Tach revs up 300 to 800 rpm on its owne.at hiway speed.
While driving on at about 100klms an hr.the tach goes up in rpms 300 to 800 rpms. it just jumps up for 2 or 3 seconds then returns to where it was. it also does it about 2 or 3 times in a row. then its good. a very sparatic problem, that just started today.the engine is a 5.2L V-8 the engine has 156000 klms. on it . any help would be great . thanks. chip
Re: tach revs up 300 to 800 rpm on its owne.at hiway...
My 1998 5.2 Dakota did the same thing... I removed the Idle Air Control valve and cleaned it with carb cleaner and my problem has been fixed (FOR FREE). At the same time I removed the Throttle Position Sensor and inspected it. I have read that running a very good fuel system cleaner in a tank of premium gas will help clean the carbon buildup on the sensors and throttle body. These two sensors are located on the Throttle Body and remove by unscrewing two Torx screws... the entire process took me less than 5 minutes. I know it is called an IDLE Air Control Valve (or solenoid) but my truck also did it while going down the road at certain speeds.
How to Clean the IAC Solenoid: This is recommended at every Tune-Up to prevent excess carbon buildup on the IAC plunger. In some cases, you'll notice a slightly erratic idle quality. This is the first step in taking care of that problem. IAC = Intake Air Control (Solenoid).
Remove the Air Hat from the Throttle Body
Disconnect the sensor harness from the IAC Solenoid (Rear of Throttle Body)
Remove the two Torx-25 Screws
Remove the IAC Solenoid (Be careful not to lose the rubber O-Ring)
Spray some Carb/TB Cleaner in the IAC port on the Throttle Body and let it sit
Spray some Carb/TB Cleaner on the tip of the IAC Solenoid and wipe clean (Do NOT forcefully twist or push the plunger - You will damage the Solenoid. Wipe very gently.)
Spray a little bit more Carb/TB Cleaner in the IAC port on the Throttle Body and wipe clean with a thin/lint-free rag
Reinstall the IAC Solenoid (Make sure you don't lose the rubber gasket on the solenoid)
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It is impossible to calculate with out knowing the over drive ratio (5th gear) and the diff ratio and tire size but with most vehicle with 5 speed boxes it should be in the 3000 to 3500 rpms range
The average vehicle at 74 miles/hr or 120 k/h runs around 3200 rpms
it doesn't matter how many cylinders or if 4x4 or make of vehicle , the rpms is tied to the ratio of the gear and the diff and the circumference of the tires
Sorry , it cannot be more exact than that
driving in over drive mode actually is what gives the economy as the engine rpms will be around 300 less than direct drive . Lower rpms = fuel savings
OD should come in around 60 klm/hr and drop out at around 50 klm/hr. When you are accelerating hold the pedal in a set position and watch the rev counter (rpms ) and each gear change you will see the rpms drop and then build back up as the vehicle speed increases At 100klm/hr the revs should be around 3200 rpms or less but if over ( say 3500 rpms) then may be the OD is not coming in. One way to test a box operation is to find a speed shop with a dynomometer and test the gear selections against loads and engine rpms
Nothing, you have hit the rev limiter. The up and down is the computer controlling the rpm. If you drive it, it should rev past 3,000. The computer is designed to keep free wheeling rpm to that level. It will only allow a higher rpm if vehicle is in gear and moving with a load.
2 issues, 1: MPG, you failed to say MPG, 15mpg? or 39? is 39 low? what MPG? you never said it?
2: rpm cruise. (what drive line, A/T M/T ?) what tranny? first google hit , is this it? this yours? engine: 1.5-litre 4-cylinder petrol, 75 kW/133 Nm Transmissions: 5-speed manual, 4-speed automatic, FWD
3300 RPM in 5th and 100km if you wish to now what is normal, find the final drive ratio, listed in the FSM. Id say this is normal. typical of tiny engines, with low torque.at lower RPMs.
if you have the A/T and IF the trannywere to slip, the TCM will infact throw DTC codes, telling you it did. IS IT? (scan tools show you this fact as might that glowing CEL lamp on the dash, on driving.
RPM my 1.6L spins 3000 RPM , at below tranny options valve counts. 54/59mph (104km/hr = 59) 5sp MT. 64.6 4sp A/T (goes fastest due to more aggressive OD + axle ratio is lower.) 56/.53 2sp A/T see how drive line effects RPM? so will your cars options.
likely what you are seeing is the first signs of slipping. If permitted to continue, likely it will get worse and you will then lose a bit of speed when it happens. In warmer weather the trans runs a bit hotter and will react to that. If you cannot hear the revs increasing but the tach says they are, it's also possible that for some reason the tach isn't reading correctly. Any good tech should be able to tell the difference. Problem I have is that I'm here and can't drive it to give you a "definite" on either.The only way to verify this yourself would be to attach an external tach to the engine and compare the rpms of the one in your dash to that one.