Hello -

I'm new to rotaries but do have a bit of experience with cars. I picked up my FD about a month ago and I'm still just getting to know it. It has a single turbo conversion, I put some basic info about it in my intro thread: https://www.rx7club.com/introduce-yo...otary-1171433/

One issue I'm chasing is lean under ~5 lb of boost. AFR gauge shows ~ 10.5 under low boost but then at 5lb or so it starts to climb. APEXi FC commander says the injector duty is low when this happens, maybe ~40% on the display. So my next thought was either fuel pump or fuel pressure regulator.

I checked the vacuum line to the FPR and didn't get the sense that there was fuel in there. Next, I did a quick and dirty experiment with what I had lying around and hooked up a hose and syringe to the boost reference port on the FPR to simulate vac and boost. I have a compressor, but wasn't sure I could reg it down to something reasonable and I didn't want to cause more problems.

Pics and a vid linked below, but the gauge shows:
- 43 PSI at idle with manifold vac attached to the FPR
- 50 PSI at idle with syringe attached but static.
- 45 PSI at idle with syringe vacuum applied
- Needle oscillates quickly around 50 PSI with syringe 'boost' applied.

This video shows vac and boost applied with the syringe.

https://drive.google.com/file/d/1n1V...usp=drive_link

I feel like I'm applying similar vac and 'boost' with the syringe, so I estimate I'm simulating 5lb of boost.

This is my first time with a boosted application, so I'm just kinda guessing, but is this a valid test? If it is, it seems to me the fuel pressure regulator is unwell.

What do you all think? I can get a mityvac or a more accurate way to test pressure, just wondering if this is enough of a smoking gun.

Thanks in advance.

Pic of the fuel pressure with manifold vacuum connected:


My redneck boost simulator:

 

I borrowed a regulator for my compressor and tested again with shop air at ~20 PSI and got the same results. Time for a new fuel pressure regulator.

 

Good job testing that the regulator was faulty, it's nice to know things like that before just throwing parts at a car hoping for a fix. If the entire weight of the fuel pressure regulator is being supported by that threaded adapter, I would try to build a mounting bracket to support the weight and reduce the chance of the threaded adapter failing.

And judging by the rust on the regulator, I would replace the fuel filter at the very least. If you're mechanically inclined I might remove the fuel injectors and have them cleaned and flow-tested, and maybe swap out all the rubber fuel lines. Another weak point of the FD fuel system is the factory bulkhead electrical connector for the fuel pump, there's a great install video from Full Detail Automotive on youtube. . I mostly followed that but used the bulkhead terminals from EFI Hardware in Australia: https://www.efihardware.com/products...inals-hex-head.

 

typically an oil filled gauge is used for this application, what do you consider "lean" at 5PSI? 12.5AFR isn't out of safe range at that boost level, i usually start to drastically ramp down AFRs around 8psi or so. gotta really be trying to blow up a motor below that in boost.

 

I don't have any logging currently, so it's just me trying to watch the AFR and boost gauges while doing a pull. If this rain ever stops I'll get a video of the gauges.

What I see is ~10.5-11.2 AFR from around -2 PSI up until 5ish and then it skyrockets quickly and will lean pop.

There's a rotary guy not far from me that I'm planning to take it to to go over the tune and dial things in, I'm still just getting to know the car mechanically and trying to address anything I can before I take it in.

Longer term I do want to get more self-sufficient with tuning. All my tuning experience so far has been with a screwdriver and jets.

 

it's quite possible you have a staging issue with the secondary injectors. i have seen that a LOT over the years with poor tunes.

personally i try to move the secondary transition to around 3000 RPMs and at around 3-4 psi of boost for safety reasons, the closer it is to peak torque range, the less safe it is for the engine. this isn't great for fuel economy but who drives a 7 for fuel economy... heh

you may also have one or both secondary injectors not working at all. either pigtails came loose, injectors seized up from sitting unused for a long time, settings in the PFC are way off, or a wiring/power issue to one of both of them. your fuel pressure being at 50psi isn't a concern, however if it is dropping under a LOAD it would be. that would require video recording your gauge or getting a remote one that you can monitor.

 

All great tips, thanks!

Fuel filter is on order. I have yet to dig into the rest of the fuel system, but do plan to at least pull the pump and give everything a good peek. The regulator feels pretty well supported but I'll double check that too.

Thanks for mentioning the wiring, will add inspecting that as part of the winter checklist.

 

OK awesome, learning a lot here. I'll see if I can jam a gopro in there the next time I go out.

 

Some reading for you on the Power FC that might help you check and tune your car:
https://www.rx7club.com/power-fc-for...aster-1167351/
https://www.rx7club.com/3rd-generati...esome-1161545/