SL500 R129 M113 1998 no start - any suggestions

[Dipstick36]

Hi guys, I have a no start on my '98 sl500, 65k miles, and would welcome any thoughts you may have. First a bit of background to the problem. The engine turns over, I have good spark, fuel pressure at 55psi and average compression on all cylinders at 185psi. The IRRC is working as it should and DAS2b is showing as being start enabled on STAR. The ECU is also showing as being fine with no error codes. The car has brand new crank position sensor, cam sensor, fuel pump relay, spark plugs, fuel injectors, fuel pump and filter. All parts are either Mercedes OEM or Bosch. The coil packs have been checked on my 2004 M112 350sl and no issues found. The car was not fitted with Aux air pump from factory so I guess I can eliminate as a cause. I have checked for vacuum leaks and there are none present. The car backfires to the extent that it has destroyed the original inlet manifold which literally exploded as unburnt fuel ignited inside it. With the manifold removed I can clearly see spark present while cranking and looking into the inlet port. The cam timing has been checked and, with the locking tool in place they are spot on 40 degrees as per spec. The engine has never been apart until I checked the timing so I can eliminate clumsy workmanship. Timing chain looks like new and is tensioned as it should be. Crank sensor trigger ring also looks good from what I can see. What I'm struggling with is how can I see a visible spark through the inlet valves on crank? How can the timing be so far out? Is it likely to be an ECU issue? Anyone have any recommendations for ecu testing? Apologies for the lengthy post but I am struggling with this one. Cheers

 

[pcthrillrider2]

you shouldnt see a spark on inlet valve both valves should be shut plug leads in correct order?

 

[Dipstick36]

you shouldnt see a spark on inlet valve both valves should be shut plug leads in correct order?

Thanks and I agree 100%. The coil LT connectors/loom only fit one way on the m113 so I can't see how that could've the cause. The static timing is spot on so how could the coils send their charge to the plugs with inlet valves open? Im trying to find a pin out diag for the ecu to test all wiring for issues. I've done similar on my 94 SL600 with a full engine rewire but I go on those seems easier to obtain. Maybe I'm looking in the wrong places.

 

[Will]

What’s the background of the car - did it cut out whilst driving, or been parked up and just refused to start?

 

[alabbasi]

If you have spark fuel and air which you do, it should start. If it's not starting I'm guessing that it's the crank sensor. A good scanner will trigger codes for it.

 

[Dipstick36]

What’s the background of the car - did it cut out whilst driving, or been parked up and just refused to start?

Hi Will, it's been parked up for a couple of years and just refuses to start. 3 of the original injectors were leaking so I've replaced all with brand new Bosch items. I've done the same with all of the usual culprits too. It splutters and backfires but will not run. I've checked the exhaust for blockages but that's fine. I have a STAR diagnostic and it shows no codes for the engine and drive access is showing start enabled. No visible issues with any wiring eg rodent activity or water damage but I am yet to test continuity on all ecu cables/connectors. I'm wondering if the ecu is somehow corrupted. Thanks again for your input.

 

[Dipstick36]

If you have spark fuel and air which you do, it should start. If it's not starting I'm guessing that it's the crank sensor. A good scanner will trigger codes for it.

Thanks alabbasi, I have a STAR diagnostic and it's showing no engine codes. I've tried 3 new crank sensors and tested all on another m113 and they all work fine. I've even disvonnevted the CPS plug to check if STAR picks it up and it does so I can't see that bei b the issue. As you say, spark, fuel, air and good compression is recipe or a start except where timing is out which it must be on my car if I can see sparking through the inlet ports. I will take a video and post it so you can see what I'm seeing. Thanks for your input.

 

[alabbasi]

Timing is why I thought it's the CPS. If it jumped time, it would likely bend valves and you'd lose compression in one or more cylinders

 

[Will]

Hi Will, it's been parked up for a couple of years and just refuses to start. 3 of the original injectors were leaking so I've replaced all with brand new Bosch items. I've done the same with all of the usual culprits too. It splutters and backfires but will not run. I've checked the exhaust for blockages but that's fine. I have a STAR diagnostic and it shows no codes for the engine and drive access is showing start enabled. No visible issues with any wiring eg rodent activity or water damage but I am yet to test continuity on all ecu cables/connectors. I'm wondering if the ecu is somehow corrupted. Thanks again for your input.

Was it running fine before it was parked up though?

Did you recently buy it ‘as is’? Just trying to understand the history behind it - could it have been parked up because of an engine issue and could someone have already tampered with stuff?

Trying to understand in the first post it says the chain looks new but then it also says you don’t think it’s been apart before?

 

[Dipstick36]

Timing is why I thought it's the CPS. If it jumped time, it would likely bend valves and you'd lose compression in one or more cylinders

The cam/crank timing is spot on hence no valve to piston or compression problems. It's the electronic timing that is way out and somehow spark is being sent to the cylinders at the wrong time. I'm going to delve deeper into the wiring to see if there is anything going on with it and continuity test everything. It was laid up but there is no evidence of any rodent damage anywhere that I can see including under the dashboard.

 

[Bellow]

Hi Will, it's been parked up for a couple of years and just refuses to start.

Same, or fresh fuel?

 

[Dipstick36]

Was it running fine before it was parked up though?

Did you recently buy it ‘as is’? Just trying to understand the history behind it - could it have been parked up because of an engine issue and could someone have already tampered with stuff?

Trying to understand in the first post it says the chain looks new but then it also says you don’t think it’s been apart before?

Hi Will, the car was running fine before it was laid up and apologies for any confusion re the chain. It looks like new (i.e. it's in great shape) but is definitely the original. I am 100% confident that I am the only person who has looked into the engine ie removed injectors and rail, intake manifold, Throttle actuator, rocker covers etc.. I did take a look last night with the inlet manifold removed and the Throttle actuator connected and noticed that it does not open more than about 15% when the accelerator is depressed fully. It's not jammed and moves freely enough by hand so it doesn't seem right to me and I probably need to check the signal going to it and test the throttle position sensor although there ae no codes on STAR to suggest a problem.

 

[Dipstick36]

Same, or fresh fuel?

Tank was drained before it was laid up and only fresh fresh premium fuel used.

 

[Bellow]

With the manifold removed I can clearly see spark present while cranking and looking into the inlet port.

On how many ports is this visible?

Throttle actuator connected and noticed that it does not open more than about 15% when the accelerator is depressed fully. It's not jammed and moves freely enough by hand so it doesn't seem right to me and I probably need to check the signal going to it and test the throttle position sensor although there ae no codes on STAR to suggest a problem.

If we're talking FBW, I wouldn't get hung up on that. There's no reason for an ECU to command WOT on an engine not turning and indeed, a running one at less than close to maximum rpm.

 

[alabbasi]

The cam/crank timing is spot on hence no valve to piston or compression problems. It's the electronic timing that is way out and somehow spark is being sent to the cylinders at the wrong time. I'm going to delve deeper into the wiring to see if there is anything going on with it and continuity test everything. It was laid up but there is no evidence of any rodent damage anywhere that I can see including under the dashboard.

Yes, that's what I mean. If there's good compression in the cylinders, it should start which brings me back to the CPS. If you're able to scan codes through the 38pin, you might find more information. Maybe security system or inertia switch.

 

[Dipstick36]

On how many ports is this visible?


If we're talking FBW, I wouldn't get hung up on that. There's no reason for an ECU to command WOT on an engine not turning and indeed, a running one at less than close to maximum rpm.

The visible sparking is present on at least 3 cylinders of the left hand bank. I've not cranked the engine many times but I need a second pair of hands to turn the key while I look at both sides of the engine. I will try and get video footage of what I am seeing but that won't be for a couple of weeks now as I am away on holiday from tomorrow.

It bis a FBW but I did also check it while cranking and it WOT did not happen then - Could be it's a red herring so I wont focus on that. If I could get it to run for a few seconds by syringing some fuel straight into the inlet ports it would be something but it just backfires. I admit that's not a very scientific approach but I figured it was worth a go.

 

[Bellow]

The visible sparking is present on at least 3 cylinders of the left hand bank.

Are you sure there isn't 'cross-firing' present? V8s are notorious for it.

 

[Jobsworth]

Are you sure there isn't 'cross-firing' present? V8s are notorious for it.

That tends to be on older cars with a distributor.

Are you sure you haven’t flipped over the coil pack loom, and the bank one is now on the bank two? I can’t be certain this is even possible, but I’m struggling to see what can have happened considering how thorough you seem to have been. It sounds like the crank trigger wheel has moved, but that isn’t a realistic possibility either

 

[alabbasi]

Are you sure you haven’t flipped over the coil pack loom

That would be very hard to do. The coils are literally right on top of the cam covers.

 

[Bellow]

That tends to be on older cars with a distributor.

True, but plug leads in contact with each other can induce cross-firing also.
A timing light or neon tester connected to a lead and observation of that cylinder's spark appearing at that (not another) cylinder would/should confirm/deny the presence of cross-firing.

Are you sure you haven’t flipped over the coil pack loom, and the bank one is now on the bank two? I can’t be certain this is even possible, but I’m struggling to see what can have happened considering how thorough you seem to have been. It sounds like the crank trigger wheel has moved, but that isn’t a realistic possibility either

Can the low voltage coil connections be misconnected?


Question to OP: all the replacement parts - as part of recommissioning after lay up or to solve no-start issue?