I just had a 305 TPI motor replaced with a 350 TPI motor. The car is a 1986 IROC and is a MAF setup. The 350 came out of a 1991 speed density car (Z28). The issue that I'm having is the 3 vacuum ports on the plenum. 1 goes to the FPR and the other 2 go to what? The car runs until I plug either one of these ports up, then stalls. Can anyone tell me what I'm missing here? I know the MAP sensor was plugged in here on the '91. Thanks in advance.

 

Something to think about, since you didn't mention it, I assume your trying to run a '91 350 with '86 305 ECM?
What about EGR, is it vacuum or digital?
The other port is for A/C head, vacuum reservoir, and cruise control.
Not sure of differences in EVAP, EGR, and A.I.R system between '86 and '91.

 

You must have a problem with your IAC, because those ports should be hooked up. RGarcia63 is correct, one goes to the MAP, the other goes to the vacuum controls for the A/C and the cruise control.

The EGR valve is different, as the MAF cars had a temp sensor screwed into the EGR to detect if its working or not. The MAP cars have no screw-hole, as they used manifold vacuum to detect EGR status.

 

No I didn't even think about any of that. The emissions is not hooked up physically and not diabled at the ecm, so no O2, A.I.R., Catalytic conv., The EGR is from the '91 and yes the car has the 305 ecm. I did a search and found out that the '87 IROCs used the same ecm ('7165), but the esc mod is different. I will check the IAC today.

 

Okay, first, thanks for the replies. I reset the IAC and readjusted the TPS today. I also plugged in the vac line for the a/c control. The TPS has one of the screws broken off in the TB, but seems to be holding for now. I got the base manifold, fuel rails & injectors, plenum, and the runners off the motor that came out of the car. Hopefully the plenum will clear some of this up. The car runs out real good and pulls strong once warmed up, but still runs rough up until then.

 

Your running in limp home mode.
Another assumption - Check engine light is on, you don't have it connected, the bulb is burnt, or you're just ignoring it.

I can understand not using the air pump, cat, and EGR, but you need to be either in open, or closed loop, but without the O2 limp home mode is all you'll get.

 

Okay, so if I get the O2 hooked up, that will take me out of limp home mode? I will try that next. Thanks for the advice.