Unable to Ohm Injectors

[franknitty69]

hi,

i have a 95 q45 that just had a check engine light come up. so i hooked up the usb cable and fired up nissandatascan and got a code 51. so i tried to ohm my injectors at the harness.

i get no reading (infinity or overload) when ohming all 8 pins.

i'm using a fluke with the neg on the pins and pos on the battery (+).

the meter works fine, i just tested 3 brand new resistors from mouser electronics.

does this mean anything, can i get a reading somewhere else?

[Q45tech]

Lack of training in reading schematics and posts, plus failure to follow directions and pictures could lead to this problem.

Don't feel too bad about half of college grads cannot get a light bulb to illuminate with a battery and a single piece of wire.

[franknitty69]

i'm not even going to respond to that. please don't post in this thread if you are not going to offer solutions.

i have a computer engineering degree from the ohio state university so i am more than capable of reading schematics btw. so we can rule out stupid. i am using a $200 fluke dmm so we can rule out the meter. the car starts and runs so we can rule out that all 8 injectors just magically died.

back to the problem...

the pins are not giving a reading. i want to know from anybody with experience if there could be a reason for this.

so i ran an active test on all cylinders one at a time. the only when that didn't cause a drop in idle was #8. i'll assume this is the culprit, but why can't i get a reading from the injector harness?

[goody90q45]

Try ohming #8 FI directly on the pins and see what reading you get. You can do the same with 1 and 2 but you'll have to remove the plastic center engine shroud.

[Q451990]

I agree with Mike... try ohming one at the injector itself. Otherwise, and don't take this an an insult, but are you ohm testing the correct harness? If you're going by the pictures in the tutorial, remember that the harnesses can be put in the wrong place by a previous tech.

Also, try it with the ignition switch turned on. There is some talk that the injector circuit may be switched on the later models, but I haven't confirmed it.

Heath

[SteveTheTech]

Do not take this as a slight to your intelligence or degree but not being there to see how the test was performed we need to start from the beggining.

First off the meter zeros out when set to ohms range and the probes are connected in series.

Having the key on will have no effect on verifying resistance on injectors when the circuit is isolated. If you disconnect the engine harness from the injector subharness and perform the test using the connectors listed below from the EC section of the 95 Q manual.



Power is supplied with KOER and the ground circuit is interrupted. So keep that in mind when you are performing basic power supply and ground verification. Having no resistance reading on any injector means one of two things.....either your internal meter fuse is open or your not testing the right terminals. Sorry to kick you while your down but it's the sad truth.

The picture below is the connector you want.

[Denver90Q]

hi,

i have a 95 q45 that just had a check engine light come up. so i hooked up the usb cable and fired up nissandatascan and got a code 51. so i tried to ohm my injectors at the harness.

i get no reading (infinity or overload) when ohming all 8 pins.

i'm using a fluke with the neg on the pins and pos on the battery (+).

the meter works fine, i just tested 3 brand new resistors from mouser electronics.

does this mean anything, can i get a reading somewhere else?

Your not the only one. I haven't been able to get valid ohm readings on my 1995 Q45 injectors thru the subharness either. I have followed the instructions precisely and have no trouble getting ohm readings on my 1990 following this approach. I was able to get valid ohm readings on injectors 1 and 2 when checking directly at the injector. Has anyone been sucessful in getting readings thru the subharness on a 1995 following this approach? Does anyone know if the Nissan Consult has a subprogram for injector ohm readings? Also, is it necessary to completely remove the plenum to replace injector number 4?

[goody90q45]

This is just a wild guess but are you unplugging the 4 pin connector next to the 8 pin injector connector while you're ohming the injectors? It should stay connected during the test. It is the temp probe circuit and I believe it's part of the ground circuit?

[SteveTheTech]

I have performed this test and I know that it works if you are using it correctly. This is the easiest way to do this test. One many models if this does not work or yield appropriate results the plenum should come off and the injectors should be tested indivually, this test is only done when a break in the power signal is suspected.

It is crucial to this test to make sure that the the meter works, test it from the block to the negative battery cable and verify meter operation. If this works and you disconnect the male side of the harness and perform your testing with the key off and the harness disconnected. With the engine sensors disconnect the respective circuits are isolated and you should test multiple terminal locations before throwing the towel in. Electrical diagnostics are not easy, and are often frustrating.

Just a side note. If one of your injectors is suspected of finishing it's serviceable life it may be about time to think about replacing all of them. With new injectors and a thorough cleaning your Q will run better than it has ever before. What I usually tell people who are in this spot is to save up a little cash and do it the right way instead of having the remove the plenum several times, as they will indeed all require replacement at some point. It may take them a while to give out but over time the efficiency of the injector itself decreases.

[Q45tech]

We really don't know how to correlate injector resistance [increases] with expected power balance rpm error.Actually the apparent resistance may vary with voltage supplied by VOM but it is a decent low cost test. Because the copper coil heats up without cooling from gasoline flow

I double check by viewing the current flow under operating conditions for each injector........................you can see the changes in injector open time in the graph of current ramp up.

http://www.picoauto.com/applic...s.jpgh ... x....ement

[franknitty69]

i am measuring resistance at the 8 pin connector from the pictures, i followed the directions posted by wes in the tech help section.

my positive probe is on the positive battery terminal, and my negative probe is on the the pin side of the 8 pin connector. the meter reads overload/infinity as if it was not measuring any resistance. if i put the leads on a resistor, i get a reading. if i measure voltage at the battery i get 12 v with the car off and 14.4 with the car on.

i measured cold, i measured hot. i measured with the 6 pin knock sensor connector connected and disconnected (electrically doesn't make a difference according the schematics).

btw, does anybody know where connector s51 is (EC schematic below) is located?

also along with my power balance test i was able to determine injector operation by supplying power to each injector. #8 did not operate just as the power balance test showed.

i've already ordered all 8 injectors, knock sensors, harness, pcv valves and gaskets(tb, iac, egr). i'm going to do a complete plenum job (except replacing hoses as they are all fairly new). i'm also going to replace the valve cover gaskets, spark plugs and clean everything.

[goody90q45]

.......btw, does anybody know where connector s51 is (EC schematic below) is located?

It's the 4 pin connector in the bundle with the 8 pin injector connector and the 6 pin KS connector (see pic). I'm not too good with electrical schematics but I think this connector goes to the coolant temp probe and is also the ground for the injectors. Steve the Tech has been trying to explain it to us but I'm lost (sorry Steve). This is the 4 prong connector I wanted to make sure you had not disconnected while ohming the injectors.

It's none of my business but with #8 being the only bad injector why are you replacing them all? #8 injector is easy to replace without removing the plenum and the 94-96 injectors are much more reliable than the 90-93. I've only had one FI go bad on my 94Q in 3 1/2 years of driving with ethanol laced fuel. IMHO, unless you've got some other reason for removing the plenum I'd save my money and see what replacing just one injector does.

[SteveTheTech]

i am measuring resistance at the 8 pin connector from the pictures, i followed the directions posted by wes in the tech help section.

my positive probe is on the positive battery terminal, and my negative probe is on the the pin side of the 8 pin connector. the meter reads overload/infinity as if it was not measuring any resistance. if i put the leads on a resistor, i get a reading. if i measure voltage at the battery i get 12 v with the car off and 14.4 with the car on.

i measured cold, i measured hot. i measured with the 6 pin knock sensor connector connected and disconnected (electrically doesn't make a difference according the schematics).

btw, does anybody know where connector s51 is (EC schematic below) is located?

also along with my power balance test i was able to determine injector operation by supplying power to each injector. #8 did not operate just as the power balance test showed.

i've already ordered all 8 injectors, knock sensors, harness, pcv valves and gaskets(tb, iac, egr). i'm going to do a complete plenum job (except replacing hoses as they are all fairly new). i'm also going to replace the valve cover gaskets, spark plugs and clean everything.

I am at work so I don't have time to break down this procedure now, but I will (if others do not beat me to it). Basically you are doing it wrong, sorry. With the injectors isolated (harnesses disconnected) testing from the battery cable will not yeild any results, becuase you need to put your positive lead on the power signal wire at the injector harness.

Think about the concept of a resistance verification test. You need to remove the wires that connect it to the car and measure the component resistance by hooking your meter up in series to allow the meter itself to supply the voltage to your component and the negative lead must be on the terminal that connects to the engine harness. When I get home I will try to make a diagram showing how this needs to be done.

The process illustrated in the above quote will not measure anything unless you are trying to measure the resistance of the power circuit (power is always supplied, and the ground is supplied to operate the injector).

[maxnix]

Basically you are doing it wrong, sorry. With the injectors isolated (harnesses disconnected) testing from the battery cable will not yeild any results, becuase you need to put your positive lead on the power signal wire at the injector harness.

Think about the concept of a resistance verification test. You need to remove the wires that connect it to the car and measure the component resistance by hooking your meter up in series to allow the meter itself to supply the voltage to your component and the negative lead must be on the terminal that connects to the engine harness. When I get home I will try to make a diagram showing how this needs to be done.

The process illustrated in the above quote will not measure anything unless you are trying to measure the resistance of the power circuit (power is always supplied, and the ground is supplied to operate the injector).

Yep, operator error.

Now report back the resistances for injectors and KS. You only need to replace #8 if KS are fine. However, it is nice to have the plenum out of the way when replacing valve cover gaskets. And if it and the lower runners, EGR and IAC valves were not cleaned to spotless last time......

[franknitty69]

probably operator error. i've never done this before (ohmed injectors) so i don't know if i'm doing it wrong. anyways i believe (according to the schematics) that s51 must be connected for you to ohm injectors. i believe that s51 is one of the connectors next to the 8pin injector harness. when trying to ohm, i unplugged all the connectors, because my 8 pin is on the bottom. i have to unplug the 2 above to get to the release tab of the clip.

i'll verify this weekend, before i rip apart the plenum. if that is the case wes might want to add that caveat to the instructions.

i love this forum, there isn't any other make/model of car that contains so much wealth of knowledge of available on the internets.

[maxnix]

i love this forum, there isn't any other make/model of car that contains so much wealth of knowledge of available on the internets.

\It truly is one of the joys of owning these cars. Reading the previous posts is so informative. I have started going back to the early ones to refresh my knowledge and to reacquaint myself with old friends who are no longer here.

[Denver90Q]

Finally figured it out! The ignition switch switch needs to be on to test 1995's injectors (unlike 1990 where there is always power to the injectors). Duh! Guess the injector was ok and just a bad connector. So used to the high failure rate on the 1990. I figured it was likely the injector coil. The dealer wanted to charge $1000 to replace #4 injector and told me it had failed open! A simple ohm check confirmed it was ok. Another $100 Consult hookup fee for nothing, but at least the jack-offs didn't get my $1K.

[Q45tech]

One of the advantages of buying 25+ junker customer Q is a ready source of parts..............like harnesses and connectors.

Every shop has a set of adapters [made from harness] that plug into injector connectors that simplify ohming injectors and a separate KS + coolant sensor emmulator.

The above points out that you should use and check/compare the exact year FSM as there may be changes.

[fixer]

if you connect one of the ohm meter probes to the battery and not getting reading, then you must have the 4 pin connector disconnected. the injectors are grounded through the 4 pin connector located next to the 8 pin shown in the above pictures. excuse me but not grounded but common power seeing as you would connect to battery positive. when I ohm injectors. I use one end of probe on top left hand connector pin of 4 pin connector and other end on injectors 1, 3, 5, 7. then I would connect one end of ohmmeter probe to bottom left connector pin of 4 pin connector and test injector 2, 4, 6, 8 on the 8 pion connector. the connector pins on the 8 pin connector are as follows. starting from top left as you looking at it , 1764, bottom row 8352. I hope that helps

[Denver90Q]

Didn't see where the '95 FSM said to turn the ignition switch on. Must be in Japanese engineer code. There is however a step to check voltage thru the four pin connector by turning the switch on. Also, I'm pretty sure I was able to get ohm readings on my other 1995 which I sold w/o turning on the ignition?

Actually, the connector was likely just loose or corroded as it came off easily when I checked it at the injector. I would have never been able to get the #4 connector back on my 1990 without loosening the plenum first.

[Q451990]

Also, try it with the ignition switch turned on. There is some talk that the injector circuit may be switched on the later models, but I haven't confirmed it.

Finally figured it out! The ignition switch switch needs to be on to test 1995's injectors (unlike 1990 where there is always power to the injectors).

I'm glad that you confirmed this! We need to update this on q45.org

There was a theory floating around for a while that the constant power on the injectors in the earlier models caused electrolysis through the water in the ethanolized fuel and resulted in the injector failure - but that has never been confirmed. The essentially equal failure rate in the OEM phase II injectors since the widespread introduction of E10 also seems to disprove the theory too.

Heath

[jimbyjimb]

While on the subject how are the injectors in your car doing? Everything peachy? I'm curious to see how these hold up over time. Hate to ditch my Q for having to constantly replace injectors. Maybe a top feed system is in order.

[Q451990]

So far so good on the BWDs. I don't have that many miles in service yet though... so it's not a great sample.

Heath

[Jesda]

This thread is awesome. THANK YOU all for finding this information! Updating the article...

[tashmore1]

On early model Q45 the plus side of the injectors are hard wired to the +12v source (+BATT terminal). On later model Q’s to connect the plus side of the injectors to the +12v source the ignition key must be turn to the ON position. The injectors can now be ohm at their (-) side (found at the injector harness eight pin connector) To the injectors plus (+) side (found at the battery plus terminal). An electrical activation test for the injectors can also be performed by turning the Ignition Key to the ON position and listening for a tick at each good injector while connecting each pin of the injector harness 8 pin connector to the BATT negative terminal (-12v). Contact at each pins should be brief.