1970 280SL Starts cold, runs 4 minutes then stalls won't restart till cooled

[CoreyJ]

We have a 1970 280SL that has been in storage for nearly 20 years. Upon the first start up it will start cold fine, run fine for about 4 minutes then just stall like you turned off the ignition it is that sudden - and it will not re-start for about 30 minutes allowing it to cool. Leading up to this we drained and cleaned out the fuel tank, had the injectors professionally cleaned & tested, fuel filter replaced. Ignition wise new points and rotor. Seems to be as the temperature increases causes the failure. Could this be a WRD issue. I appreciate your thoughts of what to pursue. Thanks!

[Pawel66]

I am not a qualified mechanic, so be careful with my advise, but I have been seeing similar issues many times and experienced some of them as well. With these symptoms (no hot start), especially after long time of no work, it may happen that fuel lines are still clogged, even though you drained the tank.

The simple test is to run the fuel pump for a couple of minutes to let it warm up, witch it off, detach the return fuel hose from its fitting in the tank, put it in some empty canister and run the fuel pump again to see if you get 0.7-1.0liter in 15 seconds. If you get 0.5 - 0.6 liter of fuel - engine is not getting enough fuel.

If the fuel flow is low, you have: filter in the fuel tank, screen in the inlet of the fuel pump and then the main filter to check. Sometimes intermediate filter is mounted between tank and fuel pump as well (I would do it if it is not). Sometimes the fuel pump is clogged. The return line may be clogged as well (may need to be blown with air - when detached form tank and with a piece of cloth around the end you insert the air gun).

There are a lot of posts on hot start issues.

Yes, the WRD may need fixing, but maybe it is good to see if the basics are there ok.

[Vander]

I agree with Pawel66, my initial thought was fuel system clog. Did you clean the inlet screen inside of the fuel pump?

[mrfatboy]

Another possibility is the engine is stalling out during the “lean dip” of the WRD warm up cycle. It could just be getting too lean at that time.   This happens around the 4-5 minute mark. 

Once the WRD is in the “lean dip” and it won’t start it makes sense you have to wait for the engine to cool down to start again.

The easy fix is to add some shims underneath the WRD.

A quick test would be to loosen the 2 screws attaching the WRD to the FIP simulating thicker shims. Just turn the screws slightly at a time and try starting car. The WRD shim thickness can be anywhere between 0 - 1.3mm in total.

You can check out the FIPi simulator in the tech manual and see what I am talking about with the lean dip.

[Cees Klumper]

But what does not add up in this scenario is the suddenness, as reported, of the stall. The idle 'dip' during the warm-up cycle happens gradually, not instantly. Also, even with that dip, applying some throttle should allow the engine to continue. If it gets enough gas for the cold start and initial 4 minutes, when the mixture is extra-rich and so requires more fuel than when the engine is warm, it does not make sense to me that it will then suddenly just stop, if it's a fuel issue. So I would not rule out an ignition problem, like a defective coil or condenser - or a poor wire connection that interrupts as it heats up - something along those lines. Perhaps it could be a combination, like the fuel pump actually cutting out once it gets warm enough (rather than slowing its delivery rate).

[mrfatboy]

I’m only offering a possible solution. The PO’s symptoms are classic excessive “lean dip” issues. Clogged fuel flow that has been suggested is another.

I am assuming the PO is also starting the car and let warm up and idle. Not trying to apply throttle and keep going.

More detailed info will lead us to the solution👍

[Tom in seattle]

I’m offering an experience, not a solution:  I acquired a very infrequently run SL.  When acquired mine would start, then died like yours.  It would get a bit warm in the motor and then die and my wife had to salvage me in the neighborhood.  I went through all the ignition issues to no avail.  Finally I took the fuel filter off and the paper filter came out in 100 pieces.  It obviously had not been replaced in many years.  My prognosis was that the filter fragments would fall away when there was no fuel flow and would allow fuel to flow.  But when fuel was active bits would clog the outflow.  But you have replaced the filter.  I suggest blowing out all fuel lines into and out of the fuel and injection pump.  There is also a filter in the inlet to the fuel pump.  I have added another filter between the tank and fuel pump. 

[ejboyd5]

Swap in a known good ignition coil.

[Tyler S]

Diagnose first. Find out what is missing when the problem occurs. Check for spark at a plug wire. If present, Then move on to fuel.
If the car runs with your foot on the accelerator then check for proper linkage adjustment.. Followed up by the idle enrichment setting.
Search the forum for “split linkage test” to find out if the engine is going lean. This will point you in the right direction.

[Shvegel]

Speaking as a lifelong mechanic (40 years) when something just stops like the key was turned off I always think ignition.  Fuel loss usually causes sputtering.  check for spark when it dies by removing the center wire of the distributor and placing it 1/8" to 1/4" from some metal on the engine,  let go of the wire and crank the engine while watching the wire.  You should see a healthy blue spark between the wire and the metal.

What you are experiencing seems to be heat related. Your car should be fitted with a factory electronic ignition.  If so the green wire from the distributor should snake under the battery rather than go directly to the ignition coil.  The electronic box would be my first suspect(if fitted) followed by the ignition coil. 

We may be able to remove some steps if you post a picture of the distributor,  Inside the distributor under the distributor cap, the top of the ignition coil and the ballast resistor at the base of the hood prop rod which should have a blue strap.  That way we can determine if it has been messed with and if so was it messed with properly? Sometime people bypass the electronic ignition improperly and it causes other issues to be introduced.  For example the original distributor is not designed to take the full power of switching the coil so if bypassing the ignition box you need to change the distributor as well.

[ja17]

Hook up a pressure gauge and monitor the fuel pressure until the problem occurs. If the fuel pressure drops below 11 psi. then you probably have a fuel delivery problem (clog). Most likely you will have dirt and rust packed up against the filter screen in the electric fuel pump (intake fitting).  After the stalled engine sits for a period, the dirt and debris settle away from the clogged screen and the engine will start again and then repeat the cycle until it clogs again!

[MikeSimon]

I have exactly the same problem which was the reason my car has been "parked' for 25 years. Nobody back then, no Mercedes mechanic, not even Ted Gottfried did offer a solution. So I did not do anything and let the car sit. Finally some suggestions pointed towards the in-tank fuel pump and several issues with that, e.g.: clogged return line due to sediments in the bottom of the tank.
I am working ever so slowly now to get the car back into running mode. It will involve a thorough cleaning of the fuel conveying system.

[Iconic]

CoreyJ,
Lots of info from people with experience.
I'm voting for the clogged return fuel line. (and Joe, isn't it true, that if you have a clogged return fuel line, it will show 15 psi throughout the entire system up until that clog? CoreyJ, if you don't know, Joe (Ja17) is an expert.)
So, all it takes to prove it is not ignition is to check your spark when the car won't re-start. If it sparks move to fuel.
Fuel is DANGEROUS.
Disconnect the return to tank line, turn on fuel pump, measure flow.
If not up to spec, start looking for a clog. Yes, I've heard of clogs in several parts of the fuel system, but the one that is talked about most frequently for cars that have been sitting is the clogged fuel return to tank line (as mentioned already by others here). That's what happened to me and ever since I've cleaned out that line, I've been enjoying the drive.
Good luck,
Mark
P.S. CoreyJ, you really should join as a full member. The value is incredible and if you are having this kind of issue, you will probably need all the information that is available for full members.

[mdsalemi]

Hi Corey,

1. Take Iconic's advice. Join as a full member unless you plan on getting rid of the car shortly.
2. When I had my car restored 20 years ago, the first thing EVERY restorer asked me was, "It hasn't been sitting too long, has it?" There's a reason why they asked this question. Sitting is bad. Very bad. Very, very bad. It's not good. Get it?
3. So you've got good advice on ruling out a couple of things to solve the immediate problem of "fuel or electrical"? It's a good thing to try and narrow it down, but the advise on the fuel system here is solid. I'll go one further: you'll need to renovate your fuel system.

Starting at the back, you have the fuel tank. Your tank is now half a century old, and half that time it's been sitting. In a nice climate controlled facility, with a special preservation fluid, full, in the tank right? Yeah I thought so.  . If you don't need to replace the tank now, you will soon enough. Inside the fuel tank is this thing called "the flower pot". (Registered trademark of another expert here, Dan Caron a/k/a Dr. Benz). I think you can pull the sender unit from the trunk/boot, and use one of those fiber optic cameras. Sometimes a lot of junk collects in the pot and makes the return fuel flow a problem. By now you've got the idea that fuel RETURN is as important as fuel flow.

Then you have the fuel supply pump at the back, along with a couple of hoses and lines. All has to be checked. The two rubber lines? Replace them. Don't bother to "check them" just order new ones, unless they were a recent change. Be careful to check the electrical connections to the fuel pump. Proper voltage is critical. If you are reading, say, 9V at the pump supply, you've got a wiring issue. (Ask me why I know...)

Do check the hard lines for blockages. Blow them out with compressed air.

We do have an expert here, BaronYoungman, on the fuel supply pumps. If your pump isn't making the requisite flow and pressure, it needs rebuilding or replacement. Replacement may be a shocker; Bob can help you with a rebuild. Find him, contact him.

Hard lines up to the FI pump. You've already been told to check for blockages, etc. You already changed the fuel filter. Assuming you drained the old fuel and added new of course.

I've had plenty of fuel issues. Pump issues. Tank issues, Supply line issues, ignition issues.

Welcome to the club. The GOOD news is once some of these issues are sorted out, your car will last a long time. Mine was restored 20 years ago. After suffering a few issues with the aforementioned, it's been great ever since.

One more thing: you are in Saco, Maine. You think you are in the middle of nowhere when it comes to Pagodas, but one of the foremost experts is in the Portland area, Gernold Nisius of SL Tech in Arundel. There's also a forum member here, Keith Morgan that lives not far...so don't hesitate to make a few new friends.

[CoreyJ]

In the past couple weeks we have made some updates - we did purchase a rebuilt fuel pump from Bob at BaronYoungman, changed the fuel filter again. Same situation - it starts and runs OK, then after 4 or 5 minutes it just dies (like it's too lean) - then it won't re-start until it has sat for a while. Again, this car sat for many years, we had the fuel injectors professionally serviced, changed fuel filters, fuel pump. Tomorrow we will see what we are getting out of the return line. Possibly still clogged somewhere.

[FGN59]

I once had a car (an Audi for what it’s worth) that did just that. It was the (electronic) ignition which stopped working when it got hot. Once I had it changed, everything worked fine.

[JN]

Did you replace the fuel injector thermostat?


JN

[ja17]

Did you check the screen in the fuel tank drain ? 

[CoreyJ]

Latest info - we tried to blow through the return line back to the tank. We could blow air through  the return lines right up to the fuel tank. Putting an air gun right up to the gas tank return tube, we can't blow any air back through the tank. We even took a small rod and pushed it in as far as we could and still can't blow any air through. Should we be able to blow air through into the tank? Thanks!

[Iconic]

Yes, the return is for fuel to flow back into the tank. If you can't push air through it, then the fuel system can't push fuel through it either. Without the fuel circulating through the whole system, cooling the whole system, the FIP get's vapor-locked after some time running.... vapor-lock, might or might not be the correct term. 
You found the issue !!!
But, if you have a clog there, other tubes in the fuel tank for venting air and for fuel flow might have issues.
Was your tank ever "re-sealed"? If people don't understand the specifics of this tank, sometimes they seal the wrong things.

Oh, and by the way, just because you could hear air through the return line, it still might have restrictions in it and you really need to measure the flow of liquid through the line .... or just replace it.

[Shvegel]

I am a big fan of new gas tanks.  There is quite a bit in the tank, most tank restorers mess it up unless they have specific knowledge and your wildly expensive mechanical fuel injection system hates tiny particles of rust.  New tanks are available from Dansk and are not stupidly expensive.

[CoreyJ]

That was it! Clogged venting in the tank, the fuel could not circulate. We took a piece of wound cable from an old window regulator (like a speedo cable but slightly smaller diameter), put it in a drill and kept working into the fuel tank vent tube. After a few tries it suddenly pushed further easier and whoose! Reconnected the the return hose, started the engine and now runs fine! One test we did to confirm a blockage was the issue was running an extra length of the return hose right up into the fuel fill neck. Sure enough the engine started and ran for 20 minutes no problem so we knew we got it. We were thinking new tank but gave this last try with the flexible cable and it worked clearing the venting. We are now installing an additional in-line before the transfer pump for additional protection of sediment. Nice to end with a fix! Thanks for everyone's suggestions.

[Worldflier]

Congratulations! 👏

[stickandrudderman]

My advice is to still fit a new tank. Clearly there are issues inside yours and fuel systems don't like contamination of any sort.
Just last month we had a regular customer's car in with exactly the same issue. We had had the tank refurbished just four years ago and still we now had a blocked return line. We've now fitted a new tank and expect the fuel system to be reliable for the next 30 years or so.

[CoreyJ]

Agreed, long term fix will be a new fuel tank. At least we know that was the problem.