'80 300se start,stall,start,stall,start,stall - Page 6 - PeachParts Mercedes-Benz Forum

brewtoo · #76 08-01-2009, 10:41 PM

Perhaps someone mentioned this already...Is this a fuel pressure issue? The fuel pressure may be falling while the car sits and it may be taking a couple of tries to bring it back up.

You know, this fuel injection system is all about pressure. The injectors to not pulse (open electronically). They depend on pressure to force the fuel through them and they spray continously.

lorainfurniture · #77 08-02-2009, 12:58 PM

Correct me anybody if im wrong, but I think the test for fuel pressure is to cycle the ignition key a few times before cranking? I have tried that, with no help.

Bolemister, One thing I think you should keep in mind is that your MB is just under 200k, and mine is just under 100k. I know this doesnt sound very technical, but I would be hunting for an "age" related problem, not a "use" related problem.

I think a dry rotted, or corroded something would be the culprit.

Again, Im just guessing. What do you think?

brewtoo · #78 08-02-2009, 01:41 PM

Quote:

Originally Posted by lorainfurniture

Correct me anybody if im wrong, but I think the test for fuel pressure is to cycle the ignition key a few times before cranking? I have tried that, with no help.

But are you sure the fuel pump is actually running when you cycle the key?

bolomiester · #79 08-02-2009, 07:05 PM

Quote:

Originally Posted by lorainfurniture

Correct me anybody if im wrong, but I think the test for fuel pressure is to cycle the ignition key a few times before cranking? I have tried that, with no help.

Bolemister, One thing I think you should keep in mind is that your MB is just under 200k, and mine is just under 100k. I know this doesnt sound very technical, but I would be hunting for an "age" related problem, not a "use" related problem.

I think a dry rotted, or corroded something would be the culprit.

Again, Im just guessing. What do you think?

Lorainfurniture, I think you are on the right track with the age related therory. I bought this car in early March and it did not have the fault it does now. It started doing it about 2 weeks later. However, after replacing everything anyone could suggest it still does it. I'm not sorry I replaced all those parts. The car is in great shape, but I got it without records, so now I do have records, for this group anyway. I keep searching for dry rotted or corroded stuff and I fix anything I can find, but so far nothing has helped except making the EHA a little richer. It's been suggested that in doing that I'm just covering up the real problem and I think that's probably the case.

I'd like to pursue the fuel pressure leak-down therory next. What's a good procedure?

lorainfurniture · #80 08-03-2009, 09:42 AM

Quote:

Originally Posted by brewtoo

But are you sure the fuel pump is actually running when you cycle the key?

Usually you can hear the fuel pump cycle when you turn the key. The only real way to test is to ensure flow/volume by disconnecting a fuel line and measuring..

Im not sure as to this procedure, maybe one of the pros can chime in with this, otherwise, I will research it in one of my MB books and post back.

brewtoo · #81 08-03-2009, 11:04 AM

If you have a spare fuel pump relay you might try swapping it. I'm not sure if yours has a separate relay or if it is built into the MAS relay. The older cars had a separate relay.

I'm wondering if your relay is actually energizing the pump when you turn the key to on, or only when you crank the engine. Also, the system is built to keep the pressure up when the engine is off. If it's leaking down it will be hard to start.

Surely a search would reveal a lot of info about this.

lorainfurniture · #82 08-03-2009, 11:12 AM

Quote:

Originally Posted by brewtoo

If you have a spare fuel pump relay you might try swapping it. I'm not sure if yours has a separate relay or if it is built into the MAS relay. The older cars had a separate relay.

I'm wondering if your relay is actually energizing the pump when you turn the key to on, or only when you crank the engine. Also, the system is built to keep the pressure up when the engine is off. If it's leaking down it will be hard to start.

Surely a search would reveal a lot of info about this.

I believe the relay you are referring to is the black box next to the klima relay? I have an extra one of those, I will look in to that this evening.

fiat · #83 08-14-2009, 02:53 PM

Well what happen now? did you fix it? just want to bump up this thread...cheer

johnathan1 · #84 08-14-2009, 03:29 PM

Have you replaced the Fuel Pump Relay yet? I would also look into testing the injectors, and residual fuel pressure...also check for vacuum leaks. (Don't forget the injector seals too)

Do these cars use a coolant temp. sensor??

bolomiester · #85 08-16-2009, 02:06 AM

Still not fixed. And I think I may have flubbed my dub. I picked up a used computer, which worked fine but didn't solve the problem. So I turned the EHA adjustment another 1/4 turn CW. Which seemed to make it little better but did not make the start/stall/chug-chug behavior go away.

After I readjusted the EHA, I started to reset the duty cycle. When I hooked up my meter the KOEO reading was 70%. This is a California car, and the first time I set the duty cycle I got the correct 85% reading, so I must have installed a federal computer. I replaced it with the original but the KOEO reading is still 70% and I'm having a hard time reading the duty cycle. It doesn't seem to read accurately anymore. At the moment I have the mixture set be feel and by ear, and the mileage is down from 20 to 16.

Did I damage something by installing the federal computer in the California car?

BALDEAGLE1953 · #86 08-21-2009, 12:17 PM

Had the very same problem,changed the crankshaft sensor,o/k so far.

Quote:

Originally Posted by bolomiester

I finally got the coolant temp sensor replaced. The first 22mm socket I bought wouldn't fit because of interference by the valve cover. I was tempted to loose it enough to make room but since it doesn't leak, I decided to try finding a thinner wall socket first. I took it back to Sears and learned something I didn't know. Wall thickness, at least on Craftsman brand, is thinner on sockets for smaller drives. I swapped the 1/2" drive socket a bought the first time for a 3/8" drive and it fit!

I think the car runs slightly better, (it's hard to tell since the car runs and idles very good already), but the start/stall is still there. The first start of the day is 2 trys. First time it fires instantly, revs to about 1,000 rpms then drops straight to zero and stalls. Second time it fires right up, revs to about a 1,000 rpms, drops to about 300, goes chug-chug a for a second or 2, revs back up to about 800 rpms then settles down to a smooth idle. If I then turn it off, it will restart perfectly with no sign of the start/stall thing. If I then let it sit for awhile, say 15 minutes or more, it will do the same thing it does on the first start of the day, though sometimes a little worst, maybe 3 or 4 trys before it settles down. But, again, if I turn it off then restart it, it's perfect.

I've replaced a ton of parts, but so far the only thing that seems to have made it better is turning the EHA adjustment 1/2 turn CW and resetting the duty cycle to 50%.

It just seems so odd that once it goes through its start/stall/chug-chug thing, it will restart perfectly until it stands for 15 minutes or more. I'm scratching my head to know what to look at next.

BALDEAGLE1953 · #87 08-21-2009, 12:25 PM

My old 1990 300se developed the start stop syndrome,if i left it running for about 5 mins it would just cut out, no drop in revs. After 15 mins or so it would start but then after 5 mins cut out again. Fault was traced to a faulty crankshaft sensor. Replaced that.So far so good.

bolomiester · #88 08-25-2009, 06:44 PM

Quote:

Originally Posted by bolomiester

Still not fixed. And I think I may have flubbed my dub. I picked up a used computer, which worked fine but didn't solve the problem. So I turned the EHA adjustment another 1/4 turn CW. Which seemed to make it little better but did not make the start/stall/chug-chug behavior go away.

After I readjusted the EHA, I started to reset the duty cycle. When I hooked up my meter the KOEO reading was 70%. This is a California car, and the first time I set the duty cycle I got the correct 85% reading, so I must have installed a federal computer. I replaced it with the original but the KOEO reading is still 70% and I'm having a hard time reading the duty cycle. It doesn't seem to read accurately anymore. At the moment I have the mixture set be feel and by ear, and the mileage is down from 20 to 16.

Did I damage something by installing the federal computer in the California car?

I decided, at my local indie's suggestion, to replace the oxygen sensor. It didn't fix my start/stall/chug-chug/start/run problem, but it did allow me to set my duty cycle to 50%, and the engine is smoother and idles better. I filled it up this afternoon, hopefully my mileage will go back up to normal.

Chowbow · #89 08-26-2009, 01:21 AM

If you find out any info on fuel pressure testing, be sure to post some info. I'm going to look around too and talk to my Indy as well, see if he has some tools or a procedure to follow.

Ivanerrol · #90 08-26-2009, 03:35 AM

An often overlooked cuase for stalling.
Hall effect sensor on the back of the speedo. It can cause intemittant havoc.
It seems that once you take your foot off the throttle and you are slowing down, this sensor's signal tells the software in the EFI module to prepare for idle mode, without it the computer thinks you actually want the fuel supply to stop all together and as such, shuts down because that is what it thinks you want it to do. Something so small can cause so much grief .