SR20Fastback

Last week I took my car to one of the local shops in town that has a mustang dyno. The owner is a friend of a friend, and they've got some pretty badass cars there. They're also a motec dealer/installer/tuner, I think I'll likely be employing their services for that down the road.

Anyways, onto the dynos. The first run was performed with simulated dynojet corrections, the last two runs were done with the standard mustang dyno corrections. What is concerning is how lean the car seems to be running. Pump 91 chevron octane at all times here. The car has a vitesse MAF kit, so my thought is to email them and see if there is any kind of correction they can make.


First run (dynojet corrections): 301rwhp, 254tq

Second and third run (mustang corrections) 231rwhp, 211tq


Anyone have any thoughts on the AFR for these runs? It was moderately warm that morning (high 70s low 80s). You could definitely tell the car was pulling timing on the 2nd and 3rd runs. Until I get this sorted, I've kind of put the track day I had planned in September on hold.

-nick

I'm not sure what is happening in the simulated pull, but the hp/tq numbers are definitely unrealistic. The mustang results are very close to my mustang runs with a 100% stock engine/exhaust/chip which put out: 215/233 hp/tq but with a much richer afr throughout. With a 93 octane Wong chip I gained +5tq and +8hp (peak). Are you all stock other than the maf? If so, I would chuck it for a Wong chip. I wouldn't trust any maf conversion. What makes you think that timing was being pulled?

911 jared

Spyerx

share these w/ steve wong, it looks like it is running lean. he can fix.

SR20Fastback

I sent him an email last weekend, and he sent me a reply late Sunday night. I have to go pull the DME to see what is going on in there software wise.

He also suggested pulling the MAF and software, and going back to an AFM and stock airbox. Unfortunately I didn't receive either of those when I bought the car. Guess I should start looking.

SR20Fastback

Haha, yeah I was like well maybe the PO did a 3.8 and neglected to tell the dealer he traded it into. Either way, I was pleased with that run, and then obviously got the heartbreak dyno numbers next.

SR20Fastback

As far as I know, it's basically all stock sans the Vitesse MAF, and a cat bypass.

HDA

Ahah I could totally see myself thinking the same!

kylejohnston1

Before you remove the MAF, maybe reach out to John at Vitesse and get his thoughts? He may be able to offer tech support and tune remotely, just as Steve Wong does.

http://www.vitesseracing.com/html/contact_us.html

Spyerx

Agreed on contacting Vitesse first. It looks like they have custom software to handle the input signal for the MAF, seems like a piggy back type setup on the ECU.
I don't think Steve would be able to program that (would have to check).

getting a stock AFM and either a cone filter or stock airbox shouldn't be too much work, but I'd show those #s first to Vitesse and see what they have to say.

You're sure your motor has no other mods?

-nick

Cat bypass would explain it. With a more open exhaust I had to add fuel in almost exactly the same places that you're showing the lean peaks. My guess is that the maf kit has the fuel tuned for a stock engine/exhaust. You either need a new chip from vitesse, or swap it all for a Wong chip + afm. Personally, I'm not a fan of the piggy back maf approach (nor of bypassing the cat...).

SR20Fastback

Just emailed John with the dyno files. If he can't help, I may just fo back to the AFM/stock airbox until I find enough change in my couch to do ITB's

kylejohnston1

Let us know what you hear from John. I have a Vitesse MAF and cat bypass, as well. AFM's wear out over time and need to be opened up and refurbished. So, if you buy a used AFM, I would inspect it before you install it. There are threads here which cover the refurbishment. At any rate, my AFM was acting up and I had an opportunity to buy a used Vitesse MAF kit at a great price or refurbish my AFM. I went with the Vitesse MAF kit thinking I could always sell it and recover the cost if I didn't like it. I know all the experts say that for an unmodified car, a MAF offeres no gains over the AFM but this assumes the AFM is in perfect working condition. As our cars approach 30 years old, many AFMs are getting pretty tired, just as mine was. I keep my AFM in the garage and always will, but the MAF kit really woke my car up and instantly improved the throttle response and other issues that were being caused by my AFM. I've been very happy with the kit and Vitesse gets lots of love on the 944 forum. However, now I am wondering if I am also lean in certain areas. I guess I should invest in some dyno pulls to monitor the air/fuel ratios.

SR20Fastback

It was always in the back of my mind, I'm glad I know now. Definitely slowing down on the whole hammering it at all times thing.

John replied, and said it didn't look like a normal 964 AFR reading, and he thought it may be a vacuum leak. The car has never had any issues idling, so it's hard for me to wrap my head around that, but I'll likely try to rent a smoke tester in the next couple of weeks to double check.

fast951

After exchanging numerous emails trying to diagnose the lean AFRs, which are not normal with our MAF conversion, we concluded.
- The MAF kit is probably over 8-10 years old, based on the serial #.

- The MAF kit, mainly software on the Chipboard, were configured for late style DME (non FQS). However this car has an early DME. So there a mismatch there.

- many items could cause the lean AFRs, some of which: faulty fuel flow (pressure or injectors), vacuum leak, bad TPS/WOT switch, mismatch between I jectors size and software, failing sensor(s).

Obviously full diagnostics are a required. Considering the MAF kit appears no. Original to this car, we cannot tell if it was configured for larger than stock size injectors. Original MAF owner gets all this I formation, and apparently it's missing.

OP decided to sell the MAF kit, hopefully going to AFM and a chip configured for his car helps in the diagnostics.

The Vitesse 964 MAF kit runs correct AFRs, so the question remains if the problem is mechanical or if the MAF sensor is on its way out or if the software is configured for a different setup. We will never know.