issue at low rev acceleration

[Vikinger]

Hi, I am hoping for some help with my engine.

I life in Europe, own a EURO spec 94 E500 with 120k km on it. Recently I replaced all wiring harnesses on the engine, it received a new fuel pump two years ago. The Ignition cables, rotors and distributors were recplaced one year ago.

Three things are annoying me a bit, they might be linked to eachother. As I have no car to compare with, I was hoping you could give me some feedback.

1) I thought MB engines would usually allways start on first turn. Mine needs 3-4 seconds but starts reliably and equally at any outside temperature, regardless of engine being cold or warm. Is that normal?
2) When accelerating with moderate throttle, it shows light signs of stuttering/vibrating. The idling and acceleration at full throttle and high rev seems fine though.
3) When driving at moderate speed in highest gear and doing a kick down, it will only switch down one gear. The engine will accelerate from +/-3000 revs lacking the punch you would expect from a 5 liter V8 and that it gets as of 4000 revs. Is it not suposed to switch down 2 gears?

Thanks in advance for any thoughts.

 

[195910]

Moien,

It needs to be checked with the diagnosis to see the live data.

 

[Vikinger]

Moien,

It needs to be checked with the diagnosis to see the live data.

Salut!

It has no OBD2 yet I assume, hence I have no tool to scan it unfortunately. Any idea who would be good to get it done here in Lux (where you don't wait 2 weeks for an apointment)?

 

[195910]

Yes its not OBD, I do my own diagnostics so I can't recommend anyone.

 

[maw1124]

For issue #3, I would say check and adjust your Bowden cable first, so that all of the pedal travel is being communicated. Be very careful, and adjust 1mm at a time.

That “might” also be linked to issue #2, but that’s a guess and a bit of a long shot.

As for issue #1, search the forum for “extended crank”. It’s been discussed a few time here but I don‘t remember the resolution. 1995 E420 - Slow starting (extended cranking) | 400E / E420 Discussions I don’t recall you mentioning the fuel pressure regulator or fuel pump relay, but since it happens whether the engine is warm or cold, I suspect the fuel pressure regulator. You might also swap a new fuel filter as a potential aide to issue #2.

GL

maw

EDIT… now that I think about it, the FPR also “might” be related to issue #2, if you’re losing fuel pressure too quickly. And if the car is new to you, before you start mashing the pedal for double kickdown, do yourself a favor and change your transmission fluid and filter.

 

[gsxr]

Moien, It needs to be checked with the diagnosis to see the live data.

This. ^^^ Either buy an SDS that supports HHT-Win, or find someone who has this. The 500E has OBD-1 with full live data available, but you cannot use OBD-2 scan tools. Yes it will cost $500+ USD to buy the SDS kit, but it will be worth it in the long run.

1) I thought MB engines would usually allways start on first turn. Mine needs 3-4 seconds but starts reliably and equally at any outside temperature, regardless of engine being cold or warm. Is that normal?

No, it is not normal. You need further diagnostics. I'd start by checking fuel pressure at the rail when cranking. The fuel pumps should run for 2 seconds after turning the key on, before the starter engages, and should be 50-60psi at the rail before cranking begins.

2) When accelerating with moderate throttle, it shows light signs of stuttering/vibrating. The idling and acceleration at full throttle and high rev seems fine though.

This is not clear. It only acts up at part throttle? But pulls cleaning to redline at full throttle? Need more details.

3) When driving at moderate speed in highest gear and doing a kick down, it will only switch down one gear. The engine will accelerate from +/-3000 revs lacking the punch you would expect from a 5 liter V8 and that it gets as of 4000 revs. Is it not suposed to switch down 2 gears?

It depends on vehicle speed. It will not always drop 2 gears. Lack of power would be a separate issue, not related to shifting. Time it with a stopwatch from 0-100mph, if much slower than 15 seconds, power output is below normal.

 

[Vikinger]

Thanks for the hints, have had little time to follow up on this Though.

Perhaps the fuel pump in the back of the car is rather noisy, not sure if that can be seen as normal. Unfortunately I have no pressure gauge to measure the fuel pressure. I will go ahead and replace the FPR and filters, before replacing the pump.

other thing I have notices, is the low watertemp it is running at. It hardly goes over 70 in normal drive, slightly over 80 if I push it hard. Hence I am going to replace the thermostat.

I have also beein trying to figure out my way through the forest of available tools. Would prefer a software and a plug that I can install on my old laptop as standalone. Does anyone have a good hint?

 

[gsxr]

Perhaps the fuel pump in the back of the car is rather noisy, not sure if that can be seen as normal. Unfortunately I have no pressure gauge to measure the fuel pressure. I will go ahead and replace the FPR and filters, before replacing the pump.

A fuel pressure gauge is not expensive, and can help avoid buying parts you don't need. However, if the FPR and fuel pumps are original from 1994, they should be replaced proactively.

other thing I have notices, is the low watertemp it is running at. It hardly goes over 70 in normal drive, slightly over 80 if I push it hard. Hence I am going to replace the thermostat.

The new t-stat should cure this, assuming the temp gauge is accurate. There are early & late versions of the t-stat which are not interchangeable, visibly different if you look at the outer housing. Search the forum for photos & part numbers.

I have also beein trying to figure out my way through the forest of available tools. Would prefer a software and a plug that I can install on my old laptop as standalone. Does anyone have a good hint?

There are extremely few options that will show live data from these old OBD-1, LH-SFI systems. The best solution will be Star Diagnostics (SDS) but it must support HHT-Win. Some of the older C3 hardware (MUX) are defective and will not communicate with the EZL/DI, if you buy one of those make sure it works with the EZL when you receive it. The C4 costs more but I haven't heard any issues reported with EZL - yet. You may not be able to run the SDS on your old laptop, unless it's with an external USB drive, which may have very slow performance. Search the forum for more info.

 

[Vikinger]

Just wanted to follow up on how this ended after all. Again I got trapped by a too simple to be true thing, missed the forrest from all the trees…

it turned out that there is a plastic cap on the kickdown switch that had come off and drpped behind the accelerator pedal. This not only prevented kickdowns from being possible, but also the pedal to move all the way down.

finally I removed the ifnition caps and rotors and cleaned the contacts. Now it runs beautifully with explosive power as it should.

 

[maw1124]

I suppose the pedal physically not traveling could be it too…

The simplicity of these cars is greatly underestimated IMO. Glad you got it sorted.

Enjoy,

maw

 

[Unavita]

FYI on the scan tools: Our site friend from the former sickle and hammer regime went dark on me after I placed the order. I am supposing that there invasion of Ukraine is one of the reasons there. So do not look there for a system. To my knowledge that leaves only the other place... with a gold star and several smaller ones on it's flag.

 

[Unavita]

Indeed.