Loss of power uphill or under a load

[Xanzgod]

What's up guys

I have an 02 Yukon Denali
I keep having loss of power uphill. I have no idea why. It justs sputtering going up hill. It won't die on me or anything.
I'm also having rough cold start when's it's below 40 degrees outside.
I've done a spark plugs and wires.
With the tr5s and 409s
And cleaned the TB and maf.
What else could it be?
The Intake manifold gasket? Or clogged cat? Or the fuel pump?

Thanks guys

 

[swathdiver]

What's up guys

I have an 02 Yukon Denali
I keep having loss of power uphill. I have no idea why. It justs sputtering going up hill. It won't die on me or anything.
I'm also having rough cold start when's it's below 40 degrees outside.
I've done a spark plugs and wires.
With the tr5s and 409s
And cleaned the TB and maf.
What else could it be?
The Intake manifold gasket? Or clogged cat? Or the fuel pump?

Thanks guys

Hi Daniel, well, yes, it could be the fuel pump, works fine at normal loads but pressure falls off under a larger load. Could also be the cats. If there are no codes, you definitely want to get a scan tool that can see your fuel pump if possible and run a graph of your O2 sensors and fuel trims.

Do you have one of those OBDII Bluetooth or Wireless adapters?

 

[OR VietVet]

Like James, I suspect the cats or the fuel pump and lean more at the fuel pump because that could also effect the cold start. I am wondering why the cold start problem seems to happen below 40 degrees though. Need to know what the fuel pressure is at those starts and while pulling uphill. Need a back pressure test on the cats. Quality of fuel? What brand of fuel and octane do you run and where the hell are you located? I ASSUME your air filter is free of restriction? How old is the fuel filter?

 

[Xanzgod]

Kinda. I have a programmer that kinda reads codes and data logging. Is that well?

 

[Xanzgod]

Unfortunately I'm in Kent Washington. (Originally Texan)
And honestly the gas ain't all that great it could be the gas I put in it.
Right after I did the tune up it started acting up. Like if the tr5s made it lose power? I'm not sure.

Would the 10mm larger wires affect the spark?

 

[SnowDrifter]

What did you gap the plugs to?

 

[OR VietVet]

So, all was ok TILL you did the tune parts? That would be good to know up front in your original post. Most of us here say, "stick with the stock AC Delco tune parts and wires and filters and such". Some have found better performance from other sources. You could have gaped plugs wrong but most of the time the plugs are gapped to where they should be if you use the correct application. Can you state the steps in order of how you cleaned the MAF and throttle body and what you used to do it with? Did you replace tune parts to just do maintenance and then these problems started or were you trying to address a problem? Were the parts replaced and then the problem and then the MAF and TB clean to try and chase the problem down?

 

[SnowDrifter]

Plugs are most definitely not gapped out of the box. They're manufactured, not spec'd

 

[OR VietVet]

Plugs are most definitely not gapped out of the box. They're manufactured, not spec'd

Really? The last 4-5 times I bought plugs for my last 2-3 vehicles they were gapped at the correct spec when I got them. I do always check them for correct spec and not assume that they could not have been damaged/bumped during manufacture and shipping and stocking but I guess I have been lucky.


Back in the day I had to gap plugs all the time but I also set point gap as well and adjusted timing and adjusted carb.

 

[Xanzgod]

These ngks tr5 says they are gapped to .40
I was trying to address the problem. By doing a basic tune up.
It did have the rough idle at could start but that's it. After I did the tune up it started acting up going uphill

I did spark plugs first. Then Taylor 409 10mm wires.

Cleaned the maf with maf MAF sensor cleaner let it dry for about 40 mins
Then I cleaned the TB (which was gunked up) and it actually look very nice afterwards. Almost new.

I might also add on cold start when it's still cold and I shove it into drive and it accelerates itself.
That's why I thought vacumm leak. (Intake manifold gasket)