twcblackhand6970

Lately my car has been feeling like a miss was occuring so I went outside and did some multimeter testing on all the injectors and their harnesses.
I can only feel a really subtle stumble at low rpms but at idle the exhaust sounds like a cylinder is firing.

These are the multimeter readings I got.

#8 - +12v, 12.7ohms #7 - 11.95v, 12.8ohms
#6 - +12v, 14.1ohms #5 - 11.99v, 12.8ohms
#4 - +12v, 14.5ohms #3 - 11.99v, 12ohms
#2 - +12v, 12.1ohms #1 - 12v, 13ohms

I measured the voltages and resistances in a counter-clockwise direction starting from #8 which is why I think the voltage started decreasing at the end, but I'm not sure. I measured the voltages from the pink wire to the battery ground and the resistances across the injector itself. The frequency ranged from 35Hz to 60Hz but was usually about 42 to 50Hz at idle with a idle close to 575RPMs. The only injector that was kind of off was the number 7 injector which was usually 30Hz.

I was mainly concerned about the resistance of the 6 and 4 cylinder because it was a lot higher than the rest and the car seemed least effected when they were unplugged.

Any help?

Maverick_997

From what i learned injectors should all be within 1.5 ohms of each other for normal operation(someone correct me if im wrong). not sure if it would cause a miss that you are experiencing. On the other hand the 30hz pw from the 7th cylinder might be causing the cylinder to run excessively lean giving that sort of stumble but not a full on miss IMO

Jeremy

twcblackhand6970

How could I fix the low frequency at cylinder 7? And what should the stock injectors resistance be?

Injuneer

You should be OK if the resistance is withing the range of 12-15 ohms.

30Hz is not a "pulse width". Pulse width is measured in milliseconds, and is going to be about 1.5-2.0mSec at idle. You can't measure it with a frequency meter. What you are doing is counting the pulses. At ~600rpm, in full sequential, each injector is firing 300 times per minute, or about 5 times per second. So your "Hz" values seem questionable.

How were you measuring "Hz"? You need to measure the pulses on the ground wire from the PCM, since that is connected to only one injector. If you measure the pulses on the pink wire (+12V) you may be seeing the reflected pulse of all 4 of the injectors that are fed off a single fuse. All you really need to do is put a 'noid light on the each injector and verify the PCM is supplying the ground to fire it. If at any time there is a fault on the injector circuit, it should set a code in the PCM, but the fault has to last for 5 seconds.

twcblackhand6970

Okay, well I'll recheck the frequency tomorrow because I don't have a noid light.
Just measure using the non-pink wire and the battery ground?

Injuneer

Measure across the two terminals of the injector wire clip, not to chassis ground. Not sure what you are trying to find, though?????

twcblackhand6970

I was trying to see what was wrong, my car seems to sputter slightly like a miss at low rpms and was trying to rule the injectors out first since I've got new plugs and wires.

The first frequency measurements above were across the injector harness connectors.

I measure these frequencies with the positive diode at the non pink wire to the battery ground and got these. The second number from each set is the pink wire to battery ground. All taken at about 575rpm idle.

#8 - 730hz, 245hz #7 - 490hz, 5-20hz
#6 - 600hz, 6-20hz #5 - 120hz, 350hz
#4 - 700hz, 5-20hz #3 - 120hz, 190hz
#2 - 750hz, 5-15hz #1 - 150hz, 200hz


Reread your first reply. I measure the frequency on my first post from the pink wire to the non pink wire on the injector harness. And how much do noid lights cost and where could I find them?

Injuneer

Still not sure what you feel measuring the "frequency" measurement will tell you. If you could tell me what you are testing for, it would help me to understand it. I've just never seen anyone measure the frequency of an injector circuit to identify minor variations in circuit voltage.

You're measuring a switched DC circuit, that will produce a square wave with values of 0V and 12V. You might be trying to measure the number of injector pulses, but your results aren't rational. As already noted, each injector should be pulsing 5 times per second at 600 RPM idle. Since the injector load is an inductive coil, you may be measuring the natural circuit voltage oscillations of the peak voltage at the top of the square wave. Do you feel the injector may be "chattering" and causing erratic flow?

I think a set of 8 'noid lights is available for less than $20 at places like Harbor Freight.

twcblackhand6970

Well the side that is lean, left bank, seems a lot louder, like a lot of ticking. And the side that is rich is pretty quiet. I can even hear tapping under engine on the left side. I was measuring frequency because I have no way to measure duty cycle. Anything else I can read with a AC/DC multimeter that will help?

Injuneer

You can't measure duty cycle, you can only calculate it. You have to measure pulse width, then divide the pulse width in milliseconds by the number of milliseconds it takes for two crank revolutions for the specific RPM you are measuring the pulse width. You need a scanner to measure the pulse width the PCM is setting.

The formula is (PW x RPM) / 120,000 = %DC

For example, an 18 mSec pulse width at 6000rpm

(18 x 6000) / 120,000 = 108,000 / 120,000 = 0.90 = 90% DC

After you have measured pulse width, what do you feel it will tell you? The PW off a scanner (there will be a left and a right value, since each bank of the engine is controlled independantly) is the time the PCM turns the injector on for. Its does not reflect the actual results at the injector, nor will it show a variation for each of the 8 injectors. It calculates a pulse width and applies it to the 4 injectors on that bank.

At 600 rpm idle with a 2mSec pulse width, the injector will only be at 1% DC.

It idle, a dirty or a sluggish injector will have a major impact on the balance of the cylinders, since any delay in opening or closing the injector, or any blockage of flow changes the amount of fuel delivered vs. what the PCM wanted delivered. These minor variations MAY become less significant at higher engine loads.

twcblackhand6970

Yea, at higher rpms the noise seems to go away, but then again I can't hear it over exhaust. When I'm in the engine bay revving it, it sounds nice and powerful, no odd ticks. The left pulse width and right pulse width that pcmcomm gives is like 3.14ms for the right and 2.8ms for the left, or the other way around. When I was unplugging the injectors to test voltages and what not, some of the injectors seemed to make a small impact while others affected it pretty vastly.

Another thing I'm concerned about that I've posted before was the right o2 sensor voltage dropping and going into open loop and resetting back into closed loop and repeating and the car seems to run worse while the voltage drop is occuring.

While I'm in open loop, my o2 sensors voltages range from 450-560mvs, but when I hit closed, they drop fast and my BLMs go with them. But after running around town for awhile, they seem to stay on.

My long term left bank BLM is 130 and my right bank BLM long term is 115.

I don't know if any of this matters, just trying to give you all the info I have right now just incase it helps.

twcblackhand6970

Another think that's been happening is sometimes it takes the car a while to start, like it'll crank over and over till it catches. But sometimes it starts immediately.

Injuneer

Dropping O2 voltage should be increasing the BLM's.

twcblackhand6970

How could I tell if it was an o2 related? besides swapping them because my headers makes it a pain to do.

Injuneer

Most O2 sensor problems are easier to diagnose with a good scan log.