Hmmm.... That Shouldn't Be?

"Brickman" (legomaniacman) 03/28/2016 at 12:49 • Filed to: None

0

19

So im testing continuity on my 96 Caravans PCM. I put one lead on the coil #1 pin and I touch any ground pins I have continuity (beeps). Put the lead on coil #2 and I have none on the pins or any others.

When I tested the coil plug with my 12v test light (red wire to batt + and neg to sensor wiring), the #1 wire would stay lit, even while cranking and without the key in the ignition!

The #2 coil wire stays off with the ignition off, and flashes as the engine is turning over like it should.

So with my diagnosis I suspect the ignition is grounding out in the PCM preventing me from getting any spark. I removed most of the wiring harness to look though any wires that could be worn, touching the chassis or anything. Ohmed out every wire from the 40 pin connectors to the sensors they go to, grounds, and all check out fine.

Any further thoughts?

And the pin outs for the connectors.

KatzManDu > Brickman 03/28/2016 at 12:55

0

PCM fried?

Brickman > KatzManDu 03/28/2016 at 12:56

0

Possibly, but just the ignition part. Everything else works fine

Dash-doorhandle-6 cyl none the richer > Brickman 03/28/2016 at 13:00

0

mmm, technical. You got access to a pick-a-part pcm for cheap to check against?

Brickman > Dash-doorhandle-6 cyl none the richer 03/28/2016 at 13:02

0

Nope, best bet is to order one. It’s about $200. They even put the VIN and milage in.

Dash-doorhandle-6 cyl none the richer > Brickman 03/28/2016 at 13:06

0

Just check all ground wires to everything before you shell out money. My old honda ate money and sensors and it was a ground that looked ok but was hiding corrosion.

JGrabowMSt > Brickman 03/28/2016 at 13:12

1

If I’m reading this diagram correctly, you have the wrong pins circled.

That said, it’s possible there’s an internal fault to the PCM, but you’d have to open it up to find out. Opening it means that 1) the waterproof seal will then need to be replaced and 2) the gel inside will likely break apart.

You may find that it easier to search for a U Pull or an ebay junkyard that would just have a “new to you” PCM. Those Caravans still have the “black key,” meaning they pre-date the Sentry Key systems, so swapping a PCM shouldn’t leave you with the resulting bill of a tow to the dealer, plus an ECU unlock, VIN programming and changing the key to match.

JRapp: now as good as new again > Dash-doorhandle-6 cyl none the richer 03/28/2016 at 13:37

0

Agreed. And extra ground straps never hurt anything either. Helped stabilize the idle on my Fiero once upon a time.

Scott > Brickman 03/28/2016 at 13:37

1

First what is the primary issue you are trying to fix?

Also are you measuring to the PCM, or out to the coils? I am assuming the later, but it is not entirely clear.

Also be careful trying to use the continuity check on relays, coils, solenoids, etc. Continuity is intended for testing diodes, and wiring, so it will beep if you have very low resistance. While a coil is basically just a wire, it can have high enough resistance that the continuity check will fail, but the coil is still good. In fact I would be more suspicious of the one that showed continuity, it may be shorted, and that is why you get continuity. That's not to say it is not, coils are often borderline, so both could be good, but one is just low enough to give continuity, the other just high enough it does not.

Personally I prefer to check everything with a Multimeter, and have an actual resistance measurement in ohms. I almost never use the continuity test. Assuming the 2 coils are the same, at least electrically then you can compare the resistance of both coils. Even if not identical eclectically, you should expect a low resistance, but not a dead short. Also it should not have a very high resistance, and obviously not be open.

Since it sounds like you have, or suspect you have an ignition issue, I am assuming you have done a basic spark check, at all your spark plugs, and this has failed? Just wanting to make certain the basics have not been skipped.

Brickman > Dash-doorhandle-6 cyl none the richer 03/28/2016 at 14:06

0

Went through all that. Everythings all clean and tight :)

Brickman > JGrabowMSt 03/28/2016 at 14:33

0

Thats the connector pin out. Mirror it and it’s the PCM. I matched the connector wiring to the PCM pins to make sure. :)

I took the three screws out, motherboard is covered in red silicone and theres no seal under the black plate I removed, has some dirt in there.

Dash-doorhandle-6 cyl none the richer > Brickman 03/28/2016 at 14:53

1

Mine was from the head to the rad support, 16 strand copper, looked clean, the 8 down the middle were clean, the 8 touching the crimped on ring connector had some green crud. caused misfire between 25-3500 rpm, and sent all kinds of meaningless codes. I’m pretty good at this sort of thing and that ground took 9 months to find.

Dash-doorhandle-6 cyl none the richer > Brickman 03/28/2016 at 14:54

0

Good luck, looks like you know what you’re yer doing, Electrical problems suck, let us know when you find it.

Brickman > Scott 03/28/2016 at 14:56

0

Diagnosing a no spark issue. Im measuring the continuity of the PCM itself. I have a Fluke 175 multimeter.

I checked the coil, wires, spark plugs, cam and crank sensor, all fuses, relays (even 12v tested them), fuel pump, injectors, all grounds, checked wiring from end to end. I even put new spark plugs, wiring, and coil to make sure that wasn’t it, but it’s not.

For the ignition coil I followed this test:

http://easyautodiagnostics.com/chrysler/2.0L-…

I dont have a spark tester ( I should) I did it the old fashion way of grounding it to the cam cover. Have no spark to any of the plugs.

Checked for 12v for the green/orange wire, which I am getting. Used a 12v LED test light to test for the pulse signals. one wire (blue) I get pulses when spinning the engine, but the other stays on (grey wire), even with the ignition off.

I pulled the wiring harness tape off to check for any broken wires and found none, traced the wire im having a problem with to the PCM. I put a lead from the voltmeter on the grey wire and touch it to a ground or anything metal and the meter beeps. Tried it with the blue wire and nothing. I remove the PCM and test the wires end to end and they ohm out fine. I test the PCM itself and where the grey wire would plug in and I touch a ground pin I get ohms, but not with any other pin.

Brickman > Dash-doorhandle-6 cyl none the richer 03/28/2016 at 15:01

0

Will do. I hate electrical problems!

Dash-doorhandle-6 cyl none the richer > Brickman 03/28/2016 at 15:05

1

I enjoy them when they’re not my problem, I like looking smart when I find it. Hate my own electrical problems.

JGrabowMSt > Brickman 03/28/2016 at 15:57

0

Your connectors are upside down compared to the pinout you posted.

Brickman > JGrabowMSt 03/28/2016 at 16:29

0

No clue why, unless it’s different in a 98. I have a 98 service manual.This is how it fits and correct PCM orientation. The grey wire thats closest to the top of the connector is the coil driver #1. Camera flash didn’t light up the PCM pins too well though. It’s correct in my illustration. I followed the wires to where they go.

Scott > Brickman 03/28/2016 at 18:12

1

based upon what you have said, it would sound like it is indeed the PCM. Always difficult to do a continuity check on a module like that, but I would expect similar results regardless. Most likely both should have some kind of isolator on the output, and it would be the same for both, so they should read the same. As others have pointed out your image is upside down, which does make it confusing to make sure you are checking the correct pins. However, it does seem to be correct, just upside down. the drawing does not help in splitting the connector, in a way that is difficult to make sure which side is which.

Brickman > Scott 03/28/2016 at 18:28

0

I shouldn’t of put those diagrams :P

Thanks. If I know computers (kinda), is that each pin is supposed to be separate and have no draw from any other component. Something must of opened up, cracked solder, or something.

I hope to order a rebuilt PCM in a week or so. If that doesn’t solve the problem then I might just sell ol eggmobile :(