High RPM's while driving.

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  #1  
Old 11-04-10, 06:12 AM
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High RPM's while driving.

Recently my RPMs have been running unusually high while highway driving in 5th gear. I've checked on civic forums, but no one has been able to help, so i thought i would try here.

These are rough numbers, but the RPM's run close if not higher than these at the speed listed.
3.5k @ 65mph
4k @ 70mph
4.5k @ 75mph
5k @ 80mph.

This seems pretty high and I recall it used to be in the 4k when I would hit about 80mph.

Any ideas or suggestions?

1992 Honda Civic LX, 4 cylinder: 1.5 liter, 5 Speed Manual.
 
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  #2  
Old 11-04-10, 08:07 AM
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When was the last time the clutch was replaced? Notice any slipping in the lower gears?

Know how to do a quick and dirty clutch test? First...find a big tree......
 
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Old 11-04-10, 09:17 AM
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Clutch has never been replaced to my knowledge.
But i have no signs of clutch wear or slipping. Clutch grabs when released, shifts smooth, no burning smells. I can drop it and spin tires.
 
  #4  
Old 11-04-10, 09:43 AM
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Just to ask perhaps what might be a dumb question. Are you sure that the engine is actually going that fast at those speeds because of the engine sound, or are you trusting only what the tach is reading in the instrument cluster. 5k at 80mph would have the engine pretty close to screaming and the valves getting ready for a hood dance. Is this the actual case?
 
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Old 11-04-10, 09:58 AM
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Not a Pro mechanic...but I've turned a few wrenches in my day.

Well..it still sounds like your clutch is worn. Since its a manual...you have a (relatively) solid connection from engine to wheels. The only area for slippage would be the clutch.

Since it's a hydraulic clutch..things like linkage wouldn't really come in to play...though that should be checked for adjustments if there are any.

From an Internet search I found this...
"To test the clutch for slippage, set the emergency brake and start the engine. Place the transmission or transaxle in high gear. Then try to drive the vehicle forward by slowly releasing the clutch pedal. A clutch in good condition should lock up and immediately kill the engine. A badly slipping clutch may allow the engine to run, even with the clutch pedal fully released. Partial clutch slippage could let the engine run momentarily before stalling"

We used to put the car against a large tree or solid block building, using an old tire as a cushion if needed, and did the same thing. Back then everything was rear wheel drive so the e-brake thing wouldn't work. Of course we also had inspection covers on the clutch to allow visual checks as well.

Oh....you may want to get your tach checked for accuracy just in case.
 
  #6  
Old 11-04-10, 10:11 AM
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equinox.
I pay attention to that on my drive home today.
Right now im going by the tach, which used to read lower.

Gunguy45
We checked for a linkage a couple weeks ago, but there wasn't one to adjust.
I'll give the 5th gear stall a try when i leave work, see if it stalls or not.
 
  #7  
Old 11-04-10, 10:22 AM
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As I see it ......
1) Is your tach correct?
2) Is your speedo correct?
3) Is your clutch slipping?
4) Are you indeed in 5th?
 
  #8  
Old 11-04-10, 10:31 AM
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1) Not sure.
2) About 95% sure it's correct.
3) Doesn't feel like it, but it's possible.
4) Yes
 
  #9  
Old 11-04-10, 02:08 PM
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In addition to what has already been posted you should:

Ignore the “MIL” and scan the “PCM” even if the “MIL” is off. If there are error codes, post them so we can see them. Disassemble the throttle body, and thoroughly clean each part separately in a parts cleaner. Reassemble and reinstall the throttle body using new gaskets.


IAC Leak

(Idle Air Control Valve) Disconnect the IAC connector. The idle speed should decrease. While the connector is disconnected, block the hole or pinch the hose that connects to the IAC valve. If the idle speed decreases the valve is leaking. This situation may or may not set a code.


ECT sensor

(Engine Coolant Temperature Sensor). Voltage at the ECT should be around 3 volts at 60 degrees Fahrenheit, and between .55 & .7 volts at normal operating temp. Voltage that is above .8 volts at normal operating temperature will cause a rich mixture and a high idle speed. If thresholds are not far enough out of normal operating range a code may or may not set. You should also know that ECT sensor will not read temperature correctly if the coolant is low.

Vacuum leaks due to:


Loose vacuum hose connections.

Worn, cracked, split, or dry rotted vacuum hoses.

A leaking intake manifold gasket can cause high idle as well as idle fluctuations. You should also rule out a vacuum leak at the PCV valve grommet, and confirm an operational PCV valve. Since the car is a 92 better off just changing all the vacuum hoses.


TPS (Throttle Position Sensor) Confirm .5 volts with the throttle closed.

Confirm the cooling system is full, and burp the system to rule out an air pocket.

Remove the air boot from the throttle body and cover the throttle body with something that will stop the airflow. With the engine running, the throttle body covered, and no air entering the engine, confirm that the engine stalls. If the engine does not stall, find and repair the vacuum leak (at least one leak) that is present.

Busy right now.
More info coming.
Check back in a few hours.
 
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Old 11-04-10, 02:30 PM
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Sam...did I miss something? You seem to be responding to a different post. No mention of high idle or trouble lights.....
 
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Old 11-04-10, 04:59 PM
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So on the way home I tried 2 methods to see if the clutch was slipping.
1) Test 1
Car stalled on me almost instantly

2) Test 2
Did this and car was sluggish, and rpm's dropped

So this leads me to believe it may be another issue.
I've removed and cleaned the throttle body, I've checked for leaks on vacuum hoses.
 
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Old 11-04-10, 05:19 PM
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Do you have stock tire size or have you altered it?
 
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Old 11-04-10, 05:43 PM
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Tires are correct size.
How can i check to see if my tech is messed up?
 
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Old 11-04-10, 06:46 PM
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With the engine running and the coolant temperature above 90 degrees Fahrenheit, confirm that vacuum is not present on the lower port in the throttle body. If vacuum is not being lost, check for a defective fast idle valve on the bottom of the throttle body. However do so only if the coolant hose is in good condition and hot. Confirm the base idle screw (top of the throttle body) is not turned all the way out. If necessary re-adjust the base idle and see if the high idle issue continues. The upper port (front of the throttle plates) feeds the (IAC) and the base idle screw. If the IAC is unplugged and the base idle screw is turned all the way in and there is still airflow through the upper port, check for a stuck open IAC valve.
 
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Old 11-04-10, 06:52 PM
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(Quote) Sam...did I miss something? You seem to be responding to a different post. No mention of high idle or trouble lights.....

Gun,

Well, its way past “Happy Hour” buddy and you should be proud of me. I started at 7:07 this morning and I just started second bottle of “Beam”.

Today 06:12 AM
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(Question) High RPM's while driving.

We’re talking “Honda” here buddy. Great car, but weird at times. More times than not, engine/PCM doesn’t know the difference between high idle and high rpms. Sounds like a clutch issue to me as well, but believe it or not buddy all I posted needs to be ruled out, before faulting the clutch.

Seen it
Been there
Done that


Countless issues caused by failing “EGR’s as well.

Cling to your bible
Cling to your gun
Semper Fidelis
Buddy
Sam
 
  #16  
Old 11-04-10, 11:41 PM
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Checking the tach calibration at various RPM's with another tach would be a way unless the PCM is involved at Sam said. Having someone hold the RPM's steady at 2, 3, 4, and 5 K intervals would let you know if something is wrong. It could still be a clutch problem but you have almost ruled that one out through the stall test you did. Did you confirm if the engine sounds seem to reflect higher revs than in the past at those speeds indicated on your speedo?
 
  #17  
Old 11-05-10, 03:46 AM
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Unless you have something slipping, a higher RPM would produce a higher road speed, regardless of what the PCM is doing. Equinox suggests "sound", and that is a good indicator as well. Does it "sound" different? I have a racing lift pump on my Dodge cummins and I can detect a distinct "sound" difference when the intake heater comes on. It puts a drain on the electrical system, affecting most everything. RPMs of the pump decrease until the heater goes off. That constant whirring sound is ingrained in my brain and I know when it gets "off".
 
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Old 11-05-10, 04:04 AM
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(Quote) the PCM is involved as Sam said.

Not necessaraly the pcm....Could be....But in this case I'm thinking more an engine issue....In any event.....Good show equinox

junkit,

Just a reminder....A Honda is a great car, but it has a history of presenting issues in a wierd way....For the rpm issue you're describing....An engine/pcm issue must be ruled out....Before a clutch issue can be ruled in.
 
  #19  
Old 11-09-10, 04:41 AM
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Ok, so yesterday afternoon i'm driving home on the highway.
I'm doing about 75-80mph and tach was running between 2 1/2k to 3k.

Then I watched the tach jump to 4k. Then it started fluctuating for a little bit then rode steady.

This morning everything was back to the RPM's from the original post.

The engine sounded the same during this entire processes. Think it's just a faulty tach?
 
  #20  
Old 11-09-10, 06:34 AM
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Junkit, yes, it sounds like a faulty tach reading as what I first thought. Check your harness connection at the distributor as a first step to make sure that it is clean and properly clipped/connected before doing anything else. After doing that and assuming however that it is a bad tach in the cluster you could decide to install an aftermarket tach as one easy option. This link shows a video that someone put together doing their '93 Civic. It's not a pro installation but shows the basics. The other option is of course to just drive it the way it is until it is time to donate it to the local yard. That is probably what I would do. Many of us have driven lots of manual cars and trucks that never even came with tachs, nor needed them.

YouTube - How to:Install a tachometer(rpm gauge)
 
  #21  
Old 11-09-10, 06:41 AM
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Thanks for the help guys. If anything else pops up, i'll be sure to return.

I'll probably just keep the tach as is, since its a very old car. Trying to put only enough $$ into to keep it running with good gas mileage.
 
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Old 11-09-10, 12:51 PM
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Thanks for the help guys. If anything else pops up, i'll be sure to return.

junkit,

You're very welcome. Just a small reminder that we are still waiting for answers to our questions.

Note that we must ask these questions because we don't have your Civic in front of us. Since we're doing online auto repair we need your feedback.

That feedback can only come in the form of answers to our questions.

Let's start with a really simple and obivious quesion.

Are there any codes?

Use the link below to answer

Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical
 
  #23  
Old 11-10-10, 03:55 PM
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Ase,
I ran the test and i didn't get any sort of Trouble Codes. The check engine light came on when the car started up as usual and went off.
 
  #24  
Old 11-12-10, 12:06 PM
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Ase,
I ran the test and i didn't get any sort of Trouble Codes. The check engine light came on when the car started up as usual and went off.


Good.
Baby steps, but we’re getting there.
There are still many unanswerd questions and unresolved test results.


Let’s move on to an oldie but a goodie.

[COLOR="black"]That would be an engine vacuum pressure test.[/COLOR

Drive with a vacuum pressure tester attached to the engine and post the results under different engine loads.

Still too soon to tell.
Need more answers and test results.
If vacuum pressure test results go as I'm thinking.

We're looking at a possible pressure plate issue here.
 
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