I'm rebuilding a 91 RS origionaly a V6 car. I took a motor out of an 88 IROC, rebuilt it, and dropped it into the RS. After searching around, I located a 'speed density' wiring harness from a 1991 Z-28, and installed that onto the car as well. I finally turned the key and to my suprise... the car started!!!!! My problem tho, is the car won't stay running. It starts up fine, idles roughly, then stalls. If I give it some gas, she stays running but very rough, and no power (I tried to move it in my driveway, and felt like i was driving a honda . Its missfiring almost as if the timing is off, but that doesn't seem to be the case. It has been retimed 6 or 7 times, by a few different mechanics and always the same issue. I'm wondering if anyone else ever had this problem.

I know on the air intake tube on the 88 is the MAF sensor and on the 91, there is no MAF sensor on the intake tube. I was told that this could be a problem for the motor if this isn't plugged in, but I have an ECM from the 91 Z-28 as well, so my thought is it would just bypass what it doesn't need.

I'm also going to check fuel pressure, it has a new fuel pump, so it SHOULD be okay, but I know thats an easy test, just havn't had the time.

Anyone with any help or suggestions would be great! Thanks

 

You do not need the MAF sensor at all if you swapped it to speed density so disregard that advise. is the MAP sensor connected to a good vacum source? I'm not sure but the V6 ESC module may be different the the V8. thats all I can think of rigt now

 

Thanks for the reply, I've been real busy and havn't had any time for the car Its being neglected. I'm home for a few days tho, and I want to get it running, I will check the vaccume lines on the MAP sensor. Also, where exactally is the ESC located, I read somewhere its in the distributor, is this true? I really don't know, if it is, then do you know if its different from 88-91? Thanks again for your help! I want to hear her purr!

 

Battman, I checked the vaccume line on the MAP sensor and sure enough, it seems to have done the trick, The car is running real good now. Thanks for the advice!!!

 

That's good news that you got it running a lot better. One other thing you might want to look into is the knock sensor that's screwed into the passenger side of the engine block. The speed density knock sensors send a different frequency to the ecm than the MAF knock sensor. If you still have the original 88 knock sensor in the block, you need to replace it with a 90-92 sensor. The wrong frequency being sent to the ecm can cause it to retard the timing at the wrong times. Also make sure you get the right one for your size motor. The 305 and 350 sensors have different sensitivity levels. As far as the ESC goes, you don't need to worry about that anymore, on speed density cars, it's controlled inside the ecm. Your ESC module is located on the driver's side of the firewall behind the brake booster. It's a flat looking piece with 5 prongs sticking out where the plug goes. You can go ahead and remove it to clean up your engine compartment if you want to.