CDT Lumpy tickover

[Paranoid Carlos]

Had a little problem for a while that has irritated me for too long now, the tickover seems very lumpy when cold, it seems to drop 50 revs and then recover. When the engine is hot and returns to tickover it drops once and then stays stable for about 20 seconds then drops again. Its not noticable when looking at the engine but you can hear it and see it on the rev counter. I have had this issue for about 6 months adjusting the Mafam makes no difference neither does turning the Tu3 off.

I'm thinking does the Maf wire need a wipe?

[M47Rman]

Originally Posted by paranoid

Had a little problem for a while that has irritated me for too long now, the tickover seems very lumpy when cold, it seems to drop 50 revs and then recover. When the engine is hot and returns to tickover it drops once and then stays stable for about 20 seconds then drops again. Its not noticable when looking at the engine but you can hear it and see it on the rev counter. I have had this issue for about 6 months adjusting the Mafam makes no difference neither does turning the Tu3 off.

I'm thinking does the Maf wire need a wipe?

You could try cleaning the AFM, it certainly will not do any harm. Also check for air leaks around the inlet manifold, intercooler pipes etc. Not likely to be the EGR system, as you say it does it when the engine is cold, and as far as I remember the EGR does not kick in until the engine has reached a pre-determined temperature (I think it was 30C, but that may have been L series).
If you have had the air filter changed in the last 6 months, check that the air filter box (cover) has been re-fitted correctly.
Only other thing I can remember off hand that used to cause idle instability, was the engine cylinder balance, which minutely adjusts each injectors pulsewidth to even out all four pistons relative acceleration. We occasionaly had problems with sticking injectors, which meant the cylinder balance system could not compensate quickly enough, it then ramped up the injector pulse width, leading to an eventual over compensation, and a momentary change of idle speed. I have to say though this is extremely unusual, and is not a problem I remember in production vehicles.
I would be looking at AFM and/or air leaks first!
Andy

[Keith]

There is a routine on T4 for checking and adjusting the engine balance on the CDT and for fine tuning the tickover which might be worth a try

[Ti Rich]

Originally Posted by M47Rman

You could try cleaning the AFM, it certainly will not do any harm. Also check for air leaks around the inlet manifold, intercooler pipes etc. Not likely to be the EGR system, as you say it does it when the engine is cold, and as far as I remember the EGR does not kick in until the engine has reached a pre-determined temperature (I think it was 30C, but that may have been L series).

The EGR is vaccum operated from what i can see on the M47R. I can't see any interaction with the ECU at all, hence why it doesn't matter is you disable it.

[Roverron]

Try cleaning the PCV as owners are reporting a more stable idle and improved smoothness and less engine noise as well as less smoke.

My engine does feel smoother after cleaning mine and I have been able to use a lower mafam setting on my Synergy.

Check the thread out:

http://www.the75andztclub.co.uk/foru...1&goto=newpost

Ron

[M47Rman]

Originally Posted by Ti Rich

The EGR is vaccum operated from what i can see on the M47R. I can't see any interaction with the ECU at all, hence why it doesn't matter is you disable it.

You can disable EGR (by blanking off the vacuum feed to the valve) and the engine will run quite happily. However the EGR system IS controlled by the engine ECU, via a vacuum modulator, which controls the opening and closing of the EGR valve, by modulating its vacuum supply.
Andy

[Roverron]

Originally Posted by M47Rman

You can disable EGR (by blanking off the vacuum feed to the valve) and the engine will run quite happily. However the EGR system IS controlled by the engine ECU, via a vacuum modulator, which controls the opening and closing of the EGR valve, by modulating its vacuum supply.
Andy

The ecu will know its been disabled* and will possibly log a fault code but this is irrelevant.

* Since it uses the maf signal to monitor the airflow into the engine, when it opens the egr valve this reduces slightly as fresh air is replaced with exhaust gas which does not flow past the maf sensor.

Ron

[M47Rman]

Originally Posted by Roverron

The ecu will know its been disabled* and will possibly log a fault code but this is irrelevant.

* Since it uses the maf signal to monitor the airflow into the engine, when it opens the egr valve this reduces slightly as fresh air is replaced with exhaust gas which does not flow past the maf sensor.

Ron

Exactly right!
As you say, when the system is disabled, the (unlikely) fault code is irrelevant, but your cleaner inlet system certainly is not!
Have you noticed an increase in engine noise Ron, with EGR disabled, particularly at light load? I disabled the system on my Gem 3 a couple of years ago, and noticed a fairly distinct increase in part load combustion noise (although it did not come as a surprise)
Andy