Jack Straw

Howdy,

New to Miata's, not to forced induction.

Just picked up a 1992, 1.6 obviously, with a TD04-15. Runs, and drives, albeit with a litany of niggling issues.

Mods that I know of:

TD04 turbo
cast manifold of some sort (w/ relief cuts)
upgraded fuel pump (indicated by independent wiring/30 amp relay wired inline)
RX7 550cc injectors
RX7 AFM
Bosch 710 diverter valve
Stock FPR (apparently)
oil cooler (GM type, coolant operated)
Stock ECU

So, the main problem I'm having at this point relates to fueling. I'm in the process of acquiring and installing an AEM wideband, in a secondary bung, so I can actually see real AFR data. For now, it's running a shitty little autometer gauge off of the narrowband output. Not enough data to extrapolate numbers, but enough to know that I'm running quite rich up top (4,500RPM+, 10lbs boost). Runs rich enough to choke on itself half the time. No indication of leaning out nor knocking, in fact, quite the opposite. I enjoy the level of safety, but washing down the walls is not good, either.

Additionally, I'm blowing oil out the back of the valve cover, not enough to affect level, but enough to drip on the downpipe and make a bit of smoke when driven hard and stopped. There's a PCV in the stock location, running to the intake mani, and a PCV inline between the driver's side of the valve cover and the pre-AFM part of the intake. At idle, it varies between 14-18inhg vacuum, while it's around 22inhg when coasting with the throttle closed. I'm thinking this may be a PCV problem, and considering running a catch can to ameliorate it.

Anyone have any ideas on the fueling? My next step was to install a wideband and start soldering resistors into the AFM. I'm at a loss. If I end up having to go megasquirt, I'll do so, but if I can put that 800 dollars to use elsewhere, I'd rather do that. I just don't know enough about the fueling on these cars to know if the pump and injector upgrades are adequate in the absence of an adjustable FPR.

Halp

Braineack

iTrader: (62)

you've probably washed the cylinders down so much with gasoline that oil can now freely make way past rings...

if you're running a stock ECU then you need stock injectors and AFM.


there is no level of safety with your setup.

Jack Straw

Well, one thing I do know from the records, is that this build has been on the vehicle for at least 40k miles. I haven't compression tested it, but it starts a lot cleaner than it would if the rings/walls were shot.

So, assuming that the rings aren't completely done for, next step has to be a piggyback, or full MS, correct?

Asulen

iTrader: (1)

Only two oil seals on back of valve cover I'm aware of are the valve cover itself and the CAS seal. EDIT: I meant to add that I'm uncertain if fixing the PCV issue will fix that, or if the seal is just bad from adjusting timing.

I believe most will agree that the megasquirt would be a high priority; I'm just not certain if they would put it, or the 1.8 swap first in line. If the engine is roached, that will clear up the priority list in a real hurry.

The stock ECU has no provision for running injectors that size- that is your problem.

Jack Straw

I figured that I could fool the stock ECU by tuning the AFM outputs and dropping the pressure a bit on the rail. I don't need it perfect, I just need it to not choke on itself under full load. Not to mention, the wastegate preload is all fucked, intermittently boosts between 12-15 depending on load/throttle.

I guess I gotta compression test it and see where the bottom end is at. I have 2 other vehicles, so if it comes to the point of needing a new engine, I'll probably just throw it on a back burner for a year or two until I have the funds to do it properly. If the compression is a bit low, but within spec, I'd probably just leave it be. It doesn't need to be mint, again, it's sort of a fun toy car, but if the cylinders are over 25psi out of line with one another, I guess I know what I gotta do.

Braineack

iTrader: (62)

problem: The ECU goes into open loop at ~5.5K + you have double the stock injector size + you're increasing fuel pressure.

Solution:
remove the fuel pump.
remove the FMU (im assuming this kit has the Blue Vortech FMU?).
remove the AFM.
remove the stock.
install an aftermarket ecu that can actually control the injectors AND spark timing.


in the least you need to swap out the 12:1 ratio FMU diaphragm for something around 4:1.

Jack Straw

That's the strange thing: under the hood, there doesn't appear to be any sort of FMU, in fact, it appears to be the stock system. I'm probably gonna pull it all apart, there's a hairline crack in the exhaust mani which I need to braze. Would that FMU with that disc be at least a temporary fix?

BrownMiata

Pics Pics Pics! They always help!

Braineack

iTrader: (62)

The GReddy kit was shipped with a Vortech FMU with a 12:1 ratio disc -- it was good for getting the fuel pressure up to +100psi with boost so the stock injectors could adequately fuel 5-6psi. Since you have double the injector, you don't need much extra fuel pressure, if any at all, to provide enough fuel when in boost. 550cc injectors can fuel over 250rwhp on a stock fuel system.

I'm curious what your AFRs at idle are even at. The stock ecu, even in closed loop with a larger tinkered with AFM, still can't really trim the PW enough (batch injection makes it that much harder). Then when you hit open-loop at 5K, and the fuel map dumps in a **** ton of fuel I'm surprising youre not getting spark blowout and bogging.

this is what AFRs look like when the stock ecu idles 550cc injectors:

https://www.youtube.com/watch?v=yuyQLsmEHqQ

Jack Straw

That's exactly what I'm trying to say re: choking, it's experiencing bogging and spark blowout at 5,000+.

Here are a few pictures, no FMU to be seen. I took a couple videos of the idle, haven't uploaded them yet, but it is kinda lopey, sort of like a cam, but moreso due to the stock ECU trying to keep it stoich and bouncing around miserably. It's a reliable idle though, I have it set right around 950-1000, so it doesn't stutter when loaded at idle.

Jack Straw

Purchased the aluminum Moroso separator from Moss, and a 323GTX PCV valve from Treasure Coast. Hopefully helps some of the oil burning. I wasn't gonna replace the valve cover gasket until I solve the crankcase pressure issue, of course.

Question re: the routing. There's the PCV valve in the stock location, between the intake mani and the PS of valve cover. And there's one between the DS of valve cover and the pre-turbo, post AFM side of the intake. I figured I could cap the intake mani, run the separator off of the PS and DS of the valve cover, with a T fitting between them and the separator, and run the outlet for the separator with the second PCV up to the pre-turbo intake pipe. Sound about right?

EDIT: I see how Moroso outlines it, installing it on the PS firewall routed between the intake mani and PS VC. In theory, this shouldn't be a problem with a PCV valve which stays closed under boost. But, I'd rather not have the intake mani involved at all; I can pull permanent vacuum from the pre-turbo intake pipe. Idk, help y'all.

Braineack

iTrader: (62)

If it were me, I'd put stock injectors back in with a vortech FMU, or get spark/fuel management.

ryansmoneypit

iTrader: (6)

Previous owner must have been a Buddhist Monk. No regular everyday dude could have the patients to drive a Miata that sputtered at 5k, for 40,000 miles.

Jack Straw

I'm not gonna change the injectors or any other fuel system component until I've A.) Welded the hairline crack in manifold and B.) Installed a wideband. The RX7 AFM has clearly been tinkered with in a big way, based on the fact that it even idles these injectors. I'm also gonna pull the fuel pump and figure out what the flow is so I can start doing math. Could I get away with Supra 305's and the FMU? I'm not trying to go standalone yet, saving for a 1.8 swap.

I guess I wasn't clear enough, this behavior is intermittent. The car ranges from full on bucking under boost, to a soft middle ground where it pulls through the gears, but without true gusto, to the occasional *****-to-the-wall freight train pulls which show me the potential. When it's running correctly, that rare moment, 205 rubber isn't enough. It's legit a 40 or 50whp difference between the worst pulls and the best pulls. I'm just trying to squeeze some repeatability/reliability out of it; if I have to go back to stock or nearly-stock injectors, I can do that, but I'd rather fix all of the niggling little issues re: PCV system/intake plumbing etc. so I actually have a real baseline to tune.

The possibility of building a MS or even rewiring/changing resistors in the stock AFM as a temporary measure isn't entirely off the table.

asianalpha

if you are building an ms.. then just get rid of the afm all together and run MAP and retune for the 550 injectors. the pump and 550 is overkill for the stock ecu to handle.. i believe the 1.6 ecu could only handle up to 305cc.
direct replacement from a supra 89-92 non turbo 7mge with light green top injector number 23250-70080

Braineack

iTrader: (62)

it can only "handle" them in the fact that the motor doesn't get completely flooded...

Jack Straw

So, guys, I did some normal wear items, specifically plugs and wires (NGK blues to Bosch BKR7E iridiums) and replaced a few couplers with stuff from my friend's aircraft shop, and, lo and behold, it runs like a champ.

I have no idea what kind of black magic is occurring under this hood, but it idles fine, still fluctuates a bit, probably a shot injector O-ring, as I ruled out any other vac leaks, and the boost is controlled in quite the ghetto fashion, with a helper spring from the wastegate bracket. It's showing 11-12psi now, pulls hard, gonna leave it be for a while until I can shell out for a proper MS build.

From all of my other reading, you're all right, it shouldn't even be able to idle these injectors on a stock ECU. There's no aftermarket control of which I'm aware. So, idk, what's going on, but it's working, screw it.

Thanks for the help, y'all.

Braineack

iTrader: (62)

what are your AFRs?

No one is questioning the fact that you're actually idling and driving on them, the problem is, the ECU can't adequately reduce the PW small enough for an injector more than double the stock size.

if you really want your miata to pull hard, you'd actually set it up so it didn't run like absolutely trash, fuel wash the clyinder wall, and make no more than 8mpg. I bet you're only making 150rwhp...

Jack Straw

Man, I get it, you've got plenty of noob retards coming on here asking the same questions every day, and you, as the resident guru, have to deal with it.

This isn't my first rodeo, so I know there is truth to what you're saying.

But, I don't have the same income as I did when I built my last two vehicles, and also have two other vehicles to maintain, 36k college tuition, full time job, etc etc etc.

That said, assuming I got a wideband and welded a separate bung in a more friendly location, so I had a baseline way to estimate tweaks, what would be YOUR, the guru's suggestion, regarding the most cost effective, dollars-per-horsepower solution to this **** show of a vehicle? Would the FPR/FMU and 305's be the ticket? I believe it has a 190 in the back, definitely not stock pump - 30A relay inline from battery.

Thanks.