1993 400e runs great, turn off, restart runs like crap

[mespe]

Been having problems with the 1993 400e, runs great when you first start, drive several miles all fine. turn the car off and wait 5-10 minutes, restart and sputters and coughs. When floored, coughs a little then zoom take off G's are pretty awesome.

It's the idle, light to moderate load that sputters. I experienced this once before, after runnign through a puddle of water, eventually started runnig fine again back then.

Now first start/drive is Fine Start when hot = terrible running condition.

First thought was O2 sensor, but looking at it, I don't feel like changing that out in an attempt at swapping parts out to fix the problem.

will keep posted at my attempts

[babymog]

Fuel pressure regulator leaking into the vacuum hose?

[mespe]

So I should smell fuel if I pull the vacuum line going to it? But why would it take me to turn the car off? I need to let it cool, and drive it a bit further without shutting down, and see if she misbehaves,,,

[samiam44]

Well.. I don't think that's a good check.

You want to put a gauge on the system and measure pressure- it should be without a check valve. You can have a bad fuel pump check valve or there is an accumulator which maintains pressure back with the fuel pump. Could also be a regulator as noted- just pull up the manual and check the few things out.

M

[mespe]

I don't see the correlation between the engine being hot (up to temp) and the car running bad after a restart, and the fuel pressure, when the car ran fine before it was shut off.

[rayhennig]

Got a 300CE-24 with KE Jetronic. Had exactly those symptoms.

Checked resistance and various temperatures of all the temperature sensors. The air intake sensor was open circuit.

Changed it (€12 at MB) and that altered the duty cycle from around 50% to 90+%. Adjusted it back and the only problem then was a minor hesitation after hot start. New Beru (€20) spark plugs cured that.

All this is with the original 19 year old 300K KMs distributor cap. I'll change that next.

Look at the cheap things first.

RayH

PS: mespe said, "I don't see the correlation between the engine being hot (up to temp) and the car running bad after a restart, and the fuel pressure, when the car ran fine before it was shut off."

I do!

When the engine's been off for a few minutes air intake temperature rises considerably. The entire engine compartment is hotter and the fine tuning really needs to know about the heat in the air intake.

[samiam44]

what's the correlation-

Fuel gets hot it vaporizes.. then it runs like crap. If there is insuffiecent fuel pressure in the system, it has mixed liquid and vapor.

Honestly, it sounds like you need to find a good shop. Tools and time are going to cost you much more than the repair.


Michael

[samiam44]

Hot run conditions can also be coils on these cars...

[rayhennig]

Originally Posted by samiam44

what's the correlation-

Fuel gets hot it vaporizes.. then it runs like crap. If there is insuffiecent fuel pressure in the system, it has mixed liquid and vapor.

Honestly, it sounds like you need to find a good shop. Tools and time are going to cost you much more than the repair.


Michael

But fuel vaporisation is guarded against by an accumulator that maintains the pressure. I also believe that (in my case) the air intake temperature sensor plays a part in telling the system that very hot (and thus less dense) air is entering.

Also, as you say, ignition issues play a part. I have had distributor cap, rotor and spark plugs, the replacement of which has dramatically improved hot performance. My cheap (Bremi) replacement cap failed hot after less than 2 years and the 19 year old original went back in and all's well for the moment. A new MB one will be installed soon.

Certainly for ignition parts (that get VERY hot in my car), I say, "Buy genuine MB ONLY!" Ask them for a discount, I got 15% with little effort.

Bonne chance.

RayH

[mespe]

Originally Posted by samiam44

what's the correlation-

Fuel gets hot it vaporizes.. then it runs like crap. If there is insuffiecent fuel pressure in the system, it has mixed liquid and vapor.

Honestly, it sounds like you need to find a good shop. Tools and time are going to cost you much more than the repair.


Michael

How long will the fuel be vaporized, when it is returned to the tank? I could see maybe 10 seconds of rough running until the vaporized fuel is purged from the fuel lines/accumulator etc, but this is not the case.

I have just begun to troubleshoot this, I have other things to do so I will get to it as I get time.

[mespe]

Originally Posted by rayhennig

Checked resistance and various temperatures of all the temperature sensors. The air intake sensor was open circuit.


Look at the cheap things first.

RayH

Thanks Ray, that's a good starting point from here.

I do have issue with the 4 prong coolant temp sensor, the connector is keyed, but the sensor is not, however, the car ran fine for 1000's of miles the way that is hooked up, so I doubt that is a concern.

Ever since I got the car, it's been spitting a code about 2ndary coolant temperature sensor out of range, or something like that, maybe I'll pull the codes again too,,,

[mespe]

Correction to the title, runs like crap after it warms up.apparantly, I hadn't driven it long/far enough in my first test drive.

I pulled codes on pin 4 LH Sequential multiport pin, and got codes 3, 17, and 18

I've seen those codes before, now that the car is warmed up, time to check the sensors again,,,

Sensor Ambient Hot
4 plug 1.8 K Infite (both pairs on a diagnol)
2 plug 4.7K 550 Ohms
1 Plug 522 64 Ohms

The incoming air temp sensor seems to work as when I put it in the sun, the numbers started going down,,, not a calibration test, but a go/nogo

I reset the 3 codes mentioned earlier, and drove the car until it started to sputter, I rechecked the codes, and none of them had tripped. hmmm Does it take multiple failures before the codes are tripped?

[rayhennig]

Originally Posted by mespe

Sensor Ambient Hot
4 plug 1.8 K Infite (both pairs on a diagnol)
2 plug 4.7K 550 Ohms
1 Plug 522 64 Ohms

The 4-pin sensor is the one to change. Measurements of resistance across the diagonals should be about the same. Only that and the air intake sensor will influence running conditions. Change the 4-pin and, for the sake of around €12, change the air intake sensor too.

The other two sensors are for the aux fan and interior engine temperature gauge.

Let us know if that alters anything.

RayH