Started cat today ?'s....


Active Member
Apr 11, 2003
Well i had timing nailed(getting a little better i guess), and she fired right up. I let the car go through the first heat cycle while burping the coolant system. Gauges are installed, exhaust is still a little loose, and some other tedious things before it goes to the shop for the gear install:banana:

Anyhow now for the questions.

Before these heads, i had it where it would idle halfway decent, now it will idle rock solid for around 7-8 minutes(timed it roughly), and then it is like it will surge up, have a really high idle for a minute. I unplugged the IAC motor, and it seemed to have no effect on whether it would do this or not. Can exhaust leak cause this? Can the JMS chip be off that much now that there are different heads on the car? I also seem to be having a fluctuation in my fuel pressure. (causes?) After the car shuts off the Fuel pressure gauge drops to around 18 psi instantly and holds that... It has a new 190LPH pump. i believe i have it installed correctly, i have a paxton fuel regulator on the car and a kirban waiting to go on? Could the paxton be causing the problem(is it boost referenced?) I will switch them this weekend,

I still haven't installed the MSD 6AL, so is it possible its the ignition. I am going to check the torque specs tomm., that will be the initial cool down check/retorque, i can change the FPR while the upper intake is off if anyone thinks that is the problem...

BTW>>>> sounds same at idle, but rev it :drool: I think i am gonna enjoy it(although i haven't driven it yet) :nono:

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I think the reason that it idles perfect for the first 7-8 is because the car is in "warm up mode" (Grady I know could tell you the correct ford term. But basically the computer has a fuel and spark program for warm-up (open loop I believe) then when the ect gets to the predetermined temp it goes into closed loop (not sure if I have these two terms switch around). This is the the normal operation mode and the fuel and spark tables are different at this point. That is were you are having your touble. I would say the idling part is due to you tune in closed loop. Hope this helps and doesn't confuss you more. The point I just made would have to do with your idle and not neccessarily your fuel pressure.
When the car is hot, it is in closed loop. The car is in open loop for 30-120 seconds or so upon start-up (till the O2's light off, which is quick with HEGO's). Then the car is in various stages of cold, warm, etc strategy, using the ECT, lambda and other sensory input to determine fuel trim.

Jason, does there seem to be any rhyme or cadence to the irregular idle? How long does it take for the idle to come back down?

I aint no Grady, but it sounds purely like an engine management/tune issue (not a hard part fault). I also wonder what will happen as the puter adapts to the new components.

WHen you retighten things, double check the vac lines too (leaks).

Good luck Jason.
one thing i though of is that the car has a fact. temp thermostat, and when they did the chip, they tuned it for a 180 comes on early etc....

thanks for clearing up the open closed loop thingy...