D-Jetronic engine problems - Page 2 - PeachParts Mercedes-Benz Forum

GGR · #16 09-02-2009, 07:53 PM

Check if your cold start injector leaks. If not, disconnect the plug and do another testdrive. Or at idle with a warm engine, disconnect it and see if there's a variation in idling.

meltedpanda · #17 09-02-2009, 08:14 PM

thought Id post a picture of the gaskets, this is off a kjet, but may give you an idea of what you may be getting into

Graham · #18 09-02-2009, 09:27 PM

Quote:

Originally Posted by meltedpanda

thought Id post a picture of the gaskets, this is off a kjet, but may give you an idea of what you may be getting into

It's not something I really want to do.

But from what I can see, it's just a matter of clearing stuff off the top of the manifold - Injectors, sensor wires etc. Drain some antifreeze. Disconnect coolant hoses front and back. Remove the 16 or so bolts and then lift the top half off. R&R the rubber sleeves and the gaskets and out it all back together.

Sounds simple eh? What could go wrong? Well maybe a couple of stripped threads

Anyone with first hand experience? Someone said to allow a couple of days - What takes the time?

meltedpanda · #19 09-02-2009, 09:38 PM

that would be my greatest fear, stripped (or broken) bolts, rest seems pretty straight forward, particullary on a Djet

Graham · #20 09-04-2009, 12:19 AM

Just an update.

I have checked the following in trying to determine the cause of the rich running:

Sensors - all check out in accordance with the specs.
HT wires - all have same resistance and are quite new
Coil - Resistances are correct
One ballast resistor is cracked, but still reads 0.4ohms.
Distributor cap and rotor are new
Trigger points - removed and cleaned
Throttle switch - disassembled, cleaned and set so idle switch actuates properly when throttle is closed(may not have been)
Injectors were recently replaced with another used but cleaner set along with seals and pintle caps
Fuses are all new and fine.
Sooted plugs have been cleaned up and reinstalled
Vacuum connections checked - no obvious problems
Checked leak down of injectors/pressure return valve -with cold start clamped off - leakage was within specs
Checked fuel rail pressure using bourdon gauge as well as dash mounted gauge - within specs 28-31 psig.
Compression check showed all cylinders at 150psig.

What I did notice, was that the throttle body below the throttle plate and the inside of the intake manifold (that I could see) were both black and the bottom the manifold looked "wet".

I started car with vacuum gauge attached. It ran very roughly and read ZERO vacuum. When I pinched off the aux air valve outlet, car almost stalled. Surprising with enough leakage to read zero vacuum! I checked and port for tube that leads to distributor is plugged up. Had to quit my testing at that point.

So, I still don't know vacuum level. I also don't know what caused black deposits in intake that caused the vacuum port to plug up. Maybe wrong setting on throttle idle switch contributed? Maybe cold start valve opening when it shouldn't? (I have it clamped off at present). Was not able to blow out vacuum port - job #1 for the morning.

A friend kindly has loaned me an exhaust analyzer - But I need to get car running half decently before I use it!

Back at it after long weekend.

Tony H · #21 09-04-2009, 12:14 PM

Rich running can be caused by a ruptured or leaking cell in your pressure sensor. If the pressure sensor is faulty it will read less vacuum resulting in more fuel being injected. Here is a excellent article explaining the process.

http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm

Graham · #22 09-07-2009, 08:23 PM

Quote:

Originally Posted by Tony H

Rich running can be caused by a ruptured or leaking cell in your pressure sensor. If the pressure sensor is faulty it will read less vacuum resulting in more fuel being injected. Here is a excellent article explaining the process.

http://members.rennlist.com/pbanders/manifold_pressure_sensor.htm

Thanks Tony. I had not checked the MPS vacuum side recently, but just did and it holds pressure.

Latest:
I started car after clearing the plugged throttle body vacuum port. It started immediately even with the cold start valve pinched off. Vacuum at start was about 10"HG but it built gradually and eventually settled at about 17" with the engine running quite smoothly.

I noticed the vac gauge was wavering back and forth by about 0.5". I wanted to check the rubber connectors between the upper and lower sections of the intake manifold for leaks, so discharged some propane through a plastic tube down through the cavity around the outside of the throttle body. This caused the engine to slow down and run roughly. Vacuum had dropped to about 12" and was fluctuating by 2" or so. I even heard engine knock once or twice.

By now engine had warmed up and it would no longer run smoothly. I took it on road for short run and it was running very poorly, bucking and when I slowed, idle speed was low - 500 rpm or less. When I got home, idle was rough and I decided to call it a day!

Graham · #23 09-10-2009, 06:45 PM

An update:

Finally found the cause of the extremely poor/rough running.

As several suggested, the trigger points were the problem! BUT, not because of oil.

I pulled the distributor, and set up a test to check the points by attaching a spare distributor plug to a multimeter. I checked each set of points individually by slowly rotating the distributor shaft. Three sets opened for something just less than 180deg. But the other set stayed closed most of 360deg but jumped open briefly in two different places.

I did similar test on spare distributor and found that it depended on just how the trigger points were clamped in place with those two little screws. I had to mess around with them and even squeezed the piece that holds the points inwards slightly. I fixed both distributors so points operated properly.

With original installed, car ran well for a short run, but then reverted back to the rough running. I pulled the distributor again, and installed the spare set of trigger points. I checked them first. I now have about 30 miles on those and the car is still running fine.

I can now get back to the original problem, which is rich running especially after short stop when hot.

I checked vacuum and it is only 16" Hg. The AAV is leaking, but when I eliminated it by installing a needle valve which I gradually closed, the vacuum did not improve - I had to open the idle screw to avoid stalling the engine. I guess it just leaked more somewhere else. I checked hoses and connections using propane, but did not notice any change. I suspect it might be the manifold donuts that are leaking. (see separate post on this issue)

I checked CO and first time, when car was up to operating temp., but not hot, it was at 1.5%. After a long run with engine quite hot and aux fan coming on, the CO had increased to about 2.5-4%. I would have thought it would be lower. I could adjust for this, but think I need to track down vacuum leak first!

Graham · #24 09-12-2009, 10:05 AM

Once I adjusted the timing, I was able to get vacuum in 16-19.5 "HG range. So that does not seem to be my problem. CO still increases when engine is hot.

More likely it is a problem with the trigger points. See separate post under title Trigger Points on old D-jets

ctaylor738 · #25 09-12-2009, 04:25 PM

Did you change the game when you unplugged the vacuum port? Are the plugs still sooty? Your hot CO readings are about right, maybe even a little lean and I would expect the plugs to reflect that.

Your lean reading when "warm" could be the aux air valve not being fully closed. So when really hot it closes and the mixture richens up a bit.

Graham · #26 09-12-2009, 05:34 PM

Quote:

Originally Posted by ctaylor738

Did you change the game when you unplugged the vacuum port? Are the plugs still sooty? Your hot CO readings are about right, maybe even a little lean and I would expect the plugs to reflect that.

Your lean reading when "warm" could be the aux air valve not being fully closed. So when really hot it closes and the mixture richens up a bit.

Chuck - I have not pulled the plugs again. As mentioned in another post, the CO readings have been much higher on recent tests (4-6%). The car runs unevenly and it is more than likely the trigger points malfunctioning (they are not opening and closing for same duration when hot). I see soot coming out of exhaust.

My AAV does not usually close 100% - And you are right, when I am messing with car and it idles for a long time, the temperature creeps up, aux fan comes on and the valve is closed. This no doubt affects the CO readings. I need to get the valve to close earlier or replace it with a new or an electric valve. But that is probably not the main problem because it has been like that for some time.

Graham · #27 09-15-2009, 10:38 PM

With the spare trigger points installed, CO adjusted to minimum (but not quantified), timing set to 5degBTDC at idle with vac, car seems to be running quite well.

I have reasonable vacuum (about 16.5") at this amount of advance.

I pulled the plugs that are easiest to get at tonight. Here are some pics:

http://home.cogeco.ca/~mbz/SLplug2.jpg
http://home.cogeco.ca/~mbz/SLplug5.jpg
http://home.cogeco.ca/~mbz/SLplug6.jpg

These are same set of plugs as in post #1 (but I did clean the soot off before re-installing

Local shop has sophisticated exhaust measurement equipment - might have them check where I now am.

Tomguy · #28 09-16-2009, 07:48 AM

If you got it that good, leave well enough alone! I doubt you'll get it better adjusted. Remember, CO @ min is the leanest tolerable setting, and you'll get better MPG @ sacrifice of some power.

Graham · #29 09-16-2009, 08:23 AM

Quote:

Originally Posted by Tomguy

If you got it that good, leave well enough alone! I doubt you'll get it better adjusted. Remember, CO @ min is the leanest tolerable setting, and you'll get better MPG @ sacrifice of some power.

You are right!

But, I am interested to test it on pro equipment. I was surprised to find that a local shop in our semi-rural area has everything needed to do it. Even a dyno! Will cost me 1hr of labour and I may learn something.

I will just have them CHECK it first and at most adjust the ECU idle screw. Only touch the MPS if something shows up to be completely out of whack.

GGR · #30 09-16-2009, 08:28 AM

They look quite lean. You should check if your engine is running hotter than before. Too lean a mixture have engines run hot.

Also, I don't know the factory spec for the 4.5 but for the Djet 3.5 engine ignition advance at idle with or without vacuum should be 3° +/- 1° after TDC.