I have a 96 talon with a HRC stage 2 kit, sfmu with dark spring and largest disk, running 95psi fp at 7psi boost with stock injectors. My car is still running lean on top end above 4k rpm. I used a scan tool and noticed that my MAP voltage did not get above 3.89. I thought that this might be do to the hrc voltage clamp, so I removed it to see if I would hit fuel cut off going into boost, but it did not change anything. I then replaced the MAP sensor because I thought it might be bad, and installed a homemade voltage clamp (the one with 2 diodes and a pot.), but again, nothing changed. The MAP sensor is getting its full 5 volts and the output signal changes, but will not go higher than 3.89. Sometimes the car feels like it hits fuel cut at random times just driving normally. I can reset the ECU and it clears up but will happen again at random. I have also replace the coolant temp sensor and both o2 sensors. Thanks for any help.

That's a weird one.

What's the map output with the car ON, but not running? How about that same situation, with no fuel cut defencer of any kind?

me and pyschdragon(casey) have been trying to diagnose the samething on his car, his is doing the very same thing. i'm starting to think one of his sensors has gone nuts and the ecu is cutting spark above 4k. He noticed on datalogs his o2 voltage gets to 1V right before the cut, you having the same issue? Have you tried swapping out your ecu w/ another 2gnt and seeing maybe if the thing has just fried itself. I don't know what sensor would do this at 4K but his is doing the same thing.

back in the day when my HRC FCD went bad, it was clamping my MAP volts too low, causing a lean condition, no matter what my fuel pressure was..At the time, i said screw it, and took it off completly..I NEVER hit fuel cut, until around 4000+ rpm...under that, it ran great..over that, motor bucked like all hell..As Dino said, measure your map voltage with the key on, motor not running, and you should get 4.5 volts, +/- .1 volt. If its any different, then the Map is bad. Also, double check your wiring harnesses..If its still on the motor, that damn EGR tube likes to melt wiring harnesses..could be causing a short in your map wiring possibly? Just throwing out some ideas..

I get fuel cut ~4.65vdc.

So after you reset the ecu it will work right for a while? Then eventually drop again? That is weird. Like Matt said try swaping an ecu.

Fuel cut or serious issues after 4000 RPM's usually means the ECU is not receiving any type of MAP sensor input, or, it is receiving input and decides it's bunk. The cool part about a speed density system is that you don't NEED a MAP sensor for the car to work (i.e. you can get from A to B without one, because the ECU will fall back on a pre-determined fuel map based probably on every other important sensor but the MAP)

A few months ago I had a similar problem. Regardless of what kind of MAP sensor I used, if i had a Missing Link in there or not, if I had my voltage clamp in there or not, the voltage would get stuck around 1.6 volts after a minute of operation.

So how did I fix it? I checked the wiring. It was all screwed up. I went to the junkyard and found a Sebring with the same MAP sensor harness. I cut it about 1' long, and soldered it to the stock wiring on my car. All of my problems vanished, instantly.

Originally posted by ner947
Fuel cut or serious issues after 4000 RPM's usually means the ECU is not receiving any type of MAP sensor input, or, it is receiving input and decides it's bunk. The cool part about a speed density system is that you don't NEED a MAP sensor for the car to work (i.e. you can get from A to B without one, because the ECU will fall back on a pre-determined fuel map based probably on every other important sensor but the MAP) A few months ago I had a similar problem. Regardless of what kind of MAP sensor I used, if i had a Missing Link in there or not, if I had my voltage clamp in there or not, the voltage would get stuck around 1.6 volts after a minute of operation. So how did I fix it? I checked the wiring. It was all screwed up. I went to the junkyard and found a Sebring with the same MAP sensor harness. I cut it about 1' long, and soldered it to the stock wiring on my car. All of my problems vanished, instantly.

You are right to an extent... the average speed density system will still run with no MAP or a screwed up MAP, but it is an important adder in the overal fuel PW equation...

Also, on my car, if I have no MAP signal (if using stock ecu for fuel) then the car will die at any speed over idle...