KV6 engine racing - Page 3

clf · 7th October 2023, 17:31

https://www.the75andztclub.co.uk/for...winter+gremlin

hogweed · 7th October 2023, 19:02

Your car probably has a completely different throttle body to my TF, but it suffered from a similar problem, and I tried all the recommended fixes to no avail.

Then somebody here (Trikey maybe?) said there was a plastic part in the TB (I think) which swole up with age, and stuck.

There was a repair kit available from Rimmers, but I haven't got round to it yet

SD1too · 7th October 2023, 19:19

Thanks Alan for your link to the "winter gremlins" thread. I have read through all of it and of course icing of the throttle body isn't a consideration in mid twenties October temperatures!

The other subject discussed is the blocked crankcase breather pinhole in the cam covers. I have experienced this and posted advice on it many times. It noticeably reduced my engine's performance but in my case it didn't cause excessive engine speed when the throttle is closed.

Thanks for your response Alan.

Simon

SD1too · 7th October 2023, 19:32

Quote:

Originally Posted by hogweed

Then somebody here (Trikey maybe?) said there was a plastic part in the TB (I think) which swelled up with age, and stuck.
There was a repair kit available from Rimmers ...

I know the plastic part you describe Roger. It sits in the outlet port of the idle control valve as it enters the manifold chamber. It serves only to reduce the area of the machined port. I've no idea why it's necessary but mine is in good condition and even if swollen it would reduce the air flow rather than increase it which is my car's problem.

However, thanks for putting forward your thoughts. All ideas are welcome as I hope that one day, success will follow!

Simon

SD1too · 10th October 2023, 18:46

Quote:

Originally Posted by SD1too

I'm making arrangements to temporarily replace the manifold pressure sensor ...

I did this today, fitting the sensor to my engine from a 2.5 V6 which runs perfectly.

The fault remains.

Simon

trikey · 10th October 2023, 19:55

Quote:

Originally Posted by SD1too

I know the plastic part you describe Roger. It sits in the outlet port of the idle control valve as it enters the manifold chamber. It serves only to reduce the area of the machined port. I've no idea why it's necessary but mine is in good condition and even if swollen it would reduce the air flow rather than increase it which is my car's problem.

However, thanks for putting forward your thoughts. All ideas are welcome as I hope that one day, success will follow!

Simon

Check that it's not distorted Simon, this has been the cause every time of what you describe.

For the price of a new one and 20 mins, I'd change it anyway.

Sent from my SM-G780G using Tapatalk

SD1too · 12th October 2023, 09:56

Quote:

Originally Posted by trikey

Check that it's not distorted Simon, this has been the cause every time of what you describe.

I have checked Andy and it's not distorted (it was new in April 2017). I can't recall anyone else having a KV6 which refuses to return to idle!

Simon

SD1too · 12th October 2023, 10:13

I'm drawing a blank with this so here are three facts. Can anyone make any sense of them?

When the engine is stopped the idle speed stepper motor references itself to a position for starting. Mine is doing this. I then unplugged it so that it couldn't move and I started the engine. It idled nicely at 800 rpm. I then opened the throttle. Chris & I have observed that when the throttle is opened, the idle air supply is closed (but this couldn't happen). The engine pulsed and stalled. Why didn't it run smoothly on the air it was getting through the throttle butterfly and stepper motor valve?
The T4 stated that the "minimum throttle angle", which RAVE says is automatically learnt on the KV6, is 13.47˚. T4 also says that this should be close to zero which is obviously isn't. Yet the throttle position sensor has been renewed and the resistance meets the spec. and it is reaching the ECM.
With the engine running and the fault present, the T4 reported that the ECM was requesting an idle speed of 769 rpm but the actual speed was 1,400 rpm. The number of stepper motor steps was matching those requested.

I'll be interested in any thinking which could explain these three things.

Simon

StewartIngram · 12th October 2023, 15:02

Going back to when I had my engine racing earlier this year:-

The throttle cable from the pedal is attached to a grooved cam on the throttle body. When the pedal is pressed, the cam rotates, turning the shaft which moves the butterfly round.. At an easy glance it is possible to assume this is all that happens, but a closer examination shows a 2nd smaller cam (& butterfly) below/behind the 1st, when viewed from the normal position. This 2nd one was sticking on mime.
May or may not be your problem?

SD1too · 12th October 2023, 16:22

Quote:

Originally Posted by StewartIngram

The throttle cable from the pedal is attached to a grooved cam on the throttle body … the cam rotates, turning the shaft which moves the butterfly round … but a closer examination shows a 2nd smaller cam (& butterfly) below/behind the 1st …

Thanks very much for your suggestion Stewart. I’ve inspected the throttle body closely and the shaft on which the grooved cam is mounted rotates in a blind hole. Via a peg and slot mechanism this then rotates the shaft closer to the air cleaner to which is mounted the single butterfly.

The air supply keeping my engine running at high revs is entering through the idle control valve not the throttle butterfly.

Simon

7th October 2023, 17:31	#21
clf This is my second home MG ZT CDTi Join Date: Jan 2014 Location: carrick Posts: 7,859 Thanks: 3,494 Thanked 2,657 Times in 1,973 Posts	https://www.the75andztclub.co.uk/for...winter+gremlin __________________ It is not gloss primer .............. it is duct tape silver!

7th October 2023, 19:02	#22
hogweed I really should get out more....... Vauxhall Insignia CDTi; MG TF 135 Join Date: Jan 2010 Location: Norn Iron Posts: 2,970 Thanks: 942 Thanked 378 Times in 297 Posts	Your car probably has a completely different throttle body to my TF, but it suffered from a similar problem, and I tried all the recommended fixes to no avail. Then somebody here (Trikey maybe?) said there was a plastic part in the TB (I think) which swole up with age, and stuck. There was a repair kit available from Rimmers, but I haven't got round to it yet __________________ Past cars: MGB GT; Escort 1300 Sport; Vauxhall VX4/90; Marina Coupe TC; Celica ST (1972); Montego Turbo; Astra GTE 16V; Astra GSI 16V; Golf GTI 16V (Mk II); Sierra XR4x4 Estate; BMW 325i (E30); BMW M3 3.0; BMW M3 3.2 Evo. Left some of the more embarrassing ones out. And about 30 motorbikes.

7th October 2023, 19:19	#23
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: 20,650 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Thanks Alan for your link to the "winter gremlins" thread. I have read through all of it and of course icing of the throttle body isn't a consideration in mid twenties October temperatures! The other subject discussed is the blocked crankcase breather pinhole in the cam covers. I have experienced this and posted advice on it many times. It noticeably reduced my engine's performance but in my case it didn't cause excessive engine speed when the throttle is closed. Thanks for your response Alan. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

12th October 2023, 10:13	#28
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: 20,650 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	Two relevant symptoms I'm drawing a blank with this so here are three facts. Can anyone make any sense of them? When the engine is stopped the idle speed stepper motor references itself to a position for starting. Mine is doing this. I then unplugged it so that it couldn't move and I started the engine. It idled nicely at 800 rpm. I then opened the throttle. Chris & I have observed that when the throttle is opened, the idle air supply is closed (but this couldn't happen). The engine pulsed and stalled. Why didn't it run smoothly on the air it was getting through the throttle butterfly and stepper motor valve? The T4 stated that the "minimum throttle angle", which RAVE says is automatically learnt on the KV6, is 13.47˚. T4 also says that this should be close to zero which is obviously isn't. Yet the throttle position sensor has been renewed and the resistance meets the spec. and it is reaching the ECM. With the engine running and the fault present, the T4 reported that the ECM was requesting an idle speed of 769 rpm but the actual speed was 1,400 rpm. The number of stepper motor steps was matching those requested. I'll be interested in any thinking which could explain these three things. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce. Last edited by SD1too; 12th October 2023 at 10:16..

12th October 2023, 15:02	#29
StewartIngram Gets stuck in Rover 75 Connoisseur 2.5 V6 auto Join Date: Jan 2008 Location: Chatteris, Cambridgeshire Posts: 921 Thanks: 320 Thanked 159 Times in 127 Posts	Going back to when I had my engine racing earlier this year:- The throttle cable from the pedal is attached to a grooved cam on the throttle body. When the pedal is pressed, the cam rotates, turning the shaft which moves the butterfly round.. At an easy glance it is possible to assume this is all that happens, but a closer examination shows a 2nd smaller cam (& butterfly) below/behind the 1st, when viewed from the normal position. This 2nd one was sticking on mime. May or may not be your problem?