alright i had to have an engine replaced about 4 months ago (shortblock)

ever since i have had a check engine light. they have replced the injectors, coil packs, plugs, and maf.. it is reading a multi cylinder misfire code and the tech that is working on it now (cause the other guy quit) also said at 2500rpm it bounces back and forth from reading rich and reading lean

any of you engine guys out there got a idea?

 

I hope you get a answer to this because I have the same problem. My car runs great never a problem when I am on the gas but when its idling I get the same multi cylinder misfire code. do you have any mods on your car, my car has the greddy twin turbo.

 

one of the test procedures for the po300 code is a problem with the O2 sensors. looks like most of the rest of the things associated with the code have already been replaced. but he should be able to pick up a big variance in the O2 sensors with the consult-2 easily. i would assume he checked that already though, but worth a shot.

 

is this CHECK ENGINE LIGHT the same as SERVICE ENGINE SOON light?

 

yup

 

****... that thing is ON for me...
I think its the Test pipes kicking in...

 

figure out the code and do another thread so not to highjack this one. maybe can help ya with it.

 

yea replaced the o2 sensors as well....knew i was forgetting something...lol

the reading bouncing from rich to lean were found using the cunsult. car seams to run fine (idles a little rough) but otherwise is good. is it a possibility the cams maybe a little off causing it? i work for the dealership and watched pretty much the whole process and everything as far as cams and chains were marked and everything and put back dead on from what it looked. i doubt the cams would cause a misfire but im at a loss as to what else it could be...

i pulled all the mods off the car before i put it in the shop to have the shortblock replaced and other than the short throw shifter its stock. all the way down to the air intake.

im worried about putting the stuff back on as alot of it leans the car out (plenum, exhaust , test pipes, intake) and if it has an intermitant lean condition already im worried about putting them back on the car

 

i had my intake cam gears switched when i put mine back together. it through the po300 code all the time, but it idled ok and just ran like crap at part throttle conditions and good under heavier throttle. if this was the case with yours, you would see a big difference in a/f between the left and right side cylinder banks, also easily detected with the consult 2. unfortuneatly, they don't even list the difference in the 350z shop manuals. but it creates a noticeable drivability prob.
if the car is bone stock now, it eliminates alot of possibilities. another could be improperly installed pcv plumbing. if the consult 2 isn't seeing anything wrong as far as all the sensor readings, you will have to start looking towards things that are not diagnosed or read by the ecu. which will start to narrow it down alot too. good luck, i chased mine for awhile as my prob wasn't even listed as a potential for the po300 code.

 

anyone else got some ideas?

 

have they checked the crank angle position sensor?
that's pretty common to act up, and spit random cylinder misfire codes...
I think if a cam was off, that it would run a lot worse...

the cams in that motor, what cams are they? if they are aftermarket cams, then you're going to get random cylinder misfires as a normal thing, if they are stock, i'd guide some attention to the crank angle sensor.

also, make sure that the motor and ECU are of the same production dates....

 

stock cams in the car, and i would think if it was cams that it would run worse as well...all i get is a slightly rougher idle , runs strong other wise.. how would i find if the block and ecu are diferant production dates? where would i find that on the motor? i have the same heads and cams that the car came with just a new short block.

ill look into the crank angle sensor. would a vacume leak cause it? i dont hear any off hand but hey , you never know.

also if they didnt set the ecu to re-learn and only cleared codes you think that would have anything to do with it?

im just worried about putting everything back on the motor having this light on.


also i did find out it is supposed to cycle back and forth showing rich lean to protect the cats from burning so ive stopped tying that into the problem

thanks for all the help guys

 

so is the code up even right on start up and stay on? or does it take a few for it to throw the code?

 

no its right away......

 

but you have been driving it and it drives fine? through all throttle positions?

 

have they looked into the throttle body sensor? That's the sensor that controls the idle air and what not. Just a thought, but it may need to be checked as well...???

 

yea got 20k miles on the new motor and it runs great except for the slightly rough idle

 

thanks tony

ill look into both things you mentioned

 

what rpm is it idling at? does the idle rapidly change up and down or steady? the throttle motor should be able to be checked against the sensor on the peddle to see if they match. if it was just a prob at idle i would assume the light would go off during freeway driving or constant movement.
the only reason the ecu throws a po300 is a difference figured in the crank pos. sensor thinking there is a misfire. so you have had the light on for 20k miles?

 

i cant remember the exact idle rpm but i think around 750-800. it is steady. like i said it runs great except for a SLIGHTLY rougher idle...its not bad at all...just a little rougher than normal. and yea i have had it since 29k and im at 53k miles now.