91 350 TBI rough idle and no power at all

[sdrgac]

hey guys, i recently aquired a 91 chevy C2500 with a new rebuilt 350 tbi. problem is that i cant seem to get the truck to idle or run correctly. it will run while fluttering the pedal but that is all. changed temp sensor, ERG, cleaned and rebuilt the TBI, replaced all vac lines, fuel filter, added sea foam....and a few others. i have read that it could be the fuel pump (small connecting hose) i have yet to check the fuel pressure but with the in-let off, the pumps runs well. with the MAP vac line plugged it idles better but still dies after 30 secs or so. help please.....

[Scrapper]

Originally Posted by sdrgac

hey guys, i recently aquired a 91 chevy C2500 with a new rebuilt 350 tbi. problem is that i cant seem to get the truck to idle or run correctly. it will run while fluttering the pedal but that is all. changed temp sensor, ERG, cleaned and rebuilt the TBI, replaced all vac lines, fuel filter, added sea foam....and a few others. i have read that it could be the fuel pump (small connecting hose) i have yet to check the fuel pressure but with the in-let off, the pumps runs well. with the MAP vac line plugged it idles better but still dies after 30 secs or so. help please.....

first i'd check fuel pressure and change gas filter if you haven't already? could be out of timming also and are you sure you put vaccum where they was before you started changing them? i'm thinking fuel pump tho. also did it run good when you bought it?

[sdrgac]

i have changed the fuel filter. and no the truck was not running, it was a trade for an old junker dune buggy. motor has a fresh rebuild--less than 1 hour run time. truck was parked for 2-3 years due to a burned piston. i need this to run but dont have a bunch of funds to repair. hopeing it is something simple

[MT-2500]

Originally Posted by sdrgac

i have changed the fuel filter. and no the truck was not running, it was a trade for an old junker dune buggy. motor has a fresh rebuild--less than 1 hour run time. truck was parked for 2-3 years due to a burned piston. i need this to run but dont have a bunch of funds to repair. hopeing it is something simple

Any check engine lights or codes set?
You can pull codes by jumping pin A and B on diagnostic connector.

[sdrgac]

thank you for the replys. there have been no check engine lights and the diagnostic tool i have is for a newer model. (plug is not the same)... i am in the process of finding a gauge set to test fuel pressure. i have read that optimum is 12-13 psi. what is the absolute lowest that the truck will operate at. also while watching the 2 injectors, the fuel does not spray out it trys to but more often than not it seems to dribble or run out. to me this says the pump pressure is bad... am i right in thinking this? thanks again

[MT-2500]

Originally Posted by sdrgac

thank you for the replys. there have been no check engine lights and the diagnostic tool i have is for a newer model. (plug is not the same)... i am in the process of finding a gauge set to test fuel pressure. i have read that optimum is 12-13 psi. what is the absolute lowest that the truck will operate at. also while watching the 2 injectors, the fuel does not spray out it trys to but more often than not it seems to dribble or run out. to me this says the pump pressure is bad... am i right in thinking this? thanks again

Specs are 9-13 lbs.
Anything in that range is good.

You can jumper pins A and B and get codes.
If any codes post back code no.
Does it have good injector puls and good hot blue spark to all plugs?

[sdrgac]

spark is hot. but the injector pulse is a little weak. why would the motor run more smoothly when you plug the MAP sensor vacuum line? it idles better when it is plugged. could these two items be related?

[MT-2500]

Originally Posted by sdrgac

spark is hot. but the injector pulse is a little weak. why would the motor run more smoothly when you plug the MAP sensor vacuum line? it idles better when it is plugged. could these two items be related?

May be a bad MAF sensor.
What is voltage reading on MAF at idle and 2K rpm?
Check for codes and then clear codes and recheck for any codes coming back.
Post back any codes you get befor and after code clear.

[sdrgac]

MT, first, thank you for the input...
i am by no means a mechanic but i do know how to turn a wrench, lol.

what are you guys taking about when you say use a paper clip to test between pins? or would it be easier if i just took the truck to a mechanic and let them fix it? i am hopeing that i can do this on my own as i have low funds at the moment.... i have a MAF sensor that came off of an older 87 350 tbi... tried it and same issue, there seems to be way to much vacuum on the line that runs to it from the TBI.

can these vehicles run without the vaccum system hooked up? i live in texas and this will be an off road vehicle only so emissions is not going to be an issue to pass. this will primarily be a hunting truck and farm use vehicle. just need it to run as best as it can.... thanks

[MT-2500]

Originally Posted by sdrgac

MT, first, thank you for the input...
i am by no means a mechanic but i do know how to turn a wrench, lol.

what are you guys taking about when you say use a paper clip to test between pins? or would it be easier if i just took the truck to a mechanic and let them fix it? i am hopeing that i can do this on my own as i have low funds at the moment.... i have a MAF sensor that came off of an older 87 350 tbi... tried it and same issue, there seems to be way to much vacuum on the line that runs to it from the TBI.

can these vehicles run without the vaccum system hooked up? i live in texas and this will be an off road vehicle only so emissions is not going to be an issue to pass. this will primarily be a hunting truck and farm use vehicle. just need it to run as best as it can.... thanks

The paper clip can be used for a jumper for jumping pin A and B on diagnostic connector.
Best to check codes and then clear codes with a neg battery disconnect and the hook batery neg back up and drive and retest for codes.
Anything metal that will connect the two pins together.
And then turn key on and read codes from check engine light.
Count both long and short flashes for code.

No way you can get to much vacuum on map sensor.
It has to have full engine vacuum and be hooked up for it to run engine right.
Unpluging it will make engine run full rich if sensor is good..

[MT-2500]

http://www.troublecodes.net/GM/