my truck runs rough
03-17-2009, 09:39 PM
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my truck runs rough My truck runs ruff, sorry about the speling...
Im a little embarrassed about this, but i have a 1991 chevy Z71, and it want iddle and its running rich and it surges really bad. Its not the EGR Solinoid, or the EGR it self, and its not the MAP sensor, but it acts like the MAP sensor if you know what them TBI trucks acts like when it comes unpluged or goes bad. I put a brand new GM crate motor in it 2 summers ago.
Im a GM mechanic and dill with **** like this an a day to day basis, but this bothers me that i cant figure out what is wrong with it. It is got to be something simple.
This is not my dailey driver, it only gets drove about 5000 miles a year.
Sorry about the THREAD but please help if you can.
Im a little embarrassed about this, but i have a 1991 chevy Z71, and it want iddle and its running rich and it surges really bad. Its not the EGR Solinoid, or the EGR it self, and its not the MAP sensor, but it acts like the MAP sensor if you know what them TBI trucks acts like when it comes unpluged or goes bad. I put a brand new GM crate motor in it 2 summers ago.
Im a GM mechanic and dill with **** like this an a day to day basis, but this bothers me that i cant figure out what is wrong with it. It is got to be something simple.
This is not my dailey driver, it only gets drove about 5000 miles a year.
Sorry about the THREAD but please help if you can.
Last edited by Greg Pippin; 03-17-2009 at 09:55 PM.
03-18-2009, 02:11 AM
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What the map sensor voltage @ idle? pulling good vacuum @ idle?
I remember alot of crap grounds on these at the intake, thermostat housing & the back of the head too.
I remember alot of crap grounds on these at the intake, thermostat housing & the back of the head too.
03-18-2009, 04:58 PM
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MAP is at Around 5v at idle, great vacuum at idle.
when i pull the brake booster vacuum line off it will clear up and run good???
when i pull the brake booster vacuum line off it will clear up and run good???
Last edited by Greg Pippin; 03-18-2009 at 07:06 PM.
03-20-2009, 01:15 AM
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5 volts at idle! That should be about 1.5 1.8 volts @ idle on the signal wire with 17-20hg of supply vacuum to the map. Over 4 volts with 0 hg manifold vacuum. There's your first issue. The booster hose off your creating a large vacuum leak which helps it deal with the overfueling.
You need to see if you have a a map issue, a wiring issue, a mechanical engine problem preventing proper intake vacuum or an ECM issue.
You need to see if you have a a map issue, a wiring issue, a mechanical engine problem preventing proper intake vacuum or an ECM issue.
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03-21-2009, 12:11 AM
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ok, thanks. im going to get it out when i get off of work tomorrow and mess with it some more. i have 3 of them trucks, two 1991s and one 1992. if i cant figure it out im going to swap parts around and see what happens. if yall can think of anything ealse, just let me know.
