M103 W126 Misfire/Sputtering only at certain times
 

Hi All,

Wondering if I can get your expert M103 advice. I've been working on 617 and 603s for a long time, so I'm kind of green on the gassers.

Working on my 91 300SE. 270K miles.

Heres what I'm experiencing:

The car starts and idles fairly smooth, if you accelerate gently, there are no problems. However, if you give it more like 1/4 to 1/2 throttle, the car sputters and coughs, and stops accelerating, then eventually will work itself out and go back to normal. This is especially fun when pulling into traffic.

In the driveway, idling in park, if you rev it gently, you can work up the rpm just fine with no drama. If you give it 1/4 to 1/2 throttle to rev it up, the engine does the whole "chug, cough, sputter" like its about to die, then comes back alive again and acts normal again.

Car has new:
Fuel Filter
Plugs (non resistor)
Cap
Rotor
Plugs
Wires
Engine Mounts
Oxygen Sensor

Any advice?

Thanks in advance!:D

Sounds to me like a fuel issue...Check out your mixture and EHA functionality. If you have a fuel pressure gauge that will help too, although it cannot show functionality of the EHA, only that is is regulating the correct pressures.

there is a small filter at the end of fuel pipe end connection to the fuel distributor It .may be clogged;.engine should run fine in warm up mode as the oxygen sensor,EHA is not operating - open loop mode.
mak
300se

'Theoretically' yes, but in application this is not true. EHA's can cause strange power and fuel issues even if everything else checks out fine.

I f faulty , the EHA can be disabled at the connector ,Checked with a cold engine ,warming up stage and finally operating temp.
mak
300se

Could be a fuel pump or fuel pump relay problem also. My sister's 190e has slightly noisy/weak pumps and it sputters a bit if you punch it.....but is fine otherwise.

Did you try checking for codes stored by ecu? Might be a good starting point , How were the spark plugs looking when you removed them? Broken electrodes? Carbon Deposits? Build up?

I have driven the car, not totally convinced it is fuel related (such as a restriction or weak pump) as it seems to pull fine at full throttle. It has new cap/rotor/wires/plugs.

I am thinking it is a part throttle electronic adjustment as I do not recollect the EHA tower ever being opened or potentially TPS dead spot.

Vac is pretty stable from memory but have not looked to see if the injector cups leak or anything else related to the CIS system.

Just food for thought: When I bought my 260E I had a massive lack of power at anything below 3000rpm. Soon as it hit ~3k it would accelerate VERY hard. I did a complete tuneup and problem still persisted. I checked fuel pressures and everything was to spec. Your description sounds almost exactly what I experienced except my 2.6 never 'sputtered'. It just pretty much just stopped accelerating entirely for about 3-4 seconds then slowly spin faster and faster until it would open up fine at above 3k.

I swapped out the EHA for the hell of it and suddenly it was a completely different animal. No more bottom end power issues and it passed smog too. Fuel pressures were still the same as well showing it was not a simple condition of the new EHA providing a richer/leaner condition.

The EHA can influence some very strange running conditions that don't make sense according to K-Jet diagnosis and spec. Remember these engines are old and may not always act as suspected.

I would suggest going to a local junkyard and grabbing 2-3 of them so you can rule them off. Seeing as it is only 2 bolts, it is easy to swap.

Fiddling with a new EHA isn't a terrible idea, but I would make sure to have two brand new EHA o-rings before taking the old one off. They probably won't want to seal again.

I've had similar issues when one side of my coolant temp sensor died. Easy to check......

Picked up a used EHA off Fleabay, will install and report back!

Maybe TPS as hitman mentioned, or a sticking main air valve in the throttle body. Let us know results of the EHA testing.

DG

This might be the problem that I once had. Check this before everything else: pull off the signal wire of the lambda sensor, it's under the front passenger seat.

The logic is this: defective lambda sensor sends the wrong signal to the ECU making it wrongly command the EHA leading to the problem of irritating acceleration.

If that's not the one then check other things.

this issue sounds directly related to the one im experiencing,i replaced both fuel pumps ,the filter, the opv and the eha,the car still does the same thing as described here,i still need to replace the o2 sensor,i dont see that an o2 sensor can solve all these issues,the eha i purchased was used on ebay,im thinking its a defactive sensor,i would def. check your eha,there about $45.00 on ebay,$250.00 brand new

UPDATE:

I borrowed a duty cycle meter.

Hooked up positive to 3 and negative to 2 on the connector, and got 81.43%.

Started the car, which is already at operating temp, A/C off, and was still at 81.43.

Revved it up to about 2000 rpm and started to see it move, let off and back at idle, it was moving from 81.43 to 80.99 and 81.76 never leaving that range. I revved it back to 2500 rpm and the 3 values above still showed up.

Turning the AC on made no difference.

I think someone posted here a while back that if it stays around a certain percentage, that translates to possible faults.

80% was coolant sensor?

Any help is appreciated.