Diagnostic port Troubles
 

So, my 86 GXL is experiencing Lack of the ability to idle after a 15-20 year no start.

Compression seems good. Coolant seals also seem good thus far.

The problem is when I plug my LED Diagnostic tester into the DIAG port, and key to "ON" I do not get the standard light up for a few seconds LED.

I moved the ECU to my other FC, which is an 87 base, and it fires the Diagnostics LED as it should for a few seconds then shuts off. My Base FC is known working fine and I drive the hell out of it.


The Previous owner has taken the drive-train out of the car at one point, but it has been re-installed and gone through IMO really thoroughly. I cannot find any loose grounds to speak of and the car seems to run over 2k rpms.

What could be causing this?

Does the Black/White wire in the diagnostic plug have 12 volts w/key to on? If it does then you could do a continuity test on each of the other wires in the plug and one of the ECU's plugs. The Yellow wire is pin 1D. The Y/R wire is pin 1B and the Y/B wire is pin 1A.

I just checked it with the ecu out of the car, and I have 12.4v at the BLK/W wire with key switched to on. not sure I need the ECU plugged in or not. I'll perform a continuity test after work. thanks for the quick response satch.

The B/W wire powers the ECU. If the ECU was connected previously and the car would not start then the ECU would need to be connected for testing purposes as it relates to the B/W wire, otherwise it would not need to be connected.

Alright. I'll test that again with the ecu plugged back in the car. The car does fire up and runs "kinda" over 2k rpms. This is what prompted me to check the diagnostic port to begin with.

Also just so I am clear and not fry my ecu ( I am fairly novice with wire troubleshooting, yet work on electronics all day long. go figure) When you say continuity test on the ecu and plug. are you saying unplug the ecu from the harness and put one probe on the ecu pin that corresponds with the wire at the Diagnostic port?

Also I imagine this is with key off?

Sorry if this seems dumb and obvious. I know how to check voltages, but continuity is fairly new to me. I gather that I probe one end of something, and probe the other end and see if electricity can get from point A to point B.

EDIT: I looked it up on google, looks like I back probe the ecu plug and then probe the diagnostic connector at the other side.

I'd hold on for satch's response if you're not sure.

You're checking for continuity on the yellow and yellow/red and yellow/black wires between the diagnostic plug and ECU plug. I'd say key off, ECU unplugged, but let satch confirm. Maybe it makes no difference if it's plugged in and backprobed, but I'm not sure.

When testing for continuity/ohms you always make sure there is no voltage on the wires being tested. Also, you make sure the plugs are disconnected from whatever they are plugged into if anything (in this case it's the ECU). And when looking over the ECU plug make sure the wires being tested aren't pulled back and thus not making contact w/the ECU when it is plugged in.

After you check for continuity you can reconnect the ECU plug and test for voltage on the 3 pins. 1A should have below 5 volts for the first three seconds after the key is turned to on and after that it should register 12 volts. Pin 1B should behave in the same manner as pin 1A. 1D also should mimic the other two pins.

W/respect to the rough idle the fuel pump, fuel sock, fuel filter, and injectors should all be either replaced or serviced in addition to the fuel tank being drained and cleaned.

Thank you satch for the update. As for the fuel. New (used but clean) fual tank, brand new fuel pump/sock, new filter, injectors sent out for rebuild and flow tested. I also cleaned out the fuel lines. Fuel system is for all intensive purposes brand new. It was one of my biggest concerns on a 34k mile car that sat for 20 years. I have ripped this thing down to the keg to clean /replace everything that had fuel/coolant going through it.

Even flushed out the radiator, heater core, and keg itself. Im suspecting some loose and faulty wiring myself, but we will see tonight when I get off work to test it.

I will check the FSM for what the ohms should be plug to plug.

thanks again ~!

In doing a continuity test all you need to know if there is continuity and the meter will sound out if there is, thus you don't really need to measure the actual ohm value. If you do check the ohm reading then set the meter to ohms and the reading should be really low.

Also, there might be some carbon deposits within the engine from sitting all this time and the exhaust might also be somewhat restrictive from being clogged.

carbon would be a concern. Exhaust is from my other FC. newish and free flowing. I did a restoration more less to bring the cars systems back to how a 34k mile car should be. very pristine. I did take out the 5/6 ports and clean them up, they barley moved when I had the LIM off from being so jammed with carbon. They spin nice and free now (even though im more worried about idle then 3800rpm)

Ok, with the edu installed and key on I get .4v at the diagnostic plug b/w wire. That seems problematic

It would appear so. At the main relay are two plugs. Focus on the plug w/four wires. Measure the voltage on the White/Blue wire no key necessary. It should measure 12 volts. If it has 12 volts then measure this same wire w/key to on and see if the voltage stays the same or drops.

Stays the same. Right around 12.34-12.44v with key both on and off.

When you checked the voltage in the diagnostic plug's (B/W wire) did you use the battery negative terminal for the meter ground? If not, then recheck the voltage on the B/W wire w/key to on, again while using the battery's negative terminal for the meter.

I certainly did use the battery ground. Looked like the best choice. I also checked continuity on the edu clip and the diag clip. I think I did it right, the Meyer I'm using doors not make noise, but when you touch the probes together the meter goes to zero. but when I probed the wires mentioned it was zero on all three.

Go back to the relay and measure the Black/Yellow wire w/key to on. If it registers 12 volts then take a short lengthed wire bare at both ends, shaped in the letter U, and jumper the White/Blue wire to the B/W wire in the same plug and verify that the jumper works which means w/no key measure once again the B/W wire in the diagnostic plug and it should read 12 volts. If it does then start the car and see how it runs.

The wire next to the b/w it's blk/green. Same thing?

Don't worry which wire is next to each other. Focus on the Black/Yellow wire w/key to on, and the plug connected to the relay.

http://i1274.photobucket.com/albums/...psoldpcwfr.jpg


Phone is not letting me embed. I don't have a blk/yellow at the egi comp location.

Edit: album public now:

No one mentioned the EGI Comp. I'm talking about the main relay's 4 wire plug. They are B/W, B/G, W/L and B/Y. Post #17 said to go back to the relay as in main relay. Got it?

I'm an idiot. Ok. I confused main fuse and relay. Ok so at main at main relay plug with 4 wires, the black yellow wire does not read 12 volts with key on it is around .4

Then w/key to on check the B/W wire in the 2 wire plug at the main relay. If it reads 0 volts then chances are the 15 amp engine fuse (located in the INTERIOR fuse box) is blown. If the B/W wire reads 12 volts w/key to on then either the Black wire (ground wire for the relay) in the 2 wire relay plug is problematic or the relay is no good.

Right on the money. 12v at b/w wire with key on. Now I just needed to track down where that grounds to. Pm me a PayPal or something. This info is worth it for me to gift something in return.

It could be the relay as well. The ground wire runs to a cluster of ground wires (5 or 6 of them) bolted to the driver side fender between the strut tower and the trailing coil (somewhat below the coil though and removing the coil from the bracket might be necessary to access these ground wires). If that's the problem you can unplug the plastic plug housing the ground wires, unbolt the metal part from the fender's strut tower and sand it down, sand the metal part which plugs to the plastic plug housing the ground wires as well, clean the plastic plug and replug after applying some dielectric grease.

You could also jumper a wire to the ground wire at the relay and ground it to the battery and see if the B/W wire and B/Y wire at the 4 wire relay has 12 volts w/key to on. If it doesn't then either the jumper ground isn't stabbed into the back of the Black wire well enough or your relay is kaput.

And if you jumper the B/G to B/Y and W/L to B/W then you will bypass the relay and the car should start up and also allow you to check for codes if need be. Don't leave the jumpers in overnight for it could drain the battery.