My DD (the 03 in my sig) is acting weird. He would idle roughly, and around 10% of the times I would start him, he would act like he was out of fuel. Massage the throttle for a minute or two, and then he would take off, nailing you in the seat. I had a slew of 02 sensor codes, so I replaced all of them. This didn't fix it; in fact, I still have occasional O2 high voltage or heater codes. I put my Harbor Freight fuel pressure gauge on, and had my brother turn the key. It built up to 10 psi. I bled off some pressure to purge the air. It took four "key on, engine off" turns to get the pressure up to 47 psi. He started the engine, and the pressure held steady. Then the engine began to stumble again, and I suddenly heard a distinct "sucking" sound. I pulled the intake hose off and started him back up. He began to stumble again, and I heard the sound again. I put my fingers over the IAC passage. This made the sucking sound louder and made the stumble worse. I checked the fuel pressure. It was now at 32 psi. I bled off some fuel, and it dipped, then came back to 32 psi. I hooked my scanner, which displays some live data, into the jack and watched the MAP sensor. When the idle was smooth, it displayed 17" of mercury; then when the stumble started, it went to 20".

Today I was pulling a small load of around 10,000 lbs. And this time, he was less than happy about it. I checked the MAP values; when holding a steady speed, it read 20"; under full throttle, it dropped to around 10" of mercury. That can't be right.......

I have a new IAC motor and a new fuel pump I hope to install tomorrow. But if any of this means anything to anyone, please chime in......

 

Update: I installed the new fuel pump and IAC motor over the weekend. My power has returned; although, it's still not what I imagined a V10 to be when I was building it. :-) I suspect a weak OEM program to keep from frying the transmission. But, this morning I was hooked back up to the same 10,000 lb. load. At first, he still had a rough idle, and was slow to "wake up", as in he was kinda sluggish, and little power. Then, he straightened out, and I was good. One other thing I've noticed is that the shift tables were kinda high with a load; and that to get Overdrive, I had to let way off the throttle. My problem is I don't know what's "normal" for this old, used truck. Thoughts?

 

Do want to tow in OD. Very hard on the transmission

 

Okay, another update. Now, I know a little about engines and vacuum. At idle, the engine should produce around 17" to 22" of mercury. When you throw the throttle open, the vacuum drops down quite a bit. Then you snap the throttle shut, the vacuum skyrockets, then drops back down to idle levels. The problem is that as I watch the live data from my scanner, it shows the opposite. At idle, it jumps between 9" and 20". Under heavy acceleration, I've seen as high as 29" in WOT.

I priced a replacement through a dealership. They asked for $247 and a 5 to 7 day shipping time, unless I sprung for the $15 overnight option. I called O'Reileys and got one for less than $30, but it won't plug up, unless I'm on the wrong sensor. My Haynes manual doesn't exactly cater to V10's....

 

If it helps you any, my 01 V10 shows vacuum numbers like you posted yours should. I'm at 22-23 for idle. Step on it and the numbers drop to 3-5, let off the throttle and it jumps to 27. Cruising along at 65 on level ground the numbers are between 14 - 16. This is with a stock V10 and a sct tune from Hemi-fever with a glow-shift vacuum gauge.

 

I may be wrong. But vacuum bouncing around, is either vacuum leak. Or sick engine internally. Not sure of your mileage. Maybe time for a fresh engine.

 

Thanks man, but the engine only has about 30K on it. I rebuilt it, and went all out.

UPDATE:I bought a new MAP sensor from Advance. The idle has improved. However, my power levels are up and down in my opinion. I swapped the sensor in the parking lot, and the motor had NO power going home. I had to work to outrun a Honda!! The next day, power levels had come back slightly, but sometimes the truck will really take off, others it's just sluggish. I'm wondering if I need to disconnect the battery for a bit to trigger a reset/relearn.