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MegaSquirt w/ stock sensors and harness


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I would like to know if any of you have tried running MegaSquirt with the original equipment sensors and stock wiring harness from a fuel injected 280Z L28. I am preparing a 1978 280z for competition in SCCA's improved touring class. I am allowed to use any engine management electronics that will physically fit inside the original box. It also must connect only to the original harness with only the original connector. Does anyone know off hand the dimensions of the megasquirt box? I thought I found those dimensions on the MegaSquirt web site once but couldn't find them today. The original box is quite large and I'm sure I can physically make it fit. During practice and testing another harness with O2 sensor and whatever other modern sensors and data acquisiton could be used to develop fuel maps and then for the actual races the original harness and stock sensors used. Anyone's opinion or advise who is familiar with the system would be appreciated.

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Do you need to run the AFM in SCCA ITS? If so, does it need to be fuctional? The Megasquirt is a speed density system, so it doesn't require an AFM.

 

I did read somewhere about someone using the stock harness and ECU case for a Megasquirt, so I think it is possible. You need to change the calibration tables for the Nissan sensors, and you also will need a 240SX (resistor type) TPS (may not be legal).

 

They allow you to run any EMS that will fit in the stock box and use the stock harness? This rule is in place just to make it difficult to make these kinds of mods. There is no other reason besides the fact that retaining the stock AFM will limit your performance. What SCCA should require is to retain the stock AFM, even if it isn't actually doing anything (kind of like a restrictor plate). Then they should allow you to use any ECU, sensors, and wiring harness. Using the old harness will effect reliability, leaving stranded race cars on the track.

 

When I do an MS install, especially in a competition vehicle, I always start with a new harness, connectors, and sensors. Do it now, and save yourself a lot of headaches later.

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First, Z-ya, thanks for replying

Do you need to run the AFM in SCCA ITS? If so, does it need to be fuctional?

This is debatable, the rules in IT are in many ways very ambiguous and I think eliminating the AFM might be possible depending on your interpretation of them. Obviously there would be great advantage to doing so. The AFM, if retained, must be unmolested and functional.

and you also will need a 240SX (resistor type) TPS (may not be legal).
That is a big no-no. Must use all stock sensors including the stock tps. I know that's a bummer because stock 280z tps is more like a four position switch. But I think that could be worked around
They allow you to run any EMS that will fit in the stock box and use the stock harness? This rule is in place just to make it difficult to make these kinds of mods.
Exactly... you would not believe the controversy and debate this rule has generated.
There is no other reason besides the fact that retaining the stock AFM will limit your performance.
That is assumed to be the exact intent of the rule
Using the old harness will effect reliability, leaving stranded race cars on the track.
There is also huge debate concerning the stock wiring harness rule as well. You are allowed to 'repair' the stock harness though and this to I believe could be made to work

Thanks for your thoughts

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  • 1 month later...

I just converted my eagle talon to megasquirt and I unsoldered the factory ECU connector and then wired it to the DB37 so now I just plug the megasquirt directly into the factory harness ECU connectors, worked out really slick. You could so something like that to get started.

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There is a potentiometer tps out there that will bolt right up to a 280z tb. The thing to look for is the width of the 'wings' on the tps and a three wire connector coming off the side. Im sure if you come up with a wiring diagram that mates a megasquirt to the stock harness, you would have a lot of interested people.

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There is a potentiometer tps out there that will bolt right up to a 280z tb. The thing to look for is the width of the 'wings' on the tps and a three wire connector coming off the side. Im sure if you come up with a wiring diagram that mates a megasquirt to the stock harness, you would have a lot of interested people.

 

true, but then you would only have control of fuel, which is not what alot of people want.

 

p.s. potentiometer tps comes off the 240sx

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  • 2 weeks later...

wow... I'm really glad this thread generated some more interest. I hadn't checked it in a while. I am still planning to attempt to use MS for my project, but have been busy with other parts of the build.

As Moby said, I believe the stock harness / ECU connection can be made to work. Brad-ManQ45's comment about MS needing a potetiometer type TPS is more of a concern for me because I must use only the stock TPS (SCCA ITS rules). Can't I set up MS to expoliate(sp?) between points on the stock TPS? (I don't know if I'm stating this correctly) Does MS require a variable resistance reading from the TPS or what? Like a signal voltage that varies with the resistance of the TPS? MS also reads the RPM right? The stock TPS in a 78 is really two sets of points. So I get idling, WOT or in between.

And Brad-ManQ45 could you expound on your idea of using the AFM and mass air code?

And Moby any more on how to use the MSnS_extra029 with the AFM?

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Can't I set up MS to expoliate(sp?) between points on the stock TPS? (I don't know if I'm stating this correctly) Does MS require a variable resistance reading from the TPS or what? Like a signal voltage that varies with the resistance of the TPS?

 

I think you mean interpolate between the points. But the stock TPS only has two points, on and off so that wouldn't work. MS does require a varying resistance TPS which produces a varying voltage like you say. I have not investigated yet but I believe you can run without TPS altogether and use MAP for all calculations including accell enrichments. I want to try this on my 454 and avoid using a TPS sensor if possible. I am sure there is more info about not using a TPS on msefi.com but I haven't looked for it yet because I'm not ready to try stuff yet. Somebody here mentioned it, that is why I think it is possible.

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...I have not investigated yet but I believe you can run without TPS altogether and use MAP for all calculations including accell enrichments...

 

Moby for my application I'm not sure if hooking the MAP up would be legal. (I'm trying to use it for SCCA IT) Can't MS run using the MAP or alpha-n or something? Where the MAP wouldn't work because of lack of vacumn signal because of radical valve timing ect. For the MAP sensor built into MS, you run a vacumn line directly to a port on the box?

As far as the tps, maybe I could come up with a way to simulate the voltage input for the TPS with another black box.

Anyhow, I know I don't know $hit about this, and I really appreciate you guys helping me out!

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I've been reading the documentation. If I understand it right, I can choose to run speed density or alpha-n as the control algorithm. Speed density uses the MAP sensor and RPMs and Alpha-N uses TPS and PRMs. From reading the documentation I've deduced that you do indeed need to run a vacumn line from the intake manifold to the MAP sensor. I don't think I can legally do that (SCCA IT ruleset) so I may be forced to use the alpha-N. I only have to comply with the letter of the rules during actual racing, so I plan to use an O2 sensor and maybe even run the speed density algorithm while setting up and tuning, then switch to the alpha-N to race. I assume most people use the speed density, does anyone have any experience with the alpha-N?

My next hurdle is the required sensors. (I can't add any, factory only) I have a water temp sensor. (may have to be calabrated to work) My understanding is that water temp is only used for warmup enrichment. Inlet air temp, haven't got one, could I possibly mount it inside the ECU box? or deduce a number from the water temp? or pick a static air temp and set it using a potentiometer mounted inside the ECU box? The O2 sensor I only need to run closed loop so I can live without that, I think. And lastly the throttle position sensor. (TPS) I'm still working on this one. The stock TPS consists of two sets of contact points. Say I send the 5 volt reference to the TPS, add a resistor to the first contact connection adjusting the voltage down to the lower end of the scale to indicate idle or closed throttle. Then I have to figure out how to send mid range voltage to indicate mid throttle opening when neither contact is touching (3 volt source voltage?), then step it up to 5 volts when the second set makes contact. Granted it wouldn't be linear curve but my understanding is low powered IT cars usually use the throttle more like a light switch anyhow so this might work.

I'm going to reread the rule book. There may be some relief in there. Any thoughts anyone?

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Guest Bulldog55

I am currently resurching installing MSnS on a 77 280z 2+2 I would like to have it in the origanal ECU location. I commend the knowlage and info given in threads such as this.

That being sied. I will not need the afm, allready have a sx 60mm tb with tps attached. (yes, I do plan on porting the intake to match.):) By what is stated above I can recalibrate the MS to use existing water temp. and map senser that is in the unit, adding a WB O2. I should have eveything with the exception to the crank trigger correct?:icon56:

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Well after spending a little while with my nose in the fuel injection bible, I've figured out that the stock system does include an air tempeture sensor. It's mounted inside the air flow meter. After thinking about it, I figured it must have one, how could it work with out it.

So... I've got water temp sender, air temp sensor and a crude throttle position sensor. For a fuel only system (no ignition) this may be enough.

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