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  #1  
Old 02-27-2000, 05:14 PM
meb
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Hello, great forum! I found out i should try to post a question about my Mercedes to see if anyone can help me.

My 190E (1985 euro) has suddenly become hard to start. When cold, it will start within a second on the first crank, but dies right away. On the second try, it start just as quickly and keep running for about 2 seconds before it dies. On the third attempt it usually keeps running, but the revs are low at first, slowly rising to about 700 rpm, and it's running rough. If I try to push the accelerator while this happens, it stalls right away. When started with a warm engine (or with the use of a block heater), it starts just fine. When the engine has reached operating temperature, it runs fine, but the idle is maybe a little high (about 1000 rpm in Park)

Could this be an faulty overvoltage relay or fuelpump relay? Or could the injectors be clogged in some way? It feels like it's not getting the fuel it needs. I tried to change the plugs, but to no help. It seems like it's time to take it to the mechanic, but it would be nice to fix it on my own...

Regards
Meb
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  #2  
Old 02-27-2000, 08:02 PM
christopher
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Replace the cold start valve. It worked for me..easy to do yourself!
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  #3  
Old 03-01-2000, 01:22 PM
meb
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Thanks for the suggestion! But somehow, the car suddenly began starting ok again, even though I have to push the accelerator the first couple of seconds to prevent it from stalling. But now I am bact to my "old" problem. With a cold engine, the rpm are held at about 1000 rpm (due to the idle control valve, I guess). But after just a minute or so, the idle speed drops quite fast to about 700 rpm, like the valve is closing, and the engine runs quite poorly for a while, until it warms up. How long should the idle control valve work when the outside temperature is about 0 C ?
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  #4  
Old 03-01-2000, 03:57 PM
rbdrost
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Our past experience with this type problem revealed that the problem was a relay. The relay, which is located behind the engine on the firewall may be identified by it having a "GM" type fuse on the top. First, carefully check the fuse, if it is good, consider replacing the relay.

------------------
Bob1
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  #5  
Old 03-01-2000, 11:05 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
this is the overvoltage relay. It is behind the battery. You have to remove the plastic shroud to get to it. It has a red top and the fuse is under there. I'll bet you jumped the car off recently.

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  #6  
Old 03-02-2000, 12:37 PM
meb
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Thanks again for the help. I will take out the relay and check the fuse, and if it's not blown, try to replace the whole relay.
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  #7  
Old 03-11-2000, 06:45 AM
meb
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I checked the fuse in the overvoltage relay, and since it was not blown, I replaced the whole relay. But the car still acts the same. Runs ok for a minute or so, then the low and rough idle begins, goes away slowly as the engine warms up. My next guess will be a faulty temp sensor or bad injectors...
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  #8  
Old 03-11-2000, 01:27 PM
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Join Date: Mar 2000
Location: Gainesville FL
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quote:
Originally posted by meb:
I checked the fuse in the overvoltage relay, and since it was not blown, I replaced the whole relay. But the car still acts the same. Runs ok for a minute or so, then the low and rough idle begins, goes away slowly as the engine warms up. My next guess will be a faulty temp sensor or bad injectors...



Sounds like you could use some diagnostics. Because I am not sure of the on board diagnostics on that euro MB you should start by monitoring the EHA current. This can be done simply with a $30 multimeter in the 2amp mode.

You will have to make a jumper to allow for a current reading (in series).

All forms of fuel enrichment are controlled by the current flow through the EHA (electro-hydraulic actuator). This value for 190s only is 8ma with NO enrichment factors. A proper set-up (US version) lambda closed loop value would be 8ma with an obvious + and - swing of 1-2ma above and below at regular interval as determined by exhaust temp. A car close to zero will be correcting for a rich mixture by reducing current flow. A car cycling at 10-12 would be slightly lean and it would be correcting by higher current flow.

DURING cranking the value should jump by around 50ma. If the car was also cold the current would also add a temp correction current of more than 20ma (depends on temp - this is the part that the sensor affects). This temp correction current drops slowly and is responsible for the enrichment function done by a choke in a carburated motor.

Most of our techs keep a cheap multimeter wired for quick insertion between the EHA connector and the EHA. The whole system can be monitored in little more than the time it takes to remove the air cleaner.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #9  
Old 03-11-2000, 01:39 PM
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A proper set-up (US version) lambda closed loop value would be 8ma with an obvious + and - swing of 1-2ma above and below at regular interval as determined by exhaust temp.

One point of clarity. The 8ma uncorrected value only aplies to early 190s and VWs all other KE-Jet MBs are uncorrected at 0.0ma which makes their limp home driveability so good. They actually need no electric correction except for lambda and acceleration on all six and V8 motors...and late 190s.

The early control units didn't have the ability to go negative current flow for correction thus the middle of the correction for lambda was 8 with high of around 16 and a low of around zero.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #10  
Old 03-11-2000, 04:52 PM
meb
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Thanks again for the response!
I have been suspecting the EHA myself, since it seems like the engine don't get the extra fuel it needs when cold. The reason it don't stall unless very cold is probably since idle is set too high. I will try to test the EHA like you described. If the EHA is faulty, will the whole unit need to be raplaced? What will the cost of such an operation be?

By the way, my car does not have a catalytic converter, and thus no O2/lambda-sensor, like the US-models.
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