Originally posted by ez
No doubt Terry, I would love to have one of those. I'd like to get my hands on one just to understand the behavior of the stock ECU. For example, how does the ECU know there is an issue with the injectors even if you put the correct impedance on the injector output wires? It would be great for those of us who want to piggy back the stock ECU and not go MS, for the purposes of CEL-EXTERMINATION...

Depending on your method of loading the injector wires, it could be as simple as sensing the difference between a resistive and inductive load.

Its not inductive or resistance. Its the ECU realizing that as it shortens pulewidth the afr doesnt change.

Interesting. So in order to keep the ECU from firing a code, the O2 sensor also has to be intercepted and some logic algorithm input so that as PW decreases, O2 voltage changes by a specific amount.

Originally posted by ez
Interesting. So in order to keep the ECU from firing a code, the O2 sensor also has to be intercepted and some logic algorithm input so that as PW decreases, O2 voltage changes by a specific amount.

which will cause a check engine light for too lean/rich. it's a circular problem.

my fix, remove the damn bulb or rewire it so that it only comes on during the initial startup

Originally posted by Star Turbo Talon
Its not inductive or resistance. Its the ECU realizing that as it shortens pulewidth the afr doesnt change.

Not to stray too far off-topic, but what about in open loop mode?

That might be an idea paul!

Let me see if i can split this topic because i think we have a great concept going here.

Originally posted by VelocitaPaola

Originally posted by ez No doubt Terry, I would love to have one of those. I'd like to get my hands on one just to understand the behavior of the stock ECU. For example, how does the ECU know there is an issue with the injectors even if you put the correct impedance on the injector output wires? It would be great for those of us who want to piggy back the stock ECU and not go MS, for the purposes of CEL-EXTERMINATION...

Depending on your method of loading the injector wires, it could be as simple as sensing the difference between a resistive and inductive load.

Actually he's right, as far as the injector/circuit malfunction codes. I've got an injector simulator i put on when I was using an emanage, and it's just a black box that simulates load on the injector's circuit, and the codes went away. And maybe the scanner cartriges have been like that a while, but we had seperate asian, domestic (thru '99), domestic (96-'01), blah blah blah. We just got the 7.2, then up'd it to the 7.4. By new I meant the 7.4, I'm assuming it's been around a while to get to that version! lol Tried those autoxray, and otc, and they're crap. I suppose i just say it's okay mainly for that refresh rate, having the graphin attachment would probably make a huge difference if it's more real-time *shrug*.

Well if you think that works all you need to do is hook up the injectors to the factory ECU and tuck them someplace in the engine bay. Let the MS control the 4 in the intake. After 20 mins you will have injector circuit codes. Done believe me, then go try it.

maybe it's somethin again with the '95 ECU then, but 8 months with this and no codes. I've got every other code under the sun egr, coil, etc, - but not injector! lol

First of all, thanks to Terry for splitting up the old thread so that this could stand alone. This topic deserves some good discussion. Fortunately I see that there are already some smart people involved in this thread - so to keep the ball rolling...

Question for Paul - Are you suggesting keeping the ECU in open loop forever? Pursuing this route concerns me a little, because isn't this in itself grounds to flunk sm*g? (Or is the ECU not checked for being in closed loop during the diagnostic dyno run?)

Question for Terry - Can you possibly give more details on what you saw when the injector code was thrown? What year was the ECU that you looked at? What conditions was the car under when the code popped up?

Comment for Justin - Actually, that's kind of what I was expecting from a 95 ECU. We should be specific in this thread about separating the OBD-1 ECU from all the other years that had OBD-2.

FYI, I have a little birdie that gave me some info from a Satan insider. It confirms what Terry is saying, that the stock ECU is sending a different pulsewidth and expecting the O2 sensor to respond in a certain way. Unfortunately, this person wasn't allowed to divulge too much info.

So what I'm looking for is some empirical data showing us what exactly is happening when the code is being thrown. Is this a diagnostic test that the ECU does at certain times (analogous to the EGR test the computer performs at *specific* times, with expected *specific* sensor signals.) For example, the EGR test is performed during cruise, causing hot exhaust to recycle into the engine, displacing oxygen, thereby causing the O2 sensor to respond in a certain pattern. Now, does the injector issue arrive after a certain diagnostic test is performed, or is it monitoring for this event all the time, or is it only under certain driving conditions (like decelerating or a decreasing load where the pulse width is progressively becoming smaller.) Terry you may be the only one with enough experience on this to answer. I'm talking with a lead engineer from a major player in the aftermarket world, and any insights would be of great value.

Originally posted by ez
Question for Paul - Are you suggesting keeping the ECU in open loop forever? Pursuing this route concerns me a little, because isn't this in itself grounds to flunk sm*g? (Or is the ECU not checked for being in closed loop during the diagnostic dyno run?)

No, it was purely hypothetical. I only mentioned open loop mode because the ECU supposedly disregards O2 sensor feedback at that point. Injector pulsewidths are solely determined from internal data and thus the ECU shouldn't have anything to which to compare injector efficacy (except for possibly reverse EMF from an inductive load which would be absent with a resistive load, though I somewhat doubt the ECU's capability of sensing this). I believe you're right in that the ECU must be in closed loop mode for any sort of diagnostics information to be obtained.

Originally posted by ez
We should be specific in this thread about separating the OBD-1 ECU from all the other years that had OBD-2.

Better yet, FCC from SBECIII.

Originally posted by Star Turbo Talon
Well if you think that works all you need to do is hook up the injectors to the factory ECU and tuck them someplace in the engine bay. Let the MS control the 4 in the intake. After 20 mins you will have injector circuit codes. Done believe me, then go try it.

I never did. I had four dummy injectors installed when I was running a Gen 6 DFI, and never had a CEL for inujector circuits.

It was a '95.

The 97 I have is smart enough to throw injector circuit codes when 4 dummy injectors are hooked up but it did take about 15-20 minutes to throw the codes.

I tried resistors and as Paul suspects the inductance of the coils obviously weren't present and the ECU picked it up right away.

Its now apparent the 95's arent that smart which means some of the 96's will also be satisfied but finding which ones will be trial and error. Here in IL 95's are a mute point, we dont test them anymore.

Terry

Yeah the CEL isn't checked on mine anymore for inspections, some still try to pull it on me but I'll more than generously point out it's a 95 that only needs an ASM test and then it's all good. I may as well pull the bulb out...