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Injectors and fuel pump for Boostzilla Stage 2

17 February 2024
Hey all,

I just took delivery of my first NSX, a 1991 5MT with the Dali Racing Boostzilla Stage 2 kit.

It doesn't start most of the time, and when it does, it has a rough idle and is shaky at low speeds. Gets better as it gets up to temperature. The startup issue is that it cranks but doesn't fire up, smell of gas and a bit of coolant after a couple attempts. Aux systems like lights and dash have power. Jumping didn't fix it, and rebuilding the starter and replacing clutch+gas stop sensors didn't fix it.

I've been like looking around on the forums (and Wayback Machine) a lot to figure out which parts are included with the kit.

Trying to replace components to get it starting and running well.

From what I've seen, it uses HKS FCON piggyback engine management, 6.3 PSI pulley.

What injectors and fuel pump did the stage 2 kit use?

The old archived site mentions ethanol injection for stage 2, but I don't think this car has it. Curious if others that got the kit had that feature included.

Any advice on the startup issue also welcome.
smell of gas and a bit of coolant after a couple attempts

'smells of ..... a bit of coolant' is not good. Have you done a basic health check on the engine? A compression test and in your case a 24 hour coolant pressure test would be appropriate. If you have a head gasket issue tweaking the F-CON isn't the solution.

If the engine is mechanically OK then, assuming that the supercharger set up ran well at some point then you might have a fuel system mechanical / electrical problem of some kind. You would need to do the basic checks such as fuel pressure, flow test the injectors, temperature sensors. Unfortunately you do have a bit of an orphan engine and if you did not get any documentation on the supercharger installation you are kind of lost as to what is correct so you don't know what you are looking for. In this case you would need to know that this thing actually ran well at some point.

If in fact this is somebodies bodged project car and it never ran well because it was never fully sorted, then the problem might reside with F-CON configuration, or it may be that the collection of parts assembled on the car just does not work. Assuming it is an F-CON configuration problem, HKS still exists and they still have an F-CON product line although they no longer have a piggy back for the na1 NSX. You might be able to obtain the configuration software from HKS that will work with your piggy back (once you confirm that you actually have an HKS piggy back). Of course, that assumes that you have the skills to do this. I think Prime member @RYU uses the HKS F-CON and may be able to provide some guidance. Otherwise, MotorMouth93's suggestion would be the path to take.

Assuming that the engine is mechanically OK. As a suggestion, since you seem uncertain about the 'collection of parts' that you have on the engine, consider returning the engine to stock - remove the supercharger and associated bits including the F-CON which would allow you to operate on the OEM ECU. This would give you a nice driving car and then you have the time to try and sort out how your collection of supercharger stuff is supposed to work. This would be cost effective if you still have all the original OEM parts. If you don't have the OEM parts and have to purchase them then it is a tougher decision as to whether you invest to return to stock or invest to try and fix your set up now. I expect that if you haul your NSX off to some tuner and say 'make this work' that is not going to be inexpensive.

I like to drive my cars rather than repair them and I am old enough that I don't want any more projects taking up space Personally, I would never purchase a modified car unless the seller has all the documentation required to support those modifications or it came with a really good $ discount.
First, welcome to NSX Prime! Second, you have the finest supercharger system ever designed for the car. It's too bad more of these weren't sold, but well Dali Racing...

Anyway, the advice above is key. You should warm the car up (radiator fan comes on at least twice) and perform a compression test and then a block gas test to make sure the head gasket isn't blown (a known issue with the 3.0 engine and FI). That's Step 1.

Assuming your head gasket is ok, then you can proceed with troubleshooting. Finding someone to tune (or even access) the HKS is going to be really tough. There might not be anyone left in the US who has the license key. Thus, I agree with @MotorMouth93 and you should look at a new engine management system. The Haltech is a good product with modern support. Also, the Link system from Science of Speed is a good route too. @stuntman uses the Motec and I'm sure he can help you set that up too. There is another member here (@bogle) who is tuning the Link system for his supercharger. I'm sure he'd be willing to help you get it set up. All of those systems have good logging tools that should help you figure out what's going on.

Keep in mind the Boostzilla never really left the prototype stage, so there really isn't a standard parts list. The number one problem with superchargers on the NSX is fueling. I would test the entire fuel system starting at the fuel pump and ending with the FPR to make sure the injectors are getting enough gas. I'd toss whatever 20-year old crap is in there and replace with Injector Dynamics 1050cc units.

Assuming your engine is mechanically ok, the right path here is probably going to be a modern ECU and component overhaul.
Welcome to Prime and hello fellow primate.

Oooof... this might be a tough one because your symptoms could be caused for any of a variety of things, but it looks like you're willing to get your hands dirty so not insurmountable. Everyone on this thread has gone through some level of troubleshooting and all have provided great advice.

Here is mine FWIW - Strip the engine down to as stock as you can get it then go from there...

The Boostzilla was pretty much a custom kit. IIRC it was available without an engine management. I have no idea how even an F-Con made it into your NSX as it's such a rare and thinly supported product even when it was sold by HKS USA for the NSX. Chances are the hardware is still good but finding a tuner and finding the HKS Powerwriter software with a licensed key is nearly impossible these days. The suggestion by @MotorMouth93 is a good one which is to swap out the ECU for something better supported. Now, since you have the piggyback the wiring to get back to stock shouldn't be a big deal. Then once you get the car to more or less stock (i.e. remove the Boostzilla) then you can better figure out what exactly is wrong. You can then decide to add back the boost or not.

This is just one of many approaches you can take. It's just how I like to do things given what you're facing. In my experience if you continue to try solve one problem at a time, installs like these have habit getting other problems later. I like to start from scratch and wipe the slate clean.

Is this a USDM car? Where was the car originally built? My guess is SoCal. Give us a some history on it. We might be able to point you to previous owners or shops that might have history on it.
This is extremely helpful, thanks all. I will continue to troubleshoot for now and report back on findings, but definitely going to pursue modern engine management as suggested as soon as possible. There's a speed shop here in Wilmington, NC that would probably be able to sort out the initial tune just fine - but probably not on the piggyback.

Planning to get new gas in it, replace main relay and ignition switch over the next week or two which perhaps could help if it's a spark issue.

I agree with the overall idea of trying to get back to stock - in fact, I'd be completely fine with not running any boost, reliability and enjoying the car are my top priorities. Doesn't seem like it would be too much of an undertaking to rip the supercharger off and put the stock airbox / pipe back on.

That being said, I could be wrong about the FCON. It shows on the archived Boostzilla Stage 2 page that the kit includes HKS FCON, but I haven't actually located one in the car yet. The stock ECU appears to be in place in the panel behind the passenger's seat - perhaps there is an FCON tucked away somewhere nearby. Some further research needed there... not sure where it would be.

I took a look at the injectors and they are RC 440cc SL9 injectors.

Install of the Dali parts was done at Revenge Motorsports in El Cajon, CA. Looks like their website doesn't exist anymore.

Invoice says "dyno tune/test" and there's a dyno chart, so there's definitely some custom programming/mapping going on...

Got the car on Bring A Trailer, it was an Iowa car for much of its life and is a USDM 5 speed manual
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Here's the documentation from the tune if anyone is curious


  • Supercharger Invoice.pdf
    644.6 KB · Views: 4
  • Dyno Chart.pdf
    515.4 KB · Views: 5
First observation - $150 doesn't buy you anything in the way of setting up the configuration variables in the ECU firmware. $150 is about 1.5 hrs at the shops going labor rate. That cost is probably the cost to roll the car on to the dyno to fire it up and make sure it works. The dyno charts do not include AFR ratios which would be the first ingredient in configuring the fuel settings.

The F-Con is a piggyback system so it has to be inserted in-series with the wiring harness from the ECU to intercept the injector and ignition outputs (I assume it does both fuel and ignition and not just fuel). The piggy backs usually came with an adapter wiring harness to insert the unit into the OEM ECU harness so it would typically be very close to the ECU. On some adapters one plug on the adapter would plug into the ECU and the other plug would be female and match up with the vehicle wire harness making for an easy install. Some adapter harnesses required that you de pin the existing wires and insert the adapter harness wires into the plug and then connect the existing wires to another plug.

In the NSX Prime library (red banner at top of page) you will find links to the 1991 service manual. Download the manual. In section 11 starting on page 11-8 you will find the pin assignment. Injectors are A1-A6 and ignition is A21, A22 B3-B8. At the bottom of 11-9 you will find the plug diagram showing the location of those terminals. Locate the A and B plugs on the ECU body and find the injector and ignition outputs pins. If you have a piggy back then the wires at those pins should lead you to the piggy back unit and you can confirm what it is. If those output pins go to wires that go directly into the original engine harness (i.e. directly to the igniter and the injectors) then it would appear that you do not have a piggy back unit - which would be interesting.

If you don't have a piggy back then your RC injectors have to go. If you are using the stock ECU fuel maps to start the car the fuel pulse widths will be way too long and you are grossly over fueling at start up. That would be consistent with the 'smell of gas' that you report in the first post. If you have been trying a lot of starts I might be inclined to consider replacing the oil since you may have washed a lot of gas into the crankcase. With original size injectors and fuel pressure spec the engine should be starting just fine with the OEM ECU - the presence of the supercharger will not materially alter starting conditions. If there is no piggy back present then I definitely would be considering removal of the supercharger to return everything back to stock. You can't run a supercharger with the stock fuel maps in the OEM ECU. Get the engine back to stock and you can then take your time to figure out what the next steps might be with the supercharger system.

With luck the engine is mechanically OK and restoring to stock should give you a nice running car. However, as Honcho notes, forced induction and C30 head gaskets is kind of bad juju, particularly if they tried for whatever stage 2 boost is.
like most non critical problems in life this sounds like a combination of time money and aggravation so don't sweat too hard over it. first thing is get better and more modern engine management. Regarding the blower, i don't know what makes it the finest supercharger system out there as there are plenty of excellent more modern systems but that's whatever. It's a good system with proper tuning and setup. that's the important part. You'll find a cornucopia of excellent advice here and i do believe there are some highly qualified techs near you to deal with the mechanical issues.