simster571

my 96 trans am has had a horrible misfire for ahile now. it has been in 4 shops so far with noone able to figure it out. it shows a p0300 (random misfire) code. it constantly misses on cyl 1 and misses on cyl 2 sometimes and cyl 7 a little less often than cyl 2. My neibor is a mechanic he has been working on it mostly here is everything that has been done to this car so far:
new distributor
new plugs/wires
new intake gasket
new computer freshly flashed
tested injectors they are fine
new catalyic converters and o2 sensors
compression test its compressing fine at 180 psi

most of the time he can get it to quit misfiring after we clear the code or do something to it and it will run without misfire for forever while its jsut sitting there but you drive it down the road 2 miles and that check engine light comes right back on. this thing has us compleatly beat does anyone have any ideas or any advice to give at all im almost willing to try anything?

also and on bank 1 the injectors are staying open for about 3.3-3.7 ms and on bank 2 they stay open for 4.0-4.7 ms. this is definatly not right especially that the 2 banks are diffrent. any ideas on what could be causing this?

thanks for any help im about to just blow the thing up and get insurance its driving me crazy!

Guest47904

How were the injectors tested? I suspect they were merely raised up and pressurized to see if any are leaking.
It's quite common for the injectors and even the rails to have a build up of residue over time. If any of the injectors on bank 2 are clogged or partially restricted, the duty cycle would be increased to compensate. What doesn't make sense is you have more misfires on bank 1 then you do on bank 2. However, bank one could have a cylinder misfiring rich and bank 2 could have a cylinder misfiring lean. It would appear that you have a restriction in the fuel rail more so than the injectors since the cylinders at the 2 extreme ends of the fuel rails are misfiring. Perhaps.

First try swapping injectors from good to bad cylinders. I always recommend professionally cleaning injectors. I do mine on the rail with 3M cleaner. Takes 10 minutes, you don't have to remove them and the process cleans the rails too.

simster571

ok it just got finished today. turns out they put the spark plug wires backwards on cyl 1 and 7. kinda irrates you when its something so simple...but to answer your question they were switched out. and it still missed. im not sure if its still doing the bank thing or not i guess ill find out after my neibor runs a scan on it with his scanner.