Have been emailing with gearhead and they say are saying a weak HPOP is causing the low ICP/power. When in position one I have 3000PSI of ICP with 50-60% DC and FIPW OF 3ms. If I switch to position 6 then I have 2000 PSI ICP DC of 80-90% but a FIPW of 5.3MS. They say the FIPW is high because of the low ICP. Looking for suggestions here on how to proceed.

 

I am far from a Guru on this but...my understanding is that high FIPW results in low ICP, not the other way around.

 

He says that they set there FIPW at 3.5MS so I'm not sure how it is going to 5.3MS either. Getting tired of this thing.

 

Without getting too involved in this thread, the way the PCM calculates things and the "shape" of the pulse width map dictates that relationship. Yes, lower-than-desired injection pressure CAN AND DOES cause excessive pulse width.

Maybe tonight I can get a little more into detail, but for now that's all I'm willing to type out on a pocket electronic leash.

 

Easy.

​​​​​​​I may be able to show you tonight.

 

Well showing too much isn't going to work because once again the tuning computer took a giant dump. Why did Microsoft have to ditch XP? I refuse to use a computer with a newer operating system. Anyhoo, I'll try to explain it using a stock pulse width map that I searched through 754 replies of another forum's thread to find.

Here is a stock 99-03 pulse width map. I have darkened a couple of lines on it (using ms paint on my other XP machine).

Pulse width is a calculated value based on Mass Fuel Desired (MFD) and injection pressure. Mass Fuel Desired is based on accelerator pedal position and RPM and Injection pressure is based on RPM and MFD. This means that ANY deviation from DESIRED Injection Pressure (Actual Pressure) will have a direct impact on Pulse Width for any given MFD. Per the map, you'll see that as pressure decreases, the pulse width goes up. This is all to maintain the given MFD on the right margin regardless of injection pressure. Of course, not all of the points are possible to attain, but in the case of failure of anything, the data is there for the PCM to look up.

Now, this is just one map and EVERY different tuning company is going to alter this map differently for different injectors. There is also another map called the Pulse Width multiplier (offset) that is calculated by oil temperature and injection pressure. Consider that a lot of tuning companies will alter this map to "multiply" the base pulse width map shown as the injection pressure increases.

Enough explanation, let's get to math based on the picture.

I have darkened the 13Mpa line (1900 PSI) and the 100 MFD line (which would theoretically indicate a matted accelerator pedal) since 3000 PSI is not attainable per the data in this thread. At 3000 PSI, the calculated pulse width in this map should give approximately a 3mS pulse width. The stock pulse width multiplier would be "1" and the actual injection event would be about 2.5mS after mechanical latency of the injector. At 1900 PSI, it appears that the calculated pulse width would be about 4mS to maintain the desired MFD of 100. Assume that aftermarket tuning puts a multiplier value of 1.4 at 1900 PSI. This will put the commanded pulse width at 5.6mS instead of the 4mS commanded by the base pulse width map.

Pulse width is a product of Injection Pressure. It's easy to see by this map that the pulse width will increase drastically when the injection pressure drops and it's a vicious cycle because excessive pulse width makes injection pressure fall.....and falling pressures make pulse width increase even more!

EDIT: Sorry about the MFD line in the middle of the map...I was going to get on a tangent about something else but will save it for another time. Ignore that one.

 

So now the big question, is it a weak HPOP or injectors? What is the thought there?

 

50-60% duty cycle on a 3mS calibration at 3000 PSI is too high ("stock" tune I assume) although stock desired ICP is around 2800 PSI. Low 40's is where you should be in that case.

 

The 50-60% with 3ms and 3000 psi was on setting one of gearheads canned tunes.

 

I'd use that tune and not the other one. It doesn't like your truck.

Any sign of HPO loss like a black fuel filter?

 

IF I have digested this correctly...lower HPO pressure requires a wider pulse width to get the fuel through the injector and the PCM or the IDM perform the calculation and adjust FIPW accordingly. The longer FIPW causes a lower ICP and gets caught in a vicious cycle.

 

Obviously the Excursion doesn't like it hence the thread. I did injector o-rings when I had to do injector cups and am pretty sure I don't have a HPO leak but will pull the filter again today and look.

 

Mark, regarding the mapping example (or ANY 7.3L tuning), the changes affect the PCM only. The IDM only does what the PCM tells it to do.

 

Nice to see Cody in here.

Speaking of Cody... is there a recent Cody test after all the cup and O-ring work? It's nice to know everything is new in there, but I've had many, many "new" failures... most of which were injector hold-down-bolt torque related.

If you pass the Cody test, then I strongly suspect the HPOP. My T500 holds 3000 PSI at 42% IPR on bigger injectors and nozzles (more of a challenge for the HPOP). Many stock trucks with stock injectors and HPOP can hold 3000 PSI ICP with 40-45% IPR on performance tunes. 50-60% IPR with 3000 PSI ICP and 3 ms FIPW is a total fail. You are either leaking oil internally, the HPOP is starving, or the HPOP has seen better days.

 

Yeah I should have listened to my gut earlier in this thread about the HPOP, but was convinced by others that it was the tuner I had. When I had issues getting it started after the cup job I did pressurize the oil rails and had no leaks. I will check that again and also pull the fuel filter and check it. Whats the best way to check for a starving HPOP?