I’ve not used FORScan data myself other than reviewing on FTE posts to try and help out.

I would say record both psi and volts for the ICP, unless there’s a limitation I’m not aware of.

I think there’s benefits to both.
PSI is easy for us humans to visualize.
Volt will show signal loss.

If you graph the 2, it should be very easy to see when the PCM drops signal (voltage) and thus starts using default tables instead of converting the voltage to psi.

You’ll always be making some sort of guesswork about the signal when looking at psi, but voltage should tell the tale on the signal aspect.

 

What are we guessing at, though? As soon as we see an idle ICP reading of 725 PSI at idle, something very easy to check, we know the PCM is ignoring the sensor. Especially given the DTC. We can go by the voltage signal the PCM is reading - seeing it go to zero or go erratic. That brings us to the same conclusion, doesn't it (sensor or wiring)? How does the greater resolution of ICP (V) help us troubleshoot further? What do we gain? Would it help distinguish between sensor and wiring faults?

Graphing the two is interesting. I've put ICPV(V) in place of FUELPW. Compare it to the blue ICP trace. This is the southbound leg, where the ICP signal is wavering, but not yet ignored by the PCM, resulting in rough running. That ICPV(V) is pretty rough.




This is the northbound leg again, where the ICP sensor signal has already been ignored by the PCM. ICPV(V) is dropping to zero at times now.

 

it is obvious, that ICP volts has better Resolution,
ICP pressure seems to be an average of the sensor input.


I have to monitor my sister's Blood Pressure every few hours.
the new BP monitor has an Average button on it, which is the first thing you see when you touch the Mem button.

that confused me at first, until I recognized that the actual BP readings are 2 more steps down.

that is Analogous to what is going with with Volts and Pressure in the graph above.

 

Good Evening Gents,

Very informative responses and I have a much better understanding of it all. I have several runs completed today which I will upload. I tried to label them well. RR stands for Riffraff on the files. Tomorrow I will be swapping out the engine harness. I kept the old one which hadn't given me any troubles... I replaced it for a new OEM (same vendor) as part of maintenance.

Thanks for all the help and insight! I have the same engine in two buses I'm planning to convert into RVs and love the platform.

It looks like I will have to upload in two messages due to size.

 

Here's the 2nd set of files.

 

How did it drive with ICP sensor unplugged?

 

Won’t get any from me. You’re the resident expert and I certainly appreciate what you’re able to do with and the help you provide with FORScan. (And yes, I know the fencing reply was in fun )

My opinion is the gain lies with folks less proficient on reading the graph data. Your trained eye will pick up on the ICP-psi going to default, but for someone less knowledgeable like me it’s easier to spot with the voltage signal. You were also able to notice the fluctuations in ICP-v before it went to default which could be beneficial.

And yes sir, I was thinking this may help us differentiate between sensor versus wiring faults to some degree. Not sure how that might play out yet but if seeing it a few times we may spot a trend.

My job in the past dealt with investigation of suspect parts where pressure, solenoid command, and solenoid amperage could be watched. I trained folks to use the amperage as an indicator of electrical versus physical issue. By watching the relationship of solenoid command to amp draw we could see if it was following as expected. If amps fell out then it was within the wiring or solenoid coiling. Otherwise it was a physical issue with the solenoid or other related part.

(Side bar) Speaking of that… is there a way to see IPR amp draw or voltage? If we could chart the command versus response it could help determine between wiring or IPR related defects.

 

@bwst Hey Jeff, it ran good while unplugged. Idled a bit rough. How it is possible to run good without the ICP sensor plugged in is a bit of a mystery to me. It couldn't stay at the default 725 and have sufficient power. The only thing I can think of is that the tuning uses throttle position?

I swapped the wiring harness out this morning and put the old one back in. She started and idled fine. Here's a quick file of it idling but no codes are present. I will take it for a longer spin later today and see how she does.

 

Good Afternoon Gents,

I think we have it figured out! I drove several hours today with a mix of driving interstate, city, small town, etc. and zero service engine lights came on. The truck ran perfectly. I even got her up to 100 MPH once, briefly. This is the fastest I've driven her in the 22+ years I've owned her. Anyhow, I couldn't have done it without all of your input. This forum is one reason I've kept my truck so long.

I really appreciate it!!!

I've attached some recorded data from today's runs in case anyone wants to take a look. Like I said though, no service engine lights came on. I think the new OEM engine harness was the culprit.

 

So you had a fault in the new engine wiring harness?

 

Correct. I installed the engine wiring harness along with new injectors, other upgrades and maintenance. Drove about 1000 miles before I started to get the engine ICP codes. Took me a long while to figure it out which you can see from reading this thread. She's doing great now with the old harness installed.

Well, now I have the rear driveshaft out to rebuild....

 

Whence came the wiring harness?

 

Riffraff. I usually have good luck with them and they are working with me to get store credit for the harness.