603 vacuum pump failure (How to Diagnose?) - PeachParts Mercedes-Benz Forum

bustedbenz · #1 03-04-2011, 11:48 AM

Symptoms: Started the 300SDL (603.961 with replacement head) this morning (40-45 degrees F, parked for 10-12 hours) and let it warm up for 30 seconds or a minute, as usual (while waiting to pull out into traffic) and then pulled out and started accelerating up the hill. Engine sounded normal and ran normally at this point.

A mile later, with no warning, no new symptoms, and no obvious change in smoke color or density, I suddenly started hearing a metallic tapping/hammering, in time with the engine RPM. My first immediate thought was "tapping lifter" because, it sounded almost EXACTLY like lifter noise that this car has demonstrated for a while. However, the "usual lifter noise" goes away a few minutes after startup, and typically can't be heard from inside the cabin. THIS noise had the same "character" and the same frequency, but was *dramatically* louder. Heard it over the radio, with all the windows closed.

Throughout this entire event, oil pressure remained pegged at 3 (except at warm idle). Plenty of oil on the dipstick. "Low oil" is therefore completely and categorically ruled out as a cause, UNLESS it's an internal situation.

Nothing to do but keep driving the rest of the 2 or 3 miles to school. As I drove, I noticed that the vacuum brakes were more easily "drained" than usual. They WERE assisting me -- the first time I pushed the pedal rolling up to any given stop. But whereas normally I can floor the brake pedal 3-4 times in rapid succession before it "runs out of vacuum", this time it ran out consistently after just one good press. When I parked, the engine DID shut off with the key, so it's still making at least PARTIAL vacuum. I would have thought that the vac pump was either "working" or "not working" but not in between, but there you go.

When I got out and got under the hood, I could hear that the tapping/hammering was coming from the front of the engine. If I were going to draw an oval from above over where it sounds like it's coming from, it would include the upper half of the fan and belt drive area, and extend back to the oil cap or the first two injectors. This does include the vac pump region. However, I can't isolate the noise "closer" than that --- I am going to go out later today after some classes are over and do some more checking, and at that time I may be able to use a broom handle or something and pinpoint the noise. I will do so ASAP but I can't get back out there until this evening.

The vac pump IS the updated style with the visible bolt heads or screw heads or whatever they are on the front cover.

My working theory is that the bearings or the mechanism in the vac pump shredded themselves, whether due to cold-engine-accelerating-up-a-hill stress or just because it was their time to go, have been held captive by the updated style pump that's supposed to prevent catastrophic debris in the timing area, and that now, somehow, the pump is compromised and producing partial vacuum.

So, differential diagnosis.
1. What else could cause this noise? The belt tensioner/shock mechanism failed last year, and was replaced with new parts. This failure was characterized by the belt visibly running at an angle across its pulleys, which is not happening this time.

2. I am 100% aware that driving something with loose debris in the timing could result in catastrophic engine-becomes-an-anchor failure. However, almost my only option due to tool availability AND working-on-car-at-apartment issues, is to drive it 100 miles home to the garage. I don't really even have the choice of taking the vac pump off, looking at it, and putting it back on, until I get home tonight. So... if I don't accelerate it hard, and if I *accept fully* that it's a gamble, HOW risky is the gamble of "limping it home" with this noise occurring? I'm figuring that if there's any hard-parts damage, it happened within the first 5 seconds of the noise, so what's done is done.

3. Should have made this #1. IS this noise a possible result of vac pump failure? I have to describe it as metallic, and... either "hammering" or "slapping" would be the best word to describe it. I *think* I would know a lifter when I heard one, but I can't rule it 100% out. This engine has always had a few lifters at the BACK cylinders that have a bit of a dull knock to them until they get warm and oily, but this is most definitely at the front, and most definitely a sharper noise.

I know driving it is risky but I have few choices. Mostly looking to see if this is likely vac pump or likely something else entirely, and to judge my odds of getting it home before a WORSE failure happens. I guess it could be trailered home if the answer is "you're lucky you didn't already drop parts in the chain, and every single mile is doubling the odds that you will" but if it's "things will probably hold together for just a little tiny bit longer" then I think I'm going to try.

86-300sdl · #2 03-04-2011, 02:14 PM

Think worst Risk Case. Start preparing for a trailer, or lodging, or something else but don’t drive it. Just is not worth the chance of wrecking it. Your dreams may go up in smoke ‘cause it is a tough call to put the kind of bucks into to fix the shredded motor or just part it out. Ask any SEL owner about timing chain rails.

I have the same car, same paint, same concern, well still have vacuum but the oils seems to leak out after a few hours of sitting and I get a similar noise as you. I don’t know for sure that it is the pump, but because I can’t pinpoint to within 3 inches to were the sound is coming from (like I can a lifter), I have to go with the worst risk case scenario. After much ado I’ve just rented a car until I can get the pump in this weekend.

But if the belt tensioning spring or shock is going it will make a very similar knocking or tapping noise. Take your broom stick, etc and push down on the plastic pivot piece where the spring and then where the shock attaches and if it is stops knocking that may be your noise source. Then on to your brakes, which would be something else but do check out the belt tension spring and shock condition.

aaa · #3 03-04-2011, 03:47 PM

A bad vacuum pump is the good scenario in this case. I don't think "how far can I drive it" is answerable. The consequences if it does grenade are known though.

winmutt · #4 03-04-2011, 05:06 PM

Quote:

Originally Posted by aaa

A bad vacuum pump is the good scenario in this case. I don't think "how far can I drive it" is answerable. The consequences if it does grenade are known though.

Updated style it wont cause problems. Either way I would not drive it.

vstech · #5 03-04-2011, 05:31 PM

ya need me to bring you a used pump that's known good and rescue you?
I have a few spares.

babymog · #6 03-04-2011, 05:46 PM

Pulling the vac pump to check is a 15minute job, 30minutes if you have to stop and buy tools to do it. If the pump is fine, put it back on and you weep a little oil until you properly seal the gasket. If not, you might be able to gut the pump and re-mount so that it keeps the oil in and you can get somewhere to properly repair it (like John's place).

It's pretty easy to inspect for failure, and if it is failing you are in a situation where even starting it to drive it on a trailer could total your engine, or maybe not, how lucky do you feel?

Like Russian Roulette; You might win, but the consequences of losing aren't worth the gamble.

bustedbenz · #7 03-04-2011, 11:21 PM

Interesting story of getting it home. Left Boone with the noise still rattling just as it had been that morning. Decided to chance it, knowing the risks, but having an instinct that it wasn't going to get much worse. Was really figuring that whatever damage was done, had been done within the first revolution.

About 20 miles into the trip, the noise went away completely. Simultaneously, ALL vacuum disappeared. Previously, it had been sort of making "half" its usual vacuum. Once the noise stopped, there was none. Brakes were fully mechanical, and engine shut off didn't occur with the key. Drove it the rest of the way home without incident.

Got home, took the pump off my parts engine so I could see what I was in for. This engine is removed from its car and sitting on a sheet of plywood on concrete blocks, so it was easy to get to. It LOOKS intact, but I have no idea if it's "good" or not. Tomorrow's project is making that determination.

I'm sorry to disagree with whoever all said I could pull it off to inspect it in 15 minutes, but it took a LOT longer than that with two people working on it. Loosened the belt to get it out of the way, but still could barely get to where I needed. The bottom two bolts are TORTURE; i have no idea how on earth we'll get them started again. Can't remove the fan shroud without removing the radiator hoses and losing coolant, and typically the radiator has had to come out too whenever we worked up near the front. So we left that all intact and just worked around it all to remove... but we may still remove the radiator and fan shroud and possibly the fan to reinstall. Or the power steering pump and pulley which was the main obstruction for the right side bolts.

I'll post pictures of what came out tomorrow. The entire "spring" assembly; the main guts of the pump, was completely broken loose from the housing. It came out in pieces, and the metal "bowl" shaped thing that is attached to the block in the hole where the pump came out of, has been gouged in several places where the pump mechanism was driven into it. Will post pics of that too. Going to remove the "bowl" in the morning and hope to see no damage to the gears and such behind it. Assuming it's that simple to replace (we have those parts on the donor engine as well) then we'll be back in business, IF that vac pump is good.

Any good way to test a vac pump on the bench or do you have to just bolt it up and see if it works? Besides looking for visual damage I mean. Is there a way to test the mechanism?

Conclusion: The slapping noise was the pump mechanism halfway broken away but still lined up with the plunger enough to make partial vacuum. When this finally all shook loose after 20 miles of driving, it laid in the bottom of the housing where it fortunately couldn't get turned sideways enough to drop down the hole. At that point, all vacuum production ceased and it was an uneventful trip home.

It may only take 15 minutes if you are really good at removing the fan shroud and all the other associated bits and pieces. But last time we tried to do this, IIRC, the lower rad hose is threaded through the shroud, which means taking THAT loose and then re-bleeding the entire system afterwards, to say nothing of catching the coolant, and then even after you do that you still have to pull the radiator to get enough clearance to put a socket or wrench on the fan, and get something in there to hold the fan still........ there just ain't no way. And there's not enough clearance to do it quick-and-easy without; it's a matter of sticking wrenches and such in and getting one ratchet click or 1/32 of a wrench turn and then repositioning and taking the next 1/32 until it finally comes out one bolt at a time.

compress ignite · #8 03-05-2011, 05:32 AM

I'd Not Put Anything but a New Mercedes Pierburg pump on that Engine.

(I think your "Warning Phase" has exhausted itself with that system)

[AND,You've experienced about ALL the Warning these Pumps Give.]

The Diagnosis IS the Failure.

tony597fitter · #9 03-05-2011, 09:58 AM

Happened to my 83sd.
Only difference is I had a 3 piece camshaft then

compu_85 · #10 03-05-2011, 10:17 AM

Assuming you didn't screw up the timing device. I wouldn't want to ruin a new $300 pump.

Hmm, come to think of it, I have the good one I pulled off my car somewhere. If you're interested in a good used pump with ~50,000 miles on it shoot me a PM.

-J

86-300sdl · #11 03-05-2011, 10:20 AM

Check the race on the timming gear that the pump bearing roller rides on. Could be trashed after running it in "broke mode". If it is and you don't replace the gear as well you just trash the next pump.

babymog · #12 03-05-2011, 02:45 PM

Sounds like you have all that you need to repair it, other than gaskets.

If your car has the "dam gasket", the one that holds oil in the bottom with an extended flap of gasket, be sure that you use that one again (or go by engine number). Later blocks use a regular gasket as they have an oil squirter for the vacuum-pump.

Sorry about the low time estimate, I have done it in a 201 and 124s, and the process is much easier (fan and shroud removable with the radiator installed and all hoses on it).

Also, you might consider a Stanley ratchet, they have a design where you can twist the handle as well as swinging it to rotate the socket, works EXTREMELY WELL in tight spots instead of going one-click-at-a-time with a conventional ratchet wrench.

If I had to choose between my air-ratchet and the Stanley, I'd keep the Stanley.

compu_85 · #13 03-05-2011, 03:09 PM

Quote:

Originally Posted by babymog

Later blocks use a regular gasket as they have an oil squirter for the vacuum-pump.

So that's what the difference is! My car has the squirter, and still has the oil stain on the radiator from when I started it without the vac pump installed

-J

bustedbenz · #14 03-05-2011, 03:15 PM

Vacuum pump gear lobes are trashed.

Is there any way to remove the gear (with the lobes apparently attached; looks like a 1 part assembly) without dropping the timing chain? We're trying to figure this out on our parts engine now and there isn't enough room to get the chain slack enough (with the front cover on) to remove the gear that drives the vac pump.

Is there a trick to this? We're headed down now to pull the timing cover (this is gonna be FUN with the engine in the good car) off the parts engine and see what that reveals.

EDIT: I may be using bad terminology. When i said "vacuum pump gear lobes" I meant the metal curvy piece that is like two up hills and two down hills at 180 degrees from each other; it's mounted to the front surface of the gear that the timing chain goes around behind the vac pump. It looks like the thing that causes the pump mechanism to get pushed and released.

bustedbenz · #15 03-05-2011, 03:20 PM

Reading the threads on injector timing locking tools and all that sort of stuff now. We won't go into this blind, no worries.