shdoug

(Search yielded nothing)

Now that I've discovered the kickdown switch, another issue has come up.

So, I'm flying along with the RPMs in the red, pedal to the metal, and then the transmission shifts into 2nd (or 3rd). As soon as the shift hits, the engine cuts out for a half second and then it's right back at it again. Sometimes it cuts out and resumes twice before it lays into it again. It's not like a spark misfire; the engine actually goes dead for about a half second. It only happens during a hard upshift when the RPMs are close to or in the red. It is fairly consistent, although it does not cut out every single time. During normal driving the engine runs so perfect and smooth it's scary. No CE light; no codes stored.

I've examined the heck out of my harness and I have never seen any copper showing or signs of damage. It seems a bit stiff where the wires connect to the 3 ignition coils but not frayed. I've tried wiggling the wires in various places with the engine running and have never triggered a misfire or cut out.

I think the spark plugs may be the original as they are rusty around the ceramic on the outside of the plug. The combustion end of the plug has the usual white buildup but no sign of worn electrodes. They are Merc plugs. I only have the service records from 138,000 miles (now 157,500) and no plug changes were done. If this problem were caused by old plugs I would think it would misfire under other conditions as well. The previous owners did all the maintenance religiously so when ever the recommended change interval is (if it's recommended) they were probably changed.

As I mentioned, the engine pulls strong up to the point where it shifts, so I don't suspect a clogged fuel filter. I can't think of anything else except some wierd computer or electronic problem. I know that the engine will faithfully cut out when it hits the middle of the red to avoid over-revving, as it does this when stuck in the snow (big blizzard recently).

Has anyone else experienced this problem?

myfirstbenz

i'd replace those plugs with some NGK's stat! These motors don't mind high rpms, but what are you doing in the red! There is probably some safety mode where the 'puter will cut you off. Could be fuel pump relay?

shdoug

All of these W124s that I've seen go slightly into the red before they shift. It does not cut out when it's in the red, only after it shifts and the RPMs drop.

myfirstbenz

Uh, that's not right. 3 in my family and none of them do that.

shdoug

http://www.youtube.com/watch?v=ovEuGp0DsVI

Pay close attention to the tach...Shift to second gear occurs at 6500 RPM, well into the red, but no cutting out. Mine does the same, but cuts out when the RPMs drop after the shift. You're saying yours all shift at or before 6100 RPM? I didn't think that was adjustable. Changes to the Bowden cable adjustment seem to have no effect at WOT.

myfirstbenz

Oh they'll redline if you are flooring it, but not under normal conditions.

shadowgriffen

wow...that's just wrong, I couldnt redline my car even if I wanted too!

Sounds like a trans problem to me.

shdoug

Perhaps "Red line" is the wrong choice of words. It goes into the "Red Zone", which starts at 6100 RPM. I think the shift occurs shortly above this.

Forget the red line thing; that is not the problem because it does not cut out until the RPMs drop to 3500 or so AFTER the shift. The hard shift seems to trigger the cut out.

shdoug

Let me try a different angle. Does anyone think this could be the spark plugs? Does anyone have the maintenance handbook to look up the change interval for the factory plugs?

mbenzman

No. They not supposed to shift in the red "zone" Should shift right at the edge (6000 rpm). The video you posted as an example is a modified car, don't expect your to be the same. It sounds to me as if you've hit the limiter. Back the bowden (shift) cable out a tad.

kiasu

with that vid tehres that orange light that comes on..my dash looks exactly the same but i dont think i have that warning light..is it only on certain models after 89' ?

shdoug

I think that is the ASR (Traction control) warning light, which is optional. If not the ASR light, it might be a Euro option of some kind. I love that video!

shdoug

I've adjusted the Bowden cable several times, different directions. It has a huge effect on what RPM the shifts occur at part throttle, but does not seem to effect the WOT shift points. Is it supposed to? What else might control the WOT shift point?

Also, I forgot to mention that this cut out also occurs occasionally and much more briefly on a forced kickdown. The RPMs jump up to say, 3500, then quick pause (quarter of a second) then hauls a$$ down the road.

Side note: My car feels like it gains another 20 horsepower as soon as it passes 3500 RPM. You can feel it kick in every time like a switch. Is there variable valve timing or something like that?

shdoug

Update: I replaced the spark plugs, made no difference. Incidently, since I received no answers in regards to this, the spark plugs should be replaced every 30,000 miles under severe conditions and checked every 30,000 miles and replaced only if necessary for normal conditions. This is from the maintenence guide I recently acquired.

I noticed today that this cut out seems to only occur, or is at least more noticeable, if I let off the gas slightly before the shift. I sometimes chicken out for fear of the sheriff lurking around. I guess I won't worry about it. No one is likely to challenge me to a drag race out here in the burbs, anyway.

Next project: engine mounts. They are both cracked and giving me a hellacious massage while sitting at stop lights.