I just finished a MAF swap on my '87 with the 302. I used a mustang ECU and re-wired the engine harness to match. The MAF is calibrated for 24 lb/hr injectors, and I am running 24 lb/hr injectors. The motor is otherwise stock.

Here's the problem: It pings really bad anywhere under 3000 rpm. I have a mass air meter calibrator, and I can richen the mixture up, which helps a little bit, but it still pings until it's so rich that black smoke is coming out of the exhaust. When it doesn't ping, the O2 sensor shows ~.87 volts, which is way rich. When the O2 sensor bounces between .4 and .6 V like it is supposed to, it pings like crazy. I've got the timing set dead on 10 degrees BTDC, but I will double check that when I can get my hands on a timing light. The tps reads ~.95V at idle, which is where it should be. The only things I can think of are the BAP (I re-used my old MAP, just disconnected the vacuum line), the O2 sensor, or badly clogged injectors. Anyone have any experiences they can share with me that might be of use? Thanks in advance.

 

I wonder how you're cam timing is? It's one thing to check your timing assuming that the crank, chain, and cam are all in perfect alignment, and another when one of the 3 is out of whack. That's the only thing I can think of, as I assume you've already done the plugs, wires, cap... tune-up round. If you can get it enough fuel to stop pinging, and you've got enough spark to burn it off, than that would be my guess. However, definitely check the MAP/BAP, and O2 sensor as you already mentioned. Those can be huge contributors, especially if you're basing your Air/Fuel mix readings off the O2 sensor.

 

I just replaced the timing chain thinking that was part of the pinging. I'm confident that the cam is lined up correctly, because it runs very well otherwise. I drove it yesterday with the O2 sensor unplugged (running only from the MAF sensor) and it ran much better and was more responsive to the changes I make with the calibrator. I may have an O2 sensor reading out of whack. It only pings once it warms up, so I'm planning on checking the ECT sensor as well, although I'm not sure how much that affects spark advance. Thanks a lot for the response, I'll keep digging into this, and I'm sure I'll eventually figure out what is wrong.

 

ECT makes sense to be a reasonable option to check, as it will make it run lean if it is telling the comp that you're hot as *****, when you're really not. Only problem with leaving the O2 sensor out of the loop, is you end up running open loop the whole time and the computer has no play in it whatsoever. It then reverts back to the default a/f mix of 14.7:1 which will make it hard to figure out where your problem lies. That's probably why it smoothed out for ya... it wasn't doing anything but running in open loop (just as it does when it's cold).
and if I got open and closed confused again, then someone please gimme an easy "logical" explanation to relate which one is which. The logic I try to apply to the terms when trying to explain 'em always gets me confused as to which one I'm talking about.... LOL
now off to figure out why mine just started eating crap... just died on me outta the blue....

 

I think you have open/closed loop correct. I think of it as an open/closed electric circuit. I'll see if I can't pull the ECT and see what kind of resistances I get. You're right about the O2 sensor as well. With it disconnected, the computer only uses the MAF to control fuel with no feedback from the O2 sensor, and probably reverts back to limp mode as well. Thanks.

 

Let us know what you find out about your ECT. And thanks for the example! That's probably what they meant in the first place, when talking about open/closed. LOL