300SD Not Starting, Need Expert Help - PeachParts Mercedes-Benz Forum

Lew · #1 09-12-2007, 07:35 AM

Hello, all. I've finally trailered my Benz back home and am ready to begin getting her back on the road. For an overview of the issue, please read Won't Start, IP Trouble?.

I will undoubtedly need the assistance from the wise folk here.

The car: 1983 300SD, 265k on car, engine rebuilt at 196k - OM617, W126

The Problem: Will not start. Once fogged to run, runs great at 1500+ rpm, but at idle will stall.

The Symptoms: For 3 weeks prior to no start, vehicle would often hesitate and stall. The day of no start, idle would always stall. I changed secondary filter in parking lot of autozone, filling with Sea Foam, and car has not started on its own since.

So Far: I had it towed to a diesel tech who rebuilt and balanced injectors, replaced glow plugs, and replaced fuel delivery valves on IP. No change in starting ability. Diesel tech reports that IP does not appear to build enough pressure to pop injectors at starting/idle rpm.

Possible Cause?: I've run this car on a heated WVO blend (no more than 80% wvo) for the past 35k miles. Early in the summer, I ran out of oil and filled with diesel. Within 20 miles, these same symptoms - idle stall - cropped up. Topping off with WVO solved the problem. Does this indicate a timing issue, allowing the different (lower) cetane of wvo to run but not the higher cetane of diesel? Does this indicate wear in the IP that the higher viscosity wvo blend overcame?

I humbly ask for help from you experts. What do I do now?

rrgrassi · #2 09-12-2007, 10:05 AM

Have you tried the diesel purge yet and using fuel lines into a bottle? How is the primary filter? How is the tank screen?

lonewolftek · #3 09-12-2007, 10:14 AM

Quote:

Originally Posted by Lew

Does this indicate wear in the IP that the higher viscosity wvo blend overcame?

This would be my guess. Timing issue is possible but unlikely, given that I've seen the timing on an OM617 be massively off (34 degrees) and it still ran, though it sounded terrible.

Lew · #4 09-12-2007, 11:27 AM

Haven't done a diesel purge. Primary and secondary filters are new, tank screen is removed. Fuel is flowing to injectors. Cracking the lines while turning over engine shows fuel weep. While in the shop it ran on straight diesel out of a jug rather than on my blend - starting via fogging the intake with something, I guess. While it ran at rpms over 1500, it died at idle.

Is a Diesel Purge my first step?

It is due for a valve adjustment. Could improper adjustment cause this issue?

vstech · #5 09-12-2007, 11:58 AM

once again, this seems to be a water/debris wearing out the IP. My bet is you will need a replacement IP to remedy the idle for this motor.

Lew · #6 09-12-2007, 12:05 PM

Before I go through pulling the IP and repairing/replacing it, I'd like to exhaust all other options. Should I adjust the valves before going any further?

rrgrassi · #7 09-12-2007, 02:15 PM

Valve adj won't hurt it, but by the growing list of symptoms, it poits to a thrashed IP.

Magoo · #8 09-12-2007, 03:33 PM

Quote:

Originally Posted by rrgrassi

Valve adj won't hurt it, but by the growing list of symptoms, it poits to a thrashed IP.

Exhausting all other options as you mentioned, would definitely include valve adjustment, and compression check as rrgrassi mentioned on the other thread. It would be good to know what the compression looks like anyway- you may decide to swap the entire engine.

That said, I must agree, it seems to point at the IP...

Fuzzball · #9 09-12-2007, 03:52 PM

If there is water, might there be some algae? Have you tried hitting it with a biocide to see if it made a difference?

I'm not an expert, but I know that algae will kill your performance...

CRSMP5 · #10 09-12-2007, 06:48 PM

i have a 81 ip from a junkyard engine... never ran though since car was crashed.. was full of fuel and lines too when i removed it..

Lew · #11 09-13-2007, 07:18 AM

I can definately adjust the valves and check the compression and will report back once that's done. In the meantime ....CRSMP5, how much would you need for the boneyard IP?

Lew · #12 02-27-2008, 12:20 PM

Update. I finally had some opportunities to work on the car.

I was amazed to find that, after charging the battery, she started up with a few cranks. She even held an idle for a short while ... then died again and wouldn't start.

The next day, I was able to start it up again, this time feeding it Diesel Purge out of a bottle. Again, it eventually lost idle, stumbled and shut down and wouldn't crank again.

Again, however, she fired off the next day, which is when I finished the Purge and took it for a spin up the road and back. She felt sluggish (but that could have been my imagination after driving my other - more powerful - vehicle for the past few months). It died when I got back.

The next day, it started right up again, held an idle, revved up and and seemed to run fine. I let it die on purpose. This time, it fired back up. It still won't hold an idle.

To make a long story short, it's now running on the fuel that was in the tank, a blend of diesel and WVO, and seems to be starting OK and running OK but will not (yet) hold an idle. Power when driving seems to be lacking but is definitely driveable power. I have not adjusted valves or tested compression, thinking that both are fine for now.

Given this information, is it still the opinion of the wise that the IP itself is at fault? Should I check/adjust timing first? Could there be some sort of building vacuum that is shutting things down at idle?

CRSMP5 - is the IP you mentioned still available? If so, let me know cost.

kerry · #13 02-27-2008, 12:25 PM

Here's what I would do. I'd rig up a bottle of diesel fuel in the engine compartment, running input and return lines into the bottle. I'd run it on that system for a while and see what happens, If it runs ok with that system, the problem is not the IP but something in the fuel delivery system. If it didn't start and run right on the alternative system, I'd check the lift pump before condemning the IP.

LUVMBDiesels · #14 02-27-2008, 01:18 PM

Give this a try... pull the vacuum line from the shut off valve on the IP.
I had a similar issue with my 300SD where it would run fine and then slow down and die. It turned out to be the shut off switch in the dash leaking vacuum into the valve on the IP. Vacuum would slowly build up until it shut off the fuel rack.

JimSmith · #15 02-27-2008, 01:40 PM

Quote:

Originally Posted by LUVMBDiesels

Give this a try... pull the vacuum line from the shut off valve on the IP.
I had a similar issue with my 300SD where it would run fine and then slow down and die. It turned out to be the shut off switch in the dash leaking vacuum into the valve on the IP. Vacuum would slowly build up until it shut off the fuel rack.

Sounds like a very promising avenue to explore. I would also change filters again. The behavior seems to be inadequate fuel flow, and switching between Diesel and WVO may have loosened and then flushed some gunk into the filters. Or, an inadvertent vacuum actuation of the shut off valve as noted above. Seems to me the injection pump is probably ok. Jim