Testing fuel injector wiring 86 v12 convertible

I pulled my fuel injectors out to check and clean. Before I reinstall them I went to test the wiring to the injectors with a test light, I tested each injector on both A and B banks and I have light. Power to each injector both banks
To further test with multi meter I test the left bank connected through each connector, each one tests 12v, as I test the right bank connected at connector, same way I did left bank, I get no reading. If I ground to bare metal, again I get a 12 v reading but nothing at the terminal alone. Seems to me a bad ground in the harness on the right bank. Is there a common point where the right bank would be bad or somewhere else I might check. If the fuel injectors are installed would it ground through the injector. Thanks for any info

Sorry but I can’t understand your testing process…
Does the engine work?

All injectors have 12V permanently and they are grounded via the ECU when they need to open.
The easiest way to check is with a noid light or a oscilloscope.
An other quick way to check is to turn the throttle turntable fast with ignition on, you should hear all the injectors click once.
The way to test the ground side of the wiring with a multi meter is put one probe at the injector side and the other at the corresponding pin of the ECU plug and check for continuity.
Also, if a ground wire shows 12v it means you have a short circuit somewhere.

Hope that helps.

Thanks for the info. What I was saying short version is no ground on right bank. Light when testing with test light grounded to bare metal on both a and b banks. No light when testing B bank grounded through connector. Multi meter testing shows same situation, no ground on right bank. Is that the only ground for B bank located in the ECU. I will check wiring at ECU to determine wiring or ECU fault. Thanks again.

To answer your question further. I have had it running but never good enough to even move it without stalling. It was taken off the road in 2009. Previous owner said it was running when he stored it. After broken wire repairs, mouse chewed pickup wires in valley, broken wire in steering column for anti theft (long time finding that problem)clean all grounds I could find, clean sump,new injectors, new filter, new spark amplifier,coil, wires,cap. 1 1/2 plus years off due to health issue I’m itching to get it moving again. Thanks Rod

This is how it’s supposed to be.
The ECU grounds the injectors. You would see no ground when the engine is off, you would see a pulse with the engine running.

I presume you talk about the positive lead, which means both banks see 12V and it’s correct.

Again, there should be no light.
If you connect the test light at the plug terminals and the light is on you have a problem, it means that the ECU is grounding the injectors permanently. It could also be that the ground cables are shorted to ground somewhere, but I doubt it if it’s the entire bank.
If this is the case on your A bank better disconnect all the injectors because they are going to fry…

As I said, connect the test light or the multimeter to both terminals and give the turntable a quick spin, you should hear all the injectors fire once, the light should flicker once or the multimeter should show a spike.

And some useful info:

Between your advice and my playing around testing and retesting I`m beginning to understand this system better all the time. I will install the injectors and see what happens. Thanks for your help

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Well, I found out where some of my confusion was. I was looking at the wrong schematic for what I have. I discovered that mine is the digital fuel injection, not the federal or uk/europe version.

Eureka, success, finally got it running and running well. Cleaned fuel injectors, tested good, double checked coil ,ecu, tested fuel injectors and thanks to Aristides keeping me on track I came to understand the system better, tomorrow I`ll change oil, and check a few other things and wait for my convertible top cylinders to come so I can put the top up and down and finally get it off the dollys. Thanks for you help. Rod

Glad to hear you got it fixed Rodney.
You didn’t say though, what was the problem?

It came down to what I believe is that I had inadvertently turned the motor over last year when I had the distributor cap off, inspecting pickup, making it to be 180 degrees off. Rookie mistake even though I knew better… Not thinking about it until it ran, but not well. This time I had it running and revving for about ten minutes or more watching for leaks and listening. Restarted several times each time firing right up. Thanks again for your help.

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Happy as a clam, finally progress, I went out to my garage ready to move on with my 86 XJS convertible V-12. I thought I would fire it up and revel in my accomplishment, let it warm up before draining the oil. AAArgh, no start, right back to where I was a week ago. Cranks over, fuel to and from rail, test for spark at B3 cylinder (easy access) had blue spark but didnt seem strong to me so I tested at the coil with screwdriver 1/4" from ground, no spark, same test at 1/8" no spark, I tested at less than 1/32" hardly any gap, finally a spark so Im thinking bad coil. I tested the coil according to my manual and it tested ok but on the lower end of the scale. I tested the old original coil and it tested the same as the new one in the car. I also tested the secondary coil (not connected but still there) just for the heck of it and it also tested the same as the other two. Can any one give me a better explanation or another idea of what Im seeing or should I say not seeing. I also have a new coolant sensor as gregmo suggested. It is acting like it did before the last time I started over. Could I have ruined the coil from one day to the next because of the spark gap then have it recover on its own to start, then not start the next day. this happened the last time too. I am stumped again. Any help again would be appreciated. Digging deeper tomorrow. Thanks Rod

One more quick question. I had the secondary coil hooked up while it was running as well as the main coil unintentionally oops. When I tested main coil alone I had gotten primary readings of 1.1-1.31 ohms with a secondary reading of 6000-7000,.with second coil connected primary reading was .7ohms. would the lower reading affect the output of the other coil or would they even each other out. Thanks again Rod

Coils is a bit of a gray area forme as well, @Frank_Andersen is more of an expert on this.
But I think that the two coils are connected in parallel, so the difference in the resistance readings you get would be correct if this is the case. Look at the wiring diagram to verify, and there are lots of posts on the archives about coils misbehaving.

The second coil is there because at the time there was no single coil capable of supplying 12 plugs with enough spark above 3.500rpm.
Later engines have a single coil.

An other common culprit for this kind of intermittent problems could be the Ignition Amplifier Module, an easy and inexpensive fix. If you don’t know the history of the one in your car it’s highly recommended that you change it anyway. Get only the GM module.

Good luck.

Frustrating, Put old coil back in with old secondary coil also installed just for the heck of it. Nice blue spark from coil to ground 1/4" away. Spark at plugs. No start again. Put old spark amplifier back in, again just for the heck of it. Still good spark. Installed in line gauge for fuel pressure to monitor fuel pressure 38lb pressure while cranking, when key is switched off holds at 30lb. Seems to be no problem there. Anyone with any ideas. Should I be thinking about another ECU yet? I`ll be checking fuel injectors tomorrow and wiring, again. Thanks for any insight. Rod

I had some odd it runs/it doesn’t run two years ago. After testing/fixing everything else, i guessed it must be ECU, and it was. But that could be an expensive test. I would double check everything, and also check continuity from sensors to ecu, before looking for another ecu.

For the heck of it, i just went ahead and bought the new replacement coil that allows you to remove the secondary coil up front. Much easier setup.

And just throwing this out there, but all this trying to start and only running 10 minutes, is your battery fully charged? This engine needs a fully charged battery to start. I would trickle charge mine a lot when i was going through diagnostics.

Could very well be the case. Had the same intermittent no start and it was the ECU.

Unfortunately the only way to check it is with a known good ECU.
As Greg said you should eliminate all other possibilities before.
Are your injectors clicking while cranking and no start?
Also check the Throttle position sensor. Details in the Book.