E420 1994 limp mode at 55mph and above !?!? - PeachParts Mercedes-Benz Forum

kafklatsch · #1 04-04-2011, 01:11 PM

Background: Plastic guide rails caused lose of timing chain. Replaced engine. I was able to wrestle an 1994 e420 engine away from a guy who wrecked the car in 2000 with 42,000 miles. His plan was to eventually repair the wreck. you know the story, 1 year turned into 10 years and he never got around to it. he maintained the engine running with periodic oil changes. It runs like a dream and was spotless (brings back memories of when i opened the hood on my E420 15 years ago. ). His engine number was within 200 of my own and I have verified all critical parts cables harnesses and modules to be indentical (EPC Startek data)

The engine was installed and ran perfectly, after about 75 miles I took it to 80mph and the ASR triangle lit on the dash. Thats how it all started. The engine ran perfect below 80mph for a short time, but now the light comes on at 55mph.

If I let off the gas, the triangle light goes off and all seems good if I stay below 55.....the rpms shows about 2500+/- and if I down shift, the rpms shoot up to 3200+/-, BUT the speed is still limited to 55 before light comes on - no matter which rpm (gear) - any hints there?

The car now surges at idle. It jumps between 530 and 650rpms. however, It does not shut off. I have a MT2500 scanner and got several codes when i first replaced the engine. I cleared all codes and started with a clean slate. A code 24 & 25 on the LH-SFI module (short in the camshaft circuit) led me to replace the module after verifiying the wiring and camshaft coil ohms. The module no longer shows camshaft circuit errors.

I do see an error DTC 14 (S29/3 idle position switch?) - on the EA module, but it is intermittent. where is it located? could this cause both the idle problem AND asr light at speed?

No other codes have reappeared as far as the MT2500 shows.

I have replaced the following (with dwindling funding);
MAS (bosch reman)
LH-SFI MODULE (used)
Crank sensor
Camshaft sensor.

the crank sensor appears to be the only part that changes engine characteristics.... thus I wasted money on the others.

I reset the Throttle from instruction here. The humming never stopped, but the mechanical sounds did. I read ALL sounds should stop, does this include the humming - should it stop also?

the car idles roughly, but is very smooth when on the gas. The triangle lights above 55, but goes off when i let off the pedal.

I am using the replacement motor's engine harness as it was in spectacular condition, Although, my original harness has never suffered the breakdown commom to the MB's of that time. the p/n's are the same (EPC)

The car ran very good until the timing chain broke. no issues at all.

OF NOTE: when I went to adjust the throttle cable after the engine install, I noticed that part of my kickdown switch is missing. The gas pedal cannot reach the remaing switch part. I swear I remember it being like that for years with no problem. ??? I will replace it this week

Please..... any helpful suggestions are welcome.... I am stuck.

duxthe1 · #2 04-04-2011, 02:20 PM

Are your tires all the same size and inflated properly?

kafklatsch · #3 04-04-2011, 04:51 PM

Quote:

Originally Posted by duxthe1

Are your tires all the same size and inflated properly?

amazingly, a front tire was cupped, I replaced both front tires AFTER I changed engine.....

the fronts were 205/60.... i went to 205/65's.....

I do remember the car worked perfectly during the test period and then it didnt..... the tire change split the two conditions.....

my fingers are crossed..... wont be able to change tires until this weekend....

thanks so much...

duxthe1 · #4 04-04-2011, 08:49 PM

That will do it. As you drive faster the wheel speed differences are enough to trigger ASR function.

Jim's500E · #5 04-06-2011, 11:37 AM

Disconnect the speed sensor (big barrel connector) by the CAN before switching tires...if the car doesn't go into LH mode at speed after that then its a sure bet then the tire diameters are not jiving.

JohnM. · #6 04-06-2011, 04:32 PM

What about just running the bigger diameter tires in back (as in staggered fitments), that shouldn't affect the ASR?

duxthe1 · #7 04-07-2011, 01:39 AM

It will. Gotta have the same size tires on those cars.

kafklatsch · #8 04-09-2011, 08:38 PM

well.............I matched the tires sizes and took her up to 100............ no dash lights.......... problem is solved.......... my temporary 205/60 and 205/65 combo was a no go..... thanks Duxthe1

car still idles fine 90% then surges for a short period only to return to normal....

my MT2500 scanner shows an intermitent "idle speed contact switch" (s29/3) error, where is this located?

would the switch be the result or the cause?

Quote:

Originally Posted by duxthe1

That will do it. As you drive faster the wheel speed differences are enough to trigger ASR function.

emerydc8 · #9 04-09-2011, 10:20 PM

Unfortunately, the 29/3 idle speed contact switch is inside the ETA.

http://www.k6jrf.com/MB_EA.html

Hopefully it was just transitory.

kafklatsch · #10 04-09-2011, 10:46 PM

Thanks, can you point out the part of the "link" that says where s29/3 is located. i dont see any verbiage.

I just looked for replacement on a parts website, and, they list "gas pedal" location, I dont recall such a switch down there.

can someone confirm location?

Quote:

Originally Posted by emerydc8

Unfortunately, the 29/3 idle speed contact switch is inside the ETA.

http://www.k6jrf.com/MB_EA.html

Hopefully it was just transitory.

emerydc8 · #11 04-10-2011, 05:33 AM

Upon further research, it looks like I was mistaken. The S29/3 switch is located on the accelerator pedal. http://autorepair.about.com/library/a/1i/bl119i.htm

Here's the attached picture and parts list from the EPC. It looks like the switch is #28 in the picture. Sorry, and let us know how it goes. I may need to replace mine soon too.

Here's the part on Fastlane.
http://catalog.peachparts.com/searchitem.epc?cookieID=36X0A1IXG36X0A1IXF

140 545 01 14

$61.21

JimF · #12 04-10-2011, 03:04 PM

Quote:

Originally Posted by kafklatsch

the fronts were 205/60.... i went to 205/65's.....

I suggest that you use the Miata tire size calculator to compare the "stock" tire size w/ the "new" tire size to begin with. This way you always ensure that your speedometer is 'calibrated' or, at least, very close to calibrated.

For example, stock tires/wheels for a W140 are 195 x 65 x 16". Using the link here you'll see that a compatible tire is the 225 x 45 x 18". The size match is perfect and the speedo (ASR, tranny) won't know the difference.

Not sure your "205 x 65 x ??" tires are compatible w/ your tranny and/or speedo??

The Miata tire size calculator can be found in my web page here . . . good reading about wheels and tire sizes . . .

kafklatsch · #13 04-10-2011, 03:52 PM

Quote:

Originally Posted by JimF

............Not sure your "205 x 65 x ??" tires are compatible w/ your tranny and/or speedo??.................

JimF, I am honored to have participation from you, I am an admirer of your website info. and a purchaser of products therein.

Everything has been perfect since the wheel size match........ I use the car for frequent trips between Houston and NewOrleans... the taller side wall is intended to maximize ride comfort. I calculated 2mph differance at 60mph, this is acceptable. I have driven about 100 miles around home to look for problems, I am code free, even the idle issue has dissappeared.

I just didnt associate my problems with tire size since I had just replaced the engine...

. I spent many hours tracing down my "errant" ASR issue that wasnt.

thanks again

rokacook · #14 03-07-2016, 03:36 PM

I just put 205/65-15 on the front and have 205/60-15 on rear now have limp mode, If I change just rear to match front will this resolve or do I have to buy new fronts again?

duxthe1 · #15 03-07-2016, 08:49 PM

Either / or as long as they are all the same.

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