EGR: Blank it or leave it?

MITSUBISHI PAJERO EGR: Blank it or leave it?

Over the years, I've had enquiries about excessive smoking on Pajeros and consequently how to blank the EGR valve, even where the cause of the smoke is unknown... My thoughts are that the EGR is working, it serves a purpose. If it’s shot, you could do something about it. I have compiled this so you can make up your own mind.

Currently in the UK, excessive smoke is subject to emissions testing at the MOT, but the EGR valve itself is not tested. Therefore, a blanked or inoperative EGR valve can’t cause MOT failure and may help to reduce smoke emissions. In some countries, where there are stricter environmental controls, the EGR is tested.

If your diesel is smoking and all you want to do is to reduce smoke to get through the MOT test, turning down the diesel pump is a quick-fix, without the need to blank the EGR. Remember to turn the pump back up, as you will loose performance. It's also advisable to investigate the cause of the smoke!

Here’s my understanding of how the EGR works on the Mitsi unit.

1. The Engine Control Unit (ECU) detects accelerator position, engine speed & transmission information. It decides when the EGR is needed. When needed, it sends a signal to the EGR. It should not trigger EGR at idling, low load, or full load.
2. The signal activates a solenoid, which opens a vacuum line.
3. Vacuum is separately generated by a pump as a diesel engine does not have vacuum at inlet manifold. The same vacuum is used for brake booster.
4. The spindle in the EGR valve moves when the vacuum is applied. This allows inert exhaust gas to be introduced to the engine.
5. The inert gas (exhaust) has of course been produced by the engine.
6. The engine responds to inert gas. Oxygen concentration is decreased by addition of inert gas, resulting in lower combustion temperature, and thus less nitrous oxide.

There are 3 general operating modes for the EGR system. These are some of the causes of failure.

Mode 1: EGR works properly: Engine produces less nitrous oxide.

Mode 2: Excess EGR: Poor idling, smoke when idling, flat spots when accelerating, lack of power at full power.

The main causes for this failure are:
1. ECU generates the wrong signal: Replace ECU.
2. Control signal not received by solenoid: Check wiring
3. Solenoid not moving: Replace
4. EGR valve spindle travels too far: Spring weak – Replace.
5. EGR valve spindle does not move: Stuck by debris in open, closed or intermediate position (intermittent or persistent): Clean valve or replace.
6. EGR valve spindle does not move: Diaphragm torn: Replace.
7. Idle speed too high.
8. Exhaust back pressure: Possible obstruction: Replace exhaust.

Mode 3: No EGR effect: Combustion temperature rises, adding thermal stress to engine, consider the possibility of adverse long term reliability. (I understand that in 7 years, no members have yet reported adverse effects?) Increased Nitrous oxide production, therefore increased pollution.
Possible causes of this are:
Same as points 1-5 above and
6. Vacuum line blocked or deliberately plugged: Check vacuum pressure
7. Blockage (blanking plate!) in pipe

Is your EGR valve working? Try these 2 simple tests.

1. If you can access your EGR valve stem, push it against spring pressure. It should move freely and return fully. If it doesn’t, remove the valve for cleaning or replacement.
2. With the engine at normal operating temperature, open the throttle to 2,500 rpm while watching the EGR valve stem. It should move, then return.
If it doesn't, remove the hose and feel for vacuum as you rev it again. If you find some, the valve's at fault.
If there’s no vacuum, see mode 3 above. This applies to the Mitsi units, some operate differently.

Blank it or not?

Excess EGR (mode 2) reduces the performance of the vehicle. In this case, it is possible to disable the EGR system entirely, so that it operates in mode 3. This has some negative consequences: Hotter combustion temperature and the possibility of reduced engine life.

If you plug the vacuum line with a ball bearing and the EGR valve is stuck in an open position, it will have no effect. You should blank the EGR instead.

The blanking plate will need to withstand temperatures of at least 500c, so stainless steel would do the trick. (Don't use layers of thin steel or a coin as these have been known to disintegrate and cause damage.) To blank the EGR on a Pajero, you will need to remove the gasket (between the valve and inlet manifold) and replace it with the plate. This means that the gases have no means of escape, which will help a smoke problem. They will have to re-circulate elsewhere.

How to blank the EGR valve on a diesel Pajero:

First, where is it? To find the valve, follow the 3/4 inch diameter pipe that comes up from the exhaust. It bolts on to the EGR. The top of the EGR is 2 1/2 to 3" in diameter with a 'flying saucer' and a vacuum pipe on the top.

Remove the 2 horizontal bolts which hold it to the inlet manifold. Slide out the gasket carefully (you don't want any crud going where it shouldn't.) Replace the gasket with a steel plate.

There is the option of cleaning the EGR:

It’s not too hard to do. Be aware that some dealers say never use a solvent on an EGR valve, others say go ahead. You make your own decision.

A new gasket is a couple of pounds from Mitsi. Scratch on alignment marks. Remove the EGR and soak it overnight in STP. Remove from soak, clean and dry it. Spray it inside and out with Carb cleaner. Blow it through with an air line where possible (try your local garage/petrol station). Spray the other end of the vacuum pipe with Carb cleaner. Replace the pipe, clean up both faces and refit the new gasket.

The smoke problem can be due to blocked or partially blocked pipes to the EGR or solenoid.

This can be been cured by squirting cleaner down the pipes and blowing them through with an airline. As the pipes are rubber, any cleaner should be silicone free and made for the job. Some have successfully used warm soapy water, but don't use carb cleaner as it may damage the rubber.