M116 v8 hot start issues - PeachParts Mercedes-Benz Forum

amazon69 · #1 06-01-2018, 01:14 PM

Hello to you all,

I have taken my car for its first run in 30 years today. All things considered, all was well. It didn't catch fire, it went, stopped, changed gear (albeit a bit flarey). The problem I am asking about is after the run, when all was well up to temperature, I turned the engine off, and it would not start again. Not even a flicker. It has always been a bit of a sod to start from cold, I'm still hunting that down, but start it would. Am I right in thinking that I need to check my CSV, my AAV, various vacuum lines? What am I missing on the check list? I have rebuilt all the things previoulsy mentioned, but something's not right..it really did not want to start at all, not even a cough. As my signature says, it is a w111 coupe, 3.5, 1971. I look forward to any and all suggestions of things to check, thanks. Here's a pic of it too:

Frank Reiner · #2 06-01-2018, 02:39 PM

1) Ensure that the ignition system is working; that sparks are present and correctly timed.
2) Ensure that fuel is flowing thru the system, and that correct pressure is present in the injector fuel loop.
3) Ensure that the injection trigger points are providing signals to the ECU, and that the ECU is providing pulses to the injection valves.

okyoureabeast · #3 06-01-2018, 02:48 PM

Quote:

Originally Posted by Frank Reiner

1) Ensure that the ignition system is working; that sparks are present and correctly timed.
2) Ensure that fuel is flowing thru the system, and that correct pressure is present in the injector fuel loop.
3) Ensure that the injection trigger points are providing signals to the ECU, and that the ECU is providing pulses to the injection valves.

Frank has got it.

OP, does the starter engage but not fire?

Off of point 2, I would start your check at the fuel accumulator. If the pressure bleeds off immediately after shutdown, the fuel will boil in the lines causing vapor lock.

fema · #4 06-01-2018, 02:59 PM

I'm having the same trouble with my 6.3 right now, though it turns over just won't start until it cools down. The shop manual has a troubleshooting guide / procedure taking you through fuel pressure verification once the electric pump is verified as getting 11-12V, as well as MFI linkage operation verification.

amazon69 · #5 06-01-2018, 03:18 PM

Thanks all.

I will check the spark and timing, although it started and ran like a champ when it wasn't hot.

I shall check the fuel pressure tomorrow.

I rebuilt the trigger points, but will check that again..is temperature likely to affect them?

Starter works fine, all ok in that regard. The car is behaving very differently when hot...I shall see if I have the shop manual troubleshooting guide.

It was quite amazing to drive it..it is incredibly serene and beautifully damped..it fair glides along the bumpy Cornish roads. I've got so much money in it I will have to sell it, but if I drive it any more I can tell I am going to get addicted to it..

Frank Reiner · #6 06-01-2018, 04:39 PM

Quote:

Originally Posted by okyoureabeast

Frank has got it.

OP, does the starter engage but not fire?

Off of point 2, I would start your check at the fuel accumulator. If the pressure bleeds off immediately after shutdown, the fuel will boil in the lines causing vapor lock.

D-Jet systems do not feature an accumulator!

amazon69 · #7 06-01-2018, 05:04 PM

I'm glad you said that Frank..I was scratching my head trying to work out where it was...at least I know it's not that to blame

Tomas7 · #8 06-02-2018, 09:27 AM

What an absolutely gorgeous car!!!

Tomguy · #9 06-02-2018, 02:15 PM

Another item that can cause hot start issues is the aux air valve. If it's stuck closed, you'll be pig rich and it'll never start. Another item I had on my 4.5 (Also D-Jet like yours) was when I used the idle air speed screw to turn down the idle, instead of the mixture screw on the side of the D-Jet brainbox. If you turn it in too far, it'll be too rich when you try to hot start. See if unscrewing the aux air speed screw about half a turn helps your hot start problem. If so, but it then idles too high, use the trim screw on the ECU to turn down idle instead. This MIGHT fix hot AND cold start issues.

The valve can stick over time, ultimately you can try cleaning it and pinching the bulb a little tighter to see if that addresses the issues, if opening the screw helps it start better.