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Frustrating condition


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Hi all,


i recently completed an s14 swap using a surplus programable EFI system from SDS which I had. My s14 did not come with a wiring harness or ECU so using the SDS made lots

sense. It is a simple system that is also used heavily in kit aircraft so I believe the reliability is solid.


The setup using ITB based enrichment rather than MAP based.


the car starts and runs fine for 20 minutes or so at which point it will stall and then will no longer run. it seems to me that there is a fuel issue at that point but I am leaning towards injectors as right before the condition presents my AEM

WB02 and gauge start going haywire.


I have confirmed fuel pressure, plugs, injectors filter are all good.


thoughts on steps to troubleshoot?





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Well, that's easy- just strap on a set of DCOEs and jet to taste!




Sounds like an overheat condition, if I had to make something up.


I am unfamiliar with SDS- will it provide real- time data to a laptop, so you can watch what it's doing

as it starts to fail?


If not, what I'd do to diagnose would be to put noid lights on the injectors, and see if you can see anything obvious.

Also, a timing light.


If neither of those give further clues, it's time to scope the injector pulses,

and see what happens there. 

Seems like it should barf data, though, and then it'll be pretty close to obvious...




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I'm certainly no expert on any kind of EFI (I'm a carburetor Luddite) but you can at least narrow down the probable cause(s) with a little old-style diagnostics.  


Next time it stalls out per your description, pull a plug, reconnect it to its wire and have someone crank the engine while you rest the plug on a grounded metal surface (like a valve cover).  Don't touch the plug unless you want a big tingle!  See if you have a nice fat blue spark.  If so, you've probably eliminated your ignition system as the culprit.  


Next, see if you have fuel at the injectors--and here's where my EFI knowledge gets hazy.  You can either pull an injector and see if it squirts when the engine is cranked, or check to see if the requisite voltage is reaching the injector.  


At that point, you've at least eliminated either the ignition or the electronics that power the injectors, and you can proceed from there.


Happy troubleshooting


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I know nothing of the SDS system but other stand alone systems control both the fuel and ignition.  Like Mike said when it dies pull a plug wire and see if you have spark to the plugs.  If you do that cuts out a ton of possibilities.  If you have no spark start there. Are you using a single coil and the stock distributor cap and rotor? I have seen rotors fail and when they get hot open up a crack in the rotor and ground out inside the cap.  Pull the coil wire and see if you have spark to the cap. 


What kind of crank/cam sensor are you running to trigger the ECU?  If you have no spark or injection this is probably where I would start. It is also possible your ECU may have a temperature related failure,  where is it mounted? 

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1 hour ago, Anthony said:

runs fine for 20 minutes or so at which point it will stall and then will no longer run. it seems to me that there is a fuel issue at that point

Stalls at what running mode, i.e. idle, mid power, wot?

You need a fuel pressure gauge on the rail supply to see what is going on for fuel pressure.  Is the fuel pump still running after it stalls?  I would expect the SDS to keep it running

Is the engine stock?  If not that could affect the WOT fuel requirement that the stock injectors, if used, are short on capacity.  Will SDS display injector duty or injection time.  Assume you are using semi-sequential (no cycle reset cam sensor), if so injection time of about 8.5 ms is the limit.

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