2000 GMC 1500 5.3 P0300 random misfire - anyone got matches?

[Cyborg73703]

So,

2000 GMC 1500 5.3L 4x4 Auto

 

I've got a situational P0300 coming at me.

If I start up the engine and drive right away, the engine will bog, transmission will stay in first (at any throttle position up to and including WOT), and will NOT go beyond 40-50km/h. Once the truck has been moving for about 15-20 seconds, it will slowly (over the next 10 seconds or so) drive normal. More often then not, this will spring a flashing P0300 if I've recently cleared the codes.

If I let the engine warm up for say, 5-10 minutes, this will NOT happen.

 

The other time I will get a flashing P0300 is when I am crusing at about 110km/h (and about 2200 RPM). It will not flash until this speed/engine speed, and will continue to flash until the truck governs.

 

I've also got some 02 sensor codes, P0137 and P0157.

 

 

 

What I've done (roughly in this order):

-Bought truck (Can't verify what codes were going on when bought)

-Transmission rebuilt

-Replaced plugs with AC Delco, replaced wires with AC Delco.

-Replaced B1S1 02 sensor

-Cleaned throttle body.

 

 

 

-I've replaced the intake manifold gaskets with the felpro revised gaskets. I did NOT replace the bolts or rubber washers.

Just tonight I was tinkering with this, and decided to double check they were still torqued (note, engine was warm at this time), went to go confirm at 44 in/lb in the proper sequence, and the bolts aren't tight, none of them. I went probably a quarter turn further, to what feels like should be north of 44 in/lb, so I stopped tightening there. Should the torquing be done cold? Any reason these backed off so much? Should I have replaced the bolts and rubbers?

 

-I've pulled the pigtail off each coil one at a time (at Idle, not usually where the CEL starts flashing), to listen if the engine stumbles, each time a pigtail was pulled off I did notice the engine run rougher.

-Replaced Cats (was getting a P0420 and P0430) - have not come back on since replacing cats.

-Replaced K&N air filter with paper filter, cleaned MAF.

-I've sprayed intake cleaner over any vacuum lines I can see, didn't notice any difference in engine speed over any specific spots.

 

 

Might be missing some stuff, and on my way to work tomorrow I will grab some info from the Live Data freeze on my code scanner.

Off the top of my head, seems to be

110 km/h

2200 rpm

TPS: 25%

STFT B1 12%

LTFT B1 10%

STFT B2 12%

LTFT B2 10%

But I will get accurate results tomorrow!

 

 

Throw some ideas at me, and thanks in advance guys!

 

[Cyborg73703]

Fuel Sys 1: CL-Fault

Fuel Sys 2: CL-Fault

Calc Load%: 18.4%

ECT: 90*C

STFT B1: 20.3%

LTFT B1: 24.2%

STFT B2: 20.3%

LTFT B2: 24.2%

MAP: 70 kpa

RPM: 2420 rpm

Veh Speed: 114 km/h

MAF: 42.12 g/s

TPS: 29.8%

 

These are what I get for freeze frame data when the P0300 springs.

 

 

Thanks guys.