IPR class

Reply Subscribe

Thread Tools

Search this Thread

Sep 20, 2015 | 08:29 PM

Tugly

Thread Starter

Hotshot

Joined: Jan 2011

Posts: 18,849

Likes: 179

From: Puget Sound

IPR class

I have been obsessed with keeping an eye on IPR ever since I learned it will climb with bad injector O-rings or low injector bolt torque. Since I monitor this all the time under a lot of scenarios, I thought I might share a little of what I've learned with the group, and allow for counterpoints to my conclusions. For the sake of keeping this from turning into "War and Peace", I'll keep it down to idle Injector Pressure Regulator (or Injector Control Pressure Duty Cycle) at 500 PSI Injector Control Pressure.

It's been a while since I've had stock sticks, and my biggest learning curve occurred after going to AC160/100s. The actual IPR numbers might differ a little, but the basics are the same. To keep it simple, let's say a baseline is 10% IPR on a 100% engine:

You want to know what your base IPR is with the truck running tip-top at full operating temperature and idling - this is your baseline to compare when things go awry. Mine is 10%.
A loose injector bolt (about 75-80 inch/pounds of torque) will allow the injector to lift a tiny bit during the combustion cycle - compromising the seal on the copper washer. This, in turn, allows the ICP to bypass the injector O-ring into the fuel. This can also allow combustion gasses to sneak past the bottom fuel O-ring and enter the fuel. A loose injector makes a weird knock, and there is nothing good about this scenario. The IPR will read about 2% higher than normal at idle to begin with, but it will climb as the injector works its way out of the hole. At some point, the cup is in danger of being compromised by the intense heat and pressure. This is none too good for the fuel side of the injector, as those gasses, pressure spikes, and soot wreak havoc in the fuel rail. Checking injector torque is crucial if you get the big IPR and weird injector knock. The book says replace O-rings if the torque is below 50 inch/pounds. I'll leap out in front of this and proclaim 75-80 inch/pounds and a knock indicates it's O-ring time.
When one injector doesn't fire, the oil demand drops - so the IPR will drop about 2% for the first dead injector. I am unsure how far the IPR will drop with a second bad injector - or a whole side.
When the injector O-rings are bad, there is no telling how much oil they leak, but leaking ICP through the O-rings will raise the IPR above baseline at idle. The convenient tattle-tale here is a black fuel filter after the problem has existed long enough. You can also experience long crank times, blue smoke out the exhaust... or a no-start.
When the Engine Oil Temperature reaches a "sweet spot", you will see the IPR creep down a little while the ICP stays the same. This happens when the engine tune decides the oil is warm enough to drop the ICP to 500, but the engine has not reached full temperature. I'm not the oil expert, but I assume this has to do with the changing of the viscosity of the oil with the climbing temperature.
The sign of a good idle with a tune (and a good working engine) is a very stable IPR. If the fuel map is off, the IPR will drift all over the place in an effort to compensate. My IPR will drift less than 0.8 percent at idle - a tiny amount of drift is expected. If one were obsessed with the display, one might say "HEY! It jumped by 0.4% in one movement!" Yup. That's one "step" up or down, not 0.1% like you might think.
If the IPR reads stupid low, the truck is anemic (and has a soft-sounding idle), yet the ICP shows 500 PSI - that could very well be the ICP sensor failing. My experience has shown that the ICP reads a false high when it starts to give out. The IPR will then lower to get the "alleged" ICP in line. This is actually a good thing. We wouldn't want an overdose of fuel because of a bad sensor, worse things than anemic power can happen here. There are two tattle-tales to confirm a bad ICP sensor is making the IPR read low: Pull the plug on the ICP sensor and look for oil in there, then drive with the plug out (SES light will flare up, IPR will jump, and the PCM sets a "fake" ICP value). If your power is restored, then you nailed it. I had this once - I cleaned the oil out, put some silicone lube in the connector, and connected the ICP sensor. My power was restored to normal until I could get home and install a new sensor.

I should point out something very important: I mentioned a 2% difference in IPR at idle with some of the situations above. That's not small. For me, that's a change of 2 from 10 - a 20% difference from the norm. Think of it like fuel economy - you wouldn't just blow off a 3 MPG difference in either direction.