'73 450se warm running issue - Page 3 - Mercedes-Benz Forum

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post #21 of 55 (permalink) Old 09-30-2013, 11:22 AM Thread Starter
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Date registered: Sep 2012
Vehicle: 1973 450 SE (minor stuff to bring it up to par)
Location: Portage, Mi
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Thanks for that info. I did unplug the temp sensor after it was already running bad and it seemed to make it worse but it is so erratic that it is hard to say. I will try moving the throttle switch with the ignition on and I will try it unplugged.
I have not pulled the trigger points as the way it is situated I would need to pull the distributor to get it out. Will try that after the TPS.

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post #22 of 55 (permalink) Old 09-30-2013, 02:35 PM Thread Starter
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Ok...... so I tried to check the ohms on the TPS. I could get a reading from the harness but never did get anything from the TPS itself. I tried every combination to get a reading. However.... with the ignition on I do hear the clicks. I also loosened the nuts and tried to get a reading based on several videos saying move it to get a reading. I did not get one. BUT when I started it up it sounded fine. I started to drive and it died. Started back up and died again. I unplugged the TPS and it drove ok then the same ole thing started in. The miss. I got back home loosened up the TPS and put it pretty much back where it was before and it wouldn't start. I pumped the gas and it started and idle real low. I put it in gear and it died. Does any of this help sort it out at all?

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post #23 of 55 (permalink) Old 09-30-2013, 07:38 PM Thread Starter
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Ok.... so I let it set for a while and when I started it the idle was real low and barley running. Put it in gear and it stalled. I unplugged the TPS and started it up. It was again idling low then I reved it up and it sort of picked up and then idled smoother. It is obvious that my messing with the TPS caused a problem. However.... is this an indication the TPS is bad? Or is that it just needs to be set correctly?
Also as I mentioned I unplugged the TPS and although it ran ok my missing problem still showed up when normal operating temp of 175 to 180 was reached.

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post #24 of 55 (permalink) Old 10-01-2013, 09:34 AM
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Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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I know you have replaced wires, but if it misses when hot, in my mind it is likely an electrical issue since insulation is less effective at higher temps. I had a similar issue once on a non MB vehicle. I broke a plug wire when changing plugs and replaced it with a new one. Car ran great cold, but would barely run when hot. Opened the hood at night, and the new plug wire was arcing all over the engine. Apparently a bad batch of plug wires.

Have you looked for any arcing at night in the dark when the car is hot?
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post #25 of 55 (permalink) Old 10-01-2013, 11:57 AM Thread Starter
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No I have not... I will look tonight.
Soooo... I had changed the ignition points and set it with a feeler gage. I was picking up a few things today and noticed a dwell meter on the shelf. I picked it up. (i had ordered a digital multi meter with dwell on ebay but they sent me one that had no dwell) So I checked the specs and it should be 30-35. It checked 24. It held steady on the number too. I adjusted it and now it is at 34. I don't know if this can cause my problem or not, I will drive it later to see what difference it makes.
Temp sensor will be here tomorrow.
Any thoughts on the TPS based on the what I said a couple posts back?

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post #26 of 55 (permalink) Old 10-01-2013, 12:33 PM
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I personally do not think the TPS is your issue. The TPS has a series of slip contacts that incrementally increase/decrease the resistance in the TPS switch so the analog control unit knows what the throttle position is. It also has a fuel cutout feature that stops fuel to the injectors when RPM is between 1500 and 900 RPM under lift throttle conditions. If the TPS is misadjusted, the most common result is engine surge at idle (The TPS intermittently shuts off fuel until RPM drops and then starts fuel again. I don't see how the TPS would cause a miss.

I think a miss has to be spark, not fuel or air. The other potential issue maybe faulty grounds (either between the fuel injector grounds and the engine or the engine to chassis), but my money would still be on spark.
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post #27 of 55 (permalink) Old 10-01-2013, 06:08 PM Thread Starter
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Drove if around and it seemed to run a bit better, although cold it runs fine anyway other than the higher idle. It seemed to idle better. However..... Once warmed up the same old problem came back. The other temp sensor will be here tomorrow.
One other thing I did today, I cut off the hot wire at the battery and put a new clamp on it. Lots of corrosion in the strands. Cleared as much out as I could. The old clamp was broke and couldn't be tightend up, though it was pretty solid. There was a ton of green stuff on the head when I got the car. Swapped out the battery but didn't change the clamp. Figured it would be good to make sure that was right.
Bottom line is.... Cold = solid running. Warmed up = rough running and missing throughout the driving range.

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post #28 of 55 (permalink) Old 10-02-2013, 06:42 PM Thread Starter
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Ok... so the saga continues.. I change the other temp sensor this afternoon. That is the big one that the blue connector goes on. Started it up (first time today) and I heard a funny noise. So I shut it off. I popped the hood and didn't see coolant anywhere. I thought the noise may be it spraying out around the sensor. But nope all dry. I left the hood up and started it up again. Funny noise was the fan in the very front, outside the radiator. First time I ever heard that before. I was concerned while driving off but at a stop sign about 3 miles away I could no longer hear it. So I drove for the farthest distance I have ever driven without an issue, maybe 15 + miles. Ran great. So good in fact that I figured if I made it the last 3 miles home without an issue I would call it fixed. 300 yards from the house it started acting up. SOB!!!! Parked it for a while started up ran like crap. Let it set for a few hours longer and it started up and seemed to idle ok but then got a little off kilter and then I could smell fuel. Shut it down for the night. Now.... when this warm up issue occurs... it doesn't just go away after the car sets a few hours or even 5 hours. I will leave it be over night and maybe around 7:30 am will drive it. Then it is fine until it warms up.
Could a ballist resistor be a culprit?
By the way.... started it up in the dark tonight and could see no spark anywhere.
I'm at my wits end. The local shop keeps saying to run more Lucas thru it.

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Last edited by fishigan; 10-02-2013 at 06:44 PM.
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post #29 of 55 (permalink) Old 10-02-2013, 08:42 PM
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Do you get the 20 clicks as the throttle is moved ,ignition on.?
Ignition: the ignition module or coil could be defective at higher temperatures.
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post #30 of 55 (permalink) Old 10-03-2013, 07:40 AM Thread Starter
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With ignition on I got the clicks. New coil, same problem. Haven't touch the ignition switch though.

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