On "Microsquirting" the Porsche 914 - Part 9, Tuning

Tuning

Back to Part 8 

Wow. You've made it this far...? Good for you, you're no "TL;DR"! Or did you cheat and skip ahead...?

Tuning. Another "oof, I have no idea what I'm doing." Gotta figure it out though.

I began with a baseline tune from Mario at The Dub Shop (if you're gonna do this, buy from Mario)  and that's what I used to fire up the car. But Mario has not done a setup like mine; Mario has his individual throttle body setup for Type 4 engines. That's overkill for a dead stock engine like mine (and outside of my target budget). So I needed to improvise. But he knows these engines so I requested a base tune.

I adjusted Mario's tune for a few things like injectors and fuel pressure. The stock FPR would only do 36psi; the injectors I used were rated at 3 bar (43.5psi). So I used the TunerStudio program and an online calculator to adjust the injector size and edited that into the tune. I reviewed all the other settings and for the most part they looked OK (not that I really knew what I was looking at...)

You saw the start in the last part. I was quite surprised and happy. But after start, the car kinda/sorta idled but I could tell the AFR was all over the place. I could drive it up and down the driveway but driveability was very poor. I guess that should be expected since we really didn't know where this combo needed to be in the fuel table. I tried to take it around the block but it was horrible: running like crap at partial throttle, bucking, stumbling, really undriveable. AFRs bouncing all over the map. I nursed it home and took the whole map down a few notches and that seemed to improve things but it was still not good. Going further down didn't improve it. I let it sit in my driveway and warm up and I played around with the cells where it was trying to idle, messing with timing and fuel to get it to idle nicely (it helps that this engine starts to RPM surge a bit when it gets too lean; just fatten it a tad and it's happy; 13.8 AFR or fatter cold is about right). It was starting and idling OK. 

But when I took it out on the road again, it still drove like crap during throttle transition and mid-range. I flipped on auto-tune to get a rough idea where it needed to be, and while I could get it to run at idle and at full throttle, anything in between was terrible. The brother-in-law and I tried a few radical changes in timing map, AFR targets, nothing worked; bro almost lost his lunch from the bucking!

The Dub Shop Fuel FPR

I started reviewing the logs (excellent bedtime reading) and noticed that the TPS map was inconsistent. Fuel enrichment was scattered. I'd also noticed that I had to set and reset the TPS range a few times as it didn't seem to come back to exactly the same ones. I logged just the TPS trace without the car running and even at the stops of idle and full throttle it was wavering a few percent. I began thinking that maybe I had a bad TPS that was causing accel enrighment to kick in even with steady throttle. So, on a hunch, I changed my accel enrichment from 100% TPS-based to 100% MAP-based and took the car around the block...and the car smoothed out and ran like a champ! AFR targets started coming in and the fuel map started to get smooth and consistent.

So was the problem was bum TPS/accel enrichment? I began questioning the value of having a TPS at all! Or, I'm wondering if the cheapie eBay $15 TPS was at fault.

I had already planned to buy a new Bosch 3-bar FPR from Mario, so I decided to add in a new Bosch TPS to the order ($54, ack). Parts came in soon enough (thanks again, Mario!) and were a quick install. I doubled-checked I had a consistent 3-Bar fuel pressure (I did) and I reset the TPS range in TunerStudio MS Ultra (check) and did some neighborhood auto-tuning runs.

It ran about the same as it did with the old TPS. Initial auto-tuning showed big changes in the fuel map; not surprising, given we had a baseline map that could not have been expected to be accurate. But the poor driveability was gone so I could see that things were progressing. Having smoothed out the map, both automatically and manually, I adjusted my targets for AFR and ignition timing to be a bit more aggressive. Car was running better. Things were looking up!

Oil, oil, everywhere...

But there was serious unrelated problem: I had one HELL of an oil leak. I mean, enough oil that the exhaust on the left side was getting covered and burning it. Right side was bone dry. Sounds like a valve cover, right? I replaced the VC gasket and the problem was exactly the same. I had enough of an oil leak to where I'd stop, look under the car, and could see the oil drip-drip-dripping down. I was unamused.

I commiserated with Chris Foley via text (over a beer; we like beer) trying to brainstorm what this could be. I put the car on the lift and could see oil everywhere on the left side, seemingly more toward the front. Right side dry. But I had replaced all the seals up front, the VC gasket looked good, the pushrod tubes seals were new and looked good, and what could there be over there causing that oil? Where else can oil come from?

It wasn't doing this before I pulled the engine so I started thinking about changes I had made. New crankshaft seals, I'm sure they're good; new Tangerine stainless pushrod tubes and seals, those look fine. I replaced the oil cooler with a Tangerine remote oil cooler block but that was over on the right side, so that's not causing a leak on the left side. And since I was doing the remote oil cooler I removed the factory flapper and thermostat bellows system...hey, wait a sec...

"The Hole"

Greg: "Hey Chris, is the hole where the thermostat bellows mounts a blind hole...?"

Chris: "No. The bellows mounts to two studs but the pulley screw hole goes through."

Greg: s**t.

See that little threaded hole in that photo, way up there? That's the mounting stud hole for the pulley for the small cable that ran to the air-control flappers. And Yours Truly had removed that pulley, along with its mounting bolt and the thermostat bellows, not realizing that that little hole opened all the way into the oily parts of the engine innards (why, VW?? I dunno). I'd been dumping a lot of oil out of that hole, and it made a freakin' mess. Leak fixed with a bolt and a copper sealing washer. Amazing how much oil comes out of that little hole...

At this point I had a lot more confidence in the car and took several opportunities to setup and use the auto-tune to build a solid fuel map. I even got brave and took it to work a couple times! The setup was still at 100% MAP-based accel enrichment* (update below) and I'm pleased with how it's driving so I'm not clear how much TPS could improve it. However, I'm working with Peter Forance of PF Tuning and he's going to take my current tune and work some of his magic with it. From there I'll work on warm-up enrichment (the engine really likes to be fat when cold, but tolerates leaning out when hot) and then play around with AFR targets and decide how aggressive I want to get on ignition timing. Maybe I'll even build a separate map for 87 octane versus 93 octane (though, as little as I drive it through the year, I won't save much $$ with 87...but hey, tuning is free!) That's probably something I want to work on via some dyno tuning; John Malapetsis of Performance & Styling has a DynaPack, my preferred dyno. I've worked with him in the past on race car tuning. I probably should also get a CHT gauge...

*3/22/20 Update. Peter Florance sent me an updated tune that adjusted quite a few things, including the TPS/MAP enrichment. Car is improved, still no more bucking/stumbling and a bit snappier on the throttle tip-in.

One other design note: the factory tach does not work with the Microsquirt. There's an easy enough fix: Pelican Parts sells Ashlock Tech's "Tach-Adapt" tachometer adapter. It took 20 minutes to install with basic wiring hand tools and I mounted it behind the factory tach. If you want to get fancy, there are forum threads out there on modifying the gizzards of your Porsche tachometer to install modern electronics while keeping it looking stock, but for $70 the Tach-Adapt was my easy button. Yeah, the stock tach is still lazy (it's just sweeping past 5600 when I hit the 6000RPM redline) but mine's a street car, it'll work great for me.

Or, if you'd like a modern tach that will pretty much slide in, SpeedHut makes a 4-1/2" tachometer that looks really close to factory and can be easily installed. I bought one of those for the race car; I'll post some photos when I install it later this year.

Warm-up enrichment (WUE) is pretty good. Our ambient temps are now 30s to 40s at night so I can't tune warm-up for below that, but I rarely if ever drive the car when the ambient are much below 40F. I'm still trying to find a good balance for WUE that allows the car to idle on its own within 30 seconds - remember, no idle control valve - and idle nice when it's hot. We're picking at the edge now.

Update: please read the addendums...I discovered how to use ignition advance to core the idle. It works really well...

So, that's pretty much where I am at the moment. It's running (yay!) and dependable (yay!). I'll also try some tuning changes to see what happens and to learn more. I suspect my hardest part will be getting into the 914 and not feeling compelled to connect the laptop to do that last nth tuning...

Someone online asked me how it drove. I replied,

Hard to say since I've not fully tuned it, but it drives a lot like...a solid perfectly-working D-Jet system. It shouldn't be surprising, given that the D-Jet system was pretty good, especially in context, despite being from 50 years ago.

Startup is smoother and easier, no throttle needed. I removed the aux air regulator and did not install an idle air control valve, so I have to tickle the throttle for about 30 seconds before it will idle, but I think I can tune this with ignition timing and warm-up enrichment. No external idle control needed.

Tip-in with the engine cold is very good, no stumbling at all like I used to get with a cold D-Jet engine. Throttle response, even dead cold out of my driveway, is improved.

The one thing I really noticed is improved driveability, both in neighborhood streets and on the highway. The car seems to be running much, much smoother.

My confidence level with the engine management is significantly improved; no more occasional stumbles, wondering if it'll catch (the D-Jet left me on the side of the road one time last year, wire problem).

This modern system has some advantages:

• Easily-obtainable, lower-cost replacement parts. For the vast majority of the design, I can replace anything from a FLAPS;

• Electronic ignition. No more disty and its associated mechanicals (vacuum and centrifugal);

• Related to the above: built-in rev-limiter;

• Tunable. If I make any changes to the engine (cams, compression, displaement, etc) I can whup out the laptop and change things to accommodate;

• Economy/power compromises. I can move it toward economy at the low load/throttle settings, while moving it toward performance on the higher-end. Or create a different setting for 87 or 93 octane.

So, is installing Microsquirt "better" than the D-Jet for a dead-stock engine? Sure. The vast majority of the D-Jet system is available and the 914 community still supports it (and, frankly, prefers it to carbs for a stock engine). But all it takes is one D-Jet MPS rebuild ($450), one 1-2-3 distributor replacement ($500), and one new wiring harness ($500) later and you're at the cost of this Microsquirt system. But for a modified engine? It's absolutely better than D-Jet. And for a highly-modified engine, Mario's ITB Microsquirt setup is the way to go.

Would I do it again? Yep. I'm very pleased with it, I enjoy the tinkering, and I learned a lot. And I trust my car a lot more.

I'll post more tuning details here as I learn.

10/18/22 Update. New to tuning? DIY Autotune - SUPER guys - are offering a free guide, The EFI Tuners Guide – Learn How EFI works! Highly recommended.

On to Part 10: The Design Details

TDC - Top Dead Center, the firing position for #1 cylinder
CPS - Crank Position Sensor, also known as CAS, Crank Angle Sensor
TPS - Throttle Position Sensor
MPS - Manifold Pressure Sensor
IAT - Intake air Temperature sensor
CLT - Coolant temp sensor
AFR - Air-Fuel Ratio
FLAPS - Friendly Local Auto Parts Store
FPR - Fuel Pressure Regulator