I have a CAT 966H loader serial # A6G03785 which suddenly the engine became unstable and it sounds like the rpm is going up and down but while checking with ET adapter I found no change in the RPM readings. The only values that are changing are the following: - Fuel Pressure: from 77 psi to Abnormal/incorrect data - Fuel Pressure (absolute): from 92 psi to Abnormal/incorrect data - Turbo Inlet Pressure (absolute): from 14.90 psi to Abnormal/incorrect data Video of the loader while starting: Video from CAT ET showing the parameters reading:
Try first fixing your electrical fault that is causing the sensors to go from "normal" to "abnormal/incorrect". My bet would be that there is a common harness connector somewhere (probably located somewhere on the engine) that feeds both the fuel pressure and turbo inlet pressure sensors. Do you have an Electrical Schematic..? If not do you want one..? A machine Serial Number would be needed to provide the correct one. Last questions: How many hours is on the machine and is the engine original..? There is an outside chance that the problem could be inside a harness rather than in a connector.
I have an Electrical Schematic through SIS and I'm checking all the connectors but until now everything seems to be OK. The machine has 4217 hours and it's as shipped original engine. I thought that maybe it's a nad ECM so I removed One from another 966H with almost the same serial and the same flash file but the problem still the same.
The reason I asked about hours was to get an idea if the harness may have hardened with age. I've seen a lot of high-hour engines suffer from harness problems. Get hold of the engine harness in various places and check whether it's still flexible or not. If it's hard then you could potentially still have an internal harness issue. Also try pulling and twisting the engine harness in various places between the fuel pressure/turbo inlet pressure sensors and the common connector CONN 5 with the engine stopped and ET connected to see if there is one place that pulling the harness causes those two sensors to go from normal to abnormal state. If that heppens, there's your problem. What's the S/N prefix (there are 10 to choose from) of the machine..? I'd like to download the schematic myself and have a look to see if anything obvious jumps out. I looked at a typical one and CONN 5 is the connector that jumps straight out at me. I would have thought a bad ECM would be the last thing in the diganositc list, but you've ruled that out already.
The loader serial is A6G03785 and the engine serial RSX14739
Guess what..? That's the schematic I was looking at. If not inside CONN 5 itself, then somewhere between the two sensors and CONN 5 would be my bet.
Can I ask you please which sensors are pointing at. Really I'm not that good in reading schematics.
When I get back to the house I’ll post some screenshots and a description of what’s where...
OK, let's start from the beginning. In your OP you mentioned that both the fuel pressure (Absolute) and turbo inlet pressure (Absolute) readings were alternating between genuine pressure readings and "Abnormal/incorrect data". The common factor in both of these is the atmospheric pressure sensor, because the reading from that sensor is added to the pressure reading from other sensor to give and absolute pressure reading. As a first step your should download the RENR6332 Electrical Schematic from SIS. It will download as a 25-page pdf document. When you have it downloaded check the index on the LH side of the page. As you scroll down the index you will find the 3 Volumes of the Schematics in the penultimate section. Open "Volume 1 of 3 - Chassis". It should be Page 19 of 25 in the document. You will note that on the edges of the page are Grid References, starting in the bottom LH corner with A-1 and ending on the top LH corner with J-14. Go to Grid reference F-10. There you will find the 194-6722 turbo inlet pressure sensor. The wire numbers are F713, J843, & J844. If you follow the harness it goes straight back to the ECM (Pins 2, 3, & 15 on connector J1) with no harness connectors in between. Go to Grid reference C-13. there you will find the 239-2396 fuel pressure sensor. The wire numbers are G828, G829, & C991. Follow those wires and they first go to Connector 5 (CONN 5), then to Pins 17, 40, & 72 of Connector J2 on the ECM. If you follow the black line to the right of CONN 5 upwards you will find the atmospheric pressure sensor in Grid D-12. Before going any further I sugges that you open up the connector (circled) for the Atmospheric Pressure sensor and give it a good cleaning with electrical contact cleaner.