Who here is running fuel only setups? I am at the limit of my carb and now I am on price/performance verge of do I go EFI or do I get a bigger carb. I see lots of people here running spark/fuel through the megasquirt.

Some general observations:
It seems that to run sequential injectors it will need an ignition signal that the distributor cannot produce to fire the secondaries.

Haven't seen many people do just fuel only (is there a reason for this?)

S4/S5/S6 TPS compatibility, which is the preferred sensor for MS to read?

BAC is a must

Troubles running just 2 injectors? IE: does it requires high impedance which is difficult for the MS to read.
OR
large injectors/high duty cycle = hard to maintain proper low speed/idle conditions?

I'm still doing my homework on this method but I'm curious to hear input from everyone before I completely go down the rabbit. Feel free to debunk me assumptions with facts.

 

wont let me edit....

but I wanted to note that application would be N/A with no plans of boost with a large streetported 13b T2 irons, n/a internals currently running a dizzy based ignition. I think MS3 would be overkill for what I need, MS2 should be fine.

 

get a microsquirt and do fuel and timing for lees than $400.

 

Then why aren't people doing that? I don't see a lot of microsquirt builds here.

More helpful information: I already have a wideband 02 sensor and it is in a FC race car setup (see sig links for too many details in build thread) so there already is a very simple harness installed in the car.

I like the notion of just sticking with my current ignition setup because it works, really well (FC leading coil re wired and distributor with MSD blaster coil) and its simple which is why I am leaning on fuel only setup.

 

microsquirt does not have enough ignition outs to run trailing.

 

You could probably sell your distributor and coil for what it costs for a used FC CAS and T/L coils.
I think the fuel side of the install is where 90% of the money goes anyways.
FC TPS's suck. S4 is only from 0-25%, S5 has low and full range sensor. I've had terrible reliabilty with both. I using a Ford mustang (IIRC) with a thin sheet metal bracket. I notched the end of the throttle shaft and use the sheet metal to suspend the sensor next to the TB. By no means elegant, but I get a linear 0-100% and my 0% is always 0%. Not sure how it'd hold up on a rally car, though.
Here's the best photo I have atm.
http://i33.photobucket.com/albums/d8...psap85cx8l.jpg

 

I've done several 13B fuel only Megasquirt setups, all turbocharged, using locked on distributors.

I wouldn't bother in a turbo application because locking out the dizzy is a compromise with too many downsides.

But since you mention you are an NA application, then certainly it can be done. Obviously you give up ignition control but fuel control is the same. Closed loop, auto tune, staged injection, etc. etc. But no sequential injection, you will be stuck with batch.

The S4 TPS does work fine if you want to use it. But, because it is only a 1/4 range TPS it is only useful for on/off idle detection and you would want to use blended AE. TPS can supply AE at light throttle when you really notice it, then MAP can supply AE when the TPS is out of range as it will be less critical. However with the rather minimal effort require to retrofit a Ford TPS, it seems like the downsides of using the S4 TPS aren't worth it with the fix is easy.

But, in the same sense, upgrading to ignition control is little cost above the base Megasquirt. MS3X supports it all out of the box. MS2 just needs the addition of a VR board (Zeal) which is about $40. Finding an FC CAS and set of coils isn't too hard for little money.

 

ken the microsquirt with the extra code give you 4 spark channels.

 

Yes but you can't run that and seq fuel. They use the same timers. Better to go with MS3.

 

I have I think 11 CAS in a box, I would have to re-wire my leading FC coil and source a secondary coil, I am pretty sure I have S5 fuel rails sitting around but it's been so long since my car has had EFI I have forgotten about some of the minor details. IE S4 TPS is crap.

Hrmmm, well this gives me a better idea at least of what I have to work with. Thanks for the input all.

 

Way to overcomplicate things....

I went years on a S3, S4 NA, and S4 T2 manifolds running only two injectors. You just need a GSL-SE fuel rail OR a S4 primary rail and an external regulator.

Never did ignition control. Never did idle control. Never had four injectors. Never used anything but MS1 and the generic (B&G) code. Everything worked out just fine.

The S4 TPS is crap but it's acceptable since you don't really need acceleration enrichment past half throttle anyway. Run the map sensor hose to the back of the plenum (not the runner where Mazda put it) and I think I had my TPS threshold set to 1.6v/second. In fact I think I still do, because the TPS setup on my holley is also pretty crappy.

I did just buy an MS2 from DIYAutotune because I killed my 1.01 unit with a voltage spike, and the 3.0 board I replaced it with was soldered poorly and the car would randomly shut off/relays clicking when the computer was cold. But I want to play with having four coils in the future. Otherwise, I'd have just bought a prebuilt MS1 and kept going.

 

I was waiting when you were going to chime in...

I probably have an S4 primary rail laying around somewhere too.

 

S5 might work just fine too, I've never seen one though.

 

same thing as S4 but no plastic FPD thingy.

 

The biggest issue seems to be everyone hatred/complaint of the factory TPS. Are GM or ford ones more preferred/more accurate? I would think if I find a big enough truck TB and just get an adapter machined and utilize that.

 

The factory TPS can sometimes stick and hang down when you open the throttle. This is easily seen in a basic MS install by the acceleration enrichment LED not winking at you when you open the throttle, then a few moments later it does wink. Of course this is noticeable by the drivability hiccups as well, but the LED on the front of the case shows you what it is doing.

The only problem I have with a full range TPS is that throttle enrichment isn't needed at higher throttle openings. My tuning for instance is kind of a mix between not enough enrichment at low openings and a touch too much at high openings, because of the full range TPS.

I did the single throttle body on stock manifold. Even hacked up a T2 intake to remove the plenum divider. Lost a bunch of torque in spots and generally I didn't like it, so i undid it.

 

I'm thinking about the subject again, whats the pros v cons on sequential v batch injection?

 

sequential will give you better idle and throttle respond but h.p wise you going to make the same amount of h.p.

 

Its a race car that is carb'd currently and it has a decent idle, I can't imagine it would get any worse with EFI. Most of the time it is running is above low throttle (if I'm doing it right).

 

Even batch firing your going to be fine so I would do it

 

I can use engine speed from the trailing coil, but would I have to muffle the signal, is it too strong?

 

If it's a track car, then idle control isn't really that important. And if running at mid to high throttles most of the time, batch injection will be fine as well.

You can pull the tach signal from the trailing coil as well.

Like the leading coil, you may need a resistor in series. I usually experiment a little, ending up around 10K.

 

Probably true for rotary, but not always true.

For the rotary it'll also reduce fuel consumption set up properly.

 

Well next paycheck I will be pulling the trigger on this setup. I have already gathered the required stock parts I need to operate this. Now its time for the brains and guts.

What about sensors, what "vehicle" do you guys use to get proper GM IAT/CLT? I see on DIY autotunes site that there is open and closed element sensors. Does it matter which one we need?

With no plan for boost, I plan on running a 1 bar MAP. Simple, cheap and effective.

 

Open is for air temp
closed is for water temp