tjbreen

I just installed a low mileage later model used Vitesse MAF and I am monitoring the A/F ratios with my WB. Idle is reasonable (14.7 ish) but it is lean on boost getting only to the high 13s.

I have corresponded with John and he as suggested some reasonable things to check like vacuum lines, TPS, and FPR but I wanted to see if the listers had any additional ideas or suggestions.

Tom M'Guinn

I assume you are using VR software too. Are you sure the software is set up for the injectors and fuel pressure you are running? My VR software, for example, is set up for 83lb injectors. If I ran smaller injectors, I'm sure it would run lean.

tjbreen

The PO told me that this chip board was setup for 75LB injectors, which I am running. I have emailed the PO to confirm as there is no way to determine the required injectors by external inspection of the chip.

choinga

hmmm...3BAR FPR, I'm assuming is installed? Time for the piggyback.

tjbreen

3 bar is installed. I tested the FPR and damper for leaks and found none.

I was hoping to solve the problem so as not to disquise some intrinsic weekness in the fuel delivery system. After I pump about $500 into an adjustable FPR, FP guage, and new fuel pump, I will then have to piggy back it into shape.

I just set the FQS to position 3 to see if the +6% fuel makes a difference. I will take a run tomorrow to get some data.

choinga

hmmm...do you have a fuel pressure gauge? And yes, it would be ideal to fix the issue without having to do it with a piggyback. I have a Vitesse MAF and I still haven't fine tuned it - but at WOT it bottoms out at around 11.8 or so, which is where it's supposed to be. What about your O2 sensor? Any idea if/when it was replaced?

It might be worth working with John (@ Vitesse) to take a look at your chip and make sure everything is OK. Stranger things have happened...

+6% on the FQS is a lot. If I stick it there on my car, it chokes to death. That's not where you want to go to fix this problem.

If it's lean at boost only - maybe it's vacuum leak somewhere? I can't remember, but I think that a leak would make you run lean. Sometimes leaks don't show up at idle but when you hammer it and the pressure builds, you expose one. Have all the vacuum lines been changed/upgraded with silicon lines or are you still running any of the factory hard plastic ones? What about any other rubber hoses in the vacuum system?

When I did my MAF I gutted everything - all new rubber and all silicon hoses and I bought the throttle body rebuild kit. I did the whole thing, but replacing the ring gasket was my primary goal - it's an easy spot to generate a big leak at boost. Also, I'd highly recommend the ratchet clamps instead of the cheap screw down ones for you connector hoses on the intercooler pipes. Those are problem leakage areas as well...I blew the rubber one off where the intercooler pipe connects to the throttle body several times before I finally put in hard pipes and bought the ratchet clamps from Lindsey.

Anyway, I'd pull your intake and replace everything under there - and do a venturi delete if you have an aftermarket dual port wastegate installed. Removing that venturi system will clean up about a half dozen connection/clamp points that can cause problems.

fast951

Tom, since you purchased the unit used,You should have received instructions from the MAF's previous owner. In the instructions we specify the Fuel Pressure, using a different pressure is just a band-aid to a cover a problem.
Also, the FQS settings are unique per chip/board, they will be specified in the FQS/Installation document which we supply to the original owner.

For the car to go so lean under load, there is something wrong! Raising the fuel pressure, or adjusting with the FQS will not solve it, but it will hide it.

Hopefully it will be something simple. I'm sure you are not too excited about purchasing a used item with no warranty or support then have to deal with a problem like this. I would start by getting the FQS document from the original owner.

tjbreen

Choinga - I have done many of the things you suggested like venturi delete, dual port WG, full vacuum line replacement with silicone, throttle body reseal, and new OEM oxygen sensor just last year. I even have one of those adapters that allows me to pressurize my intake with my compressor to look for leaks in weak lines and have found none.

My understanding of the intake is that if I had a leak, under pressure the air that had been measured would escape causing the A/F ratio to go rich. At idle, when under vacuum, I would expect the opposite.

One very strange and what I think is a new phenomenon is that when parked, if I push on the throttle to raise the RPM, the vacuum actually increases from 18 to a peak of 20 at about 2000 RPM, then moves back towards zero. I never noticed this before but I can't say I was looking. Shouldn't the vacuum decrease with RPM even it it was unloaded? The only time I saw any vacuum reading over 20 was while engine breaking with throttle closed and RPM high. Can you check your car to see if when you push the throttle the vacuum doesn't increase? Under load, it immediately heads towards zero.

John - My first step will be to check the fuel pressure and pump performance. I am heading out this morning to cobble together a way to measure fuel pressure from autostore parts. FPR or pump volume/pressure is the only thing I can think of that would cause the combination of issues I am seeing. This prestine MAF kit was bought from a the original owner with about 100 miles of use so I am very confident it is not a kit problem but a car problem. I track this car and value reliabilty over everything else so I am painfully pleased that this install has shown any weakness in my current setup while there is snow on the ground and at least three months until my first track event.

I am like choinga in that once I get started on a problem I don't stop until it is fixed. So, if I can't get this debugged in the next week or so, you will see this kit back up for sale and you will be receiving another order for the same kit so I can tap into your full support.

tjbreen

I tested my fuel pressure and regulator this morning and found that everything was working properly.

I then took the car out to test the FQS change I made earlier (FQS position #3 +10% fuel). I previously I stated that FQS position #3 was +6%, which was not correct. With the fuel at +10% I am seeing numbers that are much better on boost (nominally 11.5 at 15 PSi on-brake steady boost with an occasional peak to 11 with a fast rise) and a little too rich at idle (14.25 to 14.5).

Now thinking about FQS position #1 which corresponds to +5% fuel to see if I am still as rich but the numbers above don't seem bad to me. It is curious that my car needs this much more gas to be happy. Has anyone else had to adjust their FQS switch. The instructions for the chip board state that if you hear knocking, to adjust the FQS to position 0, 1, 2, or 3 but I have not heard anyone mention that they touched the FQS when installing.

I have had some headwork done and the car has always seemed strong. Previously, I was able to keep close to a friend driving a Turbo S with a full Vitesse Stage 2 kit on a long straight. I have since deleted my catalytic but this is a 2.5" exhaust 1987 117K mile stock turbo car.

I will continue to monitor AF and improve my datalogging capabilities to include RPM and boost when I add a piggy back.

Thom

What turbo are you running?

When not running the piggyback I must add 10% fuel with the FQS to have acceptable AFR figures, otherwise the engine runs dangerously lean - with FQS on position 0 AFR on idle is about 18.
My engine still runs lean with +5% fuel.

With the piggyback I can run the FQS on position 0 but I must add with the PB the fuel substracted when switching the FQS from position 3 to position 0.

I am not running a Vitesse turbo.

fast951

There are many things that cause the engine to run lean. With 100s of MAF running fine, I would start looking at other things. Interesting in both applications, you supplied your own injectors and still using the factory pump.

choinga

I have a Vitesse MAF with a Bosch 3BAR, stock fuel pump (a new one - not the original) and 83# injectors that came with the MAF. My brand new autometer gauge on the fuel rail shows me 40PSI at idle and 44PSI with the vacuum line detached from the FPR. My FQS is at the 0 position (no fuel or timing adjustments) and my car is where it needs to be on the AFR with no adjustments to the piggyback. That said, I have made a few minor tweaks at lower RPM's / non-boost where I noticed the car was running a bit rich, but the car idles and cruises fine at 14.7 and at WOT is at 11.8. One of these days when I get some time I'm going to reserve some time at a dyno here in town and get this thing where it needs to be...but for now, it's fine.

Keep in mind that with a MAF any electrical/grounding issues that you have will be amplified. The MAF is super sensitive so any voltage fluctuations or ground problems can cause these issues as well. I added a supplemental ground, replaced my battery negative cable to the bellhousing, cleaned every ground on the car and then had more predictable results with the MAF.

For what it's worth - John's support is

fast951

Thom, I think your statement above is misleading. Based on emails and logs you sent, your AFR varies greatly.

Originally you used the Stealth setup with a 3L and a large turbo, which I do not recommend. Stealth is for K26 size turbo and not designed for a huge turbo as the air box opening is restrictive.

At one point you had lean AFRs, then perfect AFRs using FQS #0, then without changing the software or the MAF, the AFRs changed. This tells me there is something causing the different AFRs. The software does not change, the MAF does not change (it cannot read rich, then lean, then rich, the lean. It works or doesn't). Now if the MAF installation is creating turbulence before or after the MAF then all sort of things can happen. This is why we recommend using the J-pipe and filter which we supply.

Thom

Hi John,

Yes, the AFR changed with no modifications whatsoever to the car. I noticed this as the weather got suddenyl colder and corrected it with the PB - that's what it's made for, isn't it?

For two weeks I've been running a cone filter and a MAF pipe (from SFR, as I had cut the one you supplied to make a J-boot to work with the airbox), but the engine still runs lean with the "out of the box" fuel map (no PB + FQS#0).
As far as I can tell the fuel map doesn't need much adjusting when using your turbos, but it might not be quite perfect with all other turbos.

fast951

Thom,

As I said, something is changing on your car. Why would the AFR is fine with FQS #0, then it is not? Something is changing, it is either the installation or something else.

The PB is for fine tuning, this is correct. However out of the box it will not run lean. As I mentioned earlier, it's best to figure out the "real" cause, anything else will cover up a problem.
Adding 10% via FQS or making huge adjustments in the PB may be a band-aid to a problem. (note: when using performance cams, some adjustment will be needed, but that's not the issue here).

The fuel pump does not care what turbo you have, however the condition of the pump is important. The pump must be able to support the HP, it makes no difference which turbo it is.

Injectors play a huge role as well. I have seen it when the same brand injectors do not perform as good as others. This is why we supply our own (which neither of you is using).

TPS, Engine Temp sensor,..... Many things could affect the AFRs.

When everything on the car is functioning properly, the MAF works as it's intended. When the customer starts mixing and matching parts and making modifications, then you will see unexpected results. There is a reason why we build the J-pipe the way we do, there is a reason why we use the cone filter we supply, there is a reason we supply our own injectors which we get from one reliable source.