What you described is exactly what happened to my 96. Loss of power and economy over time, didn't really notice at first. Pulled it apart and wow big gap, blow out gasket. Threw the factory pan in the junk and bought the Hughes Plenum Kit with new bolts. Put it all back together, got the power back right away but the economy while improved was still not what it was. Ran a can of AMSOIL Power Foam through the engine and economy is back. Plate first, power foam second. Bought mine from www.snyoilnow.com

 

This clean probably cleaned off the back of the valves like I mentioned earlier.

To the OP when you remove the plenum shine a flashlight into the ports and look for carbon buildup on the back of the valves. If there is it might be worth spraying something in there that will sit on them and loosen up the carbon deposits.

 

Why was this thread so long? This was textbook plenumn gasket.

Someone went off on a tangent about it running rich, and then about O2 sensor brands... wow.

These trucks should come with plenumn gasket subscription plan.

 

Does the brake booster vacuum line feed all the cylinders if I use Seafoam?
1998 1500 with 5.2L

 

yup.

remember that keg is a Multi Port Fuel injection, which pulls air from a common corridor (plenum), which sucks that air through the runner, which gets a squirt of fuel just before feeding the head itself.. If you suck in seafoam through the brake booster line, you are filling the entire common air supply for the whole engine.. and the cylinders (if all are the same compression) are going to equally drink the stuff.

 

I did the Seafoam treatment.
I did it in the vacuum line and the fuel tank.
I am not to keen on putting it in my oil.
Well I hardly got any smoke, It did smoke, but not bad and nothing like these vehicles that are posted on YouTube.
I then took it out for a 5 minute beat the ***** off it run.
It does seem to idle a little smoother.
I have run Mobil 1 synthetic 10W-30 since I bought the truck new.
I have 103,000 on the truck.
I always get a steady 10-10 1/2 mpg.
I am 6" of lift with Goodyear 35" MTR Kevlars.

 

If I didn't get much smoke, does that mean that my engine was pretty clean ?

 

honestly, I'm thinking you might have put it in your oil anyway..

pull the dipstick on that thing and check the appearance of your oil to see if it looks diluted.. If you've a leaking plenum gasket, you could have poured it straight through to your valley.. given, that would be a bad leaking pan, but still: hardly any smoke? weird..

I don't blame you for not putting it in your crankcase.. There is no way I would either..

 

I'll check tomorrow.
My oil never smells like fuel and my mpg has been the same for 11 1/2 years now.
It did change slightly when I put the MTR tires on in the summer, but not by anything to mention.
I was Leary about using the Seafoam because I really am not having any issue at all.

 

When you did the treatment did you only use 1/3 of the can like the instructions say?

I followed the instructions to the letter when I did mine. The first 1/3 can treatment did not smoke much at all. The 2nd and 3rd did a lot.

I wouldn't put it in the oil. Remember that the intake is under vacuum so fluids will go in but not run out.