high rpm bog down

[riotpolice75]

the past month or so anytime i really get into the gas it seems to just fall flat on its face around 5000 rpm. this has really been buggin me so today i pulled it into the shop in school and hooked up a scan tool to it. nothin out of the ordinary, everything looked good so i took it for a ride with the scan tool hooked up. i was mostly interested in seeing what the short term fuel trim did when it bogged out. i got on it and right on cue it fell flat on its face 4 separate times. i made a movie with the scan tool four separate times and every time everything looked good. the fuel trim # changed by about 10 points max but thas to be expected when your really into the gas.



its NOT spark related, that im fairly certain of. its not missin, it definately feels like its just runnin out of fuel or like the valves are floatin. i dont think its valves though, its only started doin this in the past month. can yous think of anything im overlooking?







smith

[rayL]

what was your 02s reading? What exactly was the short term fuel percentage. also what motor we speaking of?

[spacecadet]

Sounds like the fuel filter may be starting to get a little dirty. Chances are if you look into the movies it will show you that you are starting to lean out the air/fuel ratio too quickly. See what the O2 counts are.

Note: However, some vehicles will kill them selves in order to be not \"blown up\" due to being over reved.

[ZR1BLAZER]

dont you have a 305 TBI motor? that actually sounds right. i cant see it living in the 5000rpm range. i say check the filter and with the scan tool you should be able to see what the timing is doing at 5000rpm. like space said. it might be trying to protect itself. once those motors get some miles on them the ecm will protect it. timing and fuel?? thats about all i can think of.

[riotpolice75]

to be exact, the short term went as low as 121, nothing to be concerned about. the o2 is switching between .120 and about .890. the highest i saw on the o2 was about a .915 and the lowest was about a .047. yea, its a 305. as far as over revving it goes, i normally dont shift till about 4500 or 5000. thats right about where its missin at. if im really on it im revvin it to 6000. i wouldnt say i do it regularly, but it sees 6000 at least once or twice a week.



sadly its an OBD1 and it dosent give me timing info. the 2 things i wanted to see were that and the injector pulse width. another interesting thing i discovered today. im runnin about 11:1 compression....at least by my calculations. now i need to figger out how.







smith

[ZR1BLAZER]

go to smokemup.com they have some good calculators. OBD-1 305 TBI with 11.1 comp?? im surprised you havent had problems earlier. good luck.

[riotpolice75]

i compression tested it and it came back at about 200 psi per cylinder +\\-10 psi.







smith

[coppergmc]

Unplug the wire that the book calls for when setting the timing. Set the timing where you want it and see what it does. If nothing changes, you know it\'s not a timing problem and you can reset the timing and hook the wire back up. 200 psi is too high. Ping city without race gas.