RPM jumps

G

Guest

Guest
Hi all,
I have a questions related to sudden RPM jumps which I recently observed
. The thing is that driving 120 km/h on the straight highway using the
same tires and carrying the same load the rpm are different. Usually I'm
getting 2600 RPM but sometimes I can get 3000 or 2800 for long time but
it can just suddenly jump to lower value. The odd thing is for example
that whet the RPM are at 3000 (I'm talking about driving 120 km/h for
some time so the engine is warm enough) i reduce the speed and
accelerate again and the RPM goes to 2600 at same speed.
To be honest I can't hear the difference in RPM so I'm suspecting that
it might be some RPM measurement malfunction. (or maybe I just hope it
is ...: )
I checked the RPM gauge buy replacing it with friends and I got the same
result. One option would be that the RPM sensor is malfunctioning - but
I would expect that it would occasionally drop to 0.
Any ideas what might be the reason for RPM jumps ?
Regards,
Tomaz
--------------------------------------------------------------------
1996 HDJ80 (1HD-FT 24V, manual gearbox), OME Lift (6 cm), Safari
snorkel, Front runner long ranger tank (170L)
 
G

Guest

Guest
Tomaz,
Location:
FSM Body Electrical Systems
Page BE-48
Diagnostics:
FSM Body Electrical Systems
Page BE-56
Tachometer System
1. INSPECT TACHOMETER (ON-VEHICLE)
(a) Connect a tune-up test tachometer, and start the
engine.
NOTICE:
=95 Reversing the connection of the tachometer will damage
the transistors and diodes inside.
=95 When removing or installing the tachometer, be careful
not to drop or subject it to heavy shocks.
(b) Compare the tester and tachometer indications.
If error is excessive, replace the tachometer.
2. (Diesel Engine)
INSPECT PICK-UP SENSOR
Measure the resistance between terminals 1 and 2.
Resistance: approx. 730 Q
If resistance value is not as specified, replace the sensor.
--
Rgds,
Roman (London, UK)
'92 HDJ80 (auto)
On Wed, Mar 5, 2008 at 9:58 AM, Tomaz Sustar <[Email address removed]> wrote:
 
G

Guest

Guest
Hi Roman,
thank you very much for this info - I'll do that today and I'll post the
results.
Regards,
Tomaz
 
G

Guest

Guest
Tomaz,
First I would check what the rpm vrs speed should be for a given gear using
a gear calculator. One here http://www.4lo.com/calc/gearratio.htm
It's American so the units are English ;). You will need to know the tire
diameter, gear ratios, enter the speed 120kph=75mph and you should have rpm.
Then check what provides the reference to the tacho and if it's something
like a mag pickup on the flywheel then use a meter with Hz for a scope to
check that, alternatively if it is a pickup try substution with a good one.
If it is a pickup check it is fitted well and doesn't have a metal swarf on
the end.
I am assuming this isn't happening when stationary?
Malcolm
Stafford (UK)
FJ45 '75 & FJ45 '76
Any ideas what might be the reason for RPM jumps ?
Internal Virus Database is out-of-date.
Checked by AVG Free Edition.
Version: 7.5.516 / Virus Database: 269.21.1/1299 - Release Date: 26/02/2008
09:08
 
Don't like the adverts? Remove them by becoming a supporting member.   Click here
G

Guest

Guest
Tomaz
Mine does this too from time to time. I just ignore it because -
mostly - it seems to cure itself if I leave it for a day or two.
If you *do* find a reason I'd be interested.
I have never found any correlation between the (dis)appearance of this
and usage, humidity, temperature, vibration, etc, etc. I've always
assumed that the sensor is Zen Buddhist and the gauge Shinto, and that
from time to time they argue - but that can't really be right because it
doesn't seem to be affected by the phase of the moon either ...
Christopher Bell
Devon, UK
1996 1HD-FT
| I have a questions related to sudden RPM jumps which I recently
observed
____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses
 
G

Guest

Guest
Hi Christopher,
in the beginning I observed the jumps when the engine was relatively
cold but now I can see them even when the engine is hot. But the fact is
that after they disappear the engine runs perfectly and the values of
the RPM are always at lower value - so I think that the correct value
would be 2600 rpm at 120 km/h.
But anyway I will first check the resistance of the sensor as Roman
suggested and I will post the results.
Regards,
Tomaz
 
G

Guest

Guest
Tomaz
When I see it the error is at all revs: tickover "pretends" to be at 200
- 400rpm, and 70mph "pretends" to be anything from 2600 to 3000rpm, with
the needle flickering from time to time.
Because mine is a manual gearbox I know the tacho must be wrong, since
engine speed must match road speed! For me the correct value at 70mph
in 5th gear is a shade over 2500rpm.
I worried about it when it first happened a few years ago, but it *did*
go away and I now only see it very rarely. By all means try to sort
it out, but if your experience is anything like mine it will go away all
by itself given time. I've seen it once so far in 2008 for about an
hour.
Suggestions I have been given over the years include loose earth strap
on engine and bad sensor. I *think* the sensor is magnetic, and I
suspect that it is just dirt or oil in there resulting in a noisy
signal.
Good luck anyway.
CB
|
| Hi Christopher,
|
| in the beginning I observed the jumps when the engine was relatively
| cold but now I can see them even when the engine is hot. But the fact
is
| that after they disappear the engine runs perfectly and the values of
| the RPM are always at lower value - so I think that the correct value
| would be 2600 rpm at 120 km/h.
|
| But anyway I will first check the resistance of the sensor as Roman
| suggested and I will post the results.
____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses
 
G

Guest

Guest
Hi Tomaz
My rev counter jumps quite a lot some times, like it gets a shock from time
to time.
It has done this for years so most of the time I dont see it and have not
noticed any differance in the actual sound of the revs or performance.
I have put it down to just another thing I have to live with.
I know mine is the auto and older but at 120km or 130km my revs would be in
the early 2000s.
john 92HDJ 80 1HDT
 
G

Guest

Guest
Thank you all for your answers !!
i did the measurement of the sensor resistance and it is within the
tolerances in the Toyota manual for 1HD-FT (I checked the book in Toyota
garage). The only thing I know for sure is that the jumps are more
frequent when the engine is cold.
As John mentioned I also can't hear any difference in the actual sound
of the revs so I guess I will just stop bothering about it ...
Thanks & Regards
Tomaz
--------------------------------------------------------------------
1996 HDJ80 (1HD-FT 24V, manual gearbox), OME Lift (6 cm), Safari
snorkel, Front runner long ranger tank (170L)
 
G

Guest

Guest
Problem with resistance measurement is exactly that, you can only measure it
easily cold and with the engine not running, the sensors no cars always seem
to fail in a warm mode.
Odd coincidence, workmate has just gone to tow his wife back home in her
diesel Fiat Punto, crank sensor has failed and even though it's diesel the
engine stops - seem to be known for it. I suppose sometime newer Toyota
diesel probably do the same or go into a limp mode, another spare for the
long distance travellers.
Malcolm
Stafford (UK)
FJ45 '75 & FJ45 '76
-----Original Message-----
From: [Email address removed] [mailto:[Email address removed]] On
Behalf Of Tomaz Sustar
Sent: 05 March 2008 13:18
To: [Email address removed]
Subject: Re: [ELCO] RPM jumps
Thank you all for your answers !!
i did the measurement of the sensor resistance and it is within the
tolerances in the Toyota manual for 1HD-FT (I checked the book in Toyota
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.516 / Virus Database: 269.21.4/1313 - Release Date: 05/03/2008
09:50
 
G

Guest

Guest
Malcolm
I have got to a stage that if the cruiser goes and keeps going I dont
really care about the extras that I did enjoy.
But It does seem interesting that it only takes a small sensor to fail in a
more modern vehicle and you could be left stranded.
john 92HDJ 80 1HDT
 
G

Guest

Guest
True, on some of the Perkins electronic diesels we use for generators there
are two sensors, one on the cam, one on the crank, they keep running if one
fails - new Toyota engines might use the same method for all I know.
Malcolm
Stafford (UK)
FJ45 '75 & FJ45 '76
-----Original Message-----
From: [Email address removed] [mailto:[Email address removed]] On
Behalf Of john byrne
Sent: 05 March 2008 14:49
To: [Email address removed]
Subject: Re: [ELCO] RPM jumps
Malcolm
I have got to a stage that if the cruiser goes and keeps going I dont
really care about the extras that I did enjoy.
But It does seem interesting that it only takes a small sensor to fail in a
more modern vehicle and you could be left stranded.
john 92HDJ 80 1HDT
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.516 / Virus Database: 269.21.4/1313 - Release Date: 05/03/2008
09:50
 
G

Guest

Guest
"The only thing I know for sure is that the jumps are more
frequent when the engine is cold."
My 100 series 4.2 diesel normally idles at about 600rpm. When starting from
cold it still idles at about 600rpm, but then suddenley increases to about
1000rpm. My guess is that this may be related to the alternator working
overtime following the natural electrical drain at time of start up
(pre-heaters, starter motor.........plus, of course, the heated seats, and
power heater, and CD player cranked up, etc)
After a couple of minutes the revs drop back to about 600.
So....maybe your problem has some relevence to the above scenario ? On the
other it may not ?
----- Original Message -----
From: "Tomaz Sustar" <[Email address removed]>
To: <[Email address removed]>
Sent: Wednesday, March 05, 2008 1:18 PM
Subject: Re: [ELCO] RPM jumps
 
G

Guest

Guest
Hi Ken,
I know what you mean but the jumps I'm talking about occur even you are
while driving for some time - they are just sudden drops or RPM in a
range between 200 and 400. If you are not concentrating on the RPM gauge
you wouldn't notice them since there is no real change of sound coming
from the engine. But in my case you can also notice that at the same
speed the reading on RPM gauge can be different.
Luckily it stabilizes and everything goes back to normal.
Regards,
Tomaz
 
G

Guest

Guest
Hi Ken
AFAIK this is the cold start mechanism which ingages to help help the
engine warm up nicely.
john 92HDJ 80 1HDT
SNIP
 
G

Guest

Guest
Thanks John,
Something learned today.
Cheers
Ken
----- Original Message -----
From: "john byrne" <[Email address removed]>
To: <[Email address removed]>
Sent: Wednesday, March 05, 2008 5:09 PM
Subject: Re: [ELCO] RPM jumps
 
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock    No Thanks