Weirdest electrical issue yet

[michel3171]

Well, after reading trough alot of the forum posts, nearly reaching the stage of driving my E53 X5 into a wall, I've decided as a last resort to create an account and ask for help. Im Michel, 23yo and live in the Netherlands.

Background on the car:

E53 X5 2003 (pre facelift) with the M57D30 engine. Bought the car with a broken engine (crankshaft/rodbearings gone), and replaced the engine with a very low mileage one, together with the gearbox. Replaced some gaskets and fluids, and the car drives without any mechanical issues.

ELECTRICAL ISSUES:

Since I've had the car, even with the old broken engine, the battery light would always randomly flicker. It still does, even with a new alternator. Battery reads 12.5 volts, so should be good aswell.

Depending on how much load the engine has/amount of throttle applied, the light and issues change. At a standstill, with engine off, all electrics work fine without any battery lights. At idle, 95% of the time the electrics work fine, and almost no battery light.

When applying full throttle, the following symptoms occure:

Battery light flicker/constant on
Power windows dont work, if they were in the process of rolling down they will stop doing so
Sunroof doesnt work, same as power windows
Speedometer stops climbing, just stays in the same spot untill throttle is released, then slowly climbs and suddenly jumps to the right speed
Wipers dont work, when mid-wipe they will also stop.

When applying slight throttle, the symptoms are the same just more intermittent.

I've been driving around with my laptop hooked up (INPA), and with the secret menu displaying voltage. Both devices show approx. 13.8 volts when driving, with no changes in voltage.


I like to call myself a pretty good mechanic, but I've got no clue what to do with this issue. The juttery electrics have already messed up 1 wiper motor, the PDC, aswell as my mental stability. Im going to start unplugging modules and accessoires such as an aftermarket headunit, to see if that solves it. If anyone has any clues, please let me know!

Thanks!

[TriX5]

Michel, welcome!

Upon re-reading your post it seems like a wiring break. Since you only get this problem in motion. This will be tough to find but some scouting might show where work has been done on the loom or maybe from installation of aftermarket electronics.

The other things that come to mind, make sure your ground connections are tight. Some of the items you mention are governed by the GM module, windows, wipers. GM modules are cheap and could be worth trying a swap.

As to help, the only good BMW indy I know about is in the north, Autohuis Buursema in Leek. If you are near there, you might try them, they seem capable.

[timmyc]

TriX has a great suggestion: Check the grounds. All of them!

I seem to remember swapping a motor years ago on an older Bronco and we didn't tighten the ground strap from the block to the firewall and I was having all sorts of weird happening. Turns out that's what it was. We had only put it on finger tight, so when we were looking around, it looked like all was well. Only after putting a wrench on it did the ground actually ground. Coincidentally, I just had another ground issue that was making my lights wonky. Grounding is very important in the electrical loop!

Welcome and good luck!

[workingonit]

Originally Posted by timmyc

TriX has a great suggestion: Check the grounds. All of them!

I seem to remember swapping a motor years ago on an older Bronco and we didn't tighten the ground strap from the block to the firewall and I was having all sorts of weird happening. Turns out that's what it was. We had only put it on finger tight, so when we were looking around, it looked like all was well. Only after putting a wrench on it did the ground actually ground. Coincidentally, I just had another ground issue that was making my lights wonky. Grounding is very important in the electrical loop!

Welcome and good luck!

I had a similar issue with my '73 Volvo 142 back in 1976. It would drive fine, then sputter, and the lights would flicker, and suddenly be OK again. After a dozen incidences, I put it in the local Volvo shop for that problem, and one other (Bosch fuel injection surging at idle), and they couldn't find any electrical problem, even after miles of test drives.

Within twenty minutes of leaving the shop, the sputtering/flickering occurred again, so I drove to my Grandfather's house to park it (and borrow his car). I went directly to Radio Shack and bought my first good multimeter, and long test leads & clips. Then, I proceeded to test every ground in the car. I found nothing wrong, so I asked my Grandad what he thought.

He said that he'd disconnect/reconnect all electrical grounds one at a time. He reached over and grabbed the main battery ground in preparation to disconnect, and moved it about two inches, when my meter showed no continuity. I then removed the cable (good condition on both ends, with a light blue plastic sheathing...I can see it in my mind), and stripped the sheathing off of it; there was a corroded section at the mid-point of the cable, with zero corrosion showing elsewhere.

If I, or the Volvo techs had simply flexed the cable far enough, the problem would've been spotted. Afterwards, I figured that the sputtering/flickering incidences had all occurred on roads bumpier than the smooth city streets that the techs test-drove on.

[wpoll]

Welcome Michel.

You might want to check two critical connections.

One - the B+ at the bulkhead jumper terminal (although I suspect this is not the likely issue) - note below as a union splice, and,

Two - the main power connection on the side of the BST at the battery B+. This is VERY suspect in your case (based on symptoms).



The BST connection (to the rear power distribution) is shown here: -



These connections are know to become loose and cause symptoms like yours.

[andrewwynn]

Check the back of the B+ jumper point. That is the primary disconnect for positive.

Twice a year that ends up being the cause of such on xoutpost. It's the easiest thing to fix (just be very careful not to short tools you will turn a wrench into an arc welder quick).

Second most likely especially since engine replaced is the main engine ground. That ends up behind the problem at least once a year on the forum.

Meausure the voltage from the vs. Block to the B- jumper on the fender while running some heavy electrical loads like the seat heaters and the rear defrost then have somebody rev the engine.

The voltage should only be millivolts not like half a volt.

Also: measure the voltage directly from engine block to B+ and B- to B+

[bcredliner]

Originally Posted by TriX5

Michel, welcome!

Upon re-reading your post it seems like a wiring break. Since you only get this problem in motion. This will be tough to find but some scouting might show where work has been done on the loom or maybe from installation of aftermarket electronics.

The other things that come to mind, make sure your ground connections are tight. Some of the items you mention are governed by the GM module, windows, wipers. GM modules are cheap and could be worth trying a swap.

As to help, the only good BMW indy I know about is in the north, Autohuis Buursema in Leek. If you are near there, you might try them, they seem capable.

Welcome!

[TriX5]

To complete the sum-up, there is an engine ground strap under the AC compressor that is in an awkward place and could be loose or become corroded (since you are in a winter-salting environment). Worth a quick check.

Nevertheless, it still sounds like a bus communication issue. Grounding connections play an important role but the "standing still vs moving" symptom would indicate a continuity problem.

[michel3171]

Well, I've tried a couple of things:

Replaced ignition switch.
Replaced battery
Replaced alternator
Checked grounds in trunk and passenger footwell
Measured alot of voltages and resistances around the car
Unplugged All the modules in passenger footwell.

So, what have I found?

Engine running
Voltage engine block to B- in engine compartment : 0.02/0.03 volts
Voltage B- to B+ : 13.5 / 13.8 volts
Voltage Ignition module : 13.5 / 13.8 volts

(NOTE) The voltage on the ignition module drops to 0 volts after pressing the gas pedal a few times, and doesnt come back untill the ignition is turned off and on. Both switches did this.

I have found a big connector under the drivers kick panel, going to the Sound Modul. None of the cables on this connector have a connection to B+ or B-. But then again, I don't have a radio plugged in right now.

I will post up some pictures of the modules, connectors, and INPA readouts!

?!!!? Im going mad.

[andrewwynn]

Measure AC on your B+ to ground.

One possibility is a problem with the voltage regulator leaking AC. The frequency will go up with rpm and that could easily interfere with the comminations.

You can disconnect the alternator once started (at B+) and rev the engine to test this theory. You'll be running off just the battery so short test drive.

My DMM will show me frequency and duty cycle as well as the true RMS voltage.

Feels like a voltage regulator problem to me. New ≠ fixed though you said the problem was there with old alternator so you need to check the ground and the B+ "splice".

In my case the "splice" is a bolt terminal. Several times a year somebody with similar mystery power problems finds the B+ loose.