190E 16V Hot Start ("Hot Soak") Problem

[Jim Herold]

My 1987 190E 16V exhibits classic hot start ("hot soak") symptoms according to what I read and copied from a post elsewhere in this ShopForum:

Engine cold - no problem starting
Engine warm but not fully warmed up - no problem
Engine fully warmed up (30 min driving) but only parked a short while - no problem
Engine fully warmed up (30 min driving) but parked a long while (over 1 hour) so it cools down - starts (but idle is so low that engine will die-- need to keep foot on accelerator until idle returns to normal)
Engine fully warmed up (30 min driving) and parked about 10-30 min - turns over normally but will not start

The car runs perfectly in every other respect. From reading various posts, I suspect a faulty fuel accumulator. At the minimum, testing the accumulator seems like a logical place to start.

I have a C.I.S. fuel injection pressure tester which I have never used on a Mercedes. I would appreciate advice on making the proper two hose connections (one for the hose with the valve on it and one for the hose without the valve) and the correct way to test for the drop in pressure that would identify a faulty fuel accumulator.

I also copied the following test procedure from another ShopForum post. This test doesn't require any test equipment:

"The accumulator is located by the pump, back of the right (passenger side) rear wheel. It has 2 fuel lines pre '80 and 1 fuel line post '81 and all have a little fuel hose on the back side running back to the fuel feed hose from the tank. The testing is kind of low tech. Plug/clamp the little hose on the back side going to the feed hose then disconnect it from the accumulator. With pan to catch the gas start the car and look to see if fuel comes out the back side of the accumulator. You will have a squirt of gas when you first start it which is normal, remember it is hooked to the fuel feed hose, but after that NO fuel what so ever should come out of it. I really mean NONE! Let the engine run a couple of minutes and watch it to see if it leaks. Shut off the engine and watch it some more to see if any fuel drips out of the accumulator. If any fuel comes out while it is sitting or running the accumulator is bad and needs to be replaced. I replace the check valve in the end of the fuel pump whenever I replace an accumulator just for good measure plus they are cheap."

If I'm on the right track, I'd very much appreciate any advice on the best way to make a test of my fuel accumulator.

Thank you very much--Jim Herold

[mbdoc]

clamping off & removing the hose from the accumulator & running the engine is the best test for the accumulator.

The fuel gauges connected to the cold start injector line will check system pressure & you can also watch for fuel pressure bleed off as well.

[Jim Herold]

I removed removed the hose from the accumulator and ran the engine. A very minor amount of fuel was seeping from the accumulator so I replaced it with a new Bosch unit.

This did not fix my hot start problem.

What should I check next and how should I make the test?

Thank you very much,

Jim Herold

[mak]

Surprisigly An old fuel pump relay can be affected by high underhood temp. clean pins and resolder or replace to remove this as a cotributer.

On my 300se i am very pleased with the low underhood temperatures after i installed an Exhaust heat wrap on the pipes. In summer the heat sink was tremendous and affected hot starts.
Amazing difference from the 40$ wrap.
mak
3oose

[mbdoc]

Jim, have you connected the fuel guage & see if the fuel pressure does bleed off?

If it does bleed off....the fuel pump check valve OR fuel pressure regulator are the most common problem after the accumulator.

IF it doesn't...then the secondary ignition system would be the problem.

[Jim Herold]

I have not connected my tester to confirm that the fuel pressure bleeds off.

Do I simply disconnect the cold start valve at the fuel distributor and put my tester in line? Then do I run the engine to normal operating temperature, turn it off, and watch to see if the pressure drops?

For many minutes should the system pressure not drop off? What is an acceptable pressure level?

Thank you..

[mbdoc]

Yes Jim,
Connect to the port for the cold start injector. That is system pressure.
Should be 5.6-5.8 bar at idle & drop to approx 3.0 bar with engine off.

Needs to hold 1.5-2.0 bar after 1/2 hour.

[Jim Herold]

I my ran the engine at idle for 30 minutes and it showed a steady 5.8 bar of fuel pressure. With the engine off, pressure dropped to approximately 2.7 bar and held steady at that level for over an hour. The pressure gauge showed no leak down within one hour.

Background: For years this car has had a periodic "low idle" hot start condition where the engine would always start but want to die unless I kept the idle up with my foot on the accelerator for several minutes. That has worsened to the current "no start" hot soak problem.

I always suspected some temperature sensitive electrical component was causing my periodic hot engine, low idle condition. With this as background, what should I check next and how?

Thank you.

[mbdoc]

There is a good chance the problem is related to secondary ignition.

During hot soak re-starts the secondary ignition system has to have it's highest out-put available.
Is that system in perfect condition?