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89 Caprice Timing unstable, advances too much
Well here goes. Totally new to this site. I bought an 89 Caprice last year for a work car. It is a carbed 305. Well, this winter I took off the RH cylinder head as three exhaust manifold bolts were broke. Reinstalled everything and now after assembly, the thing will barely run after you plug the four wire connector back in at the distributor. During all of this stuff I did take the ignition module out and clean things up in there as there was lots of green gunk.
Here are some things I've discovered. It idles smooth and revs pretty good with the four wire disconnected. If I plug the four wire in the timing advances just a little, 3-4 degrees. However, if you crack the throttle at all it advances wildly and spark knock occurs. I am verifying this with my timing light as I am doing this. So, I said load and speed cause the timing to advance. So, I unplugged the MAP sensor and everything runs really smooth, even revs up nice instead of spitting and coughing. OK, bad map sensor. However, I backprobed the middle wire of the MAP sensor and 0.5V with engine off, key on, which would be the same as wide open throttle. With engine running I have about 3.9V at idle. Which seems pretty good. I just can't believe the MAP sensor is bad, however, if I plug the MAP back in at idle, with the four wire connected, it will just about kill the engine. My worry now is maybe the full MAP signal voltage is not getting back to the ECM.
It really isn't driveable without the four wire connected as you have crap for road power as there is no spark advance.
I have checked spark plug wire location and firing order 100 times. Also, checked to make sure the valves weren't too tight.
Any ideas anyone?