I have an AF Interceptor, but it does read pulse width.

Whatever the reader, does it measure it, or does it just report back what the PCM is calling for? I assumed it was the latter, so figure I should verify that the IDM is actually outputting what its being told to output.

if the its actually providing a reported reading from the PCM, then my value is standard as compared with my other truck, anyway - nominally 1.4 ms almost all the time, dropping down to ~0.8 ms when the truck is coasting.

the other element to IDM output is voltage, though, right? if either voltage or pulse width are low, the amount of fuel output by the injectors will be lower than commanded, correct?

 

Pulse width is a representation of how long the injector is open I believe.

From what I know the IDM takes 12vdc amplifies it up to 110 VDC which is 120 VDC on the later trucks. This is what powers the armature and forces it in the open position.

So I believe you are correct, but below 110 VDC I don't believe that the armature will get powered/moved and the injector won't work.

 

...or how long its told to be open - a subtle difference.

yep, amplifies the voltage and then shoots it out according to the timing provided by the CPS, via the PCM.

this, i'm not sure about. not sure i'd expect it to be an all-or-nothing event, but this is what i'd be looking to test. say it puts out voltage at 50V instead of ~100V - will the injector open only half as far, allowing just some fraction of the fuel into the cylinder? or, if there is a capacitor issue in the IDM and it can't maintain the pulse width for the commanded duration, clearly not as much fuel would be delivered, thus lower power and lower boost.

this is all just speculation until i'm able to get ahold of a scope. who knows - maybe the PO on my truck even tried the 120V IDM mod, but screwed it up. i'd like to just throw my back-up IDM in there, but if its a wiring issue, I don't want to fry that one as well before testing it all out.

I bet Jim Rosewood, or Justin from DP Tuner (I think its Justin - my apologies, if I have it wrong), would be able to correct my logic for sure though. ...hopefully they come across this thread.

 

Hopefully indeed!

 

My thought is that the armature will only fire with x amount of current, in this case no less than 100 VDC. Swamps has a fantastic article on these IDM's, but a lot of it is over my head since I am not an electrical engineer lol.

 

This may be a pointless post from me but all 7.3s I've drove have accelerated quicker with rolling into the throttle vs pedal to the floor from the get go

 

I would agree with that, but I think our problem is a little more severe than one's habit with the go-pedal. in my case, when the problem is happening - which is more and more often now - acceleration is OK up to about 1/4 throttle, then falls off almost entirely above that point. like something is limiting the pedal position (and thus the power) at that point.

as for my IDM test, I think I may have lined up an oscilloscope, so that'll answer that part of the question.

i'm thinking i'll also start looking into any potential HPOP leaks. for the longest time, I didn't think this would be the culprit, based on ICP and IPR DC readings, but i'm kind of at a loss now...

could the black fuel bowl (just black, not slimy and bluish) that we've both (JM and I) seen be engine oil getting into the fuel system (by means of leaking injector O-rings)? I just changed my engine oil, so it shouldn't come up black again for a while, but is this plausible?

in other words - and correct me if i'm wrong - but the middle o-ring separates fuel from HP oil , then the upper o-ring keeps the HP oil from escaping out into the valve cover area. if the middle o-ring fails, you get oil in your fuel. if the upper one fails, you'd get oil bubbling out from under the injector. right? looking for bubbling oil is easy enough with the valve covers off - a leak into the fuel system would only be diagnosed by a black fuel system, right?

 

I've always been told that black fuel = leaky injector O-rings. Thankfully I have always had just the normal colored fuel in the bowl when ever I have changed out the fuel filter.

 

As far as your boost goes, I would not trust the reading on AF interceptor. I have one plus a regular boost gauge and it does not give a true reading. Back in Florida it is almost dead on with the mechanical boost guage. At elevation in Colorado it was off by almost 4 psi and at start up showed -4. As I head back east (lose elevation it is getting closer to 0 at start up and closer to mechanical gauge). Thought maybe the MAP was bad bought new one from FORD, no difference. Then found AF website/ forums and evidently this is a fairly common issue. Just my 2 cents.

Paul

 

thanks for the heads up paul - sounds like an altitude discrepancy - which the BARO sensor is supposed to account for, but maybe the AF isn't taking that into account.

in other news, for the heck of it, I fired up my parts truck (haven't started gutting the powertrain, but will soon and took it for a ride with the scanguage hooked up. apparently, there is a big difference between 96 and 97 pcm tuning OR something is wrong with my 97 PCM - or I have a small HP oil leak on the 97 that the PCM is not identifying as a problem.

in short, my ICP maxes out at ~2300 and the IPR DC maxes out at ~25% on the 97 truck (the one with the power loss problems). on the 96 truck (the parts truck - with no known powertrain problems, but lots of rust :-) ), the ICP goes up to 3000+ with the IPR DC up around 35% under full throttle.

also, the 'gun it in neutral' test is much smoother up to 3000+ RPMs on the 96 truck, whereas there is a slight lag from 2400-3000 RPMs in the 97 truck. so that, alone points to leaky injector O-rings, right?

but why is the IPR duty cycle not going higher than 20% in an attempt to compensate for the low ICP reading? like I've been saying, its almost like the PCM doesn't know the throttle is floored - I've replaced the pedal assembly already, but maybe the signal wires to/from the PCM are bad. like if the pedal isn't getting 5V, the return signal to the PCM will be artificially low.

...just more stuff to check out once I get my trans swap done :-)