Ok, I spent some time with some help of a friend playing with the IDM and a scope today. From the way it looks the PCM is sending 2 signals per injection event to the IDM. So this brings up the question of is this because of my split shots? Does anyone know exactly what is changed when you have a computer stock flashed to run single shots that is not increasing fueling just switching to run properly to use the single's.

I was unable to find anything about this doing serches. I'm just playing around trying to learn as much of how the IDM works as i can. So if anyone has any screen shots of a scope from any IDM testing they have done and would like to post it or email it to me let me know and i will PM my email. I am willing to swap my knowlege with others knowlege.

I also Measured the output voltage while runing and was very shocked on how low the actaul output to the injectors are compared to what i have read the working voltage is. My stock 120 IDM was only putting out 66 volts to the injector Noting near the often qouted 120 volts.

When I think i have found as much info as i can and if any more tweaks can be done other than the normal resistor IDM mod i will repost what i have found. This is going to take a few weeks as i DD my truck and am working with a busy schedule and cold weather.

I'm most importantly looking for the difference on the idle of a stock AD truck vs a single shot truck's idle.

And what are you thoughts as to why the pulse width is cut out on these trucks by the PCM at higher rpm's?

I'll update info ASAP along with some pics.

 

Interesting post. I too am curious about the single vs split programming. From what I think I know the split is built into the injector itself so I would think it goes to the activation period. Now as for your voltage to the injectors. That is obviously not what is expected. I would make a few recommendations but I am fairly confident you have checked the alternator output. I will be following this thread.

 

Another interesting topic, you must like to tinker as much as I like to analyze. See what you think of my idea for improved cables from the IDM to the injectors, to make the injectors fire faster and harder.

Awhile back I got interested in the IDM, because I replaced my IDM thinking it was bad, but the problem turned out to be the UVC on the passenger side. Now this is from memory, but I think I read that the IDM has it's own little onboard computer/microprocessor, and that the PCM sends the IDM digital words which instruct the on and off time for each injector pulse. I think the two signals you see are the one word for on and the other word for off. Also, the off pulse is reverse polarity to drive the solenoid in the off direction.

Since there's one power stroke per cylinder per two crank rev's, that gives four injectors firing for each rev, so there's 4 pulses per rev or [(4)(RPM)]/[(60)] pps. At 3000 RPM=50 RPS that gives 200 pps. Also, each rev is 20,000 usec, so each crank degree is 55.55 usec, and that's the timing accuracy required to control the injector firing to within 1 crank degree at 3000 RPM. Some body needs to check this math as it's late and I'm on my third beer.

The following is from some notes to myself that I put together awhile back, and never followed up on. I don't remember where I found this stuff or how accurate it is. Injectors are very inductive loads, the IDM turns on the injectors faster by supplying a 7.5 Amp initial current and then a 3.5 to 4 Amp holding current. The voltage is what pushes the current thru the wire, but it's actually the 7.5 Amp pulse of current that activates the injector solenoid. The magnetic field in the solenoid depends on the current not the voltage.

Being a EE, I think it's possible that improved cables from the IDM to the UVCs might enhance the IDM mod, and might even provide similar improvements as an IDM mod by using just the improved cables with a stock IDM. It's the current pulse that needs to be optimized by connecting the IDM to the injector with an optimized transmission line. The idea is similar to using coax cables to hook to the individual RGB guns on a CRT to get the best rise time on the video pulses. The objective is to better match the inductive load of the injector solenoid to the IDM so as to improve the rise time and turn the injectors on faster and harder.

To provide optimized fast rise time switching of an inductive load (injector solenoid) at a long distance from a pulsed source (IDM), requires a properly designed transmission line to minimize the distortions in the pulse as it propagates along the line. I've been meaning to brush up on transmission line theory, do some calculations, and see what improvements might be possible, but I just never got around to it. How many people would be willing to pull their VC's and install 4 coax feed through connectors on each one, and run coax cables from their IDM to the VC's?

 

Yes the alternator output was checked a few weeks ago just doing routine winter prep.

Also while the scope was on this. i turned on my headlights, A/C on high and reved the engine a little. Nothing changed. stayed 65-66v. Now after thinking about this and posting this same post on another place, I don't remember if the GP's were still on when this was being tested. But i doubt it would drop it that much. This will be retested to confirmthe GP's being off the next time the scope is hooked up.


And when the IDM is on but the engine isn't runing its holding about 112V.

EDIT I forgot to mention about the split shot part, It is built into the injector, but i know everyone is changing the tuning for them, Id just like to know what it does? if it changed the main charge until later or what since there is no prime shot? I don't have the screen shots infront of me to try to figure it out but i will get into it later tonight when i get them.

 

I was hoping you would find this post.


I am on my way to work and don't have time to really read and get into this right at this time. And also this is a group effort between myself and a coworker who is also very into testing and tweaking of things. Mostly we are out to find out a way around the limiting RPM factor for these engines.
I do have some pics, and i might be able to post them up after i get the screen shots from the fluke. and let you see what i see to better help the situation. we had channel A the Cylinder identification signal and channel B was the fuel delivery command. We are trying to figure out what actually marks cylinder 1 on the CIS. If it is the fall or the rise.

To be continued later. with pics for you. I might be able to post them from work. If not i will when i get home somtime around 6am

 

ernesteugene: How about instead of coax a RC network in paralell to the injector? 22 ms would be perhaps a .01 mfd and about a meg (really way old school trick to speed up inductor saturation) Should work if you can tolerate the decayed leading edge of the pulse.

2nd $.02: 66 volts would be only a bit low if your meter is reading RMS instead of Peak to peak. most flukes and etc read RMS on AC. add a bridge and use the DC scale for p2p.

 

And what are you thoughts as to why the pulse width is cut out on these trucks by the PCM at higher rpm's?

This may help you with above statement, In the PCM there is a table called "Adder to Pulsewidth Multiplier"....in stock tables at higher RPM's and at higher Manifold Gauge Pressure, programmed from factory, they are pulling out as much at 70% , that’s -.70. out of the pulsewidth.
Keep in mind this is a multiplier table that will have major effects on fuel delivery on the overall pulsewidth.

 

The time interval for each one degree of crankshaft rotation is {(1)/[(6)(RPM)]}, so in order to maintain the injection of fuel over the same interval of crank degrees, the injection pulse has to be shortened by a factor, F~{(1)/[(6)(RPM)]}.

At 3000 RPM, for example, each crank deg is 55.55 usec, and I'm just guessing here, that the pulse width, PW, is about 555.5 usec, so that fuel is injected over a 10 deg interval of crank degs in the vicinity of TDC. At 3400 RPM, the PW needs to be reduced to 490 usec in order to preserve this same 10 deg injection interval.

Now if you're saying that there's an additional shortening of PW at higher RPM which is more than F~{(1)/[(6)(RPM)]}, that possibly has to do with the rate at which diesel fuel combusts. If you kept the same 10 deg crank rotation injection interval at ever increasing RPM, the fuel would still be burning at closer to BDC, and this wouldn't be efficient use of fuel and would reduce MPG, it might also increase soot and other emissions, and it would tend to increase EGT. I haven't had a beer yet today, and I might come up with a better explanation about 3 AM, so stay tuned.

 

Ive heard that the IDM electronics are not quick enough to process getting full PW. More than just the resistor would need to be changed(the actual semi-conductors inside). Thats just what ive read tossing that out there.

 

Transformer recharge time at high rpm's is the limiting factor.

 

I confess I am rapidly approaching the dumas level here. I know that the 7.3 will fall on it's face at about 3k rpms. I also know that it is because a number of reasons including valve train/air flow capabilities, and injector limits. So now we are saying even bigger injectors are limited by a transformer recharge? I am too lazy and disappointed after the ball game tonight to look up that in the manual. What transformer are we talking about? Where is that rascal?

Also, my manual says 110 volts+ to the injectors from the IDM at about 8 amps give or take. If the scope is measuring something else, then a conversion will account for that. I am learning stuff here.

 

http://www.shol.com/shadow_tech/test.html

This is what is had now. If it is somthing you want to keep i would download it now as I am not sure how much bandwidth will be allowed.

 

As far as I can tell, the IDM employs the same approach as a 12 VDC to 120 VAC inverter, except the AC is then rectified to provide a DC output. Transformers don't have a recharge time constant, but capacitors and inductors do.

The question is why does the PCM program the PW to decrease as the RPM increases? I know the first reason I gave is valid, and I'll have to do some research on diesel combustion burn rate to see if the second reason I gave is also valid.

 

This is a follow up to my post #8 concerning the question... This graph shows how HP for a 7.3L PSD depends on Cylinder Mean Effective Pressure MEP during the power stroke. The PCM programming controls the Injection Time IT*=crank degrees, and the injection Pulse Width, PW*=crank degrees. These parameters control the timing and the amount of fuel injected, and this in turn tailors the peak combustion pressures in the vicinity of TDC, and this is what determines the cylinder MEP and resulting HP.

To program for maximum HP, you want to control the IT* and PW* to maximize MEP at each RPM. Of course the Ford PCM programming has to worry about other things as well, including emissions, MPG, and reliability.

In terms of time, each crank degree, CD*, has a duration of... CD={(10^6)/[(6)(RPM)]} usec. This gives a PW* measured in time as...

PW={(PW*)(10^6)/[(6)(RPM)]} usec.

Below a summary of some timing data on a diesel test engine, but it's probably not much different from a PSD...

At 3000 RPM, an injection pulse at 30* BTDC, is followed by a 20* ignition delay, then a 5* delay as pressure rises to a maximum, so maximum occurs at 5* BTDC. So if you could inject all the fuel instantaneously at 30* BTDC, you'd achieve the peak combustion pressure at 5* BTDC.

In my post #8, my 3-beer guess was "... and I'm just guessing here, that the pulse width, PW, is about 555.5 usec, so that fuel is injected over a 10 deg interval of crank degs in the vicinity of TDC..."! Well if you use this estimate of PW*=10, this spreads the injection over 10 crank degrees and gives...

Pulse injection from 30* to 20* BTDC, then 10* to 0* BTDC for initiation of burn, and maximum pressure at 5* BTDC to 5* ATDC!

So my original guess of PW*=10 appears to be about right, as it spreads the peak pressure over the plus and minus 5* centered at TDC.

Now at 3400 RPM, to get this same peak pressure centered at TDC, you need to consider that the 20* ignition delay is time based, so it becomes 22.7* at 3400 RPM, likewise the 5* pressure rise becomes 5.7*, and a PW*=10 becomes PW=490 usec. At 3400 RPM, this gives...

Pulse injection from 33.4* to 23.4* BTDC, then 10.7* to 0.7* BTDC for initiation of burn, and maximum pressure at 5* BTDC to 5* ATDC, just as before at 3000 RPM.

Well the above reasoning is why I think the PCM programs a shorter PW=490 usec at 3400 RPM compared to a PW=555.5 usec at 3200 RPM. These numbers probably aren't exact, but I think the general principle explains "why the pulse width is cut out on these trucks by the PCM at higher rpm's?" which was the question being asked!

I wonder if we can talk Jody into giving a class at Smokin to explain how the PCM runs the engine. Not his secrets, just the fundamental principles with a few typical numbers to aid our understanding. I know that I'd gladly pay the price of a dyno run for a one hour class including some Q&A!

 

To whom it may concern (which is apparently on one!) the equation I pasted on my graph above has a typo!

It should read... HP={[(MEP)(RPM)]/[(1780)]}