Lean Running

[Coz]

I have the early style Comptect SC on my car along with Comptect Headers and Mufflers.

It was running lean above 6,000 RPM per the dyno results done with SOS.
So working through some things, we found that the front injectors were different from the rear injectors. So they were all replaced with 250cc injectors. Still ran lean. The the FMU was replaced with a Comptect FMU.

$1337.00 later, it's running better but still on the lean side at the higher RPM's.

Now I'm told that I should do the Stand alone EMS and everything that goes with it for another $3500.00 to completely fix the lean problem.
Also told it would probably add another 40 RWHP.

I don't mind spending the money as long as I'm not chasing my tail and tossing good money after bad.

Granted, the injectors and FMU had to be done....

But now with the Stand Alone, that puts me $4800.00 into fixing this problem....Lot of money to fix this situation....

What have you guys done in this situation ?
Is the Stand alone the fix ?

 

[MJK]

Fuel filter? pump?

 

[Coz]

Fuel filter ok, pump putting out 75-80 in pressure and holding steady.
Lines are clear.
New over bore throttle body.
New 250cc Injectors
New FMU
Also running the Cantrell Concepts Airflow Induction System.
Results of the dyno today were 329 RWHP.
Seems a little weak numbers wise.

 

[DDozier]

Fuel filter ok, pump putting out 75-80 in pressure and holding steady.
Lines are clear.
New over bore throttle body.
New 250cc Injectors
New FMU
Also running the Cantrell Concepts Airflow Induction System.
Results of the dyno today were 329 RWHP.
Seems a little weak numbers wise.

for a Whipple on a 3.0l those numbers are in the normal range, you have to remember not all NSX's are created equal and almost every dyno will be different. Do you have before and after dyno runs? Can you post the most recent dyno run?

If you are setting the car up as a daily driver or even a weekend toy, and do not track the car, then I would resolve the problem without going to the stand alone EMS. The first thing to look at is fuel delivery, presure and volume are not the same thing, you have to have both with the Comptech FMU to get the injectors to flow more fuel. My guess is the pump is getting a little weak. No disrespect to SOS, but you should get a second opinion at least on your options. There are several things that can be done to the FMU and to the fuel system to solve this problem and keep the factory ECU.

Try talking to Shad at Driving Ambitions, or Mike at Autowave, let them know you are looking for options, let them know what work has been done to date. Then bounce those ideas off Chris at SOS. There are plenty of people running around with CTSC and are not having issues with the basic setup so you should be able to work this one out.

If you want to make the move to a stand alone you will have more options and power down the road, just make sure you are willing to make a few trades for the power. Besides the cash, you need a very good tuner and the patience to get the car dialed in.

Dave

 

[Coz]

Wasn't really very happy with the results and the "new" next fix cost and left without it. Will get a copy and post it.

The car is being set up as a daily driver and will see some track use. How much track use at this point I'm not sure, but it will be at least 4 to 6 times a year.

SOS has looked at everything fuel delivery wise and can't find anything wrong presure wise. It was felt that going to the 250cc injectors & the new FMU would solve the volume issue. It did to a point and it's a lot better than it was, but not like it should be yet.

I agree, going to talk to a few perople before throwing $3500.00 into this problem. If need be, I'll drive the car up to Shad and have him look it over and see what he thinks. It's just a little dis-hearting to spend $1300.00 to fix a problem that isn't totally fixed, and then be told it's going to take another $3500.00 to fix it. My only thoughts at this point is what happens next if this $3500.00 fix doesn't fix anything and now I'm into trying to fix this problem for $4800.00 and it's still not right. I'd be pretty pissed off. No, I'd actually be flamming mad.

I'm going to discuss this situation with a few people before going any further with it. Feel like I'm a fish on a line right now.

I thought my GT5 was pricey...I could have rebuilt the motor in my GT5 for this $4800.00 and never have any of these problems. There is something to be said for the simplicity of older V8's and what it takes to keep them running right. I'm beginning to think I made a mistake buying a NSX and wanting the power it should have.

Sure hope not though because I like the car and enjoy driving it.
We'll see where it goes from here.

 

[dynomike]

I have come across this problem many times with the Comptech sc. I have a good idea what it is. 329whp is very low considering the dyno you were on. I have been on that dyno a couple of times to tune cars for SOS and that thing always reads way higher than what I normally see here at my shop.

 

[jmp]

Follow the good advice of all above - entire fuel system (even consider having your fuel tank removed and cleaned) check and "clean". After that if too lean, you have no choice but to go AEM or the like ,along with 440 to 550 injectors and 255 walbro fuel pump and 1:1 regulator.

After the install of my autorotor CTSC, we spent 6-8 months jerking around with Apexi fuel "computers", bigger injectors, 7th injectors (yes extra injector) and its own "computer", until I left my former mechanic (who all along was disuading me away from the standalone), installed the standalone, picked up 26 whp (350 whp to 376 whp) running in the 11.5 a/f range all the way up, and have since put on 5000 to 7000 miles of daily driven fun without a hiccup.

Peace of mind comes at a price but it is worth every penny.

 

[ScienceofSpeed]

The fuel delivery is good on this particular car now that the various oddities have been fixed (mismatched fuel injectors, vacuum lines, & high boost pulley resulting in air fuel ratios in excess of 17:1 AFR). The system now develops a steady pressure as designed.

The mechanical FMU included with the standard supercharger does not generate a flat air/fuel curve and although it can be adjusted, the adjustment affects the entire RPM band, not specific areas that may be overly lean or overly rich.

With the FMU, you are still relying on the factory computer for fuel injector pulse width and ignition control that was programmed for a naturally aspirated car.

The stand alone engine management is the best approach as it allows full control over the engine including fuel and ignition mapping that is ideal for forced induction.

Not saying that the original fuel management is not adequate - however, when you're pushing the envelope with supporting mods that are increasing the power of the engine in a demanding race track environment - there's a point where you begin to push the reliability of the standard set up.

cheers,
-- Chris

 

[ScienceofSpeed]

Seems a little weak numbers wise.

The numbers you achieved were the highest I have ever seen a Whipple based Comptech supercharger produce on the type of dyno used.

Remember, this is wheel horsepower. A standard NSX produces around 230 rear wheel power on this dyno. Your setup is netting more than 100 hp increase at the wheels. Definitely not on the low end.

The numbers you are most often used to seeing from manufactures is crank horsepower (ie. your 1994 NSX is rated at 270 SAE hp).

regards,
-- Chris

 

[Coz]

I couldn't agree more.
Thanks guys for the impute. It's appreciated.

Peace of mind comes at a price but it is worth every penny.