M104 280 (320also?) 1994 Cannot read HFM codes from Pole 8 of 16 Pole diagnostic socket

[rayhennig]

Hello All,

Sorry, 280 only, not 500.

This concerns a new-to-us 1994 280. I'm trying to resolve a number of issues related to very strange throttle response.

I tried reading codes from the diagnostic socket, using my blink LED device. It worked fine on Pole 6 (Airbag), 1 blink, no errors.

On Pole 8, nothing. Not even 1 blink.

I've done lots of diagnostics on my 1991 300-24 and my tester has saved the day many times.

But on this later car I'm baffled.

Any ideas, anyone?

Upper harness replaced by MB with late Delphi harness.

Throttle body state unknown.

As for the engine ECU, don't know. Does lack of reponse indicate a problem with the ECU.

As said, baffled at the moment.

Best to all.

RayH

 

[rayhennig]

Just to update this thread.

I’ve modified the accelerator cable to, effectively, shorten it. This is a genuine MB part but I think it’s wrong. The result is now MUCH more travel on the pedal and the car is now a pleasure to drive.

But I still cannot read codes so I started throwing parts at the car but after I’d tested both engine temperature sensor and air intake sensor - both close to spec.

But we still had uneven idle and occasional stalling.

I put a new Pierburg MAF in and idle is now pretty good and it hasn’t once stalled. I still suspect vacuum leaks so we get the smoke test into play when I’m next with my son and his 4-post hoist.

The remaining annoyance is its insistence on changing up (722.4 auto box) into 4th as soon as it can. When I drive it like a manual I really rather enjoy it but absolutely not as an auto. Vacuum leak? Bowden cable adjustment makes no difference.

So, life’s improving and I am cautiously optimistic.

But I do need any and all inputs from the brainy people.

Thanks to all in advance.

RayH

 

[gsxr]

The remaining annoyance is its insistence on changing up (722.4 auto box) into 4th as soon as it can. When I drive it like a manual I really rather enjoy it but absolutely not as an auto. Vacuum leak? Bowden cable adjustment makes no difference.

Vacuum only affects shift firmness, not shift RPM.

The Bowden cable adjustment SHOULD make a difference in all shift RPM's.

Does it upshift normally 1-2 and 2-3, but only the 3-4 is too soon? Or does it jump 1-2-3-4 in rapid succession without allowing RPM's to increase proportional to accelerator pedal position/travel?

 

[rayhennig]

Vacuum only affects shift firmness, not shift RPM.

The Bowden cable adjustment SHOULD make a difference in all shift RPM's.

Does it upshift normally 1-2 and 2-3, but only the 3-4 is too soon? Or does it jump 1-2-3-4 in rapid succession without allowing RPM's to increase proportional to accelerator pedal position/travel?

Thanks for responding.

I seems to change through all the gears in short order to get to 4th/top before 30 mph. E/S seems to make no difference. As said, manual shifting makes the car drivable.

I've got the central console off now but when I've reassembled I'll get it up in the air and look at the gearbox connections.

R

 

[gsxr]

I seems to change through all the gears in short order to get to 4th/top before 30 mph. E/S seems to make no difference.

OK... if the upshift RPM's do not change at all between light throttle (say, 10-20%) and heavy throttle (say, 70-80%)... it sounds like your Bowden cable is either broken, or disconnected inside the transmission. You'll need to investigate further.

 

[rayhennig]

it sounds like your Bowden cable is either broken, or disconnected inside the transmission. You'll need to investigate further.

I've just verified that the Bowden cable returns when pulled from the engine end. It feels as if it's connected and returns smartly. The spring at the gearbox end is obviously installed and working.

Surely if it were not connected inside the gearbox it would not return so smartly? I did not need to pull very hard so does that indicate anything?

R

 

[gsxr]

I've just verified that the Bowden cable returns when pulled from the engine end. It feels as if it's connected and returns smartly. The spring at the gearbox end is obviously installed and working.

Surely if it were not connected inside the gearbox it would not return so smartly? I did not need to pull very hard so does that indicate anything?

That does sound like it's connected inside the gearbox. Something is weird here.

If it were my car... I'd next drop the pan and eyeball the movement while someone pulls the cable from the engine compartment. If that still looks normal, next up I'd swap in a spare valvebody from another of the same transmission (722.433 or 722.504, for your 124.028 chassis). Without a spare VB available, I'd drop the VB and disassemble / inspect / clean it... many hours of painstaking work.

 

[rayhennig]

Without a spare VB available, I'd drop the VB and disassemble / inspect / clean it... many hours of painstaking work.

Haha. No spare available. I may refer any such "internal" work to someone who knows what they're doing.

I'll try to keep you posted.

Thanks again.

R

 

[gsxr]

Haha. No spare available. I may refer any such "internal" work to someone who knows what they're doing.

I'll try to keep you posted.

The typical specialists will usually just recommend a replacement transmission, or a complete rebuild... which is likely unnecessary. Nobody does actual diagnosis and repair anymore. I am curious what you find out though. Hopefully it's something simple.

 

[rayhennig]

The typical specialists will usually just recommend a replacement transmission, or a complete rebuild... which is likely unnecessary. Nobody does actual diagnosis and repair anymore. I am curious what you find out though. Hopefully it's something simple.

One thing I shall try is ignoring completely the alignment of little arrows on the accelerator linkage. My plan is just to tighten the cable and see what happens. I haven't done this yet as I'm trying to do things "by the book".

Won't be for a while as you can see here. Lots of dirt and I'm waiting for a replacement mirror adjustment joystick.



I think I'm right in saying that tightening is what I need and there seems to be a lot of available slack I can take up. We shall see. Or, as we say here, "On verra"!

R

 

[gsxr]

YES! Do this first. I thought you had already tightened the cable beyond the "nromal" setting...

 

[gerryvz]

Moving this thread to OFF-TOPIC DISCUSSIONS as it is M104-related and has nothing to do with the key focus of this forum, the M119 engine.

All non-M119 LH related engine threads, should ALWAYS be made in Off-Topic Discussions, NOT in the core engine sub-forums of this site. Thank you for your compliance.

 

[rayhennig]

YES! Do this first. I thought you had already tightened the cable beyond the "nromal" setting...

Well, when working by the book fails, burn the book.

We now have a functioning gearbox. Changes up and the right times. Changes down when you accelerate.

The only thing it doesn't do is hold on a very steep hill. Fairly steep, yes. Very steep, no.

But major progress made.

Many thanks for your input.

R

 

[rayhennig]

I checked the part number required for this RHD car. And it does not match the MB part recently installed. It's basically too long. But I compensated for that using a cable stop. This means that the spring is now under compression, thus keeping the pedal in the uppermost position. Otherwise, the pedal never returned to its "home" position, if that makes sense.



R

 

[rayhennig]

This concerns a new-to-us 1994 280. I'm trying to resolve a number of issues related to very strange throttle response.

I tried reading codes from the diagnostic socket, using my blink LED device. It worked fine on Pole 6 (Airbag), 1 blink, no errors.

On Pole 8, nothing. Not even 1 blink.

Just an update. I can now read codes from HFM Pin 8. 1 blink = No errors.

What has changed? No idea.

Why would the ECU suddenly start returning error codes???

RayH