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

__________________
'78 W123 280E, 58,000 mi!
'97 Mazda Miata
'94 Isuzu Trooper, 4WD
'03 MB C240 4-matic Wgn - Wife's
From the Archives:
'73 2002
'68 TR-250
'67 Austin Cooper "S"
'59 Austin Seven (Mini)
various p'up trucks

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

__________________
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.

Hi Chuck,
Can you explain more about the vapor lock? That sounds like one of my theories I had for my Toyota problem. Is that the fuel boiling in the fuel rail? Could that cause an over-rich condition?

Thanks,

Mike

__________________
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

... here goes.

You shut the engine off hot, and it cools down, but not enough to activate the cold start mechanisms. The fuel in the system contracts as it cools leaving a vacuum in the system. For some reason, it takes a lot of cranking and fuel pump running to overcome this and get some fuel to the cylinders.

So the solution was a quick shot of fuel from the cold start valve when the starter cranks.

I am not making this up.

__________________
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

Most vapour locks are caused (in the engine bay anyway) by heat soaking up from the engine mass and boiling the fuel in the lines. This vapour can then act a gas, preventing liquid fuel reaching the injectors. In theory the accumulator in Kjet maintains enough pressure in the lines to prevent this, but it only works as long as there is no leakage path allowing the pressure to drop (ie leaking cold start injector, or main pressure regulator valve). Trying to get fuel by popping the CSV wont help deliver fuel if there is only vapour in the line, but it may alllow the vapour to dissipate?
jp

fuel pressure regulator?

__________________
'O=00=O'
bmw 2002.
long live the legend

In the fuel distributor is a pressure regulator, that allows excess fuel to return to the tank (cooler that way) - under big hex nut on the side of the base. If the O ring on the end of the valve gets tired or damaged, it will leak pressure out when the pump stops, although it may still hold correct system pressure while pump is running.
jp

I seem to be the only one up this morning, so I did a little research.

There is in fact a kit to recondition the pressure regulating valve. You can also buy just the o-ring. You need to tell the parts guys to look at Group 7/4 for the 280E. The parts are readily apparent.

Also, in the K-Jet troublshooting guide, it lists the following parts as suspect in hard starting as in they can leak and cause a loss of pressure.

- primary system regulator (as discussed above)

- cold start valve

- fuel pump non-return valve

- diaphragm in fuel accumulator

- pressure compensating valve. This is a gizmo that "is located at the inlet to the fuel filter" and acts to prevent the vacuum problem described earlier.

- control plunger or "o-ring of metering sleeve"

The test for this is to connect the pressure guage between the FD and the warm-up compensator (presumbly on a warm engine), and run the fuel pump for 30 seconds by turning the ignition on (you may have to push bridge the relay as well). When you turn the ignition off, you should see 2.8 bar holding steady. After 30 minutes, you should still have 2.5 bar.

__________________
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

Best guide I have seen to trouble shooting K-jet is a book by Ben Watson, 'Bosch Fuel Injection....', available from Amazon for ~$15. Covers all types of Bosch fi from D-jet up to LH. Has very good sections on K- an KE. Unless the MB manuals are better than Porsche, its invaluable. Has system and control pressures for all cars that ran K-jet, detailed trouble shooting steps. JC Whitney do a pressure gauge kit that fits K-jet for ~$55. You dont need a hot engine to check pressure - connect gauge in line from FD to WUR, bridge pump relay. With gauge valve open, you should see control pressure for the ambient temp; close valve, you should see system pressure. Stop pump, watch pressure drop, check how well it holds as above.
Anybody have the MB P-number for the pressure regulator kit mentioned above, as I do have a faster than normal pressure loss after shutdown.
jp 83 Porsche 928..MB 722.0? gearbox

So, what's the finding. What was the cause? Has this been sorted out? I am interested to know.