90 turbo Fuel pressure low. AFRs high. Still bad after new pump.
 

Hi guys. I've been stumped with a fuel delivery problem for a little while now and thought I would pick your brains for more info.

Here is some info on the car:
Begi t25 turbo kit
Begi AFPR
99 red top injectors
walbro 190hp fuel pump
olderguy o2 clamp

My car suddenly started stumbling and hesitating and became undriveable while I was on the road on a rainy day. AFRs on my AEM wideband went very high, 15s, 16s, 17s, and the car just wasn't getting enough fuel to go anywhere. Luckily I was just getting home when it happened.

If I start the car cold, the AFRs sit at 14.5 for about 15 seconds then shoot right up to 17. If I leave it running for a while it sometimes drops to 15 or 16, but most of the time it's in the 17s or just shows 3 dashes. If I try to give it some throttle, the RPM's raise but it bogs.

I thought that maybe the rain had something to do with it since I have a small leak in my top window that got the carpet above the pump tray wet.

Here's what I have done so far:

*Fuel pressure test. When running I would barely get 20-25 psi on the feed line before the fuel rail.
*Changed fuel pump with another Walbro unit. Pressure still 20-25. AFRs still high.
*Changed fuel pressure regulator. Still no change.
*Boost leak test. No leaks.
*Ohm'd injectors. All within spec.
*Removed Begi AFPR. Fuel pressure and AFRs still the same.

I also did the fuel pump and fuel pump relay tests in this Wiki.

The strange thing was that I'm only getting 9v to the fuel pump harness plug when I crank it. Not sure what this means, but the Wiki says I should be getting 12v.

I even tried out a spare ECU, CAS, and AFM I had laying around just for kicks.

I'm sick of the mess with the AFPR and AFM and would like to throw in a Megasquirt next month. Before that though I want to get this fuel problem situated.

Not sure what else I should be looking for. Any input would be greatly appreciated. If I find any more info or I figure the problem out, I'll keep the thread updated.

Thanks

Fuel filter

^^^^^^

I'm with them.

I'll swap the filter out today. I changed it about a year ago but something tells me you guys are right since that's the only fuel system component I didn't check. Thanks! I'll keep you guys updated if it solves the issue.

It is also usually the first thing to start causing problems with a fuel filter. With how cheap and easy they are to replace I am surprised you have not already done it to try to solve this problem.

Replaced the fuel filter just now. AFRs dropped to the 16s and high 15s at idle, but still stumbling and hesitating. Not getting enough fuel to drive. Stumped again but I'll fiddle with the car some more this weekend and see if I can't find anything else.

Not to keep you running in circles, but you may want to check for vacuum leaks again.

I'll give it another shot. I'll probably try another fuel pump relay for kicks too. Running out of ideas but I won't stop until I find the problem. Wish me luck.

Still trying to figure out this issue. Did another boost leak test, no leaks. Tried another fuel pump relay, no difference. Just got back from doing another fuel pressure test. Still sitting just below 30psi.

I'm still wondering about why I only got a 9v reading at the harness that connects to the fuel pump.

Another weird thing I noted. When I try to adjust the lock nut/screw on the BEGi AFPR, it doesn't change the fuel pressure at all like it normally should. Pressure is always at 26-28psi no matter what. Also the pressure does not change with the vacuum disconnected. Atmospheric still reads 26-28psi. I tried another fuel pressure tester from a friend at a Mercedes dealership and the readings were the same.

Any other ideas as to why my fuel pressure is staying so low, gentlemen?

I uploaded a video of the way it's behaving for what it's worth.

Just to confirm your procedure, are you jumping the FP relay under the hood and pinching off the return line? You can mount your gauge right at the tank vs in the engine bay to check if the filter is clogged. I assume the pickup sock in tank is clean if you changed the pump already.

Jumping the relay should help test it as the low power issue.

Pinching the return line will take the Begi unit out of the equation.

You can also do a fuel pump leakdown test after key off to see if fuel back feeds through it and it doesn't hold pressure, showing that it is bad but given this is your 3rd? it doesn't seem likely.

I'll go try that out right now and report back with the readings. I can try measuring at the tank, but this is the 3rd fuel filter I've changed in the last year so I'm not really counting on it being clogged. Changing the filter didn't help my issue unfortunately. The current one isn't even a month old. I installed a brand new pick up sock when I changed the pump a couple of months ago.

I'll go and do the pinch test now. Thanks for the help, I really appreciate the input.

When you said Wiki, I assumed you meant the MT article... you need this in your life right now Fuel Pump - Miata Turbo FAQ

Did the pinch test and found something interesting. When I jumped the fuel pump and ground pins with the car off, I listened for the pump turn on and heard a squirting/spraying sound coming from the tank. I pulled the pump and removed the seal. Looks like the ID of the o ring is too large and it is slipping. Upon closer inspection under a magnifying glass and a light, it looks like the o ring is warped. I dug through my collection of z32 parts and found another o ring with a slightly smaller ID. Checked with my calipers and it was about 1mm different. Sure enough this solved my problem. My assembly is modified to retain the ring, I'll probably just cut and throw on a hose. This is probably what I should have done in the first place. Looks like my old pump was okay. I think I'll give it to a local Miata buddy whose pump just gave up on him. Thanks again for the help everyone. And thanks slammed200 for pointing me in the right direction haha.

Happy to help, kudos to you for circling back and posting resolution in your thread as well