230E on 3 cylinders

[markalexander]

After checking oil, fuel (decent stuff) etc, set off in my 1987 230E which had occasionally been misfiring under load, but now seemed good. after a good run of 200 miles with no problems, the missing under load returned occasionally, but otherwise 90+ cruising in a fully loaded car was fine with no ill effects. On slowing from a steady cruise, it cut to 3 cylinders and was nursed home.No noises or nastieness, just running on 3. New plugs were fitted to replace the crusted grey originals, but no difference. Any ideas? fuel injector? Rather stuck now! I have basic mechanics knowledge but wary of going into unknown territory.

 

[Charles Morgan]

Are all cylinders getting a spark? If not check the distributor cap. Otherwise could be a blocked injector.

 

[Will]

Probably distributor cap or leads - remove the cap to check the condition of it and the rotor arm. Cheap enough to replace if in any doubt (cracked/burnt/corroded etc).

Sometimes you can see the leads arcing out onto the cam cover/head if you leave the engine running and pop the bonnet open at night.

I would definitely start with checking the HT side of things first before you look at injectors etc.

 

[Ray Castle]

When it's dark, with the engine running, open the bonnet. You'll clearly see any sparks indicating faults or breaks in the ignition leads.

 

[grober]

W124 Erratic Misfire - Mercedes-Benz Owners' Forums
this thread details several areas worth checking

 

[avoidme]

Take a long screwdriver and a jump lead, attach one end to the screwdriver the other to a good ground ( not the battery terminal ) then start the car and move the tip of the screwdriver along the wires and on the distributor cap. The spark will find it's way to the ground in the arcing spot, just make sure you always grab the screwdriver by its handle and do not touch metal.

 

[avoidme]

You can, however identify the bad one by doing a power balance test. disconnect them one at a time and you will feel the one not contributing. Then you check the if you get spark using the same rig as above. If you do get spark, my money is on the plug.
Good luck

 

[markalexander]

very confused now!

Found cracked/ burnt contacts in distributor cap. replaced with new cap and arm, fitted very carefully. now will not run at all. fires but stops. put original running on 3 distributor cap and rotor back on to get back to original good starting but on 3. car will not start on that setup either. checked leads and plugs but baffled. only thought car is parked nose down on slope for 4 days with about 10% fuel in tank, could this affect it?. Now waiting as battery needs recharging....

 

[optimusprime]

Mark put the new parts back in .Crack open one of the fuel injector feed pipes .See if its got fuel up to the injector .

 

[grober]

Classic fuel pump relay symptoms. Do you hear the fuel pump running to pressurise the system on ignition switch on. [ first stage] If this happens the engine may start but the FPR then switches to [stage two] which needs an engine running signal to continue to pump fuel - its a safety feature to stop fire if the car was to crash -the engine stopped but continue to pump fuel! You can test this by shorting out the main FPR contacts to see if the car will start- caution this is only temporary as the safety feature is disabled and the pump will run continuously till disconnected manually. Its that or repair[ resolder] or replace the FPR --- lots of threads about this on here.

 

[Will]

Found cracked/ burnt contacts in distributor cap. replaced with new cap and arm, fitted very carefully. now will not run at all. fires but stops. put original running on 3 distributor cap and rotor back on to get back to original good starting but on 3. car will not start on that setup either. checked leads and plugs but baffled. only thought car is parked nose down on slope for 4 days with about 10% fuel in tank, could this affect it?. Now waiting as battery needs recharging....

Have you made 100% certain you've got the leads fitted in the correct order? Did you take any pics? Or post one to compare (or have a look online )

Also possible that you may have damaged a lead on removal/refitting - especially if old/fragile or already faulty.

Obviously you need to check the fuel side of things now that is in question but if it was starting/running well enough to drive before it sounds quite possible that it's related to the work you've just done.

 

[grober]

Firing order 1342 1 is the cylinder at the front of the engine.
Distributor Cap - Service Items

 

[optimusprime]

Grober your right , but it will need to have the leads in the distributor in the right order .The distributor should be marked - 1 to 4 ..or 1342 ..

 

[markalexander]

leads on new distributor now in correct order (idiot) car now runs perfectly on 3 cylinders again. what is the best way to check ignition lead condition and after that how to deal with a blocked injector if not the lead (new plugs fitted)

 

[grober]

Almost certainly where the HT lead joins the metal suppressor cap that clips on the plug. Its easy to break them when taking them off. In the old days you would have put the car on an oscilloscope engine analayser and compared the firing lines on all the plugs the dodgy one shows up clearly. https://www.google.co.uk/url?sa=t&r...fC9vAGID6L5lBQ&bvm=bv.147448319,d.ZGg&cad=rja

 

[markalexander]

checked all 4 plugs via the old method- earthed lead and plug and briefly turned motor over, sparks on all 4. I realise that they can fail under compression, but this is the best tech I got. Air filter removed to see injectors and pump, wondering where to go next ( Used to be a motorcycle mechanic years ago, now work as design engineer, so got some mechanical sympathy, despite mixing the leads up on the distributor)

 

[grober]

Remember that you have the continuous injection system CIS meaning that the injectors are not electrically pulsed they are purely pressure driven opened above a certain fuel pressure acting on a spring and will basically open at the same time. They do have an internal filter which can get blocked.

http://www.berlinasportivo.com/Technical/lancia/Thema832/Bosch-KE-Jetronic-OCR.pdf

 

[markalexander]

Thanks for the info, now got to work out what to do with it! Car revs cleanly when the high speed enrichment kicks in, but settles back to 3 when throttle released.

 

[grober]

Maybe your fuel pressure isn't high enough primary pressure should be between 5.3 and 5.5 bar irrc--- when was your fuel filter [ beside the pump] changed last?

 

[John Jones Jr]

If the coil looks original I'd change it regardless and you should do the same for the plug leads also - good preventive maintenance on a car of that era. If you have a multimeter you could test the resistance.

But initially I'd stick with looking for an ignition fault and then move on to fuel.