So I have an 87 GT with a V6, with in the last year all sensors replaced with the exception of the MAP, TPS and IAT, all new plugs wires cap rotor and button. Fuel filter is also new, pickup coil and ignition coil are replced(MSD) for the ignition. I noticed it had a low end light load miss, so I replced the wires since they were the oldest at 2 years, no go. It ran sloppy and would hesitate for a second or two then finally kick in. I know all the plugs are gapped properly, NGK platinums, it seems to have a weak spark, from the way it starts. It doesnt hit right away it take s a second of turning over before it fires.

with the MAP unplugged it runs very well, I am going to do a reset on the ECU and see what happens first.

Should i be looking at the magnets inside the distributor, maybe replacing them, will that help? Also going to time it again to make sure it hasent fallen out of time or anything. Any suggestions would be appreciated.

It probably means that there is a vacuum line that is bad around the MAP.

I take it that you are saying it runs better with the MAP sensor disconnected.

Check to make sure the vacuum that runs to the MAP sensor is full. With engine running and the MAP electrically unplugged - then take off the vacuum line to the MAP and see if it sucks tight to your finger. If so then it really looks like you have a bad MAP sensor. If the vacuum line hardly stays attached to your finger then you have to find the vacuum leak in your line. You can compare the suck on the end of the line to the suck you get right at the manifold port.

The vacuum line that runs to the MAP comes off the manifold right next to it. It is split to run to the fuel pressure regulator (located under the upper plenum of the intake) and to the MAP.

[This message has been edited by phonedawgz (edited 12-22-2011).]

Yeah, it sounds like you're not getting vacuum to MAP. No way it should run good with no MAP sensor.

BTW: Depending on the engine, platinum plugs can help or hurt. A lot of mechanics hate them. I put a set my Chy V6 and ran good for week then real crappy, no error codes etc. A mechanic friend of my told me to get rid of the a platinum's. Sure enough, it ran perfect again. And the plugs looked great when they came out, go fig?

It sounds to me like a MAP sensor that's sending bogus information to the ECM. According to the Service Manual, if the MAP sensor fails completely: "the ECM will substitute a fixed MAP value and use the throttle position sensor (TPS) to control fuel delivery". This mimicks what you're doing when you unplug the sensor and is probably why it seems to work better that way. On the other hand, if your MAP is still working but giving faulty data, the ECM doesn't know the signal isn't good unless it falls outside of the range of acceptable values. It would throw a code 33 or 34 if that were the case.