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1ZZ Coil Dwell Times

16K views 22 replies 9 participants last post by  flyboy 
#1 ·
I hooked up a current clamp to my oscillscope to figure out the exact dwell times of these 1ZZ coils since recommendations seems to be all over the place.

First, the caveats that all engineering managers forget after 2 minutes:
* The coils have their own ground point.
* The coils are using the stock switch high circuit.
* The EMS is on its own switch high circuit because I noticed my EFI main relay had 0.2-0.3 volt drop across it. I have noticed others have the same issue.
* I wasn't willing to go all the way to 16 volts, so I set the 14 volt point and then set the voltage to 15.5 and used exclusively used the 16 volt point to set the interpolated dwell.
* The EMS fails to run at around 5.5 volts. If I set the voltage at 6 volts, the current spikes on my power supply at that low voltage were enough to cut out the car, so I did the 6 volt test at 6.2 volts.
* The lower voltages the saturation point wasn't nearly as obvious, so they are somewhat estimated within 100-200 microseconds or so.

While I do expect the above to change things a bit, I don't expect it to be by a lot.

So my map wound up something like this:
Battery Voltage (V) / dwell (ms):

6 / 7.0
8 / 5.8
10 / 4.6
12 / 3.5
14 / 3.0
16 / 2.4
 
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#2 ·
Stupid forum software chomps excess white space. Oh well, the table is still readable.

You will need a variable voltage power supply strong enough to run the car, an oscillscope and an oscilloscope-ready current clamp. You don't need a high-end scope or clamp, as these aren't quick signals in the least. I have a Hantek CC-65 and a Parallax USB scope. My power supply is a Mastec 3020.

I wanted to show you my traces but apparently the forum software doesn't like my files of 76 and 77 kilobytes, respectively. It claims I'm over quota, even though the advertised quota is 244k for a jpg file. I checked my uploaded files and there are zero. Seems like a bug. If the forum owners are watching, I suggest you fix this.

As a fall back, look here:
http://www.extraefi.co.uk/Pix/dwell_charge.JPG
This is just about exactly what it looks like.
 
#8 · (Edited)
Keep in mind my caveats. If you don't have as good a ground or power tap, then your optimal dwell will increase. Also, my EMS is measuring voltage better than most because I bypassed the stock EFI main relay for both EMS and fuel pump circuits. That relay was getting quite hot with the voltage drop my setup was experiencing despite being within nominal. Since then, I have noticed other setups with this issue.

That's why it's optimal to experimentally derive your values like I did instead of relying on canned values.

If anybody lives near my location, I would be happy to show you how to do this. Just bring your car by.
 
#10 ·
My 2nd post has a graphic. It shows how the coil current increases during the dwell event. You can clearly see it peaking out as the dwell increases. This is an indication the coil is getting saturated. Many coils including these 1ZZ coils look almost exactly like that. Use the current clamp on either the power or ground side of the primary coil. Fire the engine and get it to idle. Start with a known-conservative dwell and increase it 0.1 ms at a time until you start to see it peak out like the graphic.
 
#11 ·
My noodle is cooked so I'll just ask this stupid question outright:
I have a AEM Series 1\these coils and wanted to check my dwell times.. but the dwell vs battery table is in percentages not milliseconds.. Can this be converted? Am I missing something obvious?
 
#12 ·
The AEM engineers didn't bother to do the trigger to time math for you, so you have to do it for yourself.

Ultimately, if the base map is setup right, you should just be able to adjust that dwell vs. battery table until your waveform looks like what I described.

If you don't have the current clamp, then you can setup the AEM software to output the "dwell time" parameter while idling then adjust the dwell vs. battery table until it matches the above values.
 
#13 ·
I was going to start my own thread but this would be good info here if answered.
On my haltech ps1000 it does not have a dwell map, only one dwell value. I have been driving around at 5ms for about 3-4k miles because that is the lowest dwell the car would run well with on the dyno.

Am I correct in thinking this one dwell number should equal the dwell at 13.8-14.0v? Why am I so far off the recommended time, my ecu 12v is run strait off a brand new battery with a circuit breaker and a new toyota alternator.

I just started to get some breakup if I quickly hit full boost. I will throw a set of plugs in it and if nothing changes I will be following you and hooking up the picoscope.
 
#14 ·
Your numbers might very well be different than mine. Keep in mind my caveats. I ran a dedicated power and ground to the coils. If you need more dwell and you get a benefit out of that, then fantastic! My numbers aren't to be taken as ideal for all situations. I tried to pick numbers that just approach the ideal saturation. That doesn't mean there isn't a tiny bit more to be had.

The drawback to excessive dwell would be heat. You tend to pop coils sooner and easier.

Also, realize ignition break up can be from a huge range of things! It's not always the coils or the dwell. For example, excessive timing can actually bring on spark break up on systems close to the edge.

If I encounter a system that is close to break up and I have other things in the ignition system where I want them, I will always go with more powerful coils to pull me away from the edge of break up like that. My car isn't making much power at all (~350 whp tops, uncorrected), so these coils work well for me. For more powerful coils, I suggest you take a look at Porsche's Cayenne coils. For a cheaper setup, the LQ9s are good if you want to put up with wires, same with the IGN1A setup.

The PS1000 is a fantastic EMS offering several fantastic things. However, one of its shortcomings is it only does one dwell value. This is improved in the newer Elite series ECUs and then some! It allows dwell adjustment by fuel type, if you so desired. It's the definition of flexible. This isn't the end of the world, put it where you need it for normal operation and call it good.
 
#17 ·
Oops I meant to say excessively retarded timing.

5 ms at 14 volts might be a bit excessive. Emphasis on might. Make the measurement and see if it is. If it is then drop the gap or run better plugs or make sure you don't have corroded terminals on one of the coils or swap to more powerful coils or something like that.
 
#23 ·
I'm not sure what you are measuring here. What equipment do you have hooked up to what wire?

If you are pulling the voltage off the igniter trigger line then your voltage shouldn't be varying like that.

With regards to dwell, there are ems systems that could be setup to allow dwell to vary with load I suppose, but if yours isn't set that way then this is a problem.
 
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