Misfire-cant figure it out on my own

[1GNMAN]

I bought this car back in Nov. 2009 and have been fighting misfire from time to time. I washed the motor today and it got really bad, as soon as the boost comes in and the check eng. light flashes but does not stay on and shows no codes. The car is stock except for new 255 Walbro(changed last month) with fuel pressure set @ 42psi, adj. fuel pressure regulator, adj. wastegate actuator with 15lbs of boost, tt chip(92 octane) Things I have changed over the last few months are plugs, wires, coil pack, New Kirban Gm stock MAF meter.


scanmaster readings(@ idle)
02s 690-720
af 04
l8 33
bl 140
ats 85
rpm 725
tps .42
iac 08
cc 09
temp 170

Take it easy on me, this is my first GN.
Thanks in advance!

 

[GNRick]

I bought this car back in Nov. 2009 and have been fighting misfire from time to time. I washed the motor today and it got really bad, as soon as the boost comes in and the check eng. light flashes but does not stay on and shows no codes. The car is stock except for new 255 Walbro(changed last month) with fuel pressure set @ 42psi, adj. fuel pressure regulator, adj. wastegate actuator with 15lbs of boost, tt chip(92 octane) Things I have changed over the last few months are plugs, wires, coil pack, New Kirban Gm stock MAF meter.


scanmaster readings(@ idle)
02s 690-720
af 04
l8 33
bl 140
ats 85
rpm 725
tps .42
iac 08
cc 09
temp 170

Take it easy on me, this is my first GN.
Thanks in advance!

BL indicates a vacuum leak. S/B 128. Misfire could be a bad TPS sensor which only shows a dead spot under load. Or a bad crank sensor. Or if you have a stock MAF it could be going bad. Usually in these "misfire" threads, someone usually suggests that you disconnect the cam sensor after the car is running, then see if the misfire clears up. If it does you have a bad cam sensor (or bad cap, not really sure). Reconnect the cam sensor or the car won't start after you shut it off. You might also try increasing the fuel pressure to 48 line off.

 

[mtocrs1]

Does it start to miss at a certain RPM or a certain boost pressure? What are your pluggs gapped to?

 

[1GNMAN]

As soon as the boost starts to come even at an easy throttle. Plugs are gapped 32.

 

[1GNMAN]

BL indicates a vacuum leak. S/B 128. Misfire could be a bad TPS sensor which only shows a dead spot under load. Or a bad crank sensor. Or if you have a stock MAF it could be going bad. Usually in these "misfire" threads, someone usually suggests that you disconnect the cam sensor after the car is running, then see if the misfire clears up. If it does you have a bad cam sensor (or bad cap, not really sure). Reconnect the cam sensor or the car won't start after you shut it off. You might also try increasing the fuel pressure to 48 line off.

Thanks, I will check these suggestions out. The MAF is a brand new rebuilt GM unit from Kirban.

 

[Cme2fly]

Thanks, I will check these suggestions out. The MAF is a brand new rebuilt GM unit from Kirban.

module.

 

[bmackinnon]

140 BL doesn't necessarily indicate a vac leak.... 160 yes, 140, probably not.... perfect is 128, +/- 10 is fine. Nor do your symptoms indicate a vac leak. Add a couple pounds of fuel pressure and see if the BL comes down a bit.

Regarding the misfire, agree with cmefly... probably ignition module and/or coil pack... pretty common, typical symptoms....

 

[1GNMAN]

Just added a new ac delco coil Saturday, will try a new module. I try to get all parts AC Delco but does the module need to be AC Delco brand or can I cheat with that part?

 

[TurboBuRick]

I think everyone is missing the key factor. The ce light. Did you try and pull a code? What chip?

Check your battery cables at the battery and the motor. Check the positive cable for worn spot where it could be grounding out. A common spot is the exhaust header. They burn the wire coating and then ground on the header when the motor tourqes to the side.

One thing I do not see in the sm readings, voltage.

 

[Cme2fly]

Just added a new ac delco coil Saturday, will try a new module. I try to get all parts AC Delco but does the module need to be AC Delco brand or can I cheat with that part?

Delco or NAPA brand only.

 

[Bigjack7440]

Did u get it fixed? I was thinking the tps also like said on the phone anyway good luck .

 

[Phoneguy]

With the CE light coming on I would check the balancer to see if it has come loose and is hitting the crank sensor.

Bryan

 

[bmackinnon]

as soon as the boost comes in and the check eng. light flashes but does not stay on and shows no codes.

Bad module will often exhibit these symptoms.... flash the lite, no codes...

Also make sure the module is tightly bolted to the mount as that's where it gets it's ground, and that the connector is firmly plugged and not corroded...

AC Delco module much preferred, but I'd probably give the NAPA a shot in a pinch.... not oreilly's, autozone, advance, etc...

 

[1GNMAN]

Thanks for all the replys. I will check all these things tomorrow. Appreciate all the help.

 

[Just a Six??]

Also many add an extra ground wire from module bolt to firewall or intake. They need good grounds. Extra grounds can never hurt anything but sometimes cure odd problems.

 

[Cme2fly]

Bad module will often exhibit these symptoms.... flash the lite, no codes...

Also make sure the module is tightly bolted to the mount as that's where it gets it's ground, and that the connector is firmly plugged and not corroded...

AC Delco module much preferred, but I'd probably give the NAPA a shot in a pinch.... not oreilly's, autozone, advance, etc...

I've had good results with Napa modules in fact, I have never had to return one. They are very similar in appearance to OEM.

 

[1GNMAN]

Fixed

I just installed the new AC Delco module along with an extra ground wire and it is running great. Just wanted to let you guys know the module was the fix. Thanks for everyones input. Its good to know there people you haven't even meet that would take the time to help you. Thanks again!

 

[bmackinnon]

Good deal!! Glad we could help! You scanmaster numbers look real good. Make sure you watch close for knock retard (KR). You want ZERO. For the O2 sensor, you'd like to see 750+ mV wot hard in 3rd gear. Keep your eye on those parameters for safe hammering! Welcome to the darkside!!!

 

[Cme2fly]

I just installed the new AC Delco module along with an extra ground wire and it is running great. Just wanted to let you guys know the module was the fix. Thanks for everyones input. Its good to know there people you haven't even meet that would take the time to help you. Thanks again!

Go get em'.

 

[Bigjack7440]

I knew you could do it.