EGR blocked

[Jassper]

Hello everyone,

I decided to give it a try and disconnected the EGR on my 602 engine. There are 2 connectors that go to the turbo - one in front and one at the back. The one at front is a flap inside the intake, the one at back is a valve in the exhaust.

I believe the EGR valve is the one at back. Am I correct? Now, the rubber hose to this valve is joined in the middle by a plastic piece. I put a pin wide enough in the plastic piece and blocked the hose. Tested it, no suction possible.

I test-drove it. First without the line plugged. All went OK but the shifts were harder but not harsh and also when I stepped on the pedal the engine would rev up but there would be no shift in time. Naturally the vacuum was leaking. Then I plugged the line. I can say I think I could feel some improvement. It wasn't a miracle but there was some improvement.

I decided to take this step to improve the acceleration and overall performance of the engine and also to avoid EGR caused all sorts of sticky goo in the intake line.

The question now is - what is the function of the flap in the intake? When the engine is revved up the flap moves. When I took the intake line apart some 2 years ago I think I remember that the flap was in open position with no vacuum applied (idle for example) and closed when vac was applied. Or is it that when the engine is started the flap opens when vac is applied? One way or the other I think the flap is open at idle, right?

Is this the protection from too much pressure supplied to intake and head? Am I correct to assume that with higher revs (and pressure) the flap gradually closes to protect the head from too much pressure? Or is it exactly on the contrary - the valve is closed at idle and gradually opens with higher RPM and there is no danger of too much pressure at all because the turbo isn't capable of producing it?

If it is the former where does the surplus pressure escape then? Could it be that with a working EGR valve the surplus pressure is navigated to exhaust thru the EGR valve?

My fear is that with a blocked EGR there would be no over-pressure protection - no escape for the pressure as it can't escape through the disabled EGR valve. Or do the over-presure on intake side and (blocked) EGR valve at exhaust side have nothing in common in this respect and a possible over-pressure escapes by other means?

Please let me know. Thanks.

[SoyDriver Matt]

The EGR doesn't connect to the turbo, it connects the exhaust manifold to the intake.

[Jassper]

Originally posted by SoyDriver Matt
The EGR doesn't connect to the turbo, it connects the exhaust manifold to the intake.

Yes, thank you. Is it not so though that when the excessive pressure happens the EGR opens and the pressure escapes intake -> valve -> exhaust? Would be a convenient way.

Now it depends which pressure is higher - the one in intake to the one in exhaust - in which case the excessive pressure would escape to the exhaust (provided the EGR is not blocked) or the exhaust pressure is always higher to the intake pressure - in which case only gas recirc would take place.

If the latter is correct then disabling EGR would not harm the head because of possible excessive pressure.

[SoyDriver Matt]

The point of the EGR is to let exhaust gasses into the intake to cool the cylinders , to reduce NOx. The boost control limits the turbo from overboosting.

[Jassper]

Originally posted by SoyDriver Matt
The point of the EGR is to let exhaust gasses into the intake to cool the cylinders , to reduce NOx. The boost control limits the turbo from overboosting.

Matt,

to cool cylinders, why would someone introduce hot exhaust gasses rather than cold fresh ambient air? I can see the point of NOx being re-introduced to the system where the NOx compound is broken into N as one element which would cool the system but think cool air would be of more help. Anyhow, this is not important to me.

Certainly so, the boost control limits the turbo from overboosting. There is a boost switch near the accumulator. But what does it do? When it detects too much pressure it sends a signal somewhere. Then something is done to limit the boots. Now, there are only 2 parts on the turbo that can do something - the intake flap and the EGR.

This leads us back to my original question - does overboots sensor close the intake flap in the turbo? If this is the case where does the excess pressure escape? Through EGR? It is disabled.

If it doesn't control intake flap but opens EGR itself to let the pressure out then it's the same - EGR is disabled.

Any ideas?

[SoyDriver Matt]

Even though the exhaust gasses are hot, they have already had the oxygen burnt up, so introducing the pre-burnt gas into the cylinder it take the place of fresh intake air limiting the oxygen- fuel ratio. I'm no expert but I don't think the EGR hooks to the turbo at all. I think the wastegate controls the point that the turbo starts boosting, and the the overpressure sensor that is fed by the line coming off the intake near the firewall goes to an switch that opens the bypass valve, limiting boost. So again, I'm new to turbos, but there should be two controlers hooked to the turbo, and the EGR is a seperate system. Any experienced torbo gurus want to jump in?

[Denrac]

Hi Jassper

what is the function of the flap in the intake?

The flap is to increase the vacuum in the intake manifold when the EGR valve opens.

On the 1992 602, the flap operates in tandem with the wastegate : when vacuum is applied to the flap, the flap closes, no vacuum goes to the wastegate, the wastegate is open and no turbo boost is builded. At the same time, the EGR valve opens and more exhaust gaz is recirculated.

The opening of the EGR valve and the closing of the flap is controled by the Electronic Diesel System unit (EDS) : depending on engine speed and quantity of injected fuel, the EDS compare the actual intake pressure to a stored reference pressure to achieve optimum engine operation in respect of performance, NOx, HC and particle emission.

The EDS knows that the EGR is functionning when it sees by mean of the MAF sensor a reduction of fresh air admitted in the engine.

Overboost is controlled by the same set of components : when pressure is too high, the flap is closed and the wastegate is opened and the EDS sees a rapid drop in fresh air admitted.

When one of the component is not doing its job, the EDS cut all the vacuum to the wastegate in order to protect the engine. That's why you cannot just block the EGR valve on a 602.

When the engine is idling, the wastegate and the EGR valve should be closed, and the flap wide opened. Gradually increasing the revs to 2000 rpm, the wastegate will open (check the movement of the control rod), the flap wil close and the EGR will open.

The EDS unit stores error codes : plugging and unplugging various component can leave you without turbo boost until you erase the stored fault.

[gsxr]

1) It would be a help if you created a signature with your car's year & model, and maybe your name. Or at least include that info in your post. I assume you have a 1990-1993 300D 2.5 Turbo though.

2) You cannot simply disconnect the EGR on the 90-up engines. The EDS will know you killed it, and will prevent boost from building by keeping the wastegate open. There is a way to disable and/or remove the the EGR but it requires either fooling the electronic sensors, OR replacing your turbo wastegate with the older mechanical pressure type. Both procedures have been done successfully by members of this forum - use the "Search" feature.

3) The flap in the intake doesn't change "vacuum" because there is no vacuum in the turbo charge (intake) manifold. What it does is similar to the old air recirc valves, I believe, where it reduces boost pressure to allow more exhaust gas to enter the intake stream. Otherwise the turbo boost would reduce the flow of exhaust into the pressurized intake stream.

4) The overboost protection is totally separate. It has a sensor in the intake manifold which triggers at, IIRC, 1.10 bar +/- 0.15 bar. When that happens, it kills fuel enrichment by cutting off the signal line to the ALDA. This is what happens if the wastegate fails and sticks closed, providing too much boost.

5) You need to test your car from 0-60mph with a stopwatch on flat road. It should be about 11-12 seconds. If not, you're down on power, and probably need to either reconnect the EGR, or disable it correctly as mentioned in item #2 above.


HTH,

[Denrac]

The flap in the intake doesn't change "vacuum" because there is no vacuum in the turbo charge (intake) manifold.

I agree that when the flap is opened, there is no vacuum in the intake manifold. But when it closes, I think we should have negative pressure, even if the EGR is opened : the EGR port is half an inch in diameter and the unflapped intake is over 2 inches (the flap is downstream of the turbo : turbo is pushing on a closed door)

The overboost protection is totally separate

In 1992 model year, the overboost protection relay of the alda has been discontinued : the alda is connected directly only to the intake and the EDS pressure sensor. It's weird : if you have an EDS error code that cut signal to the flap, you are totally unprotected from a stucked closed wastegate (that situation happens if the vacumm transducer for the control flap/wastegate is defective).

I don't have access to a detailed description of the EDS system and I'm not the man who engineered it : most is interpolation and extrapolation from the sparse data found in the shop CD, direct observation of a specimen and crushed fingers field experience. Just try to share.

[gsxr]

Good info - thanks! This also points out why it's important to list the year/model being discussed.

[Jassper]

Hello Denrac,

and many thanks for your input.

'The flap is to increase the vacuum in the intake manifold when the EGR valve opens. '

I suppose when the flap closes the engine is left with no other choice that to draw from the exhaust more. Thus EGR. Am I correct? So when I rev up the flap closes not to protect the system from too much pressure but to recirc exhaust gasses more?

'On the 1992 602, the flap operates in tandem with the wastegate : when vacuum is applied to the flap, the flap closes, no vacuum goes to the wastegate, the wastegate is open and no turbo boost is builded. At the same time, the EGR valve opens and more exhaust gaz is recirculated.'

Now EGR valve and wastegate are 2 separate items? If so, where is the wastegate? The only thing I can see is the flap in intake and EGR valve that interconnects exhaust to intake above where the flap is.

'The EDS knows that the EGR is functionning when it sees by mean of the MAF sensor a reduction of fresh air admitted in the engine. '

So there is an active component in the system - a sensor. Do you have an idea where the sensor is? I haven't spotted it yet. Naturally, I haven't really looked for it either.

'Overboost is controlled by the same set of components : when pressure is too high, the flap is closed and the wastegate is opened and the EDS sees a rapid drop in fresh air admitted.'

This leaves me with a question - where is the wastegate? Do you mean the EGR valve? With the valve open the excessive pressure could escape to exhaust through the interconnection I described above. Is this it?

'When one of the component is not doing its job, the EDS cut all the vacuum to the wastegate in order to protect the engine. That's why you cannot just block the EGR valve on a 602.'

That would men the wastegate is in open position so that no sufficient pressure can build up? Speaking of which, I only unplugged the EGR valve and the car was felt faster. Apparently the turbo never worked so there could be no difference (but I can feel kick it in at approx. 1900 RMP) or no boost was cut no matter that EGR valve was disconnected.

'When the engine is idling, the wastegate and the EGR valve should be closed, and the flap wide opened. '

Flap is open. Now I see the wastegate is a different object to that EGR valve I unplugged. Forgive me for not knowing - where can it be located on the turbo?

'The EDS unit stores error codes : plugging and unplugging various component can leave you without turbo boost until you erase the stored fault.'

I had code 11, had it reset. Now it's code 1 - everything OK. I don't think I would be left with unoperational turbo though - the memory only stores codes. Or so I think. One way or the other - even with valve unplugged I had turbo operational.

[Jassper]

Hello David,

'Or at least include that info in your post. I assume you have a 1990-1993 300D 2.5 Turbo though.'

You are right. 1991 year. I have the model in my description though.

'2) You cannot simply disconnect the EGR on the 90-up engines. The EDS will know you killed it, and will prevent boost from building by keeping the wastegate open.'

The interesting thing is having the valve disconnected the car felt more responsive.

'5) You need to test your car from 0-60mph with a stopwatch on flat road. It should be about 11-12 seconds. If not, you're down on power, and probably need to either reconnect the EGR, or disable it correctly as mentioned in item #2 above.'

I already reconnected the EGR. As a matter of fact I can do the test today, just for the fun of it. Both with EGR valve disconnected and connected. Will post in a few hours.

[gsxr]

Originally posted by Jassper
Hello David,

You are right. 1991 year. I have the model in my description though.


The interesting thing is having the valve disconnected the car felt more responsive.


I already reconnected the EGR. As a matter of fact I can do the test today, just for the fun of it. Both with EGR valve disconnected and connected. Will post in a few hours.

I saw you mentioned OM602, but the reason the year is important is that there was a non-computerized OM602 used in 1987 on the 190D-T. Then the 90-91 engines are a little different than 92-93, with no ALDA safety.

It's strange that it ran better with the EGR disabled, most people find that power drops drastically (no boost) since the computer never closes the wastegate. I kind of like the idea of replacing the turbo (and possibly the intake) with the non-computerized components from an older, or Euro, model. That takes all the junk out of the equation entirely. A forum member did exactly that on a different car. I'll look forward to hearing your test results!

[Jassper]

Hello David (and everyone else).

Aww my! When I get an idea I am impossible. Just like a child I cannot wait till I do it. So in less than an hour I am back with the results.

Right. The car is a 124 300D 2.5 Turbo (250TD original European description). 4 speed automatic transmission with 125.000 miles on it. Semi synthetic Castrol 10W-40 oil and half a tank of diesel (approx. 35 litres). The ambient temp. 62 Fahrenheit (17 Celsius). All accessories were switched off - t.m. radio and airblower/ A/C.

Because it is evening here the lights were on. I also did this test with lights off. I did 4 tests for each setting, starting from a complete stand-still till the speed of 60 mph with the lever in D all the time. It should be reminded that the auto transmission itself took about 1 or even 1.5 seconds to decide to find out what I wanted from it. The values are an average of 4 runs for each combination. The transmission changed gear at approx. 4500 RPM. I must say I didn't push the engine to its limits I think I could have done harder and better (but then again I plan on keeping this car for some time to come). The fuel filter element hasn't been changed in the past 2 years. Engine operating temperature approx. 85 degrees.

Here are the result 0-60 mph:

EGR connected, lights on: 14.6 seconds
EGR connected, lights off: 14.0 seconds

EGR disconnected, lights on: 14.0 seconds
EGR disconnected, lights off: 12.9 seconds

I read the codes afterwards, still #1 - no fault.

[Denrac]

Hi Jassper

From the shop CD, the main function of the flap in combination with the wastegate is to modulate the pressure in front of the inlet valve to match a reference pressure stored in the EDS unit for different sets of engine speed, coolant temperature, quantity of injected fuel and intake air temperature. Doing so is supposed to lower particle emission under part load conditions and achieve optimum engine operation in respect of performance, NOx, HC and particle emission..

The EDS also modulates the opening of the EGR valve from the same set of variables (speed, temperature, fuel).

It seems logical to think that the closing of the flap will recirculate more exhaust gaz : I suppose that this interaction is taken into account by the EDS.

Diagnostic data shows that both pressure modulation and EGR progress in the same direction. Exhaust gaz recirculation starts when engine temperature is over 60 C, engine speed over idle and quantity of injected fuel low. Control flap is progressively closed under the same conditions when engine speed increases to 2000 rpm. EGR is reduced as engine load and speed rise, and it's logical to think that under increased load condition the intake flap is wide open to benefit from the turbo boost.

EGR valve and wastegate are 2 separate items : wastegate is located on the turbo and is not easily seen from the top of the engine. On your car (1991), you have 3 vacuum transducers (round thing with 3 hoses and a double electrical connector) : one goes the EGR valve, another to the intake flap and the third should lead you to the wastegate vacuum control. From that control, a rod goes into the turbo housing to operate the waste valve. If you look attentively, you'll see the control rod moving backward when the intake flap closes.

On that turbo (Garrett TB-025 or T-025), when the waste valve is open (it is open when no vacuum is applied to the control), most of the exhaust gaz is bypassed from the turbine to the exhaust pipe.

The MAF sensor measures the quantity of fresh air admitted in the engine. It is located in the front right corner of the engine bay and it is part of the air filter housing. EDS does not use the data of that unit to control pressure and EGR : its main purpose seems for monitoring the operation of the EGR valve and of the intake flap. The intake air temperature sensor is located in the MAF unit (1990-91).

Unoperational turbo : maybe the 1991 and 1992 EDS units are different : all I can say is that on my car, the transducer that controls the flap and the wastegate (in 1992, you just have 1 transducer for both) was bad and would generate error code 15 after a few blocks ride. Until that error code was erased, no electrical signal was sent by the EDS to the transducer and no vacuum was available to close the wastegate.