Technical How did I kill my EKP?

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
Calling all electrical gurus, as this was never my strong subject.

I tried to make a wiring harness that would override the EKP when receiving a 12v signal from the hobbs switch. Essentially I wanted both pumps to receive 12v straight from the battery when boost was over 8 psi, with a diode on the EKP wiring that would supposedly protect it from back feeding.

stg4 wiring original.PNG

The diode is an NTE5991, rated for 40A 400V. Triple insulated with DEI heat sleeve since it got up to 150 degrees F. Datasheet is attached

After wiring everything, I jumped the hobbs switch with the car at idle. Instantly the fuel pressure went to 78 psi which is what I set the regulator at. I unhooked the test lead and shut off the car after running it like that for about 5 seconds. Put the car back together, attempted to start, no fuel pressure.

After figuring out the EKP was dead, I moved the trigger to fuse 8 (cigarette lighter) in the glove box and everything's been great.

stg4 wiring_cr.PNG

Interesting thing is the car still "sees" the fuel pump, it just doesn't supply power to it. I left the diode even though it's probably not doing anything, and it doesn't get hot anymore. However there's no yellow "car on lift" service needed warning in the cluster, only a DME fault code:

CDA6 - Message (status, electric fuel pump, 0x335) faulty, receiver DME, transmitter EKP.

Usually the car gets unhappy when it no longer sees the fuel pump. When the EKP was working, if I unplugged the primary pump with the car running off the secondary, it would throw that yellow service needed warning in the cluster immediately.

Maybe someone who's better at DC circuits than me can explain exactly what happened here?

Side note, if Mike steps in here and tries to sell me his overpriced PWM controller I will tell everyone to boycott EOS.
 

Attachments

  • 712156.pdf
    60.4 KB · Views: 107

GreyNBlueE92

Corporal
Oct 3, 2018
199
50
0
24
OH
Ride
2007 E92 335i
Im guessing the ekp is trying to suck up the excess current to slow down the pump but it doesnt slow down so all the current the ekp originally sends to the pump is turned into heat...
 

GreyNBlueE92

Corporal
Oct 3, 2018
199
50
0
24
OH
Ride
2007 E92 335i
The EKP is a power supply.... I'm not sure it can suck up current like you're describing.
I have no idea what I'm talking about lol

I thought the ekp was stressed more under low load? That is why I said the above...

Instead of a diode, you could use another relay after the first relay, connected to ekp and power wire. When turned on separates the ekp and fuel pump. Turn off the code, and you're good. Of course it's a bit late now...
 
Last edited:

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
Instead of a diode, you could use another relay after the first relay, connected to ekp and power wire. When turned on separates the ekp and fuel pump. Turn off the code, and you're good. Of course it's a bit late now...

I tried that. The problem is when the EKP is disconnected from the pump, the yellow "car on lift" service needed warning comes up on the cluster.
 

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
No, that can only be turned off via cluster coding (NCS Expert). I asked around and it seems like it couldn't be disabled.
 

iminhell1

Sergeant
Jun 17, 2018
342
153
0
I think your wiring is wrong.
The way you have it, once the hobbs activates the relay, both pumps see the same voltage, cutting the EKP out,,, or the EKP sends power to both,,, depends on which is higher voltage.

The correct way should be to wire them independently, so 2 relays. But I don't know if you really need the 2nd for the 450, just let the EKP control that one and put the 525 on it's own circuit triggered by hobbs.
 
  • Agree
Reactions: GreyNBlueE92

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
I think your wiring is wrong.
The way you have it, once the hobbs activates the relay, both pumps see the same voltage, cutting the EKP out,,, or the EKP sends power to both,,, depends on which is higher voltage.

The correct way should be to wire them independently, so 2 relays. But I don't know if you really need the 2nd for the 450, just let the EKP control that one and put the 525 on it's own circuit triggered by hobbs.

It's very possible I did something wrong... that's why I posted this.

The standard way of doing most twin pump LPFPs is to leave one as EKP controlled (primary) and wire the other (secondary) to a hobbs trigger. The hobbs is in the charge pipe and set to close when a certain boost pressure is reached. This setup has the 2 pumps wired independently and only turns on the secondary pump above a certain boost pressure.

The issue with that setup is that the EKP does not expect a second pump to be in the tank, and goes crazy trying to control fuel pressure when it kicks on. You can see fuel pressure oscillations on a lot of stage 3 and stage 4 lpfp setups using the traditional harness. That's why EOS came out with the dual fuel pump controller. I'm not using it because I don't see the point of paying their price for closed loop control when I have an aftermarket FPR and return line.

I had it set up the standard way before switching it up to try and correct the fuel pressure oscillations I was seeing... 60s to 80s then 60s then 90s psi. It was crazy lol
 
Last edited:

GreyNBlueE92

Corporal
Oct 3, 2018
199
50
0
24
OH
Ride
2007 E92 335i
Completely overlooked that the way it was setup the ekp was definitely driving 2 pumps as stated above. Also wired in parallel decreasing resistance...
 

bahn

Corporal
Platinum Vendor
Nov 5, 2016
192
298
0
Iowa
10 gauge stranded
Your diode isn't preventing both pumps from drawing current through the EKP. Electricity doesn't take the path of least resistance, current is split depending on the impedence of the paths. Your EKP was still providing current (both through the positive voltage side and the ground side). I haven't measured the impedence of the EKP myself but I'm betting you sunk a lot of current through it.
 
  • Informative
Reactions: veer90

veer90

Captain
Nov 16, 2016
1,000
762
25
West Nyack, NY
Ride
e90 335i 6MT
Your diode isn't preventing both pumps from drawing current through the EKP. Electricity doesn't take the path of least resistance, current is split depending on the impedence of the paths. Your EKP was still providing current (both through the positive voltage side and the ground side). I haven't measured the impedence of the EKP myself but I'm betting you sunk a lot of current through it.

That makes sense. So a second diode before the positive junction would do the trick?

Any harm in just leaving both pumps hard wired like this for the time being if the EKP is dead?
 

iminhell1

Sergeant
Jun 17, 2018
342
153
0
If you're on a return setup, there's no need for the EKP at all.
Direct wire both. Separate relays.
 
  • Like
Reactions: veer90

shushikiary

Corporal
Jun 4, 2018
172
74
0
Ride
335xi
There's a few possibilities.... Back EMF or over current of an open collector, or grounding the EKP's output.

Because switching high current on an inductive load is no trivial task, often times they are switched with what's called an open collector setup. This means that there is a pull up on output and a transistor is used to "pull down" the output. This is often used because then the "pull down transistor" doesnt have to source as much current.

When you put the diode in series with the EKP, if its an open collector setup (not sure it is), then you removed the pump as a load when the voltage from the relay was applied, thus shoving much more current through the pull down transistor than would ever happen normally for the target voltage to be achieved when requested by the EKP. I'm pretty sure its not a PWM output after playing with it in the past.

The other possibility is that when ever you have a large inductive load and you switch said inductive load off the magnetic field in the coils must go somewhere. This causes the field to invert the voltage across the coil and spike the voltage up as high as it takes to flow current until the magnetic field can dissipate. Often times on relay's they protect the relay turn on circuitry with what is called a "free wheeling diode", or will also protect the relay from arcing when switching an inductive load in a similar way, as arcing the relay on shut off will reduce its life span A LOT. This free wheeling diode however is not enough. This is because you have to wait for the voltage to swap for it to take effect (diode is wired so that when the voltage is flipped it allows current flow), further diodes them selves take time to actually allow current flow, a normal diode is not fast enough. A zener diode on the other hand, is the right tool for the job. Further, a free wheeling diode can often times cause the voltage to flip back and fourth several times while the current dissipates, often causing the relay to "chatter" during shut off, bad bad news. A zener diode placed in parallel with the load, as close to the load as possible is the proper solution. They react faster, and help prevent the voltage inversion instead entering their breakdown voltage and allowing current flow in the original voltage polarity across the load until the voltage comes back down under the breakdown voltage.

Thus, when you switched both of the large inductive loads off (fuel pumps), with no protection for back EMF its likely there was a voltage spike large enough to either cause your diode to enter breakdown and over voltage the EKP, or a surge through the ground path of reverse voltage pulled to much current from the EKP blowing it out.


This is why an SSR or an H bridge is a better solution than the relay for inductive load switching, they have built in protection for this. What you should have done with what you're trying to do, is rather than use the diode, use two SSR's to completely swap the drive circuit for the 450 to run from the battery, and connect the EKP to a fixed resistive load (like say 7 ohms, with resistors that can handle a total of 14 watts of heat dissipation) for the duration of the hobs switch on time.

Note further, that because the diode has a 0.7v drop across it, your 450 is running 0.7 volts less than it would normally when the current is sourced from the EKP. I also hope that your relay doesnt have a NC and NO connection and have the NC connection wired to ground, as that means you just shorted the EKP to ground, another possible reason for the failure, but given that it worked to start the car up the first time, I suspect the NC Is left floating.
 
Last edited:
  • Informative
  • Agree
Reactions: kayzrx82 and veer90