Hi

I'm no mechanic by any means (more of a computer geek), but I have a Straight 6 300 that I bought for cheap and I'm trying to fix for cheap

I had a guy scan with a computer and got a P0171, and another evp ept voltage low.

I bought and changed the O2 sensor, as well as the canister purge valve (w/new hoses), per advice.

I then figured out how to run the on board EEC-IV using the CIL and got codes:

327 Electronic pressure transducer (EPT)/differential pressure feedback exhaust (DPFE) sensor/electronic vacuum regulator (EVR)
522 Neutral/drive switch (NDS)
512 Keep alive memory (KAM) fault
111 All systems OK

All I've done after that was check a hose off the EGR Vacuum Solenoid for carbon buildup, but was clean.

I was hoping to get some advice before I go spending a bunch of $$ on replacing a bunch of sensors that might not need replacing.

Thanks in advance for taking the time to help.

 

First question, how clean are the battery cables and what condition is the battery in? These engines are fairly complex and don't like to have varying levels of voltage to operate on. If it's constantly being jumped or just barely starting because it has corroded ends, bad or missing grounds then the charging alternator will take the voltages all over the place and make your sensors unhappy. Voltage variations are a common problem with older EFI vehicles.

 

My terminals are in bad shape. As a matter of fact, I have had to jump it twice due to the connection not being very solid.

 

If at all possible don't use emergency ends on you original cables. They'll only be grief later on. Install 2 new battery cables.

 

Operationally a clean source of voltage is where you need to start. That won't necessarily fix all the problems, but the sensors all work by receiving a "signal voltage", usually 5 volts, from the ECM. The sensors build up resistance in operation (temperature sensor for instance develops greater resistance as it warms up), and then it returns a lesser voltage to the ECM (let's say 3 volts at 150 degrees, 2 volts at 175, 1.5 volts at 195, etc.). The ECM then uses these return voltages to decide how it's going to control the engine.

When the vehicle is repeatedly jump started you can see how the huge variations in voltage (for instance the dead battery has 9 volts and the jump start has nearly 14 volts, somewhere around a 50% variation) would adversely affect the ECM's ability to calculate accurately. Do this for a long time and everything electronically isn't able to work as intended.

So if you want to get it running right you need to start with a good battery. To emphasize IICAP's comments, I say don't EVER use bolt on emergency type ends; they are essentially open to the air and will corrode and introduce resistance to the voltage flow in short order. Use proper cables in a substantial gauge that are at least equal to the OEM cables and have soldered/mechanically crimped ends. Make sure the alternator is charging. Get this in place and then let us know what other faults are still in the truck.