Poor Idle / Rovergauge Help

[vroom]

Hi all,

I am trying to get to the bottom of poor / uneven idle on my Chimaera and I have purchased the excellent RoverGauge from Mark and Blitz and it works a treat.

The results confirm my suspicions that I might have an air leak after the AFM as when at maximum vacuum (idle) both lambdas continuously show +100% short-term trim and will only reduce or go negative and cycle nicely lean / rich if I lift the revs to say 2000RPM, where I guess the vacuum is less and any leak would be less pronounced so the mixture can be made to go rich.

I’ve checked the obvious – plenum to servo and carbon canister, fuel regulator to stepper motor housing, pipes on the nearside of engine and vacuum advance. All look good.

I also note the target is idle is very low. What causes this? When the engine RPM drops below this value I do see the idle bypass increase which makes sense.

No signs of hissing, so I am at a real loss. Is it plenum off time or worth checking anything else first?

It’s driving me bonkers!

Nick

[vroom]

Thanks Bob,

Have tried an alternative genuine stepper but stiil the same.

The stepper goes to max when I stop it and the revs shoot to 2k RPM when I first start-up and then drop, so it is working.

The thing is, the cars smells as though it is running rich and I note that the lambda cables have been hacked and looking thru the history, it has had the occasional emission 'issues' in the past.

What would the effect be if the lambda probes had been connected opposite sides? Looks physically feasible as the cables are presently running on top of the rockers since the re-work by others.

Cheers

Nick

[vroom]

Thanks Guys,

I managed to clamp the air bleed and set the base idle to 550-650 RPM, which surprised me as I didn't think it would run at this low RPM.

Removed the clamp and I managed to get a positive idle correction to the stepper.

But both lambdas still reading + 100%. Will have another look later today.

I am regularly resetting the ECU by disconnecting the battery when I am away from the car

[vroom]

blitzracing said:

Be careful here- all this ECU resetting clears the long term fuel trim down- so the ECU has to re learn the setting. This takes at least 2.5 mins at plus 90'c at a fixed idle. So put it on long term trim, and let the car idle, and you should see the long term trim slowly move bit by bit. Assuming it sets at less than 100%, the short term should then start to cycle around the mid point again. If you just reset ECU without letting it learn or the engine is not hot enough you will get the symptoms you describe.

Will do Mark, I am having tinker tomorrow and will report back.

[vroom]

spitfire4v8 said:

I dont recognise r3101 as a tvr tune can you get the case off the ecu and show us the chip ?

Interesting, a replacement ecu perhaps...

[vroom]

Joolz / Mark

ECU in all its glory. EEPROM label has faded though

Looks like an original EEPROM as soldered to pcb...

Cheers Nick

[vroom]

Thanks all.

I have borrowed an ECU from the good man James Agger and I can confirm she is now running sweet as a nut.

I still have a few jobs to do to get her MOT'd (I have the Cerbera to play around in still) so I am in no rush for an ECU - unless one comes up in the meantime.

I am pretty handy with double sided PCBs, so will probably have a go at mounting an IC socket and re-use the ECU.

Do you know where I can get a std Mapped EEPROM from?

Appreciate all the help on this one.

Cheers once again

Nick

[vroom]

davep said:

Good to hear! Another TVR running as a TVR not a Land Rover.

it was more akin to a tractor than a Land Rover!

[vroom]

davep said:

Vroom could you do another RoverGauge screenshot post but with the replacement ECU installed?

Will do. Will be tomorrow as I got too excited today to take one! I did run a log file, but not graphed it yet in Excel.

Nick

[vroom]

Sorry all. Been busy getting car finished, through MoT and a full titivation.

Have fitted a replacement eeprom to the old ECU which has been a success with the newly installed socket.

Unfortunately I damaged the old chip (hairline crack) when removing it although it initially looked ok after I cut it out.

So which RoverGauge shots shall I take for you good chaps?

Nick

[vroom]

davep said:

A shot of the main screen with ignition On but engine not started, a shot of the same screen immediately after starting, and the same screenshot as in your first post with engine fully warmed up, please. Where did you get your new eeprom from?

Dave, 4 screenshots below:

Note that idle appears initially high (1400RPM) when coming to a standstill. Drops to 900 after a few secs. Base idle set at 500RPM and no air leaks. Was wondering if there is any mileage in restricting the stepper motor bleed to limit the RPM? Stepper motor control is working based on the manual control via Rovergauge.

Besides this, car runs spot on, smooth as silk and very responsive - but I am used to an AJP Cerb!

Before start:

|https://thumbsnap.com/xLumSjNC[/url]



Cold start (missed the initial 2500RPM start)

[url]

Warming up:



Fans on:

[vroom]

Thanks Dave

Perhaps my quote of 500RPM was a tad optimistic. It was starting to struggle between 500-650 RPM before it would stall so I just quoted the lower figure!