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  #1  
Old 08-21-2016, 01:32 PM
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Exclamation W140 (1994 S420) Engine Issue - I'm Stumped

I have a good idle, but the car has no power taking off from a stop. Regardless of throttle position, the engine will barely speed up under load and the car does move forward, but quite slowly. No missing, noises, etc., just no power.

One you get the car up to about 20-30 mph, it goes forward without a problem and seems to run just fine. You can drive it at freeway speeds without an issue. Slow down to a stop or below that 20-30 mph threshold and it acts like it has no power.

I'm satisfied that everything in the way of the MAF, ETA, plug wires, distributor caps/rotors are OK. The problem seems like there is no change in engine timing regardless of throttle position.

I'm getting a CEL all the time, yet the DAS shows random codes, such as knock sensors or ignition coils. I attribute these to occurrences at low speeds with the throttle at or near wide open. I can clear them without a problem and they'll come back again after I drive the car. Again, the codes are random and not at all repeatable. However, even if I clear them the CEL is on as soon as you restart the car. Strange.

So my question is, what exactly controls engine (spark) timing? I assume it's the EZL. I'm getting vacuum there, so I know that's right. I'm wondering if the camshaft or crankshaft sensor or pickup on the engine that is sending it information about the engine position that it might not be seeing.

I'm not in "limp home" mode that I can tell, as there is no limit on speed or RPM.

I'm about to have the car taken to a local shop for diagnosis, as I've pretty much hit the wall on this. Anything the collective wisdom of the group has to add would be deeply appreciated.


Last edited by LWB250; 08-21-2016 at 05:38 PM.
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  #2  
Old 08-21-2016, 02:33 PM
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Is the engine wiring harness the original or has it been changed?
If original, it will be bad.
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  #3  
Old 08-21-2016, 02:39 PM
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Wiring harnesses were changed years ago by the dealer. They're in good shape.

Thanks!

Dan
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Old 08-21-2016, 05:13 PM
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If you have 2 fuel pumps 1 may have failed causing a restriction to second pump, or dist caps may be carbon tracking = shorting under load, or crank sensor may have shorted due to coolant or water , last ezl ignition may be bad only firing 4 cylinders not all 8 , check test and report back
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  #5  
Old 08-21-2016, 05:23 PM
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One fuel pump, pressure is good at manifold during operation.

Distributor caps are relatively new (less than 10k) and have been inspected and cleaned.

Crank sensor was replaced about four months ago. I'm not sure what you mean by it having "shorted due to coolant or water" since it's a sealed unit and located on the flywheel housing away from any coolant or water.

Engine idles smoothly and takes off without knocking or roughness, just no power.

Thanks,

Dan
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Old 08-21-2016, 05:38 PM
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I would add that this condition started after the car had been parked outside in a damp area (next to a large open body of water) for about 10 days, during which we had about 10-15 inches of rain, too.

Dan
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Old 08-21-2016, 06:16 PM
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Even though crank sensor has o ring ive ran across 3 engines that got water in crank sensor and did what your describe poor power or little power under acceleration , easy to check pull plug and check for coolant or water leaking into crank senor plug
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Old 08-21-2016, 06:19 PM
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Also weak coil,s can cause that issue, but under hard acceleration will slightly buck or stumble
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Old 08-21-2016, 07:29 PM
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Quote:
Originally Posted by nulu View Post
Even though crank sensor has o ring ive ran across 3 engines that got water in crank sensor and did what your describe poor power or little power under acceleration , easy to check pull plug and check for coolant or water leaking into crank senor plug
And you are describing the crankshaft position sensor, or CPS, that's mounted on/in the flywheel housing, correct?

The CPS on my car is all one piece, that is, it's a molded assembly from the sensor all the way to the plug at the EZL. It's not a separate sensor that is mounted on the flywheel housing with a connector that plugs into the top of it.

I may pull it anyway to see if there is any crud on the end of it. Since it's a Hall Effect pickup if there are any bits of metal, say from shavings from the starter pinion and bring gear, on the end it will effectively short out the magnetic circuit.

Thanks!

Dan
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Old 08-21-2016, 07:30 PM
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Quote:
Originally Posted by nulu View Post
Also weak coil,s can cause that issue, but under hard acceleration will slightly buck or stumble
Nothing like that is occurring. Just lack of power at low speed. Engine runs smoothly, just revs slowly under load while you're trying to get it up to speed.

Dan
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Old 08-21-2016, 08:09 PM
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hopefully it was a Hella crank sensor.Bosch are not good ones.
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Old 08-21-2016, 08:11 PM
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I think it was a Bosch.

That being the case, why am I not getting any codes thrown if it's acting up?

Thank you,

Dan
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  #13  
Old 08-22-2016, 12:01 AM
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if its your airmass meter try unplugging it it should then be in fixed operating mode 50% setting ie computer will set to 50 percent mode and of course set code , but if it runs better at low speed may be that
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Old 08-22-2016, 07:32 AM
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Thanks! I'll add that to the list.

Because it seems like an ignition timing issue, I'm going to disconnect the camshaft timing magnets and see if it runs the same. Since they don't kick in until engine speed increases, it would be interesting to see if it has any effect. If not I know that they aren't getting a signal.

Does that make sense?

Dan
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  #15  
Old 08-22-2016, 07:37 AM
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one time I had a power issue that lasted a year.It was my crank sensor plug,not fully plugged in.

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