DIY-disabling EGR and Air recirculation! - PeachParts Mercedes-Benz Forum

rwthomas1 · #1 12-16-2002, 12:50 AM

Okay, heres what I did tonight: Remove cover from Air Recirculation Valve. Its that round thing integrated into the compressor outlet housing on the turbo. I have no idea why they would want to remove some of the compressed intake air and feed it back to the turbo inlet but that is what this thing does. Simply disconnecting or plugging the vacuum line would disable this unit. I went a step further. There is a spring that holds this valve normally closed until vacuum is used to pull it open and dump some boost. I dropped a 5/16" nut in the bottom of the valve cover where the spring seats and reassembled the valve. I did this to provide a big increase in spring pressure holding the valve closed. Neither vacuum or a high-boost condition will open it now. Next I removed the EGR valve. Again you could simply disconnect the vacuum line or plug it and the EGR wouldn't function. I discovered that my EGR valve didn't seal completely. (yes, I put a lip-lock on the thing and blew hard..... Stop laughing please!) I made a block-off plate out of 1/16" aluminium simply by placing the EGR gasket down and tracing it. Drill two holes for the mounting bolts, cut it out with tinsnips and you are in business. Install gasket, blocking plate and then the EGR valve and the hard part is done. For good measure I traced the vacuum lines for both valves to the fender. I then "cauterized" those ends with a soldering iron to seal them and plugged 'em back in where they belong. I haven't driven the car yet as it was late but I will update after tomorrow. Even a trained eye would have great difficulty seeing that anything was wrong. Hope this helps. RT

rwthomas1 · #2 12-16-2002, 11:54 AM

Update: Drove car today to see if there is any difference. There seems to be but it is very slight. It seems the EGR and Air Rec. only work at "part throttle" conditions, subject to load and controlled by throttle position, vacuum, etc. The boost seems to hit harder and sooner. Particularly noticeable on the highway when accelerating from a steady state cruise. It takes much less longer for the boost to come on which I atttribute to not having the delay of all the valves closing, etc. The engine sounds different too. I am guessing it is running with more manifold pressure now at steady cruise speeds as the Air Rec. is not functioning. Certainly feels more responsive.

In addition to the EGR/Air mods last night I also cleaned out the banjo fitting and pressure line. (It wasn't clogged but had a bit of soot in it) I also "prepped" the ALDA by removing the anti-tampering cap. I adjusted the ALDA ccw 1/4 turn after my inital test drive. It appears to make quite a difference just off idle and before the boost builds. The car is no longer a slug until the boost hits when crossing intersections. I highly recommend the above mods and tweaking the ALDA. Hope this helps someone, RT

adamb · #3 12-16-2002, 06:38 PM

Your explanation and scientific-like explanation was awesome! I did the same stuff to my car, but got rid of the plumbing to these nefarious devices and ran a vacuum hose from the egr to the recirc valve just because.
I am presently in the market for a used ALDA, as I tinkered with mine so much that i broke off the nut screw from the internal diaphram rendering it unuseable. I have it taken off the car now and it runs great with no smoke and great acceleration.
Have fun,Adam Bush

rwthomas1 · #4 12-16-2002, 10:06 PM

Glad you liked it. I try to be as descriptive as possible in the hopes it will help someone out. I sure "owe" enough people on this 'board already so I try to give a little back when I can. Too bad about your ALDA. I leaned on mine again today, so I am at 1/2turn ccw from stock. I really like the results with it there so that is where it will stay. RT

#5 12-17-2002, 01:01 PM

On my 83 300D I adjusted my ALDA screw out (CCW) until it bottomed then turned it in 1/2 turn (CW). It made a huge difference in off idle throttle response and even leaves a little cloud of black smoke if you floor it off a light

.

I have the EGR and wastegate disabled too.

Mileage has not changed, still right around a combined 24-25 MPG with around town/highway driving.

gsxr · #6 12-17-2002, 03:45 PM

I did the same thing a while ago. Works great. Photos of the ALDA internal workings are here:
http://www.w124performance.com/images/OM603_injection/

Photos of the smog junk (solenoids & vac lines) removed are here, along with before & after photos showing how the EGR dumps sooty sludge into your intake:
http://www.w124performance.com/images/OM603_intake/

FYI, the ALDA is the same on all 1982-1987 Mercedes turbo engines. You should be able to find a used one in a Pick-n-Pull from an older W123 chassis. I picked up two spares, one was bad, one is good. Test by applying pressure with a Mity-Vac, it should hold pressure with a steady needle above 10psi, and only leak down very slowly below 10psi. If the shaft seal is bad it leaks as fast as you can pump it. And if one of the brass aneroid capsules is ruptured, you're screwed and need another ALDA!

Regards,

smartin · #7 01-30-2003, 11:25 AM

gsxr - If another ALDA (from yard) is installed with tamperproof cap still on, (and holds vac) will this unit "match" injection pump? Are caps put on not only to prevent tampering, but also because adjusting screw with "throw off" internal works of the pump, that cannot be brought back to original unless pump is removed and re-set in shop. This question arises because the 2 I found in yard still had caps on. Is this screw adjustment some sort of "mecahnics secret". Lastly will adjustment of screw vastly affect mpg, to where original mpg cannot be achieved - unless pump is re-set in shop?

gsxr · #8 01-30-2003, 12:01 PM

smartin,

All good questions, which I don't have definitive answers to. From what I understand, yes each ALDA may be slightly different and technically should be calibrated to the IP on a Bosch test bench. The shop that calibrated my OM603 pump said the ALDA stays sealed, and the correct adjustment is internally (which we should't really mess with, as we don't have Bosch calibration machines!

)

If you rip of the top canister, yes that will affect the overall fuel delivery curve of the IP. Yes it will drastically affect MPG if you adjust it too rich. However you should be able to simply reverse the adjustment (turn it back) if your MPG plummets, and return to your original MPG.

What I don't know is if the ALDA adjustment can simulate a proper internal calibration. Messing with the ALDA will affect the whole fuel delivery curve - from idle to redline. If you richen it (CCW), the IP will provide proportionally more fuel at all RPM's - I think. Most folks adjust it to boost low RPM power, where most cars are dogs off the line. However this MAY provide too MUCH fuel at higher RPM's or boost levels, hurting MPG. I'd really like to learn more about this myself but information is scarce on Bosch IP calibration procedures. My 84 300D has decent power but poor MPG, and the ALDA was adjusted by a mechanic before I bought it. I'd love to have the IP recalibrated but the R&R procedure is a nightmare on the OM617.95x (compared to the OM603), and it would cost a minimum of $200 (up to ~$800) for a calibration or rebuild... and I don't care about this car THAT much! I want to sell it and replace with a 201 or 124 in the next year or two...

smartin · #9 01-31-2003, 12:44 AM

gsxr - Thanks for the reply! My mpg is really bad - worse than my Volvo. Maybe you saw earlier post. I REALLY need to get better mpg, this is my daily driver. What do you get on your 617 (You said it was'nt that good) Cab you really get good off the line power AND good mpg? Thanks again.

gsxr · #10 01-31-2003, 12:58 AM

smartin,

I assume you have a 123.133 (300D), right? Well, good power AND good MPG is the holy grail that is rarely attainable. Mine gets about 24mpg with mostly freeway driving. It has never exceeded 24mpg. It doesn't get much worse than 22mpg though. If you live in CA, expect 10% less (mine got 19-22 when I lived there, jumped to 22-24 with 49-state fuel.) I just got the front end totally rebuilt - replaced EVERY steering & suspension component, and had it aligned. I am very curious how that will affect MPG as others here claim alignment can really screw up MPG. It will take a few weeks before I can tell though.

Now, most cars like ours get 24-26mpg, which is very typical. The BEST ones can get 28-32mpg but believe me, they are rare, and if you ever get upper 20's you're doing awesome. There have been extensive threads on MPG on the forum, do some searches and see what turns up. Some folks have tried EVERYTHING to no avail. The only items left for mine are the alignment (done), timing chain stretch (need to check), and injection pump calibration (too expensive). I've ruled out everything else already. What does yours get? Also, are you 100% sure your odometer isn't slipping? This has fooled some into thinking they get bad MPG! I've tested mine, it's OK.

For the record, if you want an MB diesel with great MPG, get a 190D with a 5-speed. These can get 36-44mpg depending on which engine it has (Euro 2.0, 2.2, or 2.5). I had a 1984 190D and it got a little over 40mpg on the freeway - awesome!

Regards,

ConnClark · #11 04-06-2006, 07:28 PM

The function of the Air Recirculation Valve(ARV) is to get/keep the trap oxidizer/cat up to temp. Disabling this without disabling you trap ox/cat first may result in a plugged up trap ox/cat .

When open the ARV runs air back through the compressor heating it up thus raising intake charge temps and thus increasing EGTs. Since recompressing this air takes energy, it increases the load on the turbine thus creating more back pressure increasing EGT's further.

rwthomas1 · #12 04-06-2006, 09:45 PM

Quote:

Originally Posted by ConnClark

The function of the Air Recirculation Valve(ARV) is to get/keep the trap oxidizer/cat up to temp. Disabling this without disabling you trap ox/cat first may result in a plugged up trap ox/cat .

When open the ARV runs air back through the compressor heating it up thus raising intake charge temps and thus increasing EGTs. Since recompressing this air takes energy, it increases the load on the turbine thus creating more back pressure increasing EGT's further.

Allow me to say, politely, no, you are wrong. I have an original Kalifornia 84 300D and it does not nor did it ever have a trap oxidizer. The ARV vents from the post compressor side to the turbo inlet. This in effect is the same as dumping the manifold pressure the the atmosphere. When the ARV is open the compressor isn't compressing anything, its free wheeling. The ARV control line is connected (or was) to the same control for the EGR. It opens when the EGR is functioning, which makes sense. RT

#13 04-07-2006, 01:08 AM

Quote:

Originally Posted by rwthomas1

The ARV control line is connected (or was) to the same control for the EGR. It opens when the EGR is functioning, which makes sense. RT

It's the same problem they are having with current EGR diesels. They want more gas flow but the intake pressure is almost on par with the exhaust (turbo high efficiency/technology). The ARV lowers intake pressure to a point much lower than the exhaust manifold pressure. This allows greater flow of exhaust gasses into the intake than before (non-ARV). Higher flow results in less NOx. Current EGR diesels use VNT turbos (increase exhaust backpressure) and intake flaps (lower intake pressure) to achieve this. A notable exception to this is the Cummins ISX, they use a VNT turbo and a very restrictive venturi tube after the intercooler.

It's not to warm up the Trap, not to spin up the turbo, not a blow-off valve, and not to heat the air.

ConnClark · #14 04-07-2006, 11:37 AM

Quote:

Originally Posted by ForcedInduction

It's the same problem they are having with current EGR diesels. They want more gas flow but the intake pressure is almost on par with the exhaust (turbo high efficiency/technology). The ARV lowers intake pressure to a point much lower than the exhaust manifold pressure. This allows greater flow of exhaust gasses into the intake than before (non-ARV). Higher flow results in less NOx. Current EGR diesels use VNT turbos (increase exhaust backpressure) and intake flaps (lower intake pressure) to achieve this. A notable exception to this is the Cummins ISX, they use a VNT turbo and a very restrictive venturi tube after the intercooler.

It's not to warm up the Trap, not to spin up the turbo, not a blow-off valve, and not to heat the air.

What you said makes sense to a point. Do they really need to lower the intake pressure when the exhaust manifold typically has twice the pressure of the intake?

The mercedes shop manual states that the ARV has something to do with the ox trap operation.
"Air Recirculation Valve
(refer also to EDS Operation No. 07.1-010)
In order to create more favorable combustion
conditions for the trap oxidizer, the air
recirculation valve is continuously opened or
closed in accordance with the performance
characteristic map."

Of course this wouldn't explain the existance on of an ARV on an 84 Cali Car. So mabey we are both right.

Jeremy5848 · #15 08-20-2006, 12:49 AM

All of the threads that have pictures of the ARV are old enough that the links no longer work. Here's a picture of my 1985 300D California engine. Have I correctly found the ARV? It matches the description in the threads but I like pictures.

The vacuum line to the EGR valve has a BB in it, compliments of the previous owner; should I do the same thing to the ARV? All of the vacuum lines are still in their factory configuration, save the BB in the EGR line.