Cam Sensor and timing help

[MummifiedCircuitry]

Do you know how to bypass / disconnect the alarm harness, so you can eliminate that as a cause? I’m not sure if the alarm system disables only the ignition system, or if it prevents the starter from cranking too.

With the alarm armed it won't even crank over, just clicks like it has a dead battery, so I don't think the alarm is to blame in this case. I did notice when I was swapping cam sensors multiple times that the t-belt was tight sometimes and other times felt quite loose. I don't typically have those upper covers off, so I'm not sure if this is normal. I'm going to pull the cam sprocket cover off my running montero and crank/check the belt tension multiple times, if it's a constant tension then I think the non-running one may have a tensioner failure that I'll have to dig into. It does have a newer t-belt/tensioner/water pump about 12k miles ago with OEM/Aisin parts so I wouldn't expect them to be bad.

 

[Salonika]

The loose timing belt you are describing wouldn’t cause your no start…..IMO

 

[MummifiedCircuitry]

I checked the CPS harness and it's not getting power with the key on or cranking. It has 3 wires, power, signal and ground. The ground wire has essentially 0V which is fine, signal wire is getting 5V which is also fine, but the power feed is reading 0V instead of 12V at all times, key off, key on, cranking. I tried changing the MPI relay under the passenger dash, which is where I believe the CPS power feed is from (correct me if I'm wrong). Is there anything I should try before I rip the whole loom apart from the CPS to the ECU? Can I swap ECU's with my other vehicle 98 3.5 SOHC to 97 SR 3.5 SOHC or do these ECU's need to be programmed/coded?

 

[Salonika]

First off, FWIW, that sensor doesn’t operate at 12v. Because the sensor power is computer controlled, it may detect that it isn’t plugged in (no circuit), and so sends no power. I think you could back probe the connector on top of the engine in order to try and see the supply voltage with it hooked up.

 

[MummifiedCircuitry]

First off, FWIW, that sensor doesn’t operate at 12v. Because the sensor power is computer controlled, it may detect that it isn’t plugged in (no circuit), and so sends no power. I think you could back probe the connector on top of the engine in order to try and see the supply voltage with it hooked up.

I've already checked on my other Montero. CPS completely unplugged, on the harness side with key off it reads 0V, key on it reads 11.4V, it doesn't need to be plugged in for the harness side to supply voltage.

 

[MummifiedCircuitry]

Made some progress today, I plugged in the CPS, then clipped the power wire on the sensor side and ran 12v straight from the battery to that wire. It started right up and I let it run for 10 minutes with no issues. So it's definitely that single wire that's causing the issues. I'm thinking ECU may be to blame, before dropping money on a new ECU, is there anything else I can try short of just wiring a toggle switch to supply 12V to that wire and continue to drive it?

 

[Salonika]

I’d rig up something semi-permanent with your experiment and put in some time driving with it that way before getting too excited. Why not try and check the voltage output directly off the ECU to eliminate possibility of any harness issues?

 

[MummifiedCircuitry]

Well I eventually figured it out. I tried a new ECU, but still would get erratic voltage to the CPS, it would run then stutter/try to die and voltage to the CPS would read 12V, then fluctuate between 3V-12V. Now that it was actually running, I metered the power feed to the cam sensor and started wiggling the harness from the top of the engine back to the firewall. After stripping a good deal of the harness, I pulled the intake off and found the large main loom resting on a bracket on the valve cover, turned it over and found a badly frayed wire that had been rubbing on the bracket, it was the black/red CPS power feed wire, got it all repaired, put my old ECU back in, put the newest CPS in, started right up and seems to run perfectly now.

 

[Salonika]

Good ending. Was that section in its factory condition, or do you think something was tweaked vs where it was supposed to be?

 

[MummifiedCircuitry]

Good ending. Was that section in its factory condition, or do you think something was tweaked vs where it was supposed to be?

I've owned the vehicle for about 7 years and have had most of the engine apart multiple times, so it was likely my fault that the wiring was rubbing there. I fitted a rubber grommet on that bracket/stud on the valve cover and ziptied the harness up higher after I re-loomed it, it shouldn't have anywhere to rub now. There's a hell of a lot of wiring in these rigs, I've been looking into options for a carb'd 4-cylinder for about a year, this just makes me more sure I need to ditch this engine setup.