of additives fuels which cuase the injectors to plug. The dealer offers a cleaning for under $150 to clean the injectors. They use 80 PSI of nitrgogen to blow them clear!

[DeathtoRice]

It was the idle air control in combination with the MAF and a bad o2 sensor.

[firehawkclone]

man it was all that!

[bvr775]

In a previous tread you said it was in and out off the shop quite a bit here lately and you found all this wrong with your truck now...
The tech may be your freind and/or you may feel some loyalty to the shop, but I urge you to find anoughter shop.they don't seem competent.

This is nickle and dime stuff you could have done in your driveway with minimal tool and a free code reading from advace or some outher parts house.

[DeathtoRice]

I am not mechanically inclined. All the engines I have built (even with help from a 30+ year NHRA veteran) have failed. I'd just as soon let a shop fix it w/ a warranty, if it isn't something simple. Mabey the shop is ripping me off, But ever time they get done with it, the problem is fixed. Its not the same problem every time. It was in their shop for 3 weeks one time and they only charged me 3 hrs labor. The first time it went to the shop was a ripoff...a fuel pump for $900 and the ****ers stole my full tank of gas. The dam thing broke down 8.6 miles after I bought it 60 miles from home on the side of the interstate at 9:30 PM in the rain. Any people in the Fayetteville, GA area...Stay away from Pro Car Care.

[DeathtoRice]

Well, this does it. The goddamn check engine light is on again. I took a sledge hammer to the truck and beat its sorry *** into the ground. **** american cars.

[OBI WAN]

ASE= Another SLeeping Enitity during training!!

Doesnt mean all ASE techs, just 95% of them that have no prior years of experience and dealership employees.

Bring it here, will find and end it all!!

[DeathtoRice]

...I took a sledge hammer to the truck and beat its sorry *** into the ground...

It's in the junkyard now, so it ain't goin anywhere. I'd rather walk than go broke keeping the dam thing on the road.

[OBI WAN]

Its not that is was a GM product of anything like that!

All cars by ANY manufacturer are the same when dealing with something that goes wrong.

These tech people today dnt give a dam about anyone and it isnt there rep on the line like it is with Jake and his shop. These tech guys plug in the diagnostice scanner and retrieve the code. First thing they do instead of reasoning why is to change the sensor the thing codes for. Then they say they fixed it. Well with a new sensor and reset ECM most times it'll be ok for a short time. Once it relearns all its stuff, it comes back. There was a reason to why this code came up, but it wasnt reasoned out and the sensor was changed. Now they just guess and begin to throw parts at it if there is no tech bulletin on the problem cause they just dont think! Sometimes they dont even look at tech bulletins until theyve run out of ideas. Now independant shops, like Jakes with no advertising etc rely on word of mouth etc to get stuff fixed, they pride themselves on a one time fix so when and if have another problem later you will return. They think things through and alot of times do things free since this problem has really got them and they know its not morally or business savoy to charge you for it. But you still have to watch there locations also, good traffic streams make for shoddy repair shops alot of times. These guys sometimes are money hungry and dont care if they burn you cause there thousands of cars passing each day that are potential business!!

I just dont want you to think its just GM etc along those lines. People here should learn there best asset to fixing stuff is right under there nose. ASK around, if that doesnt provided much, follow these rules. High traffic areas and large shops and dealers, avoid! Smalle shops, located away from this volume usually offere better returns since they live and die on what they did for you!! Doesnt matter if its American made, European and Rice, all them break and then theres others ready to prey upon your wallet!!

[bvr775]

I just dont want you to think its just GM etc along those lines. People here should learn there best asset to fixing stuff is right under there nose. ASK around, if that doesnt provided much, follow these rules. High traffic areas and large shops and dealers, avoid! Smalle shops, located away from this volume usually offere better returns since they live and die on what they did for you!! Doesnt matter if its American made, European and Rice, all them break and then theres others ready to prey upon your wallet!!


right on..it's why and outher tech don't genraly see eye to eye on computer issues. If it's broke before it's time to break they was probally something else wrong. 15 years have taught me that a code scanner is a good tool, but not the only tool.
EX...I just went round and round with the honda plase over my the crv my grandmother bought. No it wasn't throwing codes, but 10mpg is a bit off for a car that only has 7k on it(this aint no supercrew) What was wrong? why is it getting bad mileage? why isn't it throwing a code? why am I about to whoop a sevice managers ars?
bad casting with the plentum causeing vacume leak..bingo small vacume leak. I found it in 5 minutes just by listening... wasn't bad enough for the obd to read out of check.. this guy was an idiot and I didn't feel like paying 500 to bail myself out...
ok so I went on little rant there, but you get the idea. exsperince counts, multimeter, vacume gauges, and stethiscope or still good tool. And a scantool is only as good as the person useing it.

[firehawkclone]

YOU can do this yourself,it's not that hard!just take your time and read and ask questions here,we'll guide you through it.

And if you did take a hammer to it and you don't want the truck anymore,how much you want for it?just kidding

[DeathtoRice]

I only got 2 good beats in before the handle snapped on the sledge. the hood was ****ed neway from the previous owner. I have been dealing with a mom and pop shop, not a national chain. They are good about explaining everything they do, but today they gave up on it. The code was random misfire, and they said they had done everything they could possibly think of, and that mabey my after cat o2 was being affected by my exhaust setup (2.5 foot of pipe w/ a turndown after the cat) or the computer was going out. At least they installed my new tailgate cables for free. LOL

[DeathtoRice]

Now my buddies scanner says its EGR. Another problem has arisen...when i hit the clutch and coast to a red light, it wont idle down til i come to a complete stop. It also makes shifting a *****, as its always going into the next gear at too hi of an RPM. It is still misfiring too. Could EGR be responsible for either of these problems? I have run 3 tanks w/ seafoam and put it in the oil and sucked it in thru the booster line too, so I'm guessing the injector poppets are fine. The shop I had the truck in claimed they had replaced the EGR valve too, and it had no effect; but my friends scanner says thats the problem.

[DeathtoRice]

Replaced the EGR valve today, and that seemed to do it. The light usually comes on when I am driving home from the shop, and after I put the valve on it, I drove for 50 miles and no light. Ran a lot smoother too. BUT it still won't idle down always when I take it out of gear. Sometimes it does, and sometimes it doesn't. Any ideas about this? Also, several people have said that my exhaust (or lack thereof) could have been what made the EGR valve go bad. What do you think?

[bvr775]

You seem like you may be a smart person, but you keep letting shops take your money and their not fixing your problem. From the sounds of it they'er just replasing parts. i don't want to sound mean, but your the type of person that gets an internal supercharger sold to him by a shady shop(happened to a guy I knew in highschool). I realise your young and all, but you need to smarten up a little when it comes to your investments. you truck is an investment you need to know at least basic mechinical skills are shops will take advantage of you your whole life. let me put it to you like. eventually your going to buy a new vehicle are you the type of person to pay an extra $1500 for liquid cooled brakes are you smart enough to know that the corrosion protection is built in when it's painted at the factory.

i'll offer you this suggestion one more time. then your on your own. it's your money,your truck. Go get a shop manule (chiltons and haynes are both really good books). spend 20bux on little knowlegde so you can save your money and be able to tell a littl batter when a shop is trying to sell you muffler beirings. I belive they even have "engine repair for dummys" now. these are really good books for explaining things in way that is not so technical.

[nomaboy]

I doubt that your exhaust has anything to do with it. I don't even have a cat or tailpipes and havent had that problem.I did find that my spark plugs foul out really quick and that causes a mis so you may want to look at that.

[DeathtoRice]

LOL, ya, I know those "superchargers" are just a scam. I have the basic knowledge, and then some....on old cars. These new ones with all their sensors and other crap go over my head. When my old truck ran badly, I changed the plugs, cap & rotor and adjusted the timing and carb, and it was fine. I have a hayes manual for my truck, but It really doesnt go in depth enough. Me and my buddy put the EGR valve on, I didnt pay a shop. Now it runs fine except for the idle issue. Now that my friend has a scanner of his own, it helps out a bit. The code was originally "random misfire" but after over a month it finally threw a code that was useful...EGR. I have not spent very much money at this shop, but it has been in there several times. The majority of the money spent was on a clutch, and master/slave cylinders, injectors and the dam $900 fuel pump (I don't go to that shop any more). They say what they have found, I come here and see if it's valid. They never did find the EGR problem, even claimed they had replaced it for free, but it didn't help so they put the old one back on. The shop was stumped....they replaced a lot of parts but did not charge me...not even for labor. Just returned them to NAPA if it did not fix the problem. They finally gave up and said I'd be better off going to a dealer. Now it seems to be fixed though. 2 days and no light or skipping.

[OBI WAN]

Replaced the EGR valve today, and that seemed to do it. The light usually comes on when I am driving home from the shop, and after I put the valve on it, I drove for 50 miles and no light. Ran a lot smoother too. BUT it still won't idle down always when I take it out of gear. Sometimes it does, and sometimes it doesn't. Any ideas about this? Also, several people have said that my exhaust (or lack thereof) could have been what made the EGR valve go bad. What do you think?

IAC valve is sticking or it has a intake tubing leak!

EGR valve could go bad merely by the extra pressure exerted by a plugged exhaust. Plugged exhaust could also be the misfires even thought the EGR helped.If the cylinders cannot escape the exhaust itself, it'll have to much inert substance top properly fire. A non fully seated EGR valve would make this worse since it also it allowing more exhaust into the intake side dliluting the mix as it enters!!

This OBD stuff isnt all to hard and all old school thought still applies. WHat we tend to do is get scared since the computer is involved is all. We think it has a brain beyond what we have, it doesnt! OBD 2 is just a series of sensors designed to aid you in which direction to look upon when the SES ligth comes on.Old days you had to wait for problems to present itself hard before you even noticed one, today the OBD2 can tell you they are arising before you would notice it. For the most part IGNORE all codes per say as there written.

I'll do one quick simple example to show you directional thought.

EGR CODE! P0400 and P0402
Both say flow problems.
Now your job is to think what could cause a flow problem.
Without going any further cause this first part confuses the outcome, why catches this code< This is important! If you go by the code itself the first thought is EGR valve, is it the only one??
The 02 sensor catches this code, how? By the oxygen content of the exhaust pipe its in.
So first you look at the egr valve physically. Is it held open by carbon, it if is you clean it.Second which is never done and Ive never seen a bad EGR valve really is to TEST IT. Simple! With the vavle off and so you can see it, stuff a rubber plug or something into the port to at least semi seal it off. Start it, it shouldnt open, rev it lightly, as soon as 1.2 volts is exceeded EGR is commanded and see if the valve opens. If it does back it back down, the throttle, does it close fairly fast, it does. Well dammit it aint bad!! That wasnt it!

How else could the 02's be seeing to little 02?? Hum a stuffed exhaust that cant exhale!!! Check the cat, another simple to do. Drill a freaking hole into the ypipe just before the cat! Does RPM change? cats bad if it does!! That not enough drill another behind the cat and use a vacuum gauge both before the cat and after, is it different by more than 1/2-1, if it is the cat is plugging or plugged!


Another thing is know your vehicles mileage and the life of some parts!! Anything over 80K is time for a new set of 02s and a cat will be fourth coming!!
Didnt want to sound rudish, but thats the part all tech do not even attempt to do. A code gices you direction and you must think of everything within this direction that could cause the scenerio. Doesnt change old school tatics at all, we just overead the OBD codes is all. If there were no OBD codes to deal with, how would you attack the situtation???

Being yours is a 2000rpm and higher miss I dont think that valve is gonna fix it for long!!!!!

[DeathtoRice]

Hmm. I had planned on replacing the cat with a hi flow unit, as well as the 3 remaining o2 sensors, because the truck has 123,000 miles on it. I will just save up and get them replaced. I finally got my muffler installed and It wasnt as loud as I hoped, so mabey the cat will help there too. The IAC valve was just replaced, so that shouldnt be the problem, but mabey it's the intake tube. Do you mean my K&N intake tube or a tube/pipe connected to the intake manifold like a vacuum line, etc...? Thanks.

[OBI WAN]

If there are any leaks after the MAF connection is what I meant. Yes the K&N could not be sealed at the throttle body, the PCV line is off-cracked etc. Or even any vacuum line itself. All these pull in air after the MAF so it never sees it to tune for it!

[DeathtoRice]

well, i sprayed everything down w/ break cleaner while the truck was running and the idle didnt change any, so I guess there are no leaks. I double checked the intake tube just in case, and it seemed fine. So I guess my cat is plugged, or mabey that crushed piece on my y pipe, or both.