96 Jimmy #3 misfire...STILL

[old_master]

A cherry red converter indicates an overly rich condition and could be an indication of a restriction, but no guarantee.


Do the same test with the sensors removed and pay close attention to how quickly the vacuum increases when you close the throttle.

[Sheriff8524]

Do you think it may be a faulty computer or I heard about replacing the whole spider injector setup. I feel like I'm just throwing darts now everything else is checking out as it should....Thanks

[Sheriff8524]

What do you think about the ignition switch or ignition control module? Could either of these cause my problem?

[old_master]

Just going back to basics.....

Are you 100% sure the distributor cap is wired correctly according to the diagram in post #2? (note location of cyls 1 and 3)

All AC Delco parts: 41-993 plugs, wires, cap, & rotor?

Coil wire is not grounding out on the transmission dipstick tube?

Have you removed the dog house and looked closely at the ignition coil at night for any stray sparks? (obviously with the engine running You might try brake torque also to "load" the engine)


Very doubtful the ECM, ignition module, or ignition switch are causing this.

[Sheriff8524]

Yes all parts replaced with ac delco.Wires are on right cylinders, Coil is good,what about the lower intake gasket going bad( could that cause these problems) Also have you heard of cleaning out some type of vent on the distributor itself?

[old_master]

The lower intake gasket could cause a missfire if it's leaking vacuum around the #3 intake runner. More than likely it would set a lean DTC along with your P0303. It's definitely worth looking into though.

There is a TSB that addresses the distributor. The purpose of the hole is to provide ventillation so condensation does not accumulate on the underside of the cap. Excessive condensation can cause the spark to arc or ground out completely inside the cap. In a nutshell: There is a screen in the bottom of the distributor housing that can get clogged with debris. The TSB tells you to remove the cap and rotor to access the screen, then completely remove the vent screen. It's rather doubtful this is your problem though, as excess condensation usually causes P0300, multiple random misfire, instead of continually on the same cylinder.

[Sheriff8524]

It's been giving me a P0300 code for the last few days so I think I'll check that screen you talked about as well as replace the lower intake gaskets. Would you recomend anything else since I'll have the intake whole intake off?

[terrypg]

Before installing upper intake recheck fuel pressure after pump turns off watch reading does it slowly drop in pressure? If so look at pressure regulator on spider assembly it is probably leaking. If you have injectors out of the manifold see if the #3 injector is dripping fuel also at the same time you do the fuel pressure test. Good luck.

[Sheriff8524]

all of that was checked earlier in the post, injector was replaced, fuel pressure is good.

[old_master]

Make sure you use the new design intake manifold gasket set made by Felpro Part No. MS98002T

Use a tap and die set to clean all threads in the cylinder head and the intake bolts. VERY IMPORTANT: Make certain the intake bolts are tightened in the proper sequence and to the proper torque. It is possible to tweek the block and bind the crankshaft in the journals from improper intake installation.

[Sheriff8524]

is there any difference between the fel-pro ms95817 and the msMS98002T
besides one having the valve cover gaskets as well

[old_master]

There is a huge difference! The MS95817 is basically OEM style, (what came as original equipment in the vehicle). It has a plastic frame and the seal is a type of silicone rubber. It will sprout leaks just as the original gasket did, guaranteed. The MS98002T is a totally different design using a steel frame and a rubber seal. It's a far superior design and if its installed & torqued correctly, it will not leak. The rocker arm cover gaskets are included in the set. You don't have to replace them, but it's a whole lot easier when the intake is removed.

[Sheriff8524]

Ok, thanks I will get the better set and try it out. Do you have any idea why it went from a P0303 to a P0300 with no other codes present?

[old_master]

P0303 to a P0300 means that instead of just #3 having a misfire, there's more than one cylinder misfiring.

With your CSFI system you can't pressurize the fuel system with the plenum removed to check for fuel leaks; inspect the area around the fuel pressure regulator and the nylon fuel lines going to each intake runner real close for signs of leaks. The lower intake manifold will appear "washed" in the area of a leak.

[Sheriff8524]

I checked the oil today and found a odor of gas on the dipstick. Could this be contributing to my problem?