1jz weird issue with boost/missfire

[naten]

hey guys,

just stuck with a problem with my 1jz. as soon as it starts to make boost like 1psi it starts stuttering/missfiring. only happens on light acceleration, if i go wot it will make noermal boost.

there is a slight miss when i first start it but isnt notiable when its idling or before any boost is made.

things ive tried:
new plugs, set of known good coil pack and my spaare ecu

in the lead up to this starting i did a boost leak test and fitted a new boost controller which ive since removed. ive since redone the boost leak test and i coudnt find any leaks, seemes to be pressurising under the cam cover though as i could heae air escaping around the oil filler. nfi if thats normal.

going to do compression test tonight just to be sure

any ideas anyone?

[The Last Streetfighter]

TPS set up and working correctly?

[naten]

checked it then, tis within range, just though
also tested (via resistance) cam position sensor, water temp sensor, tps
did compression check last night all between 175-160psi
still naught hmmmmm

[naten]

hmmmm just checked MAP, 5v in only 2.6V out with the car on but not running
drops to 1.3ish V on idle

from my understanding it should be putting out 5v when the motor is not running?

[naten]

going to try mates map next weekend though after doing some reading i think its ok

any suggestions anyone?

[wilbo666]

MAP sensor sounds fine...

http://www.toymods.org.au/forums/sho...d.php?p=601658

Cheers
Wilbo

[rshuwy]

check fuel pump voltage and pressure?

[Maverick]

Check all vacuum & boost lines, especially around the throttle body and such, I reckon that could be your problem... seen it before a few times.

Good luck

[naten]

i agree after reading the map sounds ok. ill check the fuel pump voltage this arvo and change the filter, i dont have access to a fuel prussure gauge unfort.

i thought it might of been a leak too but seems like and odd problem for a small leak, i pressure checked it on the weekend again and allbseemed well. will do it again and pay more attention.

i pulled the new plugs out too and thwy looked pretty black, except for part of the arm which was white. might take a pic this arvo to

[naten]

checked fuel pump voltage and its good, new fuel filter did mcnaught (knew it wouldnt needed to be done though)

missing on idle now, if i take injector/coil plugs off one by one runs worse, so it isnt one particular cylinder giving me grief.

havent had a chance to boost leak test, but im 99% its sealed

[Muzza]

did your problem happened out of the blue?
did u just buy it?
did a conversion?
.. did u check say the igf signal from the ignitor to the ecu?

[naten]

nah i did the conversion bout 7 years ago, seemed to appear after i did a boost leak test and installed new boost cont. like in my first post i removed boost cont.

how can i test the igf output? missfire wouldnt be intermitant if it was dodgy wire?

[Muzza]

well u can check for a 6v out from the igf... but the proper way is with an oscilloscope.. but just swap components like you have been doing, as long they are not doggy as well..
what colour are your plugs? where the electrode its.

yeah it can be intermittent if its a broken wire
there are so many things that can go wrong, basically check the easy stuff (like you have) then start getting technical.

a good way to narrow it down is to check the diagnostic codes to get an idea of the area where the problem is..
like the inputs, all the sensors from the engine to the computer
out puts, the coils, ingnitor, injectors, computer

[naten]

tried a different FPR today no difference, thought that may of been causing a rich condition when off boost.
Checked inputs at the ECU for TPS, water temp air temp all good. Dont have an oscilloscope so i just buzzed out the igf and all was well.

plugs are black with the arm of the tip white

took it for another drive and focused more on when its happening etc etc. I just cant figure out what would cause a missfire with no boost/low boost but be ok with full boost. Tis very odd.

I was thinking bung injectors, but i find it hard to believe all six started playing up together.

[Maverick]

Really, really sounds like a leak, not on the intercooler pipes, but rather the lines around the throttle body - the tiny one that runs from the bottom of the throttle body and runs to the
vaIve on the Power steer pump came of` both of my 1jz`s and they developed a misfire not unlike the one you described until I zip-tied them back on.... .