Diagnosis time with AMGtech!

"AMGtech - now with more recalls!" (amgtech) 08/16/2019 at 11:30 • Filed to: None

12

29

Nothing super crazy here, but a fun one nonetheless. So let’s jump right into it!

The subject: 2007 E63 AMG

The complaint: engine surges while idling, but only when hot, CEL not illuminated, runs well otherwise

Not actually the one pictured above, but you get the idea. This one was towed in to me last fall. It had hydrolocked due to leaking injectors. But it’s tuned and has long-tube headers. It sounds glorious. Well, at that time I had the engine out, replaced the head bolts, made sure the bottom end was good, all new plugs, injectors, cams, lifters, and a bunch of other things. Basically the engine should be bulletproof now. Every common problem was taken care of, and then some.

So why is it running poorly now? Well it’s got a thermostat fault code, and a bunch of oxygen sensor fault codes. But none of those will cause a surge. The thermostat will be covered under parts warranty by the way. The oxygen sensor faults could be caused by the surge and/or the tune/headers. So fault codes are unhelpful.

Mixture adaptation data looks slightly rich on one bank and slightly lean on the other. However both sides are almost neutral, well within normal. Again, not helpful.

So, what’s the issue? Well it sounds and acts like a large vacuum leak. Mixture adaptation data should show this, unless it’s such a recent problem that it hasn’t adapted yet. So quick, easy check; spray brake clean around the engine at idle to see if it surges! Cheap, easy, fast!

No joy.

Fine. Break out an actual tool. The smoke tester! Plug the intake, inject smoke through a vacuum hose. Still nothing. Check the vacuum reservoir, still nothing. Even tested the engine for a solid twenty minutes. I didn’t find smoke, but the gauge on the smoke tester didn’t drop to 0, which it should if there truly were no leak. On the other hand, it didn’t show full loss either.

I had to be missing something...

Any ideas?

The brake booster! I’ve honestly never seen one fail on one of these. Brake booster failures are quite rare. Notice how the gauge on the tester is showing full loss (little red ball at the top, no leak and the ball would be at the bottom). There was so much smoke pouring into the cabin it looked like something was on fire!

It always feels good to find a smoking gun when diagnosing a problem.

Highlander-Datsuns are Forever > AMGtech - now with more recalls! 08/16/2019 at 11:34

1

This diagnosis is crazy, who would ever suspect a bad booster. The brake booster on my datsun is Original, 1970, and still works. I did replace the vacuum lines leading to the booster and found a much improved pedal feel.

OPPOsaurus WRX > AMGtech - now with more recalls! 08/16/2019 at 11:35

7

i wouldn;t have been able to tell you the problem but i can tell you the solution - copious amounts of money.  

PartyPooper2012 > OPPOsaurus WRX 08/16/2019 at 11:40

3

Is this enough?

Ash78, voting early and often > OPPOsaurus WRX 08/16/2019 at 11:49

10

Funfact: The AMG smoke machine is fueled by burning $100 bills. They create just the right kind of smoke for the job.

AkursedX > AMGtech - now with more recalls! 08/16/2019 at 11:54

0

I really need one of those vacuum leak testing machines. Good work, and yeah, thats an odd failure. I wonder what the actual failure point of the booster was.

Akio Ohtori - RIP Oppo > AMGtech - now with more recalls! 08/16/2019 at 12:01

0

Interesting.  I should add one of these to my smoke tester.  Would be cool to have the extra data.  I assume the ball indicates air is flowing, which indicates after the system is brought up to pressure there is still somewhere for the air to go, which is bad?

Khalbali > AMGtech - now with more recalls! 08/16/2019 at 12:05

1

Cx9's actually have really terrible boosters, that was one of our bread and butter jobs when I was a Mazda tech, they even had a warranty extension on  them I think.

RallyWrench > AMGtech - now with more recalls! 08/16/2019 at 12:07

0

Well that’s unusual, great find and good to know . I’ve seen one booster go in a 210 that I can recall, but no other MBZ that I can think of. It’s m ore common with Volvos, VWs, and BMWs , but usually the failure has been obvious, with a lack of assist and audible hissing.

OPPOsaurus WRX > PartyPooper2012 08/16/2019 at 12:22

0

for the diagnosis, not the repair.

Variance > AMGtech - now with more recalls! 08/16/2019 at 12:23

0

Wow, that is a pretty aggressive cam profile.

brianbrannon > AMGtech - now with more recalls! 08/16/2019 at 12:32

1

I had a rough idle on cold starts in a Volvo caused by the booster

GoodIdeaAtTheTime > AMGtech - now with more recalls! 08/16/2019 at 12:34

0

You mean you can’ t just plug in the computer and then the car tells you what to replace? Heresy I say!

Anyways, the good ole smoke tester. I use mine so much (I bought my own) that I’ve burned out the heating element. Twice. But by god, it makes things so much easier. Like the BMW I am working on, been to 3 shops over the last month. I found the issue in 15 minutes. Boosters are not an uncommon failure, they are just so overlooked in routine diag, I see a bad one at least once a month.

His Stigness > AMGtech - now with more recalls! 08/16/2019 at 12:36

1

Holy shit you post on JRIT S? I saw this last night.

PartyPooper2012 > OPPOsaurus WRX 08/16/2019 at 12:49

0

Dang it. That’s the last money I had in my landfill . I was saving the rest of a paperclip

AMGtech - now with more recalls! > His Stigness 08/16/2019 at 13:11

0

As of like a month or two ago.

AMGtech - now with more recalls! > OPPOsaurus WRX 08/16/2019 at 13:11

0

$1600

AMGtech - now with more recalls! > RallyWrench 08/16/2019 at 13:13

0

Yeah I've seen maybe one or two boosters fail. More often they're caused by the master leaking into the booster.

AMGtech - now with more recalls! > Akio Ohtori - RIP Oppo 08/16/2019 at 13:13

1

Correct. Extremely useful. Particularly for evap leaks.

AMGtech - now with more recalls! > Highlander-Datsuns are Forever 08/16/2019 at 13:14

2

I’ve maybe replaced one or two ever, usually because the master leaked fluid into the booster.

AMGtech - now with more recalls! > AkursedX 08/16/2019 at 13:14

1

Internal diaphragm.

AMGtech - now with more recalls! > GoodIdeaAtTheTime 08/16/2019 at 13:17

0

Uncommon on some brands, common on others. I’ve maybe done one Benz one ever, and maybe one on something else.

MrDakka > AMGtech - now with more recalls! 08/16/2019 at 13:27

3

If you applied the sacred unguents and chanted the binary prayers, the car’s machine spirit would’ve been more forthcoming and told you the  cause of the problem.

AMGtech - now with more recalls! > MrDakka 08/16/2019 at 16:23

1

Unfortunately I skipped prayer day at tech school. So I missed out on all that knowledge!

superdave847 > AMGtech - now with more recalls! 08/16/2019 at 18:37

1

Your job is so cool.

My sister in law just got engaged to an Acura NSX technician. I love hearing about this type of mechanical  work.

AMGtech - now with more recalls! > superdave847 08/16/2019 at 19:38

1

Lol thanks! It's not all glamour though 

Future Heap Owner > Variance 08/17/2019 at 00:15

0

You can tell that by seeing one shot of the valve cover off? Just f rom those two front lobes that you can see the position of fairly well?

pip bip - choose Corrour > AMGtech - now with more recalls! 08/17/2019 at 06:52

0

i’d never think of brake booster

Variance > Future Heap Owner 08/17/2019 at 10:21

1

Yeah. The specifics of the profile and timing I wouldn’t be able to say, but there’s enough visible to see that the opening and closing rates of the valves are fairly aggressive. Look at how “pointy” the AMG’s lobes are compared to the Toyota 3S-GE cams below:

No Prius Needed > AMGtech - now with more recalls! 09/22/2019 at 16:56

0

Hey AMGtech, would you happen to know the procedure for accessing dyno mode on a C217 S63 (4.0) ? I would like to know as I am  conducting scientific research in Mexico.