'96 AWD engine misfire code PO300 when coolant is cold

[MNastroman]

Once the engine is a couple miles after fully warm (per the temp gauge), it stops misfiring and runs well for 190M.

I'm in Minnesota, its still kind of cold here too 30 to 40F (April 23). I will know what warm weather does to this in a couple weeks I suppose, (70F soon?)

I'm trying to figure out if its a fuel problem, ignition, sensor or CAT.

Its been very damp here too, why I was thinking this was an ignition dampness problem that goes away once the engine compartment dries out from engine heat. But today it was 40 and dry and still misfired until the engine was warm.

It misses at all engine speeds when engine is cool. Feels like multiple cylinders effected. Once warm it runs fine at all speeds, or at least the misfiring is not noticeable.

I installed new plugs, wires and cap about 20m ago, just for the he// of it. Ran great. MAS and EGR are about 30m old.

Aftermarket Magnaflow CAT (cheap weld in) was installed and tripped the PO420 code after 8K on it. The PO420 code doesn't seem to effect the driveability, the PO300 trips after I feel the engine misfiring multiple times. I have read the codes and cancelled them to figure out when they come on many, many times now. I realize I need an OEM cat, but I don't think that is my main drivability issue causing the cold misfiring.

I had a shop change the manifold valley gaskets 4 months ago, coolant was leaking externally drivers side front of valley. Van drove great after that until a month ago. With 2 vehicles, I dont drive this much, trying to find the problem.

So, I'll see how it drives tomorrow morning (30 and dry) vs tomorrow afternoon (40 and rain).

I have not pulled the doghouse to inspect anything like the dist/or plugs wires yet (or the water bottle spray test). Hate the thought of changing plugs since I did that 20m ago.

If this was a fuel problem, it wouldn't matter cold engine or warm right? Again, Its only is noticeable cold.

Any ideas or questions to help figure this out?

thanks in advance

[Jasen]

pop the dist cap and check for corrosion and moisture

[AstroWill]

Also when you have the distributor cap off, look for excessive play of the rotor.

[MNastroman]

Dry weather today, and ran fine.

The dist cap and rotor have less than 20m on them, BUT they were napa parts, I have heard that 4.3 motors like the stock AC delco ignition parts. I'll pull the cap and check it out for corrosion. The coil is stock 190m on it.

[MNastroman]

Also when you have the distributor cap off, look for excessive play of the rotor.

Your talking up and down play of the dist shaft? Any guess how much up and down play its supposed to have?

Does the distributor shaft/base just pull up and out of the manifold after removing the anchoring plate and bolt?

thanks

[AstroWill]

Play back and forth while you twist it to clockwise and counterclockwise. What happens is that the drive gear wears out on the bottom of the distributor. It should have some play, but not much at all.


Yes, the distributor does just pull up after you remove the retaining bolt, just make sure to mark the position, and don't turn over the engine while you have it removed.

[MNastroman]

I'll check it out when I check the cap and rotor. If all looks well, I plan on misting the wires with a spray water bottle with the engine running.

Now that its been dry for a few days its been running realy good (finger crossed), it looking more like moisure is causing the misfireing. If thats the case, I've proven to myself to only buy the best ignition parts or origional delco, since what I have was mid priced from napa or orilley and didnt last very long.

[AstroWill]

Mine was the same way with the warn out gear.