Over revving and other issues

[Stuart Rees]

Ye... strange and unfortunate the problem came back last week Tris. I had the ECU last time but the motor seemed to solve the problem. Glad we found the root cause of the high revs today. 

Stu

[Nick H]

Sounds like you found the cause of the issue. I seem to remember if the idle motor fails or shorts out it can blow some of the electronics in the idle ECU.
Hopefully it’s a relatively straightforward fix.

Nick H

[Chris Williams]

Good news, well done chaps. You may have to twist his arm but Rich is a wiz at that kind of stuff. Not sure what's in the ECU but as it's 80's tech I'm sure it's fixable if he can get the parts.
Chris

[Chris Williams]

Quote:But now it looks like I need a rather expensive idle ecu

http://dmctalk.org/showthread.php?16612-...s-For-Sale

[TristanC]

(02 Sep 2018, 21:09)Chris Williams Wrote:

Quote:But now it looks like I need a rather expensive idle ecu

http://dmctalk.org/showthread.php?16612-...s-For-Sale

Cheers Chris.
Spoke to Arran and he’s got rebuilt ones on the shelf with modern components, sounds like the way to go to me. £120 with my idle ecu as px

I’m happy with that. I should have it within the week.

[Chris Williams]

Quote:Spoke to Arran and he’s got rebuilt ones on the shelf with modern components, sounds like the way to go to me. £120 with my idle ecu as px

Fair enough, cant go wrong at that price.
Chris

[TristanC]

New ecu installed and all seems well again now.

And also replaced the bearings in the idler pulleys today too. Nice new SKF bearings.
The old ones were very noisey indeed.
I was lucky they didn’t totally give up the ghost!

Angle drive sorted too.

Just need to change the oil again and I can take her out ! Whoop.

Thanks to you all for the input and especially Stu for giving me his time and also bringing parts along to help narrow down the revving issues.

Tris

[Nick H]

Good Job Tris.

Those idler pulley bearings could have been the reason for your belt issue. 
When I worked for a race team we had a French mechanic who had worked extensively with the PRV 
Engine. I remember driving into work one day and Gilles heard the car and knew just from the sound the pulley bearings were starting to go. He explained they can jam momentarily and then free off thus damaging the belt. But when you look visually you often find all looks good. 

Nick H

[TristanC]

I think you’re right Nick.

Here’s some pics of how worn the AC belt was. (It was new just a month or 2 ago)
And a new belt for comparison.

[Chris P]

Could you let us have the bearing numbers please Tris? I'm planning on changing the belts on MGJ, so may as well do the whole job.

[TristanC]

Sure Chris, here’s the link:
https://simplybearings.co.uk/shop/p6819/..._info.html

Cheers
Tris

---

And for future reference, in case this link becomes inactive  in the future, the specs are

Inside Diameter: 15mm
Outside Diameter: 35mm
Width: 11mm

d
=
15mm

D
=
35mm

B
=
11mm

Dynamic load C
=
8.06 kN

Static load Co
=
3.75 kN

Fatigue load limit Pu
=
0.16 kN

Reference speed
=
43000 rpm

Limiting speed
=
22000 rpm

Weight
=
0.045 kg

d1
=
21.7mm

D2
=
30.4mm

r1r2 min
=
0.6mm

da min
=
19.2mm

Da max
=
30.8mm

ra max
=
0.6mm

Calculation factor kr
=
0.025
Calculation factor f0
=
13
 

[TristanC]

Well that was short lived.

Back to 1500 rpm again!!!!
Backfiring, rough running and 1500rpm

She will idle nicely for 5 mins, then creep up.
Turn her off, leave a bit, try again.... idles fine, then creeps up again..

Take out the bung from the mixture screw hole, idle decreases. Yes decreases....!

Oh Lordy.

[Chris Williams]

Quote:She will idle nicely for 5 mins, then creep up.

Turn her off, leave a bit, try again.... idles fine, then creeps up again..

On it's own? as in you don't do anything, not driving playing with it,blipping the revs?

Quote:Take out the bung from the mixture screw hole, idle decreases. Yes decreases....!

Obvious I know but either the bung or remnants' of plug are not pushing down on the operating arm is it?
Chris

[TristanC]

Yep, on its own after a few minutes warming up. Or a few mins after a restart after 15 mins being off

When I noticed the revs decrease with the bung in (Stu also saw this) I put my finger over the hole and had the same result.

———
I’ve been advised to disconnect the o2 sensor and adjust the mixture to bring the idle down. This being based on the fact I’ve been tweaking the mixture screw through out these issues.
I guess as a means to try to get the mixture correct again....

[Nick H]

(10 Sep 2018, 15:26)TristanC Wrote: Yep, on its own after a few minutes warming up. Or a few mins after a restart after 15 mins being off

When I noticed the revs decrease with the bung in (Stu also saw this) I put my finger over the hole and had the same result.

———
I’ve been advised to disconnect the o2 sensor and adjust the mixture to bring the idle down. This being based on the fact I’ve been tweaking the mixture screw through out these issues.
I guess as a means to try to get the mixture correct again....

Tris, Just to clarify “Revs decrease with bung in place”? 
If this is correct that’s what I would expect. The revs will increase if unmetered air
enters through the CO adjustment hole. 

Possibly the O2 sensor is contaminated by running rich. 


Nick H