mark944turbo

I'm using a vintage (VERY vintage) Vitesse MAF that I picked up second hand. The main reason for using this MAF instead of a new one is that it still uses the old style chips, so I can adjust them myself, which is nice. Here is a picture of the MAF as installed:



The biggest issue I'm having is a stumble when I'm cruising along and release the throttle. The ZT log below shows (in the 3 circles) that when I close the throttle, the MAF signal (User1 input) actually increases briefly before dropping. This MAF signal increase leads to a brief rich spot before the injectors turn off. You can see the rich spots right after the circles.


My first thought was that the BOV might be opening and dumping air back into the MAF pipe, but that's not it, I ran with no BOV and there was no change.

Questions:
1. To what extent is this normal? Anyone have any data to share?
2. Why is this happening?
3. What can I try changing to improve the situation? Unfortunately correcting a problem like this is beyond my chip modification abilities. I'd like to tell the DME to ignore the MAF signal if the TPS closes too quickly.
4. Is it possible that the stumble is caused by something else? I also plan to try switching back to stock ignition values, to see if there is any change.

Thanks for any help

User 52121

Assuming you've already checked for vacuum leaks and not found any... try rotating the MAF a little inside the clamps and see if it changes anything.

Crazy Eddie

I have the same MAF ( Mines brand new ) still haven't turned the key yet
What weird about that picture, is that it doesn't seem like you have a J Boot ?

fast951

The setup in the picture is not a VR setup. We never used the configuration you are showing. We always used the J-pipe.
The location of the MAF is not ideal..

Did you purchase the kit as pictured?

mark944turbo

Thanks for the idea on clocking the MAF- I can try that but I think I already have it about the only way it's going to fit without modifying other components.

I understand how the position of the MAF and the piping effects the MAF calibration, but not quite in this case. Why would the MAF signal drop slightly, then increase a lot, then decrease when the throttle is lifted? If I understood physically what was happening with the air I would have a much better shot at finding a fix.

John- I knew the piping was not original when I purchased the kit- I'm not sure who made the pipes, but I can't use a J-Boot becasue the turbo inlet is bigger. Unless I used the lindsey silicon version. Based on your experience, do you think that is worth a try?

User 52121

Air turbulence due to the closing throttle plate and/or the opening/closing of the bypass valve causing air to back up past the sensor? *shrug*

reno808

Glad you cleared up the setup is not yours. That being said why would the pipes make that much difference??

mark944turbo

Jim- I tried running with no BOV- no change. I don't think it's opening under these conditions anyway- I'm not coming off boost, just releasing the throttle when cruising along with minimal load.

The rest of the parts (chips, piggyback, MAF itself, etc) are original Vitesse as far as I know, but the pipes are someone else's. I believe that the pipes are causing the problem, just don't know why or how to fix it.

User 52121

Well... MAF sensors can be pretty sensitive to their orientation within the intake path. Sometimes altering the angle of the sensor, or the length of pipe before/after the sensor can change the calibration. If you're not using the original J-pipe that was intended for use with that specific MAF sensor and software, the flow could look different enough across the sensor to cause strange readings.

Of course, this doesn't guarantee the problem but it's definitely an unknown variable. Maybe you can get a picture of the original pipe that was used with this MAF and try to replicate it?

reno808

is that a oiled air filter?

mark944turbo

Yes, it is oiled (K and N).

I can see how having the turn in the original J boot might help isolate the MAF from turbulence around the turbo, so I'll probably try Lindsey's boot.

There are many people running pipe setups close to what I have though. How do they get away with it?

reno808

Spray down the maf with MAF cleaner. Sometimes the oil from the filter gets in the maf sesnor and plays with the signal.

mark944turbo

Tried that one already. That would be too easy!

fast951

Mark, the J-pipe that was used required a unique angle between MAF and pipe. The clocking on the MAF was critical, and the filter had to be oriented properly to the MAF. You want the MAF as far away from the turbo as you can.
The old sensors (7-8+ years ago) were very sensitive to air flow. No idea what you have, but we had to use a PB to get them working properly.

I never used the J-boot with the old setup, can't advise, sorry.

BTW. I noticed the water injection, how do you like it?

mark944turbo

Thanks. I'll report back with any progress I make.

Regarding the water injection- that's actually a pool filter with the insides removed that I'm using as a vacuum catch can. Much cheaper than the common options and it accomplishes the same purpose. It hasn't melted yet anyway.