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Old 10-31-2022, 06:25 AM   #1
Mini-Skoolie
 
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Cat C7 Oil Pressure Reading Anomaly - 1.6psi?

The Cat C7 (KAL1 series) on my '06 Thomas MVP-EF has been showing some strange oil pressure readings, and I'm not sure what to make of it.

Under all conditions (start up, slow/fast idle, driving), it is showing about 25psi on the dash, and 1.6psi via the Bluefire. No change under any circumstances; pressure on both dash and Bluefire remains rigidly fixed.

Oil level is fine. No excessive knocking. No diagnostic code. No change in sound/performance from before I noticed the anomaly (had to drive across town to get it back home).

Oil pressure should be between 35-70psi, and anything under 5psi should result in a diagnostic code.

Sensor issue? Not sure where to start on this one.

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Old 10-31-2022, 08:23 AM   #2
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You start with another, known-good gauge and verifying what the oil pressure is actually doing.
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Old 10-31-2022, 10:08 AM   #3
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Quote:
Originally Posted by Booyah45828 View Post
You start with another, known-good gauge and verifying what the oil pressure is actually doing.
That may be where I start.

But if both the Bluefire and the gauge are showing screwy readings and the ECM is not logging a low oil pressure code, it stands to reason that the issue lies somewhere upstream of both the gauge and data link, but downstream or on a separate branch from the ECM? I don't understand why I'd be seeing both showing so low w/o the ECM throwing a tantrum.

I'm still learning my way around automotive electronics, but based on the attached schematic (think it's the right one; provided by Boyd Cat here in Louisville), I can't even find where the oil pressure sender connects to the ECM.
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Old 10-31-2022, 05:14 PM   #4
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I would use a mechanical gauge for test purposes.
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Old 11-03-2022, 09:45 PM   #5
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I would use a mechanical gauge for test purposes.
That makes perfect sense - thanks!

Next question - anyone have any guidance on where the appropriate point is to connect a mechanical pressure gauge to a C7? My engine manual doesn't specify, and Adept Ape's C7 videos, which have been amazingly helpful, are silent on the point.
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Old 11-04-2022, 01:03 PM   #6
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First, it might be worthwhile to just change the oil pressure sensor at this point. Second, are you sure the BlueFire is reading the right sensor? I haven't had that issue with my very similar bus and BlueFire but it's still a possibility.
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Old 11-04-2022, 03:55 PM   #7
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There's a log manifold rearward of the injection pump that has the oil pressure sensor.

I'm not familiar with bluefire. If it was me I'd be checking with cat ET, the bluefire might be pulling the wrong pid/spn.

I believe cat montiors oil pressure for the c7 and will throw a code if it's incorrect. If I had to guess, I'd say that your thomas pressure sensor has failed, and your bluefire isn't reading correctly. I'm not sure if the gauge cluster on an 06 thomas was fed data off the can bus or not, or if the gauges were all fed data from their respective sensors.

What's the dash gauge read Key off and key on engine off?
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Old 11-04-2022, 03:59 PM   #8
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Quote:
Originally Posted by Booyah45828 View Post
There's a log manifold rearward of the injection pump that has the oil pressure sensor.

I'm not familiar with bluefire. If it was me I'd be checking with cat ET, the bluefire might be pulling the wrong pid/spn.

I believe cat montiors oil pressure for the c7 and will throw a code if it's incorrect. If I had to guess, I'd say that your thomas pressure sensor has failed, and your bluefire isn't reading correctly. I'm not sure if the gauge cluster on an 06 thomas was fed data off the can bus or not, or if the gauges were all fed data from their respective sensors.

What's the dash gauge read Key off and key on engine off?

wierd thing is ive seen them both ways.. data link and non data link for oil pressure.. im not sure if it was a year thing or a manufacturer thing.. I do remember on a 2005 bluebird that there were 2 separate sensors, one for the computer and one for the gauge.. I havent poked around a thomas enough to see if there are separate sensors or not..



the engine is a HEUI engine so if there truly was no oil pressure the injection system would fail to operate and engine shuts down..
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Old 11-04-2022, 04:38 PM   #9
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FWIW, again with probably this exact bus but one year older I’ve had the entire cluster fail because the gauges are all running in a data bus. You could just have a bad gauge and a BlueFire configuration issue.
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Old 11-09-2022, 09:31 PM   #10
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A mechanical gauge uses a small tube that allows the oil to directly press on a lever attached to the needle in the gauge. NO electricity is involved except to illuminate the gauge in the dark. An electric gauge uses a potentiometer to vary the resistance changed by oil pressure. The dash gauge and the Bluefire might both be connected to the same oil sensor on the engine. I'd first check and clean the wire(s) connected to the sensor. Next, check your ground connector between the engine and the frame or negative battery terminal. Bad ground connections can cause many gremlins to create issues. I've even seen a bad voltage regulator in the dash power supply cause inaccurate gauge readings.
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Old 11-11-2022, 04:01 PM   #11
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Where does one connect a mechanical pressure gauge to a Cat C7?

The engine oil manifold?
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Old 11-11-2022, 05:07 PM   #12
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A quick Google search of 'mechanical oil pressure gauge install' will show a number of YouTube 'How To' videos. if you want to ADD a mechanical gauge to the present electrical gauge, a 'T' fitting is typically put in the old sensor location and a 'T' is threaded into the engine. The old sensor goes in one end of the 'T' and the compression fitting for the tubing of the new mechanical gauge connects to the other leg of the 'T' fitting. If you don't want the electrical gauge, just put the compression fitting in place of the electrical sensor.
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