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Discussion Starter #1
Can anyone give me some help please.

I recently been noticing that, especially recently in the hot weather when the car get hot(the temp dial on the oil is nearly at the 6 o.clock and the water temp is at the is slightly over the 12 o'clock ) that on a balanced throttle or low acceleration there is a noticeable judder/hesitation like if you where running out of fuel but the tank is half full. It doesn't stop, but on hard acceleration it seems to be fine.
I did a diagnostic and it only showed the fan on the ecu.

Would the overheating of the ecu cause this ?

Any help would be most appreciated.
 

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Anything past 12 o'clock for coolant temp on public roads is too hot, so I would first troubleshoot the cooling system. What is your KTEMP reading?

The judder/hesitation that you're feeling could be the ECU pulling timing to prevent detonation. Or the fan clutch is fully engaged and you're simply feeling its parasitic drag.
 

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Hi Sweeney, Many thanks for answering.
The KTEMP sits at 81 degrees C. with the outside temp 23 degrees C and going at a constant 70mph. When slowing around junctions etc it rises to 85-6 degrees C and slowly drops back to previous temp.

I also changed the E-Box Fan just to rule it out as I bought it a while ago but never got around to fitting it.
 

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I did a diagnostic and it only showed the fan on the ecu.

Would the overheating of the ecu cause this ?
Maybe, there are several failure modes that trigger that code. Some have symptoms some do not. In all cases they should be fixed. The issue is not the ECU over heating, the more likely situation is that right under the spot the air blows from the fan is an ECU temp sensor. If the fan is not blowing at the correct speed the temp that sensor is reporting may not be correct. The fan has two speeds. The temp sensor must be important because the ECU runs the fan when the starter is engaged, it is not doing that for cooling.
Also the power that is supplied to the CPS comes from the same place as the power to run the fan. If there was a short or other fault it may change one of the voltages in the CPS, not a fan of that theory but I can't argue against the logic.
If you have a fan fault code it seems like a no brainer to fix it first.
 

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Discussion Starter #5
Hi Sailor, Many thanks for replying.
I suppose I'll have to see if the E-Box Fan replacement sorts it out. Although the run which I had taken the above temperatures was just a 10 mile round trip around local roads with no busy traffic. The problem arose when I was making a 1 hour journey to my destination and on the return journey back home around 30 mins in I started having the juddering etc. This was through busy stop start traffic at the beginning and an outside temp of 30 degrees Celsius.
 

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Could just be CPS issue too. Your complaint would be in a egr zone and the CPS affect how much exhaust gas is returned to the system. The fan seems more likely as the symptoms for it are near the same as bad CPS.
 

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Discussion Starter #7
I replaced all 4 CPS's a couple of years ago. Can you do an individual test on these?
 

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If you replaced them I would think they are OK. I have not had to replace the newer version, but others have. If you were not getting misfire codes then I am not sure you could figure out things anyway.
 

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Not to hijack but I am troubleshooting the same exact issue. I just took possession of a car and experienced the exact same symptoms. My ecstasy was short lived as after approx 15 miles of driving the ECU threw multiple misfire codes and rich bank conditions.

initial symptoms are exactly as you describe - Happened when I was driving on highway in the mid day heat (onboard ambient temp read above 100). Hesitation came on at 3k rpm and although motor would rev higher it was extremely lethargic. Shuddering, bucking, I was worried it was something more serious but now I’m convinced it’s sensor related. Just hoping it’s not VANO$

At first I thought it may be fuel pump as the symptoms seemed like it was not getting but after reading this I am not so sure. The codes didn’t appear until I limped the car home and restarted it to try and replicate the issue. I’ll try posting a video of a second and third gear pull here but any insight would be most welcome. In addition to misfire and lean bank, I got misfire after start code, too.

Car does have afe I takes and I cleaned the MAFs with CRC but they looked pristine. Help I am stumped, too!
 

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Not to hijack but I am troubleshooting the same exact issue. I just took possession of a car and experienced the exact same symptoms. My ecstasy was short lived as after approx 15 miles of driving the ECU threw multiple misfire codes and rich bank conditions.

initial symptoms are exactly as you describe - Happened when I was driving on highway in the mid day heat (onboard ambient temp read above 100). Hesitation came on at 3k rpm and although motor would rev higher it was extremely lethargic. Shuddering, bucking, I was worried it was something more serious but now I’m convinced it’s sensor related. Just hoping it’s not VANO$

At first I thought it may be fuel pump as the symptoms seemed like it was not getting but after reading this I am not so sure. The codes didn’t appear until I limped the car home and restarted it to try and replicate the issue. I’ll try posting a video of a second and third gear pull here but any insight would be most welcome. In addition to misfire and lean bank, I got misfire after start code, too.

Car does have afe I takes and I cleaned the MAFs with CRC but they looked pristine. Help I am stumped, too!
Exactly what are your codes? Do you know if the CPS have ever been touched or if they are original? Do you know if the vanos boards have ever had maintenance?
Just a note you can't see what might contaminate your mafs by eye. Even when they were a wire you had to use more than a magnifying glass to see the deposits. Not likely your issue anyway but how you test for that is to unplug the MAFs electrically and see if the performance changes after 50 miles of travel.
 

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Thanks Sailor. Fair winds and calm seas! I had a Pearson 26 before kids came into the frame. Miss the bot and sailing a lot. The M5 was bought as an alternative to a “day of boating” as I am over two hours from the Chesapeake. Anyhow...

The codes were as follows:
P0172 System too rich bank 1
P0175 System too rich bank 2
P1342 Misfire during start cyl 1
P1348 Misfire during start cyl 4
P1350 Misfire during start cyl 5
P1354 Misfire during start cyl 7
P0136 Miafire detected on startup (first 1000 revolutions).

it’s worth reiterating that the car didn’t throw the codes WHILE it was presenting the symptoms - after getting back to my driveway, shutting it down, panicking, and starting it back up, the SES light illuminated. I went to my buddy’s house and got his code reader, read codes, cleared codes, and waited 30m or so. Got back in car and did some laps around my block and the same lethargy presented itself - I was able to capture a short video of this. When giving full throttle in second the rpms rise very slowly almost like a 4 cyl car lugging in a high gear.

Regarding maintenance history it’s very thin but the car is in excellent shape so you can tell it was loved. I bought the car last week. It was a 3 owner 86k miles car, and is in very good shape but based on the carfax history, most of the miles were logged early in its life. The last owner put 2k miles on the car in the six months of ownership and didn’t relay any issues. I had a PPI performed in Eurofed Penns Creek outside Atlanta. No issues reported. I have a feeling it sat a lot in a garage before moving to owner 3’s possession. Biggest sign of it’s “road hiatus” are 11 year old tires.

Compounding my ability to diagnose the engine problem is a slipping clutch:mad:. I did take the car back out in the evening and it ran normally but I wasn’t able to driver her hard enough to generate the temperature.

I was back in touch with the seller and he suggested it might be heat soak causing faulty MAF readings and that doing something like the Turner Motorsports remote temp sensor would resolve the issue but I don’t agree - it’s more than diminished performance it’s almost a “limp mode” type manifestation. He never had any symptoms like this and I tend to believe that he’s being up front with be - benefit of the doubt and all the time I’ve spent chatting with him in the run up to the sale. To be honest it’s a complete divergence from the way the negotiation and sale went and I know he feels terrible about the issues too.

What else would help troubleshoot? I’ll upload a video of second gear. Thanks for your insight guys.




Exactly what are your codes? Do you know if the CPS have ever been touched or if they are original? Do you know if the vanos boards have ever had maintenance?
Just a note you can't see what might contaminate your mafs by eye. Even when they were a wire you had to use more than a magnifying glass to see the deposits. Not likely your issue anyway but how you test for that is to unplug the MAFs electrically and see if the performance changes after 50 miles of travel.
 

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I don't know but it sounds like the car might not have been as well maintained as people think it might have been. A slipping clutch does suggest something. Either the PO never drove hard enough to see that, which would likely mean not hard enough to see other things, or he was good at ignoring things. It also suggests the PPI guys never drove the car.
You likely have bad mafs so unplug them and drive it for a bit and see how it runs. If they are really bad you can get misfires but not usually misfires during warmup, that usually points to CPS. Unplug the MAFs and see how the car runs.
The only good thing is when the tranny is out it is easy to to access the CPS so pull them out and look if they are the new style or old style. If they are the old just replace them, there is a reason they got updated.You will find pics of the old and new in some of the CPS threads. Read the mafs threads and CPS threads to see if your symptoms are the same.
Remember while reading that you might have the two problems not one so add the symptoms together in your head.
 

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Unplugged MAFs and no issues but it’s a much cooler day and I didn’t wind the car out at all. Babying the clutch...

If I’m understanding the logic sailor, faulty CPS would generally throw a code early in the warmup phase? I got the car up to temp w MAFs unplugged but didn’t get the engine as hot as Monday when it threw codes.

Pulsapharer check out the video - is that similar to what you experienced?
 

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When you unplug faulty mafs it takes time for the adaptions to change so how it drives now will be different than how it drives after 100 miles and the adaptions change. I have the tools to watch for the changes to the fuel trims, so just seeing them change would be enough for me know. But you can only see those changes when you plug them back in.
CPS are hard to understand because they almost always go hand in hand with vanos boards that have not had the maintenance done. It is actually the vanos boards that are causing the code the bad cps just compound the problem.
All do respect it is way to big a topic and I can't explain little pieces because the picture is to big, read the threads. There is not one thread that has it all in it, the picture is much bigger than one thread.
 

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Pulsapharer and medik212: I'm struggling with the same issue exactly as you are on my MY2000 with 86k miles. Same heat conditions >110 degrees at the pavement on super hot/humid day in NY. Oil temp got to where it shows in your video which it never has done before and car went into choke mode/bucking/stalling. Had installed new clutch and new MAFs in the past 6 months, and CPS about 16k miles ago. I'd been getting the e-box fan code also before this happened and already ordered the fan which was in the mail when this happened. I took it to an indy who has a lot of experience with BMWs and despite them test driving it for 30 mins and getting the engine box very hot, wasn't able to recreate the experience (albeit on a cooler day). He reset the MAF adaptations which maybe helped the car drive a tad smoother but the mystery remains. I was about to mark it up to perhaps old gas sitting in the car during covid for months until i read your post... I've driven it locally with no problems but now don't have confidence to go very far until I've replaced the e-box fan which i hope to do in the next few days. Will let you know how it goes.
 

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I unplugged MAF and took a short drive in 2nd and 3rd gear. No misfire codes but I did get the two air flow circuit low (bank 1 and bank 2) plus intake air temp Sensor circuit 1 high.

Sailor - is there any merit to unplugging the battery and letting DME “forget” so I could let it idle/rev and thus drive driving less miles, then plug my code reader in to watch trims? I get that it’s a big mess of variables and am hoping I can eliminate at least the basic stuff that an Indy will charge me $150/hr to perform when I can have the satisfaction (read: frustration) of doing it myself while escaping my wife in the no climate controlled comfort of my garage.

I am also surprised to see there’s no comprehensive writeup on the DIY on misfires but there are a lot of good ideas and advice. If I get the itch I may try to map out a decision tree based on my understanding of what others have done to successfully eliminate or identify root causes for the same issues.

Multiple or single misfire
Bank 1/2/both
Lean vs rich
Etc...


I did read the entire (two) threads about the poor guy who threw damn near every trick in the book at his misfire on cylinder 5 issue and was frustrated to see it ended up being idiopathic. Hoping I don’t go this route myself.
 

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is there any merit to unplugging the battery and letting DME “forget”
These car are elephants I guess, because they don't forget. Unplugging the battery does do something but nothing that will help you. The car will adapt by itself.
You can read what you want but Wayne's thread was different and of little relevance to your situation. The punch line of that thread was it could have been a computer problem where a block or two went bad. The last place he took it the car was reprogrammed sort of by mistake and that fixed the misfire.
As far as the codes you got, try reporting them as numbers please, adding the definition also helps but numbers avoid confusion or sloppy reading. You should have those codes because the MAFs are unplugged and the air temp sensor is part of the maf.
How does it pull when you get on it? That is what you need to be looking at, if it pulls strong. Then plug the MAFs back in again and see if it pulls weaker after a couple of blocks, then watch to see if it gets weaker as the miles click by.
Bottom line is if you feel a difference with the MAFs unplugged you either have bad MAFs or a vacuum leak above the throttles. My bet is when you plug the MAFs back in the fuel trim codes will come back even if the misfires don't.
 

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no comprehensive writeup on the DIY on misfires
Because there is not one but there are steps that relate to most common problems with these cars.
1 codes
2 air and there are 3 things there MAFs, unmetered air leaks or leaks above the throttles and then air leaks below the throttles.
3,4,5, etc are other things
depending on how your MAF test goes your next step is to replace the plugs and that has not been mentioned because replacing the plugs is not really replacing the plugs we want to look at them but plugs are cheap and there is no sense in putting old plugs back in. But the real reason is because there is a very common air leak that you can't see and likely will not expect. It is the valve covers and because this car runs with a vacuum in the crank case leaky valve covers = air leak not oil leak. You will see oil around the spark plugs however. So you will deal with that before the next step.
These are not normal cars you almost have to set aside a lot of your previous experience.
 
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