Max Blast

Check out YouTube channel legit streetcars… He is a Mercedes tech and uses an (Autel?) scan tool that has functionality very close to what I see in my MB star system.

That’s a decent commercially available compromise from having to go see a dealer and will pay for itself in short order.

eric_in_sd

MP808 will run the alternator load test. However, that may not diagnose voltage that has spikes and dips. But it certainly would be a must-have data point.

Diagnosing with just the OBD codes is like trying to get directions to a party from a girl who is already there. She's drunk, the music keeps drowning her out, and when you can understand, it's gibberish like "turn right at the shoe store and left at the yoga studio".

eric_in_sd

Switch your voltmeter to AC and check the AC voltage. If the regulator is functioning properly, AC voltage should be near zero.

jtb33

Ok. I went to O'Reilley and had them do a battery test on my February 2021 battery and they said it tested "bad". I went ahead and spent $270 to buy a new AGM battery (previous one was as well - but a Wal-Mart brand). I just put it in this morning and reset all the CEL's. We'll see if that does anything.

eric_in_sd

This makes me think you have a failing alternator. No way should a AGM battery die that fast. Especially Walmart, which should have a fairly rapid turnover. That said, I bought a battery at Autozone and found it was DOA because it had a manufacture date of 5/20, and I bought it 12/21. Even stored on a trickle charger, the best lead acid batteries wear out.

There are just three or four lead-acid battery manufacturers that serve North America, and Walmart is almost certainly buying from one of them.

But something killed that battery long before its life should have been up, and if it wasn't pre-storage, it was weak charging by the alternator. So you should definitely investigate. If you go back to O'Reilly, they probably still have the battery, and you can try to figure out the manufacture date. And don't forget to do the more in-depth alternator diagnosis.

Good luck - and a word of advice: If you plan on parking your GL for longer than a day or so, you ought to put a trickle charger on the battery. There is standby loss, which the charger will offset. The batteries are expensive enough it is worth it, in my opinion. I have a Noco Genius plugged into an overhead outlet, and when I pull into the garage I pop the hood and connect it to the engine compartment terminals.

jtb33

FYI, here is a list of the codes it has thrown since the Check-engine light first came on a month ago:




Voltage regulator appears to have gone bad, per O'Reilley testing today.

They did confirm that the battery I just replaced (from 02/21) would only hold up to 80% charge which for them, would mean it's bad and would be covered under warranty. They suggested I try to take it back to WalMart (has a 4 year replacement warranty), but they couldn't take the new battery back since I had installed it. I spoke to WalMart and they just suggested that I keep the old/bad battery and bring it back a few months before the 4 year warranty is up to get the free replacement in January 2025.

Anyway, back to the voltage regulator and alternator. This one is not a job I'm willing to do myself, so I will have to have our mobile mechanic do it, but I can buy the parts. I'm not sure if mine has an external voltage regulator or not, but perhaps it's time to just buy an entirely new alternator anyway. Already shelled out $270 for a battery. I usually buy from Rockauto and while I try to Bosch parts, I'm not sure that I want to spend close to $500 on an alternator, plus the cost of labor to install it - given how sparingly this vehicle is used.

Bosch - $422 + tax and shipping
Valeo - $323 + tax and shipping
TYC - $204 + tax and shipping
or I can do with a remanufactured one for about $130-150 after getting the core charge back.

Any thoughts on which one?

Any pre-emptive parts that should be replaced that could be done conveniently while the alternator is being done?

I do have a couple trickle chargers - we usually leave them plugged into our UTV and ATV. This GL450 is probably only driven on average, twice a week.

Max Blast

You do not need to buy a whole new alternator unless the bearings on the one you have are bad. Just get the alternator out and change the voltage regulator on it and put it back in. If you’re really slender you might be able to change the voltage regulator with the alternator still installed.

If you have to replace the alternator body the only true choice is a name brand Bosch. Everything else is trash and will fail in short order.

eric_in_sd

Last I checked, Rock Auto was selling rebuilt Bosch alternators. That is what I installed.

Alternators don't have any magic dust in them, but it is surely possible to assemble them poorly. So the quality - price curve looks something like this:


Yes, it's another MS Paint piece of artwork. The problem with rebuilders is you don't know whether they are rebuilding with Chinesium ingredients. That is why I went with a Bosch rebuilt. I have no clue what the vertical axis on this chart is like; it could be that a Chinesium alternator would last half as long as a Bosch - but the OEM on mine lasted 180K miles!

The Chinesium air pumps are awful, which is no surprise. They last just a small fraction of the AMK brand. Motors, etc., are much more tried-and-true, but: I have an electric log splitter that sometimes won't start in a certain position, and if I jog the motor just a tiny bit, it runs. That is the brushes on the motor shaft, and Chinese manufacturers cutting corners until the motor just barely works. Someone in another thread said that Chinese suspension components are hit-and-miss, and that is the oldest technology going around.

The voltage regulator is part of the alternator on these vehicles. It is bolted on the back.

Replacing the alternator is not terribly hard, but if you don't feel comfortable with it, don't do it. Remember to check the voltage drop from the alternator post to the firewall post (while the motor is running); those cables have a tendency to develop resistance at the alternator lug - that cable carries both the current from the alternator and from the battery to the starter - and that resistance tends to self-increase. For cheap you can sister a cable from the alternator to the firewall post.

You can probably sell the battery locally, like on Craigslist. Sell as brand new; do the swap when you go to do the sale.

It is a tough lesson I have barely learned: It is tempting to do all kinds of detective work, but the humble mechanic thinks first of the mundane problems. Don't feel too bad; I spent $1300 on an ECU and throttle body before I thought to simply peek inside the cylinders to see what I could see. Now I know better. You aren't out of the woods yet, but you know you need to get the electrical system tip top before you proceed. Keep an ear on your starter, too; if it starts to go it can easily drag the battery down, which drags the alternator down, which drags the battery down ... you get the picture.

eric_in_sd

The brushes and rotor contacts wear out, too, not just the bearings. On the one I pulled at 180k, the contacts had deep grooves worn in them and the brushes were pretty well worn. I'm not sure how it would work, but I believe when those wear the voltage can sag.

I would bet an off brand alternator was installed. Whether full on Chinesium or a brand that at least tries to be good is anybody's guess. But the voltage regulator failing - ffs it is just a few beefy diodes!

eric_in_sd

One more thought: Your local parts store may sell rebuilt Bosch, saving on the Rock Auto shipping.

jtb33

Following up... I ended up taking it to a shop that specializes in MBZ and BMW since it had some other unrelated work that needs to be done (ball joints, boots, drive seal, etc). They diagnosed the CEL and reported misfires to a faulty fuel injector for Cylinder 2 - and just suggested replacing all 8 as a preventative measure. They said the alternator was good and the battery was fine. They suggested that optimally, I'd need to use a trickle charger if I only drive it once a week (someone suggested that earlier in this thread). I'll probably want to find a way to permanently install that. Any threads on the best way to do that on a GL450?

Max Blast

Trickle charging solved here (NOT via 12v socket!)

https://mbworld.org/forums/gl-class-...2v-socket.html

Wrt injectors I’d just replace the one and see if the misfire reappears in another. Could be a contamination root cause for this issue.
(Pragmatic solutions for palliative car care problems.)

jtb33

Given all the work to get to them and remove the fuel rails, wouldn't it just be wise to replace all of them while I'm there? Vehicle has 220K miles on it and I bought it when it had ~180K.

eric_in_sd

There typically is a fair amount of debris around where the injectors enter the intake manifold. If the shop is not very careful to clean around the port, debris will fall inside the intake manifold and go in the motor. You would not see the effects for a long time, should the piece of grit fall inside the motor and get lodged between the piston and cylinder wall, on top of the piston rings. So I would replace just the one.

The injector failure may be due to contamination or it may be electrical.

If you are sure the area around the injectors is clean, it is not difficult to remove them and blast with carburetor cleaner. There is a jig one can get for cheap, which activates the injector, allowing you to spray the solvent through.

BlownV8

Injectors typically do not go bad in the GL regardless of the miles.

jtb33

Bad news for me. After some additional inspection and no luck with changing out the one fuel injector, he used a borescope to look at the cylinders.

Here's cylinder #2:




So, I suppose that means I need a new engine...

Max Blast

First picture, is that a ring rest and flaked off coating?

second picture is that a crack in the piston?

if so just drop in a 08+ 4.7 or 5.5 for two grand

or; drive this one into the ground, part it out and move on.

I’m seeing lowish mileage 550s around here for 10 to 15 grand so that’s your competition

jtb33

That's what the mechanic said - a crack on one and a scratch on the other.

While it's super-rough to drive it, if I drive it until it dies, what is the end result of that? Meaning, does that one piston just seize up and the engine won't turn over anymore, or does something else happen to the engine that's potentially dangerous?

eric_in_sd

I can't tell what's what in those pictures, so y'all are better than I.

If the cylinder walls are not scratched, technically the piston could be replaced. But whatever caused the failure in the first place - do you have any clue? - might be impending on the other cylinders as well. Certainly the vehicle is "exciting" to drive, but since the ECU will have shut off the affected cylinder(s) injector(s) the piston will not be under as much stress as when it is producing power.

I would absolutely follow the advice and drop in a used 550. MB built a LOT of these motors, many more than the 4.7. The vast majority are well maintained and driven gently. MB even has a feature to shut off the fuel pump in the case of an accident, so the motor does not continue running when a tree is hit. Translation: While there could be issues with a used motor, your odds are good.

Real sorry for all your struggles. This is unusual.

jtb33

Appreciate the replies. This is an engine with >220,000 miles on it, so I am cognizant that it's moving towards the upper threshold of expected life. I paid only $6500 for the vehicle about 5 years ago when it had ~180K miles, and I've probably put about $3K into it over that span (oil changes, batteries, brakes, airbag strut replacements on fronts, and other minor things). All-in-all, that's a pretty good run of it. My biggest hesitation to disposing of it is that other than this issue with the engine (lol), it's in relatively great condition - both cosmetically (interior almost looks new) and mechanically. It had no oil leaks, etc.

Still waiting on the mechanic to get back to me on a quote for replacing the engine and the cost associated with that job. If it's more than $2K, I don't think it'll be worth it. If it's $1500 or less, I will likely do it.

BlownV8

There is little to no chance of fixing that for $1,500. Get rid of the car and update to the latest X164 or x166. The biggest issue with the 164 is the roof seals deteriorate, water intrudes, and causes major issues with the electronics. My 2007 was totaled a year ago from just that. If you could solve all the water intrusion issues, the gas X164's are very reliable and safe. Of course, the early 450's had the issue with the timing chain sprocket failures so, if you decide to keep, I would upgrade to a later model engine and don't discount dropping in a 550 engine as others have mentioned.

eric_in_sd

Several of us have compared notes and concluded the repairs and maintenance cost us about $0.15 per mile. We do most work in our garages. Add to that gas ($0.20 per mile) and insurance ($0.10 per mile), and you are still under the standard operating cost per mile as allowed by the IRS - which is probably a bit light. Certainly an older Toyota would be cheaper, but the question is, how do you enjoy driving? My main drive these days is a 40 mile round trip, and all in all I like driving my GL more than any other vehicle I have owned.

I would be quite interested in why the motor failed. 220k miles is actually young for the motor to catastrophically fail. If I recall correctly, forum member alx reported on a Sprinter that had finally been put out to pasture at 700k miles. I don't recall if it was on the original motor or two, but the point remains: Well cared for, these motors last a very long time.

Also, there is a lesson here: Do a basic series of diagnostics whenever issues pop up. A lot of heartache would have been saved by peering inside the cylinders to begin with. You can get a nice borescope for something like $150. I got a Teslong, and was able to diagnose carbon on the undersides of the intake valves; if I had done so earlier I would have saved myself $1300, and a lot of grief, in unnecessary repairs.

P.S. I got elbow mini-cats and solved my 420/430 check engine light problems: https://binzstore.com/90-degrees-des...road-vehicles/

Max Blast

Sideline this one and use as a parts car for one with less miles on it, one that you’ll get and keep us all informed of the hunt.

eric_in_sd

ngl I'm tempted to buy it as a parts car