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Old 02-23-2018, 12:35 AM
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1984 Egr control rpm vr sensor help

Alright folk I have a question that hopefully someone might be able to shed some light on. Basically I have a om617 engine out of a 300sd california emission package that I have swapped into my 1984 Jeep Cj7.

The issue I am having is that I need to get a tachometer signal to my EGR control module so that I can retain the functionality of the EGR system. The reason I need this system operational is because I live in California and in order to get my jeep refereed it must have all the equipment present and working. As soon as it gets refereed I will be removing all of the EGR garbage but until then it has to work enough to pass the testing.

Alright here's where my problem comes in. I no longer have the mercedes transmission adapter plate or flywheel because I'm using a adapter plate from mercedes4x4.com to mate the 617 to my jeep automatic transmission. I have everything for the EGR control wired up and even have the vr sensor that goes to it but no way to use it in the way the factory intended.

What I'm try to determine is what the vr sensor was reading originally, was it the teeth on the ring gear? In that case will it read the teeth on my jeep ring gear and function correctly? I know there is a rpm sensor on the harmonic balancer as well for diagnostic purposes from what I understand and give a different signal from what is required for the EGR control. Is there a way to run a modified tach amp to give the correct reading. Or perhaps there may be a way for a product like the dakota digital tach to produce a signal that would be compatible.

I've been searching the forums for hours and can't seem to come up with any solution for my specific issue. Any help would be greatly appreciated as I'm at a loss and this is the only thing that's holding me back from getting my jeep refereed and being able to get it out on the road and enjoying it.
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Old 02-23-2018, 01:50 AM
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the vr sensor on the rear adapter plate is reading the ring gear teeth. as there is no BITE (built in test equipment) system in the EGR computer it shouldn't care if the teeth number is slightly off. as far as i know without an extremely special mercedes test set specifically for the om617 egr computer there is basically no way to know if it is working beyond the output to the egr/arv regulator vac solenoids. as the instrument cluster tach signal is pulled from the egr computer you may have some issues using your jeep ring gear for the sensor with the tach reading off but it depends on the number of teeth difference between the 617 and your ring gear.
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Old 02-23-2018, 02:38 AM
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Okay awesome this information is very helpful. I have already procured the tach pickup, amplifier, and associated wiring to run the pre 84 style tach haven't got my hand on a tachometer for the cluster yet so I'm not all that concerned about it being super accurate as long as it works enough for the EGR to function. Do you know if there is any test procedure for the EGR and ARV? I have checked the EGR for function using a vacuum pump and it passes that. I talked to a guy here locally that specializes in European cats and has been helpful in the past he said if I bring the rpms up to what would simulate cruising speed there should be vacuum present at the EGR valve bit that's about as much as he could tell me. With how limited the information is about this system and how to test it I'm wondering what exactly the smog referee will be able to do to test functionality of the system.
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Old 02-23-2018, 02:56 AM
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Alright so I was able to determine through an internet search that my jeep ring gear has 164 teeth. I was able to find one source that claims that the original mercedes ring gear had 140 teeth I'm not sure if anyone on here can verify that information.
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Old 02-24-2018, 11:34 AM
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is not the egr,only for starting a cold engine? If so can it be done manually? Like a choke on a old car to pass emissions.I thought the diesel motor were exempt.
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Old 02-24-2018, 12:31 PM
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Quote:
Originally Posted by oldsinner111 View Post
is not the egr,only for starting a cold engine? If so can it be done manually? Like a choke on a old car to pass emissions.I thought the diesel motor were exempt.
EGR is an acronym for Exhaust Gas Recirculation. It showed up on gas engines in the late 60s or early 70s and on diesels in the late 70s. The idea is to circulate some of the exhaust gas back into the intake stream to dilute the oxygen charge and reduce the temperature of combustion, thus lowering NOx production. Great idea on paper with quite a few operational issues, not the least of which is clogging up the intake manifold and eventually blocking off the EGR port so it doesn't do anything anyway.

It has nothing to do with starting, the valve opens with engine RPM and load to circulate larger volumes of exhaust gas at higher RPM and loads.
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  #7  
Old 02-24-2018, 01:44 PM
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Diesels pre 98 are smog exempt in California but if you convert a gas car to diesel in California it has to be ref'd to make sure all the requirements were met. As soon as thats done it gets a diesel title and is exempted from smog. I was on alldata and actually was able to find the test procedures for all of the EGR related emissions components. Hopefully this weekend I can get down to business a test the function of some of these components unfortunatley it looks like my transmission will be coming back out so I can figure out how to mount the VR speed sensor.
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Old 02-26-2018, 02:55 AM
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Why not just have the EGR valve permanently open for the purposes of the test then block it after?
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Old 02-26-2018, 03:30 AM
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Unfortunately the smog ref will require that the EGR is functioning correctly. I imagine he will pull up alldata as I did and go through the test procedure. Make sure it opens at 500+ rpms when the coolant temp is between 109 and 190. Got to love California but on the bright side when this is over I wont have to worry about smogging it ever again so I can get rid of the EGR and everything that is a vaccum consumer besides the fuel shut off which will tidy things up a bit.
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Old 02-26-2018, 10:43 PM
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Bugger. Can't rig up a remote control can you...
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1978 300D, 373,000km 617.912, 711.113 5 speed, 160cc superpump, HX30W turbo...not yet legal
1984 240TD>300TD 121,000 miles, *sold*
1977 250 parts car
1977 280> 300D - 500,000km...Daily

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  #11  
Old 02-26-2018, 10:56 PM
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Nope no funny business I did think that maybe I could use the vacuum modulator on the back of the injection pump to give vacuum to the EGR but he'd spot that in a heart beat. The smog ref in my area is actually a really nice guy I've talked to him several times on the phone throughout this process. However it's his job to make sure everything is legit and he's good at it so I will be going in with everything operational and a silent prayer that everything is done to his liking.
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