280k miles needs some acceleration

[Oil-e-coyote]

For years I've been kissing the driveway when I get home that my old LSC it still making its way in the world. I also have myself convinced that my acceleration problems going from 40mph to 50 mph are because of the car's age. The tachometer has not worked in years so I haven't that # reading for when it dogs out. But it grumbles like it wants to go home. Its back to its own self again at 60mph and has always been good in lower gear acceleration. I'm no stranger to the mechanic's shop and have been through some head scratching sessions with a tranny guy and my engine guy. It sounds, to the engine guy, like the engine would sound if its running hot (no its not). He tells me to go to the tranny guy but those guys at AMMCO ran tests and had no answers. This has been going on for years. Anybody have some respect for a 280,000 mile original LSC and have a suggestion on how It can keep its pride next to a U-haul van out of the Florida Turnpike gate like it still should.

I have recently cleaned the fuel injectors. Maintain the oil. Notice some improvement with additives but its not a tell for anything. Tranny has been rebuilt in the last 4 years and no tranny symptoms.

 

[Mark8Murder]

Welcome to LVC! Just my opinions here, but with 280k on the clock I would say it's a senior citizen in car years and it should be treated as so. If you want to get it moving again, I'd go with a heart transplant and drop a fresh low mileage motor in.... but as the saying go's "if it ain't broke, don't jack with it".

Again, just my .02, but welcome to the party! Lots of cool peeps on here with some nice rides!!

 

[Oil-e-coyote]

Thanks Legend,
you may indeed be right. I drive this car on the highway 80 mph for 60 miles every day in case anyone has concerns about when its time to start taking viagra.

I will spare everyone the pictures of my mule. That is unless anyone wants to see what the Miami sun does to you original paint after 20 years, The thing is some days I wonder if if I'm not just being overly resigned to the age and overlooking something. I mean wouldn't the valve tappets be tapping if it was a wear issue. What are the signs of a loss in compression? This mule can still charge from a standstill, it just reaches the higher gears and begins to trot along in confusion before finding itself again after about 55 mph. "I can't drive 55"

 

[Elessee]

Under very mild acceleration, the tranny shifts into Overdrive somewhere near 45 to 50 mph. On my car it's about 47mph or so, @ about 2,000 rpm.
But if I'm cruising on a flat road at 43-44 mph and suddenly take my foot off the accelerator, it'll most often shift up into OD.
Then, RPM drops down from 2,000 to about 1400, which is way below anywhere the engine can develop any appreciable torque.

At this point there is no acceleration at all.. unless I step on the gas, whereupon the tranny immediately and correctly shifts back down into 3rd gear, RPM spikes, and the engine has power to accelerate.

If the transmission is shifting from 3 to 4 a little early, and/or is not downshifting 4 to 3 when it should, acceleration will be very poor right around 45 mph.

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You notice poor performance at a particular road speed... but the engine has no idea how fast the car is moving. All the engine knows is it's own RPM. Low RPM means low torque, low horsepower and poor acceleration.

The engine might have a problem within some RPM range, but that problem would exist (within that range) and should be evident in every gear, regardless of road speed.
However, you don't notice a lack of power anywhere except 40-50 mph. Apparently the car runs just fine everywhere else. So, my guess is both the engine and tranny are basically in good shape in and of themselves.

Maybe the tranny guys' diagnosis is purposely focused on basic transmission functions, and their tests deliberately exclude extraneous things like linkage troubles or adjustments....
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The Shop Manual's transmission "diagnosis and testing" section offers possibilities for any condition. If we assume some flavor of improper 3-4 gear shifting and therefore low RPM is suspect..

Under "AOD: Shift hunting 3-4 , 4-3":
One possible source is "Poor engine performance - EGR solenoid worn or damaged" (Tune up engine; replace solenoid)
The other source is "Manual linkage misadjusted" (Check and adjust or service as required)

So, who would suspect the EGR could cause this?

Linkage problems is one of those universal troublemakers.. and almost every transmission problem might be about "fluid level.."

When you say someone looked at the engine, and a shop checked the tranny, can it be assumed that all of the boring little things have been checked and taken care of?
Since you have to ask "What are the signs of a loss in compression?", that any mechanic took a close look at this car, much less that it has had a thorough tuneup and inspection is hard to fathom.

 

[blacklsc1]

im going with the converters being clogged. have they ever been changed?