codrus

The downside is that it introduces one more critical failure point that can destroy the motor. If that vacuum line blows off or gets damaged by an impact under the car then it goes massively lean under boost.

Not pictured: the screws holding the hard line brackets to the FM frame rail braces that that had their Phillips heads ground flat and filled up with crud from having bottomed out the car on speed bumps and the like.

--Ian

patsmx5

iTrader: (16)

Well it's up to you. I have my regulator in the engine bay, just used a vacuum line about 2' long, and zip-tied it on both ends. Of course basically zero chance of that hose being damaged in the engine bay. But I zip tie every vac hose, and hose clamp everything that I can buy a clamp for.

If my regulator was in the rear I'd still hook the hose up though, the improvement in idle-stability to me is worth it. But I also need the fuel, these 1Kcc injectors are at the limit if I don't keep my fuel pressure up in boost. Could you just run the hose for a few days and see if it's "worth it"? If you can't tell a difference then don't run it. Or, you could run the hose through the cabin of the vehicle instead of outside. Or shield it. Or buy a fuel hose instead of vac hose, it's way tougher.

aidandj

iTrader: (5)

Or be a big baller and run an line.

codrus

The car idles fine on id1000s when it's tuned right, the problem isn't that the injectors are too big, it's that they're not consistent. If fixing the fuel pressure regulation fixes that, then it's good, there's no need to run manifold reference line. If it doesn't, then sure, I'll run it. It's a small risk, but if there's no reason to take it then it's easy to avoid.

FWIW, FM says they don't run the vacuum reference on most of the cars that they put this in, and it's fine.

--Ian

codrus

So the Seven is off to its new home in Utah:



I originally bought the car to autox it, but the club that I autoxed with fell apart six months later. It also turned out not to be as done as I thought it was, and I discovered that I really don't have the time for two project cars. So when I got email out of the blue from a guy who'd tried to buy it from the original builder, asking if I wanted to sell it, everything lined up.

--Ian

Jeffbucc

Where in Utah?

I have pretty dead reliable fuel regulation with my AFPR having a vacuum reference. You could always sleeve your vacuum line with plastic wire sleeving if you are worried about it rubbing/blowing off.

aidandj

iTrader: (5)

<p>Just listen to me and use AN line </p>

Jeffbucc

I find it odd that FM doesn't use a vacuum reference, as to me, it adds stability to your injection due to it responding to what your engine load is demonstrating.

Super simple to setup too. Clamp your vacuum line to get your static pressure dialed in, the release the clamp...done.

You can buy tiny vacuum hose clamps at vatozone for like $2 that will never loosen either...

EO2K

iTrader: (37)

Unless of course you are using the stock NB ECU and a voodoo controller. That might make issues.

Jeffbucc

I did not take that into account, I guess I assumed most were on Megasquirt with a build thread here...

aidandj

iTrader: (5)

<p>Ian is on MS, G is just being confusing </p>

codrus

I'd be surprised if anyone were trying to use an FM BFK with a Voodoo because the factory pump & regulator supply plenty of fuel for the stock injectors. Most people who'd buy it probably have a Hydra.

In theory, a manifold referenced FPR is going to be slightly less consistent than an atmo-referenced one, because rapid changes in MAP will need rapid changes in fuel pressure and there's a bit of mechanical lag. I have no idea if that's actually significant or not, though.

The Seven is going to somewhere in southern Utah, probably pretty close to where you live Jeff, but I forget the name of the town.

[edit]And yes, I have an MS3, had a Hydra before that, and a Link Piggyback before that. Never had a Voodoo.

--Ian

EO2K

iTrader: (37)

Aidan, I was answering the question about why they wouldn't just add the vac reference to the instructions. If you have a standalone you are probably at the level where you understand the benefits of said reference, but remember that all of FMs customers are not exactly at "our" level of understanding.

18psi

iTrader: (76)

Never underestimate n00bs and their foolish ways

codrus

Spent some more time messing with the fuel system today. First, I got another straight -6 AN adapter from FM, put that in in place of the 90 degree, and the feed line to the AEM is much happier:



Then I did a long-term install of the fuel pressure sensor. -6AN hose for remote mounting:



The 90 degree end goes on the tee coming off the fuel supply:



Straight end goes to the sender:



I also ran a manifold reference to the AFR, and set the base pressure to 45 psi. It started up, we took it out and retuned the VE table for the new pressure reference, things looked good, but noticed that the fuel pressure was a lot noisier than it had been before. After dinner we grabbed TK's oscilloscope and looked at the variance in the fuel pressure (yellow) vs the MAP sensor (blue):



This is at idle, the MAP sensor is cycling by 20 mV at 40 ms intervals. 20 mV is about 1.2 kpa (it's a GM 3 bar MAP sensor), and 40 ms is 1500 RPM. The engine was running about 750 RPM, so that's the intake valves opening.

The fuel, OTOH, is varying by 300 mV (8 psi) at the same frequency, which is huge! We noticed something else interesting -- clamping the pressure reference not only made the fuel pressure go up, but it made the noise go away completely. (note: fuel pressure doesn't appear to rise in this video because the scope is auto-ranging it)



We then tried using a needle valve to bring the pressure in the reference line from atmospheric down to manifold reference relatively slowly, and got this (yellow is fuel pressure, blue is MAP, again):



What appears to be happening is that there's a critical pressure below which the regulator can't properly compensate for the spike in pressure when an injector closes. Poking around in the AEM instructions (what?!?! read the instructions?!?!?) reveals that the weirdo fittings in the FM kit that I couldn't identify are actually alternate-sizes discharge orifice fittings for the regulator, intended to compensate for larger fuel pumps. The AEM comes with three, the smallest (.100 nominal) is factory installed, and the two larger ones (.150 nominal, silver, which is more like .180 actual, and .200 nominal, gold-colored, which is more like .250 actual). It sounds like I need to pull the AEM out again and install one of the bigger orifices.



After deciding to take the regulator out another day, we ran over to the gas station for more 100 octane. On the way there it was running really rich, which made no sense because we hadn't actually changed any settings in all that testing with the oscilloscope. Whatever, we ran the autotune on the way there and it took a ton of fuel out. Filled it up, got back in, started it and went to drive home and now it was really really lean. Took the fuel back out and it ran OK again, but that makes no sense, WTF?

One interesting sight at the gas station:



Looks like someone unloaded the 87 fuel truck into the 91 tank and the station got in trouble for it. Fortunately, the 100 tank seems to be fine.

--Ian

aidandj

iTrader: (5)

Wow. That would be a shitty way to pop an engine. Think you put in 91 and get 87.

EO2K

iTrader: (37)

I seem to be fighting this as well, I feel like its a combination of things compensating for temp. I've found that a composite log helps a lot at showing what corrections are active at any given time. The MS seems to be SUPER aggressive with this stuff. Not that I need to tell you any of this like you don't know...

Anyway! I'd love to see what you come up with.

codrus

The behaviour before/after the gas station smells like a software bug to me. We'd driven it a bunch, the VE map was reasonably well-tuned, then sat in the garage for an hour, occasionally starting it up and running it for a minute or two while looking at scope traces. Then we drove to the gas station, and on the way there it was pig rich (reporting 10:1 AFRs or richer). No real drivability problems, this was just city/residential streets so I wasn't going fast, and by the time we got to the gas station (about a 10 minute drive to get 100 octane) it was making proper AFRs.

So I fill it up and leave 5 minutes later and now it's so lean it will barely run at all. I stalled it 4 times just trying to leave the parking lot, then twice more in the 200 yards to the traffic light. Turn on autotune and it starts putting back all the fuel that it had just taken out (like 30%).

It's not that the AFR was reading wrong on the way there, because the car drive fine just before shutting it down, then really badly after restarting. It's not fuel temperature changing the injector dead time, because the problems started immediately on restart, and it'll take at least a minute to use up the fuel in the rail and delivery line. So I dunno. Smells like a software bug.

--Ian

codrus

Screwed around with it some more this evening. Good news and bad news.

Bad news is that we swapped the large orifice into the AEM regulator, and it made no difference to the noisy fuel pressure below the ~ 38 psig level -- so much for that theory. Good news is that the it doesn't actually seem to affect the way the car runs that much. We went out and did some more fuel tuning, it seemed pretty happy all the way up to 240 kpa. At 270 kpa I thought I heard some pinging, but since we didn't have the hardtop on it wasn't really audible over the wind. We decided to turn it back down to 240 and worry about that another day.

The other good news is that we managed to reproduce the wacky drive-to-the-gas-station-and-its-rich failure that happened on Saturday. I commented at the time that it sorta seemed like a bad barometric correction reading, because it fixed itself on restart, but that it couldn't be because barometric correction wasn't enabled. Well, apparently it *is* enabled, we just didn't understand how to read the table. It seems that when it starts poorly, sometimes it winds up taking the barometric correction reading at the wrong time while the manifold still has vacuum in it, and winds up running rich. Fortunately, since I have a GM 3 bar external MAP sensor running the MS3 now, I can solve that problem by switching it to use the internal MAP sensor for barometric readings.

--Ian

codrus

Here's a data log of the fuel pressure/etc at 270 kpa:



The fuel pressure swings are over 10 psi! I think it needs better fuel pulse damping, it wasn't anywhere close to this bad when I was measuring it with the stock setup that includes the pulse damper on the fender. Unfortunately, putting that damper back into the system is likely to be a pain, because it has two push-lock connectors that point up which is very much not where the current AN lines want to go.

Poking around online I found this:

https://www.radiumauto.com/Fuel-Puls...Kits-P751.aspx


Anyone know anything about it?

--Ian