Need some guidance. 1994 E420 with 305,000 miles. Reliable daily driver. Transmission shifts normally however something odd is happening at wot acceleration. Following kickdown the engine reaches what appears to be a rev limiter at about 5200 RPM and kind of bounces but the transmission never upshifts. When I release the accelerator the transmission upshifts smoothly. Where does the rev limiter normally come on?
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Rev Limiter upshift problem
- Thread starter Phoenix127
- Start date
Rev limit is 6300rpm, and after 10 seconds it is reduced to 6000rpm. Full-throttle (kickdown switch engaged) upshifts should occur right around 6000rpm (maybe ±200rpm) for all upshifts.
What you describe at 5200 rpm sounds like a different problem; possibly the EZL is limiting RPM if it doesn't recognize the gear position indicator properly. Have you checked fault codes on all modules? Has the NSS ever been replaced? And does your car have ASR?
What you describe at 5200 rpm sounds like a different problem; possibly the EZL is limiting RPM if it doesn't recognize the gear position indicator properly. Have you checked fault codes on all modules? Has the NSS ever been replaced? And does your car have ASR?
NSS has been replaced a few times. No ASR. I have not checked codes recently.
I have just now replaced the NSS with a new Mercedes part and the problem persists. I am wondering now if this might be a fuel pump or filter issue? The engine never misfires it only seems to hit a limit and then begins surging back and forth. The RPM seems to be different each time, but generally above 5000 RPM. Suggestions on how might I proceed?
I had (...or still have because it's not fixed yet) the exact same issue on my Limited. I assume my car still has the original NSS, so that could be a reason. Maybe the kick down switch is playing a role on this as well? However, I was also recommended to adjust the shift point/pressure on the valve body. The discussion starts midway in this thread:
Short clip of possible EZL failure (...which was a rotor & cap breakdown) | Troubleshooting and Diagnostics
Short video clip of possible EZL failure?? Hello. The Limited recently went into LHM mode, that's what I think it is based on the strange and missing sparks on the plugs. Spark plug #1, #6, #7 doesn't work, and #4 has a strange frequency. Here's a short clip. Any thoughts...
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One slight question -- have you aligned the NSS upon installation, as indicated by the factory procedure? Just checking, as this one small step has been known to be overlooked by others.
I wonder if you could be experiencing a restriction in the catalytic converters, with the inability of the car to go beyond a certain RPM area.
I wonder if you could be experiencing a restriction in the catalytic converters, with the inability of the car to go beyond a certain RPM area.
I have what I believe to be a procedure to use for aligning the new NSS. 1) Pace the car in Park. 2) Loosen the mounting bolts. 3) Insert the alignment dowel and tighten the two bolts.
4) Remove the dowel.
I will report back..
The procedure should be done with the shift lever in NEUTRAL position. In Park, there won't be any holes to line up.
FSM doc here, check out the installation note on page 3:
FSM doc here, check out the installation note on page 3:
I readjusted the NSS and no improvement. I may wait until my next transmission service and look closely at the adjustment to the throttle body Allen screw. I don’t think the cats are clogged as the car pulls strongly to the the point where it doesn’t. It behaves exactly as a rev limiter. Doesn’t miss or ping. It only occurs after kickdown acceleration approaching the upshift. Doesn’t matter the gear 2-3, 3-4. If anyone has further guidance I will check back. Thanks for all the responses!
I am happy to report that “after further review” the car is shifting properly now after carefully following the Mercedes adjustment procedure. Thank you all for the very helpful comments. Love this car!
Hello eveyone,
Same problem here, my NSS has just been replaced and adjusted following the factory procedure, but still the same problem.
In Park limited to 5500 rpm which is normal, but also in Drive with wot exactly 5500 rpm is the max. When releasing the accelerator the transmission upshifts smootly.
GSXR is mentioning ASR in the text above. Is there any link between ASR and the rev limiter? Overload switch has also been replaced.
Thank you for any response.
Same problem here, my NSS has just been replaced and adjusted following the factory procedure, but still the same problem.
In Park limited to 5500 rpm which is normal, but also in Drive with wot exactly 5500 rpm is the max. When releasing the accelerator the transmission upshifts smootly.
GSXR is mentioning ASR in the text above. Is there any link between ASR and the rev limiter? Overload switch has also been replaced.
Thank you for any response.
What part number NSS was installed? The NSS is NLA, which makes me wonder if a 6-cyl NSS was used... this won't work properly on the 034/036.
A proper check would be to view live data from HHT-Win while moving the gear selector to each position, and verify the live data readout matches the gear position.
ASR should not have any effect on the rev limit. They are separate systems.
You are absolutely right the NSS in NLA 
like many other parts. It’s gettting very very difficult to get any original part. I bought one which is modified to function like the one for the 036. I will check the live data tomorrow. I was just wondering about the ASR link. Thank you for the information. I keep you informed.
like many other parts. It’s gettting very very difficult to get any original part. I bought one which is modified to function like the one for the 036. I will check the live data tomorrow. I was just wondering about the ASR link. Thank you for the information. I keep you informed.
Your photo only shows Park recognized. Did HHT-Win show "D" recognized when the shifter is in Drive?
How was a non-036 NSS "modified" to function like a proper 036 NSS? AFAIK that isn't possible. You'd need to get a good used 036 NSS and refurbish it internally as needed. If the "modification" forces the same gear position reading at all times, it should not read "P" at all times, this would cause the 5500rpm limit.
Yes it showed D when in Drive, N Neutral etc. I bought it in germany, i don’t know how they modified it (Kurth Classic Autoparts). I have my old NSS ( A0005456206) so maybe it’s possible to refurbish it. There’s also a faultcode for the abs sensor on the differential, so maybe that might be a possible cause.
OK - as long as each position indicated correctly, that should be fine. I am familiar with Kurth but not with this "modified" NSS. I am curious what exactly they are doing, and what the "donor" NSS is.
Search for the HOW-TO thread on this forum which shows how to refurbish your old one.
Nope, the ABS/ASR functions should have no impact on RPM limiting. That's strictly engine management, not traction.
What part number EZL is installed, btw? And what part number LH module?
Me too.
- for the HOW-TO thread on this forum which shows how to refurbish your old one. -
Thank you, I will have a look.
- part number EZL is installed, btw? And what part number LH module? -
I have to check, but a bit busy …
@MikeB - I refurbished the NSS a couple of years ago, have a look at the enclosed thread. Post #74 describes the refurbishment:
HOW-TO: Replacing Neutral Safety Switch (NSS, S16/3) | "HOW-TO" Tutorial Articles
When I had the Trans Rebuilt on the C126and E500, they both got replaced. (no it wasn't URO) :stickpoke:
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Ahh thank you very much
Hello again,
I am still trying to find the fault in my 500E which limits the rpm to 5600
I still have the same problem with the rev limiter as mentioned above. And I still have a fault #9 when checking pin #7; Left rear axle vehicle speed signal (L6/3) from ASR/ABS module (N30/1). I have a 1992 car with ABS and ASR.
I do have an original Mercedes Service book and I found the following information; when the vehicle speed signal is lost the rpm is limited to 5600 rpm in B, 2, 3 or D. So you won’t exceed 250 km/h (attached the text in German).
Thats exactly where my rpm is limited. And the left rear sensor is the one used for the vehicle speed (I did found that information somewhere here or on w124performance.com site, can’t remember).
Under de left rear seat I found the X62/8 connector and I measured approx. 690 ohm on the left and right sensor which is ok I think.
I was trying to follow the wiring cable towards the ASR module. In some documents a connector under the front passenger kick panel (is mentioned (X62/3). I cannot find that connector, I removed everything but no X62/3. It would like to measure the wires from the connector under the rear seat to a place near the N30/1 (ASR module), to see if there is interruption/broken wire.
Anyone got an idea or do I have to remove de ASR module, and if thats whats need to be done, how do I remove it without damaging it. I do not have the original removal tool…
thank you for any advice,
Grtz Michiel
I am still trying to find the fault in my 500E which limits the rpm to 5600
I still have the same problem with the rev limiter as mentioned above. And I still have a fault #9 when checking pin #7; Left rear axle vehicle speed signal (L6/3) from ASR/ABS module (N30/1). I have a 1992 car with ABS and ASR.
I do have an original Mercedes Service book and I found the following information; when the vehicle speed signal is lost the rpm is limited to 5600 rpm in B, 2, 3 or D. So you won’t exceed 250 km/h (attached the text in German).
Thats exactly where my rpm is limited. And the left rear sensor is the one used for the vehicle speed (I did found that information somewhere here or on w124performance.com site, can’t remember).
Under de left rear seat I found the X62/8 connector and I measured approx. 690 ohm on the left and right sensor which is ok I think.
I was trying to follow the wiring cable towards the ASR module. In some documents a connector under the front passenger kick panel (is mentioned (X62/3). I cannot find that connector, I removed everything but no X62/3. It would like to measure the wires from the connector under the rear seat to a place near the N30/1 (ASR module), to see if there is interruption/broken wire.
Anyone got an idea or do I have to remove de ASR module, and if thats whats need to be done, how do I remove it without damaging it. I do not have the original removal tool…
thank you for any advice,
Grtz Michiel
Attachments
I think the question is, what specific signal the LH module is using to determine vehicle speed?
The ASR module gets individual signals from each of the 4 wheels. Somehow a vehicle speed is sent to the LH module, which then limits RPM based on the criteria stated in the factory manual.
Could be this is being transmitted via CAN data. Ideally you would use HHT-Win to view live data and observe indicated vehicle speed and determine if this is accurate or not.
The ASR module gets individual signals from each of the 4 wheels. Somehow a vehicle speed is sent to the LH module, which then limits RPM based on the criteria stated in the factory manual.
Could be this is being transmitted via CAN data. Ideally you would use HHT-Win to view live data and observe indicated vehicle speed and determine if this is accurate or not.
You are right, I was looking into a lot of documents (w124performance, benzworld, original Mercedes books and this forum)and found somewehere that the rear left and front left are the ones used to determine the vehicle speed. The speedometer in the instrument cluster is using the sensor at the automatic-transmission so should be completely independent.
I need to check the (rear) sensors it with hht-win.
I attached a picture of the ECU area. Just behind it is a connector, I looked into a lot of documents but could not find this one, is this the connector from the rear axle? I disconnected it and used some contact spray…. you never know…..
I need to check the (rear) sensors it with hht-win.
I attached a picture of the ECU area. Just behind it is a connector, I looked into a lot of documents but could not find this one, is this the connector from the rear axle? I disconnected it and used some contact spray…. you never know…..
Attachments
You are correct - the speedometer in the instrument cluster is using the sensor at the automatic transmission, and this should completely independent. This signal is also used for the radio volume control and maybe another one or two items. It's also where the speed signal is obtained for an electronic FGS module.
I've not head the LF / LR claim before. I am curious if that is accurate.
The item circled in red is, IIRC, the coaxial connector for the camshaft sensor. This is NOT a wheel speed signal.
The rear wheel speed signal goes through the normal wiring harness under the seats/carpets, into the bottom of the ASR module connector. The pinouts for the ASR (and LH) module are in documents here.
To remove the ASR module, use an L-shaped hex/Allen wrench to gently lift the ears of the module upward until it is loose enough to pull out with your fingers.
I've not head the LF / LR claim before. I am curious if that is accurate.
The item circled in red is, IIRC, the coaxial connector for the camshaft sensor. This is NOT a wheel speed signal.
The rear wheel speed signal goes through the normal wiring harness under the seats/carpets, into the bottom of the ASR module connector. The pinouts for the ASR (and LH) module are in documents here.
To remove the ASR module, use an L-shaped hex/Allen wrench to gently lift the ears of the module upward until it is loose enough to pull out with your fingers.
Does the engine hang at 5500 and not upshift? Or is it upshifting at 5500rpm? These are 2 separate, completely different problems.
@MikeB - any update on your issue?
I assume this is the 1-2 upshift.
Most likely the kickdown solenoid is not energizing. First, try selecting gearshift position "B" and slowly accelerate from a stop. The trans should stay in 1st gear all the way to redline (6000). If it upshifts to 2nd in "B", the kickdown circuit is not working and needs investigation / repair.
That's interesting. My 300CE-24 does that. Most of the system is fairly new but it has done this both before and after major rebuild and several EZLs.
The only component that doesn't measure well - to me at least - is the throttle position switch. I have a spare and it measures as it should. The one that's installed seems illogical. This is the thing I'm on about:
The part in question is the switch (NLA, obviously) A0065459424. As said, I have another the measures well. But right now I can't be arsed to dismantle everything to replace. I only see the problem at very high speeds and that usually gets me into trouble with our 130 kph limit.
As said, this thing seems illogical and I wonder if it could affect the WOT upchanges?
By the way, the car has ASR.
All the best.
RayH
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OK - this is helpful. That means the B switch, kickdown solenoid, and solenoid wiring are all working correctly. But, you are not getting voltage to the kickdown solenoid at WOT.
Something is up with either your kickdown switch S16/6, the BM/GM (Basic Module / General Module) N16/1, or the wiring. This is what provides the signal to the kickdown solenoid at WOT. First, double check your kickdown switch is working, and that the floor carpet is not interfering with the switch at full throttle.
Full schematic is at this link. Screenshot below.
S16/6 = kickdown switch (WOT)
S16/8 = B switch in shift console
Y3 = kickdown solenoid at transmission
Ray, your C124 with CIS has a completely different setup vs the LH-SFI cars. If you are also not getting WOT upshifts at redline, check the kickdown switch behind the gas pedal first. The throttle position switch should not be in the kickdown circuit. You also have a kickdown (KLIMA?) relay involved, which is not used on the LH cars (that function was integrated into the BM/GM).
Hi, and thanks.
Yes, I know the system's different. And no KLIMA relay as, I'm pretty sure, klima issues are handled by the MAS box - the special one for cars with aircon.
R
Thanks alot for your help much appreciated. Is there any adjustments that need to be done on the bowdencable vaccum Actuator ? As its from a donor car?
Attachments
No adjustment should be necessary at the vacuum actuator portion of the Bowden cable assembly. That part is VERY difficult to replace / install with the transmission in the car. Make sure the cable is properly connected to the linkage rod inside the transmission before re-assembling.
Yes, the 124.034 and .036 use the same GM. (Some 140 chassis also have a compatible GM.)
I tested this on my car. The kickdown voltage on/off does NOT switch to "On" with the engine off, at full throttle with kickdown switch pressed.
I think this will only show "On" when driving at WOT, i.e. when the BM is sending a kickdown signal to the transmission.
I think this will only show "On" when driving at WOT, i.e. when the BM is sending a kickdown signal to the transmission.
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