P0304 Code driving me crazy

[MazingerZ]

Hello, first of all sorry for the long post,

My 97 Tahoe (2Dr) with a 383 and 225k miles went for a engine refreshment after experiencing severe misfiring, hesitation, backfiring and drinking 1litre of water per day(Intake Gasket).

Performed a compression test and all cylinders had 175psi except Number 7 that had 120psi.

So I decided to take the engine out and torn it apart, everything was ok.

Got a machine shop to machine the crank 0.010", pressure test the Edelbrock 60989 heads, the block was in excellent condition.
Replaced Rings, all bearings, FelPro Gaskets and Genuine GM Gasket for the Lower Intake Manifold.
Replaced the cam with a new one COMP Cams 12-422-8 CS XR270HR-10 (same cam it had), as metal shavings from the distributor gear marked the adjacent cam lobe.
New Timing set Cloyes Gear C-3001K
New set of Edelbrock Valves, springs, Seat, Cups and Retainers.
New High Volume Oil and Water pumps.
New Delphi Distributor. (Would the gear on the dist be Melonized?)
New Delphi Injector Spider MPI conversion Assembly
New Spark Plugs Champion RC12YC and Accel 9042 Extreme Cables.

After assembly, it fired up no problem, followed some guidelines to set the cam retard in the correct position by turning the Distributor assembly so that the screw on it is 1mm away from the intake manifold, it worked like a charm.

A few hours of running, then the engine started to misfire on cylinder number 4 setting the code P0304 with a very strong smell of gasoline (running rich)

So, I fixed an exhaust leak it had before the cats, hoping that it would solve the misfire. It improved the engine idle but still sets the P0304 code and now the smoke is white then blueish (burning oil?)

The mechanic has opened the valves cover; re adjusted the valves and says that everything should be ok.

What do you think it could be guys?

Any help would be appreciated (sorry for the long post)

Thanks

 

[BURBAN GUY]

Check your fuel presure reg. or fuel spider is going, intake gasket. That all I can think of right now.

 

[Chris]

Are you still on the stock PCM? That thing needs a tune before it will ever run correctly.

 

[MazingerZ]

Thanks for the responses,

I can check the fuel pressure, however the engine was running rich, which suggest that fuel delivery is not a problem, I also got a positive result when I did the spark test on cyl 4.

The PCM was tuned by fastchips when the 383 went in for the first time (100,000 miles ago) I just "refreshed" the engine.

A new compression test has been done, all cylinders are 175psi except cylinder number 4 that has 150psi, the difference is deemed acceptable.

 

[BURBAN GUY]

If the reg is leaking it will be dumping fuel down the #4 runner making it rich, or the popet is leaking on that cylinder making it rich.

 

[MazingerZ]

If the reg is leaking it will be dumping fuel down the #4 runner making it rich, or the popet is leaking on that cylinder making it rich.

I have been thinking that maybe the New Delphi MPI injector spider is defective from factory or something...

 

[BURBAN GUY]

Kindof sounds like it to me.

 

[MazingerZ]

reporting back,

I haven't had the chance to check the fuel pressure but I did remove the new Delphi spider assembly and fitted the old spider back on.

Code P0304 is no longer a problem but I now have code P0301 with the occational bank 1 O2 sensor code too.

The engine shakes between from idle to 3000RPM after that it sounds/runs stronger.

I am going to return the Delphi assembly and get a Delco replacement (even though it may be the same one)

any thoughts?

 

[RHamill]

You probably just need o2 sensors guy..

 

[MazingerZ]

thanks for the response, I am thinking to replace at least the O2 sensor on Bank No.1... any pointers?