ok .... i got a 2000 LS that has a misfire PO300 .... ok lets see if i can put this into words... i have never seen this before in 40 years.. i have other problums but the misfire is the one that has me stumped. it has been sitting for 6 years. . so i did all the bring her back stuff. and she was ok ... untill it started missing at idle. .. ok snap on sez cly 5 and 7 ... ok lost spark and had a coil code. (K) never seen that before. new coils still misfire. did a comp test .. checked that i had spark .. all is well. so while in data mode everyone is home but for 5/7. take it off of idle 1200 or so and no 7 comes back BUT i drop no 6. so off idle i have 5/6 misfire. but wait .. theres more ... now the MAP shows 3.0 HG and -0.02 volts. key on engine on OR off. MAP plugged in or not i run the wiring looking for mice damage and all i found was snake skins so thats good. so am i fighting a lifter problom??? i have heard of it before on a 5.3. sence the misfire was there before the MAP i will deal with it later.... im just looking to find out why the misfire is there and why it is changing holes ...... thanks .... any help would be nice. . what am i missing??? im sure it something simple but not knowing much about the LS don't help.

 

With a car that has been sitting for 6 years I would guess you have some clogged injectors…what do your long term fuel trims look like at idle ??..if around 13-16 % that’s most likely it…do you mean 30.0 inHg and not 3.0 ??

 

trim is ok with left bank a bit off do to the misfire .... but showed good on a injector balence test ....and flow fuel. i did take them out today and test them. And yes .. i mean 3.0 in HG and -0.02 on the volts. with no change running or not .. plugged in or not. im going to change the oil and run some stuff in it and change it again and see if that helps. just kinda strange the misfire changes holes depending on engine rpm. thats why i was wondering if the mds mite have something to do with it. ...

 

Your MAP should be around 30.4 KOEO or so and 10.0 inches of Mercury or so at idle…you will need to check the wiring and if OK you’ll need a new MAP sensor..what’s your MAF read at idle ??…should be between 6-7 grams per second with engine warmed up. What’s the long term fuel trims look like at idle ??

 

it don't matter if its running or not ... plugged in or not ..... it reads 3.0 HG and -0.02 .... and the meter sez the map is ok but it had the miss thing before that happend. so i don't think that the 2 probloms are conected. runs just the same now as it did before the map thing started. figured id look into that more after i figure out the misfire.