TomZVB

I wouldn't worry about the crazy numbers... I restarted the car at that point - it would have had to be an issue during the restart (it was still recording data - there would be burst lines with that much pressure - not possible).


You asked about low pressure vs RPM? What do you mean? I'll grab the RPM data next time. I can actually grab a lot with the live data part of the app... I turned off a lot of what I had being captured so that I could see the screen better. Let me know what specific data points to grab and I'll get.

What's the proper ratio for the STFT and LTFT on these cars? Most of what I've read is that if it's not much above 10%, it's not doing too bad. The spread between bank one and bank two seems to be close to some others that I looked up.

Need to see if I have some older data stored from when I got the car, too (I might).

Thanks!

CaliBenzDriver

Capture both the in-tank fuel pump pressure and the engine RPM.

We want to see how stable or unstable is your low pressure supply under load.

Your engine being lean causes lesser accelerations.

You are really "saving gas" now!

maw1124

I’m just quoting this post to make sure I get your attention.

When my S55 acted like that it was fuel pump on the way out. It was preceded by like 2 years by an intermittent long crank that a CPS didn’t remedy. You have to check the fuel pressure at the rail to catch it, which my guy did. Sure I could limp around (these are Benzes after all), but anything like AMG behavior was a no go. Fuel pump(s) and filter and no more issues. I don’t even recall if it was one or two.

I read somewhere above in the TLDR that you had a strange fuel pressure reading, and then I skipped to the end, for the reasons I stated above. I suppose you could start with just the fuel filter (clogged) but how much time do you want to spend?

GL

maw

TomZVB

Thanks for that!

The fuel pressure spiked to some crazy number noted in the next to last post by Cali. Like almost 13k PSI! No way it could make that - I noted it above. Just an error from the device capture or whatever the ECU spit out at that moment. Has to be, right?

Interesting to note... Sometimes it starts right up without even a crank. Other times it might be a second, maybe two at most. The car has 90k miles on it - I do know from history that it's had a high pressure pump replaced and I'm pretty sure the pump in the tank was done, too.

If someone could help gather a full VMI with damage report, I'd be really really grateful!$ (the one I got from the former owner had none on it).

TomZVB

Did some looking in the M157 group on FB and found someone with a similar issue. Misfire on the left bank and AFRs out of whack. Possibly oil in the harness especially at the O2 sensor and a small pigtail connector for the injection harness on the left side.

The sporadic behavior of the O2 sensor (mentioned above), and the way it was working for a couple of spirited passes and then fell on its face seem to point to some weirdness that may just be connection-based.

Can’t hurt to look before throwing money at it.

CaliBenzDriver

You can't fix unknown problems by throwing money up in the air.

Both bank Trims are nearly balanced, saying the same thing.

So I am not going after ignition, Lambda, VVT or CKP... but fuel delivery.


Of course there's a list of maintenance parts waiting for you after this issue is fixed. It's a bad idea to shuffle evidence with random parts: dozen of things can cause misfire. Here its a lean engine.

billvp218

My SL63 was doing that sometimes extended crank for awhile also. I had my coils and plugs replaced, and the issue went away.

TomZVB

I understand what you’re saying, but when looking at general troubleshooting guidance around fuel trims, the numbers do not indicate a seriously lean condition. If the trim indicated a total of 25%, then I’d be more convinced. A 10% increase may even be proper for an engine with 90k+ miles on it. Fuel rail pressure also seems to be good, too, and increases as you’d expect with rpm.

Does anyone have any fuel trim data available they could share for a stock P30 M157?

TomZVB

Looking at the log file I sent, the lowest pressure recorded is 98 bar/1427 psi. That is not under load.

If I’m understanding correctly from one of Taso’s many videos, the minimum pressure, under load, is supposed to 100 bar/1450 psi. According to the log, we’re well above that.

If there was a real problem there, we’d see a P0087 code, but we do not. To see everything second by second, we have the log to refer to and the log doesn’t support fuel pressure issue.

I can run the driving tests via Xentry to see what we get for fuel pressure, but I think the data we already have doesn’t support the need.

Thoughts?

JettaRed

iTrader: (1)

You could reach out to @BenzNinja as he is very familiar with diagnosing these problems.

I agree, trims less than +/-10% are generally normal. Anything reaching or exceeding +/-25% will throw a code and turn on the CEL.

Sorry if I missed where you said whether plugs and coils have been replaced. If they haven't, it wouldn't hurt. BUT, make sure you get the right plugs and index them properly when installing them. Don't assume even factory plugs index properly.

TomZVB

Agreed too on the fuel trim numbers. Pretty sure it was tracking max increase at 10.9 percent STFT+LTFT. I’d have to go line by line to be accurate, but that’s what I I saw under boost (sections marked in green in the log).

Coils were probably not replaced - I only replaced the one that the obd system said was bad (so much as said, “open circuit.” Could have been antifreeze shorting it from when I replaced the crank case vent line). Anyway, I ordered a new set of Beru coils that should be here Saturday. Plugs were done at approximately 70k miles (might have been 80k miles - going off memory).

Thanks for suggesting reaching out to BenzNinja. I will do that. His Xentry setup is what I have (purchased from another member).

chassis

@TomZVB start throwing parts at this car.

Measuring, re-measuring, and re-re-measuring isn't going to do anything except tell you to throw parts at this old car.

Measuring the car to death isn't going to fix the problem it has.

TomZVB

Not sure I'd classify my SL as an, "old car," but that's not really the issue here.

Chassis, I couldn't tell if this was directed at me or not, but I am a firm believer in using Xentry and other diagnostic tools to properly fix a car. "Throwing parts at the car," to fix it until a solution is found is one of the reasons why mechanics are given such a bad rap these days. Seems no one knows how to get in there and figure it out. No offense given, it's just my belief.

Looking at the Carfax records I found last night, the plugs were replaced at the 7-year mark to align with required maintenance. The good thing with this car is that all maintenance was performed by MB at yearly intervals despite mileage indicating previous owners cared for the car properly. A, "fuel pump," was replaced in 2020. Which fuel pump I'm not sure (I thought I read in another report that it was one of the HPFPs)... doesn't really matter though because reported fuel rail pressure is well above minimum under load - Xentry found no issue during idle tests either. The left bank downstream O2 seemed a little jumpy, but that could have been from inaudible misfires at idle - the car sounded smooth while running in the garage and hooked up to Xentry so who knows. I'll check it again after replacing the coils.

First point of attack will be the coils, and they'll be here sometime later today. I may run up to MB of VA Beach to grab a set of plugs, too, just to make sure I have them on-hand.

Appreciate all the help everyone has given! Again, if anyone can run a VMI with damage report, I'm happy to make a donation for services rendered! PM me.

-Tom

chassis

The owner of the old car in this thread should throw parts at it. Playing video games again and again with an OBD reader doesn’t solve the broken and worn out parts problems that exist.

OldManAndHisCar

When ever I try to replace car parts my mom gets mad that I leave dirty hand prints on the walls going back to the basement to play video games....

That said, as I had said - I had the exact same thing...it was coil 7.

JettaRed

iTrader: (1)

That's not a disciplined approach, but I'll play along. Which parts should he throw at the car without understanding the root cause of the problem? Taken to the extreme, why not just rebuild the car from lug bolts up?

TomZVB

Now I’m starting to take offense. Here’s how a good thread can go down the sh*****.

Video games?

I data logged with a OBD reader that had the capability. That could provide useful information, and since this particular subforum seems like a good place for this, why not post it up to have a discussion about what the problem could be?

For the actual diagnostic work, I’m using Xentry Diagnosis. I’ve run the test that I’m able to - and the car checks out with exception to a slightly out of spec intake MAP reading and a jumpy buy in spec O2.

I am replacing the coils this afternoon because they are a failure point of this platform that’s easy to apply a preventative measure.

So Chassis, per JettaRed’s question, should I go ahead and rebuild my, “old car,” from the lug bolts up?

TomZVB

LOL

Coils should here in an hour or so.

jcarsnz

@TomZVB Any particular reason why you went with Beru coils rather than Bosch etc? Price/quality/availability?

Keep up the great work on your fault finding investigations, you're doing a brilliant job (had to laugh at someone recommending the 'parts cannon' approach!)

TomZVB

Thanks!

Regarding the coils, I saw a mention of Beru being oem and decent - and I could get them immediately.

TomZVB

And she’s back to being a beast again. It was the coil pack on number 6.

I took the car for a quick drive to warm up to make things easier. The car was still symptomatic radically as it got warmer. Normal driving was okay, but anything over 3250 rpm caused a misfire (according to Xentry’s log).

So, I got to work. The coil pack pulled out effortlessly - and left the plug insulator insulation in the hole. Shoot! Not easy to get it all out but I did.



Inside you could see that it was scattering spark. Under heavy load, I’m guessing it was enough to ground out the coil pack. Or it was outright failing internally. Anyway, I went ahead and replaced them all. Took a couple hours and would have gone quicker had I. It had to dig pieces of the insulation out of the plug well. I did not pull the plugs.

Appreciate all the help here guys! Glad to have her back up and running full strength again.

PeterUbers

Once again for the record:

you do not need a CEL for a bad coil as a culprit


nice work, congrats

JettaRed

iTrader: (1)

That is surprising. A few misfires may not trigger a CEL, but there should be some codes. Every other car I've ever owned would throw a code and CEL with misfires. It seems Tom was able to see the misfires with live data, but I wonder why they didn't trigger any codes.

TomZVB

Initially, it did not throw a code, and I’m thinking it was because as soon as I felt it misfire, I got out of it. My guess is that the insulation was doing enough to contain spark under less demand. If the Mrs was driving, it could have gone on for quite a long time before becoming known.

It finally threw a code during testing. I pushed it harder and it started to flash the CEL A little bit more and it set the code. Shutting down and restarting would clear it.

I’m just about positive that the coils were original to the car so I’m glad they’re all done.

Side note… Xentry really allows you to see some data! The record for the stored misfire events was full of details that the BlueDriver app couldn’t provide. I’m glad I made the purchase.

JettaRed

iTrader: (1)

From what I have read, our cars will spark up to 5 times per ignition cycle. I can see where a marginal coil could start to miss some of those sparks.