P0300, P0304, and other random code issues SOLVED

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tseohs

Newbie
Joined
Jun 6, 2021
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Location
WA
Hi folks,

Many threads on here without resolution so I wanted to share this experience.

I had done the intake manifold gaskets and general tune-up on my 1996 5.7. I inspected the distributor when it was out and it looked and felt fine and was able to set the CMP to +/- 2. After the work, I drove it a few hundred miles and it suddenly started throwing random codes: P0102, P0171, P0300, P0304 and multiple O2 sensor codes.

I cleaned the MAF, installed new O2 sensors and changed cap, rotor, and plugs again but the P0300 and P0304 persisted no matter what I did. It misfired consistently when cold and plug 4 would fire randomly. Also, the misfire consistently went away when the engine warmed up which was confusing. This made me think it must be related to something that was getting triggered when warms up but was slow or broken. It wasn't an O2 sensor that wasn't warming up or the coolant temp sensor. Nothing on the scanner was providing data to indicate the root cause. This was very frustrating and I was considering selling it.

Because the distributors are known problems, I took a chance and installed a new one. I was reluctant to do it because the distributor was original, it's a low mileage truck, and the gear and everything looked fine when I had it out and then it ran fine. In fact, it still looks almost new when I took it out. Problem is solved. No more misfires and no more codes.

Thank you all.
 
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