Power coming out of my ECM grounds???

Spent a few hours last couple days tearing apart this complete harness and checking every single wire end to end. Still had 5.xx volts coming out of a sensor ground and an ECM ground. So I pulled the wires from ECM so I could check what was happening at ECM without wires...

Voltage went up a little to 8.1 volts on a sensor ground and a ECM ground?

Power in on Orange wires is 12.xx and so is key on Power on Pink/Black wires, ohm'ed every wire in system to be fine, by now probably quadruple checked all wiring...

1228708 ECM. Green C5 Sensor ground and C6 ECM ground. There are a couple other abnormalities in voltages from the test list but just variables... other sensor grounds are fine. One other abnormality from wiring diagram to this ECM and harness we pulled from car is it had 2 Batt Orange wires going in a D17 which is listed in wiring diagrams. But ECM and harness came with Batt Orange also to C1 which in diagrams says "Not Used" That pin with no wire does measure same 12.xx volts as D17.

Never had dealt with this before? Is this a faulty ECM?

The schematic for that ecm is very similar to the 1227727, at least for power and ground. Ludis / exatorque site has diagrams. Use Ohm meter to check resistance between C1 and other battery supply points... one of them is connected. Sometimes GM uses extra wire with peak and hold injectors.

Measuring grounds... how? Ground connected on sensor end, ecm connected at other and powered up? Measure from block to wire? For C6 that could mean high resistance in wire between measure point and ground. For C5, problem might be due to C6 not being connected properly. Could also be due to poor connection at ecm. Try pulling each sensor and rechecking voltage?

Wrong way to test is to disconnect C6 and measure to ground with ecm powered up. That would show voltage as ECM is looking for ground connection. Could also throw C5 high if C6 is open. Make sure wire is grounded during testing.

Did you ever get spark to work?

Attached is the schematic I've been using for my 1228708 Test Bench.

dave w

That diagram shows the second Batt 12 volt Orange wire at C1, so that helped. Also shows some extra wires I have that are EGR CA only, along with some differences between A and D VIN cars.

Quote:

---

Originally Posted by 1project2many

The schematic for that ecm is very similar to the 1227727, at least for power and ground. Ludis / exatorque site has diagrams. Use Ohm meter to check resistance between C1 and other battery supply points... one of them is connected. Sometimes GM uses extra wire with peak and hold injectors.

Measuring grounds... how? Ground connected on sensor end, ecm connected at other and powered up? Measure from block to wire? For C6 that could mean high resistance in wire between measure point and ground. For C5, problem might be due to C6 not being connected properly. Could also be due to poor connection at ecm. Try pulling each sensor and rechecking voltage?

Wrong way to test is to disconnect C6 and measure to ground with ecm powered up. That would show voltage as ECM is looking for ground connection. Could also throw C5 high if C6 is open. Make sure wire is grounded during testing.

Did you ever get spark to work?

---

I was not measuring grounds during this, I was using the ECM Plug/Pin voltage test sheet as a check when I found the voltage on ECM and Sensor ground. Disconnecting the extra (now known as OK) Batt power wire made no change.

Have pulled each sensor and rechecked. Then ohm'd each wire to each sensor. My first thought was... 5.xx volts on sensor ground? I must have got a 5V ref signal tied into the sensor ground... but at this point there is no signs of that. Harness is all wide open for visual inspection again as well as Ohm check each wire end to end.

Have not even looked at spark since starting these voltage checks...

Going to re-do grounds and recheck today.

I didn't see how you are measuring your grounds? Ohm or Volts? Volts under LOAD is the key and best. Please connect DVOM to the Neg Battery terminal. I've seen a few chase problems in buy-backs for hours where they were using the ECM case to connect the DVOM Grd.
I saw one car that had unusual unwanted voltage on an O2 circuit. Measured o volts key off, key on aprox 8 or 9, running 9. Finally took the harness out of the 87 Monte Carlo with a 5.0L carb and found the harness pass through at the door area that was sealed up and hot glued had chafed wiring connecting together to an ignition wire to the O2 circuit.
These were odd but can happen again. Seen some wiring terminals that were crimped on the wire BUT the end of the insulation was in tact. So connection was very poor. Was an EST wire and would set Code 42 on occasion.
QUAD 4 engines I personally would run a ground strap to the coil cover. The Module gets it's ground there and I've seen a bunch of poor runners.

All the above post was measuring voltages, there were no ground tests. I did ohm wires one by one and wiggled looking for an issue. But I built this harness and know every inch. Doesn't mean something could have gone wrong.

When I use my Scope, DVOM, GMM to check for grounds I connect one side to Batt Neg, then other to whatever being tested and should read 0.00 ohm... if you check calibrate the meter you would touch both wires and should read 0.00 ohm but may be off by 0.001-0.002 depending on meter. Then I move the one connection from neg Batt terminal to where ever the ground is attached to engine and should also be the same reading.

The DIS I'm using is not Quad 4 but from Caviler etc... 87-92. It does have a ground wire. Is there any other issue with this type that would need another ground? It's in a conversion so original mounting plate is not used. Mounted on aluminum plate off valve cover of a Toyota 22RE.

Like this one...

No extra ground for the DIS needed. It's very much liek my 6 cylinder DIS modules. I simply attach the ground wire to teh engine ground and then mount the ICM and coils wherever is convenient. I've mounted them to the firewall, engine block, strut tower and inner fender well, and all act the same way.

Well I'm tidying up, separated a few grounds that I usually tie together just because it's a new to me ECM.

Did the highly technical ECM test from GM and tapped on it... voltages change!!! So waiting for the new, reman GM ECM in box I found on eBay, should be here today or?

Truck would not start from get go but did spit and sputter, thought it was crank trigger timing, NOT, had a relay buzzing and my fault for running power to a ground relay. Still spit and sputtered, then sometimes spark, then no noid lights? Got the wiring diagrams with voltage tests and well it was no good either... Just been a bugger... Quad 4 ECM, four cylinder TBI DIS, my first crank trigger built system. Then wiring diagrams for same car showing differant pins, or added, then VIN A or VIN D... Just not been something I know like back of my hand and, well not thinking clearly do to low calories for months making it hard to think let alone learn new stuff! But with some new meds and a nutrionalist have been eating enough last few days and feeling better, so the plan is coming together. Actually back to enjoying it! :thumbsup: