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93 Astro kicking out of overdrive?

3K views 16 replies 8 participants last post by  sixsix 
#1 ·
Hi all,

My parents have a 93 Chevy Astro with 220k+ miles on it. It's had an issue for a while where you can feel on the highway occasionally it 'loses power', as my dad describes it. I've felt it too when I've driven it before, it's very soft and very intermittent and never throws a code, and after experiencing a significant number of issues with the transmission on my 97 Buick Lesabre, it feels to me like it's more a transmission problem than an engine problem to me. He's had several different mechanics look at the vehicle and has replaced spark plugs, ignition wires, distributor & cap, one mechanic repaired some vacuum leaks... I'm not sure what all else, I keep asking him for a comprehensive list and he hasn't gotten it to me yet.

I'm suspecting the transmission is dropping out of overdrive for some reason, that is what it feels like to me. I asked him to take it on the highway in 'drive' instead of 'overdrive' the other day and he said it didn't seem to have any issues. But I'm kind of stumped on where to go from there. There are so many parts that send a signal to the overdrive! Where do I start looking?

Also, is there some kind of scan tool I can use to check RPM, vacuum, coolant temp, etc.? It's been invaluable to use my OBDII reader and Torque when I've worked on my Lesabre, but the Astro is too old for the OBDII.

Thanks in advance!
 
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#2 ·
rawheight said:
I'm kind of stumped on where to go from there.
The answer "may" be a LOT simpler than you realize.

Assuming everything is working correctly.. when an engine starts pushing 220K+... it is not as strong as it used to be. You may simply be pushing the throttle harder in some cases, to maintain speed. This will signal the trans to drop out of lockup as intended, to cause the torque-converter develop more torque. A slight incline or maybe even a gentle headwind can easily cause this condition.

Sidenote: This is the reason for the "tow/haul" switch. The extra load of pulling a trailer will cause the trans to constantly unlock to compensate for the need for more torque. The little 4.3 is only capable of limited torque at low cruise rpms.. so the torque converter will unlock to attempt to do it's job and make more torque. But running like this constantly would produce damaging heat and lead to premature trans wear and failure, so the switch tells the converter to stay locked up longer, and prefer a down-shift when needed. You can actually try using the switch and driving without a trailer this way, but it won't make the engine any stronger.

There is of course always the possibility the converter has an issue, with this much mileage on it. But my guess is this may not likely be the case. Dropping the pan while doing a filter change will reveal if this high-mileage trans is starting to develop issues.

You may find however there is absolutely nothing wrong, leaving everyone "stumped" on trying to find a problem.

PS: Welcome to the site.
 
#4 ·
That issue can cause also TPS, especialy in overdrive, it almost looks like the transmission want to slip, check if this is ok. You can see it the best when you drive, the revs jumps up amd down, how it want to shift. But I am not sure if your transmission is electronicaly shifted orbit has kickdown cable...
 
#5 ·
Mmusicman said:
You may simply be pushing the throttle harder in some cases, to maintain speed. This will signal the trans to drop out of lockup as intended, to cause the torque-converter develop more torque. A slight incline or maybe even a gentle headwind can easily cause this condition.
If this is the case, would it happen in both "Drive" and "Overdrive"? This is why I had my dad drive the van on the highway in "Drive" the other day, to see if I could isolate if it was an Overdrive issue or not. I may have to borrow the car for a week and drive it around myself to get a better idea of when the issue is occurring.

Thanks for the welcome, and thanks for the help!
 
#6 ·
LumaWJ said:
That issue can cause also TPS, especialy in overdrive, it almost looks like the transmission want to slip, check if this is ok. You can see it the best when you drive, the revs jumps up amd down, how it want to shift. But I am not sure if your transmission is electronicaly shifted orbit has kickdown cable...
Unfortunately the van does not have a tachometer. This is why I was looking to see if there is some kind of reader that can be used with these vehicles and something like the Torque app?? I don't have any way to check to see what the RPM is doing otherwise. Although I can say, just based on engine sound, it sounds like the RPM is constant.
 
#9 ·
rawheight said:
I asked him to take it on the highway in 'drive' instead of 'overdrive' the other day and he said it didn't seem to have any issues.
rawheight said:
If this is the case, would it happen in both "Drive" and "Overdrive"?
No, the opposite. The problem would be far less likely to happen in drive, than over-drive.
Increasing engine rpm (dropping down a gear) dramatically increases horsepower/torque output.
There is less strain on the engine and trans. This is why "Drive" is suggested for towing... not OD.

You're description of the problem "seems" to support my suggestion of "possibly" weaker engine output.
I'm just guessing old age, unless something is actually causing the trouble.
 
#12 ·
I absolutely Love these types of threads.
Starts off with a guy ( whoolps, a person ) wondering why his _____ ____ ( fill in blank(s)) is not running like it did way back 25 or 30 years ago...

LOL - I wonder too, I get it up the top of the driveway, but just don't last long before I am going over the curb and making a mess...

but I digress.

Then they devolve into noone knowing what was or when it wasn't avail on Gen 2.5.
And I looked at Will's links ( last word? on Astro Safari ephemera ) and could not find the start of the Tow/Haul Feature.
Maybe 2000.
G00gull did not help either ( some stuff, really important stuff like this is horrifyingly ( LOL ) missing.

Yup, pretty dull
 
#13 ·
@sixsix SO sorry to have bored you - _ - perhaps next time you can just move on without burdening yourself with commenting?

I understand the car is old. I would like to run through some paces to make sure I can rule out everything else before just saying 'the car is old'. If anyone has any ideas of what parts I can look into to check and see if they are sending the wrong signals to the overdrive system, I would really appreciate it.
 
#16 ·
https://sites.google.com/site/astrosafa ... enerations gives general overview about what has changed over the years, reading with open eyes required.

rawheight said:
I understand the car is old. I would like to run through some paces to make sure I can rule out everything else before just saying 'the car is old'. If anyone has any ideas of what parts I can look into to check and see if they are sending the wrong signals to the overdrive system, I would really appreciate it.
Are you sure that it's completely downshifting, or is it just coming out of lockup? If it's just coming out of lockup it could be something simple like a speed sensor, TPS, or even a loose/faulty brake switch.
 
#17 ·
rawheight said:
@sixsix SO sorry to have bored you...
First off, thanks for the @sixsix "tag" - honestly, it is a 1st for me - no cell, not a texter, don't use social media.

OK, YOU did not bore me at all - in fact, your posts were the MOST informative. The rest of it seemed so futile and reaching ( Tow/Haul, a '93, really? ).
In particular, your 1st post and the 1st couple sentences you shared:

"My parents have a 93 Chevy Astro with 220k+ miles on it."
"It's had an issue for a while where you can feel on the highway...
- occasionally it 'loses power', as my dad describes it."
"I've felt it too when I've driven it before, it's very soft and very intermittent and never throws a code...
- and after experiencing a significant number of issues with the transmission on my 97 Buick Lesabre"​

We have a '92 w/ CPI FI ( "W" in the VIN ) and the 4L60 Trans - they have 200K+ on them and we have had it since '94.
It had 30K on it and it was ...in a word, Very peppy.
It represents the highest HP setup ( 200 ) used on an M or L class Van.

And if I or maybe if it wants it to be - It is still pretty darn quick - burns rubber easily on a dry day, so OK...
But sometimes... it is a dog - terrible gas mileage, hunting for gears on a hill, downshift twice on a decent grade.
A slight press and it kinda' bogs sometimes, speed indeterminate - here's to wishing them a Blue "Pep Pill".

But... still gets out of it's own way pretty well and is very reliable... Just like an old guy or gal.
- the only times it would not start is from my own stupidity x 3 or 6 times - LOL.

I would guess your parents feel sorta' close to that - maybe not. Bet it is the same style motor and stuff.
Sorry to have thrown you off a bit - I'll get back into my Hole in the Garage - playing w/ our Van Door Refurbish.

Maybe next time I'll get one of those ubiquitous "Hash # Tags" - LOL - one can only hope.

:banana: :banana: :banana: :banana:
 
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