2005 Chevy 4.3 misfire p0303 p0300 p1381

[Peachesandherb]

Looking for help with my truck, it has a 4.3 and has had a misfire since I got it. I've replaced distributor with ac delco, oem crank sensor, coil, plugs, wires, ignition control module, and coolant sensor. The truck is throwing a p0300 p0303 and p1381 code currently. The p1381 code envolves no communication with brake module which I suspect is from me pulling abs fuse due to an abs sensor malfunctioning and locking up the left side when braking. I have a hard time believing the misfire is due to that abs fuse though. Any idea on what I should check next? Compression showed 145 on all 6 cyl, all new Injectors which are bostech remans. Fuel pressure was healthy as well.

[Peachesandherb]

I should also mention the voltage gauge will show a little over 14 when cold then drop down to a little below 14. I have my radar hard wired into a fuse and when this voltage drop occurs, my radar turns off and says low power.

[sahls01gmc]

You've got your hands full!

 

The ABS problem may be related to your wheel bearings. How long since those have been replaced?

 

How good is your alternator? Have you tested it? That may help your case with the radar detector.

 

The misfire codes could be related to knock sensors.

[Peachesandherb]

Never replaced wheel bearings. Truck has 86k on it right now. It's definitely misfiring and its more noticible at low rpms.

[sahls01gmc]

When my wheel bearing went out, they caused the ABS sensor to misread and locked up the brakes on slow turn (like into a parking spot under braking). I'd look into that. My new wheel bearings came with new ABS sensors, so all is well now.

[Peachesandherb]

I'll take care of the abs issue once I get this thing running correctly. This misfire has me confused as hell right now

[Doug_Scott]

Have you checked for vacuum leaks? There is normally a troublshooting tree for resolving issues, have you followed one, or were the parts replaced by the "that didn't work,lets try this" procedure? Is the trouble code for the misfiring not also suggesting the cylinder number? Is it just the one number?

 

When doing compression test, were all plugs out, and throttle held wide open?

 

I can't seem to locate year make and model of your vehicle.

 

If you purchased the truck this way, what information did the seller offer?

[bobejones]

Sounds like a low voltage issue to me. You need to start looking close at everything electrical. Start at battery and charge system and work forward from there. Sounds more like the main power wire from the battery to the fuse buss. Check the voltage in the fuse box main to see how much loss you have. You may also have a ground issue. When you have something alerting to "low voltage" that coupled with firing issues is VERY related!

 

No, your ABS system should not cause a miss.

[rdnkcpa]

I get the same thing, a P0300 on my son's 2001 4.3L. It will only throw a P0300 code when the A/C is turned on. If you leave the A/C off the CEL will clear itself. It is very strange. I've replaced the fuel pump, twice. It died two times, new knock sensor, and new evap purge solenoid, new plugs, cap rotor, and wires. I also put in a new fuel injector spider, because I was getting a P0303. The spider cured the P0303, but I still get the P0300 when the A/C kicks on. This has driven me nuts trying to run down.

Would a weak coil cause this? I was under the impression that a coil either worked or it did not, so I've left that alone.

[02suburbanZ71]

Gotta fix 1 problem at a time. Rock auto is your friend

[insanity213]

I had random misfires and my radio would reboot when a misfire occurred at high rpm. Wound up being ground problems. I would clean up all your grounds 1st and even add a few more. Worked wonders for my 98 K1500.

[Hiandbye]

On 3/19/2015 at 1:24 PM, sahls01gmc said:

When my wheel bearing went out, they caused the ABS sensor to misread and locked up the brakes on slow turn (like into a parking spot under braking). I'd look into that. My new wheel bearings came with new ABS sensors, so all is well now.

Hopefully you’re still on this forum. When this happened were your brake spongy as well?