Ok, i need some advice here. Remember my 89 Formula with the 305tbi going to a 350TPI MAF with hella lot of goodies? Im having trouble with it. I got chips and a friend programed them for me, but we are having a hard time getting the car to run right. She's not throwing any codes, but it wont keep a constant idle and wont stay running if the rpms drop below 8-900 Here is what I have. LT4 Hot cam Vortec heads, SD intake manifold, 1.6 roller rockers #24 pound svo injectors. I dont know what needs to be changed on the prom. Im not the one making them, my friend is but we are kinda stumped. It will run damn fine at wide open throttle when reving it up, (Hasnt been driven yet) but wont hold a constant idle, the Fuel pressure is adjusted down to about 42PSI which is on the high side and for some reason, when hooked to the computer, the 02 sensor wont put out a reading at idle, only at half throttle on up. WTF? Anyone wanna help me with this one? Is the O2 causeing the horrible idle? what could i do to the computer chip, should the injector flow rate increase or decrease to adj for the added pressure? Is there something wrong with the spark curve?HELP

 

Not sure how much help I'll be since I can't get my own eng to run right, but I'll take a shot at it.

The inj constant needs to be changed to whatever your new inj are rated at. If your running 24 lb injectors and the inj constant is still set at 19, you will be way too rich.

Is the eng going into closed loop?

Mine would only enter closed loop above 60 mph. Replaced O2 sensor and now it enters closed loop within a couple of mins at idle.

Check for vacuum leaks. Check for internal vacuum leaks.
Check for leaks between the MAF and the throttle body.

Verify TPS is set to .54 volts at idle and goes over 4 volts at wide open throttle.

Verify ign timing is correct with by-pass disconnected.

Make sure MAF wiring is away from spark plug wires.

Make sure the eng, batt, and chassis are all grounded well to each other.

Pull and inspect the plugs.

Verify the MAF diag flag has not been "unchecked" using your bin editor.

Check the MAF reading at idle.

If all that looks good and it still won't idle, bring it over to my house and we can torch both of our cars in my front yard!

 

ROFL- I know just how you feel!

Looks like sensible advice to me, but on the SD (not MAF) system I'm working on, these things get into open loop "idle mode" below 5 km/hr if closed TPS. So O2S shouldn't be a factor. Is the VSS hooked up?

John

 

Ok, the injector constant was set for 24 pound injectors but these ford svo injectors are supposed to operate at 38psi and the best the adj regulater can do is 42psi, So some tweaking of the program needs to happn there.
It will enter closed loop but the hand held tool the mechanic uses shows that the value drops to 0 for the o2 sensor if you try and let it idle.
Everything else is good, timing, TPS, no leaks, as far as i know, the mechanic is doing the work
have you guys used chips from cragi moates before, any tips, maybe im doing something wrong.

 

What's the deal with the AFPR only going down to 42 psi?
Is it hitting the plenum? When I installed my Holley AFPR, I had to grind the bottom of the plenum to make room for the AFPR ****.

If the AFPR can't be adjusted any lower, the inj constant could be raised in like .5 lb increments untill it's happy at idle. At least this will work in theory. I've seen where others say to avoid adjusting the inj constant cause it can make for other problems.

 

Im not sure why it cant go lower, its what the shop told me, maybe it is hitting the plenum, I have a Crane Cam brand FPR. I guess ill have to give the injector constant a try, thanks, lets see if this works