Car falls flat on its face above 3500 RPMs under load.

[Danny]

86 325 with an 87 325i engine.



I've been having fueling issues with this thing since it was swapped in.



-New in tank and external fuel pump and filter
-CPS ohms out within spec
-Coil is getting power
-Cap rotor spark plugs and wires are brand new
-New fuel relay
-New main relay
-New fuel lines



Fuel pressure shows ~38 PSI at idle, jumps to ~45 when throttle is blipped. Fuel return gives about 16oz of fuel in ~20 seconds. Pinched return line shows fuel PSI jump to 80+ before I released it. I can sit in the driveway and rev up the car to the limiter with no issues. Hooked up a gauge while driving (under load) and at about 3000-4000 RPMs the fuel pressure drops steadily down to 10 psi or so and then goes to zero. Tach does not die. No vacuum leaks, no fuel leaks. All testing done with a fuel tank. Looking for some insight as I'm signed up for a track day in this car on Sunday.

[Sonny]

I'm afraid to bring my m10 over 2,500 rpms in fear of it imploding. I have never driven her hard. This post has me wondering am I suppose to?

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[Sonny]

Disregarding me fearing my m10 from exploding since it doesn't make me comfortable listening to her running. This is my concerns for your motor
Use your due diligence it's your car I'm not sure if im even close.

- Fuel filter clogged and cant flow the required fuel necessary for the injector output at the high end of the RPM scale.

- Voltage or CURRENT to the pump is compromised and when the pump need higher current to flow more fuel, it isn't getting it. Pump motor needs an ample supply of current to run at full capacity!!

- Ground for the electrical circuit isn't adequate and or loose, dirty or damaged. If you have a dinky ground wire or a very poor ground contact,, the pump motor cant work properly

What is the electrical supply for your fuel system: OEM circuit or an aftermarket harness? Did you enhance the circuit GROUND????????


12.XX DC on the analog gage & Digital gage indicates that your ignition switch AND OR the connector that plugs into the ignition switch are having issues. That gage DOES NOT indicate BATTERY VOLTAGE! It indicates voltage supplied


Look for carboned up/burnt ignition switch contacts.


Also I have put some crap in my fuel tank to clean it which in turn killed my injectors . Check those out. Did you aggritate the gas tank maybe you broke some debris loose, replace the filter again? Sorry if I couldn't help I'm not sure first time owning e30 it's my one month anniversary :)

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[e30davie]

The vacuum line on the fuel pressure reg goes where its supposed to go? What is the history on the fuel pump(s)?

[Danny]

Fuel pump electrica is all oem. I’ll be checking voltages during driving sometime soon. Vac line is where it’s aupposed to be. I’m gonna throw an FPR at it tomorrow and see if it’s the issue and go from there. Any other insight or similar issues would be helpful!

[Jaxx_]

Double check that you didn't mix up your supply/return lines when connecting them to the rail.

If you have an aftermarketing pump that pulls more amperage, you can have significant voltage drop on the OEM wiring--and lower flow. I don't think it would be so bad that it would cause these issues, but worth investigating.

[Danny]

Double check that you didn't mix up your supply/return lines when connecting them to the rail.

If you have an aftermarketing pump that pulls more amperage, you can have significant voltage drop on the OEM wiring--and lower flow. I don't think it would be so bad that it would cause these issues, but worth investigating.

Yeah I was worried about swapping the lines too but I verified that by pulling the feed line and jumping the pump. The in-tank pump is an airtex for a chevy vega that I put in based on a writeup found here. External is an oem Bosch from fcpeuro.

[TobyB]

Flapper door is next on my list of suspicions if fuel pressure is OK.

But do do a 'live' fuel pressure test on the road. You can zip- tie it to the wiper, and
see it pretty well.

t

[Danny]

It was a fuel filter I took all the fuel lines and blew it out with compressed air and replaced the fuel filter and it runs like a champ. We’re gonna buy like 7 fuel filters and head to the track. There can’t be that much more shit in the lines.