OT Car running at tickover on high RPM

[Gopalan Sampath]

It could be time to change air filter, from my experience!

[Brian Gaff (Sofa]

There is a bloke near me who starts his car down the street while I'm having my breakfast. Definitely a Diesel it has the knock, and when its running a bit fast he seems to simply rev it up a few times and it falls back to a lower speed. Don't as what sort, I have never been so nosey as to ask. I just think they get sooted up as they do seem to generate a lot of it!

Brian

[Harry Bloomfield, Esq.]

Max Demian formulated on Sunday :

If you meant the little screw, then no. The TPS uses a potentiometer/ variable resistor. There is sometime a calibration setting, to calibrate the ECU to the TPS, so it knows where the zero and max is on the TPS.

The actual tick-over speed is pre-set in the ECU, though it may be programmed to increase the speed when the engine comes under load from the a/c compressor, or when the engine is cold. The ECU can also be tweaked to adjust the opening times of each injector, to better balance the tick-over.

[Harry Bloomfield, Esq.]

Dave Plowman (News) wrote on 03/01/2021 :

Plenum? That is the open to atmosphere section, where air is taken in, but rain water is designed to drain out, below the scuttle panel.

[Harry Bloomfield, Esq.]

ARW brought next idea :

Difference is that there is no restriction of the amount of air volume a diesel can take in, what varies is the amount of fuel injected into the engine.

Petrol has both the air volume and fuel volume carefully metered.

[Dave Plowman (News]

If you have a petrol engine with just the one throttle body, chances are it has a plenum between the TB and inlet ports. It evens out the inlet stroke pulses.

[NY]

Does the ECU actually *increase* the engine tickover speed when the the a/c is on, or does it simply increase the fuel flow so as to maintain the *same* speed under a greater mechanical load? Does a higher engine speed (eg 750 rpm increased to 950 rpm) make the a/c perform better?

When I next go out, I'll see what happens in my diesel-engined car. I'll start it with a/c turned off and then turn it and and see whether the rpm changes. I can't say I've ever notices this, but then I haven't been looking for it.

[Dave Liquorice]

My diesel just gets more fuel to maintain the tickover under increased load. At this time of year the A/C compressor isn't likely to cut in which is the biggest load the A/C can present. I guess it might be told to come in on any "defrost" programme to "dry the air" but air at just above freezing is going to be pretty dry already.

I use the heated front and rear screens as added loads, bigger than all lights. Turning those heaters on/off makes a very noticable change to the engine note.

[Andrew]

One of these ? :-

[Andrew]

especially if you regularly tailgate other diesel engined vehicles :-).

Do the pollen filter at the same time, but watch out for vehicles where you have to tell the ecu what you have done.

[Harry Bloomfield, Esq.]

That depends on the car, mine just maintains the default revs, so it must just increase the injector open time to compensate for the increased load. It uses some sort of variable compressor system and I leave it always on (full climate system), so the only time I notice the engine note change - is when I (rarely) switch it off, then switch it back on set on minimum temperature.

Other cars I have had, did increase the rpm.

Nothing to do with the a/c, but from a cold start, if I leave it ticking over for around 10 minutes, the engine note quite suddenly changes. I have never been able to decide what the change in note is all about, but it always does it.

[Harry Bloomfield, Esq.]

Dave Liquorice wrote on 04/01/2021 :

Likewise, plus the heated seats.

[Harry Bloomfield, Esq.]

on 04/01/2021, Dave Plowman (News) supposed :

OK, I have never heard it called that before.

[Dave Plowman (News]

The Lotus developed (for racing) last version of the Rover SD1 Vitesse was known as the twin plenum. Wrongly so as it only has one, but twin throttle bodies. ;-)

[ARW]

It had a full service last year and all filters were swapped. The service light is back on but only because it's got a 12 month timer on it.

I only did 6000 miles in it last year.

[bert]

In article <3XiIH.242908$ [e-mail], ARW [e-mail]> writes

Not accidentally put air con on? Does it put it on when air flow switched to windscreen?

[ARW]

Air con does switch on automaticity but it makes no difference to RPM.

Now if it was the Fiat or Peugeot I also drive.....

[The Natural Philosopher]

many years ago, gf has a peugout hot hatch,and after a while it wouldn't keep going at idle. Ran OK above 3000RPM, but not at idle. It just died.

Once cold though, it started and ran fine, till it was warm, then it died.

Chewed petrol too, several garages failed to fix it, and in desperation I phoned up someone I knew through work, who was a specialist in injection systems. 'Sounds like water temp sensor' he said 'car thinks it needs the choke on permanently'

A short talk beyond and I knew where to find it and how to extract it. Stuck a meter across it, In spec, 2k ohms. Puzzled, I put it in a saucepan and boiled it. Not open circuit, not short circuit, *still* 2K ohms.

That is not right I said. Drove in to dealers got a new one - think it was £11 or something, put that in the boiling pan of water. 200 Ohms when hot. 2k ohms when cold.

Fitted it, Car ran perfectly till we sold it.That car also had a screw in the throttle body to set low speed airflow. Someone had removed it altogether, presumably to try and get the mixture lean enough. I replaced that as well.

Point being the car relies on sensors to do its stuff, and the ECU - especially todays ECU, can be programmed to respond to any given condition in a variety of ways. If the car is cheap and cheerful a 'engine is warm, now drop idle speed by 200 RPM' is entirely possible. Ugly, but possible.

[Harry Bloomfield, Esq.]

The Natural Philosopher wrote on 05/01/2021 :

Until I got to that bit, I was convinced you were going to say 'idle control valve' failing. The ICV failure was my first ever experience of problems of ECU's - it had rough and varying idling. A Granada.

[Dave Plowman (News]

The standard thing to check a CTS is working is to simply unplug it. They are normally a reverse acting thermistor. Unplugged - high resistance so fully rich. Hot, about a couple of hundred ohms. If unplugging it makes no difference on a hot engine likely faulty. (This really applies to old injection - I'd expect a modern system to give a code.)

On Lucas 4CU injection (very similar to early Bosch) it was recommended to replace the CTS with a 175ohm resistor which simulates a hot engine. Saves fiddling around with full checking of the sensor in boiling water.