Help!! No power under load

[Jenn Mckeown]

I drive a 2000 Chevy Silverado 4x4 4.8L. for 2 weeks now i have had no power under load, loss of acceleration, random misfires.

Things i have done so far

Replaced TPS, MAP, Plugs and wires, fuel pump, fuel filter, fuel lines, purge solenoid, vent valve,all vacuum lines as well as the PCV have cleaned the MAF, IAC, EGR, and  injectors. Have checked for vacuum leaks around intake and intake bolts. Cleaned throttle body. As well as have removed the cat's and in the process of straight piping it (still has muffler). I'm at a complete loss on what else could be wrong with her. Any help or suggestions are greatly appreciated. Have ALOT of time and money sunk into this truck and I love her.  Oh yeah it all started the day after I got her stuck in a mud puddle for a few hours if that helps or has any baring on the issues. Thanks a million 

[riverbanks]

Stuck in the mud,bummer,you now have 02 sensor problems,1,they can't breathe to atmosphere,2, connections got dirty

[Jenn Mckeown]

My cats have been taken out and O2 sensors are currently unplugged. In process of straight piping it back to the muffler.

[shadow gray 2020 hd]

Not familiar with that engine, but if it uses coil packs and an ignition module I would check them.  What cylinders are you getting the misfire codes on?  If you know what cylinders are misfiring and they are on the same coil pack, swap that pack and see if the problem is on the cylinders you swapped it to.  If the misfires are still on the same cylinders, more likely to be the ignition control module.  Some of these gm systems the module can be taken out easily and tested at stores like autozone.  

 

If on a distributor cap system, check the cap and rotor.

Edited September 15, 2020 by shadow gray 2020 hd

[txab]

3 hours ago, Jenn Mckeown said:

My cats have been taken out and O2 sensors are currently unplugged. In process of straight piping it back to the muffler.

Still need your pre-cat sensors

[Jenn Mckeown]

Ok but with them being unplugged if they where the issue wouldn't it run better? I'm so beyond stumped we have done everything we could think of either by replacing it or cleaning it. 

[txab]

Your upstream or pre-cat O2 sensors read your fuel mixtures and fueling adjustments are based on that. Without the info from them, your ECM is defaulting to parameters that will just keep it running. Post cat sensors don't have anything to do with fuel, only the efficiency of the cats.

 

So if you really have all 4 sensors removed, that's where I'd go next

Edited September 16, 2020 by txab

[Jenn Mckeown]

To the ECM?

[silveradosid]

no txab is telling you that you need to have the precat sensors hooked up

[Jenn Mckeown]

I get that I should have them hooked up but my question was if I unhook them essentially wouldn't the truck drive a little bit better than if I hooked them up if they where the issue?

[riverbanks]

You are correct, different,would be the word, not better,my thought was,you submerged the o2's in much,so,nope,what about a fuel pressure test,I see that the fuel pressure regulator was not replaced,how that failed,at the same time as mudding it,who knows, just a guess,as a pressure test would be needed

[shadow gray 2020 hd]

On 9/15/2020 at 12:31 PM, Jenn Mckeown said:

random misfires.

Assuming you are getting a p0300, moisture can cause issues with ignition systems.  Have had issues with the cap and rotor on my 98 k2500 with a 350 a couple times, random misfires and lack of power.  Every time it was moisture or corrosion inside the cap. 

 

If it were mine, especially being that testing the ignition system is pretty simple, I would go back to that if you have not already.  A simple inline spark plug test light can be a very helpful tool for diagnosing weak or lack of spark to rule out issues.  Based on what you say you have done and not done, I am guessing you have not already checked.

[chem_man]

Definitely check your fuel pressure and that your fuel pressure regulator is working properly.

[Jenn Mckeown]

Pressure is at 55 under idle and drops to about 48 under load. We did replace the FPR. Maybe fuel rails or injectors? This is my only vehicle and daily driver on top of my company vehicle. I need it up. Would back pressure cause an issue with not having catalytic converters she wants to go like you can feel her surge and want to go but it's like something's pulling her back and it's engine wise not suspension or none of that

[CamGTP]

No, back pressure is a non issue here. And your fuel pressure is okay for now. If it dropped any more that 48psi you'd have a problem. With not being able to see high rpm the pressure should rise has the vacuum in the manifold becomes less.

 

If there is still a misfire with a flashing check engine light that is the main thing to be looking at. A scan tool would let you know what cylinders to look at and what possible causes. Could be a crank sensor going out or a wiring issue to the coil packs, bad grounds on the main harness that go to the back of the cylinder heads.

 

Also make sure you didn't get water inside the transmission if the truck was stuck that high into the mud.