Fuel starvation on the Dyno with walbro 450

[Yuri]

I installed a walbro 450 and thought the last thing i would face on dyno day was fuel starvation, but that was the case. When the rpms would start to climb my fuel pressure gauge would start moving violently and eventually hit 20psi from 50. I tried everything, changed the fuel filter, even hard wired the fuel pump to the battery, but still nothing. I still haven’t checked the tank for gunk or made sure my fuel lines are not kinked. But here is my question. Below you can see where I wired in the fuel pump to the battery. the fuel pump turnes on with that plunged however, it partially runs with that totally u plugged. Like I legit forgot to plug it in after my dyno session and the car drove okay all the way home. When I got into the boost it was lien, but still it worked enough to drive normal. Here is it shows me going lien, while on the dyno. and just for fun here is my peak power at 5800 rpm on 12ish pounds. Running e85 Sent from my iPhone using Tapatalk

[JehTehsus]

Maybe a silly question, but do you have a secondary fuel pump outside the tank? On my early 325IS there is a secondary pump by the fuel filter.

[pondhopper]

1st thing that comes to mind is :PLEASE CLEAN UP AND SAFE the wiring. Im pretty sure I see exposed copper at the crimp area. There is also the 2 original wires that should be capped. Last thing you need is a spark in and around the fuel system.

2 measure voltage and amps at the pump while running.

3 any chance of getting a fuel pressure gauge somewhere to see what the readings are? Curious what the pump puts out ear the tank, what you see before/after the FPS. Fuel filter clean?

4 cant remember which is the feed and which is the return lines. Possible they are mixed up? Usually that leads to a no start.

5 evap and charcoal canister plugged? Are they even installed? Thinking about not enough air getting in the tank as the pump sucks fuel out.

[pondhopper]

BTW, nice HP and torque Numbers. So close to an even 300! I can see why the lean and FP issues are important to fix.

[Yuri]

Regarding safety, yeah totally. I was just doing everything I knew to do while on the dyno to fix it. That picture was taken on the dyno during the repair. Fuel cap, maybe. Charcole filter no. Because when I fill it up with gas there aren’t any issues. Here is a link to a video of the fuel psi gauge during a pull. You can see how it starts jumping lien. https://drive.google.com/file/d/1YY1...w?usp=drivesdk

[Yuri]

I also replaced the fuel filter on the dyno... so that’s not it. Sent from my iPhone using Tapatalk

[Yuri]

Maybe a silly question, but do you have a secondary fuel pump outside the tank? On my early 325IS there is a secondary pump by the fuel filter.

Honestly, that would make total sense. I had no idea. Granted, do you think another pump would inhibit fuel? Regardless I’ll check ASAP. Sent from my iPhone using Tapatalk

[JehTehsus]

Honestly, that would make total sense. I had no idea. Granted, do you think another pump would inhibit fuel? Regardless I’ll check ASAP. Sent from my iPhone using Tapatalk

If you're running an early model then it should have the secondary pump, I don't believe any later models do though.

I can't say for certain, not sure about the internals of the pump, but if you have an aftermarket in tank pump I would definitely get rid of the secondary pump.

[Northern]

'87 likely has a second pump. I think the fuel pump setup change coincides with the physical fuel tank change, so if you remember an "S" pipe between both sides of the (early style) fuel tank, it probably has a second pump at the filter.

Something like this:

[SLEEPYDUB]

I bet you got a leak on the feed hose in the tank. Take the pump out and inspect your lines in the tank for leaks or splits. Seen this way too many times

[ForcedFirebird]

I agree with the early model part. That big supply hose was not intended to carry high pressure, it needs to be changed if original. That big supply hose goes under the car to an inline pump. If you don't know it was there, it probably still is. When you are eating up fuel on the dyno, the fuel is being evacuated between the stock inline pump and the fuel rail.

[Fraser]

I would add another vote for leak on the feed hose inside the tank, I've personally dealt with this more than once... Also, are you positive the pump you have is a legit Walbro? I had a long standing fiasco with several pumps that ended up being fake, even though I bought them from reputable sources and all the packaging, documentation, etc...looked legit. I finally coughed up real money for an aeromotive pump and it's worked great since.

[Yuri]

Appreciate all the help here guys, just bought a house so haven’t been working on this much. Once I get things going again I’ll update the thread. Sent from my iPhone using Tapatalk

[Yuri]

Just want to comment on this. The problem ended up being was the fuel line connected to the walbro inside the tank. The clamp just needed to be tightened up. That being said my fuel pressure still drops At full load. Not sure if that is normal or not. For example I set my pressure to 60psi and under full throttle(at a stand still) it dips to 40psi. I should say the fuel pressure gauge frantically bounces from 40-60psi. I checked my voltage at the pump and it’s 13v. Side note my 90amp alternator seems to barely keep the car running. It’s between 13.0v-13.6 Volts all the time without accessories on. For example my headlights dim at idle and get brighter under throttle. From what I’ve read those voltage number are normal. Is it true that the e34 750i 140amp alternator will bolt on to the m20? I’d like higher amperage while driving. Finally, going for round 2 tomorrow on the dyno. Crossing my fingers that everything will tune smoothly. I added some pics of the project just for fun. Appreciate you guys! Sent from my iPhone using Tapatalk