92 300CE-doesn't start after warmed up
 

My new /used 92 CE300 is a joy-EXCEPT. It leaves me stranded randomly. It starts perfectly 99 out of 100 times.
Then she fails to start after about 1.5 hrs of use. I leave it alone for 3 hours, and she starts up. Then she's great for another week.
Any advice on how to trouble shoot this situation is appreciated.
Thanx

Possibly dirty injectors.

* Poway, when you turn the key does it crank ok and just not start, or does it not crank at all?
* If it doesn't crank, that takes your diagnosis in one direction. If it cranks fine but doesn't start, it takes you in another direction.
* Assuming it cranks fine, take a fuel pressure reading (you'll need the appropriate gauge, but the hookup on the M104 engine is very convenient). If you had no fuel pressure while it cranked, that would tell you the problem was in the fuel delivery. And you could decide on your next step down that path.
* If you have fuel pressure, you ought to check for spark next. I believe your engine has coil packs (rather than a distributor cap and rotor arrangement). You may need to remove the top, center panel on the motor, exposing the plug wires, etc. (M104). Some sort of inductive current probe is handy here to check a plug wire while someone cranks the engine (you can also do it alone using a remote starter). If there's both spark and fuel pressure, the next step is different than if there's no spark.
* To back up for a moment, if you have a scan tool it wouldn't hurt to scan for faults in the engine management systems before doing anything else (and you don't have to wait till the engine won't start to do the scan).
* I assume that you have a small window of opportunity when this failure happens. So it may mean being rehearsed and carrying a few tools in the car. The times I have seen this occational failure-to-start-hot problem, the engine also died while running and would then crank fine but not restart until it cooled down. Then it would start like nothing had ever happened. In that case the crank position sensor was defective (and there was no spark). You've got several diagnostic directions possible here, so you need to start by getting some of the basic data. Good luck.

Check dist cap/rotors and OVP relay.

Robert, a 1992 300CE has a standard coil, distributor cap/rotor set-up. Faulty crank position sensor or OVP relay sound like 2 possibilities. Although I think with a faulty OVP relay the 'Check Engine' light would come on ... that's the scenario on a 1995 E320 (104 engine with the coil packs).

Sorry abot the lack of detail.
Key turns, with no starter turn over. An audble relay clinking noise is heard on key turn over. I wait 3-4 hours and she starts great for the next week or month.

First check is a simple test :
Put headlamps ON and try to start..if headlamps go off when condition exist, you have a bad/poor battery connection/post.

If headlamps check OK, then you could have a bad starter solinoid or starter feed problem
This could be anything from a NSS/ign sw , etc. to a bad connection.
Another quick test for that is :
Just to the left of the brake master, there is a 3 wire plug on the firewall between the engine and the master. This is X27 connector to starter circuit. The center terminal is feed. If you unplug the harness and bring a jumper wire from bat + to the center terminal at the firewall connector, the starter should spin..if YES, then the problem is upsteam..if NO, the problem is downsteam from that X27 connector going at the starter/solinoid.
This is just a convienient spot we use to seperate the problem from under the hood or in the cabin.
You will have to perform both test only when condition exist, so it may be a good idea to clean battery post beforehand anyway, just in case that is the problem.

The car has died once while driving. It cut out on my son, 5 months ago. At the time I thoght it was due to a low fuel tank ( no worries dad's here for gas $). Same problem starter would not turn over. Car re-started in 15 minutes.
Headlights look great on start up. Posts/ battery connection recleaned and spotless. I have no engine fault codes or lights. I'll be ready next time with Arthur's technique. Hopefully she won't leave me stranded.
Any additional advice I'm all ears. I'll post my results.
I appreciate all your wisdom. Thank You All! You Gents Rock!

Another trick if it happens again is to try and start in "N" if it does not crank in "P"...that would indicate bad Nuetral switch of shifter bushing.
..this will save you a tow and get you home if that is the condition..


Might also want to tighten all the ground cables , ...specially on the chassis next to battery and the cable from the chassis to the engine. That one is at the bell-housing.

Thanx Arthur, I tried shifter position last time, no affect on problem.

Very good..that would indicate that the NSS is OK.
You have to try all these things b/c you have an intermittant problem and each test will help narrow it down..
Check those grounds.