3.0 slow and possible throttle problems

[55trucker]

If you've got this......

under your '92 (which is what is under my '98) you won't find that for $50, if you suspect that the cats are clogged get under the truck and give both cats a rap with a ball peen hammer, if the sound is a dull thud they are more than likely still good but if the sound rings or has an echo to or you can actually hear loose pieces inside moving about then the substrate has collapsed and usually collects at the tail end and being the way they are manufactured if one has gone then you're replacing both of them. Cats don't generally fail on their own, something upstream in the fuel system has gone wrong and over a good period of time will take them out.

 

[RonD]

$20 vacuum gauge is a tool you should have

Engines are self powered air pumps and a pressure gauge is needed to test any "pump"

Doesn't matter how many changes are added to "the pump", i.. distrubutorless, fuel injection, sensors up the wazoo, lol, its still a "pump"

Have a read here: https://www.gregsengine.com/using-a-vacuum-gauge.html
I found this the easiest to read instruction site for vacuum gauge tests

Vacuum is the level of air the engine wants but can't have because throttle plate is closed, so is a negative number
Engine size doesn't matter, intake manifold vacuum of a running engine should be 17"-21" of vacuum

If exhaust is getting clogged up then "air" can't get OUT as fast as air should come in, so engine may show a lower vacuum level at idle
But if its a partial clog it may only show up at higher air flow
You can "blip"(open throttle wide and let it snap closed), you show see quick drop to 0" then a quick increase in vacuum after throttle plate closes, usually above 25" then back to 17-21" level
"Quick" is the key word, slow to go down and slow to return to idle level vacuum is a clogged exhaust