450 SL in Denmark
- Dr-DJet
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how is ignition timing and dwell at 1500 and 3000 rpm? And what vacuum does your MPS see at idle?
Viele Schraubergrüße - best regards, Dr-DJet Volker
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- Pcircle
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Here are the readings
Idle 1500 rpm 3000 rpm
Dwell 30 dgr. 30 dgr. 30 dgr.
Timing 1 5 ATDC
Timing 2 15 dgr. BTDC 20 dgr. BTDC
Vacuum 1 12,5 inHg (315 mmHg)
Vacuum 2 16 inHg (410 mmHg)
Timing advance is right on spec and so is dwell at idle, 1500 rpm and 300 rpm.
I have used two different vacuum gauges, and they show different results - see also pictures. I tend to rely mostly on the hand pump version, which is also the one showing the lowest reading. That reading is too low.
With a warm engine I also performed a smoke test to see if there are any obvious vacuum leaks. That did not show anything. No leaks. These tests tell me that my problem is probably not injection or ignition related, but rather mechanically related. Could be many things, such as piston rings, wrong valve clearence, etc. But it points towards a compression test and even better a leak-down test, correct?
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Best, Peter
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- Dr-DJet
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that vacuum level is too low in idle - even if both pressure gauges are scrap. I use a class 1.0 100mm pressure gauge -1 to 0 Bar.
Either you have a vacuum leakage or piston rings or valves are the issue. You should have >500 mBar at idle. Your vacuum level also makes the MPS signal load to ECU where there is no load.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107
Workshops D-Jetronic 20.9.(ER)
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- Dr-DJet
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Viele Schraubergrüße - best regards, Dr-DJet Volker
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- Pcircle
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Best, Peter
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- Pcircle
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Here are the test results of a compression test. I've enclosed a photo as well, but will table it out here:
Cyl. 1 ==> 10 bar and spark plug looks fine
Cyl. 2 ==> 10 bar but spark plug looks a bit fouled (rich)
Cyl. 3 ==> 11 bar and spark plugs looks fine
Cyl. 4 ==> 10 bar and spark plug looks fine
Cyl. 5 ==> 10,5 bar but spark plug looks a bit fouled (rich)
Cyl. 6 ==> 11 bar and spark plug looks fine
Cyl. 7 ==> 11 bar and spark plug looks fine
Cyl. 8 ==> 10,5 bar but spark plug looks a bit fouled (rich)
It cannot be faulty trigger points as the fouled spark plugs do not sit in the correct groups.
I'm surprised about the compression levels as this is supposed to be a low-compression US-spec engine. Is this normal?
Is the next logic place to look the injectors themselves? I've already made a pressure test and the fuel pressure only drops 0.2 bar after 20 minutes and that is OK. Could it still be that these injectors are stuck open?
What now?
Best, Peter
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- Dr-DJet
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looking at spark plugs, your injectors in 2, 5, 8 are from 3 different groups. So it cannot be ECU. Pressure loss test was done. That should exclude valve shafts and oil rings as well. Have you done a cleaning test of injectors and have you verified ground connections of injectors?
Viele Schraubergrüße - best regards, Dr-DJet Volker
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- Pcircle
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The wiring harness is new, but I will check the grounding connections to be on the safe side. I will also try to find someone in DK who can clean the injectors professionally.
Have you any experience with the solonoid in the injectors going bad, so that the injector does not close fast enough? - meaning that it continues to spray even if the signal is no longer there?
Best, Peter
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- Dr-DJet
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well injectors can clog and normally that blocks them. But sometimes needle is fixed in a way that it cannot close and leaks permanently.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107
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- Dr-DJet
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Viele Schraubergrüße - best regards, Dr-DJet Volker
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Workshops D-Jetronic 20.9.(ER)
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- Pcircle
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With the compression test done and showing encouraging results I couldn't leave the uncertainty about manifold vacuum. I have purchased a proper vacuum gauge with glycerin and it now shows 560 mBar at hot idle. That gives me peace of mind. The engine still runs rich and somewhat uneven, so next up are the injectors.
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Best, Peter
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- Pcircle
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Well, I have now changed the three injectors associated with the three fouled spark plugs and also changed all the spark plugs with new NGK BP5ES. The engine is however still not behaving and is sputtering/misfiring in idle and at low speeds/load and it has problems getting up to speed. It smells of fuel in idle and when I changed the oil today the oil also smelled of fuel.
I have pulled the ECU out and measured according to Norbert's (I believe) check list. Please see enclosed table (measured at ambient and warm temperatures). To me it looks as if the values are within spec. although I am a bit doubtful about the coolant temp. sensor value when the engine is warm.
Since changing the spark plugs I have driven 100-125 km. and I also pulled them out today and they look even. There are no apparent signs of rich running, but perhaps that would not show itself in just 100-125 km. of driving? I don't know myself.
The idle mixture potentiometer is turn all the way counter-clock wise (lean) and it seems still to run rich.
I am really beginning to doubt if I will ever get this car to run right, but I am also not known to be a quitter. I need all the help I can get.
Best, Peter
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- nordfisch
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I agree there are no signs of rich running to be seen on the plugs. More than 100 km should be more than sufficient to show abnormalities.
All your readings seem to be o.k. for me, too...I've read all through the thread now and thought about the symptoms.
I don't remember having read about the MPS having been confirmed to be correctly adjusted.
Has this been done?
Regards
Norbert
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- Pcircle
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The MPS could be the culprit. However, I acquired it from Volker and I am sure he was diligent in his testing before selling it. It holds vacuum.
Before I took the car for another run today I performed a smoke test to see (again) if there are any false air leaks. That was not the case. I then took it for a run and from cold and up to operating temperature it runs and pulls like a champ. When it reaches operating temperature and when accelerating moderately until ca. 2000 rpm it stumbles and jerks. Once the rpm is between 2-3000 or if I accelerate hard, it goes away. Not completely, but much better. At cruising speed (70-90) there is practically no issue. At highway speed (130) it drives and accelerates without problems.
When I got home and with a really warm engine I performed yet a smoke test and suddenly I saw smoke coming from below and behind the throttle housing. At first I thought it came from the TPS sensor shaft, but after having carefully looked again I am pretty certain that it comes from the intake manifold behind the throttle housing. False air would certainly "confuse" the MAP sensor into believing that the engine is under load, thus sending a signal to the EDC to increase opening times, right?
Could I perhaps be on to something?
Best, Peter
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- nordfisch
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if I had known you have a MPS from Volker, I wouldn't have considered it could be faulty.
Yes, you are correct: ECU injects more fuel when the absolute pressure in the manifold rises.
A vacuum-leak lets the pressure rise...
Regards
Norbert
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- Dr-DJet
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sorry to hear that you are still in search of your problems and sorry for late reply due to holidays. Any false air leakage causes troubles. The lower engine load the more it will be. MPS will report wrong load to ECU and that will enrich fuel mixture.
Viele Schraubergrüße - best regards, Dr-DJet Volker
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Workshops D-Jetronic 20.9.(ER)
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- Pcircle
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From the picture cylinder 1 and 4 and maybe 7 do look as if something has been going on there. There are no apparent signs of leaks in the intake gaskets, but the rubber grommets between the lower and upper manifold are very hard. I have not inspected them in detail yet.
Best, Peter
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- Dr-DJet
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Viele Schraubergrüße - best regards, Dr-DJet Volker
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did you check the ignition timing following the instruction given by DB and noticed by Volker before?
It is really important especially in the lower engine rev's range.
I don't remember you reported having checked this in full.
Regards
Norbert
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- B.M.G.
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I fully agree with Norbert. Ignition timing and its change over rpm and vacuum is something you should check well. I once had a 350 SLC of a friend and his igntion distributor timing would create the problems you describe now.
More than 600 mBar vacuum in idle is a good value.
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