LatitudeDancer

Every once in a while I will accelerate in my neighborhood (10-15 mph up to 30+) and it feels like I've got a 10,000 trailer behind me. Sometimes at high RPM and speed (2,500+ and 60mph+) the same happens when trying to pass or getting on the interstate. The RPMs are there, the engine sounds like it's doing work, but no power. Every once in a while the power might cut back in while doing this (and might cut right back out). But just a return to normal power, not a slam like a tranny slip.

Fuel pump is 3.5 years and 60,000 miles old, new fuel filter, fixed a vacuum leak (bad o-ring on the brake power boost vacuum line). Issue still there. Fuel pressure with key on/engine idling is 52-55 psi. Goose the throttle and it spikes to 58psi.

Other than occasionally while passing or "aggressively" accelerating in the neighborhood, runs and idles well.

Could the O2 sensors be messed up/dirty from running for years with a bad fuel pressure regulator and therefore too rich a mixture (fuel economy went from 14 or so mpg to 16.5 on the highway)? Or should I go back to vacuum leak searching or wait for the fuel pump to take a dump? The fuel pressure is kind of low but seems odd it happened as soon as I changed the fuel pressure regulator.

Could a bad pressure regulator lead to low fuel pressure with the key "on" and/or engine idling? Or is the test port before the regulator and therefore pressure 100% up to the fuel pump

Also, I believe the last 2 times I had the codes reset, the check engine light came back on not while doing the above, but while idling at stoplights or something passive.

tech2

check the cats...give them a hammer fist and see if they rattle. if yes, they are loose and causing an exhaust restriction which is exactly what your describing. This will even cause funky fuel trim readings.

if there is no rattle from the cats they may be clogged; unscrew the front 02 sensors and test drive; if the power is back the cats are the problem.

LatitudeDancer

Interesting. Just before finally getting the fuel pressure regulator replaced (been bad for years), I got a P0420 (catalyst system efficiency below threshold). I figured it was just because I was in the Denver area running high octane fuel with a rich mixture (leaking pressure regulator). The truck has spent its life below 1,000' before that, and I'm back down there now.

Didn't have the above mentioned acceleration issues + lean codes before though. Can they clog that fast?

Edit: gave 'em a couple whacks. Sounded like a couple of suspended pennies rattling in one of them. But could have been shoddy mounting brackets for all I know...

Would be kind of random for both to be loose?

loosebearing

Fuel pressure is a little low.. should be 60 to 65 psi . Does pressure hold steady .. after you turn truck off?
Even a few psi will cause problems.
But try cleaning mass airflow sensor ... check air filter.Check all downstream of maf.. any un metered air will cause your symptom .
Maybe fuel filter.

LatitudeDancer

The air filter and fuel filter are new. I did not try the remove the O2 sensor suggestion, but did clean the MAF with a can of CRC MAF cleaner. Could be in my head but throttle response seems better than in a long time. It's been a few 100 miles with no acceleration issues, but the weather has changed a bit. I'll post back if it winds up being anything else.

Also, kind of weird, the first acceleration issues I noticed were about a few weeks ago while driving in ice fog in southeast CO for a few hours at high speed. Read about it but never experienced it. The next day when my popsicle of a car defrosted, there was a black sooty+oily sheen funk covering all of it. Perhaps it inhaled too much and got all over the MAF wires/sensors. Would have been random to have happen the day of getting the fuel pressure regulator fixed, but one never knows