Storch MAF Install Issue

[NCGermerican]

I can't believe I didn't come by this post sooner - I need to stop putting all my attention to the turbo forum.

By the way - did you guys see that Rennline has partnered with Storch and now sells them on their website, along with Pelican Parts? I think the price is slightly higher than the Storch site, but you don't have to pay any tariff's or duties:
https://www.rennline.com/porsche/944/pr ... ort=newest

I actually need to reach out to Julian - because of my LR j-boot putting rearward pressure on my Storch, it broke one of the small (3D Printed, I assume) retainer clips that hold the "tube" portion to the part that bolts to the factory airbox. They're only held in by one screw each and i wish it was held in by something a little more sturdy. I'm sure if I had the factory j-boot installed it wouldn't be an issue.

So much in this thread that is exactly what I was experiencing with the Storch MAF. Granted, I had so many other variables at play (low idle vacuum, John Behe chip, larger injectors, etc). I also have no faith in my AFR readings because of the documented exhaust leaks I documented on my YT channel.

However, with the Storch installed, the AFR gauge showed lean at idle until the o2 corrected in closed loop. Once I gave it some gas, it was 15.5 - 16 at around 2K RPM (stationary). Scary enough that I didn't even take it out to drive it.

That being said, I had a lot of trouble with the Vitesse MAF system a few years ago, despite John Vitesse doing everything he could to help. One thing he noticed on one of the logs.....LOW IDLE VACUUM! Initial hesitation was so bad (I pressed the throttle, nothing happened) that I almost got rear-ended at a stop light. At that point I went back to the AFM and sold the Vitesse kit.

I still plan to test out the Storch again after 944Fest (will be in a future video) but I'm not too convinced I'll have better results. First will be with the LR MAXX HP chip, then I'll try out the 3 John Behe chips with the 50lb injectors.

Welcome to the party!
Glad to hear someone else had a similar experience. When you say low vacuum, are we talking closer to true vacuum or closer to ambient pressure? I could always put a gauge on one of the manifold ports to check. I kept the MAF, for now, hoping to find a solution.
That hesitation off a stop almost had me roll into the car behind me on the test drive. Nope. Enough of that!
To the best of my knowledge everything is stock. I haven't opened the DME to take a look at the chip. Seems highly unlikely based on everything else on the car though. A wideband may be in my future, even if just installed temporarily for diagnostics.
Let me know when you get a chance yo test it out again. Wish I was headed to the fest!! If it's at VIR again next year, I'll be there.

I have an aftermarket boost/vacuum gauge on my a-pillar (along with an AFR gauge). I've had low idle vacuum (15 in HG) for years - even before I replaced the short block. I've repaired all the vacuum leaks I found and nothing changed - at all.

Yep - having that big of a hesitation when starting from a stop will definitely leave you a little puckered - especially when you're in traffic.

I'll definitely chime in once I try out the Storch again after 944Fest.

[johnb]

This is interesting. I've often wondered how these conversions handle acceleration enrichment. The stock system relies on the overshoot of the AFM, which is definitely different with a MAF. To some degree, the overshoot is caused by the extra air that has to fill the manifold (which should happen with both) but it seems that the mechanical vane of the AFM overshoots more than that:

This is a trace I captured when doing some testing with a MAF and the stock AFM, pulling air through both at the same time with a shop vac - blue is the MAF, red is the stock AFM:

Screenshot_2026-09-04_09-28-19.png (40.65 KiB) Viewed 141 times

In the stock chip there's some extra enrichment based on how quickly the output signal ramps up, but for US cars that it only during warm-up. On RoW cars, this extra enrichment remains at full temp. Also, from the trace above we can see that the MAF ramps up more slowly with sudden air increases, aside from the smaller overshoot. So even this extra software enrichment will probably be less than with the AFM.

My explanation of how this works is here[1] - the first half is pretty easy to read I think, before it gets into the technical details.

Anyway, this kind of thing is exactly what would push me towards a true MAF conversion (including new software) like Vitesse if I was looking for an upgrade. I don't think the transient behaviors of a MAF are ever going to match the AFM, and that is bound to affect driveability imo. The stock chip also does some transient fuel adjustments, for instance it slightly reduces fuel during tip in after a gear change, presumably because the AFM overshoot is too much.

One thing you might try if you're up for a little effort is switching over to the RoW maps. To do this you need to unplug the altitude switch and connect a 1.8k resistor across the plug in place of the switch. Then it would probably make sense to unplug the O2 sensor too. Then you should have more enrichment at tip in. If you still have the cat this might be risky though, I am not sure if it's good for the cat to run without the o2 sensor.

[1] https://jhnbyrn.github.io/951-KLR-PAGES ... rough.html

[PSU_Crash]

This is interesting. I've often wondered how these conversions handle acceleration enrichment. The stock system relies on the overshoot of the AFM, which is definitely different with a MAF. To some degree, the overshoot is caused by the extra air that has to fill the manifold (which should happen with both) but it seems that the mechanical vane of the AFM overshoots more than that:

This is a trace I captured when doing some testing with a MAF and the stock AFM, pulling air through both at the same time with a shop vac - blue is the MAF, red is the stock AFM:

Screenshot_2026-09-04_09-28-19.png

In the stock chip there's some extra enrichment based on how quickly the output signal ramps up, but for US cars that it only during warm-up. On RoW cars, this extra enrichment remains at full temp. Also, from the trace above we can see that the MAF ramps up more slowly with sudden air increases, aside from the smaller overshoot. So even this extra software enrichment will probably be less than with the AFM.

My explanation of how this works is here[1] - the first half is pretty easy to read I think, before it gets into the technical details.

Anyway, this kind of thing is exactly what would push me towards a true MAF conversion (including new software) like Vitesse if I was looking for an upgrade. I don't think the transient behaviors of a MAF are ever going to match the AFM, and that is bound to affect driveability imo. The stock chip also does some transient fuel adjustments, for instance it slightly reduces fuel during tip in after a gear change, presumably because the AFM overshoot is too much.

One thing you might try if you're up for a little effort is switching over to the RoW maps. To do this you need to unplug the altitude switch and connect a 1.8k resistor across the plug in place of the switch. Then it would probably make sense to unplug the O2 sensor too. Then you should have more enrichment at tip in. If you still have the cat this might be risky though, I am not sure if it's good for the cat to run without the o2 sensor.

[1] https://jhnbyrn.github.io/951-KLR-PAGES ... rough.html

That's great information, thanks!
I can definitely put a 1.8k in place of the altitude sensor. I unknowingly ran without the O2 even plugged in for a bit, so I'm not concerned about that. If the cat has an issue (assuming mine isn't hollow) I'll happily replace it with a straight pipe. By the way, replacing the O2 made no noticeable difference for me.

Let's say I do that and it runs as it should. Is there any danger in leaving the altitude switch like that? I often do mountain runs here where the elevation changes between 900' to 5400' quickly. It would just run a bit rich at altitude, right?

[johnb]

This is interesting. I've often wondered how these conversions handle acceleration enrichment. The stock system relies on the overshoot of the AFM, which is definitely different with a MAF. To some degree, the overshoot is caused by the extra air that has to fill the manifold (which should happen with both) but it seems that the mechanical vane of the AFM overshoots more than that:

This is a trace I captured when doing some testing with a MAF and the stock AFM, pulling air through both at the same time with a shop vac - blue is the MAF, red is the stock AFM:

Screenshot_2026-09-04_09-28-19.png

In the stock chip there's some extra enrichment based on how quickly the output signal ramps up, but for US cars that it only during warm-up. On RoW cars, this extra enrichment remains at full temp. Also, from the trace above we can see that the MAF ramps up more slowly with sudden air increases, aside from the smaller overshoot. So even this extra software enrichment will probably be less than with the AFM.

My explanation of how this works is here[1] - the first half is pretty easy to read I think, before it gets into the technical details.

Anyway, this kind of thing is exactly what would push me towards a true MAF conversion (including new software) like Vitesse if I was looking for an upgrade. I don't think the transient behaviors of a MAF are ever going to match the AFM, and that is bound to affect driveability imo. The stock chip also does some transient fuel adjustments, for instance it slightly reduces fuel during tip in after a gear change, presumably because the AFM overshoot is too much.

One thing you might try if you're up for a little effort is switching over to the RoW maps. To do this you need to unplug the altitude switch and connect a 1.8k resistor across the plug in place of the switch. Then it would probably make sense to unplug the O2 sensor too. Then you should have more enrichment at tip in. If you still have the cat this might be risky though, I am not sure if it's good for the cat to run without the o2 sensor.

[1] https://jhnbyrn.github.io/951-KLR-PAGES ... rough.html

That's great information, thanks!
I can definitely put a 1.8k in place of the altitude sensor. I unknowingly ran without the O2 even plugged in for a bit, so I'm not concerned about that. If the cat has an issue (assuming mine isn't hollow) I'll happily replace it with a straight pipe. By the way, replacing the O2 made no noticeable difference for me.

Let's say I do that and it runs as it should. Is there any danger in leaving the altitude switch like that? I often do mountain runs here where the elevation changes between 900' to 5400' quickly. It would just run a bit rich at altitude, right?

Other than the cat, I can't think of any other concerns. The WOT fuel and timing maps are the same.

The PT maps are different. The US PT fuel map is rich, and the o2 sensor control pulls it back. The RoW PT fuel map is leaner.

The RoW timing map does have a bit more advance at higher rpm/higher loads. I can't promise you that it's safe - and I don't want to give the impression that I'm an experienced tuner, which I'm not - but these are the maps used by RoW cars so I don't see why they wouldn't be safe.

What will happen to the AFR at altitude, that's a good question! With the MAF, it shouldn't affect the AFR. If you mean with the stock AFM, then I really don't know but I would love to find out if you get a chance to test it. The altitude switch only came with US 944s, which also all have the O2 sensor, which should be able to correct the AFR at that altitude anyway. So RoW cars had no way to compensate for altitude. Did they run rich at high altitudes? Hard to get good info on this.

(Not to derail the thread, but I'm on a quest to find out: what does the AFM really measure, volume, mass or some combination of the two? Everyone says they measure volume, but no one seems to have any evidence for that, and it's hard to imagine how that would work. How could it not be sensitive to air density? All I know so far is that everything I've seen in the DME code and the maps very clearly assumes that the AFM measures air mass. There's nothing in there that looks like a density compensation based on air temp. Everywhere the air temp is used, it looks like it's being used for temperature related stuff that has nothing to do with density. So yeah if you or anyone has chance to compare how the AFR is with the stock airflow meter at that altitude, with no o2 sensor interfering, that would be great info to have!)

[PSU_Crash]

Other than the cat, I can't think of any other concerns. The WOT fuel and timing maps are the same.

The PT maps are different. The US PT fuel map is rich, and the o2 sensor control pulls it back. The RoW PT fuel map is leaner.

The RoW timing map does have a bit more advance at higher rpm/higher loads. I can't promise you that it's safe - and I don't want to give the impression that I'm an experienced tuner, which I'm not - but these are the maps used by RoW cars so I don't see why they wouldn't be safe.

What will happen to the AFR at altitude, that's a good question! With the MAF, it shouldn't affect the AFR. If you mean with the stock AFM, then I really don't know but I would love to find out if you get a chance to test it. The altitude switch only came with US 944s, which also all have the O2 sensor, which should be able to correct the AFR at that altitude anyway. So RoW cars had no way to compensate for altitude. Did they run rich at high altitudes? Hard to get good info on this.

(Not to derail the thread, but I'm on a quest to find out: what does the AFM really measure, volume, mass or some combination of the two? Everyone says they measure volume, but no one seems to have any evidence for that, and it's hard to imagine how that would work. How could it not be sensitive to air density? All I know so far is that everything I've seen in the DME code and the maps very clearly assumes that the AFM measures air mass. There's nothing in there that looks like a density compensation based on air temp. Everywhere the air temp is used, it looks like it's being used for temperature related stuff that has nothing to do with density. So yeah if you or anyone has chance to compare how the AFR is with the stock airflow meter at that altitude, with no o2 sensor interfering, that would be great info to have!)

The barn door takes density into consideration just based on less dense air will move the door less, I would think. ?

"The WOT fuel and timing maps are the same" This tells me that adding a resistor and disconnecting the O2 probably won't completely resolve my issue. At WOT and revs ovr 4.5k it falls on it's face with the MAF.
I don't have a wideband installed or any datalogging capability. Although I'm definitely interested in at least being able to see AFR. One of these days I may get some time to upgrade that capability. Too many projects, too little time.
You mentioned the low vacuum and that's something I can measure quickly. Report to follow, tomorrow.

[johnb]

Other than the cat, I can't think of any other concerns. The WOT fuel and timing maps are the same.

The PT maps are different. The US PT fuel map is rich, and the o2 sensor control pulls it back. The RoW PT fuel map is leaner.

The RoW timing map does have a bit more advance at higher rpm/higher loads. I can't promise you that it's safe - and I don't want to give the impression that I'm an experienced tuner, which I'm not - but these are the maps used by RoW cars so I don't see why they wouldn't be safe.

What will happen to the AFR at altitude, that's a good question! With the MAF, it shouldn't affect the AFR. If you mean with the stock AFM, then I really don't know but I would love to find out if you get a chance to test it. The altitude switch only came with US 944s, which also all have the O2 sensor, which should be able to correct the AFR at that altitude anyway. So RoW cars had no way to compensate for altitude. Did they run rich at high altitudes? Hard to get good info on this.

(Not to derail the thread, but I'm on a quest to find out: what does the AFM really measure, volume, mass or some combination of the two? Everyone says they measure volume, but no one seems to have any evidence for that, and it's hard to imagine how that would work. How could it not be sensitive to air density? All I know so far is that everything I've seen in the DME code and the maps very clearly assumes that the AFM measures air mass. There's nothing in there that looks like a density compensation based on air temp. Everywhere the air temp is used, it looks like it's being used for temperature related stuff that has nothing to do with density. So yeah if you or anyone has chance to compare how the AFR is with the stock airflow meter at that altitude, with no o2 sensor interfering, that would be great info to have!)

The barn door takes density into consideration just based on less dense air will move the door less, I would think. ?

"The WOT fuel and timing maps are the same" This tells me that adding a resistor and disconnecting the O2 probably won't completely resolve my issue. At WOT and revs ovr 4.5k it falls on it's face with the MAF.
I don't have a wideband installed or any datalogging capability. Although I'm definitely interested in at least being able to see AFR. One of these days I may get some time to upgrade that capability. Too many projects, too little time.
You mentioned the low vacuum and that's something I can measure quickly. Report to follow, tomorrow.

Yes, that's what I think about the barn door, but then it would be measuring the mass correctly, and wouldn't run rich at altitude.

Sorry I missed that you have that higher rpm issue, I was thinking more of the hesitation thing. I agree changing maps isn't going to fix that.

[PSU_Crash]

Other than the cat, I can't think of any other concerns. The WOT fuel and timing maps are the same.

The PT maps are different. The US PT fuel map is rich, and the o2 sensor control pulls it back. The RoW PT fuel map is leaner.

The RoW timing map does have a bit more advance at higher rpm/higher loads. I can't promise you that it's safe - and I don't want to give the impression that I'm an experienced tuner, which I'm not - but these are the maps used by RoW cars so I don't see why they wouldn't be safe.

What will happen to the AFR at altitude, that's a good question! With the MAF, it shouldn't affect the AFR. If you mean with the stock AFM, then I really don't know but I would love to find out if you get a chance to test it. The altitude switch only came with US 944s, which also all have the O2 sensor, which should be able to correct the AFR at that altitude anyway. So RoW cars had no way to compensate for altitude. Did they run rich at high altitudes? Hard to get good info on this.

(Not to derail the thread, but I'm on a quest to find out: what does the AFM really measure, volume, mass or some combination of the two? Everyone says they measure volume, but no one seems to have any evidence for that, and it's hard to imagine how that would work. How could it not be sensitive to air density? All I know so far is that everything I've seen in the DME code and the maps very clearly assumes that the AFM measures air mass. There's nothing in there that looks like a density compensation based on air temp. Everywhere the air temp is used, it looks like it's being used for temperature related stuff that has nothing to do with density. So yeah if you or anyone has chance to compare how the AFR is with the stock airflow meter at that altitude, with no o2 sensor interfering, that would be great info to have!)

The barn door takes density into consideration just based on less dense air will move the door less, I would think. ?

"The WOT fuel and timing maps are the same" This tells me that adding a resistor and disconnecting the O2 probably won't completely resolve my issue. At WOT and revs ovr 4.5k it falls on it's face with the MAF.
I don't have a wideband installed or any datalogging capability. Although I'm definitely interested in at least being able to see AFR. One of these days I may get some time to upgrade that capability. Too many projects, too little time.
You mentioned the low vacuum and that's something I can measure quickly. Report to follow, tomorrow.

Yes, that's what I think about the barn door, but then it would be measuring the mass correctly, and wouldn't run rich at altitude.

Sorry I missed that you have that higher rpm issue, I was thinking more of the hesitation thing. I agree changing maps isn't going to fix that.

Ahh, yes. Hence altitude switch wouldn't be needed. We are on the same page.
Might be time to cut my losses and pass the unit on. If I want to improve response, fuel and timing, then I would go megasquirt. Also not a pro tuner, by any means, but I have built, installed and tuned a bunch of them for myself and others. I always lead with the disclosure. I'll make it run well. You need the dyno tune to make it run right.
For the time being I think I'll just enjoy it as is. She runs very well for 175k on the clock.

[cda951]

Ahh, yes. Hence altitude switch wouldn't be needed. We are on the same page.
Might be time to cut my losses and pass the unit on. If I want to improve response, fuel and timing, then I would go megasquirt. Also not a pro tuner, by any means, but I have built, installed and tuned a bunch of them for myself and others. I always lead with the disclosure. I'll make it run well. You need the dyno tune to make it run right.
For the time being I think I'll just enjoy it as is. She runs very well for 175k on the clock.

You must be into box flares . There is a shop a couple of blocks from my house that had 3 of the Starion/Conquest cars at one point, but now they are all gone. LS power sounds like fun.

I am greatly enjoying this AFM vs MAF discussion because I am a nerd, but a good aftermarket speed/density system allows much greater flexibility. I think a simple standalone system like the VEMS unit I have or maybe a Haltech Elite 750 or MegaSquirt, et al is a great idea for the 944 platform. Sure, there is a learning curve, but the nice thing about being a 1980s car is that things like factory cruise control, radiator fans, etc are completely independent from the DME and will thus work as-is with no additional setup. A/C idle-up input is easy.

I have only ever done road tuning on my 951 and got it running great, far better throttle response than stock, same MPG during light cruise and highway, super smooth idle, can even pass CA tailpipe emissions/smog test if need be, all with 850cc fuel injectors! A dyno session would be great, but that car is currently a parts storage bin .

[PSU_Crash]

Indeed! The box flares are how I ended up in the StarQuest world. I wanted a 944 back in the 90s and stumbled into a Conquest. Similar look. Great performance.

I'll hook up a vacuum gauge on mine tomorrow, because we all want to know at least that one variable

[NCGermerican]

Ahh, yes. Hence altitude switch wouldn't be needed. We are on the same page.
Might be time to cut my losses and pass the unit on. If I want to improve response, fuel and timing, then I would go megasquirt. Also not a pro tuner, by any means, but I have built, installed and tuned a bunch of them for myself and others. I always lead with the disclosure. I'll make it run well. You need the dyno tune to make it run right.
For the time being I think I'll just enjoy it as is. She runs very well for 175k on the clock.

You must be into box flares . There is a shop a couple of blocks from my house that had 3 of the Starion/Conquest cars at one point, but now they are all gone. LS power sounds like fun.

I am greatly enjoying this AFM vs MAF discussion because I am a nerd, but a good aftermarket speed/density system allows much greater flexibility. I think a simple standalone system like the VEMS unit I have or maybe a Haltech Elite 750 or MegaSquirt, et al is a great idea for the 944 platform. Sure, there is a learning curve, but the nice thing about being a 1980s car is that things like factory cruise control, radiator fans, etc are completely independent from the DME and will thus work as-is with no additional setup. A/C idle-up input is easy.

I have only ever done road tuning on my 951 and got it running great, far better throttle response than stock, same MPG during light cruise and highway, super smooth idle, can even pass CA tailpipe emissions/smog test if need be, all with 850cc fuel injectors! A dyno session would be great, but that car is currently a parts storage bin .

I’m also not ruling out going standalone in the future, but if I do it will be the MaxECU kit from Kroon- mainly because it’s supposed to be the most “out of the box” kit, which obviously includes the wiring harness. Correct me if I’m wrong, but speed density can basically compensate for any minuscule vacuum leaks.

The problem is….it’s $5k. Plus, to truly dial it in for peak performance requires a dyno and a tuner. There isn’t any (that I know of) tuners in the Raleigh area of NC that are experienced with MaxECU.