first E39 need some help

[g.k101]

Just bought my first E39 528I.
unfortunately the cylinder head was cracked and replaced it with a M50 head, same cast etc.
used the cams and trays to the car.
properly set time and replaced single vanos seal
the problem is, anything under 3k RPM I have littler to know power, and randomly I will have proper power
I have been reading forum and it may be electrical related which I am inclined to believe since I have other issues.

As follows:

Radio randomly comes on and off
Fuel gauge refuses to work
ambient air temp stays at a steady -40 at all times, but is one of the fuel sender wires is powered it reads just fine
Car can sit overnight at 12 degree weather and w/o turning the engine over will read temp pinged to red, after about 5min of running it comes to blue and wont leave blue (no air bubbles)

Really need a hand or just a bit of help
talked with 2 BMW tech (my neighbor for a bmw dealer) and a shop, both are stumped
the Local bmw dealer wont even look at it as per the service manager "most of my techs are younger than your car, just get rid of it"
reaching out for any advice, thank you.

[JimLev]

Welcome to the forum.
Really nice that the dealer just blew you off.
Here's a start.
Do you have a check engine light on?
Your -40 temp reading is a bad or disconnected exterior temp sensor that is under the bumper on the pass side.
Sure the timing is correct?
Check for cracked bellows on all the air intake tubes to the engine.
Might want to look under the carpet and foam on the pass side just in front of the right side seat rail. There is a fuse panel there that gets very corroded if water has ever leaked in thru a bad door seal or a bad sun roof drain.
That fuse panel powers almost everything in the cabin and engine compartment.

[killian665]

Man I’d sell that shit.

[Aubergine]

I would almost say the electrical problems sound like a bad alternator or the ignition switch going bad. The radio symptom is the part that really makes me think that.

[edjack]

Verify that the battery and alt are working correctly. A fully-charged battery measures 12.6 V. The alt should put out 14 V at 1200 RPM.

The erratic temp gauge may be due to a bad dual temp sensor.

[adm750]

+1 to everything these guys said...even killian...

all kidding aside, check everything those guys said and report back...

I'm right in your neck of the woods if you need a hand...

tony

[1823alex]

1. Pick a different shop

2. Check your thermostat (for the temp issue)

and for the -40 that's a disconnected / malfunctioning / non-functioning exterior temp sensor, it's located in the front of the car on the passenger side near an air duct I believe. If you live in a warm climate, you'll want to get that fixed soon as iirc your A/C will not function.

[pleiades]

....anything under 3k RPM I have littler to know power ....

You might want to get the car's fault codes scanned with a BMW-capable scanner. This bit about losing power under 3K RPM would make me suspicious of the Vanos-related things like the intake cam sensor and the solenoid.

Also I agree with others that suspect the ignition switch for weird electrical gremlins, and the t-stat for the temp peg.