KV6 engine racing

[SD1too]

Originally Posted by xsport

Are you confident about the outcome Simon ?

Not until the car's back on the road properly for full testing. It can now go to the bodyshop for a previous bodged repair on one sill to be rectified.

Originally Posted by xsport

... were there any EML lights or codes stored or the O2 sensors playing up ?

No Stefan, none, but that's not surprising really as the air-to-fuel ratio was always correct as you've said. Unfortunately the diagnostic system didn't relate the closed throttle with the racing engine, or that the stepper motor was having no effect (the ECM doesn't know it's actual position).

Originally Posted by xsport

Hope this draws a line now for this issue , and the old girl behaves herself. ...

Thanks very much Stefan, and it was reassuring to read of your similar experience with those Torx screws so thanks for that too.

Simon

[KWIL]

I would add that when refitting these types of screws, always turn counterclockwise until the screw moves forwards as the "thread" picks up the engaged position, then and only then drive clockwise.


This will help to reduce the possiblility of cross threading especially when the screws have been " abused" in the past.

[bl52krz]

Hi Simon. I have the 2.5 Connie on sorn at the moment, but still start her up every three/four weeks. The last time I started her up, the revs were rather high. It started straight away by the way. I wondered what it could be, so lifted the bonnet for a nose round. Tried the accelerator cable, nothing altered. So felt the quadrant that the cable goes over to the throttle body. The car is fitted with a cruise control, and this is obviously fitted to the throttle control. The arm under the quadrant, I noticed that it moved down when I touched it, and the revs dropped to normal. I then got in the car and used the accelerator, and revved it up, and the revs stayed up. I have since oiled the arm and it now works ok. Will wait until I start up again to see if that has cured it.

[stocktake]

As a slight aside, my top left screw stripped the thread on the manifold years ago. Drilled it straight through with a long nut and bolt end of problem

[SD1too]

To recap, this was the situation in early November:

Originally Posted by xsport

Are you confident about the outcome Simon ?

Originally Posted by SD1too

Not until the car's back on the road properly for full testing. It can now go to the bodyshop for a previous bodged repair on one sill to be rectified.

I ordered a jacking turret and rear sill repair section from Tom Hobbs. These are not metalwork they are works of art. The bodyshop observed that the turret was higher quality than the original factory item (what little was left of it). We all stood there staring at Tom's achievement in awe.

Anyway, I got my 75 back in time for Christmas service to visit family, racking up a couple of hundred miles. I am pleased to report that every time I came to a standstill, the idle was "text book perfect"! Automatic gearbox downchanges on a trailing throttle were also much improved as a result. It did take a few journeys for the throttle position sensor values to be "learnt".

Just a reminder that this fault started way back in 2006 as an occasionally hunting idle which progressively worsened over the years to regularly over 1,000 rpm until it became so high that the car was undriveable by this summer.

The fault was loose Torx screws between throttle body and plastic manifold chamber. They were probably insufficiently tightened when the car left Cowley because I remember my surprise at how easy it was when I first released two of them. But what I wasn't prepared for was just how tight they have to be to stop suction at that joint, even with a brand new seal fitted! RAVE quotes 7 Nm. I will have to check what value I ended up with. Since these screws are driven directly into plastic with no metal insert as far as I can tell, a degree of caution is always necessary.

My thanks again to everyone who joined with me to try to solve this unusual fault.

Simon

[xsport]

Thanks simon for giving a final post, and im glad all ended on a high. It could be of benefit to others with similar problems once the idler repair kit did not prove to be the solution. As with stocktake , i had one of the threads strip on the plastic manifold , and his solution was a better definitive one , rather than drill and retap the holes as i intended to do. My intended solution was never needed fortunately, as my temp repair has stood up well ! The threads in mine were still half existent and i was still able to compress the gasket slightly. I used a non silicon based gasket sealer to face each side of the gasket and the threads of the mounting holes before nipping up. (victor reinz) REINZOSIL gasket sealant , the same used by kaiser on the metal thurmostat.This did the job and has given no issues for years now. The best way is not to remove the throttle body from the manifold in future repairs or serviceing , but remove as a whole unit together with the manifold, wherever possible. It did cross my mind just to look for slightly larger self tap screws , but im glad i did not as the plastic im pretty sure would have split ,being extremely brittle in nature. When and if the time comes to remove the throttle body at a later date , i will follow daves (stocktake ) definitive method as it would be stronger and easier than a re- tap. Thanks again for the update simon , and im glad alls well ... that ends well !! ...

[xsport]

Originally Posted by SD1too

To recap, this was the situation in early November:


I ordered a jacking turret and rear sill repair section from Tom Hobbs. These are not metalwork they are works of art. The bodyshop observed that the turret was higher quality than the original factory item (what little was left of it). We all stood there staring at Tom's achievement in awe.

Anyway, I got my 75 back in time for Christmas service to visit family, racking up a couple of hundred miles. I am pleased to report that every time I came to a standstill, the idle was "text book perfect"! Automatic gearbox downchanges on a trailing throttle were also much improved as a result. It did take a few journeys for the throttle position sensor values to be "learnt".

Just a reminder that this fault started way back in 2006 as an occasionally hunting idle which progressively worsened over the years to regularly over 1,000 rpm until it became so high that the car was undriveable by this summer.

The fault was loose Torx screws between throttle body and plastic manifold chamber. They were probably insufficiently tightened when the car left Cowley because I remember my surprise at how easy it was when I first released two of them. But what I wasn't prepared for was just how tight they have to be to stop suction at that joint, even with a brand new seal fitted! RAVE quotes 9Nm. I will have to check what value I ended up with. Since these screws are driven directly into plastic with no metal insert as far as I can tell, a degree of caution is always necessary.

My thanks again to everyone who joined with me to try to solve this unusual fault.

Simon

It may well have been adequate in terms of tightness when it left cowley , all those years ago. Together with the ageing process / compression / and under bonnet temps , the gasket may have flattened somewhat. (familiar story ) All of these plastic engine component parts cannot have been chosen with a long term strategy in mind from the designers point of view , but more of an economy saving excercise.Enough to outlast the manufacturers basic guarantees after new sales i would imagine. At least you were able to buy a new gasket !!!

[xsport]

Thinking back to owners who had experienced the throttle sticking , at times during extreme cold conditions , freezing the flap pivots inside the throttle body, very scary and dangerous ... to say the least .... It does make you wonder if this would have happened had the plastic inlet manifold had been one made of metal instead ? Certainly there would have been heat from the engine rising and keeping the throttle body metal casting warm. Another downside of the plastic peril ... im sure ...

[SD1too]

Originally Posted by SD1too

The fault was loose Torx screws between throttle body and plastic manifold chamber.

There is a sequel to this and it doesn't make for happy reading.

The tightened Torx screws didn't stay tight for long. I thought that engine vibration might be responsible. I tried adding spring washers but they didn't help. I was back to a 1,200 rpm idle speed.

I decided that a permanent repair was necessary and motivated by Stocktake's idea I looked at fitting threaded inserts into the manifold chamber. After much technical discussion with the manufacturer, dimensions and the 7 Nm screws torque put an end to that ambitious plan. I therefore had the blind holes drilled through (as Stocktake had done) and purchased long Torx M6 screws and deforming locknuts. With the manifold chamber removed I took the opportunity to clean the inside of the cam covers, cleared the breather holes (one partially blocked, the other fully) and renewed the gaskets which had begun to shed their coating after 25 years service. With everything reassembled I put the champagne on ice and went for a test drive.


Far from a smooth, stable 800 rpm idle I was horrified to be back to square one and 1,200 rpm! To recap, the idle is perfect immediately after starting the hot engine but as soon as the accelerator is touched it rises by 50%. I've systematically plugged every connection to the chamber downstream of the throttle butterfly to check that the various tubes are not allowing extra air to be sucked in but the fault stubbornly remains. I've fitted another power VIS actuator in case the seal has been flattened but no, it hasn't.

I think that the manifold chamber is going to have to come off again for close inspection. Through the VIS actuator's mounting I did notice pools of engine oil but then every KV6 has this and I seem to be the only one with this idle fault!

Simon

[xsport]

Any further joy with this one simon ? I still have bias towards this being of a physical nature ,rather than a mixture/air problem. Has the throttle body been replaced or original ?. Has the throttle cable been replaced ? . Is it routed correctly through and beyond the firewall? . Does the tickover go back to normal with a quick slap down on the pedal ?. I did have the return spring on the throttle body wear a groove on its mount that prevented its smooth return. Also the throttle cable does wear a channel into the outer cable at points, especially at bends and tight routes through the firewall. This can also give rise to one or two strands of broken cable. Have you had this off to clean out and lube up ,or replaced the cable ? I do know that on my new throttle body at tick over it can sometimes not return fully and if pressure is applied to the stop the revs will drop very slightly. Lastly does the cruise rod or lever have any drag or interference along its path or leverage arc. Ingress of dirt here is always like a grinding paste effect on the fulcrums for both the moving parts and spring returns. Long list simon ,but whilst its off ...