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Loses power driving up mountain pass

Driving Southbound on Interstate 5 aka the Grapevine I turn off AC and drive up the mountain pass and will suddenly lose power just slower no matter pressing the acceleration, the gauges all are in normal ranges, no overheating, no smoke. Pull off to the side turn off ignition wait about 10 min restart a little bit of rumble and slow moving to start but get up to 45-50 mph able to continue to the summit and drive home fine speeds back up to 70’s, does L.A. foothills fine This happened first about 8 months ago and again yesterday . Brought to mechanic today but he can’t see until Tuesday. Any thoughts as no other issues, my mechanic just tuned 2 weeks ago w new oil.

What year, how many miles, what engine and transmission? It helps to have this information.

Bad plugs, weak fuel pump, clogged fuel filter, clogged air filter, worn engine, could be a lot of things. How many miles on the engine, what year, maintenence history, is the check engine light on, if it is what code is it showing? Need to know a lot more to help you with this.

By any chance on the two occasions when it happened to you purchase gas at a different station?

Really poor performance on upgrades is usually caused by…
Worn engine.
Clogged converter.
Slippage in the clutch or automatic transmission.
Lowered fuel pressure if this is accompanied by any bucking, etc.

There are other factors such as retarded ignition timing, faulty ignition module, and so on but you have not given the year model of the truck and engine size so timing issues may not be relevant.

Are you sure it’s suddenly? All non-forced-induction engines lose power as you gain altitude, because there’s less air up there, which means less fuel/air being stuffed into the cylinders to burn.

He said after he shuts it off and waits a while it will then accelerate normally up hill. My father in law had a Ford Pinto that started doing this randomly on hills. The honeycomb in his catalytic converter hat broken up and was all clogged with soot, when he went up hill it would sometime fall back and clog the outlet. Sometimes just pulling over and hitting the brakes would rearrange it enough to drive normally. He was in his mid 80s, living on social security and a $57 a month pension and I was out of work with 4 kids so I did a bad thing which solved his problem.

Wow . . . a Pinto

I do believe catalytic converter technology wasn’t very advanced, in the days of the Pinto

Somehow that story doesn’t greatly surprise me

Then again, even with a functioning catalytic converter, a Pinto wasn’t exactly a powerhouse, was it?

My first impression was that something in the system went awry and the electronic control module went into “limp” mode. You may or may not have had the check engine light come on but the mechanic should be able to bring up the code history. A/C is strain on the engine especially if it is getting old. The engine will get hotter running the A/C compressor then pulling the hill did not cool it down. The electronic controls tried to compensate but failed so limp mode was initiated. Once it cooled down everything went back to normal.

My 1st thought was cat converter stuffing up.

True, I ended up with my wife’s Pinto as my drive to work car. Automatic, no tachometer, I would manually shift when the engine screamed for mercy.
No power but bullet proof, except the gas tank…lol

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That was my thought that it might be altitude related, but the description sounds more sver. I wish the OP would respond to questions asked.

I began to have more trouble climbing mountains. It took me a while to implicate the fuel pump. I have a 30-year-old Toyota pickup with a mechanical fuel pump that mounts on the engine, works off a cam; most newer cars have electric pumps that live in the gas tank - so my experience may not be yours. It worked okay for mild city driving, and I don’t pass people on the freeway unless they’re doing under 50, so I’m less sensitive to power problems than many. I replaced the fuel pump (easy with these external pumps), which helped.

2002 F150xlt titanV8

It felt both times as though free fall, I keep to the right truck lanes and suddenly I’m slowing with no response to the accelerator and the RPM gauge drops out the electric still works but I’m scrambling to get out of the way of traffic so also paying attention to traffic.

I had a 1982 Pinto inherited from my grandfather who bought it used in Indiana, sold to him without the catalytic converter. I had it through college until her alcoholic oil drinking was too much. The truck handles all the other foothills and heading Northbound through the Grapevine fine, perhaps the steeper ascending into the mountains is responsible

Yes I am familiar w the AC issue and it’s always turned off at the bottom of the hills before the assent. The check engine light didn’t come on, I watched all the gauges on the way up looking to see if something would pop up or waiver.

I keep my trucks until my mechanic pries them outta my hands. The only reason I have this 2002 F150 XLT v8 is he wouldn’t return my '97 f250 w 420k on it when I brought it in for tuneup telling me no this is your truck the other one is overdue for transmission failure and I don’t wanna work on that. He had to prove to my this one could haul a trailer pulling a cow before I grumbling accepted my fate. Keep your mechanic happy and give him cows through out the years is my working motto. He still has the 97 in his collection because she is still running gggrrr :slight_smile:
I brought the 02 into him Saturday morning but he was too busy so I decided against driving it up to SLC as I need to get there by Tues pm and his shop is closed Sunday Monday

When you say mountain pass, do you mean just north of LA or mountain passes north of Redding?

I expect that’s what the OP is referring to. There’s a big hill between the central valley and the la basin commonly called the grapevine, named b/c it is full of curves, winds around the hill, sort like a vine.

OP, there’s a lot of things that could cause this symptom. Assuming there are no CEL codes, suggest to focus initially on the things that are different when going uphill vs level driving.

  • The flow of fuel is higher, so fuel pump, fuel filter, or anything restricting gasoline flow. A fuel rail pressure test while driving uphill might be required.
  • Likewise, the flow of air is higher, so engine air filter, anything obstructing intake air flow. Visual check of the entire intake air tract.
  • And the flow of exhaust gasses is higher, so cat or exhaust system obstruction. Intake manifold vacuum test is where to start.