Fuel problem troubleshooting
 

89 GXL (S5 NA). <10k rebuild with streetport. MS intake, RB headers, RB presilencer. new: fuel pump, afm, pressure sensor, tps. problem came on suddenly.

During WOT, car will not rev past 6k without leaning out like crazy and popping breaking up. Car is solid in 10.5 to low 12 afrs, then hits ~6k and starts leaning out and breaking up.

Mechanic told me that it's running out of fuel and I should change the regulator and put aftermarket secondary injectors, but I thought stock injectors could handle all this.

Thanks in advance! All answers/ideas welcome.

You can test the fuel pressure with a gauge tee'd into the feed side (w/ fuel filter). Your injectors don't need to be upgraded on an NA until you get into bridgeport/p-port territory.

Have you checked for codes: http://www.johnr.com/cpucodes.html. CEL coming on?

Also, 10.5 - 12 AFR is way rich for an NA. I'm guessing it's the stock ECU doing that, but it just goes to show you have some room to pick up a little power by smoothing that out.

There are no CEL code, neither lit, nor during the testing and looking for blinking CEL.

Is it possible injectors are just bad? Given that they should definitely be able to handle what I'm giving it.

So testing fuel pressure at that point will tell me if injectors are bad, or just fuel system in general isn't working properly, hope you saw I have a brand new fuel pump, a walbro 255 and fuel filter is new as well.

Could it possibly be an electrical issue to/from ecu? Car is grounded properly, so I don't know...

Stock ecu, I know I can definitely crank out another 30-40 hp from some good tuning, but that's if I can get the car to work right first.

First off, a walbro 255 on an NA is bad news. It's WAY overkill, and unless you put in an aftermarket FPR, your fuel pressure will be driven way up under all conditions. I put one in my turbo car briefly, and immediately removed it. You just need a working NA fuel pump. So this is a big part of the excessively rich mixture (along with the stock ECU).

What AFRs are you seeing when it stumbles at high RPM? You can test the injectors for 12v power with a multimeter.

I was planning on doing an aggressive NA tune and add a 75-100 shot, hence the overkill pump, but I think these hopes have been shot down with this issue.

When it hits high rpm, afrs shoot up from 12-13 to 15-16 and does not let the revs go past, it just gets stuck there and breaking up/popping.

Also, this might be the turning point to this situation, mechanic told me the compression (psi) on my rear rotor is in the 90s, and front is about 110 or so...and he said it should be about 150. He said either my apex seals or springs are toast. Can somebody confirm this with stock numbers? This might just be the answer to my problem all together.

Your mechanic doesn't know rotary engines very well then. 90 psi is good compression, 100+ is great. The minimum spec in the FSM is about 80 psi. Compression specs on a piston engine would be significantly higher.

I'd suggest that the secondaries may not be working, but that apparently creates a wall at about 5000 RPM. Although with your increased fuel pressure, it makes sense that you could get a little further up the RPM range due to the increased fuel from the injectors. There was a thread where someone had a problem once they hit about 5000 RPM (S5 NA too), and it ended up that the secondaries were never firing. They were running purely off the primary injectors. I did a quick search but came up empty.

Well that completely turned my day around lol, I was depressed and about to run it into the ground.

It makes sense since I have more pressure from the after-market pump.

Do you suggest I replace just secondaries or replace all given possible future failure? and if I do, would I need a fuel pressure regulator? Any info on suggested mods would be highly appreciated, thank you for being so helpful.

What most would suggest is to accurately diagnose the problem and not just throw parts at it.

Confirm that your injectors are (or are not firing) then t replace what its necessary.

That being said, having your injectors cleaned and tested would be a good idea, old injectors can't be trusted. But don't rule out a problem w/ the wiring or clips.

in that case, how can I test the injectors properly, and what kind of issue would I have with wiring, and clips being injector clips?

Here's one of the threads I was thinking of: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/power-drop-noticeable-hesitation-issue-high-6300-rpm-802779/. Solution in post #29. He was hitting a wall at 6300 RPM, and it turned out the rear secondary injector was not firing due to a faulty ground wire.

If you want to check to see if the ECU is sending the proper signal to the secondary injectors you could use an LED light. At pin 3X (Light Green/White wire) of the ECU stab the negative LED wire into this pin with the positive LED wire stabbed into the back of pin 1B (Black/White wire). Then you need to decide if you want to test the front secondary injector while out driving or in the driveway. To do the test in the driveway you need to simulate load as the secondaries only fire under load. To do this disconnect the vacuum hose to the Pressure sensor and plug it in addition to disconnecting the plug to the TPS. If the ECU does its job the LED ought to flash repeatedly as the engine rpm is increased above 4000 rpm. The same test could be done with the rear secondary injector as its pin in the ECU is 3Z (Light Green/Red wire).

ok, now it seems like I can try to figure this out

btw, does CPU, by my left foot, have anything to do with the function of the car...I may have repeatedly kicked that area, but I'll assume ECU controls everything important.

1: given the ECU test, will this verify that the ECU is SENDING a signal, or will it verify it is both SENDING and the injectors are actually RECEIVING the signal, and if so, can I be sure it's the proper signal, since I thought everything was negative controlled on this car, and any slight shorting may cause a wrong signal to be sent

2: if the LED test fails, does this mean my ECU is toast or my injectors are toast. and is it possible even if the LED test works...the injectors may be receiving a bad or wrong signal

3: does the FPR play a role in any of this

CPU controls non engine related comonents.

1. Verifies the signal is being sent only. If the signal wire to the injector was accidentally grounded the injector would fire as long as the wire was grounded.

2. If the signal isn't sent it might indicate load is not being sensed by the ECU. "Might" also indicate the CAS information received by the ECU is not accurate. If the light flashes repeatedly in sequence then the signal from the ECU should be good. What is actually happening at the injector could be a different story as this depends on whether the wire is properly connected to the injector and if the wire is sound and so on.

3. Should not have a bearing.

If you have a spare CAS I believe you should be able to check the secondary injectors but I might be wrong on this. You could definitely test the primaries and I'm pretty sure you could rig it to test the secondaries as well.

Will definitely give the signal test a try...and excuse my idiocy, but what is a CAS.

CAS is the Crank Angle Sensor and that trick of using the spare CAS only works for primaries so I was wrong on that one.

While you're in the area, I would also check continuity between the ECU connector (secondary injector wires) and the injector clips. If you have long enough leads on your multimeter that is. Inspecting the wires and contacts in both areas would also be a very good idea.

i have this same problem but the only upgrades i have to the engine is a new exhaust with stock headers big cat delete small pre cat still there. i'm leaning towards my tps since it seems to be the cause of a few other problems. is this the right idea?

for the thread's sake, this was an injector issue. I sent out my injectors to Marren in CT and they told me 1 injector was completely toast (a secondary). 3/4 were reinstalled after being cleaned, and I purchased another one online. Car ran fine all the way to the red.

Just The Answer I Was Looking For
 

Thanks for going into detail in your post. I just swapped in a 13B T in my S4 vert, I bought an AEM fuel pump and was wondering if I needed to buy an aftermarket fpr. Your post answered what I was wondering, so I will buy an aftermarket fpr to dial in the correct fuel pressure. :icon_tup: