RPMs

vando002 · #1 02-04-2008, 08:03 PM

Ever since I bought this car I've noticed that the RPMs are pretty high when driving highway speeds. My car is a 02 impala LS 3.8L engine. I have a 99 blazer with a 4.3L engine and when I'm driving steady at 70 mph the RPMs are about 2000. When I'm going 70 mph in the impala, the RPMs are over 3000. First off, is that normal? Why would the RPMs be so much higher in the car? This seems like it would kill the gas mileage in the car with the RPMs being so much higher. Just curious. Thanks.

grandprixgtx00 · #2 02-04-2008, 08:39 PM

its normal. my Grand Prix GT w/ the 3800 is usually around 2800-3000 RPM's when im on the freeway going 70ish.

w/ the L36 (3800 V6) you should be getting around 30-33MPG. i know i average about 33.2MPG on the freeway.

phewop118 · #3 02-04-2008, 11:43 PM

No. With the 3800 and the 3.29 axle ratio, which I think all Impala LS's have, the rpms should be right above 2000 at 70 mph. You might have a common problem with your 4th gear clutch preventing it from shifting into 4th (lots of $$ to fix), or perhaps a torque converter that refuses to lock up.

grandprixgtx00 · #4 02-04-2008, 11:51 PM

my bad...guess i cant compare a Impala LS to my GP

**edit** nvm, i hit the freeway today after work, and i guess my car is around 2200 RPM's at 70, sounds like you may have an Overdrive problem....have you tried manually shifting it outta overdrive, then put it back in??

BNaylor · #5 02-06-2008, 01:50 PM

Quote:

Originally Posted by grandprixgtx00

my bad...guess i cant compare a Impala LS to my GP

Why not? Same engine, same tranny and same 3.29:1 final drive gearing.

Taching 3K at 70 mph is definitely abnormal. As mentioned earlier it sounds like it is not going into 4th - OD and as a result the torque convertor clutch is not locking since it must be in OD for the TCC to cycle on and off. Also, OD will not normally engage until you are at speeds of 45 mph and above. Further, based on weather conditions (extreme cold) and until the engine is properly warmed up including internal tranny TFT it may take a few miles of driving before 4th - OD will engage on it's own.

Common problem but the worse to have for no 4th - OD is the 4th clutch shaft where the splines are stripped out. Non properly hardened material used in which the new AC Delco one is. Also, could be a shift solenoid issue (electrical). It is best to get it scanned with a trans capable scanner to see if any tranny related DTCs are stored. Note: Many do not trigger the SES/CEL light but are stored for retrieval.

phewop118 · #6 02-06-2008, 09:14 PM

It is possible to be in 3rd gear and have torque converter lockup - you'll know it when you push gently on the gas while in 3rd and the rpms don't increase, but you still accelerate. You will know if it's a torque converter problem because when you gently ease into the gas at highway speeds, if the rpms increase more than a trivial amount (more than 50-100rpm), then you are not getting lockup.

vando002 · #7 02-08-2008, 08:36 AM

Thank you all for your replies. I was wondering why my gas mileage sucked and why the RPMs were so high. I will have it checked out soon and keep you guys posted. Hopefully it's the electrical issue. It has 260,000 miles on it so I guess the 4th gear splines could be broken. Would the torque converter need to be replaced or the whole transmission?

j cAT · #8 02-08-2008, 02:38 PM

Quote:

Originally Posted by vando002

Thank you all for your replies. I was wondering why my gas mileage sucked and why the RPMs were so high. I will have it checked out soon and keep you guys posted. Hopefully it's the electrical issue. It has 260,000 miles on it so I guess the 4th gear splines could be broken. Would the torque converter need to be replaced or the whole transmission?

it could be the torque converter lock up is failing because of the brake pedal switch. with that mileage that switch is worn.....when you step on brake pedal this part of switch disables the torque converter. i believe at 70mph this would amount to 700rpm increase.........this is cheap and a easy place to start.....also as a test put in 3rd, then 4th see if it changes. then put one foot on gas hold speed at 70 and with other foot lightly push down on brake pedal you shuld see 700rpm increase if no change then this is where your problem is. most likely the switch.....

vando002 · #9 02-09-2008, 11:54 AM

I have placed it in third gear then shifted to fourth and vice versa and there is no change in RPMs at all. I can't believe I didn't figure this out earlier, I've put 10,000 miles on this car since I got it from the dealer. I could've gotten such better gas mileage too. Too bad I got the car "as is". I'll try slightly pressing the brake to see if there is a slight surge in RPMs. Just curious, why would that happen? Do you happen to know what the brake switch looks like and is it placed directly behind the pedal?

BNaylor · #10 02-09-2008, 12:12 PM

Best way to test the brake switch is via the cruise control. Get up to cruising speeds, engage the cruise control, tap brake and see if cruise disengages. Same part of the switch is used for TCC functions.

Someone else mentioned it but cruise for example at a range of 55 - 70 mph. Choice is yours as to what specific speed. Then watch tach rpms, hold foot steady on gas maintaining steady speed, with other foot tap the brake. You should briefly see the rpms increase a few hundred rpms indicating the TCC has unlocked. Now it sounds like you are in a situation where there is absolutely no 4th - OD so you may not see the TCC lock/unlock function.

vando002 · #11 02-10-2008, 01:21 AM

Today I traveled a steady 70mph and tapped the brake with the other foot. The rpm gauge nudged ahead only slightly, maybe only 100 rpms. Also, tapping the brakes did shut the cruise control off. Could it still be the brake switch? It seems like the inexpensive way to go. Thanks for your help. I'll try to find someone with a scan tool soon. Thanks again.

vando002 · #12 02-13-2008, 09:23 AM

I was wondering around Advance Auto's website and came across these transmission solenoids. Wondering if these could be the problem. Or could it still be the brake switch after I did the test in my post above this one?

http://www.partsamerica.com/ProductL...ssion+Solenoid

Thanks

j cAT · #13 02-13-2008, 11:20 AM

Quote:

Originally Posted by vando002

I was wondering around Advance Auto's website and came across these transmission solenoids. Wondering if these could be the problem. Or could it still be the brake switch after I did the test in my post above this one?

http://www.partsamerica.com/ProductL...ssion+Solenoid

Thanks

you have lost 4th gear. start a new post and hopefully someone will have knowledge about what it could be. your rpm quote is too vague.....

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