Need S-10 diagnosis

[Gn-ing]

Working on a 96 S-10, 2.2 engine...runs rough at idle.. has low vacuum about 7 hg...should be about 17...compression is about 160lbs in all clys..new vac hoses and pcv..all connections ck'd//
I pulled the timming cover,and verifed cam timing..out of ideas..can you help?

 

[87gninpa]

dont have any advice myself, but i work in a shop and one of the better techs has the same truck. ill ask him on monday, he'll know for sure....also, theres a few board memebers that work for gm and im sure theyve run into this problem, try reposting asking for gm techs...HTH

 

[myclone]

Are you getting any random misfire or IAC codes?

Random misifire can usually be traced to ign but if that checks out then take a look at the IAC for proper operation.

 

[Iceman]

Check the EGR valve.They are bad about getting some carbon in them and not closing all the way.

 

[Gn-ing]

we replaced the egr valve,and even blocked it off once to test what would happen..the only code we got was MAP high out- put,but i think it is because of low vacuum..we put on a new one ,no difference. We are presently pulling off the intake to ck for cracks or a bad gasket..I just don't get the low vacuum thing,with good compression,the vacuum should be high,but isn't.

 

[John Larkin]

I agree with the intake gasket. Have to be that unless you can hear a massive leak. Vac should 15 at idle minimum on most any production car.

 

[steveX]

It is alway good to apply a thin coat of silicone to both side of the intake gasket before installing. sometime you never know what the OEM will use and how the make they gasket, but i have seen some screwed-up gasket in new gasket kit.

also make use you don`t have any vacuum leak (hoses).

you find out if the intake gasket are leaking. You can use a can of CARB spray for and external leaks. if the gasket is leaking internally. You will have to remove the oil cap cover and place your hand over the hole while the engine is idling. if a suction is present when try to remove hand, You may have a internal gasket leak.

hope this help.

 

[Gn-ing]

Found the problem today, another owner had a used clyinder head installed,they used a cavailer head,which is the same,but takes a different EGR to cly head gasket,they used the passenger car one,which,didn't line up with the truck EGR adapter,so,the egr bipassed directly into the vacuum to the exhast all the time,so hence a huge internal vacuum leak...had to remove the head to fix..

what a headache...