OM602 Hard Start in MEXICO - Diesel Bombers

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OM602 Hard Start in MEXICO


Old 12-07-2017, 11:46 AM
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Default OM602 Hard Start in MEXICO

Good morning guys, first time posting here on DB, but here we go...

So first a little backstory (gotta love threads that start like this).

THE CAR: 1987 Mercedes 190D 2.5 Turbo. Pushing 300k miles.

This started the day[s] after moving from middle Tennessee to Hidalgo Mexico (10 hours south of the border). Before leaving on the trip, car had been running great. Quiet, good MPG, smooth, easy start (first half-crank). No issues. Developed a small leak at the delivery valves before I left, and re-did the DV seals as per FSM. Everything was spot-on.

Upon arriving to Hidalgo, I noticed the engine was a bit noisier (more diesel clack) than normal. The smooth quiet purr our OM602's can be known for was gone. Power was OK (not as good as usual) so I figured I would look into things later. Well, the day AFTER (the next morning), it acted like it did not want to start. Cranked several times (perhaps 1-2 seconds worth) and even then, it sputtered and barely "cought" before finally firing on all 5. Even then, it was very rough until warm and the louder-than-normal "clack" was still there.

During the course of the next 6 months, I discovered a slowly-deteriorating head gasket and - like Forest Gump - figured, I am changing the head gasket, might as well service the GP's, injectors, etc... I wanted to wait until I was back to the border before actually doing the work, so I drove to Laredo.. As SOON as I was back into Laredo (actually 2 hours before reaching the border), the car was already running smoother, and the "louder than normal" clack was gone. The engine was running just as smooth and quiet as before leaving Tennessee 6 months prior!

Okay, so here is what I did while in Laredo:
-> Removed head
-> 5 of the 10 valve guides removed/replaced
-> Valves and seats lightly ground at reputable shop
-> New valve stem seals
-> Rebuilt all 5 injectors with NEW Bosio nozzles
-> Lapped injector surfaces and cleaned hard lines out to surgical cleanliness
-> Calibrated all 5 injectors within 20-40 PSI with my pop tested
-> Completely cleaned and inspected pre-chambers (had spares in case)
-> All new heat shields, etc
-> All new gaskets
-> Tested ALL 5 GP with voltage and measured current - all 5 (Beru) were 100% good
-> Re-assembled everything w/ new gaskets, fresh T6 Rotella and 2 gallons of NAPA heavy duty "fleetcharge" coolant
-> New fuel filters (BOTH), new oil filter, cleaned and re-oiled the K&N Air filter
-> Everything carefully torqued using Snap-on torque wrench and following FSM to the dot.

As you can see, I service my stuff correctly...

After assembly, and a couple 10 second cranking intervals, my baby fired up without further hesitation. A few 2-3 mile drives around town later.. the engine was nice and quiet. Ran smooth, slightly better power than before (most likely because I replaced 30 year old nozzles). All was good.

Hooked my little trailer back up (yeah - I tow a small 4x8 utility trailer with this thing), loaded a few things up and headed back to Hidalgo.

Same as before. About 8-10 hours into the trip (couple hours short of Hidalgo), the engine was noisy again. And the morning after, hard to start. In fact, NOW it seems to be a tad harder to start than before.

The area (in Mexico) I live in is roughly 8,000 ft above sea level, some areas are as high as 10-12k. I have considered this as a contributing factor, but am not 100% sure.

Other items to consider:
-> I have removed the air filter completely when trying to cold-start (thinking the K&N was causing some restriction before turbo could spool), no help.
-> The outside temp does not seem to affect this. 75-80 degree morning is just as bad as 50 degree morning. Plus, when I had 40 degree weather in TN, this was NOT an issue and the car started just fine. So I almost certainly rule out ambient temp.
-> Cycling the ignition 2 or three times (to get more glow time) does not help any. Besides, these cars have a after-glow type relay and I have verified this is working correctly with amp meter and voltmeters. GP's stay lit several seconds after start. Still does not help the hard morning start.
-> I cannot imagine an injector leaking down as all 5 are replaced and I DID check for leak-down while calibrating
-> No fuel leaks, cannot imagine loosing fuel prime - why would I only loose prime when here in Hidalgo?
-> Have tried using 5 gallons of fresh diesel brought from the US with me on an almost empty tank - thinking it was crappy fuel.. Nope. Same issue.
-> I have NOT tried a fuel winterizer to see if that helps yet as it is generally not even available here
-> I would love to fill the tank with some kerosene to see if that also helps, but that is also generally unavailable here.

This only leaves altitude to consider. I did (last week) back the ALDA off a turn - made no real difference. Above 1800 - 2000 RPM, this engine comes alive and runs 100%. But at idle, and starting.. it just can not handle - the altitude?

Injection pump going out perhaps?

Thoughts? Anyone with an older Mercedes diesel had similar experience? I found lots of people on-line talk about altitude and Cummins, PS, Duramax, etc... but found no real info regarding older Mercedes diesels and issues at altitude.

Many thanks in advance!
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Old 12-14-2017, 04:22 PM
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You mentioned testing the glow plugs, but not replacing them, or how old they are. It wouldn't hurt to check them again, they should measure less than 1 ohm (typical on new plugs is 0.6 ohm using an accurate meter).

Assuming the plugs are ok, my guess is the high altitude may be causing problems. For a test you could try temporarily removing the ALDA; this may cause smoking, but if the starting problem goes away at least you know it's related to fuel delivery.

Normally there is no issue at altitudes up to 7-8k, but since you are at fairly extreme altitudes of 10-12k, I'm fairly certain that is the root cause of your problems. Especially if the starting problems are eliminated below a certain altitude when you drive back down under the cloud layer.

You may want to cross-post this over on the Peach Parts Diesel Discussion forum, that's where a lot of the Mercedes diesel experts hang out.

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