Injectors stuck ON

[alexofnazareth]

MS3 v3.57 built by DIY, 2002 Saturn SL1

Hey guys,

I was driving around with a friend for a few hours today tuning the VE map without any issues.

I parked the car for a bit and when I went to start it again, it wouldnt turn over. I pulled the plugs and geyser's of fuel came out. So I probed each injector connector and 3 out of 4 were at constant 12V.

Im not sure if a setting I changed while it sat did anything .

FullOpenInjector_flooding.msq

What are the likely culprits for this sort of failure?

[jamies]

its your wiring - you have constant power to the injectors instead of coreectly wiring them through an ignition triggered / ECU fuel pump output triggered relay

[elutionsdesign]

ECU's ground the injectors to fire them so you will see constant 12V at the injectors on BOTH terminals with the key on at rest. Only three of four means you do have a wiring issue, then you have something grounding them to squirt fuel.

[Tinkers Toy]

The injectors always have 12V by design and Megasquirt is ground switching. I had a similar problem when I reinstalled an engine cover over my wire loom. I pinched an injector ground and it was constantly on (remember the grounds run from MS to the injector) . It put so much fuel into the exhaust that I had a puddle of fuel on the ground below the muffler. Check for a pinched or rubbed injector wire from the MS to the affected injector that might be toughing ground, that would leave the injector constantly on.

[alexofnazareth]

I went ahead and recorded a video to show what Im seeing. I was grounding to the body to show what voltages where being provided on both sides of the connector.


This is what I am seeing:
https://www.youtube.com/watch?v=2uS2gGG ... e=youtu.be

First MS3 Second MS3
+ Pin - Pin + Pin - Pin
Cylinder1 13v 0v 13v 3v
Cylinder2 13v 3v 13v 3v
Cylinder3 13v 3v 13v 3v
Cylinder4 13v 0v 13v 3v

The second MS is consistent, but I'm still confused why there's positive voltage being read on the ground wire going to the MS3.

[billr]

Probing the harness sockets when the harness is disconnected from an injector is largely meaningless. You need to sneak a needle or small wire into that connector so as to read voltages while the injector is connected. In that condition, KOEO should show 12V from ground to either wire. When the engine is cranking/running the "power" wire to an injector should show a steady 12V (again, to ground) and the wire going to the injector driver should be at 12V with quick pulses to near-zero volts; a varying DCV. These pulses are easiest to see using an ACV range, and will yield fairly low ACV, I'm guessing in the <1VAC range at cranking speed. Not cranking/running, that should be zero ACV (and 12VDC).

[mike_tosen]

Check for continuity to ground on the pins that reads the low voltage.
Those should not read continuity to ground.
If you read continuity, unplug the harnas from the ms box, and check again.
If it still reads continuity to ground, you have a wiring problem.

[alexofnazareth]

Check for continuity to ground on the pins that reads the low voltage.
Those should not read continuity to ground.
If you read continuity, unplug the harnas from the ms box, and check again.
If it still reads continuity to ground, you have a wiring problem.

Ill give that a try. Otherwise I'll have to snag some injectors from the Junkyard just for testing purposes [Id rather not have to take the current ones out or leave them hooked up to the fuel rail]

[turbo conversion]

its your wiring - you have constant power to the injectors instead of coreectly wiring them through an ignition triggered / ECU fuel pump output triggered relay

Do you have voltage to the injectors with the key off.

If so this your problem, the positive side to the injectors has to be switched off with the key.

David

[alexofnazareth]

Back at it again. I found this thread explaining that seeing 12V at both sides of the connector is to be expected (injector will not fire).
If there is a lower voltage on the ground side(MS3), then the injector will open because the differential.
2 & 4 have 12v on both sides (Key On, Engine off).
1 & 3 have 12v on power side and 4v on ground side.

My wiring checks out for the injectors. It has to be the megasquirt, however, both of my MS3s are doing this.
That kinda rules out something being burned up in the MS, so Im wondering if there is a setting that is messed up.

Also those cylinders arent flooding anymore, theyre just dead now.

[alexofnazareth]

And i just hooked up the other MS and its no providing any voltage to the ground side of the connectors on 1 & 3.

Im officially frustrated.

[billr]

Understand, the MS does not source (provide) any voltage to drive the injectors; it connects that "ground side" to... um, ground.

So, with key-on, engine-off one MS shows 4V at the "ground" terminals for injectors 1 & 3, and the other MS shows essentially 0V; do I understand correctly? I don't think there are any settings that will cause that. You either have two MS units that are bad, in the same way, or your wiring is at fault. I'm betting on the latter. Can you get somebody else to check it, or follow along as you explain where the wires are going? I find that I can "see" things the way I know they are supposed to be, not the way they really are. The only recourse is to step away for a week or so until you forget all you "know" to be correct, or getting another set of eyes on it.

[toehead]

If you disconnect the MS, are you still reading continuity to ground on 1 & 3? With the MS disconnected, both sides of the injector should show no continuity to ground.

[billr]

The OP is doing KOEO voltage tests here, "continuity" (resistance, ohms...) isn't a meaningful test, whether the MS is connected or not. I'm not saying that checking wiring for continuity is always meaningless, only that it doesn't apply in this case. I don't want to get the OP confused...

[alexofnazareth]

Understand, the MS does not source (provide) any voltage to drive the injectors; it connects that "ground side" to... um, ground.

So, with key-on, engine-off one MS shows 4V at the "ground" terminals for injectors 1 & 3, and the other MS shows essentially 0V; do I understand correctly? I don't think there are any settings that will cause that. You either have two MS units that are bad, in the same way, or your wiring is at fault. I'm betting on the latter. Can you get somebody else to check it, or follow along as you explain where the wires are going? I find that I can "see" things the way I know they are supposed to be, not the way they really are. The only recourse is to step away for a week or so until you forget all you "know" to be correct, or getting another set of eyes on it.

I understand that the MS controls ground. I should not see any voltage on the ground side.

To eliminate my wiring having an effect on the result, I cut it from the green and blue injector ground wires. So now its just the MS3 and the DIY 10' harness. I went ahead and recorded another video of what I am seeing:

https://www.youtube.com/watch?v=tXxmJlL ... e=youtu.be

Summary:
the "old" MS3:
2 wires @ 0v
2 wires @ 4v

New MS3:
4 wires @ 4v

I'd love to take a step back for a week, or consult someone around me, but what the current condition is compared to what the condition SHOULD be for what the grounds are showing.

Again, thanks for bearing with me guys. I'm just going to solder on my new injector connectors and see if things behave with the New MS3.

[billr]

With the injectors disconnected, the voltage readings at the MS are meaningless. You have to have a load connected to the injector drivers, like an injector or a dummy resistor acting as a "pull-up" to 12V. Even a slight load, like a 1K resistor will do, and not have to have a high power rating.

[alexofnazareth]

With the injectors disconnected, the voltage readings at the MS are meaningless. You have to have a load connected to the injector drivers, like an injector or a dummy resistor acting as a "pull-up" to 12V. Even a slight load, like a 1K resistor will do, and not have to have a high power rating.

That test I can certainly try.
I was about getting some of those nifty probing pins since household needles didn't do the job[they bend quite easily], but resistors I do have!

Thank you Bill.

[toehead]

The OP is doing KOEO voltage tests here, "continuity" (resistance, ohms...) isn't a meaningful test, whether the MS is connected or not. I'm not saying that checking wiring for continuity is always meaningless, only that it doesn't apply in this case. I don't want to get the OP confused...

Understood.

I also didn't realize that the injectors were disconnected. My point is that if the MS is disconnected and the injectors connected and powered at 12V, you should be getting 12V as well at the injector pins on the DB37 (No voltage drop over the injector without current flow). If you get significantly less, it points to wiring issues.

[alexofnazareth]

How hot are the injectors supposed to get?
Because I plugged my 4 spare injectors in and let them sit and they got too hot to hold for more than 10 seconds.

Also I re-did all the wiring to the injectors with no change in results, still only running on 2 cylinders.

[billr]

Are these high-Z or low-Z injectors (what is the DC resistance of the injector coil)?