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Car Trouble?  
User currently offlineUSAir1489 From United States of America, joined Oct 2000, 364 posts, RR: 0
Posted (8 years 8 months 1 week 3 days 18 hours ago) and read 980 times:

I have an '86 S-10 Blazer (automatic transmission) and lately have either had the engine not going into overdrive or either it is and just running at a higher RPM. For instance, I could be driving down the highway at 65 mph and normally would show about 2,500 rpm, but have been showing about 3,000 rpm. It's also killing my gas mileage. Any ideas what could be the culprit?


Zinger Aviation Delta Oscar Tango Charlie Oscar Mike
13 replies: All unread, jump to last
 
User currently offlineBirdwatching From Germany, joined Sep 2003, 3822 posts, RR: 51
Reply 1, posted (8 years 8 months 1 week 3 days 18 hours ago) and read 974 times:

Common problem with older age automatic transmissions. Most likely a "software" problem, i.e. damaged chip. Have to go to the repair shop, no chance doing that yourself. Was back when the automatic transmission was less developed.

Soren  santahat 



All the things you probably hate about travelling are warm reminders that I'm home
User currently offlineUSAir1489 From United States of America, joined Oct 2000, 364 posts, RR: 0
Reply 2, posted (8 years 8 months 1 week 3 days 18 hours ago) and read 961 times:

I have had the engine and transmission replaced (both crapped out on separate occasions...engine is new and has 32,000 miles on it and the transmission is refurbished and has about the same number of miles on it, but slightly less, considering both events took place within a month of each other). Originally I had said to myself that I would keep it under 70 mph, fearing the engine might stall or quit because of the higher RPMs, but I have gone at least 20 miles at 75 mph and the engine was running about 3,200 rpm.


Zinger Aviation Delta Oscar Tango Charlie Oscar Mike
User currently offlineCfalk From , joined Dec 1969, posts, RR:
Reply 3, posted (8 years 8 months 1 week 3 days 18 hours ago) and read 957 times:

Sounds like the torque converter isn't locking up. Lockup is when the constant slip of the torque converter is eliminated, which effectively acts as overdrive, rather than an actual extra gear.

AFAIK, those transmissions did not have any computer chips or anything like that controling them. A sensor tells the coverter to lockup beyond a certain speed and low torque load. Might just be a $20 sensor to replace.


User currently offlineMuddydwagon From United States of America, joined Apr 2005, 657 posts, RR: 4
Reply 4, posted (8 years 8 months 1 week 3 days 18 hours ago) and read 957 times:

I believe in that transmission it is more than likely going to be a vacuum modulator common problem in old GM transmissions. I have changed a few of them. I am assuming that this is an 87(no reference for a 86 S-10 just full size)2.8L V-6, and a thm 400 transmission. The modulator is about $25.00 with tax and is common at all parts stores. Also make sure your transmission has been serviced thin fluid and a clogged filter will do the same.


Cheers Peter (ex-Chevrolet Technician)


User currently offlineUSAir1489 From United States of America, joined Oct 2000, 364 posts, RR: 0
Reply 5, posted (8 years 8 months 1 week 3 days 18 hours ago) and read 949 times:

It does have a 2.8L V6 but I'm not sure about the specifics of the transmission.


Zinger Aviation Delta Oscar Tango Charlie Oscar Mike
User currently offlineCFCUQ From Canada, joined Sep 2005, 712 posts, RR: 0
Reply 6, posted (8 years 8 months 1 week 3 days 17 hours ago) and read 938 times:

Quoting USAir1489 (Reply 5):
It does have a 2.8L V6 but I'm not sure about the specifics of the transmission.

Your tranny should be a THM700R4, 4 speed w/overdrive. The torque convertor clutch sounds like it is not locking up at cruise speed. Several possibilities, the clutch switch may have failed, or there may be a no power to switch problem. With later model GM's, we see lots of tranny failures because the alternator is not putting out a full 14volts, and therefore supplies a reduced voltage to the torque convertor switch, resulting in lots of slippage ( higher engine RPM ) until the transmission eventually grenades. I am an inspector for GMPP extended warranty program.


User currently offlineMuddydwagon From United States of America, joined Apr 2005, 657 posts, RR: 4
Reply 7, posted (8 years 8 months 1 week 3 days 17 hours ago) and read 933 times:

Quoting CFCUQ (Reply 6):
I am an inspector for GMPP extended warranty program.

Do you go out to the garages, or do you have the failed parts shipped to you and decide then?


Cheers Peter


User currently offlineCFCUQ From Canada, joined Sep 2005, 712 posts, RR: 0
Reply 8, posted (8 years 8 months 1 week 3 days 17 hours ago) and read 931 times:

Quoting Muddydwagon (Reply 7):
Do you go out to the garages

Personnally inspect vehicle/pieces at the shops, take notes and digital photos, send the whole shebang to GM, they make all decisions. I'm just their eyes and ears.
P.S. This is just one of the several jobs I have ..........
Vacation? The word is not in my vocabulary.


User currently offlineMatt D From United States of America, joined Nov 1999, 9502 posts, RR: 46
Reply 9, posted (8 years 8 months 1 week 3 days 17 hours ago) and read 928 times:

I had my Cobra washed and detailed today.

User currently offlineCFCUQ From Canada, joined Sep 2005, 712 posts, RR: 0
Reply 10, posted (8 years 8 months 1 week 3 days 17 hours ago) and read 921 times:

Quoting Muddydwagon (Reply 4):
Cheers Peter (ex-Chevrolet Technician)

I didn't know there were any Chevrolets in Sweden. Thought more likely Saabs ???????
Good to meet another slave of the General though.


User currently offlineMuddydwagon From United States of America, joined Apr 2005, 657 posts, RR: 4
Reply 11, posted (8 years 8 months 1 week 3 days 16 hours ago) and read 912 times:

Quoting CFCUQ (Reply 8):
Personnally inspect vehicle/pieces at the shops, take notes and digital photos, send the whole shebang to GM, they make all decisions

Ahh yes I used to deal with the warranty crap all the time, that was my other job in the shop. Warranty clerk

Quoting CFCUQ (Reply 10):
I didn't know there were any Chevrolets in Sweden. Thought more likely Saabs ???????
Good to meet another slave of the General though

There a some Chevrolets here and a new Chevrolet dealer in the next town over. I worked at a dealership in the US.
That is ex-slave of the general. Big grin

Cheers Peter


User currently offlineKevinl1011 From United States of America, joined Mar 2005, 2964 posts, RR: 47
Reply 12, posted (8 years 8 months 1 week 3 days 10 hours ago) and read 889 times:

Quoting Cfalk (Reply 3):
Sounds like the torque converter isn't locking up. Lockup is when the constant slip of the torque converter is eliminated, which effectively acts as overdrive, rather than an actual extra gear.

Cfalk is correct about the Torque Converter Lockup possibility...however it is not an overdrive. The torque converter (TC) is designed to allow a certain amount of "Slip" (input rpm v.s. output rpm). Torque Converter "Lock-Up" is a 1 to 1 ratio and is like fully releasing the clutch on a manual trans. The overdrive gear ratio is only present in the "D" position or 4th gear, with a 4 sp Auto.

Quoting Muddydwagon (Reply 4):
I believe in that transmission it is more than likely going to be a vacuum modulator

Negative....Sir. A modulator failure would create a high rpm upshift condition in all gears and not just cruise.

Quoting CFCUQ (Reply 6):
The torque convertor clutch sounds like it is not locking up at cruise speed. Several possibilities, the clutch switch may have failed, or there may be a no power to switch problem.

I agree this is most likely a TC lock up problem, however, the torque converter lock up solenoid obtains power from the same source as other trans.solenoids. Unless the open power circuit is at the trans connector pin for the TC, and only the TC, OR the solenoid itself, unlikely diagnosis (but not impossible) and you would have other problems.

Torque Converter lock-up is applied by the ECM (Electronic Control Module) after certain conditions are met. The ECM supplies a ground circuit the TC solenoid, which engages a "Sprag Clutch" inside the TC and locks up the converter to a 1 to 1 ratio. Not only does it need power (12v dc) but it needs a ground (neg.) path to the ECM.

The ECM will apply TC lock up once certain parameters are met. I can list a few of the items that the ECM considers to determine lock up.
1. Engine Temp
2. Throttle position
3. Engine Vacuum
4. Engine RPM
5. Brake application
6. Road speed
7. "Check Engine" light is on.
If the ECM is getting bad info on any of these items, no lock up.

You need to drive the vehicle with a Scan Tool that displays live ECM data to find out WTF. If the scanner shows the ECM is commanding lock up and it's not happening, then as CFCUQ suggested, check for power AND ground for the TC at the ECM. If power and ground circuits are good, most likely the TC lockup solenoid or TC sprag are bad.

[Edited 2006-01-14 06:30:39]

[Edited 2006-01-14 06:31:12]


474218, Carl, You will be missed.
User currently offlineUSAir1489 From United States of America, joined Oct 2000, 364 posts, RR: 0
Reply 13, posted (8 years 8 months 1 week 2 days 21 hours ago) and read 858 times:

I spoke with my mechanic and he did the scan that Kevin talked about and it concluded that everything that's supposed to happen happened...its going into overdrive and everything but noticed it was running at a high RPM. What he said he'd do is flush the entire transmission and radiator of fluid, do some sort of vacuum of the transmission and solenoids and put in new fluid. I hope this fixes the problem.


Zinger Aviation Delta Oscar Tango Charlie Oscar Mike
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