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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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Discussion Starter #1
I drove the 450sl I just got "roadworthy" (in my terms only), and drove to Pep Boys earlier today to get some Freeze12 (that they stopped carrying between this summer and now). On the way out, I had a heck of a time getting the car to start, but got it with a little light touch on the gas. Gassed up the tank to full (first time, and with premium) on the way home. No problem starting after getting gas.

Started fine (as usual) on way out. I drove my daughter in the front seat. That was a neat experience. I had my son in the front seat before, but he's not talking yet. It's different when you're sitting side-by-side driving with your daughter for the first time. It's totally different than being bus driver when she's in the back. She loved it. I loved it.

We met my wife and son at my mother-in-law's where the kids are staying for the night. Dropped off the kids, and got back in the car after a few minutes. The car was slightly uphill, and was REALLY tough to start. I tried over 10 times before lightly touching the gas to get it to start.

After the party tonight, it started right up (as usual).

So I think I have a warm-starting problem. I think I've seen others with this common problem, but I'm not sure if it was a D-Jet.

Is there a super-common D-Jet warm start problem that I should already know about? I will research (and search) tomorrow.

It's been a great week. Overall, the first date night has been a success... as long as I don't spend it all at the computer.

THANK YOU ALL FOR SUCH AWESOME HELP!
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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Come on, Mike.

Who cares if the SL started or not.

Question is........did you get laid?
 

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450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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Discussion Starter #3 (Edited)
Well, the car did start, after several tries. So all was good. All went well last night.

I forgot to mention that there's a bushing missing in the throttle linkage at the end of that spring loaded rod. I assume that's causing some extra play. So I'm wondering if my problem is due to my loose linkage or some D-jet part that I have yet to understand. Chances are good that I've got an extra D-Jet part, if that's what it is.




Sorry for typos. Can't see what I'm typing on my blackberry.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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There is no fuel accumulator on this system but the same rules for vapor lock do apply. If excess heat is allowed to get to the fuel lines vapor lock will occur and cause hard starting. Check all heat shielding is in place.
 

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450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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Discussion Starter #5
I don't believe I'm missing any heat sheilding, other than needing to replace the injector seals.

I found a nice thread on this Vapor lock in D-Jets, and some good info from MBGraham at: http://www.benzworld.org/forums/r-c107-sl-slc-class/1371416-sl-450-75-bad-hot-start.html

There's one other piece of information I forgot to provide. When I got gas (shortly after the first instance of the tough warm start) I could hardly believe the amount of pressure that blew out of the tank when I opened the gas cap. I even noticed what I think is varnished fuel on the edges of the gas cap (which may be much older).

Also, the weather was MUCH colder than usual. It was below freezing. So I don't think we've got a situation of winter fuel on a warm day, but the engine heat might be all that's needed.

VERY INTERESTING! THANK YOU RONCALLO for pointing me in the right direction to understand this issue.
 

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Premium Member
'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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This car doesn't need high test. Regular is what it should have. Avoid gas with ethanol. Ethanol boosts octane, but makes fuel more volatile.

This may be more than you want to hear, but here goes anyway!

The so called "hot start" happens even in cool weather. Up here on my '72, it used to happen more in Fall than in summer. Reason most likely being that gas companies make fuel more volatile for winter.

Modern cars use quite high fuel pressure and have no problems, but the D-Jet is only 29psig, at which pressure gas will vaporize at quite low temperatures.

First thing I would do, is check the fuel pressure. I would try bumping it up a bit to say 32-34psig (use the adjuster on back of FP regulator) That will help stop vaporization. (it will also make mixture richer once running, but that can be fixed later). Also, try turning the key on and off several times or put a jumper on the fuel pump relay so it keeps running when the key is turned on. The pump normally only runs for a few seconds. This will help get some cooler fuel up from the tank and into the injector rails.

By the way, the reason the car won't start, is that the mixture is too lean. The gas tries to flow through injectors, but instead of a liquid spray, you get vaporization and this reduces the amount of gas entering the intake.

The only heat shields, are those on the exhaust manifolds. If they are not there, they should be replaced!

I no longer have the "Hot Start" problem. Main reasons, I think, are higher fuel pressure, idle speed set at 750rpm when engine is hot hot! (its at about 1100rpm cold) And IDLE mixture settings which I set on rich side on ECU idle knob. Throttle position switch needs to be properly adjusted so engine runs on Idle mixture when throttle plate is closed and against stop.

There is some other stuff that you can do, but above would be a start. Many of these cars have this problem to some extent, but it can be overcome to some extent.
 

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Premium Member
'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I found a nice thread on this Vapor lock in D-Jets, and some good info from MBGraham at: http://www.benzworld.org/forums/r-c107-sl-slc-class/1371416-sl-450-75-bad-hot-start.html
That is an older thread I think. Hot Starts are covered in Stickies, but a bit hard to find. This post has link to a pdf I posted that had most of what I had learned in addressing hot start on my car:

http://www.benzworld.org/forums/r-c107-sl-slc-class/1542555-couple-cruise-pics-vaporlock-question.html#post4333534

I don't know if that was my latest pdf (it does need some work!) But, one thing not covered that another owner installed, was a solenoid valve in a by-pass around fuel pressure regulator (thread on MBCA site). A relay closes this valve when the key is turned on and the valve open when the key is turned off. This means that each time car is started, fresh cooler fuel is pumped from the tank. He said it worked out fine. I haven't found a need for that, but he lives in a warmer climate, I believe.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Come on, Mike.

Who cares if the SL started or not.

Question is........did you get laid?
I think he is ignoring you Nobby.
Easiest question in the thread and no answer..
 

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1975 450SL
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244 Posts
My car has this problem too, I've got my fuel pressure bumped up to ~32PSI and idle a little higher (like MBGraham suggested) so it doesn't happen very often, usually just during the fall and in the winter when I park in a parking garage that is warmer than ambient. Since she always starts and just stumbles on the lean mixture until I can get underway, I've been ignoring it since its not that big a problem unless people are standing around commenting to each other on how good my car looks only to have it start up and sound like a total POS. :)

My question is: Has anyone tried insulating the fuel rails? I was thinking about trying some foam insulation like this:

http://www.mcmaster.com/#45295k51/=a0ojxx

I'd be interested in hearing if anyone has tried this before, if not I'll be the guinea pig and let you know how it turns out.
 

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Registered
1987 Mercedes-Benz 560 SL
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973 Posts
My car has this problem too, I've got my fuel pressure bumped up to ~32PSI and idle a little higher (like MBGraham suggested) so it doesn't happen very often, usually just during the fall and in the winter when I park in a parking garage that is warmer than ambient. Since she always starts and just stumbles on the lean mixture until I can get underway, I've been ignoring it since its not that big a problem unless people are standing around commenting to each other on how good my car looks only to have it start up and sound like a total POS. :)

My question is: Has anyone tried insulating the fuel rails? I was thinking about trying some foam insulation like this:

McMaster-Carr

I'd be interested in hearing if anyone has tried this before, if not I'll be the guinea pig and let you know how it turns out.
Ineffective, I'd bet. Like putting a cold six-pack in an insulated cooler without ice, you'd only briefly slow the temperature equalization. It might gain you a few minutes of relief, but wouldn't fix the issue.

Mercedes put a fuel jacket around the cold, low-pressure AC line of its later R107s, with foam insulation around that. This was apparently an effective solution to the vapor-lock issue.

Good road,
 

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1975 450SL
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Ineffective, I'd bet. Like putting a cold six-pack in an insulated cooler without ice, you'd only briefly slow the temperature equalization. It might gain you a few minutes of relief, but wouldn't fix the issue.

Mercedes put an AC-refrigerated jacket around the fuel line of its later R107s, with foam insulation around that. This was apparently an effective solution to the vapor-lock issue.

Good road,
You might be right, but it seems that timing is everything with this issue, really you only have to insulate the fuel rails long enough for the underhood temperature to drop below the level that vaporizes the fuel.

In my case it seems like the vapor lock "window" is about 45-60min long, it never occurs in the first 15-20 minutes after parking the car, and it never occurs if more than an hour and a half has passed. So theoretically, if the insulation could keep the fuel in the rails below vaporization temperature for another half hour you might be out of the woods.

I'm not an expert on thermodynamics, so I don't know if the insulation would have to be 3" thick or something to make this work, but for $35 I might just give it a try anyway.

The refrigerated jacket scheme seems like a mighty big band-aid to me for an OEM solution. Why wouldn't they have just increased the system fuel pressure, or employed a method to recirculate the fuel through the rails back to the tank during a hot start? Also, isn't this just a D-Jet problem anyway?

Anyway, thanks for the feedback!
 

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1975 450SL
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GlueckAuf, sorry I didn't see the PDF the first time, that is interesting, and it seems that they do have the recirculation to the tank.

Thanks.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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GlueckAuf, sorry I didn't see the PDF the first time, that is interesting, and it seems that they do have the recirculation to the tank.

Thanks.
If we had that system on the D-jets there would be a couple of problems. One, we would have to have a working A/C on a 37 year old car! Then, we would have to run our A/C in cool Fall weather when this phenomenon often happens!

It is possible to buy an air cooled fuel cooler - I think they have low cost ones at Summit. I have thought of doing that.

I looked at putting insulation on the lines. Problem is, that I don't think the problem is at the upper part of the rails. I just polished mine so that they would reflect rather than absorb radiant heat. That is more likely how the heat is transferred rather than by conduction. So, if you do insulate, wrap insulation with aluminum tape. I was going to do mine with split 5/16" fuel hose and aluminum tape covering. But decided it wouldn't help much. Much of it is already covered with hose. I suspect a lot of the heat is absorbed by the injectors which are down closer to the engine and they can't easily be insulated or polished.

I think a lot of cars have rpm set too low - probably because AAV is sticky and car revs too high and surges when cold, so they turn rpm down.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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I think he is ignoring you Nobby.
Easiest question in the thread and no answer..
Since when is MeKnowNothing so serious about actually fixing his SL??
 

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Premium Member
1975 450SL
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Since you have a D-Jet, I would suggest checking your timing and dwell. Up until '76, there were breaker points in the distributor. I had a lot of problems with mine, until I changed out to an electronic system.

I suspect shaft wobble was eating the rider on my points, causing the dwell to change rapidly. I needed to adjust it about every 3 months. '75 was the last year there were mechanical breaker points in the dizzy. Dwell isn't that hard to test and adjust. All you need is a dwell meter, a screwdriver, the manual, and a little patience. Changing out to an electronic system for your year is only a little more complicated, depending on your skill level. Pertronix makes a unit for your application.

Just a suggestion from my experience, Yours may be different. Good luck
Scott
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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Ineffective, I'd bet. Like putting a cold six-pack in an insulated cooler without ice, you'd only briefly slow the temperature equalization. It might gain you a few minutes of relief, but wouldn't fix the issue.

Mercedes put a fuel jacket around the cold, low-pressure AC line of its later R107s, with foam insulation around that. This was apparently an effective solution to the vapor-lock issue.

Good road,
I'm not sure if the fuel line cooler is on the 560 for vapor lock because it is on the return line to the tank? Ina any case I don't have any problems with my 560SL even when the AC is not being used.
 

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1987 Mercedes-Benz 560 SL
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I'm not sure if the fuel line cooler is on the 560 for vapor lock because it is on the return line to the tank? Ina any case I don't have any problems with my 560SL even when the AC is not being used.
Says the manual, the fuel cooler's purpose is "To reduce the formation of vapor bubbles in the fuel system at high outside temperatures...". Isn't that the definition of vapor lock? I'm thinking the cooler was added to, over time, chill the entire fuel supply by way of the constant circulation that's going on, thereby reducing the chance of vapor pockets forming in the fuel lines that--on a hot day after a long drive--can cause stalling or failure to hot-restart (neither of which I've ever experienced in my car either, regardless of temperature or use/non-use of the AC).

Teach me. You've likely forgotten more than I've ever learned about these cars. :bowdown:

Good road,
 

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'80 450SLC Afro RHD Ikonengold
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I don't believe I'm missing any heat sheilding, other than needing to replace the injector seals.

I found a nice thread on this Vapor lock in D-Jets, and some good info from MBGraham at: http://www.benzworld.org/forums/r-c107-sl-slc-class/1371416-sl-450-75-bad-hot-start.html

There's one other piece of information I forgot to provide. When I got gas (shortly after the first instance of the tough warm start) I could hardly believe the amount of pressure that blew out of the tank when I opened the gas cap. I even noticed what I think is varnished fuel on the edges of the gas cap (which may be much older).

Also, the weather was MUCH colder than usual. It was below freezing. So I don't think we've got a situation of winter fuel on a warm day, but the engine heat might be all that's needed.

VERY INTERESTING! THANK YOU RONCALLO for pointing me in the right direction to understand this issue.
Have you tried to open the fuel cap and relieve the gases before you try to start warm engine?

I had a hard start and stalling engine on my old Mazda due to same reasons and, ever since, I just do not screw the fuel cap al the way any more. It is simpler than fixing the darn charcoal canister.
And I remember a friend having similar issues with his W124... we just driled 0.5mm pessure reliever hole on the fuel cap
 

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450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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Discussion Starter #20
Since when is MeKnowNothing so serious about actually fixing his SL??
I see Nobby and Rowdie are still interested in the divergent thread. :) This thread has TONS more information than I ever envisioned. I was originally concerned that maybe there was a part on my car that needed replacing or cleaning (which still may be true), but it seems that this is a simple defect that could have just been a design flaw, which I'm fine living with now that I understand it. It seems that the two simplest solutions to the problem are:
1) plan on lightly touching the gas pedal when doing the warm start to help force through a little more gas than usual. This seems to have solved my problems both times (after trying to start without fuel about 5 times each).
2) Maybe try opening the gas cap to decrease the fuel pressure... but wait... that's the opposite of what we want, isn't it? PV=nRT says higher pressure will keep liquid from becoming gas. But maybe decreasing tank pressure will allow the fuel to return to the tank???? Is the above solution valid?

On Nobby & Rowdie's divergent topic... I said it was a good night. I should have known you guys don't believe if you don't see pictures. So I attached a photo for you. :)
 

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