Misfire Very Similar To Forsfed's

[Shane@DBPerformance]

Damn, thats a lot of knock there. What's done to your MAS? If adding fuel on the AFC has no affect on the fueling then you might be hitting MAS overrun.

[b00stingsx]

mass airflow sensor should be just fine. i havent touched it at all. what is mas overrun.

[Shane@DBPerformance]

If your running a stock 1G MAS then you will hit overrun with your setup. Overrun is when more air is flowing through the MAS than it can accurately count. It happens fairly early on the 1G MAS. When I have had it happen on cars, the car goes lean as the MAS puts out wacked out airflow numbers to the ECU. Adding fuel on an AFC doesn't help either since the airflow values that the AFC is trying to change are all messed up to begin with. The fixes are to hack the 1G MAS, put on a 2G MAS instead, run an GM MAF with MAFT, or goto a speed density setup.

[b00stingsx]

would i get overrun even at low boost though?? i have the boost set at 10psi, and i still get a misfire at the same rpm.

Also, at idle, i get about 14-15 vaccume, and on deceleration (in gear, coasting, no gas) i get about 19. im guessing ive got a leak somewhere. i will leak test it this weekend.

[Shane@DBPerformance]

No, you probably won't get overrun at low boost. Check for boost leaks, plugs, wires, etc.

[1ViciousGSX]

Miss fires will show up as a lean condition, which is probably why his log shows sudden drops in O2 voltage in the higher rpm range. But all that knock could definately indicate a lean condition also.

[b00stingsx]

Originally posted by 1ViciousGSX@Jan 29 2004, 09:30 PM
Miss fires will show up as a lean condition, which is probably why his log shows sudden drops in O2 voltage in the higher rpm range. But all that knock could definately indicate a lean condition also.
so are you thinking that im not running lean during these misfires? could i just be running realllllllly rich?

[1ViciousGSX]

Originally posted by b00stingsx+Jan 29 2004, 11:11 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (b00stingsx @ Jan 29 2004, 11:11 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-1ViciousGSX@Jan 29 2004, 09:30 PM
Miss fires will show up as a lean condition, which is probably why his log shows sudden drops in O2 voltage in the higher rpm range. But all that knock could definately indicate a lean condition also.
so are you thinking that im not running lean during these misfires? could i just be running realllllllly rich? [/b][/quote]
It is very possible. O2 sensors pick up the levels of unburned oxygen in the exhaust stream. A miss fire loads the exhaust with unburned oxygen. You need to confirm if you are overunning the mas or running out of fuel pressure also.

[b00stingsx]

OK, i figured most of it out!!!!!

I had some time today to get into a heated garage (hennipen tech), and boost leak tested my system. i found that the 2 vaccume lines that go to the EGR valve were disconnected, so i connected them, thus fixing the leak.

After that, i just decided to make a blockoff plate for my egr, as it was fairly clogged up. I reset my safc to 0% across hi range, and the misfires are almost totaly gone. now im only getting a little misfire at about 6000.

i know there still is a boost leak, and i know where its comming from. my factory ic pipe is getting old, and needs to be replaced.

thank you guys so much for the help!

-mike

[slowbubblecar]

BTW, you can check your SAFC and see if you are/about to overrun your mas. It is the display that reads HTz. If you are comming close, LMK. 2tsiawd84 has an extra 2g mas with all install shit and a hacked mas he ran on the 16g he sold you. Maybe Iceman can show you at HTC or something. BTW, I would replace your o2 sensor if you already haven't.