LT1 SES light comes on and off

[kensz28]

My 95 roadmaster has been out of commision a week now. Last friday the SES light came on and ran like crap. It went off and on for 30 minutes til I got home. When it was on it would miss and ping and generally have no power. When off it ran great. I put new tps sensor on to no effect. Put old one back on. I cleaned iac motor and no change ( new one is $115.00) So I got my buddy with a shop to put the Snap-On on it and it showed MAP sensor out of range. I put a new MAP on and it still threw SES light on and off. No vacum leaks, no wire damage that I see. My friend says ECU might be taking a dump on me. How do I know for sure. WTF? is wrong with my car?

[5.0THIS]

Did your buddy test the MAP sensor with a ohm meter to verify that it was bad before replacing?

[Too Fast]

Sounds like a classic spark plug wire failing. Good luck changing those bad boys, if you route them like OE does. I've fixed many LT1 engines no start from a corroded ignition coil wire, maybe yours is starting that? Take the coil wire off and look for any crap at either connection, usually it is at the coil. If so, change the coil and the wire. You might be able to get just the coil wire if that is the problem.

Your MAP sensor will show out of range if the car is missfiring. Missfire = poorly running engine = low vacuum = sets the code for out of range.

Have your fuel pressure checked if the plugs/wires/distrubutor cap checks ok. Is there a waterpump/coolant leak onto the Optispark unit? That would do it also.

[kensz28]

I forgot to mention the opti and plugs are new. MSD. The motor is .030 over, all new bottom end, aluminum heads with some work done like screw in studs/guideplates. Hooker headers and a coldair intake. I keep my shiznit up. I'll take previous posters sugg as well to test MAP. A new one had same results too so...........

[DannyK]

Nr 1 ....connect the OBD1 scanner and read the codes ,.... check the fuel pressure check spark plugs ...... ..... check the ignition wire and connections...