1989 300E Intermittent start/run problem.
 

Just purchased car. 260K miles. Test drive (10-12 miles) did fine. Seller warned that car didn't always start. Started and ran fine when I picked it up from seller a few days later. Parked for a few days and it started fine when I drove it to go wash it. However, when I tried to accelerate quickly from stop into traffic, it stumbled horribly and nearly died. Was able to keep it running (or it kept itself running is more like it) but not running well. Died at stoplight but restarted. Died at carwash and did not restart (and I didn't wash under the hood). Called sister for a tow and by the time she arrived and we went to my shop to get the tow strap and came back (30 min) the car restarted and ran fine for the 2 miles back home. Today it started instantly and ran fine while I backed it out into the sunshine to check things out. I even let it idle a few minutes to see what would happen. OVP is fine (known good from other car), ICV hoses appeared ok, plugs looked good, no obvious vacuum problems... After reassembly of air box it wouldn't start! It acted like it wanted to run a bit when I released the key one time but it was nothing more than a horrid stumble for maybe 5 seconds. I gave it a little snort of starting fluid and it didn't change anything. This leads me to think it's ignition related. What could cause this? Does the coil fail like this at times? Crank position sensor? Or am I going the wrong direction? Temps here in balmy Oklahoma have been from 70 to 85 when working on the car and it doesn't seem to matter if the car is warmed up or stone cold, it does as it pleases. Thanks to all for all the help on my other car. Hope to get this one fixed as well.

Do a search for the fuel pump relay.

also
 

Try starting it in neutral when it wont. ~to rule out Neutral Saftey Switch~

Try unplugging the O² sensor (under the passenger carpet and floor pad - one green wire) when it wont also. ~to rule out O² sensor~


also:
post when it dosen't start what does it do... turn over? just a click? ...

The original post describes a crank-but-no-start condition. Why would the neutral switch or oxygen sensor address this? :rolleyes:

Sorry, that wasn't clear in the post. It cranks very well at all times but sometimes won't start. And, not to sound cynical since I sure don't know the particulars of this car, but since it does crank, can we rule out the
N-safety switch? Also, the O2 sensor part doesn't make sense to me. The ones I've seen go bad (on American cars) won't keep it from starting but will make it run poorly once started. But, I'm not well-versed on the Benz so I'm sure gonna listen (gratefully) to any suggestions.
Thanx, Chuck.

Would a faulty crank position sensor cause a total lack of spark or would it cause it to spark at the wrong time?

I had the same symptoms that you describe. It was like chasing a gremlin. I could never nail it down. I replaced , fuel injectors, fuel distributor, throttle pot, OVP, fuel relay, ignition wires, and a host of other stuff I have forgotten. I have chased this devil for 2 years. One day it had the problem in my driveway. It would not start, I checked fuel and spark and it was getting both. It took a tow behind my pickup to get it going. It's a manual transmission. Once it got running it would die if the RPM dropped to less than 2500. It would not idle until it was warmed up. Took about 20 minutes before I could idle. It then drove and ran normally. Guess what it turned out to be?

The rotor and distributor cap!

High voltage was leaking & arcking all over the inside surface of the cap. Here is proof and a picture of the evidence.

http://www.davidpetryk.net/imagepages/image727.html
http://www.davidpetryk.net/imagepages/image729.html

I cleaned up the cap and things were fine for a few months. Then it started again. I finally replaced the cap and rotor and it runs like a new car. Based on the symptoms I had, I would have never guessed that was the problem.

No spark or erratic spark, but the CKP sensor does not affect ignition timing. It only does what its' name implies...report the position of the crankshaft. The ignition module uses that information to vary the ignition timing, and the distributor makes sure the right cylinder gets the spark.

Now...on with the problem. In my case, the random stall/no start was caused by the fuel pump relay. Very difficult to detect because the durn thing would usually restart by the time I had the hood up and was ready to check anything. I eventually tracked it down by taking an old fuel pump relay, gutting it, and sticking a regular cube relay inside. When I used this in place of the fuel pump relay, the stalling ceased. So I eventually bought a new fuel pump relay and now all is well.

The nature of your problem (works fine sometimes, won't work others) tends to point towards fuel delivery, but not with 100% certainty. Since throwing parts at this issue can get spendy, I'd try to verify spark or fuel as the problem first. When the condition is present, pull a spark plug wire and attach an old spark plug. Ground the other end of the test plug and crank the engine. If you get spark, the problem lies elsewhere. If no spark at the plug wire, pull the coil wire and attach your test plug. If you now have spark, the problem is in the distributor. If still no spark, then it's back toward the coil, ignition module, and crank position sensor. Once you verify fuel or spark as the problem, you'll have a much easier time finding the problem.







...after you rule out the oxygen sensor http://img137.imageshack.us/img137/607/lmao6fo.gif

I disagree with moneypit on a few points.

1. Your statement "It only does what its' name implies...report the position of the crankshaft.". This is technicially incorrect. It generates a pulse 4 times per revolution of the engine. It does not generate any position information such as degrees etc. The pulses are made when the ring gear passes over the magnetic pickup. I agree with the remaining part of the paragraph.

2. Your statement "When the condition is present, pull a spark plug wire and attach an old spark plug. Ground the other end of the test plug and crank the engine. If you get spark, the problem lies elsewhere." is not always true.

I tested for the presence of spark on numerous ocassions. I was fooled because I also thought "If you get spark, the problem lies elsewhere." I saw spark and I was convinced that it must have been fuel related as you can see by the number of fuel related parts that I replaced.

I had spark, but it was like this -- 1 good strong spark then several small weak ones. then strong and so on - sometimes. It was only because it was at night that I was able to see the weaker sparks. I definately had good coil output and the ignition module and the crank sensor was all working as it should. It was the distributor that was not delivering spark correctly to the plugs.

The problem was cured when I replaced the cap and rotor. SO that proves that it was indeed spark related in my case. Did you look at the picture? Did you see the carbon trails leading fom the electrodes heading twards the center terminal? Spark was jumping all over the place inside the cap.

Lesson learned - dont be fooled by the mere presence of spark.

Forget the oxygen sensor - thats not your problem.

Well 'scuse me. I should have said somewhere that you need to understand what you're looking at.
Strong spark = good
Weak spark = Bad

And for the CKP...First, it's a six cylinder engine, so that would be 3 pulses per revolution, not 4.
Second, unless a guy has an oscilloscope, he won't be able to see the 3 pulses per revolution and, IMHO, didn't need that much info.

How do you feel about neutral safety switches?

Chances are the cap, rotor, and ignition wires are ancient on this car, as it will run (although badly) with the rotor burned badly and the contacts in the cap burned down to the cap material!

Check for the following:

Any signs of arcing on the plug and coil wires. Any evidence (spiderweb traces, ashy spots, burned insulation), replace wires.

Pull cap (a PITA) and inspect -- likely it will have been toast for some time.

Replace them and it will run much beter.

Also check for a cracked rotor carrier (the bit that bolts to the cranshaft the rotor is screwed onto) -- these are known to break in these cars, and can cause running and starting problems when they slip out of position, then slip again and are close to correct.

Peter

Hey, thanks for the insight. I'll enlist some help next time I work on it. I'm with you on the PITA to change the cap and rotor since I recently did just that on my '90 300E. No fun. Probably the worst part was removing the fan to make room to work. I almost hope it is the cap, rotor, plugs and wires or some combination since they are no doubt due for changing anyway. It just gets a little costly for all that.
Thanx again.
Chuck.

Yep. If it cranks it ain't the NSS.

I always sugest checking the O² sensor first because it is the easiest thing on the car to check... and it can cause an intermitent stall and no start condition (with warm engine). I know this because it happened to me. Maybe it makes me an idiot, but I would then pull the EHA to rule out any bad computer input. Again because it is a very easy test that takes almost no time and gives you positive or negetive feedback about your condition. Jumpering the fuel pump relay would also be high on my list of things to try... but you can probably just listen for the fuel pump hiss. Replaceing the plugs-wires-cap-rotor is about the best kind of throwing parts there is so thats a good place to start as well. Could be lots of stuff, good luck. :)

With all due respect, I don't see much value in checking something that can't cause the problem just because it is 'easy to check'. Might as well check the tire pressure while you're at it.

I'm curious about your belief that the oxygen sensor can cause intermitent stall/no starts. While the oxygen sensor has a large effect on how the engine runs in closed-loop and can, in fact, cause the engine to quit or not start at all, I've never seen one go intermitent. Once it fails, it stays failed. If you've a mind to, elaborate on your 'it happend to me' statement.

Yes, please elaborate as my curiosity is also piqued.