Diesel revs pickup

[FROGGY]

Whilst happily passing the time of day rebuilding "the dog", one job was fitting a new MAF unit. During playtime, I discovered that, with the MAF connected, and you give it full welly in neutral, the pickup to max revs is fairly leisurely. With the MAF disconnected however, pickup is very quick, but accompanied by a fair bit of smoke.
Why?

Mick

[RPWC]

Faulty MAF,by the sound of things,is it Bosch?

[FROGGY]

Originally Posted by RPWC

Faulty MAF,by the sound of things,is it Bosch?

It better not be faulty, it's a brand new genuine Rover unit.
It was the same with the old unit in

[RPWC]

Have you checked the wiring plug,and the wires for breaks? On my old saloon, I replaced the MAF,and once when brained the T4 on it,he noticed theMAF was not working,further inspection found 3 wires broken. My own fault,as I had cut a small corner of the engine cover away,in order to be able to remove the MAF,without removing the engine cover Should have taken the cover off first lol. Next step would be a T4 check

[FROGGY]

Come on all you "experts" who change MAFs every day.
Is this normal or not?
Mick

[marinabrian]

No it's not normal Mick.

You need to see if the connections are secure to the elbow you removed to fit the MAF, and dare I say it, have you fitted an EGR bypass?

If the EGR is not shutting correctly, be that with a lazy actuator, or indeed a badly manufactured/fitted EGR bypass, the car will exhibit the symptoms you describe.

Also if you wish, post me your old MAF sensor, and I will be happy to test it's functionality.

Many people are quick to condemn a MAF sensor, when unplugging it results in a quick pick up, and no loss of power.

The reasons for this are twofold, one with the MAF disconnected, the ECM will not operate the EGR valve, meaning it stays in the closed position.

Two, with a partially open EGR valve, the airflow readings as seen by the ECM in relation to the MAF sensor will be particularly low, in the region of 250 to 340 mg per stroke, where a health EGR MAF combination will result in a reading of 480 to 500 mg per stroke.

Back to the task of checking, double checking and seeing if anything is adrift.

If you still have the EGR valve fitted, as a temporary test it is possible to unplug the EGR actuator solenoid.

This will result in an illumination of the MIL lamp with your car as it's fitted with an NNN500340 ECM, but if the car revs freely, the problem is most likely to be the result of the EGR.

Let us know how you get on please.

Brian

[FROGGY]

Hi Brian
Thanks for the info.
Complete lack of interest has stopped play at the moment. You know what it's like when the Gods don't seem to be shining on you?


No it's not normal Mick.

You need to see if the connections are secure to the elbow you removed to fit the MAF, and dare I say it, have you fitted an EGR bypass?
Do you mean the pipework? If so, you can't see it when all is in place, but it all seemed correct.
I removed an EGR bypass and re-fitted a cleaned EGR valve. Don't know if it works though !
If the EGR is not shutting correctly, be that with a lazy actuator, or indeed a badly manufactured/fitted EGR bypass, the car will exhibit the symptoms you describe.

Also if you wish, post me your old MAF sensor, and I will be happy to test it's functionality.
Thanks for the offer. I may send you two, the old and the new.

Many people are quick to condemn a MAF sensor, when unplugging it results in a quick pick up, and no loss of power.

The reasons for this are twofold, one with the MAF disconnected, the ECM will not operate the EGR valve, meaning it stays in the closed position.

Two, with a partially open EGR valve, the airflow readings as seen by the ECM in relation to the MAF sensor will be particularly low, in the region of 250 to 340 mg per stroke, where a health EGR MAF combination will result in a reading of 480 to 500 mg per stroke.

Back to the task of checking, double checking and seeing if anything is adrift.

If you still have the EGR valve fitted, as a temporary test it is possible to unplug the EGR actuator solenoid.
Where do I find this?
This will result in an illumination of the MIL lamp with your car as it's fitted with an NNN500340 ECM, but if the car revs freely, the problem is most likely to be the result of the EGR.

Let us know how you get on please.

Brian [/QUOTE]

Just about to pour a glass of wine now, about the only thing I can do without hassle !

Mick

[marinabrian]

Originally Posted by FROGGY

Hi Brian
Thanks for the info.
Complete lack of interest has stopped play at the moment. You know what it's like when the Gods don't seem to be shining on you?


No it's not normal Mick.

You need to see if the connections are secure to the elbow you removed to fit the MAF, and dare I say it, have you fitted an EGR bypass?
Do you mean the pipework? If so, you can't see it when all is in place, but it all seemed correct.
I removed an EGR bypass and re-fitted a cleaned EGR valve. Don't know if it works though !
If the EGR is not shutting correctly, be that with a lazy actuator, or indeed a badly manufactured/fitted EGR bypass, the car will exhibit the symptoms you describe.

Also if you wish, post me your old MAF sensor, and I will be happy to test it's functionality.
Thanks for the offer. I may send you two, the old and the new.

Many people are quick to condemn a MAF sensor, when unplugging it results in a quick pick up, and no loss of power.

The reasons for this are twofold, one with the MAF disconnected, the ECM will not operate the EGR valve, meaning it stays in the closed position.

Two, with a partially open EGR valve, the airflow readings as seen by the ECM in relation to the MAF sensor will be particularly low, in the region of 250 to 340 mg per stroke, where a health EGR MAF combination will result in a reading of 480 to 500 mg per stroke.

Back to the task of checking, double checking and seeing if anything is adrift.

If you still have the EGR valve fitted, as a temporary test it is possible to unplug the EGR actuator solenoid.
Where do I find this?
This will result in an illumination of the MIL lamp with your car as it's fitted with an NNN500340 ECM, but if the car revs freely, the problem is most likely to be the result of the EGR.

Let us know how you get on please.

Brian

Just about to pour a glass of wine now, about the only thing I can do without hassle !

Mick[/QUOTE]

Mick, if you follow the small pipe from the diaphragm on the EGR valve back toward the engine, you will find a small plastic gubbins with an electrical connector.

If you unplug this connector, the EGR valve cannot open, as I pointed out earlier, this is likely to illuminate the MIL lamp, however it is only for testing and elimination purposes

Brian

[FROGGY]

Mick, if you follow the small pipe from the diaphragm on the EGR valve back toward the engine, you will find a small plastic gubbins with an electrical connector.

If you unplug this connector, the EGR valve cannot open, as I pointed out earlier, this is likely to illuminate the MIL lamp, however it is only for testing and elimination purposes

Brian [/QUOTE]


Another day, full of hope again..................

OK, disconnected the plastic gubbins, and, no change. Pickup still slow.
So what has that proved? (answers on a large cheque please).......

Mick

[FROGGY]

Been polishing it, nowt else to do at the minute..............