Fuel Rail Pressures???

[hogbody]

I've been playing with my Edge Insight Monitor. It reads actual Fuel Rail Pressure and Desired Fuel Rail Pressure. I have no idea what some of the readings mean but it is interesting to compare them and see if they read different after my new injectors are installed.

At an idle the desired fuel rail pressure reads k 4.9 The actual pressure jumps all around with a range from k 4.8 to 5.2. The pressure does not hold when the engine is shut off. It bleads down to .02 before the guage shuts off. When driving both pressures move all over the board but there is always a .2 diffence between the two on average.

Don't know if the stuff is indicative of anything or not.

[DmaxMaverick]

Sounds normal. Below 1% is normal, and you are well within that. Over 1% will cause complaint (SES) if it's sustained or too frequent. 2%+ will cause limp mode if it's sustained, or dips/peaks too often over a period of time. The pressure drops because it dumps (pressure and communication) when you turn off the key (also normal). All the numbers would seem less significant if they were in a more broad scale, such as PSI. Also consider the resolution of your meter. Actual pressure polling is not timed with PCM pressure demands, so it will skew the reading a bit, as well (if it were an analog, such as a needle, you probably wouldn't see the difference). If it gets out of spec, the PCM will throw a fit.

[hogbody]

Thanks........

I plan on installing an EGT probe and also monitoring boost as I spend most of the time pulling a heavy trailer. The truck comes standard with a fairly complete set of guages, ie: temp, voltage, tranny temp............What else would you suggest I monitor while towing? The unit covers a lot of area's and has the ability to monitor 5 readings at once. Some of the items are fuel temp, air intake temp, map pressure, engine load and so on....you get the idea. A lot of stuff that has no meaning to me now but could be helpful once I learn parmeters and what to look for.

[DmaxMaverick]

I think you're crossing into the "too much information" zone. These new rolling supercomputers do a pretty good job of watching themselves. I do recommend EGT and boost (in addition to the IPC), but the rest is just too much. If an issue comes up, and you have a reason to watch specific parameters, by all means. That's different. If you try to drive it like a submarine, you'll end up driving a submarine (off into a lake). Time is better spent watching the road, and all those idiot drivers out there. You'll be watching your 747 gage cluster while they're trying to read the part number on your tail lamps. Nothing good comes from that.

[hogbody]

LOL! Yep....I am used to distracted driving after handling a radio, radar and computer in my car back in the old days. Don't want to head into the lake. Now I have the wife to handle the cell phone and gps......I don't think she would want to take on anymore.

[Kennedy]

I'd be curious how you route that fat ALDL cable for daily use? I have a CTS here that I use occasionally for drivability tuning, but really dislike the notion of having it in a vehicle permanently.

As for the fuel pressure I think you will find that with the addition of a lift pump the actual should follow desired more smoothly. This could account for why some get a sense of quieter operation and slight increase in MPG.

[hogbody]

The cable is kind of fat. I ran it up the driver side pillar and behind my Transferflow fuel tank readout. Excess is ziptied und the dash. What is going to be interesting is when I run the EGT probe wire and the rear video camera wire......................

[More Power]

There's a specific fuel rail pressure test, performed using a Tech II scan tool, that examines the rail pressures at 2000-rpm and 3000-rpm. The difference between the "actual" and "desired" rail pressure must not exceed 20-MPa (mega pascals). If it does, a variety of trouble codes could be set.

A fuel return flow that is too high (bad injectors) could result in the Bosch high-pressure pump not able to keep up. A leaking fuel rail pressure relief valve could produce the same effect. An FPR (Fuel Pressure Regulator) problem or a worn out high-pressure pump could also cause this problem.

Most P0089, P0093 and P1093 trouble codes are due to a problem with either the fuel supply (filter, lines, air leak, gelled fuel, etc.) or a bad component in the high-pressure system. The "Large fuel leak detected" description GM associates with these codes is a bit of a misnomer. In simple terms, the system can't generate the rail pressures it is commanded to by the programming.

Jim