The exhaust side of the head looked great, just like the small block magnums. One thing to remember is the v10 has a longer stroke than a 360 so it will try to pull more air at the same rpm.

So here is where we get to my testing. I did reseal the IAC and got a new one an only marginal improvement. So went back to the shop to use their snap on scan tool. The O2 readings are all over the place. Seemed to be fluctuating with the rpm as it is now running like garbage. I is 50-80 rpm below its target value at idle and cannot achieve it. So it was getting late and called it quits to hop over to another friends house 30 miles away to help him pull the motor out of his 68 mustang. My friend who was running the scan tool suggested to swap to the old throttle body. So I did that today. It can barely run when stopping now. Its horrible, I have to use the throttle to keep it running when braking. Bogs terrible when taking off and keeps getting worse. So I forced it into closed loop mode by disconnecting the O2 sensors again and the bog is gone on take off. However it still wants to die when braking but a little smoother idle. This leads me to the conclusion whatever sensor is going out has to be something related to vacuum and fuel, like the only sensor that is related to both of those things,the manifold air pressure sensor. I actually have an old map sensor I might put in just to see. If that doesn't fix it I'll still get a new one as the other one was on a junkyard intake. Really hoping that is it.

 

Different MAP sensor made no difference. I am starting to get concerned the PCM is failing. I had some issues when tuning where it failed programming mid way through a couple times. When we were messing around with the scan tool my friend made the comment that it was taking forever to establish connection too. When the O2 sensors were disconnected it didn't throw a code, the daytime running lamps pulse like a voltage regulator going out, and there was an active code for low rpm for speed above 15mph. But even an active code didn't trip the light. What's your guy's thoughts?

 

On mine, the pcm seems really unwilling to trip any variety of codes...... I had a dead miss on one cylinder, plug wire burnt in half, it was NOT firing..... and the PCM never bothered to notify me. The engine runs REALLY smooth, so, one cylinder being down gives a VERY minor vibration, and that's it. Hard to notice if you aren't paying CLOSE attention.... Never got a missfire code, never saw a blinking CEL.

But, the truck runs great. (especially after new plugs and wires.....) So I don't know if that was intentional, a programming flaw, or something completely different.

If you can find one cheap, it may not hurt to try another PCM.

Side Note: Disconnecting the O2 sensors forces the PCM into Open Loop. Closed loop is when it is actually paying attention to the O2 sensors.

 

You're right I mis-typed. I meant open loop. The factory throttle body is none adjustable, where as the utasome has an adjustable stop. I did have it so the throttle was barely cracked open. I think that was compensating and why it ran better with that one. So I may be trying to find a pcm at least to try it. It never ends

 

I forgot to check fuel pressure. I'll do that before loading the parts cannon.

 

You probably did this already but if not be sure and try something like some Caig DeOxit on all the the connector pins and slather them all up with dielectric grease afterward. The type of symptoms you are seeing could possibly be intermittent/poor contact related kind of stuff and trying some deoxidizer would be a lot less expensive, if it works, than replacing the PCM.. There is probably something less expensive than Caig out there but it is the one I know.

 

So I finally got a fuel pressure gauge. This is what happened. It seemed ok for a few seconds then it lost all fuel pressure stability at idle.


So I consulted the FSM and decided to do a leak down test. The FSM says it should hold at least 30psi for 5 mins. Didn't even make 3.5mins. However the interesting thing to me is when it hits the 49psi it should, it drops and never recovers. I am wondering if the fuel regulator is going out. I won't be able to test if it is the rail or pump assembly til this weekend.

 

The behavior at idle is puzzling. Not like the system is vacuum modulated or anything. Looks more like the regulator is having issue. Certainly explains the rough idle.......

 

My buddy who helped me look at the sensors last weekend had noticed my daytime running lights rhythmically flash at idle and seemed to go away when revved, just like this fuel pressure issue. He also noticed that occasionally the voltage would drop to 11-10.5 volts. If it was the fuel regulator you would think it would do it everywhere, or at least somewhere other than idle. He suggested hooking up an independent power supply to the fuel pump to see if the erratic pressure goes away. I'll update as soon as I know more.

 

Just cleaned with some spray electrical cleaner, that DeOxit looks interesting, may get a can just to have/try out.