Go_Fast67

The other day i noticed my 91 firebird has a miss,its fine when its cold but once the engine gets up around 200 it starts to miss,im stumped cant figure it out,it has a 305 in it pretty much all stock.any input would be nice thanks

Gtpguy

Something is getting heatsoaked, or the problem happens once you reach closed loop. Do you have TPi or Tbi, or V6? New plugs and wires (GM or some MSDs, DO NOT GET CHEAPIES!!!), o2s, MAF relays (if TPI).

Just been there and done all that.

Go_Fast67

It has Accel plug wires that i put on last yr,i just replaced the plugs with NGK V power last weekend,its a tune port setup

Gtpguy

I totally didn't even comprehend the "1991" part. You don't have a maf, you're running speed density. Have you pulled your spark plugs to see how they are? Black is running rich which will foul out spark and cause misfires. Are there SES lights when it happens? Maybe you need a new o2 sensor. A bad o2 will cause misfiring, but nothing can be sure until you know what codes are popping up and where to look at, you know?

I'd really check the the plugs, at least the driver side. Also, run along the wires to see if they are torn at any spots. When did you change out the cap and rotor?

Go_Fast67

i pulled the plugs last weekend they were fouled but that was prob from me driving it with the miss,i replaced the cap and rotor last year,ive checked all the wires they are all still in good shape, no burns or wear marks.It hasnt thrown a check engine light,i wish it would so i could just hook up the scanner and get this over with.Just in case im going to check and make sure that the light even works lol

Gtpguy

No need to pull the cluster out to see if the bulb is good, just scan it anyway. Obd1 doesn't have a code for random cylinder misfire. Did you pull all 8 plugs out? Which ones were fouled? If all the fouled plugs were on one side, thats pointing to a bad o2 for that side.

Go_Fast67

well i messed up i just pulled them all and didnt keep track of them so idk what ones were fouled.i drove the car yesterday right about 200 to 210 is when i starts to miss,i cant feel the miss at w.o.t and car still seems to run good just at part throttle and idle is misses

Gtpguy

Have you scanned the car yet? Without a scan you can't see what codes might be pending or stored (if your light is burnt out) what the engine parameters are in real time to pinpoint a problem. Have you checked your timing recently?

I've been battling codes for 2 months in my 1989 GTA. I've replaced so many things, and just found out my ECM is crap, not reporting the o2 sensor to the MAF, and my Charcoal Canister was hooked up wrong. Both items don't throw codes. Nor do misfires. I had a friend with a good scanner and it showed us what was wrong one parameter at a time, you just got to know where to look.

Are you on thirdgen.org? If not, get over there asap. This isn't really a 3rd gen tech site.

Go_Fast67

Im taking the car to work with me tomorrow to have my co worker scan it for me,it threw a check engine light once then it turned back off.Do you know if obd1 stores codes or once the light goes off is the code gone

Gtpguy

Do the paperclip code read. The code will be stored until the battery/ecm is reset.

Go_Fast67

Ok got the car hooked today,found a knock sensor code what that cause it to run this way?? also noticed a O2 sensor wire looked to be in pretty bad shape. Only misses at idle and part throttle anything over about half throttle and wot it runs fine

Gtpguy

What was the exact code? I looked through my TPI book and couldn't find a code for the Knock Sensor.

But definately replace that o2, they are only $20 or so. And change out the plugs as they are all fouled out again and reset the battery. But let me know what code popped up.

Go_Fast67

well i already reset it but i wanna say it was code 43 but idk,also the car is staying in open loop

Gtpguy

If it was code 43, Check the wiring at the knock sensor. See if any spark plug wires are touching it as well, or any other wires and move them away if so.

Go_Fast67

today i replaced the knock sensor,if did not fix the prob,all the wires are out of the way.next im going to adress the passenger side o2 sensor.the wire is kinda messed up so im going to replace it and hope for the best