breaking up at mid-high RPM

[SteveVA]

Hope you guys can help me out with a frustrating issue. Sorry for the long message but want to provide as much information as possible.

Background - I have a 95 mustang GT that I picked up recently with a 331 stroker built by DSS, AFR 185 heads, Trick Flow Track heat intake, 75MM TB, 30# injectors, calibrated C&L and TKO 600. Not sure what cam is in it (the owner was not sure and had lost the paperwork) but it certainly has a lope to it.

Problem - The problem is actually two fold. First the car does not want to idle below 950-1000. It does not idle rough and then die below 1000 RPM...it just dies straight away. the second problem is that the motor is breaking up around 5,000-5,500 RPM. The fuel pressure at idle is 38 psi. This car seems to demand high timing. It will not run at all below 12 and seems to run best at 18.

So far, I have replaced plugs (went two steps colder because I intend to spray. Gapped at 034), replaced cap and rotor, replaced plug wires, replaced fuel filter, checked for vacuum leaks, replaced the iac, checked the TPS and it is within specs.

Any suggestions where to turn to now?

 

[JJ95GTID]

You didn't mention a tuning device like a "chip" or Tweecer, etc...

If the car is running with the stock EEC-IV then it is running with settings for a stock 302cid engine and not a 331cid. The 94-95 ECM is very touchy this way.

 

[SteveVA]

Sorry, knew i would forget to add something. It does have an SCT 4 bank chip that was tuned at a local dyno shop. The shop has since gone out of business so I am not able to get any additional information. Also, it would have been tuned with an RPM II intake rather than the Trickflow. He sold his intake before I bought the car.

 

[final5-0]

Hello Steve

Without knowing what all the past Pro Tuner messed with

You are kinda at a disadvantage

You mention fuel pressure and timing values

You would think he would have set your fuel and spark with the tables in
the pcm and if that is so ... logic reasoning would dictate setting the fuel
pressure at what ever is the OEM value and the same would be said for
the dizzy setting ... which I KNOW ... to be 10.

I then would look at the throttle body to see if the blade stop screw
is not too far out.

Then you might wanna take a look at the bleed screw, isc, iac, or what ever
you like to call it. Might wanna count the turns to seat it lightly so you have
a starting reference or you can put it back to its original positon if need be.

On a FMS 60 or 65 tb (loacated under a small rubber plug) it is usually in the
range of 1.5 to 2.5 turns out but that might not be correct with an
aftermarket tb

After those tb adjustments you would be wise to reset the pcm and give it
a while for the adaptive strategy to help you as much as it can

The VSS sensor can cause idle issues as well but check it for proper
operation before you spend the money on my say

Just a few things you could try without going inside the pcm

Grady

 

[SteveVA]

Thanks for the suggestions. I will give them a shot and see what happens.

 

[SteveVA]

Went trhough the items lsit above with no real improvement. I did however break out the code reader again to see if something popped up. I am now getting a 412 code - Cannot control rpm during KOER high RPM check.

Any suggestions on where to look on this one?