Hi all

I've posted about my S4's numerous issues before and I have since gotten it started and it starts consistently, however, I am having even more issue than I did before (go figure). The main issue I'm having now is it runs very rich, making the cats glow and making so little power that popping the headlights almost stalls it out. Obviously not ideal for street driving or passing an inspection and, after several weeks of diagnosis and research, I am completely stumped, so I now ask for your help in maybe finding some answers or if anyone has dealt with and fixed this kind of issue.

So the symptoms I'm experiencing; the fuel pressure measured before the injectors with the key on is around 45 psi, obviously outside of the ~29-38 listed in the fsm. The fuel system also does not currently hold pressure without the fuel pump running, dropping down to 0 in a matter of seconds. One of the two previous owners had wired the fuel pump to always run directly from the battery when the key is on (something I plan to return to stock but that isn't priority with current issues), so that might contribute to the pressure being too high? I admit to being a noob here.

What I've tried so far:
I've tried three different fuel pressure regulators; the one that came with the car, a oem style BOSCH unit I got off ebay (new old stock I think), and a brand new regulator from RockAuto. None of these three made any changes to the issues. In addition to the FPR, I've also replaced the fuel pump. One of the previous owners had replaced to stock one with an aftermarket unit that's rated higher than whats listed in the fsm, so I got one also from RockAuto that is closer to factory spec. This also did not change the situation. I've tried disconnecting the return line at the rats nest and at the FPR to rule out any blockages after the FPR that would raise fuel pressure, letting it dump into a bucket. Still 45 psi. To diagnose the issue with holding fuel pressure, I clamped off the return line and ran the pump for a few seconds. Pressure held very high like I'd expect, and dropped of to zero as soon as I released the clamp.

All of these diagnostics point me towards a bad FPR but it seems statistically unlikely that I have three bum FPRs, two of them fresh from the box.

As I've said before, I'm a complete noob to rotaries (and project cars for that mater) so any help or diagnostic tips would be greatly appreciated. I can provide any more details if needed, Thanks for reading my very long (and a little ranty) post,

 

Have you verified fuel hose routing? I think the stock fuel system leaves the pump to the part that screws to the tank, then to a hose, then to the hard line, to a soft line connected the fuel filter, another soft line to the rats nest hard line and then to the regulator with a soft line.

Not totally sure from there, secondary injector fuel rail, hose to primaries?, another hose somewhere to the rats nest? then, soft line to hard line back towards the tank, soft line to tank?

Please sort the wiring issue,Your car catching fire could be the least of your worries.

 

I have, actually. Yeah.
To lay it out, the fuel goes from the pump through a soft line to the hard line out of the tank, then to a soft line, then a hard line under the car, then a soft line to the high pressure filter in the engine bay, then a soft line to a hard line in the rats nest, then soft line to the pulsation dampener (deleted this with the kit from Atkins) and the primary rail, soft line to the secondary rail, then the fuel pressure regulator, soft line back to the rats nest, then rats nest to a soft line back to a hard line under the car, soft line to the a hard line back into the tank.

You're right on this. The current wiring isn't bad in a dangerous way, I don't think, just mildly strange in a way like the guy who did it didn't have the space to complete the job. None the less, I'm focusing on the wiring while I ponder the pressure issues and search for answers.

 

The regulator needs to be before the fuel rail.

https://www.atkinsrotary.com/Intake-...26-13-280.html

 

Not sure where you're getting that information. The FSM clearly shows it as the last step before the returning to the tank, after the secondary rail (section 4 page 65). The way you're describing it is exactly backwards and fuel does not flow that way. I have tried.

 

HI, my 1988 work shop manual diagram on page 4A-3 show the pressure regulator before the secondary fuel injectors!

The pressure regulator keeps only the fuel before it at pressure!
After that, the excess fuel not used is funneled into the return ( at much less pressure ) line.

So, the secondary fuel rail that supplies the injectors does not have the normal pressure!

Common sense dictates that the pressure regulator has to be after the injectors, to make sure that the secondary injectors are fed the correct amount of fuel.

On my 1988 GXL this is the correct routing of the fuel system to achieve 35.9-37.0 psi at both fuel rails that supply the fuel injectors:

Gas is pumped up through line, thru the high pressure fuel filter.
From there, it goes to the Rat's Nest intake pipe.
Now it flows into the primary fuel rail.( This has the pulsation damper attached )

From the now pressurized primary fuel rail the fuel flows into just a 90 degree angle to the secondary fuel rail.
Once the fuel is at pressure it can be used by the secondary fuel injectors.

At the right of the secondary fuel rail is where I have the fuel pressure regulator! Just before the attaching to the return line.
After the fuel pressure regulator, the gas is returned to the fuel tank at very little pressure.

The take-away, don't think that the diagram you have in front of you is what is in your FANTASTIC AUTOMOBILE has!

I was told by the Mazda service people, ( it seems that your GXL had a late summer change to it, so you have mostly 1988 parts after this some of the parts are 1989 specs )!

So, do a little research into what you want, before falling down the rabbit hole! ( I'm late......I'm late, for an important date!!!!!


[img alt="This is the back of a S4 engine bay.

This is a aluminum panel, "]https://cimg6.ibsrv.net/gimg/www.rx7club.com-vbulletin/2000x1325/bottom_pan_0122bfab7701bcb9449d5b6a693aee4b50f2d83 e.jpg[/img]
This is the back of a S4 engine bay. This is a aluminum panel,
Just for interest!

 

I was just going from memory. I might have mine connected backwards then on an '87 GXL. I am not sure why my car runs as good as it does that way?

Edit: I just checked the Haynes manual, I have it hooked up correctly. The rats nest piping must take a odd turn? The filter side goes to the front pipe. I just thought the front pipe went to the front of the engine or the regulator side. I will need to verify when I tear down my spare engine. I just finished a refresh on the top part of my engine last August. I am not taking apart my car again?

Other Useful info:
Fuel System Pressure: 34.1-39.8
Fuel System Hold Pressure: 18
Fuel Pump Pressure:
EGI: 64-85.3
Turbo: 71.1-92.4
Fuel Pump Hold Pressure: 57
Pressure Regulator(at Idle):
86-88:
35.6-37 Vacuum Detached
28.4 Vacuum Attached
89-:
27-33 Vacuum Detached
21 Hose attached

 

I should probably get a Haynes manual. That aside, in my rebuild of the vacuum/emissions on this car I have found that there are different versions of the rats nest between the S4 and S5. They appear to be functionally identical except the the feed in and return out are exactly switched. It's possible there's other difference in the routing but that is all I have noticed so far (maybe something else I overlooked is causing my issues). In the case of the S4 rats nest, the front pipe does go to the regulator side and is the return. On the S5 the front pipe goes to the pulsation dampener and is the feed.

Starting to thing I either effed up vacuum routing to the fpr (see previous quote reply) or I really did get screwed by the QC lottery on the frps I ordered. Had the car running again last night with a pressure gauge on the feed line before the rats nest and there was no perceptible change to the fuel pressure between engine off and warm idle. I'll double check the vacuum to the fpr but I don't think this explains my bleed down issue. If the vacuum routing isn't the issue, I'll think about swapping in an adjustable fpr and rule that out as an issue. That leave the door open for porting anyway, right?

 

Thanks for the clarification! The manual must show a s5 and not the s4. Mine are on backwards. I might disconnect the lines and shoot some lube or something down the pipe and see which pipe it comes out of, just to be sure.

 

This is my S4 rats nest after sandblasting and powder coating!



Can you make it anymore convoluted!

The large diameter line you see closest the camera is the RETURN LINE from the secondary fuel rail, from the FPR.
The vacuum line next to it goes to the FUEL PRESSURE REGULATOR. Makes sense.

The large line towards the back is the pressurized fuel supply FUEL LINE from the fuel filter.
This attaches to the primary fuel rail where the pulsation damper is located pointing towards the front of the engine.

So, the fuel line has a longer length fuel hose.

The return line has the shorter length fuel hose.

Do as I say, not as I do! Please attach the fuel hose between the primary and secondary fuel rails to the primary banjo bolt BEFORE you bolt on the upper intake manifold!
Mount hose with clamp to the primary fuel rail banjo bolt, on the other side from the PD. Leave the other end unattached ( put a clamp on this end ready to go ) and reachable while you bolt the UIM in place.

The take-away as I see it is that the fuel routing for a N/A S4 and S5 might be different. The shop manual diagrams might be wrong!
Probably the turbo models are different also.

Trace the hard lines on the rats nest and use common sense.
I saw somebody who figured that his battery cables were crossed. It wasn't pretty!
Oh, he's died this year. Wondered how he stayed alive that long.

 

Looks nice! Thanks for the help, I will be switching my lines around as soon as possible.

 

I did a short test swapping lines, no start. Left those in place and swapped the fuel pump line, started. Checked for fuel with the bypass method, fuel coming out of the wrong hose, no filter.

I then did what I should have done, I hooked up a spare piece of hose to the FPR hose after a disconnect and blew air through it. The rear pipe in the rats nest is the return line!! I just returned everything back to the way that I had it. I did explain it backwards initially, though.

Mine is an 87 GXL.

It looks like i read the above post wrong, too.

 

To bring some conclusion to this thread, I figured out the issue. Poked around with my smoke machine again and found that the hard line for the solenoid to the FPR is completely blocked. Bypassing that hard line with some silicone tubing fixed the issue with running rich at idle. With the motor running I now see the pressure at around 29 psi and it ran well enough to move under its own power This still doesn't fix the issue with the pressure not holding but I'm going to go over everything in the fuel take again. Either way, the pressure is mostly normal now.

That being said, the cheap exhaust gaskets I had completely cooked and blew out when the cats got red hot, so there were quite a few exhaust leaks during my "successful" test. I replaced those with some new remflex gaskets and now the whole exhaust to the y pipe, manifold and all, get glowing red and it idles at ~2500-2700 rpm at temp. I'll likely create a new thread for this issue since it seem entirely different from the original.

Thanks for the help everyone who replied.

TL;DR: Blocked vacuum line cause FPR to not see vacuum and regulate. Car ran great with that fix. Fixing exhaust leaks possibly broke car.