My car was a 5.0 tpi, the short block from a 350 has been swapped in, using the 305 heads. the porm was custom made by pcmsforless and I can't get it to idle. (I dont know if it was bad b4 the swap, I bought the car like that, not running, bad fuel pump, fixed that ) The trans is a T5, The car has headers ith AIR delete, and a 3" eldibrock cat back, acell new style 23# injectors, that the prom is setup for.
I have replaced the fuelpump, fuel filter, IAC, checked the timing, checked for vacume leaks, replaced upper and lower runner gaskets, plugs are new, wires ar 8mm msd, stock ignition system, 350 knock sensor, I have checked for vacume leaks... so I'm stumped... Could it be the EGR valve?
It will idle for around 15 seconds at 1000 RPM then falls to 700 ish for about a second then dies... it smokes a bit as well, I thought it might be the valve seals from the old heads, but it could be running rich... although my a/f ratio gage doesnt indicate a rich condition.... Any help wopuld be appreciated

 

oh man it could be alot, bc u installed the IAC doesnt mean it was calibrated correctly, u need a manual bc they have to be set correctly with a certain length...they are not set from factory/parts stores, u need to check TPS voltage, and ur fuel pressure is very important, get a fuel pressure gauge on the fuel rails and set the PSI to 50psi with vacume line disconnected, make sure ur relays are ok and that ur fuel pump is staying on, also urs is a 91 correct? so uhave speed density, and those are a pain bc of the sensors and tuning can be very difficult, so i could be the PCM chip, or just bad sensors. the EGR will affect running and u dont have the cold start injector so thats not a prob, could be a million things, check for spark etc could be a million diff things since u bought the car not running...which u shoulda fixed that before swapping the motor out. and ur 305 heads are gona be choking the hell outa ur 350

 

I didn't swap the motor out, it came with the 350 and the 305 heads all in the car... so I should look at the ignition and timing some more...

 

The IAC pintle length does not have to be set at a particular length when installing it. Just make sure the pintle is retracted enough so that it doesn't bottom out against the seat upon installation.

What are the idle IAC counts?

 

ignition or IAC, its hard to say, only things that control idle is the senors, ecm, IAC, maf, TPS, fuel pressure/injectors, distributor etc...basically everything, u just have to plug and play

 

If you suspect an ignition problem, monitor ignition primary voltage to see if it falls off. I suspect that's not going to reveal much, since it apparently starts and runs normally at the elevated idle, at least until the idle is backed off by the IAC.

If you suspect an ignition/ECM control problem, monitor the timing advance as the engine idles. If it varies widely, bypass the EST and se if it improvs the condition.

I hope that you are using a separate, diagnostic tachometer instead of that thing which fills the hole in the dash next to the speedometer. If that one indicates 700 RPM, the engine might actually be running at 450. You need to verify that.

A vacuum reading would also be useful.

 

At about the fifteen second mark, would you be changing over from open loop to closed loop operation?

Maybe that's an area to explore. The lag time from startup seems an interesting factor.

 

The fact that it fires up and idles for a short time would make me lean towards it being a fuel or air problem. Usually with ignition problems, it won't even fire, or it'll die instantly, not gradually. Try checking your IAC by resetting it the right way, and also check your TPS voltage with a digital voltmeter. There's tech articles on the main page that tell you the proper way to do these two things. Also check your fuel pressure like blackbird said. Checking your fuel pressure can tell you if you possibly have a bad pump. Also check to see how long the pressure stays up. If it drops off really fast, you have bad/leaky injectors or a bad fuel pressure regulator. If these 3 steps fail to improve anything, I'd look at your injectors. I'm sure you don't want to hear this, but many guys have had brand new Accel injectors that were no good. I've read a lot of posts where all they did was replace the Accels with Bosch or Ford injectors, and ran perfect, when it wouldn't run at all with the Accels. I could be wrong, but it sounds like your motor is running out of air or fuel since it dies off slowly. Will it stay running if you crack the throttle open some, or does it die no matter what? Btw, the EGR valve shouldn't really affect anything at all while idling, especially if the motor is cold, and still in open loop.

 

it will stay running if I crack the throttle a bit... I'll do the tps and IAC setups and get back with you... thanks for all the help so far...

 

BTW: it takes alot longer than 15 seconds for an ECM to switch from open loop to closed loop. There are two or three checks the ECM does before going to closed loop operation.

 

closed loop depends on engine temp and exhaust temp and feed back from the O2 when it reaches exhaust temp of 600 degrees. alot longer than 15s