Carpokes Porsche Forum

grabbed an sd card, here's a link of a few I took (I think 1 and 2? forget, they all look pretty similar though). not surprised it's concentrated on the thrust face. doesn't look deep, lending credence to the "I just assembled it too dirty" theory.

I think my situation here just leads to "run it", 'cause if things are screwed I'll (once again) need to do the same amount of work to fix 'em now or later, so I might as well wait and see how stuff settles in. Failing that, sleeves are still available, right?

I would run it for sure. There's a good chance you get lots of miles and lots of power out of that motor. My old 2.5 motor had much worse scoring, and it made 350rwhp and burned no oil between changes. If you really need to start over, the motor will let you know.... Maybe check them again in a few hundred miles to see if it's getting significantly worse.

If you need to redo it, as an alternative to sleeves, consider having the bores coated in Nikasil from US Chrome.

Couldn't resist. Here's where we're at:
Badly needs a proper alignment, the front bumper, and a few other sundry (er, necessary) items done.

Some small updates:

Engine feels great, it's such a blast to have it back again. Probably pushing 200mi on the rebuild, which is basically nothing - but still! Even at 6 psi this is so much fun to come back to.

I think I figured out the source of the bore scratches. I had the intercooler plumbing off, and one of the hard pipes coated lightly with something gritty. The turbo -> intercooler coupler had a bit of (slightly sandy!?) crud. Presumably that had something to do with it, oh well.


I got VEMS working too (this is why I had the hard pipes off), which has been pretty fun. The car runs so much more smoothly (especially at/returning to idle, oh my god). I have a weird issue where it seems to cut fuel above 140 kpa, the only correlation I have is that's about the wastegate spring pressure at the moment, and I'm not running active boost control. Working with Peep on that.


I guess one of the final issues that might be topical is that my oil pan seems to seep a bit. I welded in a baffle, got annoyed with how the welds looked, and blended them more aggressively (which in hindsight is very pointless). Welding cast aluminum sucks! I'll probably deep clean the outside after draining the oil next change, and try whacking some sealant on there.

four0four wrote: Fri Oct 06, 2023 11:37 pm I have a weird issue where it seems to cut fuel above 140 kpa, the only correlation I have is that's about the wastegate spring pressure at the moment, and I'm not running active boost control. Working with Peep on that.

Sometimes the engine will misfire if it's too rich and it can feel like fuel cut. Try removing 5% fuel at the 140kpa point and see if it improves. You're only running 6 psi of boost, so there's little risk of engine damage at that power level.

That sounded plausible, but logging shows that it goes completely lean - I should've mentioned that it doesn't just feel like a fuel cut, it looks like one too! The event starts at the cursor in this picture:

Thanks for attaching the log graph. If it were actual fuel cut, the injector PW would drop to zero.
The odd thing about misfires is that it leaves unburned oxygen in the exhaust, so the O2 sensor reads a lean condition.
Another sign that it might be a rich misfire is that the AFR is trending downward (richer), then it spikes lean while the injector PW keeps increasing, and kpa is relatively level. Your target lambda looks good, it's not too rich, so there might be something else going on, such as a weak spark due to a weak coil, overly large plug gap, bad wires, worn cap/rotor. Or not enough dwell time in the settings.

Sorry if I missed it but are your running gasoline or E85?

How is your egt?
Do you have a boos cut setting?
Does your car rev higher on low load?

Dave W. wrote: Sat Oct 07, 2023 11:34 pm Thanks for attaching the log graph. If it were actual fuel cut, the injector PW would drop to zero.

Of course I figured out how to log different flags after putting the motronic back - later this weekend I'll get some more verbose logs.

The odd thing about misfires is that it leaves unburned oxygen in the exhaust, so the O2 sensor reads a lean condition.
Another sign that it might be a rich misfire is that the AFR is trending downward (richer), then it spikes lean while the injector PW keeps increasing, and kpa is relatively level.

Oh! I was wondering if that might be the case - I admit I'm pretty ignorant wrt how the wideband functions.

Your target lambda looks good, it's not too rich, so there might be something else going on, such as a weak spark due to a weak coil, overly large plug gap, bad wires, worn cap/rotor. Or not enough dwell time in the settings.

Sorry if I missed it but are your running gasoline or E85?

This is largely whatever the default 944 VEMS plug-and-play tune is. Also, shoot - I meant to drop the Bosch coil back in, there's an MSD coil in there at the moment. Based on Rogue's old blogpost it should only need less dwell, but it's worth trying the original.

Gaps I set just before starting the engine the first time, but the plugs are a little older. Cap and rotor are basically new (though the rotor uh, clearanced the cap for itself a bit). I'm inclined to disqualify those based on how well the Motronic runs.

How is your egt?
Do you have a boos cut setting?
Does your car rev higher on low load?

Dunno about egt - I have a sensor that should fit but I can't get it in there with the crossover mounted, so I put that off.....it'll happily rev higher under vacuum (or only slightly > 100kpa) MAP. Yes boost cut setting, but I did try moving that around to no change.



Plans is mostly wait for Peep to respond again, try the Bosch coil and/or swap in the wasted spark setup I have sitting around.

...I've got the scope up in the garage, I could grab some coil charge current waveforms. It should be obvious if it's not reaching saturation.


Edit: Both the original coil and additional (~double) dwell time didn't seem to help.

Well, this is potentially unsatisfying conclusion: I think I fixed it by ditching the coil/distributor and going with the wasted spark setup I had sitting around :')

I did re-adjust the sparkplug gaps to .7mm (they'd drifted to maybe .75/.8?), but I've no clue if that's what fixed it instead.

Too rainy to properly check under proper boost, but I think it's in the past now.

Also redesigned by AFM delete such that no printed plastic is in the airflow (not that I think it was a risk): The 3" tube bottoms out against the airbox opening, and is just held in place by this printed adapter. Found 12" of bead-rolled 3" tubing on Amazon and cut it in about half. TPU forms the gasket. One remaining concern is the bolts loosening over time (they go into brass heat inserts) - I'll fix that by adding maybe 5mm longer bolts drilled for safety wire.
I'm happy to leave this for now though - the next sendcutsend order will probably contain an aluminum version meant for the other half of that 3" pipe, plus a bracket to mount the coils and boost control solenoid where the cruise control was.


Edit: argh, spoke too soon. It was rainy and dark, I guess I didn't goose it enough to trigger the issue. Still present.


Edit the second: threw new NGK plugs (such a cargo cult!) in and a 3 bar FPR I had sitting around along with some new Bosch 0280155968 ("Green Giant"?) injectors:
I was lazy and didn't bother to try just the plugs or just the high-Z injectors, but VEMS runs awesome now. Low/no throttle manners are just ridiculously good: