Random miss fire need HELP
Random miss fire need HELP My car was miss shifted bent 7 of 16 pushrods replaced them all with comp cam chromolly rods. Also it shattered 2nd gear and had the tranny rebuilt by sixspeedsinc. Also note the car was running rough and just the same right after the miss shift. Now after installing pacesetter LTs, ORY and new tranny it is still running the same. Also we put new plugs, and wires in and the car ran like a champ before the over rev. Now the code is of course reading rear o2 and also random miss fire. I thought if i had a bent valve it would be a specific cylinder not random and im at a loss of ideas here. All help is much appreciated as im trying to figure this out and take all necessary steps before tearing the heads off. Now what do u guys think?
I am not sure about the rear O2 but I had a bad front O2 and it made my car run like ****. It some how got damaged when I did a tranny swap. I have heard something as small as a little tranny fluid can ruin an O2 and after mine died for apparently no reason I believe it.
I am not sure about the rear O2 but I had a bad front O2 and it made my car run like ****. It some how got damaged when I did a tranny swap. I have heard something as small as a little tranny fluid can ruin an O2 and after mine died for apparently no reason I believe it.
I say bent valve. Bent intake valve will screw up your manifold vacuum and make it run like ****.
Just do a compression test and eliminate that possibility. Or confirm it.
Just do a compression test and eliminate that possibility. Or confirm it.
Last edited by 8a8mfh; Dec 14, 2007 at 09:40 PM.
Are you gettng P0300? What is the other DTC? Just remember that multiple DTC can be the result of the initial one. Solve the first DTC on the list to see if the others go reset. If not deal with them. Is P0300 the first DTC that comes up or is it the rear 02 DTC?
It is o2 DTC then random miss fire and yes im getting po300
Why don't you post the rear O2 sensor DTC? Is it bank 1 or bank 2? Exactly which DTC is it? Remember that the rear O2s are only to monitor cat efficiency, nothing more. The pre-cat O2s are used to hold the AFR at 14.7:1 by adjusting fuel and spark under control of the ECM. Are you running cats? Swap your post cat O2 sensor and then see if the DTC changes to the other bank. Hook up your laptop to your car and monitor all 4 O2s at the same time. pre-cat should switch above and below 450mVdc. The post-cat O2 values should mirror the pre-cat ones on their respective banks, but with a reduced amplitude if the cats are working properly. This stuff is called EPA speak(OBDII). Shade tree mechanics have gone the way of the Edsel.
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Why don't you post the rear O2 sensor DTC? Is it bank 1 or bank 2? Exactly which DTC is it? Remember that the rear O2s are only to monitor cat efficiency, nothing more. The pre-cat O2s are used to hold the AFR at 14.7:1 by adjusting fuel and spark under control of the ECM. Are you running cats? Swap your post cat O2 sensor and then see if the DTC changes to the other bank. Hook up your laptop to your car and monitor all 4 O2s at the same time. pre-cat should switch above and below 450mVdc. The post-cat O2 values should mirror the pre-cat ones on their respective banks, but with a reduced amplitude if the cats are working properly. This stuff is called EPA speak(OBDII). Shade tree mechanics have gone the way of the Edsel.
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Verdad Gallardo Do you know someone with a GOOD scan tool(autotap, ease, EFI Live, etc.? It sounds like you're not using a scan tool, but a basic code reader. You can't run with the front O2s disconnected. You'll stay in open loop forever that way. Not good. The codes you gave say nothing about being rear or front for that matter. They are referred to as pre cat, post cat, Bank 1 sensor1(pre cat), Bank 1 sensor 2(post cat), Bank 2 sensor 1(pre cat) an Bank 2 sensor 2(post cat). If your scan tool can't identify your sensors this way using the code reader you have you'll never be able to isolate your problem and need to upgrade to a better unit. Something that uses you laptop is best. AutoTap is kick ***. I watch 24 pids at the same time in any format I want. Vehicles are so afraid of Autotap they fix themselves.
ok i have no idea what type of scanner it was all i know is it was a snap on scan tool and yes in the first set of o2 scans it read left and right bank as neither were hooked up and also did the same for the 2nd set of o2s read and as far as the random miss fire goes thats all we could get out of it nothing more.
First i dont have cats to the rear o2s are not installed nor have they been tuned out as we just installed the LTs and ORY. Second the pre cat o2s are NOT even plugged in we worked till 5am and we were a little tired and remembered we never hooked them up. Third the code reader reads 2 sets of o2s this is the order of the codes 1.)o2 sensor 2.) random miss fire 3.) o2 sensor.
You seem to be throwing out the same info and not taking advice.
OK I MADE THE SAME MISTAKE YOU DID I CUT THE CATS AND DID NOT TUNE MY CAR AND IT WOULD READ RANDOM MISFIRE AND IT WILL RUN LIKE CRAP I DID EVERYTHING AND SPEND LIKE 1000 DOLLARS taking it to the dealer and like 3 different shops I even went back to the muffler shop and had my cats welded back on and it kept doing it because by that time my o2's were gone the solutions was replacing all the 4 o2's and tuning the car. or what you could also do is hook up your pre cats and buy the o2 simulators for the rear since you do not need the rear o2 with the ory. that is just my opinion anyway
Well my main questions were could not having the o2 sensors hooked cause the car to run like total crap and cause the code im seeing. Also if I had a bent valve would that cause a random miss fire code as i thought a bent valve would be cylinder specific not random. Again im sure i may have a floated valve as I previously bent 7 of 16 rods which started this whole mess. My question about the o2s have been answered and i just ordered extensions just now i couldnt find ne one who had some extras or didnt need them ne more. Sorry if i sounded like an ******* ill take any advice i can get as most of you know waaaay more than i do.
You could have just went to the local autoparts store and got some corvette sensors, they have longer wires. Maybe you could cancel your order and do that? If you old O2's are old.
Not having them hooked up will make it run like crap.
Not sure about the random misfire code, I had my intake off a few days ago changing my knock sensors and got that code when everything was back running, have no idea why, I did forget to connect the brake booster.
Do you live in Florida and have a 2002? I have hptuners and can delete the codes.
Not having them hooked up will make it run like crap.
Not sure about the random misfire code, I had my intake off a few days ago changing my knock sensors and got that code when everything was back running, have no idea why, I did forget to connect the brake booster.
Do you live in Florida and have a 2002? I have hptuners and can delete the codes.
Lol i wish i lived in florida I live in nebraska and its cold as crap here and I cant stand the snow. I have a 98z and yea i could check with the auto supply store today but the extensions i got were $15 a piece and $5.00 shipping for both. How much do the vette wires cost?
The vette ones have longer wires they are Bosch part# 13111 I think, they are the rear sensors for like a 2002 vette, and similiar years. They are $73 for one. I have the extensions with my original sensors but they only have 42,000 miles on them. This might be an option for you if your sensors are old and you really wanted to get it running today. Otherwise I wouldn't blame you for not wanting to spend that much and just waiting for the extesions to come in.
Yea i think ill wait in that case the car is not even close to me its 4 hours away. I needed the lift and shop for the tranny and while we took it all apart i got LTs and ORY so my buddy is goin back next week so ill just wait for the extensions to get here for that price.
yea tell me about it, I shattered 2nd gear needed a bearing kit so i had sixspeedinc rebuild the tranny and thats when this whole mess started. 
