ka8legend

Is it safe to hook up it analog voltmeter to the injector plug(s) while driving? I was concerned that it might fry the CPU; I'm not sure if it was the volt or resistance test that sends power from the meter. I followed the hayne's manual to bypass the pressure sensor and stick a stethscope to the injector while revving to over 3800k but I hear no apparent clicking, and that's why I plan to do the more accurate voltage test if it's safe to do.

Bambam7

What year is your car?
You probably have to disconnect the TPS plug too, then test it.
You won't really be able to test the injectors' pulswidth with a voltmeter.

You would DEFINATELY know if you secondaies weren't coming on, because your car wouldn't go over 4000 rpm's, and it would run like HELL at that RPM- It's really not a subtle "Hmm... I am not sure if my secondaries are working..." kind of thing! It's about as subtle as running into a cow.

As soon as the RPM's hit 3800, the ECU drops the pulsewidth of the primaries in half, and assumes the secondaries are supplementing that.
If they're not, the ECU doesn't really know, and won't compensate by bringing the primaries back up to full pulsewidth- hence, only getting half the gas you need- means- No run!!

Salguod

Its the resistance test that sends power from the meter.

If your analog VM is a decent quality one, you sould be fine. I'd look at investing in a digital one sometime in the near future though, they aren't very expensive any more. I got mine a couple of years back through Parts Express (www.partsexpress.com) pretty inexpensively.

Later,
Doug

HAILERS

Can't speak for measuring pulse width, but.... I have had two cheap Radio Shack digital meters tapped into the ECU for a primary and a secondary injector. The secondary will on the whole read the battery voltage most of the time(like 13.3 volts) while, at idle the primary will read about a half volt less if the car is running. If your driving along at 3000 rpm the secondary will read the batt voltage(no load) and the primary will read maybe like 11v. Now if you stomp the pedal, the primary voltage will drop(heavier load) and drive down towards about three or four volts. When you hit about 3800 rpm the secondary will drop to about 7 volts and at the same instant the primary will rise from about the 3-4 volts to 7 volts. Then they will both slowly drop together as you hammer away at the pedal. I'm not measuring pulse width, you name it, I'm seeing the load that is put on the secondaries at 3800 when the voltage drops from 13 something to 7 volts. What was interesting to me was the primary rising at that same instant to the same voltage as the secondaries. I pick off the ECU harness as it goes into the ECU. Make sense???????????Twenty dollar meters, digital, Radio Shack. What BAMBAM says sounds just like what the meters are showing.

Bambam7

Hmm- Just a curiosity here-
Is thre any reason why you can't determine pulsewdith by taking the proportion of injector voltage, compared with system voltage??

Let's assume 13.5 volts is system voltage while car is running.

Here- the voltage of the injector cicuit is ALWAYS going to be either 0V or 13.5V. It switches back and forth so fast that the voltmeter can't tell the difference between on and off, and reads the average. (Like your eyes blending together frames of a movie into a continuous image)

OK- a 100% duty cycle would be injector wide open right? That would be 0v (full ground time)
-a 0% duty cycle would be 13.5v- injector totally closed. (no grounding time)
So wouldn't a 50% duty cycle be 6.75v? (This may vary slightly depending on the meter)
So, if I'm not a big idiot, this equation should work-

Duty Cycle % = 1 - (inj v / sys v) * 100

Eg: Inj voltage is 10.18v at cruise, you would do:

1-(10.18/13.5)*100
=25%

You can, of course, reverse this, if you want to see what voltage you will need to read in order to match a specific duty cycle

Inj v= sys v * (100-dutycycle%)

Eg: You want to see what voltage a 25% duty cycle is, you would do:

13.5*(100-25)
=10.13v

So- by this, here's a few reference points

13.5v=0%
10.13v=25%
6.75v=50%
3.38v=75%
0v=100%


I don't know what the ecu will max injectors out at-
HAILERS- If you remember what some numbers were for your car, maybe you could post them?? Say, at redline, idle, whatever?
This could be VERY useful.

If it drops to 3 or 4 volts, than it at least goes to a 70% cycle

******
Disclaimer- I may be completely wrong, but it makes sense to me.
If I am wrong, somebody please correct me before people start using this.
******

HAILERS

BAMBAM....Sounds reasonable to me.When stomping the pedal and watching the primary go down to 3-4 and jump right up to 7 as the secondary came on line.....well I just let it go at that. Already zipping along at a good pace so I let off. Within the next two days I'll go for a ride and pay closer attention. I'll just max out on the rev limiter and take a gander. Its getting harder and harder to find a empty piece of road to max out on. Yes, I just now noticed since you mentioned it, that the 7 volts that both primary and secondary jump to at 3800, is indeed just about half of the battery voltage. Just a small hedge about what I am calling *batt* voltage. Its the voltage that I see at the secondary prior to its opening. If I turn the lights or a/c on, that voltage will drop just a touch(don't ask me to define a touch). Not significant. Just from say 13.5 to 13.1(best of my memory).

ka8legend

I have a 90GXL and had unplugged those two connectors 2 days ago to see if I hit that cow feeling at 3800, but I felt like no difference until after 6000rpm--that's when I hit a brick wall. But I did NOT feel any powerloss from 3800 to 6000 which leads me to believe that the secondaries weren't firing to begin with until after 6k.
I think I'm going to get some of those noid lights and see if they flash. An hour ago, I tried the voltmeter test and it seems to show no voltage going thru the connectors at all.

HAILERS

KA8LEDGEND.......With the key turned to on, the secondary injector connectors should have 12 volts on one socket and the other socket on the plug really should have nothing. The 12v exists all the time. What turns the injector on and off is the ECU putting a ground on and off rapidly at the injector. If you have no voltage at all with the key on, write back and let us know. Maybe we can figure something out. 12v should be there.

ka8legend

Well, this morning I extended my two black & red wires of the voltmeter to the female input of the secondary connector (for the front rotor). I even reverse the leads thinking I might been getting backward needle movement on the meter, but no movement either way when I had it floored in 1st and 2nd gear all the way up to 7k. I'm at work right now doing a 12hr shift so I try the key-on bit tomorrow morning.

HAILERS

I think I have figured it out. Its a matter of methodology(?). Turn the key on. Take a plug off. Put the neg lead of your meter to a good ground like the batt ground. Touch the positive lead to each of the two sockets on the plug. One WILL read 12v. If you are putting one lead on one socket and the other on the other socket on the plug, well....l don't think you'll see anything. With the plug connected to the injector, put the positive lead in the back of the plug to make contact with one wire or the other, and the negative on any good ground. With the key on you should have 12v. If not , you really do have a screwed up caar. If you do read 12v, then go for a ride and rev above 3800 in any gear. It should go from 12v to something on the order of 7-8 volts(lots of variables here in the way of how much load is on the engine vs the voltage seen).
By the way, my car at idle, the primary injector voltage is 13.4 and the secondary is 13.8. At 70mph in forth gear, level ground, the primary is 10.7 volts and the secondary is 13.2(parking lites on, darkness approaches). 80mph steady speed, level ground, primary is 10 volts and the secondary is 13.2 . Stomp the throttle at 80 and both went to 9 something volts and as I let up and go back to a steady 80 the secondary goes back to 13.2 (not open) and primary to 10 volts.

HAILERS

I thought that this might be relevant: http://home.earthlink.net/~burntoast/3700.html
https://www.rx7club.com/forum/showth...threadid=17974