1999 s10 4.3 miss/lack of power on highway

[nwjones18]

Originally Posted By: kc8adu
its possible you have a clogged cat but the vacuum is usually poor at 2500 rpm.
my money is on the spider.
get the updated one with actual injectors at the ends.
its not if but when the old style will fail.


If the truck wasn't getting enough gas wouldn't the O2 sensors show there being a lean condition? I'm going to replace the fuel filter anyway, but in my mind them showing full rich pretty much eliminated a fuel issue. I have heard nothing but bad things about the 'old style' spider injection though. I'm going to order an exhaust back pressure tester. This is the second time I've wanted one and otherwise I'm about to just be throwing parts at the truck.

 

[The_Eric]

Originally Posted By: thorromig
After market 02 sensors are junk. My opinion -- OEM 02 sensors are the only way to go.


I've never had any issues with Denso sensors from the parts store. Installed... lots!




Originally Posted By: Vlad_the_Russian

If symptoms are still there - I'd consider replacing a fuel pump. Shop I used to work at had an Astro Van with the 4.3L. Over 130k miles the fuel pump had to be replaced 5 times... I met a few more guys with frequent fuel pump failures on those 4.3 GMs. But definitely get a second opinion first from a reputable mechanic before yous start throwing parts at it.


Then the shop was either buying the cheapest garbage pumps out there, or someone wasn't checking the fuel pump circuit for volt drop under load. All it takes is a bad engine to frame ground strap and the pump is toast before you know it. GM had tons of braided ground straps rot out and then lose the ground that the pump relies on. I've replaced dozens.

 

[nwjones18]

Congrats to all those who said Clogged Catalytic converter. Truck passed the vacuum test, had .5 psi backpressure at idle and 3 psi at 2500rpm, which doesn't seem that bad, but if you revved it any higher that it would continue to climb and pretty much peg the gauge. I 'fixed' (gutted) the cat today and now have 0 psi at idle and 2500 rpm and the truck is running like a brand new one! Thanks!

Side note I checked the fuel pressure at the rail and it was 56 psi, and it was 95 psi at the filter with no leak down so fuel system seems to be in good shape.

 

[ltslimjim]

Wow. Glad that's fixed. Nice work and thanks for the update!

 

[lexus114]

does that have a detent cable adjustment? for propre down shifts etc? if it does, try adjusting it. that will help for the down shifts on hills.