91 TBI 5.7 Missing

[Gamikatsu]

so my 91 TBI has 130K miles on it, has full tune up, new distributor cap rotor, shaft, new wires, new plugs (AC delco rapidfire plats gapped .035)

i can't for the life of me, get this little miss... about every 2-30 seconds, kind of random, just a slight miss, you can hear and feel it in and out of gear. i pulled and cleaned the EGR, double checked the cap and rotor contacts, checked for vaccum leaks, checked the PCV valve, and can find NOTHING that would cause the miss... old plugs were about as close to perfect as you can find. very fine, light brown/grey deposits, tip and electrode looked darned perfect. Anyone have any ideas???

Thanks.

 

[Swaggerwagon]

my guess would be the coil, or ignition module are beginning to fail...but i lean more toward the coil...but be absolutely sure the sensor grounds on the intake manifold are good before buying any more parts...

 

[Gamikatsu]

Fixed it!

Well i am 99% sure the preoblem is fixed. under the advice of a 25+ year ASE master Tech, who is a close friend of mine, i put a bottle (1 QT) of Marvel mystery oil into the crankcase, and voila... miss is gone... he suspected a sticking valve. i'm going to do a few short interval oil changes using the marvel, and try and clean her out. on the lighter note, the spark plugs that came out of it, were as close to perfect as i've ever seen come out of a old chevy... and i finally got the timing issue corrected. my gas MPG's have easily doubled. I found barely finger tight spark plugs on all 8 cylinders, Bosche platinum spark plugs (garbage) and the cap/rotor were pretty torn up on the contacts so all that fixed and she runs like a champion!

 

[Gamikatsu]

and miss is back... going to toss a ign coil in and see what happens i guess....