Need help, sluggish stepper and hot start

[jamescooper47]

Hi All wise folk

So need help with a peculiar issue I’ve not faced before despite many years of classics. Just bought a project to get stuck into and had lots of vids from the seller and obviously working before, but just before delivery she has a hot start issue.

Solved one problem, TPS now replaced and working correctly - great

Issue 1
Revs go mad when driving. Cold start is fine and stepper does the business to bring idle down to that lovely V8 burble.! However, when moving - dip the clutch for junctions etc and as soon as clutch goes in, stepper fully opens and revs go bonkers. Watching on rovergauge I can see stepper instantly fully opens, and take some time to cycle down to a normal idle. Rrrg. Makes for a rough ride.
Completed following
- Checked for air leaks, nothing I can see
- I can stall engine by squashing bypass hose when idle is set low so guessing no air is finding it’s way in
- idle has been set by squashing bypass, setting to about 700rpm and releasing hose ( runs at about 2,800 rpm for ages before settling down to about between 1060 an 1120) - is this high?
- warming engine and disconnecting stepper altogether makes for a lovely drive. Smoother and no crazy idle mayhem
- disconnecting stepper does not show s fault code on rovergauge?

Issue 2 (maybe related to above)

Will not start when hot. Starter motor turns at high speed but almost like ‘choke ‘ is not right some how.

I kind of got her to start by using rovergauge to set stepper between 30-40 % open if I’m lucky and just catches. Desperate for fuel so off to the garage with the laptop plugged in, otherwise I’ve got a wait on my hands for her to cool.

Any clues would appreciated.

[Belle427]

Some very useful info here, page down to the part on the throttle position sensor to check your calibration if you have messed around with it.
http://g33.co.uk/pages/technical-fuel-injection.ht...

[jamescooper47]

Thanks, my lambdas are reading zero even when warm, so according to the thread the heater feed is not working properly somehow. Hmmmm, interesting

[QBee]

The "hot start" issue affects most of us at some time.

For me it was about 10 years ago.
In my case it was down to the way TVR had wired the immobiliser relays I think.
Solved by getting the whole Meta system replaced by Carl Baker. www.tvruk.tv
(Listens for the sound of a can of worms opening)

Beware of so called new Lucas steppers - they are chinese these days and in my experience are not a lot of use. On my car the problem was that the car would stall at junctions. After an hour with Rob at V8 Developments he said to himself "it MUST be the stepper". He rummaged in his massive parts bin, found a used original stepper, fitted it and I never looked back. You should be able to source a used and original stepper from one of the guys who installs aftermarket systems that don't use the stepper.

[sixor8]

The OP states that the starter spins so it's not the starter solenoid part of the immobiliser, unless this has already been bypassed. But it could be the fuel pump / ECU part that is failing. If fuel is being delivered whilst cranking, then it is OK.

I would second that it sounds like a faulty stepper motor. I fitted a 'cheap' one to a Chimaera in 2014 and it had the symptoms you describe. Tricky to start and very high revs at idle at junctions. It also responded badly and caused me to stall more than once. Biting the bullet and paying £90 + for a genuine one was my solution.

There is no feedback to the ECU from the stepper for it to know if it is working properly or even connected! It motors back to zero at switch off and the ECU sends pulses to reach the position it believes is required.

Edited by sixor8 on Wednesday 23 March 07:52

[blaze_away]

James has emailed over his log file and it looks like its possibly the fuel/water temp sensors being mixed up in the engine bay

[blaze_away]

Once this is reolved it could well sort out your lambda's too as right now it will be massively over fueling as it thinks the engine is cold.

So I would suggest swap the wires over then do an ECU reset (unplug ECU and the reconnect it)

Edited by blaze_away on Wednesday 23 March 10:06

[blitzracing]

The stepper motor is not controlled by the clutch in any way- so if RoverGauge is showing the stepper opening as you depress the clutch it has to be one of the other inputs- ie throttle pot or speed input. You must have throttle pot at less than 10 percent and less than 3mph for the car to enter idle mode (shown by the light on RoverGauge) and in this case the stepper should try and match the target idle with the real idle.

The raised idle conditions occurs when the car is moving above 3mph and should be about 1200 rpm. Easy test to see if this is working is to get the car up to say 25mph and then dip the clutch and listen to the idle- it should be raised until the car comes to a stop at which point it should drop to around 800 rpm- depending on your chip programming in the ECU.

You can get some really odd things happening with air leaks though (including the stepper body its self) as you get sharp mixture shifts as the plenum vacuum rises as the throttle shuts- so the stepper tries to compensate to get it correct at idle, but then when the throttle opens and the mixture changes it now may cause the RPM to be to high for its programmed 400 rpm lift.

Having said all that- if your heater voltages are correct on the lambda and there is no output (ie the lambda trim is showing adding fuel 100% on both long and trim ) then you have a very lean mixture- but it should eventually a fault code on RoverGauge.

[jamescooper47]

Thanks so much guys.

Great to see TVR community still sticking together. I sold my chim back 7 yrs ago, purchased this project now kids have grown to 6 yrs old so have a little more time,-and sleep.

Looking forward to solve this running problem so can get on with the standard stuff

[blaze_away]

The engine temp the ECU is seeing never get to 80c therefore lambda's never start doing their thing.

FYI this is what normal start up looks like for water and fuel

[jamescooper47]

Thanks so much guys.

Great to see TVR community still sticking together. I sold my chim back 7 yrs ago, purchased this project now kids have grown to 6 yrs old so have a little more time,-and sleep.

Looking forward to solve this running problem so can get on with the standard stuff

[blitzracing]

Interesting. When I measured the physical lambda outputs from cold they did nothing for about 30 seconds until they heated up but the ECU did start to cycle the mixture at that point and you could hear the engine note change as it leaned out , so something was going on from cold. It wont affect the long term trim though until its hot.

[blitzracing]

blaze_away said:

James has emailed over his log file and it looks like its possibly the fuel/water temp sensors being mixed up in the engine bay

Doh. Missed this bit. I should never assume we are starting with the correct configuration that was working. certainly the idle will be affected if the engine reads as cold.

[jamescooper47]

Horraaaaasa

Well done and thanks for help. Problem solved!

[Belle427]

Can you list the fix for future searches please.

[Classic Chim]

My monies on Franks suggestion the wires were crossed looking at this data.
That could easily be done if car had stood for sometime or someone got side tracked as both wires are in the same area.

[jamescooper47]

Hi,
Of course

Yes - the fuel temp sensor and coolant temp sensors had been connected wrong way round. Simple issue of the previous person connecting the wrong plug.

[Belle427]

Good spot that, well done.