Exhaust gasses out the intake??? M103 - NOW FIXED
 

Hi there, I've got a 1990 190e 2.6 with the KE-Jetronic fuel injection system and a 5 speed manual transmission. Circa 120k miles.

A little background to my problem first. Occasionally, when I had stopped at some traffic lights after the engine had got to full working temperature, it would die if I put my foot on the gas too quickly. If I kept the revs above 1500 or so, it would drive fine, as though there was nothing wrong. The problem got gradually worse so that if I put my foot on the gas at all, it died. Sometimes it would restart almost straight away, more often than not, it needed ages before it would restart.

Anyway, I've tested all the sensors that I can, tested fuel pump and OVP relay - both appear fine (although I did go through and re-solder all the joints on them both anyway). Idle control valve has a good healthy pulse to it when cranking, pin 3 on the diagnostic socket checks out with 70% duty cycle (checked with an oscilloscope).

I left the car on my drive for a few days, now when I go to start it, it generally doesn't want to know, and when it does try to start, it makes an awful noise (like the exhaust is blowing, but it isn't...!) and tries to blow smoke out of the air intake (air filter is off).

One thing I've (stupidly) done is mess with the mixture screw (the one that you access by putting a 3mm allen key down through the air cleaner) and have no idea where it was set. How can I re-set the position of this screw?

What's my next step? What would make it try and blow gases out that way? It's been about 2k miles since I rebuilt the head with new valve stem seals. Is it likely to be a vacuum leak (can't find one so far), or something broken within the engine (although there's no funny noises).

I'm stuck, help!!!!

Cheers, Martin

Sounds like retarded ign timing, any chance the distributor is loose, or it's internals loose? A loose distributor will slowly retard as time goes by causing power loss and higher temps. Blowing exhaust gas out the intake means the engine has rotated backwards. Not a big deal, just means it's having trouble with fuel or ignition, usually the latter has been my experience. I can't help with the idle screw, I messed with mine too, but I just had the luxury of adjusting it by feel on a normally running engine.

Timing on the M103 is controlled by the EZL module and position sensor on the crankshaft damper and is not adjustable by rotating the distributor, which on the M103 is just a secondary distribution system at the front of the head driven by the cam, but I would certainly recommend a timing check. The value is listed on the emission/tuneup label, and my '88 is 9 degrees BTC. If the timing is in spec the EZL and crankshaft position sensor are probably okay.

There may be multiple problems here, but you can start by checking the ignition timing and setting the basic mixture adjustment properly. Print out the following web pages, read them thoroughly, then set the basic mixture to obtain an average 45 percent duty cycle at idle. Sears has a VOM with a duty cycle function for about forty bucks.

www.landiss.com/mixture.htm

Also check the PCV system for clogging. Pull off the small hose from the cam cover at idle. You should feel light suction. If not, the system may be clogged forcing blowby "backwards" through the large hose that routes from the cam cover to the air cleaner cover.

Duke

You'll have to excuse my ignorance, but what is the PCV system? What does PCV stand for? Also, I'm in the UK and am yet to find a meter that has duty cycle on it. :confused:

Cheers, Martin

Positive Crankcase Ventilation

Duke

Does your car have an EGR? If so, it's stuck open.

To re-set the fuel mix you are either going to have to get the engine running or jumper the fuel pump relay to get fuel pressure, then carefully loosen the injector lines on the fuel distributor and turn the idle mix screw slowy rich until fuel starts to bleed out. This will get you into running range, you can then adjust it with the duty cycle (70 is too lean, I think). Should be 40-50% or what it runs at 2500 rpm, whichever works better.

It's also time to replace idle control valve hoses, and any other rubber vac lines that aren't in good condition. Also, check the connection for the brake booster, it can work loose and give you fits.

Terrible blowby will also cause this, but you would have to have an engine in really rotten condition for that to happen (or a blown head gasket -- worth a check).

Peter

Dummy question no.2

What's the EGR valve? Is it on all 190s around this age? I've never heard of it... Thanks for the other info too

Cheers, Martin

Exhaust gas recirculation -- meters exhaust into the intake to reduce flame temps and therefore nitrogen oxide emissions.

I don't know if you have one or not -- my 88 TE does not.

Classic stuck open failure is dying immediately on startup and exhaust gas in the intake (makeing "smoke"), and failure to idle unless the throttle is held open.

Non functioning exhaust valve will do the same thing, though -- I've never heard of a rocker breaking on an MB, but I suppose anything is possible.

Peter

Exhaust gas recirculation -- meters exhaust into the intake to reduce flame temps and therefore nitrogen oxide emissions.

I don't know if you have one or not -- my 88 TE does not.

Classic stuck open failure is dying immediately on startup and exhaust gas in the intake (makeing "smoke"), and failure to idle unless the throttle is held open.

Non functioning exhaust valve will do the same thing, though -- I've never heard of a rocker breaking on an MB, but I suppose anything is possible.

Peter

What does this EGR valve look like? What pipes/hoses/wires are going to it? Does anyone have any pictures of one? I'm fairly sure I haven't got it, but y'never know!

I've had the rocker cover off and cranked the engine, there didn't appear to be anything wrong, all the rocker arms were moving away, and there were no untoward noises. Given that it occasionally does start, and was running ok before the problems, and there are no nasty mechanical noises, I'm 99% certain that the engine itself is mechanically ok.

Cheers, Martin

Fixed it!

It was nothing more complicated than a rotor arm that had started breaking down under load, fitted a new one and she's running as smooth as ever.

Thanks for everyone's help (on this and other folk's posts) - would have struggled without you all!

Cheers, Martin

70% duty cycle is too high. 50% +- 5% is ideal. Is the duty cycle fluctuating. At idle it should rise and fall. This rise and fall is a result of the ecu responding to the O2 sensor. If you are not seeing this rise and fall go to the o2 and pin test it. Use a DVOM and put your negative lead on the o2 ground not a body ground as I have been screwed this way before. (Rust build up between the O2 and the exhaust can cause a faulty ground to o2) Put your positive lead on the o2 signal wire. Now observe the graph produced it should sweep nicely up and down on a 5s view. Voltage should be between .2 to 1. If you are not seeing this or if the o2 does not respond with a spike to throttle snaps replace it.