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Old 05-12-2011, 07:06 PM
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Question 350SL Starts and Dies - Starts and Dies ...

My ‘72 350SL has been stored all winter - full tank w/stabilizer. After checking things out and refreshing the battery, I started the car with assistance of charger just to give the battery a break. (I always unplug the coil, crank the starter – 5 seconds max – as many times as it takes to get oil pressure) As usual, it started right up and ran very smoothly. After running until it reached normal operating temp for a few minutes, I decided to remove the charger cables. At this point the engine died like someone had shot it.
I then attempted to restart the car. Nothing doing. All systems were checked, fuses all OK. Even though the car cranked well, no sign of the ingition firing. NADA. Thinking that it may have flooded, I let it set for half a day (warm temps) before I attempted to start it again. Tried again. No joy. Pushed it back into garage.

Fast forward two weeks. Today I rechecked everything again (wiring, fuses, etc.). Put the key in, rotated to "on", heard the fuel pump start, build pressure, then stop, and twisted the key to start it.
The good news is that it tried to start. The bad news is that the engine stumbled and tried to stay running for maybe 10 seconds then died. I tried several restarts with these results: The engine fired, attempted to run, but after a second or so, it died. Kinda like it was getting barely enough gas to fire up but then starved, and died.
One clue to the problem (maybe) is that, in the past, during the restart sequence, as the key is advanced to the position for starting the car, the fuel pump starts up, runs for a few seconds, and when fuel line pressure is up, it shuts off. I would then turn the key to engage the starter. Taking a pause in writing this, I just went out to try to start the car again. This time the fuel pump did not run as the key was advanced to the start position. I know it came on when I first attempted to start it today. This time it didn’t…
Checked the fuse is still OK. Maybe I have a bad relay?? Fuel pump relay.
(Here's one more symptom left over from last year. Last year, the car ran fine for about two weeks after getting it out of hibernation. One warm day, I took it out for a run of about 20 miles to a car show, parked it, came back several hours later, started it but it had to crank *much* longer than normal before starting. (normal was a second or two of cranking). Once started, it ran ragged for about 30 seconds before settling down. And that started a new pattern for the balance of the summer. Anytime the car was attempted to be started, it took a lot more cranking to start which was followed by a short period of uneven running. Lacking time and money and having too many other projects, my SL was pretty much ignored for the until this year.)
I dug into the '72 350SL Service Manual to study the wiring diagram and researched the MB forums. The wiring diagram was a big help. It identified the fuel pump relay as being on the #1 tag for the wiring harness. I got the kick panel off and there they were, seven relays that look identical. The left are numbered with harness tags 1,3,5 and the rights are 2,4,6,8.

Questions:

1. Is there a trick to removing these relays? (picture an upside down 69 year "young" guy with a piece of titanium in his back) I assumed that with a firm grip and a strong pull I could pull the %#&!! relay right out. NOT!. So before I resort to major mechanical assistance and break something, is there a clip or some other retainer I am not seeing??

2. In my manual, on page 54.1 (wiring diagram), I find a relay shown on the diagram and list as item 21, "Changeover relay air-conditioning optional". It appears to be the same relay as item 38, fuel pump relay. I would like to pull that relay (I have factory air in my 350SL) and substitute it in the fuel pump relay slot. Problem is that I cannot find item 21 anywhere else in the wiring diagrams or physically in the car. Is this an optical illusion to trick me?

2. I could find no reference to an OVP (over voltage protection) device in a '72 W107. Am I missing something? The OVP was deemed the culprit on several forum threads as causing the same symptoms as mine.

3. Does anybody have suggestions as to where I should go next in troubleshooting this problem? The 350SL service manual , as many of you know, doesn’t have a trouble shooting diagram.

4. While upside down in the car, I took pictures of my fuse panel and the relays above it. I will pass these along if they would be of help to anyone in considering possible solutions....or for any other reason.

Please excuse the long post. Thanks for the read.

Keppie


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Old 05-12-2011, 08:58 PM
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Quote:
Originally Posted by Keppie View Post

3. Does anybody have suggestions as to where I should go next in troubleshooting this problem? The 350SL service manual , as many of you know, doesn’t have a trouble shooting diagram.
Try using the link below to Download the file. Password is 107SL. Just use the regular download and enter the activation code they ask for. Don't sign up for anything!

http://d01.megashares.com/dl/35d3b25/D-Jetronic%20EFI%20Manual.pdf

Regarding removing relays, you just pull them out. I think I had to pry mine a bit.

You can jumper two pins so that fuel pump relay is bypassed. This will keep pump running - The relay is just a safety in case there is a broken fuel line, so jumping is fine while trouble shooting.

I attached a second trouble shooting pdf to this post:
72 350 SL Fuel pump problem

Graham
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85 300D,72 350SL, 98 E320, Outback 2.5
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Old 05-13-2011, 02:11 AM
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Thanks for the info, Graham. I had no problem downloading the troubleshooting sheets. When I followed the link to Megashares for the other item, I used the password you provided and "got in". I was able to "see" the item to be downloaded but every attempt I made to download the document by clicking on "normal" download had no effect. Consequently, I was not able to download this item.

From the info provided by you (the relays pull out) and the troubleshooting list will allow me to do some additional tests and checks. I will report back to the forum with results.

Many thanks, again!
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Old 05-13-2011, 07:55 AM
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Thanks Graham the links were helpful
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Old 05-13-2011, 11:50 AM
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Quote:
Originally Posted by Keppie View Post
Thanks for the info, Graham. I had no problem downloading the troubleshooting sheets. When I followed the link to Megashares for the other item, I used the password you provided and "got in". I was able to "see" the item to be downloaded but every attempt I made to download the document by clicking on "normal" download had no effect. Consequently, I was not able to download this item.

From the info provided by you (the relays pull out) and the troubleshooting list will allow me to do some additional tests and checks. I will report back to the forum with results.

Many thanks, again!
Hmm - Megashares should work, although sometimes site is busy. There is one extra step where you need to enter an activation code. I just tried it and it worked fine.

But, if you have a Google/Gmail account, you could get the file here:

Try this (Google Docs):
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0BwXNC-MZyHGVMjIyNTNkZjgtMzNlZC00ZDBmLTliZDMtM2E0NzQwMmFmNjFl&hl=en&authkey=CMKmlfQK
I will leave it up there unless for some reason I have to remove it.
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85 300D,72 350SL, 98 E320, Outback 2.5
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Old 05-13-2011, 09:50 PM
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Got it running

Graham,
First, thanks for putting that document on Google docs. I have it and it is going to be a real help!
Second, I got the 'lil beauty running. I managed to pry out (after 40 years of being unmolested, this bugger really made me sweat!!) the relay in the upper left position in the left relay bracket. This is the fuel pump relay marked as 38 on the wiring diagram. I jumpered pins 30 and 87 after checking that 12V was on pin 30 when the key was in the "on" position. I heard the fuel pump come on and stay on. Turned the key to start. It started then died. I did this a few more times before I did a "no-no" on a FI engine: I held the throttle open to maybe the 25% open position and cranked again. this time it started and stayed running. After running a few minutes, I released the throttle and the RPMs dropped to an idle but did not die. YEEEESSSS! Took the car for a short spin an all seemed to be relatively normal.

There are other issues, but at least I can drive the car. Next issue to deal with is the excessive cranking required to start the car after it has been running for awhile.

Should I open a new thread on this one or try to continue with this thread? My gut says open a new thread. What say?

Graham, thanks again! You are a real treasure to this forum.

Keppie
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Old 05-13-2011, 10:53 PM
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Originally Posted by Keppie View Post

There are other issues, but at least I can drive the car. Next issue to deal with is the excessive cranking required to start the car after it has been running for awhile.

Should I open a new thread on this one or try to continue with this thread? My gut says open a new thread. What say?

Graham, thanks again! You are a real treasure to this forum.

Keppie
I think this threads title is OK.

From what you described, try adjusting the idle screw so that you have about 1100rpm after a cold start. That is about what it should be. After engine warms up, this should drop to about 6-700rpm. If you have it too low when cold, then it drops so low it won't keep running when warm.

The idle speed is very much influenced by the Aux Air Valve. Make sure it is not sticking.

Re difficulty starting when warm. It is usually because of low flow through the injectors when gas is hot. This causes a very lean mixture. (I have O2 sensor and wideband AFR gauge on my car and you can see this happen). Full tank helps keep fuel cooler.

Otherwise, check fuel pressure and bump it up a bit to say 34 psig to reduce gas vaporization through injectors. After that, you may have to adjust the MPS, but that will need an exhaust analyzer to set %CO. By the way, before I overcame the hot start problem, I would pump a bit and if it fired at all, held the pedal all the way down. It would slowly build revs.

Good Luck.
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Old 07-24-2011, 04:30 PM
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72 350sl 107 starts then stops

Satisfied all inputs to EFI control board ok. Fuel pump relay operates as it should. Pump runs as it should at all times. Main EFI relay checks good and operates right.
Engine runs up smooth at atart but after 3-4 seconds just quits. I can keep it running if I pump pedal vigorously, but RPM drops anyway and starts missing and backfiring. Replaced the following so far:
ignition points and original coil with new brealerless Pertronics 1885 and 40kv coil. Replaced Vacuum Advance dashpot assy. Air filter, oil and oil filter. Sparkplugs, rotor and cap.
Serviced Trigger points and connector plug, which ohmed out to spec all the way to the control board, as did Air and Air pressure sensors, water temp sensor, and Throttle shaft switch. Supplementary airways clear.
Drained fuel tank and purged fuel lines from injectors to fuel filter, no contamination seen. Replaced fuel filter with new one. Vacuum lines seem tight and quiet. Tried rotating dist. shaft to adjust timing in both directions, no help.
Coolant and all fluids look great. No fluid leaks.
Cleaned all grounding connections in engine and passenger compartment for EFI system. At this point I don't suspect fuel contamination or failure of EFI system.
Coil has 12v supply at all times it should.
Could priming and warm up system cause "starts, runs for a few seconds then shuts off like somebody flipped a switch ?" symptom ?
Priming relay feels like it is working. Pulled and reseated All relays, no help. Pulled and cleaned all fuse box fuses, no help. Are ther other systems I'm missing here ? Obviously there is but what ?
There is sometimes a relay-clicking noise comming from under the
dashboard where my left hand rests on the steering wheel. Don't know what that is.
I worked my way through most of the EFI troubleshooting link you provided to another genius like me but car still dies after a championship start up... Anything you can tell me will be ultra appreciated Mike
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Old 07-24-2011, 08:41 PM
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Originally Posted by uamazeme View Post
I worked my way through most of the EFI troubleshooting link you provided to another genius like me but car still dies after a championship start up... Anything you can tell me will be ultra appreciated Mike
It does sound like you initially get gas into intake from the cold start valve. I have never tried this, but perhaps try spraying in some starter fluid and see if that keeps engine running. If it does, then for some reason injectors are not getting gas or perhaps are not getting signal to fire.

Usual suspects are fuel pump, fuel pump relay, injectors, etc. Could be ground from ecu - easy enough to check.

Maybe try jumpering the fuel pump relay. That way, pump will stay on when you turn on ignition switch (it normally cuts off after a few seconds until ECU gets signal from trigger points to say engine is rotating) Then try again. If still no start, check fuel pressure in rail.

Good luck with it.
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Old 07-24-2011, 10:08 PM
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Thank You Graham

Ok. I think I need to go back and double check everything. I'll check fuel pressure at the rail. and jumper the fuel pump relay. I'll let you know what I find. Mike

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