sudden engine misfire and self cure

[ChimpofDarkness]

Rob_the_Sparky said:

"IDL
This signal indicates that the ECU is an idle mode and should only state ON when the car is stationary. It should reflect the ROAD signal in that it will be on when ROAD is 0 and off when it is greater than 0. If not, this indicates a fault with the road speed. If it is permanently zero then the idle mode will be permanently on and the car may stall when lifting off at a junction. If teh road speed is greater than zero, then idle mode will be permanently off and idle speed may stay high."

"...may stall when lifting off at a junction." That sounds like it might be the issue.

Rob

This is all spot on, I know this because (before I replaced the 14CUX) my Chimaera had the same stalling at junctions fault.

Some time with a test meter & a bit of deep thought kept bringing me back to the TVR speed signal converter box.

In the end it was actually a bad connection between the speedo itself and the TVR speed signal converter box.

After being on PH a while now, it does seem the speed signal circuit is a common fault on our cars.

And the poor old stepper motor wrongly gets the blame most of the time.

It's not the stepper motor at fault, it's not even the ECU that drives it, it's the signal the ECU needs being broken that is often the source of idle, stalling issues & perhaps even higher speed cut outs.

It looks like Steve Heath finally understood this just before he left the scene, before he departed he was talking about making a speed signal converter box to replace the TVR one.

Did anything ever come of this?

[EGB]

davep said:

Remove the inlet port clip and air turbulence grill. Aim a short spray of carb cleaner at the air flow aperture and clean with very gentle applications of a small cotton bud, do not damage the hotwire element or the thermistor behind. Turn the AFM over and let the unit dry. Gently clean the grill with carb cleaner and lint free cloth.

I've also fitted an AFM heat shield.

With the AFM refitted I used a DVM and ECUMate or RoverGuage to verify that output voltages are correct.

That's not me in the profile pic, it's a support mechanic doing fine shocker adjustment and trusting very much in his jack.

Thanks Dave. I also fitted a heat shield to AFM. Also cleaned plug contacts with electrical contact cleaner.

Dave Byron. Perhaps? my 2mm plastic bit has overcome the speed signal converter.
Still no stalling problems on tick over 900rpm. Happy, and lucky!

Edited by EGB on Thursday 4th October 20:37

[ChimpofDarkness]

EGB said:

Perhaps? my 2mm plastic bit has overcome the speed signal converter.

Still no stalling problems on tick over 900rpm.

Happy, and lucky!

Edited by EGB on Thursday 4th October 20:37

I assume you set your TPS correctly and adjusted the base idle, before you resorted to the bit of plastic?

[EGB]

ChimpofDarkness said:

EGB said:

Perhaps? my 2mm plastic bit has overcome the speed signal converter.

Still no stalling problems on tick over 900rpm.

Happy, and lucky!

Edited by EGB on Thursday 4th October 20:37

I assume you set your TPS correctly and adjusted the base idle, before you resorted to the bit of plastic?

Dave. Thanks for the query. No never touched the TPS before or after. Mat Smith Sports Cars has checked the TPS since and is ok. Tick over is 900 and no stalling. May remove plastic bit sometime to see if I get repeat stalling. Will recheck the idle control valve sometime to see if I can make it do the work of the plastic bit. It bl.....dy well should! Cheers.

[p5000ko]

FlipFlopGriff said:

Thanks Rob.
May stall - should be will stall.
I've printed the ECU Mate pdf which is 100 ish pages. Certainly plenty to go at and I'm sure I'll get my moneys worth.
Given the car is 20+ years old and done 250k miles the electrics are a constanct cause of concern.
FFG

Did you sort this? I had the same problem for ages, it gradually got worse. Found a split in the vacuum hose which runs up to the stepper motor housing. Temp repaired, disconnected power for ECU reset. Runs so much better now. New hose on order and not taken my ECUMATE out of its bag yet!

[FlipFlopGriff]

Any update on your issues?
I've still got mine but then not driven the car since mid September, and done nought about it yet.
FFG

[FlipFlopGriff]

p5000ko said:

Did you sort this? I had the same problem for ages, it gradually got worse. Found a split in the vacuum hose which runs up to the stepper motor housing. Temp repaired, disconnected power for ECU reset. Runs so much better now. New hose on order and not taken my ECUMATE out of its bag yet!

Going to get a silicon hose Clive so start with the cheap options - looks a bit tatty anyways. My ECUMate also still in the bag/box.
FFG

[cureton]

Update from my side as I started the thread. Finally got the ecumate, nice piece of equipment and interesting to play with. Told me Fault 68 road speed sensor or wiring. No other fault codes thrown up. So will look at the speed sensor (have T5 gearbox)maybe dirty or misaligned, will also check cables.
If i can't find anything could it be the signal converter behind the dash? And if so, is there any replacement or spare part available?

[FlipFlopGriff]

cureton said:

Update from my side as I started the thread. Finally got the ecumate, nice piece of equipment and interesting to play with. Told me Fault 68 road speed sensor or wiring. No other fault codes thrown up. So will look at the speed sensor (have T5 gearbox)maybe dirty or misaligned, will also check cables.
If i can't find anything could it be the signal converter behind the dash? And if so, is there any replacement or spare part available?

When I told Dom at Power the issues I had he said it would be the speed signal box thing behind the dash. Suggest you investigate that first. Never seen one but guess its some electrical circuitry inside which can probably be repaired.
Interestingly mine (BV) has a T5 box too.
FFG

[gavgavgav]

Just to check - this isn't a code that always shows up when the car is not moving?

[cureton]

I finally got the car on a ramp and decided to start checking from speed sensor at diff side. Sits in front/above of diff, bit fiddly to get at. Two wires attached to it, one was hanging loose just touching the contact. Easy fix, hope that cured the fault.

[FlipFlopGriff]

cureton said:

I finally got the car on a ramp and decided to start checking from speed sensor at diff side. Sits in front/above of diff, bit fiddly to get at. Two wires attached to it, one was hanging loose just touching the contact. Easy fix, hope that cured the fault.

Sounds promising. Let me know if thats cured it.
Mines up for MoT in a few weeks - first time its been used since July.
FFG