Sign in to follow this  
bplaney

Rpms Too High?

Recommended Posts

My '99 GS300 has 108k miles on it now...

I also have a 2001 Honda Odyssey with a 3.5 liter V6. THAT car barely cracks 2200 RPM at 75 mph. My GS300 (running on premium gas) is about 3200 RPM at the same speed.

It is almost as if I don't have a final gear to shift into (whatever number that may be).

My gas mileage generally sucks. In town - about 14-15 mpg... If I burn a tank exclusively on the highway - I'm lucky to hit 21 mpg.

What could be wrong?

Share this post


Link to post
Share on other sites

By looks of RPM number and gas/milage, it seems your trans doesn't shift into overdrive (5 speed).

Sometimes shifting probs. are related to a knock sensor failure, causing the ECU to !Removed! the engine (no overdrive). In general, an engine warning light should pop-up, accompanied by some fault-codes. You should check this first.

Suspect may be your air/fuel chain: MAF sensor (engine lean), O2 sensors, catalyc converter, sparkplugs, evaporative emission (cap loose?), temp sensor, trans solenoid, etc.., perhaps a combination of above.

Share this post


Link to post
Share on other sites

By looks of RPM number and gas/milage, it seems your trans doesn't shift into overdrive (5 speed).

Sometimes shifting probs. are related to a knock sensor failure, causing the ECU to !Removed! the engine (no overdrive). In general, an engine warning light should pop-up, accompanied by some fault-codes. You should check this first.

Suspect may be your air/fuel chain: MAF sensor (engine lean), O2 sensors, catalyc converter, sparkplugs, evaporative emission (cap loose?), temp sensor, trans solenoid, etc.., perhaps a combination of above.

If it is the catalytic converter, how would you actually check it without removing it?

Share this post


Link to post
Share on other sites

Without removal of the converter it's a bit more complicated, but can be done. You can check by intake vacuum or exhaust backpressure. To check intake vacuum, connect a vacuum gauge to a (vacuum) port on the intake manifold. If you start the engine, read the vacuum reading at idle. Increase engine speed to +/- 2,500 rpm and hold steady. Normal vacuum at idle (for most engines), should be around 18 to 22 inches Hg. When increasing engine speed there should be a momentary drop in vacuum before it returns to within a couple of inches of the idle reading. If vacuum reading is lower than 'normal' and/or continues to drop as the engine runs, this might indicate a buildup of backpressure in the exhaust. Note that intake vacuum can also be affected by retarded ignition- and valve timing.

For backpressure, a gauge can be connected (for example) by removing the oxygen sensor and connecting the gauge to the hole in the exhaust manifold. Once you've made a connection, start the engine and note backpressure reading. The 'normal' amount of backpressure can vary per car, some handle 0 to 0.5 / 1.25 psi at idle, but should have more than 4 psi during a snap acceleration test.

If you notice a relatively high backpressure reading (for ex. 8 or more psi), there's probably an exhaust restriction, or clogged converter. This can also be caused by a collapsed pipe or muffler. If you feel the converter is bad, exclude the pipes first.

Share this post


Link to post
Share on other sites

I have just bought a GS430 with the V8 engine and I feel that mine is too high as well. When I am at 70mph it is around the 2500 rmp mark. Now I had a BMW 735 with a V8 and 3.5 litre engine and the rpm is much lower at 70 mph. What is the best way to check? are there any codes or anything of that sort to tell me if there is anything wrong?

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this