Misfire Very Similar To Forsfed's

b00stingsx · 01-26-2004

ok, im getting the very same symptoms that FORSFED was getting. my car is a 92 gsx 5sp, and is misfiring at about 4700+ rpms under wot, however under no load, it redliens just fine.

when i open up my valve cover, what exactly am i looking for? where are the "plungers of one of the intake lifters," and what do they look like. Does anyone have any pictures of this?

i want to know this so that when i go out to my un-heated garage, i can get the engine opened up, diagnnose the problem (if this is the problem), and get back inside.

thanks for the help guys!

A//// Guy · 01-26-2004

Might want to start simple and replace the plugs and wires. Those are the biggest culprit for misfires and stuttering under load only.

b00stingsx · 01-26-2004

sorry, i should have added taht... i have 8mm accels and bpr7es's gaped at .028. another thing i need to replace is my o2 sensor... but i kinda just have a feeling that its somthing different.

FORSFED · 01-26-2004

Like EclipseTurbo said, check the basic things first, any sensors or tune-up items that are not within spec can cause misfires, sparks, poor performance, you name it. As just about anyone can vouch for on this board, it is extremely rare for stock lifters on a virtually stock car to blow-out. Considering I don't know the history of the car it's hard to tell why it happened. I'm not saying it isn't your problem as well, just not too likely is all.

In any case it is an easy thing to check quick and all you need to do is look at the valvetrain. If a lifter is blown-out, the rocker arm that rides underneath the cam will no longer be in place because one end is supposed to be connected to the lifter that's wasted. It's pretty hard to miss once the vc is off. You could also check your plugs and if one shows lean and the other three a pretty good burn, that is also an indicator to the disfunctional valve problem.

**Shane@DBPerformance** · 01-26-2004

Just way too rich maybe?

b00stingsx · 01-26-2004

but if i was rich, wouldnt i be getting o2 values that are in the 90's? here is one of my loggs:

TIMA, COOL, FTRL, FTRM, FTRH,, O2-R ,RPM, KNCK
28.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.92V,,,,290 6.25rpm,1.00
25.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,296 8.75rpm,0.00
23.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,303 1.25rpm,0.00
18.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,306 2.50rpm,0.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,309 3.75rpm,0.00
14.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,312 5.00rpm,0.00
14.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,318 7.50rpm,0.00
14.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,331 2.50rpm,0.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,337 5.00rpm,0.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,343 7.50rpm,0.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,350 0.00rpm,1.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,353 1.25rpm,0.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,359 3.75rpm,0.00
16.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,365 6.25rpm,0.00
16.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,365 6.25rpm,0.00
17.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,378 1.25rpm,0.00
17.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,381 2.50rpm,0.00
17.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,396 8.75rpm,0.00
18.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,406 2.50rpm,0.00
18.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,400 0.00rpm,0.00
18.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,412 5.00rpm,0.00
18.00º,83.75ºC,81.12%,99.84%,99.84%,,,0.94V,,,,412 5.00rpm,0.00
18.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,425 0.00rpm,7.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,418 7.50rpm,7.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,434 3.75rpm,6.00
16.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.96V,,,,440 6.25rpm,6.00
16.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,443 7.50rpm,6.00
16.00º,83.75ºC,81.12%,99.84%,99.84%,,,0.94V,,,,443 7.50rpm,6.00
16.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,462 5.00rpm,6.00
16.00º,83.75ºC,81.12%,99.84%,99.84%,,,0.94V,,,,459 3.75rpm,6.00
16.00º,83.75ºC,81.12%,99.84%,99.84%,,,0.94V,,,,471 8.75rpm,6.00
16.00º,83.75ºC,81.12%,99.84%,99.84%,,,0.94V,,,,478 1.25rpm,5.00
16.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,478 1.25rpm,5.00
17.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,481 2.50rpm,5.00
16.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,484 3.75rpm,4.00
17.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,478 1.25rpm,4.00
17.00º,83.75ºC,81.12%,99.84%,99.84%,,,0.92V,,,,487 5.00rpm,5.00
17.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.94V,,,,506 2.50rpm,4.00
15.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.90V,,,,500 0.00rpm,18.0
12.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.90V,,,,515 6.25rpm,25.0
13.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.84V,,,,509 3.75rpm,29.0
10.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.92V,,,,531 2.50rpm,35.0
09.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.70V,,,,509 3.75rpm,35.0
09.00º,85.63ºC,81.12%,99.84%,99.84%,,,0.86V,,,,543 7.50rpm,35.0

FORSFED · 01-27-2004

By the looks of it you've got lean issues at higher rpm, so for some reason you're not getting enough fuel. If you're feeling hesitation from 5k up it's because there is so much knock that your timing is being pulled back next to nothing and therefore the car has no power whatsoever. You've listed an safc, why don't you try richening things up on the upper band and see what happens. You have to remember that just because your afc settings worked well in the summer, they are more than likely going to be too lean for the winter due to the cold air.

b00stingsx · 01-27-2004

oh, yah the mods are in my sig (didnt they show up?!). here they are though:

big16g w/ 34mm flapper, k&n filter, home depot spec intake, 550 rc's, walbro 190 w/ rewire, safc, pocketlogger, custom 3" exhaust, 7es wires gapped at .028, acccell wires.

i have played with my safc quite a bit, added tons of fuel to it at 5k, doesnt change.

this issue is making me so uptight. it started after i installed my walbro 190 (last mod i did).

any other ideas of what is going on before i tear into things?

ps. i didnt have the settings in the summer, i had the safc installed this winter, way before this all started.

thanks again for helpin me out!

TheBlizzard · 01-27-2004

Have you checked your fuel pressure? Have you checked for boost leaks?

CRAIG

Oh yeah and check your alternator fuse (Right Nash)? :jammin:

TheBlizzard · 01-27-2004

I was also wondering, is there computers that don't have a shift key? What do you think AJ? I am beginning to wonder since a lot of people don't seem to have one.

CRAIG

**Shane@DBPerformance** · 01-27-2004

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 · 01-27-2004

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

**Shane@DBPerformance** · 01-27-2004

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 · 01-29-2004

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** · 01-29-2004

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

**1ViciousGSX** · 01-29-2004

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 · 01-29-2004

Quote:

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** · 01-30-2004

Quote:

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 · 01-30-2004

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 · 01-31-2004

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.