Thank goodness the CPS failure on this engine is a rare occurrence

 

Thanks for the informative post. Hopefully wont be needed but hey you never know.

 

Don't forget if you have the 16pin port for analogue code reading, it is normal to get code *17 faulty CKPS if the engine is not running. This code can be ignored under these circumstances.

Why does your avatar say 2003 500sl?

 

Why does your avatar say 2003 500sl?

Yikes.... I've just fixed that Typo ...thanks

 

Yeh, those with 2003 SL would be kicked off this Forum.

 

What about ones without an SL?

 

he could stay only if he bribs the Mods.

 

I have bookmarked this - thanks! Been to Queenstown years ago - a beautiful area. I am wondering in the CPS on the M119 fails like the one on the M112/M113.

If it should be replaced under preventable maintenance.

I have not heard if this is really an issue, or it should be replaced at every 100K miles, or so.

 

The Car still runs OK-ish up to 3,500 RPM with a faulty sensor so I'm not sure I'd bother replacing it until it fails. But, glad to be of help and I'm pleased you enjoyed your time in my part of the globe.:thumbsup:

 

Replacing cps on a 91 500sl r129

Hi,
Thanks for your generous post which will help a lot of MB SL owners. I have replaced my cps on my 91 500sl r129. Still no spark/no start! My cps is the type that is held on by two 5mm(?) allen bolts. My question, which you may have mentioned in your post, where does the other end of the cps cable connect to? Not the end connected to the cps but the other plug in end. In you post you mentioned a fuse box. Does the other end connect to the EZL? I tested the cable for continuity with the cps disconnected to the plug in end at the EZL there was no continuity on either wire (ground and?) Either my cps cable has opens or I am test the wrong plug. Sorry to be so long winded but I would love to know where does the other end of the CPS cable connect to? I am try to get my 500sl running again. It won't start. It will turn over just fine but no spark. I seem to get 12v at the primary of both coils. Actually either connection (2) to the primary on either coil when my test light black alligator clip is grounded the probe end of the tester lights up! I can't imagine that both coils are bad. Perhaps I am not testing correctly. Any advice from anyone would be very much appreciated.
Thanks, Larry 91 500sl R129

 

First generation the sensors don't often go bad....

The end goes to the EZL.

From mentioning the sensor end, does that mean that you can take it apart?
If yes,
You got the wrong sensor.

You should have this part#0031539128.

Regards,
aam.

 

Thanks so much for your reply. I need all the help I can get! I bought an cps unit without the cable. The unit i bought has 2 "ears" on it that attach with two allan bolts. The cable at the cps end had a ring or clip that I took off and the cable just pulled of the old cps. I reattached the cable to the new cps i installed (which is exactly like the old cps) put back the ring or clip and it snapped on perfectly.

The problem is that I did not know where the other end of the cable went so I could check for continuity in case i had a bad cable. I can't seem to get any continuity where I thought it ended at the ezl (and you confirmed in your post as I was just guessing). Is it possible that I have an "open" in the cable between the cps and the ezl? I checked both spots within the cable (ground and ?) and no continuity.

Am I barking up the wrong tree.? My main problem is the car will turn over but no start. I have checked and there is no spark from the secondary (high voltage) out put from either coil. So far I have replaced the OVP, battery and the CPS. The car ran fine then I got stuck at a shopping center (dead battery) and had it jumped and it took a while for it to start. At that point I new something was up. I got home and there she sat and would not start even with new battery. Any help or advise would be greatly appreciated.
Thanks, Larry

 

Your jump starting 'may' have damaged some electronic modules in the car.
May be you should do a diagnostic scan instead of just replacing things that you 'think' was the cause.

 

I thought all the early CKPS were a one piece unit moulded lead to sensor, the later cars were 2 piece. Strange that yours should be different, but sounds as if it is the same as the one you took out so it is what it is.

The CKPS usually creates problems when trying to start a hot engine and not when the engine is cold.
Often diagnosed by pouring cold water over the sensor of the non starting hot engine resulting in the car starting ok.

The early R129 didn't have as many CKPS issues as the later cars, I am not sold on that being your problem.

I think the dreaded long battery jump start, may be the culprit for the issues you may now have. Maybe some electronic module/ezl damage done, I presume all fuses have been carefully checked for damage.

Hopefully other members will be able to add more input.

Haha! didn't see Ray sneak in there while I made my Coffee

 

But it would also be the wrong one was put in by previous owner and that was why things were not working:eek

(watch out for Ray, he is sneaky)

 

I find it interesting that I hardly ever see info like this with M120 engines. I understand most people have M119's, but theres simply no comparison. Once I get somewhat proficient (I say this with a large amount of SARC) with DIY, I think I will post my amateur outtakes of my SL.

Gotta start somewhere.

 

My sincere thanks to all that have responded to my post. It gives me new insight and hope to fix my 91 500sl. In regards to having it "jumped" to get home. I may be back peddling here but as I recall the service jumped me with a hand held battery jumper and not from his car. I don't understand why this would create problems as the battery was dead (due to phantom drain) and wouldn't there be a fuse or voltage regulator to avoid any problems? I was able to drive home without any notice in performance. Once I got home it was "game over". To give you a quick back round on my knowledge I was a electronic tech for the coin operated game business for 12 years. I am well versed in electrical mechanical and digital electronics down to the component level. I am, however, a novice when it comes to auto repair. I just have a gut feeling due to my situation that the problem is something that is not that complicated. But as in any repair finding the problem is the brain teaser. I still have no continuity between the cable that connects to the CPS to the ELZ. And no spark coming from the high voltage side of both coils. Any Ideas? Any help or suggestions is gratefully appreciated. Cheers, Larry

 

I think that you got the wrong sensor, the sensor that you bought, needs current to run.
The original is a magnet and a coil, on the flywheel are metal pointers, that as they pas energize the sensor.
It is ONLY for the ECU to know where the crankshaft is.
Then the cam sensors come in to play.

The other newer generations, the ECU adjusts the mixtures.

I think that you as an tech know more about this, then I. Lol.

You have CIS, hydraulic injectors. Gas is spraying all the time....

They have electric injectors. The CPS sends signals to the ECU, ECU changes the injector pulse.

Check with an OHM meter the old, most likely is still good.

Now back to your problem.

1.Check your battery, while cranking.
You MUST have 11-14 volts to keep the modules HAPPY.
If you have access hook an other good battery. See what happens.


2.Check for voltage at the coils secondaries.
Remove the wires, OHM them.

The EZL is switching the ground on/off.

Regards,
aam.

 

Thanks again to all that have posted thoughts and ideas for me. The cps i replaced on my 91 500sl was from a dealer that verified that that was the right part. It looked exactly the same and fit exactly like the old one. But like those who has mentioned that that part (CPS) is a low failure rate and not related to my problem (turn over, but no spark out of the high voltage side of either coil).

I will try the suggestions of those who responded to my post. If anybody has any other ideas for an "engine turn over but no spark problem" I can really use the help.
Cheers, Larry

 

Well This is my "last effort" to find out why my 91 500sl R129 has no spark and won't start before I take it to a trusted mechanic. I hesitate taking it to my mechanic because (1.)I live in a rural area and I have to have it towed quite a distance and (2.) My gut tells me the problem is not a major one (of course, finding the problem is another thing)! I still believe I can find the problem with some help. So far I have:
Bought a new battery
Changed the CPS (although I can't seem to find continuity from both ends of the wire assuming that the other end of the wire from the CPS goes to the EZL.
I seem to get 12v at the coil(s) primary and nothing at the coil(s) high voltage (secondary) to the distributor.
Put in a new OVP
When I crank over the starter the voltage drops from 12v(+) to 10.9v. adding a "jumper battery" helps boost the voltage but still so spark/start.
The 2 coils ohm out at about 1.1 ohms.
new rotors and distributor cap were installed by the dealer about 300 miles ago.
I bought the car used from a single owner older lady (no disrespect meant)In which I knew personally. It had 85k miles on it. I was able to drive it 285 miles before it wouldn't start.
I have all the invoices and receipts from the day the car was bought including the original bill of sale (over a 100k$ new). It has been serviced (over serviced if you know what I mean) by the dealer regularly. It does have a "phantom drain" on the battery when car is off) I disconnect the ground on the battery and put a trickle charge to keep the battery up. The last time the car was brought in to have this problem fixed the dealer just put new caps and rotors on it and added new shocks to get the bill to 2k$!
Any last guesses what might be the no spark/start problem? How about the ignition switch which I have read about on other posts? What have I forgot to check? Any info would save me a big hassle.
If I can't fix it myself through help and advice I will let everyone know what the problem was if I have to take it in. This info my help someone else and save them $$$.
Thanks for any advice you can give. Cheers, Larry

 

You haven't said which crankshaft position sensor you replaced - front or rear. The front one is also known as the TDC sender while the rear is known as EZL sender. I would assume that it was the rear except that you say that you have been unable to trace where it goes and I think it's quite easy to trace the rear to the EZL on the left side of the engine compartment.

Were I in your shoes, facing at least one long tow and perhaps two, I would invest $40 in eight of these - Inline Ignition Spark Checker Connect them between the spark plug and the spark plug wire on all eight cylinders and have your assistant hit the starter while you are watching the engine in the dark. You will get either no sparks, 4 sparks or 8 sparks. if it's 4 sparks you have one bad coil, which you can then swap with the good one to confirm the diagnosis. If it's eight sparks you may have a fuel problem. If it's no sparks you have either two bad coils, unlikely, or an upstream problem which you can then start to isolate.

 

checked all fuses for corrosion?

 

Shame - looks like OP gave up:|

 

I have a SL500 (build July 1997, model year 1998) and want to replace the crank position sensor. Is the location the same on my later M119 engine as this DIY procedure for 500SL from 1993?

I am somewhat hesitant to do this as don't want to risk breaking off the outer part of the CPS sensor and leave the remaining part stuck in the engine. I have read a lot of posts where this happens but is it really that often it happens?

Perhaps I should perform this when engine is warm though I risk burning my hand and arm.

 

M119s have this sensor.

Bimetallic corrosion between stainless steel casing of Bosch sensor and aluminium holding bracket that is bolted to rear face of crankcase. Pretty much guaranteed to be stuck after 25+ years, unless maybe the car has resided in a hot arid climate.

The new sensor pictured in the OP’s post has a plastic barrel. I have a couple of spares, one from MB, which is plastic, one Bosch from online that is steel. Plastic don’t stick. Original fitment is steel.

Engine hot/cold won’t make a difference if stuck. Penetrating oil, no help.

To avoid the worst job you have ever tackled, check the output of the sensor with a scope. Does it need replacing? They hardly ever fail on M119. Beg, hire, borrow a scope if you haven’t got one before tackling this sensor removal job. You’re looking for a good clean output, example traces come with most scopes, or you find online to compare.

If the tip of the sensor is too close to the starter ring gear, the output of the sensor can be too high. If if is higher than 3v the ECU will not recognise the signal. That’s why spacer gaskets are sometimes used.

Don’t do this job unless the sensor is toast. Save yourself a lot of grief. BTW once the job is started and the sensor breaks off, it has to be drilled out. Metal filings on the magnets on ring gear, not a good idea.

If you want to replace the sensor as part of long term preventative maintenance, do it when your automatic transmission needs a reseal/rebuild. It is more likely that your transmission will require work before the CKS sensor fails. When transmission is out the CKS removal is much easier.

 

If the tip of the sensor is too close to the starter ring gear, the output of the sensor can be too high. If if is higher than 3v the ECU will not recognise the signal. That’s why spacer gaskets are sometimes used.

I think this is not an issue as it works well when the weather is not super hot and the car starts up when cold or a drive (when the weather is colder).
However, recently we have had 33-34 degrees celcius and I have done longer drives on the motor way and shorter drives in the city. Upon restarting the engine after it has been parked for some minutes (could be as little as 5 or 10 minutes) it has a long cranking time and needs 2-3 attempts before it fires up (I don't let it crank for very long at the time).
Either this issue has gone worse (compared to last year where I din't get to use it when the weather is as hot as it is now) or it is clearly related to warm weather (was not an issue before it went into storage end of October last year).

I will be replacing it and will report back whether it has solved the issue.

 

BTW if you scope the sensor, check it when hot and cold.

 

Thanks Robm.UK,
I’ve read that the later versions had a plastic casing. Searching by part number today shows sensors in plastic. My car being ‘97 build MY98 might it have a version in plasticu from factory?
Regarding the weather I live in Scandinavia but the car is not being used during the winter, only summer.

 

Just had a look at my spares, plastic one, which I bought for a 1998 500SL, doesn’t come with a lead, it has a coax socket on top of sensor. Steel cased, purchased for 1991 500SL comes with integral lead. Both Bosch, but different sources.

Re: your Q, might yours have the plastic version? Possibly yes, I believe change point was around 1996. Someone with a 1996+ build M119 could confirm?

Otherwise could check part nos on online EPC.
[Edit: first line of your post #28, you already did this, sorry. Looks like yours is plastic]

 

Thanks!
Yes, the part number today shows a plastic one but unsure if the original one fitted is also plastic. Would be great if someone could confirm.