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  #1  
Old 10-27-2012, 10:16 AM
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Hard starting 1991 300CE (M104)

I have had ongoing running problems with this car and it is still running rich and getting poor mileage - I have posted before with little success in figuring out the problem.

Lately, the car is now hard to start - sometimes it takes 10 seconds of cranking, 2 or 3 times on first, cold start before it will finally fire up. Hot starts are OK...

It 'feels' like a fuel problem, but the fuel pumps do run when key is turned on. Problem is worse in colder weather, but once it starts, the car runs fine - no stalling, accelerates great - as stated above, still runs rich and I don't think the car is running in closed loop. My O2 sensor is a year old, but checking the voltage here indicates no fluctuation and my duty cycle drops to 3-5% and doesn't fluctuate much at all either.

I don't know if these problems are related or not...right now I'm just trying to figure out the hard starting/long cranking problem.

Any thoughts?

Thanks, ryan

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1984 300D
1972 250
1986 560SL
1991 300CE
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  #2  
Old 10-27-2012, 10:43 AM
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do you have a MAF or MASS sensor?Is it clean? Check for connections vac lines.Then try plugs.My 104 is hard on plugs,Using iridium next time.Of course I can't afford premium all the time.These are things I would check be spending major money
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Last edited by oldsinner111; 10-27-2012 at 11:53 AM.
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  #3  
Old 10-27-2012, 02:15 PM
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I have an Air Pot sensor on the side of the fuel distributor - haven't checked it. I have looked and looked and looked for vacuum issues...can't find anything. Plugs were replaced - probably 2 years/15K miles ago - regular Bosch plugs. Pulled a few recently and they looked fine...
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1984 300D
1972 250
1986 560SL
1991 300CE
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  #4  
Old 10-28-2012, 03:16 AM
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Quote:
Originally Posted by oldsinner111 View Post
do you have a MAF or MASS sensor?Is it clean? Check for connections vac lines.Then try plugs.My 104 is hard on plugs,Using iridium next time.Of course I can't afford premium all the time.These are things I would check be spending major money
Yes to all that except iridium. Don't bother with costly plugs on these engines. Bosc/Beru standard copper, non-resistor ONLY.

R
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  #5  
Old 10-28-2012, 04:45 AM
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I am not sure but could the timing be retarded because a faulty camshaft sensor.
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  #6  
Old 10-28-2012, 05:40 AM
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Ryan, have you checked the condition of the distributor cap, rotor and ignition wires? All are important to a quick engine start and smooth running ... plus properly gapped spark plugs.
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  #7  
Old 10-28-2012, 09:41 AM
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The rich running and hard start almost have to be related but, try this. Wire up a light directly to the fuel pump ( if you have 2 pumps, use 2 lights ). Turn the key to the on/run position and observe the light, it should be on for 3 seconds then shut off, turn the key off and repeat the cycle a few times. Crank the engine and see if it runs.

If it starts easily you are not building fuel pressure rapidly enough / have a leaking check valve.

I've had CIS cars ( SAAB ) with poor injector spray patterns cause cold start / rich running issues. The fuel gets drizzled in rather than atomized.

Pull the dist cap and rotor, check resistance from the coil end of the wire to the center of the cap then from each outer contact to the plug end of the wire. High resistance here can cause starting problems. Any spark plug will work, no need for the expensive ones.

Check battery voltage while cranking and see how it compares to the spec voltage for your car. ( Do this at the battery and positive side of the coil. ) I've had batteries with a bad cell that would crank all day long but voltage would dip too low and cause electronics not to function properly. This situation is much different than a discharged battery as it is more like installing a 10 V battery then running a 12 down.
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  #8  
Old 10-28-2012, 11:08 AM
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I'm using Iridium for my Nitrous
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  #9  
Old 10-28-2012, 02:04 PM
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Did you check the fuel accumulator? Did you check the fuel distributor? MAF will cause loss of performance. Do you have loss of performance? Until these are checked we can't give an answer.
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  #10  
Old 10-29-2012, 01:46 AM
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Quote:
Originally Posted by duffman1 View Post
Did you check the fuel accumulator? Did you check the fuel distributor? MAF will cause loss of performance. Do you have loss of performance? Until these are checked we can't give an answer.
I think it's the CSI system on this car so it will have a mechanical MAF. Still needs to work right though.

R
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  #11  
Old 10-29-2012, 09:00 AM
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Guys,

Thanks for all of the replies...

I have had the car 3 1/2 years - all new ignition parts (Bosch OEM) within the past 2 (?) years - new coil, cap, rotor, copper plugs gapped correctly, new wires...I guess something could have gone wrong here and I will pull the cap/rotor and take a peek. Have pulled some plugs and checked, and they looked fine (probably less than 20K on these new parts). Also, replaced the O2 sensor and the fuel accumulator previously.

This is a CIS-E system with the M104 motor - has a MAF sensor on the side of the fuel distributor - have not checked it as I'm not sure how. Also, I'm not sure what I would do if it was bad - can't find the sensor anywhere now.

Yesterday, car would not start in the morning before church - in the 30's here Sat night - car cranks and cranks until battery starts to drain, but no start. Come home and try it around 2:00 and car starts after some (less than normal) cranking. Again, I should emphasize that the car runs GREAT then - you wouldn't know there was a problem at all running down the highway. BUT, it is running rich - no doubt about that as my duty cycle issues have been documented in previous threads. But, it has been running rich for a while now - just started with this no start/hard cranking problem...

Also, I have tried turning the key on and off - and I do hear the fuel pump(s) running - but it doesn't help. When it finally starts, it does so without me touching the gas pedal at all. If I hit the gas pedal too quickly, it will die - but then it will start right up again. It 'seems' like a fuel problem to me - warm and hot starts are OK.

Ryan
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1984 300D
1972 250
1986 560SL
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Last edited by rgnprof; 10-29-2012 at 11:11 AM.
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  #12  
Old 10-31-2012, 04:07 PM
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Same problem today - car sat overnight and temps into the low 40's and it was 44 when I went out to start it. Didn't start, cranked and cranked and battery slowed down so I quit...

Went back out this afternoon - temps in the low 70's and the car fires right up...well almost. When it is working it will usually fire right up and then die unless I give it a little gas, but the second time I crank it, it stays running.

This is clearly cold weather related...

Any thoughts?

ryan
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1984 300D
1972 250
1986 560SL
1991 300CE
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  #13  
Old 10-31-2012, 05:09 PM
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Quote:
Originally Posted by rgnprof View Post
Same problem today - car sat overnight and temps into the low 40's and it was 44 when I went out to start it. Didn't start, cranked and cranked and battery slowed down so I quit...

Went back out this afternoon - temps in the low 70's and the car fires right up...well almost. When it is working it will usually fire right up and then die unless I give it a little gas, but the second time I crank it, it stays running.

This is clearly cold weather related...

Any thoughts?

ryan
The coolant temperature sensor needs to be working - it's a cheap part so worth replacing. There's also an auxiliary injector for cold starts and that will be triggered by the temperature sensor (via the injection control module).

If the car works well hot, then it sounds to me as if the mixture is not rich enough when cold. Either the system knows it's cold and is not able to inject more fuel or the system thinks it's not cold. Again, aux injector or temperature sensor.

I haven't had to think much about your symptoms because all problems I've had (exactly the same system) have been the reverse - fine cold starts, problems when hot.

All I can recommend with confidence is that you start with cheap parts if you're in doubt. There's only one temperature sensor and it's cheap. Oh, I've just forgotten the air intake sensor that we have in our systems and it's attached to the side of the air filter housing. You need to unplug it to remove the air filter housing so you can't miss it. Again, it's a €20 part so easily replaced.

It's also worth making sure that fuel filter is in a good state - although, for me, a bad filter affected hot running more.

Your MAF is not on the side of the fuel distributor, the fuel distributor in mounted above it! (unless I misunderstand). I think you are referring to the so-called governor (or EHA) which is a fine tuning device associated with the basic, electronic side of the KE-Jetronic system. I don't think that's the root of your problem. Your MAF is the hinged plate in the air intake, just under the air filter.

Your duty cycle suggests very rich mixture. Have you tried adjusting it to 50% (fluctuating)? Are you able to adjust it? What does it read Ignition On/Engine Off? Does your MAF move smoothly down when you press carefully down on the plate?

Don't throw money at the problem until you are 100% sure there's a faulty, costly part. The system is tried, trusted and very reliable, assuming it's maintained well with.

Keep calm, keep at it and report progress.

RayH

Last edited by rayhennig; 10-31-2012 at 05:24 PM.
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  #14  
Old 10-31-2012, 05:12 PM
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Possiby a bad coolent temperature sensor? I've seen other posts on the forum with a similiar issue solved by temp sensor. Try a search on coolent temperature sensor.
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  #15  
Old 10-31-2012, 05:26 PM
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I JUST replaced the coolant temp sensor with a new FAE one...It was my first suspect as well and I just ohm'd it out a little bit ago and compared it to the old one - which I still had around. They were fairly close to each other - around 2.5K ohm's at about 72 degrees ambient temperature - BUT, that doesn't say anything about what the ohms are at less than 40 degrees...

I have replaced the fuel filter as well within the last month...

How do I check the cold start injector valve?

ryan

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1984 300D
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1986 560SL
1991 300CE
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