Here's the background. The car always starts well from cold, 1st or 2nd turn and it fires right up. When off for 5 minutes after running for a while to full heat-up, it fires right up. But if I leave it off for much more than 5 minutes, it cranks and cranks, but does not fire for three to five extended cranking sessions, and then it fires up. But it spudders, like running on 1-5 cylinders, then gradually smooths to a normal idle.

This has been the case regarless of ambient temperature or moisture. Once fired-up, it always runs smoothly. New parts now include: fuel pump, fuel filter, accumulator, injectors, cap, and rotor. Ignition wires are fine.

In the MB manual for the M110 engine, there is a reference to a "Hot-start Device" (M110's '77-81) which includes a Hot-start Relay and a Hot-start Solenoid. I've tried to track down a Hot-start solenoid through FastLand and my local MB dealer, but no one has ever heard of these parts.

Anyone have any experience with the K-jetronic and a Hot-start problem?

Thanks, Alex

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Hmmm... have you checked your fuel system hoses? You may have a vacuum leak. I had two hoses with cracks on mine (BMW, Motronic system, but it had similar/slightly worse hard-starting symptoms). The car would often just refuse to turnover until the 10th crank or so when warm but starts right up when cold.

HTH

My Toyota has that exact problem although it is an L-Jetronic based system. I have researched it for 11 years and all anyone can say is that it is a "hot soak" problem. Others report it but no solutions. In my case it only occurs when car is fully warmed up after 30 minutes of driving and car is stopped for more than 15 minutes but less than 45 minutes. The only theories I have developed are 1) fuel in rail boils or 2) some heat sensitive electronic component (coil?). In my case when it is running rough it has a very rich smelling exhaust (gas smell) and being a 6 cylinder I can feel as one after another cylinder comes back "on line" until there are 6 and it is smooth again. If I leave the hood up after stopping it prevents the problem. I have experimented to see if it was leaky injectors causing flooding and that was not the case. The unburned fuel smell does make me suspect the coil or some sensor.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

My 83 Porsche 928 has this stuff on it. There is a multi pin connector on the side of the fuel head/distributor, and a solenoid in the pipe going to the WUR. When I got it, it was very bad at hot starts, but would clear ok after a few hours standing. Then I found the electrical lead with the plug hanging down beside the motor, and looked for somewhere to plug it into - distributor! After that it has been fine on hot starts, apart from a bit more cranking than when cold. My Bosch application chart doesnt list part numbers for these bits though......nor for your model
hth
jp

Checked the 928 manual. There is a solenoid in the line from dist to WUR, with a return line, connected to a temp sensor on rear of head. Theory is that while cranking, if sensor says hot, open solenoid, dump pressure lower than usual for temperature, presumably to allow rich mixture, or to allow air plate to deflect more, its not really explained much, just describes how to check that solenoid doesnt leak.
hth
jp

FWIW, my 280E had the same problem.

I was talking to one of the older tech's at Don Pool last week about cold start problems, and he mentioned that there was a kit mostly used on the K-Jet 4.5's that would pulse the cold start valve on a hot start. This was used to combat vapor lock. He said he would check his files. I will make it a point to talk to him next week.

If you wanted to test this theory, you could easily rig a push-button switch to put 12V to the valve for a second or two and see if that helps. You have replaced everything that could leak down.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

There's a thread on hot start problems on M-100.org at around November 12 and later. Go to site and select bulletin board. Scroll down to thread mentioned. The author of this thread called his problem "flooding" though I'm not sure that's what the trouble was.

Here a a couple of good k-jet links:

http://www.auto-solve.com/mech_inj.htm (good)

http://www.users.bigpond.com/INTERJECT/ksitepln.htm (lots of info)

It sounds like you've replaced the parts that are usually responsible for the symptoms you list.

It sounds like your fuel pressure isn't right when the car is hot. There's a "pressure compensating valve" and a "system pressure regulator" in the fuel distributor with parts that maintain pressures for the next start. These parts wear out.

The only way to correctly diagnose K-jet is with the pressure gauges and the exact procedures as outlined in the manual or CD.

Please post what you find when you get it sorted out.

I have a cold start problem and I think it's bad o-rings in the pressure valves allowing fuel to return to the tank and not having pressure maintained in the fuel distributor.