Thread: 190E hard start
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Old 03-11-2000, 01:27 PM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
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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