07/1998 750iL - V12 - Surging

[740ilDuke]

My 98' 750iL (72k) that I rescued back in January has been running great - aside from a surging issue.

SITREP: When I bought the car it only ran on bank 1. I found out that one DME was bad, so I bought one on fleaBay and had dudmd clone it. Summer arrived and it's been too hot to mess with, so today I got back into it. It typically only throws code 115 (MAF).

You can touch the 52 pin connector going into DME 2 (closest to front of car) and the engine will stumble then level out. However if you continue to touch the wires between both DME's you can shut the car down. This never happens unless your hands are in the box. I removed the connectors
and inspected each individual pin for corrosion and used connector cleaner to be sure they were OK. When back together it does the same thing. I even tried swapping the DME's - as they are clones the same thing happens. When you touch the wires, the engine dies down to half power.

Do I need a new harness or perhaps different DME's cloned again? Im out of ideas. BMW still sells the engine wiring harness for a cool $1030 or so. Im not happy about that prospect, much less installing it. But - with the low miles it's beyond worth doing it.

Thank you for any recommendations.

[TheAngryBear]

Wow, much different issue than normal...
What was the condition of the original DME pulled? Water damaged?
Check continuity of the harness? Sounds like there is either a shorting split in the harness or lack of grounding.
Best I can come up with right now. Will think on it some more and see what else I can come up with.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[MKIVJZA80]

look for a good used harness, there is a member parting out his calypso 750 who may still have both ECUs and the harness. i was interested, but no longer need them.

here's the thread

https://www.bimmerforums.com/forum/s...750il-Part-Out

[740ilDuke]

Wow, much different issue than normal...
What was the condition of the original DME pulled? One DME was painted black and had a label on it from the person who was working on it. It turned out to be bad. There was some moisture, but not much. I cleaned the ebox out, mostly just some loom tape. The wires arent crispy anywhere. All are plyable with good jackets.

Water damaged? No water damage. The good DME was used to clone a donor

Check continuity of the harness? No idea where to start there. Seems like replacing it might be easier short and longterm than checking dozens of wires. Im no electrician either.

Sounds like there is either a shorting split in the harness or lack of grounding. Best I can come up with right now. Will think on it some more and see what else I can come up with. Its definitely a connectivity issue. I just dont know if it's the harness or DME's. I suppose throwing those 3 pieces to the puzzle at it is one way to go, but expensive. As it's 20 years old I think the harness would perhaps solve a few headaches long term.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

.

- - - Updated - - -

Just posted asking the price. Im really on the fence about used due to age alone. Id actually bought a harness for $75 on eBay but the shop lost it. #luck
Has to be PFL too, which this calypso one is.

look for a good used harness, there is a member parting out his calypso 750 who may still have both ECUs and the harness. i was interested, but no longer need them.

here's the thread

https://www.bimmerforums.com/forum/s...750il-Part-Out

[TheAngryBear]

look for a good used harness, there is a member parting out his calypso 750 who may still have both ECUs and the harness. i was interested, but no longer need them.

here's the thread

https://www.bimmerforums.com/forum/s...750il-Part-Out

Even better as a little less work intensive.
I was going to see if you could diagnose and repair the specific failure point on the harness.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

Even better as a little less work intensive.
I was going to see if you could diagnose and repair the specific failure point on the harness.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

I spent about 5 hours today pulling the DME's out and using the newtis.info site to learn where a few of the wires
go, mainly the MAFs (code 115 inpa) - but since they are connected through the EML and to each other through the maze
of wires it just felt like an endless guessing game. I suppose if I spend the money on the harness and it still does it, it's
the DME's. But as the car runs perfect until the wires jostle, I feel like the harness has to be the solution.

[TheAngryBear]

The way it behaves I agree with you on the harness.
I started poking around mine but then remembered you are PFL. Not sure what the exact differences are but probably sufficiently enough so we can’t compare exactly.
For some reason (probably because it isn’t me... touch wood) I feel like it is something that should be “easily” identified with the DME pinout. I mean the MAF and O2s shouldn’t kill it but the CKP and CMP could. Grounds could. Etc.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

Making me curios again. lol - whats the CKP and CMP?

I dont think there's much difference. The engines are mechanically the same. Probably to do with heated catalyst, dual batteries and a couple other modules I dont have. The EKAT module (under pass seat) and Dual Battery Module (mounted on side of dual bats) are no longer being made. Luckily the PFL didnt have those. Aside from that, massage seats and lit handles are the only options I dont have. Single battery & air cooled alt.

"Due to more stringent emissions standards, the 1999 model year marked the addition of an electronically heated catalyst, variable MAP thermostat, and water cooled alternator."

The way it behaves I agree with you on the harness.
I started poking around mine but then remembered you are PFL. Not sure what the exact differences are but probably sufficiently enough so we can’t compare exactly.
For some reason (probably because it isn’t me... touch wood) I feel like it is something that should be “easily” identified with the DME pinout. I mean the MAF and O2s shouldn’t kill it but the CKP and CMP could. Grounds could. Etc.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[TheAngryBear]

Making me curios again. lol - whats the CKP and CMP?

CKP = crank position sensor
CMP = camshaft position sensor

Well, limited by my exploration but there are three grounds to the chassis on the strut tower (possible), three bundles of grounds to the chassis by the right air intake (not thinking those, to far)...
For me, my harness drops/sags right after exiting the box and before hitting the back of the engine. If anything were to get flooded that seems like natural collection point... and right over the exhaust so likely a hot spot. Sheathing failure from heat?
That is possibly a likely point I would investigate...


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

CKP = crank position sensor
CMP = camshaft position sensor

Well, limited by my exploration but there are three grounds to the chassis on the strut tower (possible), three bundles of grounds to the chassis by the right air intake (not thinking those, to far)...
For me, my harness drops/sags right after exiting the box and before hitting the back of the engine. If anything were to get flooded that seems like natural collection point... and right over the exhaust so likely a hot spot. Sheathing failure from heat?
That is possibly a likely point I would investigate...

Gotcha.

No flooding or anything like that - but when I get around to replacing the harness, ill be sure to look into insulating any areas that might
be susceptible to heat.

I have found that with the DME's switched around the car does not run as well. Not exactly sure what might cause that - or if they are intended to have the ability to be swapped around. I'm swapping them back today to the previous configuration.

[740ilDuke]

UPDATE:

Last weekend I painstakingly checked each pin on the DMEs and plug side. I pulled them out one at a time. I wasn't sure which DME was on the BLACK harness, which as I read is the MASTER cable and GREY is the SLAVE set. The car through a bunch of codes this week and didnt drive quite right. Today, I flipped the DME's around and am back to only getting INPA Code 115. This is the MAF sensor. However, there are (2) on the V12 and I do not know which side to focus on.

Any ideas?

Thanks!

[TheAngryBear]

Best I can do for you:

Firewall: blacks
Mid: greys
Bumper side: blues

I thought in inpa you had to specify which DME you were interrogating... guess worse comes to worse unplug one MAF and see if the codes change? If no change then you unplugged the correct one? I am normally playing in DIS which is more definitive on the bank...


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

Just now I put a meter in the MAF plugs, both are providing power. The surge issue totally goes away when I disconnect both MAFs. If they are connected, I can place my hand on the E-Box and push down, every single time it surges.

So, Im wondering if I have a DME problem or a wire problem. I guess one way I could approach it would be to find the pin-out and re-run the
4 wires from each side to their correct place in the DMEs.

Thoughts?

Best I can do for you:

Firewall: blacks
Mid: greys
Bumper side: blues

I thought in inpa you had to specify which DME you were interrogating... guess worse comes to worse unplug one MAF and see if the codes change? If no change then you unplugged the correct one? I am normally playing in DIS which is more definitive on the bank...


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[TheAngryBear]

Can’t find a wiring/pin out for 98... hope you have it.
What happens if you unplug the mafs and run?
I might look at the reported MAF readings in inpa and see if they make sense. Might have output but if low/high then could cause issues.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[TheAngryBear]

The surge issue totally goes away when I disconnect both MAFs. If they are connected, I can place my hand on the E-Box and push down, every single time it surges.

Thoughts?

Rereading this it sounds like a connection issue. How doe the pins and sockets look? Any junk or short pins?


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

I went into INPA and looked at each LEFT and RIGHT DME's in the status section. The MAF located on the driver side (feeding bank 1) has a wild reading of like 14.7 or so. The MAF feeding bank 2 is reading correctly. 3.75 range.

VIA PSJR:
Bank 1 MAF (located on the driver's side) pins:
Ground to a ground splice in the engine harness that eventually terminates at a passenger side shock tower ground nut.
Power from the second fuse in the tan DME fuse box
2 Signal lines to DME I (the one with black plugs) pins 9 and 23 of the middle (52-pin) plug

So, with the pinout I can run all 4 wires new to the appropriate places. It is stamped on the plug, so the above is actually suffice.

PIN OUTS <--------

Maybe this week Ill have some time to mess with it, if not next weekend.

Ill update after my next move. This approach is a helluva lot cheaper than a $1000 harness.

Can’t find a wiring/pin out for 98... hope you have it.
What happens if you unplug the mafs and run?
I might look at the reported MAF readings in inpa and see if they make sense. Might have output but if low/high then could cause issues.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

Ran new signal wires, same issue. Stutters when you touch the wires. The DMEs' have been cracked open, so Im wondering if theres something going on there, or harness needs swapping.

I guess I could run new ground and power wires and see if thats the issue. If its not, im back to replace DMEs or Harness. The question is which first. Semi leaning on DMEs since the wires seem plyable....

Ideas?

[TheAngryBear]

Which wires when it stutters? The new signal wires?

I would use your system and see what the signal is doing when you touch them. Then switch the MAFs and see what happens there. If the readings switch then you have an issue with the MAF(s). If not the likely the DME(s) contacts/internals.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

It always stays with the maf on the driver side. Avg reading is 3.75, that side shoots to 14+ when touching the harness.

- - - Updated - - -

What is required if I buy two used DME’s to make it work?

When I got the donor DME off eBay I had to ship them to DUDMD for chipset work if I recall

[TheAngryBear]

It always stays with the maf on the driver side. Avg reading is 3.75, that side shoots to 14+ when touching the harness.

- - - Updated - - -

What is required if I buy two used DME’s to make it work?

When I got the donor DME off eBay I had to ship them to DUDMD for chipset work if I recall

Is the reading in kg/hr? Iirc readings should be 10-20 kg/hr... so it sounds like when you touch the wire it is making solid contact and the “true” reading comes through. How does the harness and pins look? Any loose seatings? Before getting DME(s) I would investigate the actual connection(s) and pins.

As for the DMEs, I am not sure. DUDMD would have better insight there.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

Is the reading in kg/hr? In INPA I go to the status screen and read the MAF - live reading. Cyl 1-6 maf runs 3.75-4 on the live reading and so does the driver side maf. When i start to touch the loom it spikes to 14-16 on the driver side making the car sputter. Touching the loom makes the sputtering occur almost every time. So on occasion with bumps and driving it sputters. (not sure the measure of units, my laptop is in german) The car runs perfect until one of these connections breaks momentarily. Rerunning the two signal wires did not improve the scenario. I even replaced the pin on the DME side with an extra I had. I did not re-run the ground and power wire because I wasnt sure where to pull power from. Hell, Id considered piggy backing the wires from the MAF on the driver side to the MAF on the passenger side.

I individually removed each pin to inspect for corrosion or anything weird, no brittle wires, corrosion. It makes me thing the DME(s) could have an internal issue. None of the wires under the acoustic cover are crunchy or stiff, which makes me think the wires are ok. Just not sure where to begin.

Donor DME's are about $200 and harness is $1000. But, like I said, I think the chipset has to be moved/cloned if I try DME route. I'll reach out to DUDMD soon and see what he thinks. I know its difficult to troubleshoot 20 year old electronics.

Iirc readings should be 10-20 kg/hr... so it sounds like when you touch the wire it is making solid contact and the “true” reading comes through. How does the harness and pins look? Any loose seatings? Before getting DME(s) I would investigate the actual connection(s) and pins.

As for the DMEs, I am not sure. DUDMD would have better insight there.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

i

[740ilDuke]

Not sure if this has something to do with it or is a bi-product of it. LUFTBEDARF LL STELLER - "air LL requirement" - I checked both air boxes for blockage, all is normal.
26FC9E80-653D-4F73-BA1C-D0BF0EB77B64.jpg

[740ilDuke]

Edwin says Secondary Air Pump. Which, is working. Its not throwing a code, so this must just be how INPA sees that.

[TheAngryBear]

I suppose that makes sense to measure the SAP. Not sure how other than calculation though.

And I just tried to fire up INPA but it is back to the old “files not found” for the DMEs (everything else works though). Hope I can fix that then we can compare values.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1

[740ilDuke]

I found a vid on YouTube and the guy had similar readings, but it'd still be cool to compare.

I suppose that makes sense to measure the SAP. Not sure how other than calculation though.

And I just tried to fire up INPA but it is back to the old “files not found” for the DMEs (everything else works though). Hope I can fix that then we can compare values.


2001 750iL DD74441
Stock

RIP: 2003 540iA Sport GS56111
H&R front springs, Ultimate Cup Holder, Euro Dash & Armrest, Grom, BavSound Stage1