Kroon Harness for 944 Turbo

[NCGermerican]

Didn't Brent (Edredas) mention in a livestream he had an issue with a car that had a new wiring harness? I think he couldn't find anything actually wrong with the harness but since troubleshooting was going nowhere he had no choice but to go back to a stock harness.

As a matter of fact, he did and I actually know the owner of that 86 944 turbo. Turns out there was a short in the harness and Kroon sent a new one.

My issues are the following:

1) Low manifold vacuum
-cold start at 10 in HG
-when engine reaches operating temp, vacuum increases to about 15 in HG
-normal should be around 18-20 in HG
-This has been an issue for over 2 years and there was a stretch when the car ran just fine with those vacuum readings

2) Lean condition at all times
-I found the source of this issue and it was my fault/mistake. I go into more detail in my upcoming video to be posted in the next few days.

3) Lean condition during warm start, open loop only
-This issue started happening about 2 months AFTER I replaced the short block in August of 2025
-AFM readings of 18+ on warm start, but resolves when entering closed loop (o2 sensor corrects fuel mixture)

1. Starting at 10 cold and going to 15 warm is low, but not terribly so. Stock cam? As far as I know, I have the stock cam. I didn't even think to check it when I swapped out my cam housing for the powder coated one a few years ago.

Pretty hard to get 18+ at stock idle levels. What is your idle rpm? On my car, the vacuum goes down at lower idle rpm levels. I bumped my idle to 880 (see chip tuning guide) and the motor is just happier in every way and I now see vacuum of 18+ when fully warm. According to the ODB+ software, I'm right around 880 as well.

I'd start capping things off to see if something bumps the vacuum... Do you have a cat? Or collapsed downpipe? I have the "high flow" cat on my Fabspeed exhaust system - from the turbo to the exhaust tip. I had LR modify my crossover pipe with a junction on the driver's side Head, valves, and cam all in good shape? As far as I know. I had the head rebuilt about 2 years and less than 3k miles ago. Probably something simple but worth considering those other things that can prevent the creation of vacuum, and not just things that prevent the retention of vacuum.
That's my next plan. Just about the ONLY thing that hasn't been replaced on the car is the brake booster. Although, I'm not hearing any sucking noises or loosing brake assist. I REALLY hope it's not an issue with the ICV. I paid over $800 2 years ago for a NOS genuine Bosch one.

I'm still not ruling out my "rebuilt" AFM as the issue either. I would test it, but I have a Storch AFM that's on my workbench waiting to be installed. Might solve the warm start lean issue, but doubt it would have anything to do with the low vacuum. I need to look at my throttle body as well and ensure the stop screw is in the right position.

2. Sounds like I was right with my #6 option.
I remembered that when I found out what I did. Wait until you see the video. Hopefully it will help someone NOT make the same mistake. Just when you think you are extremely thorough.......you're not.

3. Did you test the DME temp sensor? Any other changes leading up to this, like new chips?
Just to be sure, I put in a brand new DME temp sensor when I did the Kroon harness and new AOS (and alternator/starter wiring harness.

I did notice that I have a small exhaust leak at the wastegate (Tial 38mm with billet adapters). No matter how many times I try to seal that up, I still get a leak. I'm seriously thinking about just going with a LR dual port WG so I can ensure everything bolts up like stock with minimal chance for a leak. (and use the factory WG brace on the torque tube)

[Tom]

I watched your vacuum video and am skeptical of the smoke test. Something wasn't working right there -- if no smoke comes out the disconnected FPR vacuum hose, who know what else is leaking and not smoking,... Did you ever run that machine without the hose connected to the car to see if it actually generated smoke? Either way, something's not right there.

On the intermittent lean, you might try disconnecting the O2 sensor at the back of the intake when it goes lean and see if it makes a difference. I'd also consider bypassing the KLR in case it has cracked colder joints, although I can honestly think of how the KLR could lean the motor out, but still...and trying your old DME just to rule the F9 out. I'd also log with the OBD+ and look for lean clues there. And check fuel pressure to see if it is dropping due to a bad FPR or pump.

Personally, if the AFM pot and temp sensor check out, I'd be very hesitant to install a MAF until you sort things out. That adds a whole new variable on top of an already unknown problem -- like playing billiards on a row boat.

[NCGermerican]

I watched your vacuum video and am skeptical of the smoke test. Something wasn't working right there -- if no smoke comes out the disconnected FPR vacuum hose, who know what else is leaking and not smoking,... Did you ever run that machine without the hose connected to the car to see if it actually generated smoke? Either way, something's not right there.
I should have shown it on the video, but smoke was coming out of the machine.....until I broke it and had to fix it. If needed, I'm going to run another test in the manifold itself as opposed to going through the j-boot.

On the intermittent lean, you might try disconnecting the O2 sensor at the back of the intake when it goes lean and see if it makes a difference. I had tried that in one of my previous videos and it stayed extremely lean with the o2 disconnected - upwards of 18.5 on the AFR. That was before I found the source of the "larger" vacuum leak that is shown on the video I just posted.

I'd also consider bypassing the KLR in case it has cracked colder joints, although I can honestly think of how the KLR could lean the motor out, but still...and trying your old DME just to rule the F9 out. I'd also log with the OBD+ and look for lean clues there. And check fuel pressure to see if it is dropping due to a bad FPR or pump.
I sent my KLR off to Specialized ECU Repair in Florida about 3 years ago. For my F9 DME, I had to send my original in as a core, so I don't have the original to test against the F9. I'll look at some of the readings on the ODB+ software during a warm start to see if anything stands out. I have the monthly PCA dinner tonight, so hoping to get back on it tomorrow night.

Personally, if the AFM pot and temp sensor check out, I'd be very hesitant to install a MAF until you sort things out. That adds a whole new variable on top of an already unknown problem -- like playing billiards on a row boat.
I agree. I'll do another smoke test as well as try to eliminate some of the ancillary items (brake booster, ICV, etc) and see how that turns out first.

[chrischrischris]

Sorry I can't help with the troubleshooting of your amazing build, but wanted to mention that there is a stud conversion option for the intake manifold that I had previously thought added no benefit. I like the normal stock allen head bolts. However, studs would have kept those gaskets in place.

[NCGermerican]

Sorry I can't help with the troubleshooting of your amazing build, but wanted to mention that there is a stud conversion option for the intake manifold that I had previously thought added no benefit. I like the normal stock allen head bolts. However, studs would have kept those gaskets in place.

I had no idea such a kit existed. I may look to do that the next time I have to take the IM off. You are correct, that would 100% remove

[chrischrischris]

944online has a kit.

[chrischrischris]

Regarding your vacuum reading: I don't have a vac gauge on my car but I do pay attention to the vac/boost gauge on the dash. Once the car fully warm the needle is pretty much exactly on the little "dot" on the left side of the gauge.

How far is your needle from the "dot" ?

I understand you may be hesitant to drive the car if it is running very lean, but would recommend driving a few miles and getting some additional gauge readings to compare to your prior measurements obtained after warming up the car in the garage.

[NCGermerican]

Regarding your vacuum reading: I don't have a vac gauge on my car but I do pay attention to the vac/boost gauge on the dash. Once the car fully warm the needle is pretty much exactly on the little "dot" on the left side of the gauge.

How far is your needle from the "dot" ?

I understand you may be hesitant to drive the car if it is running very lean, but would recommend driving a few miles and getting some additional gauge readings to compare to your prior measurements obtained after warming up the car in the garage.

Once I have a few more tests run, I plan to do this and log what I can on the F9 ODB+ software.

[chrischrischris]

After going for a drive today I realized that I misremembered the reading on my gauge: at warm idle the needle points to "0,4" and not at the little dot.

[NCGermerican]

I may have found the issue folks, but I'm not going to say it's 100% until I do a little more digging. And be sure to cut me some slack on my smoke testing. I could have done a better job of sealing off some of the lines, but it was getting late and I was getting tired. It's been days since I finished and my garage STILL STINKS.