CTSC Autorotor running lean over 5K - suggestions please

ilya

ilya

Experienced Member
Joined
7 February 2001
Messages
1,617
Location
CORONA, CA USA
UPDATED 8/22: See my last post for final dyno

I finally picked up my NSX yesterday from the shop with my new Autorotor installed. The shop doesn't have a dyno, so even though it's supposed to be plug and play, I babied it home until I can get it tested.

Turns out that was a very smart thing to do.

I took it to a DynoJet this morning. Below are the details of the results. My plan is to take it to Autowave on Monday morning if they are free and see if they can find the culprit. In the meantime, I would love some suggestions on what it may be. I've looked at some older threads, and I'm sure that some of you may have had a similar issue before and found the problem.

Attached is the graph of A/F and HP/Torque. You'll see that it stops at just over 5K RPMS. It seems to start OK, then slowly rises until I hit 13 at 5K RPMS, which is when they let off the gas as its too lean. They tried adjusting the Fuel Pressure regulator, but it seemed to have little to no effect.

Any ideas on what may be causing the fuel starvation as the RPMs climb? Keep in mind this is a 92 and many parts have never been replaced. I just had a complete service done - Timing belt and water pump, all seals and gaskets replaced, all hoses replaced, all fluid flushed, and spark plugs changed. The timing belt and water pump was original! :eek:
So that tells me that the fuel pump, injectors, anything else that wears over time is very likely an original part and 17 years old. A full leakdown was done and it was at 10%, and that is with the engine cold. This was all checked and done before the Supercharger was installed.

I can only guess that since this is a bolt-on, and assuming it is installed completely correct, there may be something old or malfunctioning that needs to be replaced that is causing this to happen. I am figuring that Autowave is a good place to go since they have a Dyno AND they know the NSX and can find and replace whatever is causing the problem.

In the meantime, any suggestions are appreciated. I will keep this thread updated as the problem is hopefully resolved, and what ends up being the culprit. Hopefully it will be educational for me and anyone else that ever may have this problem.

This is a low boost kit and their gauge showed 6lbs on the dyno. I want to keep the car smog legal and do not want AEM management for now. I don't want to bandaid the problem with an aftermarket ECU that compensates for this problem, but find what part is malfunctioning to cause this. Once it's running properly on a low boost kit, I may consider the upgrade in the future. So I am running lean at only 6lbs, which is low for the Autorotor from what I have read here. They placed the sensor in the tailpipe for the readings. When I picked up the car, the idle was a bit lumpy, but since then it seems the ECU has adjusted and it's pretty solid now. The power curve seems so perfect and smooth, and yet the A/F gets out of hand over 5K.

Mods that may effect what is happening.
Stock airbox
Comptech Headers
Taitec GT Lightweight
Stock Cats
No other power mods


Looking forward to getting it resolved and finally enjoying the car.
 

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Nothing ever goes according to plan. When i got my ctsc installed I was on little 15 inch wheels with ten year old tires that would start spinning at 4k rpm (long story). Three days later I get my new wheels and tires - then the clutch goes out. :eek: Waiting on the 500 mile clutch break in. Still have not been able to drive the car as planned other than one drag race with a mustang before losing the clutch.

Hope you have better luck! Keep us updated.
 
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Is it possible that with the headers and exhaust I may need larger fuel injectors than stock? We had them checked and cleaned during the maintenance.

The spark plugs are brand new, but they are also stock. Do they need to be a higher performance type? My SC kit did not come with spark plugs so we used a new set of stock plugs. Was the correct?

Finally, is it possible that the dyno was off because it was measured at the tailpipe after the cats?
 
nsxotic911 said:
..back from pouting.. for a little bit..

Are you REALLY only making 220HP? Then your Autorotor isn't 'working' or you have some other very serious problem.

You should be making at least 300, if not 320 or more. 220 is what a stock NSX puts down, if that dyno is accurate, tow, do not drive the car to a reputable shop.

As to what the culprit could be, it could be anything..for example.
-Faulty 02 sensor(s).
-Faulty IAT sensor
-Faulty map sensor.
-Clogged injector(s) and/orclogged fuel filter.
-Failing injector(s).
...or other critical parts..

For a car like yours, especially if it has 100K or more miles, I would/would have replaced pretty much all sensors on the car to minimize points of failure + add some high capacity RC fuel injectors. They're pretty cheap, pick them up and install them.

Autowave will take care of you, good luck! Hope you're making more than 220HP with the Autorotor..
Click to expand...


Take a look at his rpm's, the dyno only goes a little past 5k, which is also noted in his post.
 
nsxotic911 said:
Are you REALLY only making 220HP? Then your Autorotor isn't 'working' or you have some other very serious problem.
Click to expand...

The car is only being revved to 5k rpm, as you can see in the graph.

The car doesn't seem to be getting the fuel required as it builds power, AFR is great initially, then gets consistently leaner. Measuring AFR from the tailpipe with a catalytic converter installed is not the most accurate, but there is an alarming trend in your AFR graph.

It's a fuel delivery issue, if adjusting the AFPR doesn't cause any difference, then you're not getting adequate pressure on the rail - a fuel pressure regulator cannot precision tune the fuel system, but it should be able to produce dramatic shifts on the AFR curve. I would say possibly dirty injectors, a dirty fuel filter, fuel pump which isn't providing enough pressure after being over-volted, etc.
 
So far from the various dyno graphs I have seen on Prime using the Autorotor, they all seem to be between 220-240WHP at around 5K RPMS. That's the first thing I looked for to see if I was at least making the correct power before they had to back off at 5K.
The supercharger is definitely working. Even at partial throttle from 3-5K before I let off, it pulls like a mofo compared to before.
It's garaged now until I can get it to a shop.

I'm definitely willing to replace anything I need to fix the issue. Only hopeful is that I can stick with a carb legal setup.

I have a new fuel filter installed and the injectors were checked and looked clean, but not necessarily properly tested. Fuel pump is still original, so hopefully testing its output may give some results. I recall reading somewhere that the CTSC kit comes with a set of spark plugs. I am running stock plugs. Any possibility that could cause an issue?
 
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My suggestion is to take your car into Autowave. They have installed a bunch these kits before and can dyno test it. When they installed my CTSC, they sent my factory injectors to RC engineering to be serviced and I had a walbro fuel pump installed. The base CTSC kit doesn't start making maximum boost until around 5k rpm, so it sounds like a fuel system issue.
 
We've had a couple run on the lean side here in our area (Seattle Wa) and had nothing to do with any parts on the car. Both of the cars were newer 2002 and 2005 with less than 30k on them, in fact the 2005 had less than 5k. We shipped the piggy back back to CT-E and they reflashed them. No problems since.
One big difference though, these were approaching 9psi of boost on the low boost set up, which was only supposed to be 6 to 7 psi. We even ordered and put a larger pulley on the 2002 to lower the boost to the proper range, but the owner didn't like the sacrifice in power after driving it for comparison. So again, the answer was to reflash the piggy back.
I'm not saying this is your problem since you're car isn't here for us to diagnose, but it's just another thing for you to keep in mind.
Autowave should be able to figure it out for you regardless of the issue.
 
ilya said:
I have a new fuel filter installed and the injectors were checked and looked clean, but not necessarily properly tested. Fuel pump is still original, so hopefully testing its output may give some results.
Click to expand...

Did you test the fuel pressure at various rpms? I'd never install a CTSC on a car with a 17 years old fuel pump. :eek:
 
IM going through a similar thing 225 hp? I would like to find out whatever you find was the cause. I'm thinking it a fuel issue.
 
Well, it looks like I won't be able to get it looked at until Wednesday when their tuner is back in town. In the meantime, I'm going to go do what I forgot to do and should have done in the first place. I will pick up a wideband a/f gauge and a boost gauge to get installed so I can always keep an eye on it.

UPDATE: Just had the muffler shop install the bung right next to the 02 sensor for the upper set of headers. Picked up an Autometer wide band a/f gauge and boost gauge. Will get that installed today and have it ready for Wednesday when I can hopefully get it checked at Autowave.
It seems you can't really monitor the A/F completely with just a single sensor since the left and right banks are completely separate until AFTER the CATS. At least not without getting 2 sensors installed and 2 gauges. Was told that the 1 is what most people do, especially with my low boost setup. Even though I will still take it easy until it can get to Autowave, I'm curious to see what A/F the gauge will read in comparison to the dyno. Curious to see if it starts to ramp toward 13 as I approach 5K RPMs. Hopefully will know soon enough.
 
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You're doing a good thing by waiting to see Mike @ Autowave....he and the others will find your problem. Where are you located in Corona? Cresta Verde golf course is my backyard (15FWY and Hidden Valley). Once you have your CTSC problem taken car of and back from Autowave....if you don't mind....I would love to get a ride. I have a 91 and can't make up my mind to go Supercharger or Turbo. Let me know....send me a pm.

Tony
 
OK. So I have an A/F gauge hooked up and go for a run.
At idle, it sits at 14 or so, which I am told is normal as it doesn't function until I am under load.
I nail it in 2nd, with a passenger carefully watching the gauge. Mid 10s. Nice and rich. Let's go a little harder. Up to 6500, climbs to 11. Try again and keep going. Solid 11.5 all the way up to redline and pulls like a mofo.
Do the same in 3rd, starts in mid 10s and climbs to mid 11s all the way to redline. By that reading, that is supposed to be ideal A/F.

So now the question remains. What's up? Was the dyno doing something strange and giving false readings? I can't imagine the Autometer gauge is not so accurate as to read 11.5 consistently versus 13s and climbing.
Could there be that much of a variation between testing in the tailpipe fpr dyno and having the sensor installed at the collector pre-cat for the A/F gauge.

I am still going to park it now that I've tested this until I can get to Autowave. I'm just not sure what to make of this great A/F reading versus the dyno. Since the sensor for the A/F is only testing one side of the headers, I guess it's always possible there is something wrong with the other bank that is running lean. Thoughts?
 
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ilya said:
OK. So I have an A/F gauge hooked up and go for a run.
At idle, it sits at 14 or so, which I am told is normal as it doesn't function until I am under load.
I nail it in 2nd, with a passenger carefully watching the gauge. Mid 10s. Nice and rich. Let's go a little harder. Up to 6500, climbs to 11. Try again and keep going. Solid 11.5 all the way up to redline and pulls like a mofo.
Do the same in 3rd, starts in mid 10s and climbs to mid 11s all the way to redline. By that reading, that is supposed to be ideal A/F.

So now the question remains. What's up? Was the dyno doing something strange and giving false readings? I can't imagine the Autometer gauge is not so accurate as to read 11.5 consistently versus 13s and climbing.
Could there be that much of a variation between testing in the tailpipe fpr dyno and having the sensor installed at the collector pre-cat for the A/F gauge.

I am still going to park it now that I've tested this until I can get to Autowave. I'm just not sure what to make of this great A/F reading versus the dyno. Since the sensor for the A/F is only testing one side of the headers, I guess it's always possible there is something wrong with the other bank that is running lean. Thoughts?
Click to expand...

Can you run 11.8:1 on pump safely?
 
ilya said:
Could there be that much of a variation between testing in the tailpipe fpr dyno and having the sensor installed at the collector pre-cat for the A/F gauge.

I
Click to expand...

If your first reading was after the CATS it would not have been correct. You might have been worrying over nothing.
 
In our experience, testing behind the cats vs in front results in a less than .1 AFR difference. The engine needs more fuel. The standard setup uses a voltage boost to the fuel pump, a rising rate pressure regulator, and an electronic pulse modifier to put more fuel in the engine. You'll also want to look at the factory parts this system relies on including the factory in tank fuel pump, fuel filter, and fuel injectors.

One or a combination of those items is resulting in not enough fuel to the engine.

Cheers,
-- Chris
 
See the attached latest dyno from Autowave. Looks like I am making the proper power for a 3.0 with Autorotor. Not posted is identical dyno with boost, which was flat 6lbs all the way to redline, so that is correct.

However, they feel that this is running too lean for an Autorotor setup. Apparently my A/F varies depending on how hot/cold the supercharger is and the temp, outside, much moreso than with the older Whipple units. So on the hot 95 degree day, I was running 11.5 A/F to redline no problem. On this nice and cool morning (for CA standards, about 75 degrees), that changed to 12.5-13 by air temp alone. If you look at the leanest run, that was after we let the car sit for about 5 min before doing the next run. The supercharger simply being colder made the whole run considerably leaner than the first 2 runs.

They feel for safety, the A/F on an Autorotor setup should be in the 11-11.5 at most, because you never know when it can be colder than usual outside or I am driving up in the mountains. So they feel I should definitely do the following which will help richen it up to where I need it.

1. Send the injectors in for cleaning just to make sure they are flowing properly
2. Replace the factory fuel pump with a Walbro that can easier keep up with the fuel demand
3. Replace a "sock" (don't know the part#) that relates to the fuel delivery that gets old and corroded over the years and can hinder the delivery.
4. Replace the stock spark plugs with the colder iridium plugs that are normally included with the kit (this isn't related to A/F, but they said it will help prevent any possible detonation)

None of this is expensive and I will have all of these things done at once. Then they can rerun on the dyno and adjust the FPR and hopefully see the A/F where it needs to be.

The other option is of course AEM, which I will do if I have to, but want to get this right first. They mentioned that with the Autorotor everything has to be 100% for things to function correctly within tolerance. They just get too efficient with even moderate changes in temperature, which I noticed first hand between the 2 days I tested the car, one hot day and another cold day.

I will update the thread once this has been done to show if the results were successful.

One question. I've noticed the car is EATING gas like crazy. I don't think it's just from running it hard. My mileage seems to have been cut in half even on highway cruising heading home from the dyno. It just dropped like a rock, almost like driving my 14mpg truck. Is it possible it could be running too rich somehow when idling, cruising, or not in boost?
 

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Didn't Autorotors have a problem in the beginning with running lean in cool weather? I remember people saying you needed to get the car good and warm before getting on it in cooler weather. Was that ever fixed?
 
I have a low boost CTSC Autorotor installed April 2006 and have had no such problem.
Every now and then someone raises this question.
A post from a old thread on this is
here
 
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I had the exact same prob: Received the car and the mechanic had not dyno tuned. Took it to a dyno and too lean. Tried everything: (a) fuel system had already been cleaned, so removed gas tank and cleaned, (b) turned the fuel regulator that comes with the CTSC all the way up, and (c) when those simple steps didnt work, we added a 7th injector (bad move, long story) as well as an Apexi AFR.

Finally, had to step up and go aem, 550 injectors, 255 walbro, etc. and it has been perfect ever since. Now with meth & 8 lb pulley, I have about 20k miles on it and puts down 382 whp on a 1991 3.0 litre.

Not sure why, but my buddy had his autorotor installed by the same guy as mine at the same time and his ran sufficiently rich. Very similar but slightly different setup.

You may not have a choice but to spend more money. Good luck.
 
With my FIC at 8.5 psi my stock fuel pump couldn't keep up, and I had 500cc injectors. Went with the walbro and the problem went away.

regarding the poor mileage..

when i had the ssbox on my bbsc, even though i had demonstrateably decent AFR's when under boost, and it seemed to run at 14ish when putzing around and idling, my mileage was 16.5mpg for years. I switched to 500cc injectors, and got the AEM FIC and jumped to 20mpg.
 
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