Engine cuts out on tickover?

[Bizarro]

Managed to get out today and put a good few miles on the clock for the first time this year. Popped up to Donnington Park and saw a lot of nice cars, still love the reaction that people give the Noble, had thumbs up from a few random cars.

Recently I have noticed that when I have started the car it is very lumpy on tickover when cold and feels like it is missing for about the first half mile or so. This isn’t every time I start the car and once warm the car runs great.

While out today the car has cut out 3 times on tickover. This is when fully up to temperature, the revs are steady at about 800rpm and the engine just dies. Push the starter and it starts but runs uneven until I give it a few revs and everything settles back down and it runs perfectly.

Any ideas? Cracked manifold perhaps?

[Gadgeroonie]

give the throttle stop a quick tweak with an allen key, may be all it needs

if you are coming to the dyno day i can take a look at it then

[Bizarro]

Thanks, I'll give it a go.

[Bizarro]

Gave the throttle stop a bit of a tweak so its now ticking over about 1000rpm. Been out tonight and the problem is still there, if anything its worse but I dont think its anything to do with the speed of tickover.

It stalled once when changing gear and on one occasion while sat at traffic lights the revs dropped I tried to pick them up with the accelerator but this made no difference. Eventually the car stalled and when I started it a huge plume of smoke came out of the exhaust? This happened about 3 times in half an hour of driving.

It feels like fuel starvation or even loss of ignition as when the revs die I cant pick it up on the accelerator but once the engine has stalled I can start it straight away and it runs fine??

[Gadgeroonie]

is it a 2.5 or 3.0 ?

[Bizarro]

Gadgeroonie said:

is it a 2.5 or 3.0 ?

Its a 3.0, factory standard as far as I know.

[roi354]

Vacuum leak?

[Bizarro]

roi354 said:

Vacuum leak?

Any pointers on how to check for vacuum leak?

[Gadgeroonie]

make sure the pipe that goes onto the intake manifold from the map sensor has not been pushed on too far

if pushed on too far the air can not pass up and down the pipe

[funkybmx1]

i had that problem. it pushes on the side of the throatle boby. mine had come of to much

[D_G]

Nick,

Had the same problem with mine, you can't just adjust the throttle stop as the map reads off the throttle sensor, you can improve it slightly but not cure it. It was never great since I've had it and was getting worse.
I checked all the pipes etc, I've since had it mapped by Yellowshed and the car is like a different car now, not just in performance but it's soooo much smoother & idles great.
BTW it's a standard early GTO3.

Cheers

Dave

[roi354]

Bizarro said:

roi354 said:

Vacuum leak?

Any pointers on how to check for vacuum leak?

Err, no sorry not really. Only thing I can suggest is that you remove them one by one and inspect them for splits and blockages. I'd have thought that if there was a problem with the vac hose to the MAP sensor you'd get either the brick wall effect or inability to rev past about 3k.

Maybe someone could help further? I'm just guessing here.

Edited by roi354 on Monday 8th March 23:29

[Jim O.]

Bizarro said:

roi354 said:

Vacuum leak?

Any pointers on how to check for vacuum leak?

First thing I usually do is rev the motor in neutral to about 3000 rpm, hold it there for a sec, and then pop off the throttle pedal while watching the tach. Usually if there's a vacuum leak, the tach needle will drop, undershoot the idle speed by several hundred rpm, and then rise back up to the idle speed. A car without leaks may also undershoot, but usually by not as many rpm.

Easiest way to find a leak is to use a smoke machine, but that's not the type of equipment that most people have available. If you can't find the leak any other way, you may be able to find a shop with a smoke machine. In the States, shops that do diagnosis of emissions systems are likely to have a smoke machine.

You can use something like starting fluid (ether), propane, carburator cleaner, etc. to find the leak - with the motor running, spray a little on a hose connection, and see if the idle speed changes. Work slowly - it may take a few seconds for the idle to change, and changes are going to be fairly subtle. Be careful with the starting fluid or the carb cleaner - they may affect painted surfaces. Use whatever substance sparingly - don't want to build up a high enough concentration of flammable fumes that you start a fire...

Does your engine die as you're slowing to a halt (like when you switch from throttle to brake), or does it die just when sitting there idling? The former is probably a vacuum leak, idle speed setting, or tune issue. The latter is something else - last time I ran into a problem like that, it was an intermittant ground on the engine wiring harness. Try cleaning and tightening the battery connections, and the ground point where the battery ground attaches to the car chassis.

Edited by Jim O. on Tuesday 9th March 10:06

[Duke Thrust]

Jim O. said:

Bizarro said:

roi354 said:

Vacuum leak?

Any pointers on how to check for vacuum leak?

Easiest way is to use a smoke machine, but that's not the type of equipment that most people have available. If you can't find the leak any other way, you may be able to find a shop with a smoke machine. In the States, shops that do diagnosis of emissions systems are likely to have a smoke machine.

You can use something like starting fluid (ether), propane, carburator cleaner, etc. to find the leak - with the motor running, spray a little on a hose connection, and see if the idle speed changes. Work slowly - it may take a few seconds for the idle to change, and changes are going to be fairly subtle. Be careful with the starting fluid or the carb cleaner - they may affect painted surfaces. Use whatever substance sparingly - don't want to build up a high enough concentration of flammable fumes that you start a fire...

In the past I've used WD40, little spray here and there and watch for any smoke from the exhaust - very useful for finding air leaks on the Vitesse.

[Bizarro]

Thanks for all the replies.

Ive had a good check of all the vacuum pipes and cant see anything obvious but from the sound of things a small leak is not that easy to spot. Ive been out again this afternoon and the problem is happening more often than at the weekend so probably not a good idea for me to keep driving it!!

Ive booked it into Noble Motorsport in Chesterfield at the weekend for them to have a look. They have serviced the car before so they do know it. Also I have a warranty that came with the car when I bought it so if the problem turns out expensive I may be able to claim on the warranty

Hopefully should get it sorted by the end of the month for the Dyno day at Mikes, Ill post with what they find..

Cheers

[Bizarro]

Latest update:

Problem became more frequent to the point that when warm the car would not tick over without stalling.

Went to Area 52 last Thursday where Jason and Mike had a good 2 hours with the laptop and couldnt really see anything obvious that was causing the problem, cheers for trying, so dropped it off at JNM in Chesterfield and left them with it.

They have now had the car for a week and called today to say that they suspect it is a bug in the ECU. They told me that they are seeing the same problem more and more on the earlier 3 litre cars, the last one was cured with a new ECU!!
They have told me that MBE are aware of a bug and JNM plan to send a spare ECU back to MBE for them to update and then try in my car to see if it cures the fault.

After spending the time at Area 52 I can understand that the fault is a bug in the ECU as when not on tickover the car is 100%, but what I dont understand is how an electronic/software problem can get gradually worse?? Surely if the fault is a software bug it would have been present all the time I have owned the car?
The car only developed the fault after being serviced at JNM!!

[TuxMan]

When i first got my Noble the tickover was not great so i was advised to get intouch with Yellowshed so he could upload a new map , he did this and sorted it ,there seems to be some early software about but i,m not sure thats the problem , what did they do at service ? if it was fine when it went in i would go back to basics ,sounds electrical to me so check all ecu plugs and what plugs did they fit and at what gap ?

[Bizarro]

TuxMan said:

When i first got my Noble the tickover was not great so i was advised to get intouch with Yellowshed so he could upload a new map , he did this and sorted it ,there seems to be some early software about but i,m not sure thats the problem , what did they do at service ? if it was fine when it went in i would go back to basics ,sounds electrical to me so check all ecu plugs and what plugs did they fit and at what gap ?

It was a 12000 mile service so plugs were changed but I dont know what make or gap they were set at.

During the service they reset the turbo actuators and then had the car on the rolloing road to set it up 'correctly', they have said that they made a few adjustments but I dont know what adjustments were made, they didnt flash the ECU with updated software.

I cant be 100% sure that the problem was not present prior to the service, unless it is happening regularly I probably wouldnt have thought anything of it
JNM do have a lot of experience on Noble's, I believe a few people on here use them and do rate them highly. I would be surprised if the problem is something that they have created during the service, but I do find it very strange that a software problem can develop and get gradually worse over time/usage?

[Stella Artois]

Bizarro said:

what I dont understand is how an electronic/software problem can get gradually worse?? Surely if the fault is a software bug it would have been present all the time I have owned the car?

It might seem strange but ecu's along with other electronic systems can suffer data leakage. The data retention of EPROM, EEPROM, and Flash may be susceptible to charge leakage from the floating gates of the memory cell transistors. Leakage is exacerbated at high temperatures. Meaning your map can corrupt, as its stored data. However, this may only be as simple as a single "1" or "0" out of squillions, generating your bug.

On the other hand, whip out your Lambda Sensors and check for cracking of the manifolds as you suspected, mine was doing this but ceased after the manifolds were welded and it was remapped. Oh and the probes replaced as they had burnt away!