90 300e Warm Start Gremlin - PeachParts Mercedes-Benz Forum

ggustaf · #1 01-05-2010, 10:54 PM

My Son's 90 300E (135K) has been very reliable for over 4 years until a few days ago. He was gone for 5 days without starting the car, came back the battery was dead. Took it out and put an overnight charge on it , started right up, no problems until trying to restart after warm..car would not start. I took off the air cleaner and it refired and I managed to get it back home. Started by checking some obvious culprits, air meter valve seems to be fine, checked vacum hoses, all seem to be fine , but the breather hose is broken bad by the valve cover, have ordered a new one along with an air filter (still waiting for those to arrive), put in some techron, topped off tank, still having warm start issues. Again, removing air filter allows restart back to home, any correlation there? No cold start issues whatsoever and car runs as smooth as ever.

Before throwing $$$ at the usual suspects, does anyone have some ideas on how the battery issue might have caused this problem to appear. Maybe I bumped the OVP on removal and install of the battery or caused a short to some other component, (no CEL or abs light). I'm thinking temp. sensor first, but any ideas are welcome...

mbdoc · #2 01-06-2010, 08:27 AM

Most likely a "fuel" bleed-off issue OR vacuum leak.

Either one will lean out the mixture & cause a hard hot restart

dhjenkins · #3 01-06-2010, 09:19 AM

While engine is warm & off, rule out fuel bleed off by cycling ignition switch to on (for 2 seconds) and off 5 times to "prime" fuel system. Attempt to start. No start likely means no fuel bleed off.

Rule out vacuum leak with a vacuum gauge (they're cheap). Should pull 18-22 at idle.

Check resistance & connections on temp sensors - maybe you're bumping something when you remove the air cleaner.

ggustaf · #4 01-08-2010, 01:48 PM

Update...replaced air filter, broken breather hose, replaced some of the old vacuum lines for the peace of mind, still no start when warm. Went the electrical route... checked plugs, wires, cap & rotor....found the rotor to be very worn & rusted, replaced it with another used one I had in the bin, but in much better shape. Result...no warm start issues for last 2 days, we'll see if it is a permanent fix in the next week or so...

long-gone · #5 01-08-2010, 02:50 PM

Sometimes it's funny how problems come (and go) and sheer coincidence has one suspecting various causes (and cures).
I'm not sure how a worn rotor might cause a hard warm start, it seem more logical the other way around (hard cold start). But if it seemed to work, that's what counts.

The only thing I can come up with there is that the worn rotor might have been sending a very weak impulse to the plugs and when the car was warm the resistance in the ignition (wires/cap/plugs) increased enough to make the resulting weak spark ineffective. Maybe less compression in a warm engine + a weak spark? I dunno, just grasping for a reason it might have helped.

I was thinking worn/leaking injectors creating a flooded condition causing a hard warm start. By the time you got done fiddling with the air cleaner it had time to evaporate (removing the air cleaner/opening air inlet may also help it evaporate) and coincidentally it started afterward. As far as the fix, perhaps the Techron you added finally cleaned the injectors enough after a few days running to relieve any leaking condition, coincidental to the replacement of the rotor.

Another thought, the 1980s Volvo's had a notorious problem of cold solder joints in the aging fuel pump relays. They would start up fine when cold but when shut off and attempted to restart while still warm (like at a gas stop) they wouldn't restart until they cooled down for several minutes, then "mysteriously" start right up and be fine for the rest of (or most of) the day. This condition would come and go, with seemingly no rhyme or reason. It drove many independent mechanics crazy throwing parts at them.
Several electrical components in the same era Benzes, including the fuel pump relay, are subject to the same cracked solder joint issues, though perhaps not as severely or notoriously as those Volvos.

long-gone · #6 01-09-2010, 09:19 PM

I realize you feel you've found the culprit in this case, but for the benefit of others who may have these symptoms, after doing a bit of reading on this issue, a prime suspect might also be the fuel accumulator and/or fuel check valve down by the fuel pump.

Apparently a common failure on W124s of this age.