I've got 2 odd problems..

BACKGROUND: My 88 Dakota 3.9L 2wd is 100% original, minus radio, speakers, and wheels. I picked it up in 1992 as a highway construction truck. It's a barebones unit, no cruise, no A/C, no carpet, 1 speaker. It's been a daily driver/hauler since I've had it, and I'll admit: I'm not easy on my stuff. I've hauled bags of concrete on 2 occasions. The first time was 2,000 lbs in the bed, and 2,200 lbs in a trailer. The second time was 3,000 lbs in the bed on a pallet :S. My Dak has gone on numerous long trips- 2,900 miles at 70-85 MPH non-stop. Basically, I abused the f€(¥! out of this truck, and she finally deserved a break and a refresh. My Dak now has about 292k miles on it. I've always changed the Oil with Mobil 1 5W-20 until last year. I parked it because I thought I had a rear main seal leak: the engine was spewing oil fast. This spring I started with refreshing the Holley TBI with new gaskets, seals, injectors, fuel pressure regulator hoses, vacuum lines etc, I noticed a clean streak down my grease/oil soaked transmission (valve cover gaskets had started leaking in 2004). Turns out, my main oil leak was coming THROUGH my Oil Pressure Sending Unit and out the plug - not my rear main seal. I replaced it and my instrument cluster, (so i would have a pressure gauge). It worked great and accurately, with no more oil leaks at all. Goodbye 1 quart of oil every 40 miles! The Oil Pressure Gauge read 50% on startup, and settled around 25-35% when warm and idling. I had very little heat, and my coolant has always been acceptable levels. I flushed the whole cooling system, and replaced everything from radiator to heater core to water pump, with every hose in between has been replaced. A new Murray 195 degree thermostat was installed. The intake manifold was removed due to a snapped thermostat bolt (fixed) so while I was at it I cleaned sludge off the hydraulic tappets and lifters. The valve covers came off to clean off rockers and buildup on the rockers and valve springs. No disassembly, just a clean up. I oiled the rockers, lifters, and tappets before reassembly. FelPro gaskets were installed at every step. I replaced the temperature Sending Unit on reinstall. The distributor received a pickup coil, cap and rotor. I started the truck and ran it for 30-45 seconds to circulate any missed debris into the pan or filter, and did an oil and filter change. I set the distributor to 16 Degrees Advanced. The 88 Dakota asks for 10, but with the timing change as stretched as it is, she ran better at 16. With the computer hooked in, timing is 18-22 degrees advanced. A new ignition coil, spark plugs & wires installed. I cleaned up all the grounds, and replaced the Ground/Hot battery cables. I'm going through the truck and giving it a full rework this year with little expense spared - this truck has earned it!

PROBLEM #1: My Oil Pressure Gauge reads 100% max pressure.
When switching to Run, the gauge sets to 0. Upon starting cold, the gauge reads 95-100%, then settles down to 85-90% after reaching operating temp at idle. Occasionally it drops to 65% when idling in gear, but soon rises again. I pulled the OPSU again to see if it was plugged/dirty, and everything was clean. I changed the oil filter, and the gauge still read high. Voltage to the Sending Unit is 12.2V. A manual PSI gauge read 25 PSI on startup, 18 PSI when warm.
PROBLEM #2: My Coolant Temperature Gauge is inoperable.
It has read 0% . I turned the resistive shaft in until the gauge had a reading, and it pegged out at 100%. I have a new sender ordered (a BWD WT421), in case I installed the wrong one, or damaged it. Voltage coming through the 1 wire is 12.2V. It will be here Monday.


THOUGHTS:
- Could my ECU be sending 12V instead of 5V to sensors? I don't know what they should be receiving...
- Is there a Voltage Regulator besides the back of the alternator? Alternator puts out 14.1V.
- Is it time to replace my oil pump for low pressure OR a stuck pressure valve?

Thanks in advance to any/everyone.
Mitchka

 

1: Doesn't matter, the ECU doesn't touch the gauge sensors; those are old-school. The temp gauge sender is the one under the A/C compressor; the one on the driver's side is the ECU temp sending unit. The gauge unit has some of the following part numbers: 2133211, 25037250, 4289898, 4504201, TU122

2: There's not one there either, but 14.1V is fine. It's in the ECU. This becomes obvious when checking how the alternator is wired in the Factory Service Manual, which I highly, Highly, HIGHLY recommend you buy.

3: That pressure probably isn't low if it was at idle (18psi/25psi). The general rule of thumb is 7 to 10 PSI per 1,000 RPM is adequate.

I'd suggest doing a complete rebuild; rings, pistons, and rods can be found for the 5.2/318 and will fit just fine. The crank and cam are unique to the 3.9.

RwP

 

When you reinstalled the sensors make sure you don't use Teflon....the temp sensor for example uses the engine ground through a varying resistor...Teflon can insulate the sensor and it won't read.