1989 F-150
302
Speed density
AOD
2WD

OK.........I posted a while back about a surging idle. I forgot to mention that I changed the cam from a stock cam to a 302 HO out of a mustang. It is a comp cam out of a 90 model. Can i get a wiring harness out af a mustang with mass air flow and change it? Will it be a plug and play deal? Which computer do I need........a A9L which I think is for a 5 speed or the A9P. Is the A9P for an automatic? Can i get some links on the conversion also?

 

A MAF is a sensor. When the engine has a MAF, a TPS a O2 or two and some other goodies, it tells the computer how to fuel the engine. There are a few ways to tell a computer how to fuel an engine, not all ways require a MAF as you know. I would stick to the stock computer and find and fix the real performance or drivability problems. For surging idle, start looking at vacuum leaks or the IAC.

 

The problem I am having is the computer not recognizing the cam and firing order.......That is why i want to do a conversion.

 

The firing order is invisible to the computer, all it cares about is that the correct number of cylinders are there. Going from one V8 firing order to another only involves moving the injector plug to the right cylinder and then of course the spark plug wires have to be right. Changing the amount of air is more tricky. The computer has limits so it won't over or under fuel the cylinder. If the engine now breathes better and the O2 sensors continually show lean because the fuel limit is reached, the ECC will throw a code. The only way to correct it is to either give the computer a tune or replace the computer. On the Ford Explorer forums, there is a guy who mods computers but I don't know where he is located or his username.

 

gcancino2003, look at the IST site, they have all you need to do the conversion...plug and play. If you can find a donor rig, that will work too, but there arn't too many 90s MAF Mustang donors out there. And the people that do part them out seem to want big $$$ for the parts from what I have seen.

Do you know for a fact that the cam he used is speed density compatable? The one time I had a non SD compatable cam (unknown to me at the time) w/ SD system, the idle surged.

Also, how do you explain a vacuum leak causing a surging idle w/ a speed density system?

 

Vacuum leaks cause fluctuating idle, maybe surging idle in the context of a SD system refers to something more severe. I thought that all speed density meant was a particular type of intake on a Mustang motor. At any rate, before going to extremes trying to fix a problem, simpler causes need to be eliminated first.

 

Speed density is not a kind of intake on a Mustang. Speed density is the name of one particular electronic fuel injection theory. It uses a MAP sensor to measure the load on the engine (manifold vacuum is proportional to load) as opposed to measuring the air as it enters the the throttle body. That said, if a SD motor has a vacuum leak, the MAP sensor will detect it (the drop in vacuum) and add fuel to compensate...the result is a high idle, not a fluctuating or surging idle. To a SD system, a vacuum leak is no different from opening the throttle plates...it's all just air that enters the motor, it does not care WHERE it comes from.

 

Eco...........what is the IST site? Blueman2333......From what I have read a speed density has bank firinng which fires all 4 injecters on one side at a time, unlike a MAF which does each cyl. I also read here if you have a cam that has a "LOPEY IDLE" the computer freaks out and sends off the wall codes. Thats why i figured i would convert it.

 

Surging idle is a well documented problem with batch fire motors running a cam with the wrong firing order, others here have encountered and conquered this same problem. The fix involves rewiring the injector batches, but I'm not exactly sure what injectors get grouped together.

 

IST = Interactive Systems and Technologies

Scroll through this page and you should find what you need.

http://www.mass-air.com/Products.htm

I will be ordering a few things shortly...ie the Air Adjuster, TPS monitor and eec-iv gaskets. They are basically a bunch of Ford mass air gurus.

There were plenty of SD rigs with sequential firing injection...so not all SD rigs have bank fire injection.

The centerline being too low is the main thing I have heard of that causes any given cam to not work with SD and thus cause a surging idle.

 

Before you do all that work, it sounds like it would be worth it to resequnce the injectors. It might solve the problem. There is nothing wrong with batch firing per se, unless you just have to get as much performance as possible.

 

ECO actually you are partially correct. the MAP tells the computer the engine is under load so it adds fuel (this part is correct). but with the addition of fuel the O2 tells the computer it is ritch, so the computer then cuts back on the fuel and increasis the idel through the IAC for a moment to clear the ritch condition, then the vaccume picks up and the MAP says "no Load" cut back the throttle, then the vacuume drops agian and it all starts over = surging idle.

this is as severl other reasons for a surgin idle in a SD system.

 

^^^Thats basically what happens with a non SD compatable cam in a SD motor.

Unhook the break booster vacuum line on a good running SD motor thus creating a vacuum leak. See if the idle surges up and down or if the idle raises. It raises every time for me.

 

I had a MAF engine with a sticking IAC that "fluctuated" like a bi*ch, turned out it had a vac leak too. Once both were fixed, the non-IAC idle adjusted and the TPS was adjusted (the .96v at idle setting), it idled fine.

 

So how do you sequence the injectors? The cam came out of an HO motor thus the firing order is a 351 firing order.