Vitesse STEALTH MAF/MAP Kit

[NCGermerican]

Hey Folks. I'm currently installing the Vitesse Stealth MAF/MAP kit on my 87 951. I went with the stealth kit because this will be more of a show car than a go car, so I prefer to keep the look of the factory airbox....especially since I paid over $400 for a brand new one earlier this year.

So far I have hit a snag with the fitment of the aluminum pipe with the MAF (that replaces the AFM). Per the supplied instructions/pictures, the MAF sensor plug should be mounted upside down with the plug side slightly rotated towards the front of the car. The problem I'm running into is that it's touching the coolant manifold bar and because of this, the factory airbox won't sit all the way down in it's mounts. Therefore, my hood won't close (my brand new hood insulation seems to be pretty thick).

I'm wondering if anyone else has installed the stealth kit, and if so, could you chime in with any tips and tricks? If not, my next step is to fabricate a new MAF tube so I can move the placement of the MAF in BETWEEN the factory airbox and the intercooler to throttle body pipe instead of UNDER the IC to TB pipe. This probably sounds confusing and I'll try to take some pics later tonight.

[Tom]

Have you checked in with @Fast951 ?

[Doyle623]

It is a very tight fit, I have the same setup and there is enough adjustment with the air box mounts to raise it so the sensor isn't touching the coolant pipe.

IMG_4094.jpg (100.74 KiB) Viewed 2467 times

[NCGermerican]

It is a very tight fit, I have the same setup and there is enough adjustment with the air box mounts to raise it so the sensor isn't touching the coolant pipe.

IMG_4094.jpg

This is exactly the kind of help I was looking for! I will try to slowly raise the airbox and see if I can gain some clearance for the MAF and still be able to close the hood. My hood insulation is new and fairly thick.

Can I ask where you are pulling power from? My plan is to use the CV plug as it tested for around 12.5v keyed power.

[NCGermerican]

Have you checked in with @Fast951 ?

I did. He’s very quick to respond but no sooner did I start an email convo I came down with the flu and all work on the car stopped. He’s out of pocket until 2024 and I don’t want to bother him over the holidays.

[Doyle623]

I used to pull power from the diagnostic plug (back right rear of engine bay) and run it down to the MAF, but when I ordered my Kroon harness, I had them add a 12v power wire next to the airflow meter plug.

[NCGermerican]

Well, after Christmas, the flu and a short “honeydo” list, I was able to get back to the 951 MAF kit today. I’m glad I also have my 87 S to drive around while I tinker with the turbo.

I was able to manipulate the MAF tube a little but still couldn’t keep one side from making contact with the coolant manifold. So, I cut a short section of Rennline fuel line and cut it lengthwise to put between the coolant pipe and the MAF sensor housing.

I put it all together and fired it up. First cold start went very well. AFR was right around 14.7. I monitored the readings using my F9 DME on my laptop. Turns out my tach is indeed off. F9 shows right at 840 RPMs at idle but the gauge shows 1k.

I shut the car off to bleed the coolant since it was the first startup since replacing the water pump.

Then, weird stuff happened. On the next startup (warm) the car started right up but immediately started running lean (17 AFR) and stumbling for about 10 seconds then slowly started to normalize. I let it run for a few minutes and shut it off to bleed the coolant again. Started it again and same thing- very lean, stumbling then it would normalize.

I’m thinking of making a short video to better capture it and show a little bit of what the F9 DME is reading. It has inputs for both WBO2 and MAP sensors so I’m able to get readings and take a log. More to come soon.

[944m3]

I had similar issue with my install. Not stealth though, regular unit.

Fired right up and ran and drove though it did have a slight occasional stumble. But the second or third day, when the car warmed up it started to run rich, AFR dropped from 14.7 to 10. When the car got hotter it started to stumble because it was running super rich. But then it got weirder, after about a week of tinkering with the FQS settings with John’s help, the car decided not to start, it would crank but no start. Tried all the usual stuff but nothing.

John was helping me via email the whole time but nothing worked. So finally decided to go back to Lindsey’s A-Tune and the car started right up with perfect 14.7 AFR. I have no idea why as I didn’t change anything. (Did go back to stock injectors of course).

Just really weird because everything started great but slowly got worse and worse until it decided not to start. Crazy. My guess is that it’s something in my wiring. (Weird things happened when I converted to Nissan Quest alternator, wouldn’t work until I changed the alternator harness even though stock alternator worked fine with original harness). Or could be DME shorting somewhere. Who knows, but A-tune with MAP works great, go figure.

Next move is to replace entire harness and try again. When I get around to it.

I will add, John provided great support during the entire time. No complaints there at all. These old cars just act in weird ways sometimes.

[NCGermerican]

Update - I'll split this into 2 parts.

Part 1 - Fuel Pressure Regulator
I don't know if this is the issue or not, but after doing a fuel pressure test, I found out that the 3.0 bar FPR I installed with the "Instant Horsepower Kit" I purchased last spring is NOT 3.0 bar. I've been running it since April or so and never thought to do a check until I had the issues with the new MAF kit. Here are the numbers:

Pump Prime (F9 Tech DME Relay): 2.6 bar / 38 psi
Car running: 2.4 bar / 34 psi
After car shutoff: 2.6 bar / 38 psi
After 20 minute leakdown: 2.4 bar / 33 psi
After 3-4 hours: 0 psi

Now I need to find a 3.0 bar FPR. I've reached out to Emanuel at 944store and I'm going with a Delphi since Bosch units are NLA.

Part 2 - ICV
After I installed my new headgasket last month, I did a pressure test of the intake system (starting at the IC side). At 10psi, I could hear a definite hiss under the IM and it turned out to be leaking through the connector on the ICV. There are NO factory/bosch units available anywhere in the USA (even had a Porsche dealer check), so I opted for an aftermarket unit.

Normally, this should seem ok. HOWEVER, I also have a 1987 944 S in which I've been wrestling with idle issues (intermittent surging, intermittent stalling at red lights) as well as some other gremlins (intermittent reduction of power, etc). I had also replaced the ICV with an aftermarket unit (bought on eBay from Germany). All of my DME tests came out good (AFM, TPS, o2, etc), so I had no choice but to start swapping parts. I was able to purchase a factory ICV (over $600). It's a lot of money, but I installed it this weekend and the car IMMEDIATELY ran as it should - rock solid idle, no dips, no surges and the car overall seems to run better. For those that don't know, the ICV for the 16v's (2 pin) are different than the 8v cars (3 pin)

Back to the 951 - I was able to take apart the bosch ICV that came on the car and replace the large O-ring inside. I'm thinking about just putting that back in (even if it still has a boost leak at the connector) to see if that changes things. However, I'd like to swap out the FPR first to see if that clears it up. I really don't want to take off the IM again, since it's a PITA and I'm running out of gaskets and patience....

[Fast951]

It appears that you have a 2.5bar FPR. The software is configured for a 3bar FPR.
The difference between the 2.5bar and 3bar FP is about 9% flow. To get by while waiting on the 3bar FPR, set the FQS to +10% fuel (refer to the supplied FQS document).

FYI AFRs during the cold start should be in the 11s or even richer if cold. Then as the engine warms up, AFRs will lean out and will start closed loop around 14.7:1.