UH OH. .

If you are getting 12.4V with the key to on, that means the lambda system is not operating at all, it's not making any adjustments to the mixture. Your car is not going into closed loop for sure!

Ok. So referencing the factory manuals. 100% duty cycle with the key on, means that the system is "Operating without fault recognition". Which is not good.

KE control unit = ECU. And you've already put in a new OVP. Can you swap a good used ECU into the car? I believe that might be your culprit. I just replaced the ECU in my car, because I had failed emissions by 4500%! They do go bad. Which is what your lambda reading is indicating with the key on. My bets on that! Once you replace the ECU, that 12.4V should turn into exactly 7V. Then you will be able to take a real reading at idle, and the adjustments will actually be doing something. You want the voltage at idle to swing about 1V on either side of 6.5V.

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1991 300E - 212K and rising fast...

I'm going to get some accurate figures first thing in the morning and I'll be back with those duty cycle numbers.

No test to the 02 sensor not yet - next on my list. I failed my emissions test though about 6 months ago and they told me the catalytic converter is toast essentially. Would an 02 sensor replacement be any advantage with that in mind? Pins 2/3 will tell me tomorrow regardless.

The "Micro-Switch" is news to me. Point me in the right direction please? I'll do some searching in the meantime.

In the morning I'll redo this test a few times and pin the reading down exactly. We did it on the fly the other day at closing time but I'm almost positive it was the number above.


Yup my e-test failed miserably too. This sounds very positive and relates closely to problems I'm having. Several good OVP swaps with no great improvement hollers ECU. I suppose I could try and swap the unit from the 300E I just purchased that is running like a top. I'd hate to introduce it into this problematic car's system if it might damage it however? There's a couple of 87s on my friend's lot that I could likely try out since he uses those cars for parts. Would the ECU for the 87 be the same as the 88?

Thanks for the input John and all.

Yes, the compatible ECU range is 86-89. So the 87 ECU will swap right into the 88.

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1991 300E - 212K and rising fast...

Excellent. I'll be back later today with the goods!

You won't get a duty cycle reading with the system not going in to closed loop. The duty cycle is the fluctuations you get once it's in closed loop.
The cat won't matter, the O2 sensor is before the cat, the cat only affects what comes out of the tailpipe, not the engine.
Gilly

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The Micro-Switch is located at the throttle. It's a simple 2 wire circuit, the switch should be closed at idle. You can hear it click when you push the little wheel in with your finger. If unsure, check the continuity with a VOM.
If it's not closing at idle, then the linkage needs adjusting...(the plastic adjustment screw the cable goes into).

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

First thanks again to JohnM, slk230red and now Gilly..and anyone else my bad moemory has overlooked.

I've got good news and of course always bad news.

We ran the duty cycle test this morning. I was almost positive that idle reading was way low but oddly today (perhaps from a good cleanup yesterday of any plugs and sensors I could get to) at idle today we got 3.65 volts. Key in the on position read a healthy 6.8. Good chance my original call was off because as I mentioned it was a hurried test but today we did it right. At 2500rpm there is however no fluctuation and the readings stayed virtually the same - 6.8+- at any rpm. Ok so this rules out an ECU I assume and also looks like the OVP is doing what it should do. If I read slk230red's article right yesterday the roughly 50% ratio (3.65) voltage indicates the 02 sensor is shot - which makes complete sense. Nice to find out what it does is not realted to a bad cat Gilly. All in all things went good today - some plug changes and another set of wires later the misfire #6 seems to have cleared up nicely. Still a bit of blue smoke, no big deal. Good enough to advertise and sell.


Use this space to add anything that you care to before I go on to the "bad" news next paragraph down.




The bad news:


I drove around problem-free today after testing. Parked the car and left it for a few hours. I just went out to go for another drive - the car started fine - ran 20 seconds and quit abruptly.

I could now crank til the cows come home - it won't fire up. I can hear the fuel pump winding up for about 3 seconds after key in on position before cranking, but that noise it makes stops after those 3 seconds - first question then - should that fuel pump constantly make that buzz/clicking noise I hear when I turn the key to the on position or is it normal for that sound to stop like is now doing? Again this is before cranking at all, just listening for the sound when the key is in the on spot.

Same thing happened with the FPR a while back, but i now have three working FPRs from parts cars. I'm ruling the FPRs out - car is a no-start swapping any of the three. I loosened off the fuel line under the air filter and there is gas there for sure, I was alone here so checking for a good solid flow while cranking wasn't possible. I kind of think that fuel pump is garbage and your answer to my question about the whirring noise stopping or being continuous will tell me for sure. The gas in the line may just be sitting there and no getting enough pressure to have ignition.

Could you also let me know how to check my coil for any spark - or should I just pull a plug and look for an arc if I can find someone to crank it for me in the daylight? Assume insulated pliers would save my butt from a good shock? I'm totally stumped at this point as to why it's a complete no-start.


I've been cursed , just kidding of course, but after all the rest this week this isn't what I expected.

Of course the logical driver would say get rid of that old German junk and buy a Ford - (haha) that's part of the curse, that old German junk gets in the blood and driving a Ford is no longer an option.

Signed
Better days ahead I hope.

I'm sure I cleaned that switch yesterday. I did every plug-in I could see in fact. I remember it since it was the only one that had those two prongs with the third plastic guide pin in the middle. Odd i don't recall ever noticing the little wheel though. Perhaps it's not the one I'm thinking of. Do you have a link to a close-up photograph or drawing of a 300E motor indicating the name and location of all these plugs, switches/sensors?

and thanks for the reply.

Now that it's not starting and you suspect no spark, you could have a bad Crankshaft Position Sensor.

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1993 190E 2.3
2001 SLK230
1971 LS5 (454) Corvette Convertible

Benzborg, 3.65V is actually ~70% duty cycle. A 50% duty cycle is what your engine would optimally be at idle. 6.5V is ~50%. It's good that you are getting 6.8V at 2500rpms, means that your EHA is functioning correctly. However, A fixed value of 70% at idle indicates....

The finger is pointed at the ECU....yet again.

The microswitch referenced above is located near the throttle linkage. It's a little black box about the size of a matchbook. It's got a little roller on one end. It's primary use is on de-celleration. It tells the fuel injection to cut off fuel when you let off the gas pedal. It's worth looking at, but probably not the root cause of any of your major issues.

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1991 300E - 212K and rising fast...

I will swap it out tomorrow then *if* I can even get it started. This is one of those days I wish I'd slept right through. But a breakdown at my curb parking spot sure beats somewhere in the middle of traffic. This was a very odd shutdown. Started with the usual barely turn the key and away you go but within seconds - which only happened the one time before when the FPR gave up, the motor quit w/o warning - no sputter to a stop...just dead. As yet, not to start again since. Very confusing. All we did was clean switches, plugs etc. I took the ECU off the harness to look it over and put it back in. We've done nothing to warrant such a shutdown and as you've noticed the last few days have been rife with incidental problems. I can't imagine that anything we've done would have these drastic results. Do these OVP units (not just the fuse) give out and if they do would this cause a no-start? It all seems to be FPR, OVP and fuel pump related but I've got gas in the lines, and a fuel pump that energizes. I'll check for spark in daylight - assume gas and spark is all I need to at least get it started.
(or could a sensor come in between that happening assuming I did have gas and spark?) IOW, if it was you, how would you set out to step through what's wrong to at least get it to start tomorrow?

If it was the FPR you wouldn't hear it energize, the fuse in the OVP is fine but the unit did come from a parts car.


I'm ready to park it and pay the price to get the latest one I bought plated which will cost a bomb what with all that entails. This car has me down at this point.




And its located under the linkage toward the firewall then I'd presume?
Further back than the idle control sensor?

Do you have an OVP to swap? Fried OVP's can cause a no start symptom to the one your describing (cranks and cranks). I've seen bad OVP's with good fuses. If you shake it and it rattles....that's a bad thing too. Would be the first thing to check even before the FPR. But since you can hear the pumps priming...

If swapping the OVP doesn't do it, check for spark. Fuel is already present. I'd say your junkyard OVP gave up the ghost. There are very few things that will leave you stranded with one of these cars. #1 is the OVP. Otherwise, the car will still run with bad parts most of the time, albeit crappy, it will still get you home.

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1991 300E - 212K and rising fast...

So the car will not start w/o an OVP or if one is fried you're saying?

That sure would be the best outcome John. I do have one in the other 300E I just bought - oddly - working well in that car - it has *two* fuses in it - a ten amp and a 15 amp fuse side by side.

I'd sure hate to fry this other one too - is it a case of that OVP "giving up" or could something else fry one of these units?

Power for some key electrical components run through the OVP, so I'm sure it's needed to start the car. Chances are if it's fried internally, the car definitely will not start. If the fuse didn't blow, there was no voltage spike. So it sounds just like a normal OVP failure.

The pins have to be the same on the OVP's for them to swap over. If it does have double fuses, there's a chance it's different, but not sure. The double fused relays should have the same amperage fuses in them, though. At least they did from the factory.

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1991 300E - 212K and rising fast...