94 GMC Sierra down on power

[Orangepeel]

I put a set of valve covers, ball joints and a pinion seal on a 94 sierra 5.7l . The truck ran good after repairs were made. The next day we get a cold snap and the truck is down on power. If you ease into the throttle it does better still not perfect but noticeably better than if you just floor it. If you floor it and hold it there its obviously struggling and down on power. It starts right up idles smooth just down on power. No cel.
Map sensor is working (tested it with a vacuum pump)
Engine vacuum is 20 and does not sink when revved up. I also pulled the O2 to see if it would run better and it didn't make a difference.
Egr diaphragm is functional. I can see the injectors both spraying fuel.
Base timing is spot on.
At this point I'm thinking it's coincidental.
Tried to check fuel pressure I had 10psi at the filter but it was leaking while I was checking it. I need to figure out a good way to tap into it. I'm assuming it's a fuel issue at this point. What's the best way to check fuel pressure and how do I go about verifying a throttle body issue etc? I don't want to guess I want to be able to pinpoint the concern. Thanks everyone!!

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[Cujet]

Clogged catalytic converter? I know of a few situations where the ceramic matrix in GM cats came loose and rotated around inside the cat, causing random backpressure issues. Just a guess of course, could be many things.

 

[FatOrangeCat]

Maybe your fuel has some water contamination. Have you filled up around the time of the low power issue?

 

[spasm3]

There has been some contaminated fuel from certain stations, what state are you in?

 

[Orangepeel]

There has been some contaminated fuel from certain stations, what state are you in?

Missouri

 

[spasm3]

Missouri

This happened in Colorado.

https://www.jalopnik.com/2074816/supplier-error-diesel-gas-cars/

 

[Lubener]

I think you are on the right track with fuel pressure. Judging by your vacuum reading and it not dropping when you goosed it, I doubt it's your converter(s) or any obstruction with the exhaust..

 

[Rob_Roy]

Start with a new fuel filter, and check the heat riser (allows the air cleaner to draw from around the exhaust manifold when it is cold outside).

 

[ka9mnx]

Steady vacuum at all throttle positions would indicate a restricted intake (air filter) or cat.

 

[Marcozi]

Steady vacuum at all throttle positions would indicate a restricted intake (air filter) or cat.

THIS!

 

[Chris142]

I think it's fuel related too. It needs to run richer in cold weather and it can't keep up.

 

[Lubener]

Steady vacuum at all throttle positions would indicate a restricted intake (air filter) or cat.

Vacuum will drop like a rock when the engine is raced having a restricted exhaust.

 

[burbguy82]

I also pulled the O2 to see if it would run better and it didn't make a difference

This is suspect.

it should had made a difference.

 

[Nick1994]

Clogged catalytic converter? I know of a few situations where the ceramic matrix in GM cats came loose and rotated around inside the cat, causing random backpressure issues. Just a guess of course, could be many things.

My brother bought a ‘94 K2500 years ago that wasn’t running. Needed a wiring harness. After replacing it, the truck would run but had no power at all, like not drive-able. Turns out the catalytic converter was broken inside and was rotated, so almost no flow out of the exhaust.

 

[meep]

No mention of it running rough. That puts this firmly into the air filter / intake / exhaust camp.

If it was low fuel pressure, it would run lean and pop and spit. If it would running rich it would chug.

 

[Orangepeel]

No mention of it running rough. That puts this firmly into the air filter / intake / exhaust camp.

If it was low fuel pressure, it would run lean and pop and spit. If it would running rich it would chug.

Idles fine. But vacuum doesn't drop when revved and pulling the o2 sensor out of the exhaust didn't really make a difference which means from everything I know that the exhaust isn't restricted.

 

[Orangepeel]

No mention of it running rough. That puts this firmly into the air filter / intake / exhaust camp.

If it was low fuel pressure, it would run lean and pop and spit. If it would running rich it would chug.

Also it's tbi so you can remove the air filter and it's housing which also makes zero difference.

 

[supton]

Can you hook up a meter to the O2? I'm wondering if it's running very rich. Like maybe the temp sensor went out.

 

[ripcord]

What do the plugs look like?

 

[Orangepeel]

What do the plugs look like?