unknown miss

[dczsvt]

so i just bought a 97 cobra today, paid 5400, has a lil over 100k miles.....well it has a miss, but ive noticed after I let the car sit for a while it wont miss and will actually run great...the guy i bought it from told me that he put in reg. unleaded fuel instead of the recommended premium fuel but I wouldnt think thatd be the reason, i even filled it up from a quarter tank with premium and it still misses. my biggest guess is of course the fuel filter but figured id see if anyone else has had the same problem. also he changed the plugs to E3 plugs which ive heard from a couple of friends that they dont like them, maybe thats another possibility?

 

[Mystic SVT]

Do a full tune up on the car, that should be your first order of business to get the car running like it should. The miss is most likely plugs or spark plug wires if they are still stock. I had a slight missing at low rpm when I would give it gas, I replaced the spark plug wires and that solved the problem. Also, might be time to do IMRC deletes if the actuator isn't working.

 

[dczsvt]

what are the imrc deletes that you speak of? this is my first 4.6 so im in the learning process all over again lol

 

[Mystic SVT]

http://forums.corral.net/forums/showthread.php?p=8442189

This link will help you see where they are located and what they look like. The purpose of IMRC's is that when the engine is operating below 3450rpm (i think thats the correct rpm) the IMRCs have the butterflys closed thus the engine is only running on 16 intake valves. This helps to make more torque since on low end since the B-heads on 96-98 cobras had low intake air velocity. Over time the actuator that opens and closes the IMRCs goes out and the car will run on 16 intake valves all the way up to redline, this will kill horsepower. Sometimes they become gunked up with oil since the injector shoots down only one of the 2 valves, this means only that one valve of the two gets cleaned up by the fuel. If you do delete them you will most likely loose some tq but if you swap to 4.10 gears or higher you will not notice this loss. I actually deleted mine with 3.55 gears still in the car and I did not notice a loss in tq, the car actually felt much stronger after 3600rpm.

 

[dczsvt]

thanks for clearing that up, ill have to look more into that
as for the miss it is fixed, went ahead and changed the plugs and one plug was foul (far rear drivers side), i went ahead and replaced the plugs with NGK G-power plugs
i must say that was the easiest spark plug change EVER, everything was completely open