72 280SE 4.5 idling issues - PeachParts Mercedes-Benz Forum

bullitt · #1 11-20-2006, 06:00 PM

Hi, when i start my 4.5 when warm it doesn't hold oil pressure and the engine quits right away. I flushed the radiator and added fresh coolent. Still runs warm and won't idle after starting. When running, the engine temp is 175. When shut-off and sitting it reaches 200. Please help. Thanks.

nhdoc · #2 11-21-2006, 07:30 AM

Quote:

Originally Posted by bullitt

Hi, when i start my 4.5 when warm it doesn't hold oil pressure and the engine quits right away. I flushed the radiator and added fresh coolent. Still runs warm and won't idle after starting. When running, the engine temp is 175. When shut-off and sitting it reaches 200. Please help. Thanks.

It's normal for latent heat to cause the temp to rise after shutdown. As long as it cools back to 175 once you restart I don't think you have a problem with the cooling system. I'd be most concerned about the statement you made about the oil pressure not holding...that could lead to a catastrophic failure if the gauge is accurate. When you say it doesn't hold pressure do you mean it drops to 0? That would be bad.

bullitt · #3 11-21-2006, 12:52 PM

Hi Marty, thanks for the response. What i meant by not holding oil pressure is that when it stalls the guage drops to zero. In park, the engine normally idles at 15. But the oil gage dropping goes with the territory when the engine stalls, right? I think my inexperience is showing. I'm thinking i may have water in the tank or something causing the the engine to choke upon start-up. This same thing happened about 8 months ago, went away, and now is back again. I can't idle long enough to get it in gear. It's a pain in the rear when trying to get out of a spot in the grocery store parking lot. When i let the engine cool to about 175 it starts fine.

nhdoc · #4 11-21-2006, 02:43 PM

Quote:

Originally Posted by bullitt

Hi Marty, thanks for the response. What i meant by not holding oil pressure is that when it stalls the guage drops to zero. In park, the engine normally idles at 15. But the oil gage dropping goes with the territory when the engine stalls, right? I think my inexperience is showing. I'm thinking i may have water in the tank or something causing the the engine to choke upon start-up. This same thing happened about 8 months ago, went away, and now is back again. I can't idle long enough to get it in gear. It's a pain in the rear when trying to get out of a spot in the grocery store parking lot. When i let the engine cool to about 175 it starts fine.

OK, that's clearer, the oil pressure dropping to 0 when the engine stalls is normal too and idling at 15 is OK, a little low but depending on the oil your use it could be normal. Your car is fuel injected, electronically controlled and therefore the warm start idle condition could be related to a bad temp sensor or improper idle misture adjustment or even throttle position switch adjustment or it could be as simple as a vacuum leak. How does it run from cold as it warms up and how does it run when it isn't stalling?

Jengasan · #5 11-22-2006, 05:06 AM

Quote:

Originally Posted by bullitt

Hi, when i start my 4.5 when warm it doesn't hold oil pressure and the engine quits right away. I flushed the radiator and added fresh coolent. Still runs warm and won't idle after starting. When running, the engine temp is 175. When shut-off and sitting it reaches 200. Please help. Thanks.

Hi Bullitt

Have you checked your ignition timing, and does the car ever run 'normally' ? Any chance you could post more info re the symptoms, i.e. take us through a normal days driving including the bad bits. nhdoc is right about the heat soak, my 3.5 temp gauge always goes up a while after shut down, but is your car actually overheating when driving etc ? (175 is fine) If not your stalling problem could be a few things but rather than adjust everything on the car (been there) we could maybe narrow it down with more detail.

cheers

Tomguy · #6 11-22-2006, 09:51 AM

It doesn't say floored! It says "On a warmed up or hot engine, however, accelerate at the beginning of the starting procedure." After the next paragraph it says "After the start, briefly speed up the engine and then ease off the accelerator to prevent the engine from racing"

I have ALWAYS started my 4.5 - stone cold or close to overheating - with NO pressure on the throttle at all. And it always starts every time. Your warm idle mix is too probably too lean. Turn the ECU screw about 2 clicks to the right, see if it helps.

Tomguy · #7 11-22-2006, 05:30 PM

Ellington: I always believed those instructions pertain more to the carbed verisons than the D-Jet vehicles... but perhaps not? I'm unsure if they simply didnt change that part of the manual from the 280S to the 450SEL (as pertaining to 116). I always assumed the instructions in the 108 manual I have that suggest doing so were for the 6-cyl engine (It is for the 280SE, 280SE 4.5, and 280SEL 4.5).

bullitt · #8 11-23-2006, 06:12 PM

Hey guys, thanks for all your support and happy turkey day. I will take you through a typical day of driving my 4.5 in San Francisco for clarity sake.

1. Start up from cold. Turns over on the first try (What i love about this car. Every time). I let it warm to at least 125 before driving. Driving engine temp hovers around 175.
2. I'll drive to the grocery store, or Costco, do my shopping, usually sits 20 to 30 min.
3. Upon leaving i start the car, engine temp at about 200 after sitting. Turns over right away on the first try, but then starts to sputter out. If i'm in a parking space I literally have to throw it in reverse to get it in gear before the engine quits (Dangerous in a parking lot with people and other cars. Especially the day before thankgiving;-) Once in drive i have to rigorously pump the accelerator to keep it from stalling. A little putt putt here and there, then the engine engages and shifts and i'm on my way.
4. If car does stall it sometimes will not turn over again right away. I have to let it sit for a bit. To let the engine temp fall again.

Could it be bad (watery) gas? I only use 91 and with oil prices the way they have been i honeslty look for the cheapest gas.

This is a phantom problem. Happened the same time about a year ago but went away. Chalked it up to bad gas then. Drove the car to Monterey and back throughout the year, no starting issues. Now the same problem again.

Hope i've helped explain this issue better.

Tomguy · #9 11-24-2006, 06:26 AM

I was going to suggest the opposite. Hot running issues may mean your octane is too low, and detonating too early. Even before increasing my compression, my 4.5 would ping on less-than-91, and would ping on 92 on acceleration up hills.

It does sound like vapor-lock, but more of the type expected in racecars than the 4.5 (where heat under the hood boils the fuel in the lines, resulting in no fuel going to the engine). Sounds like it may be time to check your fuel pressure while running and observe if it plummets while accelerating and/or once you turn off the key - you may need a new pressure regulator.

Jengasan · #10 11-24-2006, 10:52 AM

.hello chaps

I'm with tomguy on this one. For my tuppence worth (that's two cents worth to you Americans) I'd add that vapour locking, or a form there of, is documented for D Jet engines, particularly large ones. The problem can actually cause the injectors to foul because the latent heat of the engine vaporises the fuel as tomguy describes, Bosch injectors apparently do not like this and some cars have even been modified with cooling systems that remain on for a while after the engine has been stopped. I gleaned that from a most interesting tome on Bosch Fuel Injection System. However bullitt's problem sounds just like the lack of fuel on a hot start. I'd be checking fuel delivery and the regulator as tomguy suggests - you may even get away with adjusting the regulator but if the pump is weak you'll be better off with a new one. If the system is in good condition regarding the pump and regulator the system should re pressurise almost instantaneously even if the fuel in the pipes has vaporised.

One thing to try in way of a clue would be, on a hot start, turn the key to on but not start, this should energise the pump and pressurise the system, give it say 3 seconds then crank the starter and see what happens....just a thought.

The fact that you had this before and then it 'went away' seems to be a common thread on these cars (from personal experience) but I see your logic regarding dirty gas, always worth giving it a check and looking at the filters / screen.

Hope you nail it soon