Signs of battery failing - Page 2

MSS · 6th December 2021, 16:49

Putting A/C on means extra load on the engine, leading to a dip in RPM. This is countered by producing additional torque which stabilises the RPM back to the original level. The car thus needs additional air and fuel to produce the extra torque that is required to maintain the RPM at a constant level. Ideally, the air to fuel ration should remain at a constant 14.7 but I suspect will vary around this value in practice. This is very similar to what occurs when driving uphill.

Mike Noc · 9th December 2021, 05:36

Quote:

Originally Posted by SD1too

Unfortunately David I suspect that what you've read contains a misunderstanding by the writer. The air:fuel ratio (mixture) must remain constant at all times. The extra load placed on the engine by the air conditioning compressor may result in the engine speed increasing to compensate. That would involve extra fuel and air. The mixture won't be enriched.

Simon

The OP has a diesel Simon so we can forget all the talk about mixtures. The ECM will simply inject more fuel to return the engine revs back to the desired idle speed.

Mike Noc · 9th December 2021, 05:51

Quote:

Originally Posted by MSS

Putting A/C on means extra load on the engine, leading to a dip in RPM. This is countered by producing additional torque which stabilises the RPM back to the original level. The car thus needs additional air and fuel to produce the extra torque that is required to maintain the RPM at a constant level. Ideally, the air to fuel ration should remain at a constant 14.7 but I suspect will vary around this value in practice. This is very similar to what occurs when driving uphill.

We are talking diesels here gents, so the air/fuel ratios will vary all over the place depending on engine load. 1000 to 1 at idle - no problem!

The engine takes in the maximum charge of air on each inlet stroke. That amount will vary depending on the air density, how fast the turbo is spinning etc, but it will always be the maximum amount - there is no throttling involved, and that is why they fit a separate vacuum pump.

MSS · 9th December 2021, 08:52

Why did I not spot that he had a cdt?

Ah well, it was a good exchange of view anyway. My comment about torque still applies, it's just that only additional fuel is injected.

SD1too · 10th December 2021, 07:21

It was David (b152krz), not the OP, who raised the question of mixture and he was referring to a claim in "something" he'd read. He also referred to his own car but without saying which one; diesel or petrol. I replied on the basis that it was his petrol KV6.

I hope that clears up the confusion.

Simon

COLVERT · 10th December 2021, 21:21

Quote:

Originally Posted by peelaaa

Hi,

Car starting okay but noticed lately when pressing window demist button, there is an instant drop in revs for a short while as if battery is struggling. Would that be the battery or alternator failing?

Your alternator converts Kinetic energy from the engine into electricity.

When you put a greater load on the electrics your alternator has to put an extra kinetic load on the engine. This extra draw of energy is what slows the tick-over down until the ECU compensates for it.

Don't worry all is well and doing what it is programed to do.--

COLVERT · 12th December 2021, 19:09

Quote:

Originally Posted by peelaaa

Thanks Simon, I've got a booster and will check the diagnostics no 9 .
Just hope its not the alternator as had it replaced a couple of years ago and its a big job

What was the result and did any of our posts help you ???

Don't be shy.--------

10th December 2021, 07:21	#15
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,337 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Clarification It was David (b152krz), not the OP, who raised the question of mixture and he was referring to a claim in "something" he'd read. He also referred to his own car but without saying which one; diesel or petrol. I replied on the basis that it was his petrol KV6. I hope that clears up the confusion. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

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6th December 2021, 16:49	#11
MSS This is my second home Rover 75CDT, Jaguar XF-S 3.0V6, V'xhall Omega V6 Estate, Twintop 1.8VVT, Astra Estate and Corsa 1.2 Join Date: Dec 2007 Location: Suffolk Posts: 7,083 Thanks: 283 Thanked 624 Times in 440 Posts	Putting A/C on means extra load on the engine, leading to a dip in RPM. This is countered by producing additional torque which stabilises the RPM back to the original level. The car thus needs additional air and fuel to produce the extra torque that is required to maintain the RPM at a constant level. Ideally, the air to fuel ration should remain at a constant 14.7 but I suspect will vary around this value in practice. This is very similar to what occurs when driving uphill.

9th December 2021, 08:52	#14
MSS This is my second home Rover 75CDT, Jaguar XF-S 3.0V6, V'xhall Omega V6 Estate, Twintop 1.8VVT, Astra Estate and Corsa 1.2 Join Date: Dec 2007 Location: Suffolk Posts: 7,083 Thanks: 283 Thanked 624 Times in 440 Posts	Why did I not spot that he had a cdt? Ah well, it was a good exchange of view anyway. My comment about torque still applies, it's just that only additional fuel is injected.