P0300 and P0302 With new long block 1996 K3500 5.7l

[Jbarry14]

I have been having a lot of problems with my 1996 K3500 5.7l

The truck has about 220K miles on it. I recently had problems with it running very rough. I found out I had low compression on two cylinders, So I decided to get a new Long Block.

I replaced a lot of other parts with it.
-Blackbear performance tune
-EGR Delete
-Headers
-Throttle body spacer
-New MPFI injectors and Regulator
-New fuel pump and filter
-New hydro boost pump and lines
-New metal body distributor, cap, rotor.
-New NGK plugs, and wires
-IAC sensor
-Throttle position sensor
-Coolant temp sensor

I need to get the truck to an exhaust shop to connect the exhaust to the new headers and also put an O2 bung in the passenger side header. So we started the truck with open headers to test the new long block and parts. We did not have the front O2 sensors connected yet. The rear O2s were tuned out from blackbear. The EGR system was also tuned out. I did check with blackbear about needing to do any relearn procedures, I was told I did not need to do that. The first few times we started it, I had no trouble codes showing up or misfire counts. But after a few times of starting it and letting it idle for a while, I got the P0300 and P0302 code. The misfire counts on cylinder 2 kept counting up. I replaced the plug, the wire. No change. I did check for vacuum leaks, and could not locate any. I did not run the engine for too long. I did not drive it either, just letting it idle and bringing the rpms above 1200 to check the cam retard, and that was in spec. Any suggestions on what to look for?

 

[alvaroemg]

I too am having this code on my 99 k1500 suburban. It started out with cyl. 2 and now its random misfires on that side of the motor. Revs up and down by itself in the morning, when the weather is cool. In the afternoon, my misfires and random reving are gone.

 

[Schurkey]

Connect a scan tool, verify EVERY sensor. Look at the fuel trims. Check out the misfire counts for each cylinder, if you haven't already.

Verify fuel pressure.

Verify cranking compression pressure of any cylinder giving problems, and a "good" cylinder to compare to.

Assure that the lifter preload isn't too tight.

Assure that the lower intake gaskets (against the cylinder head) aren't wiped-out. Common problem.

 

[Jbarry14]

Connect a scan tool, verify EVERY sensor. Look at the fuel trims. Check out the misfire counts for each cylinder, if you haven't already.

Verify fuel pressure.

Verify cranking compression pressure of any cylinder giving problems, and a "good" cylinder to compare to.

Assure that the lifter preload isn't too tight.

Assure that the lower intake gaskets (against the cylinder head) aren't wiped-out. Common problem.

This was a brand new long block I installed and just started for the first few times. First few starts and idle did not pop up these codes or show any misfire counts. It wasn't until our 4th or 5th test start that we started to get misfire codes. The engine does fire right up with the flick of the key.

I did have dash command connected to the truck when starting it. It only had misfire counts on cylinder 2. It was constantly counting up and then restarting its count.

I was going to take the valve covers off later to inspect. I will also test fuel pressure. But, I was thinking fuel pressure would effect more than one cylinder?

One weird thing was that I was not getting any fuel trims showing on dash command. I was getting them before I removed and replaced the long block. I don't know if it has anything to do with the new blackbear tuned computer, or not having O2 sensors hooked up. Blackbear tuned out the EGR and rear O2 sensors. Also, we test started the engine and let it idle with just headers and no O2 sensors.