Socal_Tom

Hope everyone is (hopefully) having a good day off, if that isn't overly US-centric of me to say.

Tried to do some testing on the Fi harness today to confirm it is at least one of my issues.

Here are the results;

0 is no resistance on the ohm meter
OL = infinite



Any ideas / comments?

Thanks!

dr bob

Tom,

What meter are you using? Checking resistance through the LJET box is a crapshoot with an analog meter, for instance, since it uses DC as the sample/sense current tp push through the component under test. Your 0/OL, and flashing 0 results are a little suspect too.

The injector harness has two conductors, each going to one pin in each of the eight connectors. So the results you see in any connector should exactly equal the results you see in any other connector. The only thing is that the connectors are, in theory anyway, not polarity-sensitive. So at any connector, one should read zero Ohms to the injection relay. The other should be open or OL to ground, no continuity at all. The no-conductivity connection in each connector should be zero Ohms to one of the pins an every other connector. If that makes sense...

SwayBar

Here is an excellent thread on troubleshooting a no-start situation, lots of tests for the LH. Follow them step by step, and you should find your problem:

https://rennlist.com/forums/928-foru...diagnosis.html

Socal_Tom

Thanks for the responses gentlemen, hope you both had a good weekend

Doc - I'm using a standard multimeter, not a two dollar one, which as far as I know is working fine. Battery is fresh. Agree that that flashing reading is odd.


I was mainly concerned to see if the readings responded to my moving the harness around, and they did it a couple points. I was also keen to see if there were the difference in different injectors for one another, and the fact that 1-4 is reading differently than 5-6 seems pretty note worthy.

I think I'm going to have to return this new to me, but used harness, and send my original one for repair to one of our go to vendors.

As others have noted - 30 years of heat soaking has not helped these and who knows what sort of life the cars lived before we acquire them.

FredR

Presumably you are working on the 84 S?

If you are testing the wiring harness then the first thing I would do is disconnect the plug to the L-jet. Nothing wrong with testing across the terminals with the plug removed- it tells you something but arguably not a whole lot. For sure I would also be testing each core for resistance from the injector plug back to the L jet plug - trust I am not missing anything.

As Dr Bob says, the values you got with the plug connected are very strange. The system is batch fired [i.e. all at once] so whatever values you get they should be consistent if nothing else and you need to establish why that is not the case. Whether there is a scenario where 1/4 can be different to 5/8 I know not- are you running on 4 cylinders by any chance? Presumably you have some issue that sent you down this path.

dr bob

The injector values (raw without anything connected) look fine.

The readings in the harness need to be taken with the harness completely disconnected, for the basic continuity and for short-to-ground. The challenge with testing the harness with just the meter is that the meter uses a very small current when testing for resistance. If just one or two of the tiny strands inside the wire are intact, the meter will show the same zero Ohms as it will with all the strands intact. The only way to test it then will require adding a load and testing for voltage at the load.

Ideas:

Figure out how to connect your meter to each injector connector so you can read voltage with an injector plugged in. Kind of like the 'noid light but with test points on it in addition to the LED's. Then go to each injector connector one by one, and plug in an injector and connect the volt meter in parallel. Using a separate power supply, inject no more than 10 Volts at the controller end. Verify voltage at the injector end is very close to the same voltage you are injecting. Any difference is caused by resistance in the wiring. The injectors are batch-fired so all the connectors are in parallel, but the way the harness is built has them ganged on each side then common. A weak wire section or connection on one side can affect one or four injectors, depending exactly on where the fault is in the circuits. There's no reason to believe that the harness has just one fault, or that the one or many faults are isolated to one circuit or the other from the controller.

Next, Second Option and maybe the better one (what I would do anyway): Once you have the old harness out for testing, you also have it out for rebuilding. Replacement injector connectors are readily available either with just the pins or with pigtails. If you have or have access to the correct crimping tool for the Amp-style pins, go with the just-pins option. Ideally you'll want to find some color-correct wire for the project to do it just right. If possible, get marine grade wire that is very fine-strands individually tinned inside the jacket. Or get with Greg/Mark/Roger/Sean/Carl to see if they have an upgraded replacement harness you can drop in. The value of getting a known-good piece with the connectors correctly crimped onto the better modern wire can't be overstated. I think Sean mentioned once that he's using the tinned-conductor marine wire throughout his/Roger's harnesses. Other folks may be doing this too.

Socal_Tom

Agree, too many variables and even if I got it going why know what other demons are lurking in there. The one that was one the car is going out for a rebuild today. Returned the other one with my testing results noted.

Thanks!