A little stuck getting started

[mjensen]

I have a '91 TBI 350 with the 1227747and ARJT chip that I am swapping into my '69 GMC. I have modified the harness (which is why I'm here LOL), and have tried to fire it up. The issue that I'm having is that I'm not getting an injector pulse. I know there are several posts about causes for that, and I've been through all of them and everything checks out. So, what I wanted to do is to hook up to the ECM to scan and see what I could be missing. I really need to figure out whether this is a wiring issue, or an ECM issue. My issue is that when I hook up to the ECM, I'm not getting any readings. Attached are a couple of screenshots of what I'm seeing (winALDL & putty). Just looking for some advice on what to check next.


11530
11531

[mmigacz]

Are you using a TBI distributor (Or a TBI ignition module)?

[mjensen]

It's using the stock TBI distributor that was in the Blazer.

[Six_Shooter]

I'd download Tuner Pro along with the correct ADX for your application and use that.

WinALDL seems to be hit or miss as far as getting good data.

And do you mean 1227747?

Do you have spark?

Does the fuel pump prime, and does it turn back on when cranking with the OPSU (Oil pressure Sending Unit) unplugged?

[mjensen]

Haha...Oops yes. I have Tuner Pro RT, and it's not pulling any data either.

I have spark (it will run when spraying carb cleaner)
All relays kick on (fuel pump runs while cranking) - I have not tried with the OPSU unplugged
Noid light on the injector harness indicates no signal from ECM
Replaced Ignition module
Traced every wire (found some issues and corrected)
Tested all voltages and resistance through the wires

This is why I was hoping to scan the computer to see what signal I could be missing, but I can't seem to get any of them to work. I'm starting to wonder if the ECM could be bad?

[mmigacz]

There are two wires going to each injector. The white and red wires should have 12V all the time when the ignition is on. Can you confirm this? The ECM creates the pulse by providing a ground (blue and green wires) to the injector.

lf you unplug the injector and put a nine volt battery across both terminals, you should hear it click. If you try this, only do it for a fraction of a second.

[mjensen]

I have verified that they have 12v and the injectors do click with a 9v battery. I've checked the resistance in the injectors, as well as the wires running to the injectors, and they are well within spec.

[uncabob]

Dumb question, but have you verified fuel is actually getting up to the injectors?

[mjensen]

I have, and we've got fuel. I'm fairly certain that the computer is just not receiving SOMETHING that it needs in order to tell the injector circuit to ground.

[mjensen]

Well, now I can't even get the software to connect to the computer. I'm taking tomorrow off, so I'm going to run over to the local junk yard and pick up another computer. I'm just convinced that I've somehow screwed this one up.

[mjensen]

Picked up a new ECM and harness from said truck. EXACT SAME ISSUE!!! So, let me ask. Can a faulty oil pressure switch, or no oil pressure cause the injectors not to pulse?

[jim_in_dorris]

when cranking, the oil pressure switch isn't used. I ran my truck for years without the oil pressure switch being connected. D14 and D16 from the ECM are what control the injectors A and B. Check for a crank signal on C9. that is what the ECM uses until the engine RPM's reach a running state. You may need an O scope.

[mjensen]

Thank you for your response! That is very helpful to know. One question about the crank signal. Where should the source be coming from? Is it different between a '91 and a '94? The only constant in all my tinkering has been the distributor, as an fyi. Maybe the issue is related to that (I have replaced the ignition module)

[mjensen]

Got it figured out! When I put the new harness in, I failed to hook up the 12V supply to the injectors...doh!