Hard (or no) startin when hot.

[aharley1]

The saga continues...
I picked my car up Friday. They replaced the fuel pump relay this time. I drove about 15 miles, shut it off, looked at a car, got back in & it wouldn't start!!! AGAIN! After much coaxing, I got it started. Drove it this weekend with no problems starting.
The worlds finest engineered car..... my others don't have this many problems!

99 Harley Davidson Heritage Softail
98 Dodge truck
88 Mercedes SL560
04 Chrysler convertible

[Tony1628]

Did you ever check the cold start valve. It happened to my 380sl. I replaced it and now it start fine...just do a search.. it is very easy to check..

[aharley1]

Well, the relay was installed, I drove 12 miles, stopped & it wouldn't start!! Drove the rest of the weekend with no problem???

[ctaylor738]

What kind of coaxing did you do to get it to start?

When it started, how did it run? OK from the get-go? Started firing on one or two cylinders, then all, then ran smoothly? Sputtered for a minute after starting? Could you hear the fuel pump when you cranked the engine?

[aharley1]

It started 3 times this morning while hot. Then I went home for lunch & 30 minutes later, no start. It tries then sputters, then cranks but won't fire. If I pump the pdal hard, sometimes it will start. I talked to a different shop mech. he said possibly the ck valves in the pumps. I couldn't find anything on a cold start relay in the shop manual. Hopefully this guy will diagnose instead of changing parts.

[ctaylor738]

It is very hard to diagnose an intermittent problem like this. The new guy is going to have to catch it in the act.

When you shut the engine off, do you hear a "glug-glug-glug" sound from the tank area (behind the rear bulkhead) that gradually diminishes? Just currious, because one of my 280SL's does that and has a warm start problem.

The service manual should refer to a 'cold start valve' or 'choke valve' controlled by a 'thermo time relay'. It's in the Injection section on the CD and should be the same as the manual.

[aharley1]

No different sounds on shutting down, however on start-up, it will sound like it's running on a few cylinders, then die. That's usually when it won't start.

[230/8]

I was reading in a buyer guide for MBs over the weekend and noticed a little throw-away line about intermittent vapor lock on some models. As I recall, it plagued several models and I think the SLs were included. Your symptoms suggest this may be the case. The underhood temp rises after you stop, and if the day is warm, or you've been running at highway speed the underhood temp after stopping may sometimes reach the critical level at which your fuel will boil. Keep in mind that this also happens this time of the year because refinerys are still making fuels blended for winter temperatures. As ambient temps rise, gas tends to boil more easily which is the reason refiners seasonally change their blend to be more resistant to summer heat. Spring is a tough season for the refiners because of the warm-then-cold-then-warm cycles to the weather.

If this sounds reasonable, then you might try insulating the fuel lines under the hood to keep some of the heat from them. Old time rodders used to crumple up tin foil around the lines to act as cheap radiators for keeping fuel cooler. Try that. Also, the book indicated that some models responded to turning the ignition off and on several times so the fuel pump would cycle several times. This is claimed to push cooler fuel through the system.

Give it a shot, see what happens, tin foil is cheaper than any indy mechanic.

230/8

[aharley1]

Thanks for the info. It's still in the shop. If it doesn't get fixed, I'll try that.

[aharley1]

Talked to the shop today. It did it for him today. He made several runs and on one of them, it wouldn't hot start. He finally coaxed it to start, BUT it wasn't at the shop, so they couldn't do much troubleshooting.

[aharley1]

The shop saya there's an intake leak. Pulling the injector system right now to see what's up. When they spray ether on it , it speeds up....