M116.982 original D-jet or MEGASQUIRT? - Page 2 - Mercedes-Benz Forum

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post #11 of 30 (permalink) Old 01-29-2012, 09:26 AM Thread Starter
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Date registered: Apr 2011
Vehicle: 1972 350 SLC PROJECT
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Originally Posted by GGR View Post
Did you replace the big filter after the pump with one of same size/flow characteristics?

Replace the small filter by a much bigger one. I had the same set-up as you have and the small filter got clogged in no time. Also try to see if the filter inside the tank is not clogged.

Measuring the pressure should be your first step though. Then flow test.

Working on 4 cylinders only would most likely be your trigger points. They are in the lower part of the ignition distributor. There are two sets and each controls a set of four injectors. Take them out and clean them well. Be careful not to damage them because they are delicate and very hard to find.

ECUs are quite durable, I wouldn't incriminate it at first. Most delicate parts in the system are the trigger points, then the MAP sensor, then the fuel pump.

The D-jet fuel pumps have a security system and they by-pass the circuit if pressure goes over 45 psi. You want to retain that security as rubber hoses (that should all be new) are the weak point of the system and countless D-jet cars died burning.
I had the tank cleaned about a month ago, including the inside tank filter...

My system has no filter before the pump yet... as my car was running on a Diesel engine, everything that was original was missing down there...

I also know the trigger points are the most delicate part of the system and that is why my first mantainance was in them... I cleaned and checked the hole thing and after all that, i did a light test and all 4 trigger points are working perfectly... That is why i blame the ECU...

When i bought this engine (i had to buy this original engine to the mechanic that pulled it off the car in the early 90') i had to search a lotof boxes to find this ECU... The ECU has the top missing so someone already opened if for a reason... If the ecu was in the car the hole time, unmolested... i wouldnt blame it but there´s a good chance this ECU was badly treated when it was off the car...

As you are saying, the first thing is to be sure the car is delivering the right ammount of fuel at the right preassure.. then try to find and fix all injection problems i have... Even if the ecu is broken, there´s a guy in here that fixes it... and if it cant be fixed, then there´s a good chance i end up going after megasquirt... That is why im interested in buying a pump that works in both cofigurations...

Damián!

PROJECT 1972 350 SLC
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post #12 of 30 (permalink) Old 01-29-2012, 09:32 AM
GGR
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2nd hand ECUs ar not that expensive. If you think this is your problem best would be to borrow one from a car thaat works and see if it makes a difference. They are aeasy to take in and out.

EFI Datsun/Nissan "Z" use a system similar to the D-jet ones and the pumps look the same. It may be easier for you to find one.
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post #13 of 30 (permalink) Old 01-30-2012, 08:12 PM
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Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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The other thing to consider is the grounds for the injectors. I had a similar issue with my 280SEL 4.5. The injectors were grounded in two groups of 4 and one of the grounds was bad. It was running poorly on 4 cylinders since the ungrounded injectors wouldn't fire.
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post #14 of 30 (permalink) Old 01-30-2012, 11:14 PM
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If you suspect the ECU maybe you could try to find a 4.5 one as a test unit-they are much more plentiful. I know the 3.5 will run on a 4.5 ECU but not sure of the long term issues. At least you would know if it is the ECU.
There are fuel rail kits available to build your own o-ring fuel rail for the Ford (and other O-ring) injectors. Eliminates many possible sources of fuel leaks.
I wound insure proper fuel pressure at the injectors. You could install a "T" in the fuel rail with a gauge or use the cold start injector line.

Tony
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post #15 of 30 (permalink) Old 01-31-2012, 04:13 AM Thread Starter
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Hey guys!! thanks for the feedback!!... I have some updates actually!!... Yesterday a friend ofmine borrowed me an afermarket generic preassure regulator, those that have the gauge on it, you know?...

Well... i went to my garage and decided to take off my original preassure regulator AND the other damper thing that nodoby knows its porpose...

I managed to install the generic one and set the preassure in about 2,2 to 2,5 bar and the car started... not great idle because he is still running in 4 cylinders but he managed to keep idling few minutes until he warmed up...

The preassure never dropped so i now can say that the fuel pump is not broken and it will be functional for a while longer

I´m a little concerned about the fact that i had to take off the original preassure regulator and the damper.... Not a big fan of loosing original parts but at least the car runs... Dont know if i´m gonna need the damper installed again or not... what do you think??

Now that the car starts i can try to make the other cylinders to work... I already know the problem is that the injectors donesnt recieve the pulse they suppose...

I´ve checked by common sence methods my trigger points over and over and i dont find a non working sign in them so i have to guess the problem is from the trigger points, to the ECU or the ECU, or from the ECU to the injectors connectors...

That is what i have to try to test when i get tomy garage... Any thougts guys!??

Damián!

PROJECT 1972 350 SLC
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post #16 of 30 (permalink) Old 01-31-2012, 04:16 AM Thread Starter
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I forgot to mention that unfortunatelly there is not a good chance of getting a spare ECU of whatever i might need to try from other car in here... You have to remember that this is a VERY POOR country that in the seventies and eighties, Uruguay was under Military government so even harder for people to get a sports mercedes benz!!! jeje

That is the main reason i try to fix everything without going to yards or whatever to find spare parts... I know there are not useful parts available unless i can use any part from a 4 door diesel mercedes... Taxis were that back then

Damián!

PROJECT 1972 350 SLC
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post #17 of 30 (permalink) Old 01-31-2012, 06:28 AM
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The damper is there to reduce fluid noise, I guess you could bypass it.

Your original fuel pressure regulator is adjustable. The more you screw the bolt on top, the more pressure. I would try to get it work and set it at 2 kg. This is the pressure you need. Don't try to adjust the engine with the wrong pressure as you will have the adjustments all off.
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post #18 of 30 (permalink) Old 01-31-2012, 06:46 AM Thread Starter
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I took the damper off je!! My guess was that the original pressure regulator or the damper were clogged... Having a new regulator to try made me take all possible clogged things off...

In fact I wasn't that wrong because this try made my car start again... So the best bet here is that the pressure regulator somehow got clogged few days ago...

I'll try to clean it up because it would be nice to e able to use the original parts I have.. Any ideas to clean it at home?

Damián!

PROJECT 1972 350 SLC
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post #19 of 30 (permalink) Old 01-31-2012, 07:14 AM
GGR
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Well, if your regulator got clogged, your injectors may not be much better which would explain why it's not firing on all of them. If you find crud in your regulator, it would be worth taking the rails out and see if the small filters on top of the injectors are not clogged also.
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post #20 of 30 (permalink) Old 01-31-2012, 09:35 AM Thread Starter
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Totally agree on that... I must check my injectors for signs of clogged mesh... Do you guys have some sort of way to clean injectors at home?

Damián!

PROJECT 1972 350 SLC
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