Idle, shunting, heated plenum and loosing the plot

[Franky boy]

Hi all, hope you are well and dealing with the current situation as best as you can.

I thought I would use the time to have a tinker and try and reduce if not resolve my shunting and rich idle issues, I have read most of the threads on the subject and have tried most of the solutions and I am left in the current situation.

The car idles nicely but rover gauge shows it running rich,( -ve) on both banks long term trim, odd 80% even 100%, idle valve showing 0-3% on warm idle ( 30-40% being the norm?). I fully suspected a vac leak but unable to find one, I have blocked off all pipes but servo and used the brake cleaner technique, nothing.

With stepper connected, pwr and vac, I can screw the idle screw in completely and the car does not cut out and stepper value does not seem to change, I thought this would make the stepper position change to compensate, can only be a vac leak? any ideas? If when idling if I pull off the stepper vac hose the car stalls. I can adjust the stepper motor via rover gauge and it operates as I would expect.

Whilst check for leaks I have noticed a strange thing, the heater connections on the under side of the throttle body are in place! these are connected to the cooling system, I am lead to believe these aren't used on the Chimaera, this means my TB is pre heating the mixture, should I just remove the connections to the TB and loop the hoses? could this be a cause of rich idle and possibly shunting?

These things are sent to test us I guess.

TIA

Stay safe

[blitzracing]

You definitely have an air leak if you cant stall the engine with the base idle screwed fully home, and the stepper blocked off. Mind you that should cause a lean mixture , so its contradictory, but finding the leak is number one as the long term trim will be incorrect anyway..The plenum preheat is no big thing, the tvr idea is a cool inlet charge provides more power, but the volume of air under load is so great it never has a chance to warm up anyway.

Edited by blitzracing on Saturday 9th May 19:58

[Belle427]

Perhaps your throttle disc/butterfly has been messed with so it’s open more than it should be.
As said if you screw the bypass screw all the way in and clamp the stepper hose the engine should stall.

[Franky boy]

Thanks for the comments, weather and hangover permitting I'll get back on it tomorrow.

I have disconnected the throttle body heater, can I just cap off both hoses or should I link them? I cant put them back on as of of the pipes was corroded to the point of falling apart.

Cheers

Frank

[lancepar]

The plenum heater flow and return pipes can be capped or joined as a loop.

If capped one pipe can be used as a coolant air bleed point.

[Steve_D]

Why did you not blank off the servo? It is as likely a leak as anything else. If it was on an 'S' it would almost be a given. Have seen many a rusted servo and at times cannot work out how they are still working.

Steve

[Franky boy]

Cheers Steve, its on my list for tomorrow.

Lots of reading tonight so a fresh approach tomorrow.

[Jon100p]

Franky boy said:

Whilst check for leaks I have noticed a strange thing, the heater connections on the under side of the throttle body are in place! these are connected to the cooling system, I am lead to believe these aren't used on the Chimaera,

Also connected on mine but never know it cause any problems. Do you have a very early Chim? Mine is an early '93 430; I suspect this heating may have been connected on the very early ones.

[Franky boy]

Hi,

After a lot of reading last night, I'm going to go through everything logically, BPR6ES plugs and leads ordered.

Only little progress today buy had to stop as upsetting the locals.

Warming pipes removed from TB and blocked, it's a 94 HC, so a reasonably early car I guess, perhaps why the pipes were connected.

Timing set, 8deg BTDC idle vac disconnected, 28deg at 3500+ vac disconnected, 18deg idle with vac, direct vac Tee'd into fuel regulator vacuum. TDC found ok to markings, wooden skewer down plug hole 1 to check as best as possible.

Will re set base idle tomorrow again to make sure the info I gave is correct,

Cheers

Frank

[Franky boy]

Hi all, a quick update, might be on to something!

I have just noticed on Rover gauge that the road speed sometimes shows a speed when reving the engine while stationary, I'm sure this is a first as I'm sure I would have noticed it before, but its a problem.

Firstly, any idea's on how to resolve this, secondly, what would this spurious reading effect? Am I right in thinking it only "talks" to the stepper motor to keep the revs higher when changing gear on the move nothing else?

For now I have disconnected the electrical supply to the stepper motor while hot with engine running, I know cold starts may be an issue but if it helps the issues I can live with that.

To top it all, having just changed the clutch master cylinder lost the pedal again today, its happened a couple of times but now have chased the leak to the pipe fitting into the cylinder, its cranked up fully and still weeping.

Onwards and upwards!

Frank

[Belle427]

This may shed some light on it.
https://www.pistonheads.com/gassing/topic.asp?h=0&...

[blitzracing]

The speedo calibration box generates a false speed signal to keep the ECU happy , its all or nothing- typically 0 mph at standstill or between 35 and 50 mph at anything over 3 mph or so. Its a horrible bit of circuitry in so much the output from the diff sensor is very low, and of you have a poor earth or dry joint in the unit it can cause a false trigger. To get at the unit you have to remove the dash. The car should show idle mode with the TPS at less than 10% and 0 mph. Above that the idle mode should go out and the idle will lift, I think to around 1200 rpm. Whatever the ECU is doing, if you block the stepper air feed, the car should run at base idle and no more.

[wily_coyote]

Have you checked the carbon canister? Lurking in the o/s wing, it's controlled by the ECU and is the 'other' pipe on the plenum next to the servo take-off. I had shunting issues on my 430 and this was one of the contributors, allowing air into the plenum when it wasn't needed.

You can safely disconnect the whole thing and remove it, but you'll need to add a small breather filter to the vent line from the fuel tank. This can be secured above the diff, allowing the tank to breath. The electrical connection to the ECU can be taped off and left in the wing.

[Franky boy]

Cheers Wily, have done this, no difference I'm afraid.

[Bristol ave fag]

Franky boy said:

Cheers Wily, have done this, no difference I'm afraid.

"I fully suspected a vac leak but unable to find one, I have blocked off all pipes but servo and used the brake cleaner technique, nothing."

Try a length of vac hose or washer pipe stick one end in your good ear and with the other end probe round the valley gasket inlets if that's leaking you can hear it. Is yours a HC?

[Franky boy]

Thanks Blitz and Belle,

Still working on the issues, will let you know how I get on.

Cheers

Frank

[Franky boy]

Hi all,

Getting there!

Although the MAF was showing the correct info on rovergauge it is the only thing I haven't changed, so against advice on other threads here, I bought a fleabay MAF. I am still waiting on plugs/leads but swapped out the MAF and result, See the following screen shot's, these are with stepper motor plug disconnected and after a 20 min run.

The idle is great and lambda sensor readings are much different, long term and short term.

Shunting is still there but reduced vastly, any ideas on how to reduce this further, plenum spacer?

Thanks for all your advice/help.

[Franky boy]

[Classic Chim]

Shunting. There’s no quick fix and forget plenum spacers but someone who bought one might disagree.

You have a number of contributing factors namely high lift cam, poor engine management or out of tune chip, but actually start again. Stop . Go to the rear of the car and work back identifying firstly an old Dif, possibly worn prop or drive shaft uj’s so a bit of slack, then into gearbox which has been stuck in the middle trying for years to ease the burden. If it’s a tight box that’s a big result, then clutch and finally back at engine. All connections along an ever loosening line x
Sorry but thems the facts with an old car that’s got a lot of power.
I replaced and or had rebuilt much of what I’ve mentioned above. Including a New MBE engine management system which all but removed the source of shunt.
But through years of it my Dif was loose so shunt could still happen at low revs. Finally I replaced the Dif last. Shunt gone, completely for me, a brand new Dif by thevway. So a combination has worked but it was actually the final link in the chain which caused it to be worse, the Dif.!
Once that was replaced it’s been marvellous. Get your Dif and compleye road train checked by someone who knows what he’s doing .it won’t be cheap but there are things that can be done but it’s not really plenum spacers. Waste of money unless your flat out all day which is the only real benifit, track car not a road car all imho .

[Classic Chim]

Replace engine mounts and anything that adds slack and go from there, check gearbox rubber mounts etc rarely knackered but can be. Dif bushes, all can wear and add a looseness. It’s caused at the engine but manifests itself through mostly the dif, check Dif is my advice