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Injector dead time on unknown injectors

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have people discovered a process to work through on unknown or injectors that are lacking the required data?

an example i am dealing with is having removed the resistor pack (unreliable due to age) and now re tuning with the low resistance injectors and no resistor pack (haltech PS1000).

whats the process? i cannot be the only person tuning older cars. (90's)


This question pops up pretty frequently and I wish I had a good answer for you. Generating accurate dead time values is beyond the scope of most tuners and requires some reasonably precise test equipment.

I'll say this again and it's probably quite controversial - I believe a little too much emphasis is put on the importance of injector dead time. Sure I'd love to have the data and if it's availavble I'll use it. I'll also go out of my way to deal with suppliers who can provide the data I need to my job the best i possibly can. I've also tuned many ECUs in the past that had no dead time compensation at all and achieved acceptable results. Sure the AFR might not be as stable as an ECU that is correctly accounting for dead time but in the grand scheme it is workable.

In the advent that you have no data you're probably as well to use the default dead time table in the ECU. It won't be right but it's likely to be about as close as you are going to get. If you want to go a little further then you can disconnect the alternator and adjust the lower voltage break points to maintain a constant AFR - This contrary to popular belief still won't give you an accurate dead time table as all you're doing is adjusting the difference between neighbouring cells but the absolute values can still be anywhere.

Andre do you find that the dead times given by injector suppliers still need tweaking when using different brands of ECU? Do the different injector drivers add more of a delay?

While the injector drives in the ECU probably do have some minor impact on the injector dead time, you're starting to get down to the last 0.5% of what most tuners are ever really going to be looking at, measuring, or even worrying about. I can't think that I've ever personally changed the dead time values based on the ECU I'm tuning.

It also comes down to the method that the ECU is tuned in, if you are mapping the fuel with a MS based map, as long as the battery voltage doesn't swing around during engine operation, then the setting of the MS value in the main fuel table takes into account the dead time of the injector.

With a VE based fuel table, then accurate injector calibrations become more important, as you are tuning the engines efficiency, not the injectors pulse width. If the ECU doesn't have the accurate data that suits that ECU's calculation process, then it could be calculating a pulse width that is incorrect for the fuel demanded at that efficiency point.

It's probably worth pointing out that on a VE based fuel model you 'can' still tune the efficiency table if the injector dead time data is inaccurate, however much like the ms-based fuel model you'll be accounting for those inaccuracies by cheating the numbers you're putting in the table. The downside of the VE-based fuel model is that when the efficiency data is wrong, the fuel model won't work correctly - ie if you alter your AFR target for example the AFR won't track correctly and compensations such as air temp will be inaccurate.

With a VE fuel model the ECU also needs accurate data on injector flow and perhaps (depending on the ECU complexity) data for the non-linear region of operation (short pulse width adder) so the required data gets a lot more involved and for the ECU to do the job correctly all that data needs to be accurate.

It is nice for example when dealing with a Motec M1 installation where we can send unknown injectors to Motec and they will characterise them and provide a detailed and accurate calibration that can then be simply selected in the ECU. This solves the problem of what to do with unknown injectors but to the best of my knowledge no other manufacturers are offering this service as yet.

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