I'm looking at a GSL-SE that's been ported and Megasquart (squirted, maybe?). It doesn't run well right now, and I'm curious if a RB-Streetported engine can be run on the stock ECU and harness, if only for troubleshooting. There are a few ways out of having to go Megasquirt, but I need y'all to keep me honest here.

Maybe there's enough duty cycle and flapper door left - If the flapper door doesn't open all the way on at stock -SE at WOT, then maybe a ported motor would suck it further open, increase the duty cycle to the injectors more, and it would just keep up okay.

Maybe higher-flow injectors - If I replace the stock -SE injectors with higher flow units (or turn the fuel pressure up) then perhaps the whole system is still scalable. At WOT and high RPM, I'm getting the fuel I need for the added porting, and at idle (where the aux ports aren't open), when the flow is closer to stock, I can turn the mixture down with the trim pot near the AFM, and all's well.

Maybe there's enough duty cycle left on the injectors, but the AFM doesn't register the extra flow - a common cheat in Spec Miata, so I've been told, is to use RX-7 AFMs to run the injectors a little fatter than stock, while still appearing exactly stock. Perhaps an S4 AFM on a ported SE motor would have a different resistance across its sweep and would actually call for more fuel from the ECU.


If none of these things are the case, then I'd have to use the Megasquirt in order to get the car running, which changes things a bit, as the car's no longer an assumed easy fix. What do y'all think? Does anyone run a ported -SE on the stock ECU, AFM and injectors? If so, do you have an Air/Fuel meter to show whether or not your injectors are keeping up?

Educate me please, so I can make a decision here. By the way, feel free to get into theory of operation and open / closed-loop thresholds. No reason not to learn beyond the simple Yes / No.

Thanks guys,
-Crit

 

I've run a streeet ported GSLSE engine with a s4 intake, factory S3 ECU and 2 SE stock injectors. I had no problem. S4 afm uses totally different resistance values not compatible with S3 ECU. I've never heard of anyone successfully swapping AFMs without an aftermarket ECU of some type.

 

Did you ever check your mixture to see that the stock injectors were keeping up? It's encouraging to see that they kept up with an S4 intake. Was the S3 motor ported?

 

Crit,

You'll probably be okay with the SE ECU. When I got my SE injectors cleaned, they were flowing 760cc/min at 2.5 bar. At this flow rate, they should be good for 102.5 - 123 HP each (depending on BSFC) with an 85% duty cycle.

So if you are pushing say 210ish HP or more, then you might have to start to worry about getting more fuel.

But, you are going to only use this amount of fuel at WOT and higher RPM. So even if the engine can produce more than say 210 HP or so, you still will not have problems as long as you don't use all of that power.

With the stock intake and AFM, you probably won't be able to flow enough to max out the injectors. If you find that the power level is boaderline to what the SE injectors can support, then raising the fuel pressure could buy you some margin.

 

on a stock -SE the flapper is open at about 5000 rpms. the good news is that the flapper is pretty adjustable, you can get it to open a little more, and thus get a tad more fuel.

the stock -SE injectors are ok, i had 4 cleaned, and they cleaned up to 700cc each, which is plenty

i had a gsl-se with an S4 block, which is a little like a ported motor, and it would run lean up top. the stock ecu caps duty cycle a little low up top. spec miatae have the opposite problem, that ecu runs AFR in the 10's, so they monkey with the AFM to get it to run leaner.

on a GSL-SE you can monkey with the AFM a little, but to get more fuel it might be better to play with the coolant temp sensor signal, or the fuel pressure.

 

Okay, so if it's pretty well-accepted that the injectors can keep up, how can we all be assured that the car can measure a flowrate higher than stock WOT at 7000 rpm? Do we know, as a community, that a GSL-SE running at full tilt still doesn't suck the flapper door all the way open, and when you port a motor or go to an S4 intake, it can flow AND MEASURE that extra air?

I'm just playing devil's advocate. I don't remember seeing it discussed, and just want to make sure.

 

My SE motor was ported. I never dynoed it, but it does have a cheap A/F meter. FWIW that meter does not show lean at WOT.

 

Uh oh Crit, whre is this mysterious car? PM me a link!

 

mine had an s4 block, and RB street port exhaust, i put a voltmeter on the afm, and it was fully open by 4500rpms. top end was very lean, in the upper gears i'd get preignition, and then it would just stop running....

adjusting the afm helped a little, bigger fuel pump did nothing.

the "fix" was a stock port gsl-se block with an s5 rotating assembly. less airflow, less need for fuel, less power too....

 

Not to be ungrateful, guys, but I've got 1 for and 1 against. Does anyone have a similar setup they can share with me?

j9fd3s ran a SP S4 setup and maxed out the AFM 500 rpm early, ran lean on the top end.
74RX4 ran a SP S3 with S4 intake, and it ran fine. Still showed rich on the top end with a cheapo A/F gauge.

j9fd3s, can you tell me more about adjusting the stock AFM? Do you break the seal and modify trim pots on the traces in the AFM, or is it done somewhere else? Kent, what can you do with the coolant signal to get the duty cycle above 85% (other than just keep it in open loop, which would kill gas mileage)? I recall that there's a thermistor inside the AFM, so I could see cheating that with a bias resistor so the ECU thinks the air's denser than it is, but why the coolant sensor?

 

my car had an S4 engine, Rb exhaust, stock s3 intake/ecu fuel etc. it ran great except it was lean up top... with the voltmeter on the AFM, its open by 4500rpms.

the afm is nice, there are lots of adjustments. the flapper is adjustable in spring tension, fully open and fully closed. the adjustment i made was the fully open stopper, i forget the detail exactly, but i got fully open voltage from like 12v to almost 13...

the coolant sensor thing has to do with the ecu programming. the ecu is programmed to have its max duty cycle at full rpms, full load (afm wide open) and full coolant enrichment. the coolant enrichment can be on the order of 20-30%. so if you say the max injector duty is 90%, then subtract 30% because its warmed up, you get about 60%. these are ballpark numbers, but thats the idea.

so if you put something on the sensor that makes the ecu think its colder, you get more fuel. the switch for closed loop is seperate, so to a point it wont be affected.

the T2 guys used to put a potentiometer in the coolant sensor wire.

as for why my car and rx4's being different, i dont have an explanation. these cars vary anyways (maybe my ecu/ect combo was leaner? since they are both modded one might be a better combo than the other . also there could have been something wrong with one of em, fpr? injectors?

the fix for mine, was to put a stock motor in it, with the 9.7 rotating assy, its down on power by quite a bit, but the fuel system keeps up. it'll still take an s2000 in the hills too....

 

Bump - curious if anyone else has any thoughts.

 

Okay, update time. I bought the car, pulled the motor out to reinstall the OMP, and it's back in the car. I sent two pair of SE injectors off to witchhunter.com for cleaning, so there's only so far I can go for now. The old, hacked harness has been removed and replaced with my spare. Front cover was swapped with a spare, so now I have one without the drive gear in it (why the kid removed that damn gear is beyond me - really painted me into a corner for a ridiculously small HP gain). Dizzy was never locked and is missing an ignitor, but it's back in for the sake of hooking things up and checking static timing. LIM was replaced with a spare, as the P.O. removed the aux port lines from the manifold by snapping them off (banjo bolts work well, but was perhaps deemed to elegant). Front housing OMP line was broken and has been remade with the reuse of a few fittings, some new tubing, and a torch to make the bends - works fine now.

The motor's back in the car with the solenoid rack and fuel hardline rack reinstalled. New fuel lines are run to the fuel rail, though it's hanging out waiting for injectors. All the vacuum lines are hovering in space, waiting to be attached to the plenum. Looks good though, for the sake of double-checking that everything's accounted for.

I'm still short the little 90-deg bend that feeds the BAC from the plenum thru-pipe, as well as the coolant line from the water pump to the TB. Fuel tank vent hardline, charcoal canister, firewall hardlines, and vent and purge solenoids were all removed by P.O. - looks like I'll just go without.

It looks like I can get the car back on the road pretty easily for the sake of testing to see if the ported block and stock injectors will play nicely with the AFM. If anyone else can chime in with a ported motor and stock ECU, please do.

Final remaining step is to bolt the ECU and sensors to the ECU frame, and secure it to the footwell. I'll also solder a 3-conductor stereo plug to the O2 sensor pickup, hot, and ground on the ECU so I can use a standard headphone extension cable to supply the signal to my Air/Fuel gauge that I move between cars for diagnostic work.

 

Sounds good Crit. Depending on how much the engine is ported the stock injectors should keep up. Looks like your getting SE fever! Any pics of the "new" SE?

 

Yeah, I've got pics from "before" with the de-OMP'd front cover and Megasquirt-hacked harness.




















By the way, I've got a few questions (not for you, Sam, I know you love your carbs and turbos). Now that I've done more studying, it looks like there's both a thermistor inside the AFM (the far right pin and third from the left) as well as a traditional IAT sensor screwed into the plenum. Any idea which one is used when?

Also, on the firewall photos above you can see that the blue and grey solenoids are missing that control the ACV - no biggie as the car doesn't have one now and won't after I ****** the RB exhaust off it. However, the vacuum switch is also missing, which is normally teed into those and hidden back behind the cold-start bottle. Is the vacuum switch just made with high vacuum (high engine speed and no throttle) and used to cut the injectors off when you back out of the throttle? Any idea if I need to find one in order for the new car to run right?

I also now have an 84 and 85 SE, so I can finally see the sole difference between the two. I've never seen the 85 setup and it's, frankly, kinda stupid. Way to go Mazda.

 

air temp sensors: it uses both all the time. basically it looks at the afm signal, and the temp in the afm, and decides the mass airflow amount. then it uses the temp in the plenum as a fine tuning.

i'm not sure what the vacuum switch actually does, but i know if its bad it doesnt pass smog.

sole difference? only difference between an 84 and 85 under the hood is the A/c pipe is either black or gold anodized...

 

That's not what I understood to be the difference. The air pickup tube on the 84 stops above the radiator with a solid driver's side radiator panel. The 85 has a thru-hole, and the pickup tube has an extra piece that extends the pickup point through to battery. This was done to avoid picking up water into the intake. Why they didn't just pull it all from the passenger's headlight rather than go through all that other effort, I don't know.

I did a little experimenting with the vacuum switch, and pulling enough vacuum to trip the switch is one of the conditions to go closed-loop. With it unplugged, the mixture stays rich, but you'd never notice it without an Air/Fuel gauge or unless you're checking your mileage.

 

I just got the injectors back from Witchhunter. Two flowed 692cc, two flowed 688. Can't get much better than that!

Once the Mazdatrix order gets in with the TB coolant line, I'll throw the manifolds on her and try to get her on the road for a little testing with the Air/Fuel meter.

 

Update time, and I need a little troubleshooting help. The TB coolant line finally came in, so I threw on the manifolds and closed up the motor. I've checked and reconnected the ignition in its stock configuration, and get spark (haven't timed it yet, but that's not an issue yet). I finished adding a 3-conductor sense lead to a radio shack stereo headphone jack, so I can plug an Autometer cheapo Air / Fuel gauge into the stock harness to see how she's running. Once that was done, the ECU was mounted and all the electrical stuff was buttoned up.

The final outlier is the fuel pump. When I short the pump connector, the relay woud click, but nothing from the pump. The PO had pinched the wires between the body and bracket when mounting the pump, but it still was crap when tested directly. It's a shame, too, because it was a new Airtex pump. If I use alligator clips to put 12V off the battery to the Airtex pump's terminals, it does nothing.

The car included an old Mazda pump off the PO's parts car, so I've reinstalled it. When swapping the pumps, fuel ran out of both lines and had to be capped by my thumb while making the switch. Now that's it's plumbed up and mounted, the engine won't start. I mounted my inline fuel pressure gauge to the supply side at the firewall, and get ZERO pressure.

If the car had a clogged line, I wonder if that's what failed the Airtex pump. Then again, fuel ran down my arm while changing the pumps, so it can't be totally clogged. Even if the return were clogged and there was no flow, I'd still have pressure on the supply side of the fuel rail.

I'm at work, so the only reason I haven't checked the lines is that I called it quits last night, but I'm curious if anyone else has had a similar problem. The car ran great and was an autocross toy prior to my buying it, so I'd be surprised to find any clogged lines.

What do y'all think?

 

- pump polarity wrong (pump running in reverse)?
- got gas in the tank?
- when testing pressure, did you grab the lines to feel for flow (reg could be stuck open.. flow, no pressure)

 

Pump polarity is right, and I checked on the Airtex too before I pronounced it dead. I added 2-3 gallons last night, just to be sure I had gas.

As for the regulator - never checked it. Do our regulators ever really stick open? I'll pull the gauge loose from the hardline and see if I get fuel gushing out once I get a chance tonight. Thanks Kent.

 

couple things ive seen

ive seen people hook the fuel lines up backwards at the engine, so the fuel is trying to go the wrong way thru the regulator (ive also seen the fuel return plugged into the oil filler!)

and 2, there IS a little filter on the fuel pickup in the tank, since we just found out about these things, its 30years old.....

 

Sure enough, the fuel lines were swapped. Standard convention is that the outboard fuel hardline is the supply, and feeds the forward line of the rat's nest. When I went to remove the "return" line in order to add my fuel pressure gauge, I was greeted with a HUGE spray of fuel, after it had sat overnight, so I knew that the hoses were backwards.

I set the high-idle cam position, gave the key a turn, and this is what I got.










I'll drive the car next week to see if the smoke clears, as this was a fresh rebuild, although it was done by the PO. Hopefully he didn't get the control ring springs backward or roll the water jacket seals.

 

runs nice! i hope someone put atf in it or something... thats a ton of smoke