I need some help with a drivability problem. What is happening is that my car is running fine using light throttle up to about 3,000 RPM at which time something like limp mode seems to kick in - a really severe power reduction and missfire. If I try to use larger throttle then the RPM point where the issue occurs is a little lower. The history is that this car has been off the road for a few months, I have just finished restoring everything back to stock from a very simplified sequential setup. While doing this, I also had the injectors cleaned, replaced the FPD, and replaced the fuel lines and filter. So, in other words I had pretty much everything off the top of the motor and it now has a completely redone vacuum setup along with new viton check valves.

The car runs fine at lower engine speeds and light throttle, and in fact I just ran it through California smog check (loaded dyno 2-speed test), and it passed very well. So low speed function seems to be okay. I have a few ECU’s that I have tried, a completely stock unit, the Power FC that came with the car, and a Petitt remapped unit. The car runs a little better with the Power FC and Pettit ECU’s, but the same problem always occurs – like a switch is being thrown at 3,000 RPM and power is cut greatly and the engine runs rough. Up to that point, the car is boosting very well seemingly.

The previous owner says that the car was running okay beforehand and I believe him. So I am guessing that something must have happened as a result of my work, or I left something disconnected, or there is a coincidence going on. I have checked that the coils are connected properly, other than that my investigation has been limited to swapping ECU’s and checking to see if there are any fault codes (there are none).

I’d really appreciate some thoughts on what could be going on.

 

Sounds like your secondary actuator (transitioning waste gate in the manifold that opens for the second turbo operation. Not the actual turbo waste gate)isn't operating. Reminds me of mine when I first bought it. It was falling on its face at 3,000rpm but it ran great. I went through everything from fuel system to ignition system. I eventually pulled the engine and went through everything. During reassembly and going through every part, cleaning and inspecting, I found that the hard line going to the transition actuator was clogged with dirt. I was pissed but glad I found the problem.

 

Thanks for that info. One thing I did not check or replace were any of the vacuum lines to the wastegates and actuators on the lower part of the motor - since they all seemed to be in good condition. I guess it is possible that something is switched around down there - the rats nest and upper vacuum lines were really all over the place. Can these lines be accessed easily if I remove the lower tray? The idea of dismantling the top of the motor is really not appealing right now...

 

I think so, but it's been awhile since I've had the stock sequential setup. So my memory isn't to clear on that.

 

You can get to the wastegate and prespool actuator hoses (from the top) by removing the intake and the two big hoses that connect to it.

 

Tell me more about the injector cleaning - where it was done, how long before they were installed, etc.

I have dealt with injector cleaning that left an injector stuck or sticking - I needed to pull them and have them cleaned again, then put them right in and got the car going perfectly.

 

That's going to be the secondary injectors coming on. If the car has sat, it's possible they're clogged or something.

I seriously doubt it will be anything with the turbo control system, the car should still run and drive OK with the turbo control system not working right.

Could also be ignition, might be worth a fresh set of plugs.

Dale

 

I was wondering about the secondary injectors. I had them cleaned and flow tested by Witchhunter, it was only about a month between the cleaning and getting the car back together.

As far as ignition, the plugs and wires are new, and the system is working very well at low engine speeds- the car had very low HC readings from the CA loaded dyno smog test. And the way the car just almost stops running when it hits 3000RPM seemed like a fuel issue. But I don't know enough about the FD ignition to know if this kind of problem could allow good low speed operation and terrible high speed.

As far as the secondary injectors, is there anything in particular that could be causing them to not function, like a ground wire or something like that?

 

I have the exact same problem. When I hit 3,000 the car won't go past it and all I can smell is fuel. If you drop the clutch at 4,000 or whatever you'll notice that the car can go to redline boosting just fine. I'm going to try the wastegate lines and cleaning and report back. To clarify, I can go past 3000 in neutral but not when I'm driving in gear. Changed plugs and wires, tested and replaced coil packs. Injectors are fine. All solenoids tested

 

It is just very strange that both injectors would have the same problem after being cleaned and checked out, and no trouble codes to indicate an electrical problem with them. The condition is so severe that whatever is happening must be occurring to both sides of the engine.


I am going to find the pinout at the ECM harness plug and try to check resistance across the injector coils and if I can figure out a way to force the ECM to drive the injector while free revving the engine, to see if there is a signal going to them at all - and if not maybe try to monitor the ECM output while driving the car. I will also pull the plugs and see if there is any fouling.

It is just very inconvenient that everything is so buried, if they were accessible it would be easy to check them out and figure out what is going on!

 

IMO if it happens at 3000rpm it cant be the secondary injectors (unless they are stuck open and its dumping fuel)

I may be wrong but I didn't think they came online until quite a but higher then 3000rpm?

 

Sounds like the secondary injectors aren't staging rather than a boost problem to me. Check your wiring. You may have to pull the injectors out and send them out again. Like mentioned if they say for a while after cleaning, they could be stuck. Also plug in the power fc and look into the sensor/switch check menu and see if anything looks off.

 

Mine is dumping fuel. Guess that means they're stuck open. Good excuse to get them cleaned I guess

 

Nope, they start coming on at 3000 RPM. That's why the stock ECU has the 3000 RPM hesitation, it's a bug in the programming in the stock ECU with the transition. It totally disappears with a PowerFC.

Dale

 

 

You are thinking of the secondary turbo, which comes on over 4000 rpm.

 

I've had to go back in for this myself - it's no fun and very frustrating. An experienced FD guy (zkeller) told me it sounded like injectors and it was not news I wanted to hear. I was thinking many other possible things. He was right. I would be doing you a disservice to not share my experience.

 

Replaced the N3A8 ECU with a USDM N3A1. Fixed everything. The entire rev-range is accessible smoothly.

 

Thank you for this, and thanks to all the others who have left info. I have had a lot of experience with other Japanese high perf cars, and this is the first time for me to have something like this happen. It is hard to get my head around, but I will have to just do whatever it takes to get this resolved. On the upside, I will probably be able to do an injector change in a fraction of the time it took the first time around!

 

Thought I'd close the loop on this; I pulled it apart this week and installed new secondary injectors. The car runs fantastic now. While I had it apart I checked the grounds and cleaned their contact points, and I also added an additional ground wire, but I really don't think grounding was the issue here since the resistance measurements I took at various points were all 0.4 ohm before and after cleaning - which is also the reading when I measure directly across the meter cables so essentially no resistance.

So I guess the secondary injectors were stuck just like you guys said. Thank you all very much for this critical info...I would NEVER have believed that this could happen and I am still really struggling with the dynamics of it but I am just going to chalk it up to a RX7 learning experience and move on.