And check and see if you can feel each injector clicking.if feel the jector clicking moved to next one.

 

Today I replaced the MAF with a brand new Delphi part. I also replaced the fuel pressure regulator with a new unit. I'm now getting P0101 and P0175. Truck is also backfiring through the exhaust under light acceleration. Seems like I'm going in the wrong direction. Misfire is worse rather than better. Also, I've noticed when I hit 3000RPM the truck has a surge of power up to nearly 6000, the feeling is almost like that of turbo lag, then a surge when boost comes on. Of course this truck is not turbocharged so I'm unsure what is causing it.

 

What mods you done to it? Is the engine shaking at idle?

 

A very mild cam is about it. Engine has a very mild shake at idle.

 

Have you checked Compression?

Did you check pushrod length after the cam install?

Did you check the injector circuit on #4 with a noid light to verify a consistent signal?

Did you check all your connections at the injectors to make sure the pins are not bent and that the connectors are seated properly?

Intake gaskets are cheap if you know where to look. Get the upgraded GM ones. If they are original, I can almost guarantee they are no good. The rubber need to be pliable and protrude past the plastic they are molded to if they are smushed down and barely sticking up, They are no good and they are not sealing properly.

Search ACDelco 89060413 on ebay. You can occasionally find them for $35 with Free shipping.

 

Try the things brick said get back with us. Mostly compression check. It beening po300 code you have check everything random misfire code sucks. Most costly code there is

 

The misfire is/was not isolated to a single cylinder so compression doesn't seem to be the issue.

Pushrod length was measured during engine build.

Cylinder 4 is no longer the only misfiring cylinder and doesn't seem to be even the primary misfiring cylinder anymore.

Pins and injector connectors have been checked.

Intake gaskets were new with the engine rebuild. I cannot find an air intake leak.

I replaced the MAF sensor and fuel pressure regulator and since then the P0300 has not come back but was replaced by P0101, P0172 and P0175. I have a new MAP sensor on the way although since ordering the tuner has told me the old one is functioning properly. Tuner sent me a new tune to account for new MAF. Hopefully that will help the rich fuel situation. When the new MAP arrives I'll load the new tune and see what happens.

 

Update: Problem still not resolved. Time, money and parts thrown at this thing with no success.

New plugs, wires, MAF sensor, MAP sensor, O2 sensors, fuel filter, fuel pressure regulator, new grounds for the coil packs, swapped coil packs around, swapped fuel injectors around, New tune, crank relearn, additional grounds run to the ECM and additional ground strap run from the block to the chassis.

Still having the same problem. Low RPM misfire from idle to 3000RPM. When the truck hits 3000RPM the misfire stops and it takes off like a rocket. It's like flipping a switch at 3000rpm. What would explain this?

 

At this point, it sounds like a bad tune.

P0101 Mass Air Flow (MAF) Circuit Range/Performance Problem
Basically the PCM detects that the Mass Air Flow (MAF) sensor frequency is below a predetermined value.
Read more at: P0101 Trouble Code - Mass Air Flow (MAF) Circuit Range/Performance Problem
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P0172 System Too Rich (Bank 1)
Basically this means that an oxygen sensor in bank 1 detected a rich condition (too little oxygen in the exhaust)
Read more at: OBD-II Trouble Code: P0172 System Too Rich (Bank 1)
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P0175 System Too Rich (Bank 2)
Basically this means that an oxygen sensor in bank 2 detected a rich condition (too little oxygen in the exhaust)
Read more at: OBD-II Trouble Code: P0175 System Too Rich (Bank 1)
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If it's that rich and there is raw gas going into the exhaust it will light off in the exhaust as you described earlier.

 

The new tune mentioned earlier fixed the codes you mentioned. P0300 is the one I'm still fighting.