230TE Poor cold starting

[AlanWT]

Hello All -

230TE, H-reg 1991. When cold, it fires and reluctantly starts but cuts out the instant I so much as glance at the throttle. After it has ticked over for a couple of minutes, it is fine and I can then drive away.

Advice/opinions welcome!

Cheers

Alan

 

[simon j paynter]

Alan if you go back a week or so you will find a thread of posts all about poor starting and uneven running from cold- no one seems to have definative answer , but there are a number of things to try- new plugs leads etc the fuses for the ECU finally there is a fix as detailed on a technical benz website elsewhere involvinf soldering a resistor inline to the air temp sensor for the mixture control on the ECU ( I think that is right ,if you find the thread you will see)
Oh I've found it on file
Rough Starting
by George Murphy, Technical Committee Chairman, Director at Large
Question:
I have an 86-300E that requires several seconds of cranking when cold to start. It dies immediately. Then it starts the second try and keeps running, but VERY ROUGH. It gets better the longer it idles. After about 20 seconds or so it’s better but still rough. It is fine after completely warming up (i.e., several minutes). Any suggestions?
Answer:
If you are sure it is not:
old spark plugs (use only Bosch H9DCO regular set at .8mm - do not use platinum plugs - they foul and cause rough cold idle)
old spark plug wires (change at 100,000 miles
old rotor and distributor cap
carbon on intake valves (add LM Ventil Sauber or Techron to the fuel tank and take car on sustained high speed trip to clean it out)
bad fuel
Then:
There is a fix for 300E's that involves a special part costing $70 that will smooth out rough idles (once all other causes are ruled out). Or you can fix it for 15 cents. The fix is to snip the wire to the injection system engine temp sensor B11/2 (rear of cylinder head on left side) - it is a green wire with a red stripe. Then splice in a 470-ohm resistor in series. This has the effect of telling the injection computer to enrich the mixture just a bit at idle.


hope this helps
Simon

 

[talbir]

The most common cause of the symptoms described is a bad OVP relay or fused OVP relay.

Behind your battery, there is a black plastic panel - pull this out and you will see a few relays, one which is silver, approx 1inch x 3inches high. It has a plastic flip lid on the top (usually red) and inside the lid is a 10amp fuse. Check the fuse - if it is blown, then this is most probably the cause.

The cold start system, i.e. the cold start injector, idle air valve etc are all controlled via the OVP relay. It also protects the ABS system.

So if the OVP is shot or fused, then cold starting is going to be very rough.

 

[AlanWT]

Re. OVP Relay

Talbir - If the OVP relay or it's fuse had failed, would the ABS warning light on the dash come on? (it hasn't). I'll be checking the fues and relay out at the weekend - be nice if a blown fuse was the problem, although no doubt a little voice inside my head would then start asking why it had blown. Nice collection of vehicles, by the way!

Simon - Thanks for that info: very helpful.

Alan

 

[talbir]

YEs, the ABS light will stay on if fuse is blown.

However, does the ABS light come on with key in position II ?

If it doesn't then the bulb may be blown so not a good check.

I would still check the OVP relay - it only takes 2 mins and just clean up all the contacts.

Also check the voltage at your idle air valve and cold start injector on cold engine. Cold start injector should receive voltage for approx 3 secs on cold start when firing engine (possibly more depending on how cold system is on start up).

 

[AlanWT]

ABS light comes on with key at position II, so perhaps it isn't the OVP. I will still check fuse and clean all contacts, however.

The reluctance to start and low idle speed and stalling if the throttle is touched before it has warmed up for about a minute would seem to suggest that both the cold start valve and the auxilliary air valve/rotary idle valve (haven't looked to see which is fitted yet! - it's a 1991 model) are not working correctly. Does this seem a correct assumption?

If so, it seems a bit of a coincidence if both parts have failed. Where does the auxilliary air/rotary idle valve obtain it's engine temperature information from - it's not the same place as the cold start valve is it?

I will change plugs, leads and disi cap before I start down any more expensive road, but does anyone know a source of reasonably priced Bosch spares?

Cheers

Alan

 

[Neilc]

If the OVP is not working, you will not be able to cold start a vehicle - or it will be very difficult to do so, especially in these cold, snowing conditions. If you can cold start a vehicle with no OVP then the baseline mixture is set far to rich and you will suffer with poor fuel economy or rough running when hot.

When starting in conditions like today, the cold start valve will squirt a little extra fuel in there to get the vehicle to run a few revolutions, then the ECU kicks in to modify the fuel delivery to run the vehicle rich until correct op. temp. is established. The sensor responsible for this procedure is the coolant temperature sensor located on the top on the cylinder head at the front of the car. I'm not sure what one you have but the one on my 190E 1989 has a conical black rubber top, when pulled off reveals 4 poles. Each pole opposite each other is a pair. You need to measure the resistance here and see if it is within spec for the given temp. If it's open/inifinity the sensor is toast. You may have a two pole sensor, only the later cars with used four, 1 pair for ignition the other for fuel mapping.

It sounds like to me you are running just rich enough in your mechanical mixture settings to allow the car to idle ok with no post start enrichment. K-Jet systems can run without ECU control, and you would normally set the baseline mixture ECU unassisted - but this is a whole 'nother topic.

When you accelerate the engine when cold it sounds like no fuel is being added by the ECU. The ECU should add this fuel via the EHA - electro hydraulic actuator located on the side of the fuel distributor. A black box with a two pin connector. The fuel distributor has all the fuel lines going out of it to the injectors and sits on top of the AFM - air flow meter.

If the CTS is open then you won't get any post start enrichment.

Unfortunately, this is only one factor that could be causing this problem. There are many others.. Do as you say first, change the ignition system components, rotor, plugs, cap + wires & coil if you want to. A weak ignition will wreck havoc on cold starts.

 

[AlanWT]

Neil -

Thanks for that. Is the CTS where the dash temperature display also gets it's information? - the gauge appears to be working OK, which would seem to suggest the CTS is working.

Perhaps the sensible thing would be to take it to a Bosch specialist for a diagnostic test.

Alan

 

[Neilc]

Where are you in the country? I know a few specialists.

The digital dash temperature display isn't related to the CTS unfortunately.

 

[AlanWT]

I'm at Taunton in Somerset. There is a Bosch specialist listed in the Yellow Pages at Chard, which is only a few miles away. Company is Tytherleigh Vehicle Electrics. Don't know any more about them than that.


Cheers

Alan

 

[talbir]

The coolant temp sensor sends a signal to the CIS Control relay, which in turn sends a signal to the fuel pump, which then acitvates the cold start injector and fast idle through idle air valve.

To check your coolant temp sensor is working ok, you can unplug the 2-pin loom at the cold start injector and test if one of the pins is receiving 12V on turning a cold engine. OR remove the two 5mm allen bolts holding down the cold start injector to the manifold and place the injector in a small injector and see if fuel squirts out into the jar on start-up of cold engine. Be careful of course.

The coolant temp sensor only rmains close for approx 3secs at 1.5degC, 1 second at 3deg C and 12seconds at -20degC. The coolant temp sensor opens up after this time and will not function until coolant temp drops below 20degC. SO you need to check on the first time you turn engine on a pure cold start.

You can cold start the vehicle if OVP relay is shot and without mixture benig too rich - it will just take time to get turning. It is harder on 4-cylinder models. On a V8, car will cold start first time even with no cold start injector.

The coolant temp guage has a different sender to the one feeding the ignition ECU and CIS ECU.

good luck.

 

[Neilc]

You should be fine with a Bosch specialist, the systems are similar from manufacturer to manufacturer with only small changes so they need not be a MB specialist. Good luck!

 

[MikeC]

Symptoms are typical of very rich mixture.

This could be that your overall mixture setting is way too rich so the addition of fuel from the Cold Start Injector takes it to the point that any additional fuel from the throttle will kill it.

Alternatively, the Aux Air Device could be faulty or it's pipe is blocked.

Soot at the end of the exhaust pipe can be a giveaway as can black exhaust smoke.

Mike

 

[AlanWT]

May have found the problem.

Followed all the advice: checked OVP relay & fuse; changed plugs, leads, cap, rotor arm & coil, then took off air filter housing and looked at electrical connections to cold start valve and auxilliary air valve. The leads supplying power to the AAV were loose. The connector block has self-gripping plastic tabs that hold the leads in, and these no longer grip the wires so that they are very loose.

Don't know if this is the cause, or if this is something that someone has done whilst previously looking for the problem. I'll get a new connector (from local MB dealer, unless someone can recommend somewhere else?) and see if this sorts it.

Alan

 

[Arnie]

hello,

I have been absent from this forum for a while and just saw this thread of messages.

I have had trouble cold-starting a 1997 300E engine (on a G-wagen) since the car was new. The dealer had several goes, while under warranty, but never found the problem, so I have just lived with it.

It normally just takes several seconds of cranking, with a pause in between, to start the engine.

A month ago, however, the car lost power when my wife was driving, sveral minutes after cold-starting in the morning and setting off. When she told me, I checked the car and found nothing. Then, the other day, it did the same to me. The engine starts somewhat rough, idles OK, but has no power when accelerating and immediately dies on pressing the accelerator. Re-starting is then difficult and rough. But when the engine is warm (temp gauge on 80C) it seems fine.

Today it was fine and so it may be an intermittent problem, but it has never done this before.

Plugs, Distributor, HT leads and ignition electrics, I think, are OK.

Could this be the OVP, fuel pumps, or something else?

thank you


Arnie.

 

[Andy]

Hi Arnie


Long time no see. I would start may be with the OVP. Fuel pump relays tend to play up more when hot. But I would not discount it.


See how you go.

Regards

Andy@ www.mercedesservicing.com

 

[Arnie]

Andy,

Yes, it's been a while, but glad to be back. Thanks for he advice. The car's been fine the last couple of days (apart from the usual hard-to-start-when-cold problem), but I'll try to look at a few things this weekend. Actually, I was not able to find the fuel-pump relay and it may all be integrated with the OVP, which does the ABS as well.

Thanks