EGR removal disconnect modulator?

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Baldric427

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I have viewed several kit instructions for removing the EGR assembly on TD5 units.
Most kits simply blank off the now redundant vacuum pipe to the EGR but leave the modulator in use. There are a few kits that also recommend disconnecting the electrical connection to the EGR modulator.
My question is: Given that when the EGR valve is open, the hot gases mix with fresh intake air, the flame front speed during ignition must be slower than it would be without the EGR in play.
Under these conditions you would expect the ECU to add more advance timing to compensate.
If it does, then leaving the modulator in circuit would make the ECU believe the EGR remains in use and it would still add more advance when, in fact, it is not required. If the modulator were disconnected, then the ECU would believe the EGR was faulty and fail to add the unwanted advance.
Forgive me if this is a daft question, my knowledge of engines and ECU's is limited to petrol where advance control is a simply electronic adjustment. I recognise that with diesel, this is not so simple and may not be adjustable by the ECU at all.
In short, should I disconnect the electrical connections to the modulator?
 
:welcome2: Welcome to Landyzone, its customary to introduce yourself in the "introduce yourself" section - you may end up with less rip taking that way.

Not really sure what you are on about as far as electrical connections are concerned, mine only had a couple of vacuum pipes - I just followed the instructions that came with the kit. See below.

EGRinstructions.jpg
 
Baldric427 said:
I have viewed several kit instructions for removing the EGR assembly on TD5 units.
Most kits simply blank off the now redundant vacuum pipe to the EGR but leave the modulator in use. There are a few kits that also recommend disconnecting the electrical connection to the EGR modulator.
My question is: Given that when the EGR valve is open, the hot gases mix with fresh intake air, the flame front speed during ignition must be slower than it would be without the EGR in play.
Under these conditions you would expect the ECU to add more advance timing to compensate.
If it does, then leaving the modulator in circuit would make the ECU believe the EGR remains in use and it would still add more advance when, in fact, it is not required. If the modulator were disconnected, then the ECU would believe the EGR was faulty and fail to add the unwanted advance.
Forgive me if this is a daft question, my knowledge of engines and ECU's is limited to petrol where advance control is a simply electronic adjustment. I recognise that with diesel, this is not so simple and may not be adjustable by the ECU at all.
In short, should I disconnect the electrical connections to the modulator?
Click to expand...

Hi Baldric and welcome.

The point you raise is an interesting one, but I think it might not apply, as ignition timing on TD5 is taken care of by the ECU using data from the crank sensor and firing the fuel injector pulses from there.
 
I left the electrical connectors on and it seems fine, I have seen instructions that say leave them off however, so will wait with you to see if we can get an experts comment!
 
thebiglad said:
Hi Baldric and welcome.

The point you raise is an interesting one, but I think it might not apply, as ignition timing on TD5 is taken care of by the ECU using data from the crank sensor and firing the fuel injector pulses from there.
Click to expand...

I can't help but wonder whether the ECU further adjusts the injector timing if it thinks the EGR is open. If it does, the benefit of removing the EGR would be compromised unless the ECU is forced to stop adding advance.
 
Baldric427 said:
I can't help but wonder whether the ECU further adjusts the injector timing if it thinks the EGR is open. If it does, the benefit of removing the EGR would be compromised unless the ECU is forced to stop adding advance.
Click to expand...

AFAIK, after a long struggle to understand the Td5's management i must say that you dont have to worry about this, cos the EGR doesnt act as a sensor for the ECM, the ECM controlls the EGR based on various sensor's inputs and it has an addaptive strategy comparing sensor inputs with stored fueling map and default values. I'll quote relevant parts from RAVE cos it's hard for me to explain it with my english(fortunately i know RAVE by heart cos i've read it all and i know here to find any statement) the most relevant are highlighted:

1. The ECM controls the air/fuel mixture and fuel injection timing via the Electronic Unit njectors (EUI), by the length of time the EUI's are to inject fuel into the cylinder. This is a rolling process and is called adaptive strategy. By using this adaptive strategy the ECM is able to control the engine to give optimum driveability under all operating conditions.
To achieve an adaptive strategy for acceleration the ECM uses input information from the CKP sensor, TP sensor, ECT sensor, MAP/ IAT sensor, and the FT sensor. This is compared to mapped information within its memory to implement the optimum fuelling strategy to facilitate acceleration.


2. Fuel delivery/injection control
The fuel delivery/injection control delivers a precise amount of finely atomised fuel to mix with the air in the ombustion chamber to create a controlled explosion.
To precisely control fuel delivery and control fuel injection, the following input conditions must be met:
l CKP information.
l Injection timing map information.
l FT information.
l ECT information.
The ECM monitors the conditions required for optimum combustion of fuel in the cylinder from the various sensors round the engine and then compares it against stored information. From this alculation the ECM can adjust the uantity and timing of the fuel being delivered to the cylinder.
The ECM uses CKP information as follows:
l To calculate engine speed.
l To determine engine crankshaft position.
Engine speed and crankshaft position allows the ECM to determine fuel injection timing.

So IMO the fact that the EGR is removed doesnt affect the management, it's only effect is that if the modulator is still connected but the vacuum is blanked the ECM will recognise and store the fault codes into it's memory.
 
Last edited:
I believe the ECU's only function re the EGR valve is to open and close it, depending on throttle demand.

In other words the EGR valve should open (permitting the mix of exhaust gases) only when on 0 or very light throttle. This is after all just a crappy solution for the manufacturer to pass it's pollution regs.

Comparing spark ignition and compression ignition engines, one can see the variable ignition timing on a petrol engine could have advantages when dealing with differing grades of fuel, but with diesel engines the timing is more about the injection timing as I said before, rather than spark timing, so I would suggestion that whilst your concerns and comments are interesting and thought-provoking, they are not relevant to these diesel Electronic Injection Units.
 
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