P0300 Misfire in all cylinders 2001 Tahoe

[Nicolai8775]

I don't understand. I've been fighting some idle issues after a TBSS intake swap and a bigger cam. During the scan cable process, Blackbear said I had a small leak probably at the intake but the tune is good to go. I sprayed starter fluid on a cold motor around the intake and TB and didn't hear any changes. I found a weak spot on the evap line, my EGR delete wasn't capped off properly, and the MAP sensor wasn't secured well enough. I fixed all these issues and now have p0300. Torque shows it's happening in all cylinders A LOT. After I fixed those leaks the idle issue went away except now it misfires terribly.

It has new plugs and wires, I've triple checked every injector and spark plug wire and nothing is crossed.

Is it a fuel delivery issue? The FAQ I used as a guide to modify the fuel system mentioned the C5 filter/regulator holds a static 58psi and I should tell the tuner to account for that. Well I didn't do that because I overlooked that on the FAQ lol. This doesn't make sense to me since I did a scan cable tune. Would he not see this?
Do I need a bigger fuel pump to power the 36# injectors that are bigger than the stock #26 injectors?

Is it timing? I had a timing chain dampener but someone I talked to at Summit said I shouldn't need it. Now I'm wondering if he didn't know what he was talking about.

I would be happy to post logs if someone can help me diagnose. I don't fully understand what to look for.

 

[Nicolai8775]

Ok I tested the fuel pressure at the rail. I'm getting 63 psi lol. So that's way higher than the stock 40-50 psi and higher still than the C5 regulator that demands 58psi. Am I getting to much unburnt fuel that's fouling my plugs and causing a misfire?

How do I get the pressure down? Tune? Remove my stock fuel filter?

 

[live2pull]

I had p0300 when I replaced plugs and wires, turned out my budget wires were not adequate, purchased some delcos and was right as rain after that. I think you might be on the right track though with fuel pressure and plug fouling as a result. May want to contact your tuner and ask?

 

[OR VietVet]

Remove some of the plugs and see if they are black, indicating too rich and fouling the plugs. Plus, like has been said, quality parts make a big difference.

 

[Nicolai8775]

I had p0300 when I replaced plugs and wires, turned out my budget wires were not adequate, purchased some delcos and was right as rain after that. I think you might be on the right track though with fuel pressure and plug fouling as a result. May want to contact your tuner and ask?

I checked #1 cylinder plug and it had a faint smell of gas, not wet, and nothing burnt on it.

The plugs are ACDelco 41-162.

Lol the plug wires are Ultima select I think oreillys brand

I've emailed Blackbear but unfortunately he only goes by email and it takes a week or 2 for a reply every single time. It's slow going.

 

[OR VietVet]

I checked #1 cylinder plug and it had a faint smell of gas, not wet, and nothing burnt on it.

The plugs are ACDelco 41-162.

Lol the plug wires are Ultima select I think oreillys brand

I've emailed Blackbear but unfortunately he only goes by email and it takes a week or 2 for a reply every single time. It's slow going.

Just like the best shops and techs in town, they are hard to get in line with for work and info. That rich look I was talking about can be wet like you saw or a black soot look and the spark plug insulator will be black soot looking as well. If the plug is wet that means that the plug is not firing either at all or intermittently.

 

[Nicolai8775]

Just like the best shops and techs in town, they are hard to get in line with for work and info. That rich look I was talking about can be wet like you saw or a black soot look and the spark plug insulator will be black soot looking as well. If the plug is wet that means that the plug is not firing either at all or intermittently.

This is the #1 plug, I can pull more after I get off work in a bit. It looks fine to me. The threads looked slightly wet and faint gas smell. But nothing was burnt on.

 

[OR VietVet]

It looks fine to me. I would still check all of them and remember what cylinder each came out of. Those plug wires? Are they the big thick 8.8 mm wires?

 

[Nicolai8775]

It looks fine to me. I would still check all of them and remember what cylinder each came out of. Those plug wires? Are they the big thick 8.8 mm wires?

They're definitely just a standard looking plug wire.

 

[OR VietVet]

GM P0300 Causes (* = Most Common)

• Faulty or worn spark plugs *
• Faulty spark plug wires or coils *
• Distributor failure *
• Faulty fuel injector *
• Vacuum leak
• Low fuel pressure
• Camshaft sensor defective
• Crankshaft sensor defective
• Engine timing off
• Leaking head gasket
• Low engine compression
• Poor quality fuel

With the work that you did you may have some problems with the cam or crank sensor.