Hi guys,
I own a 1991 f-250, i have a brand new 302 in it, and all the parts that i needed to replace to put the new engine in, I also have a K&N hi-flow air filter, and 3" flowmaster cat-back exhaust system.

However, I am only getting about 10 mpg, or so my odometer tells me, but it is probably alittle off because i have bigger tires. But I am still consuming alot of gas either way.

I also have an engine code, number 41 in cm, which means that I have a lean condition. I think that it is because i am still running a speed density sensor, and with the K&N and the exhaust, the engine is getting too much air, and doesn't know to compensate by adding more fuel.

So what I am looking for is a detailed article or write up on how to do the mustang MAF conversion, because I am a 16 year old in highschool, and can't afford to pay 800+ dollars to buy one. I am decent with a wrench, and my dad is a very good self taught mechanic. So if someone could give me a link, or a website w/ an article on how to do this, it would be very appreciated.

Thank you

Nate

 

The K&N and exhaust are not the source of the code 41, and a MAF swap certainly isn't necessary (although it can be a fun project to do it without a kit). I would check the fuel pressure first of all to see where it is. I'd also pull the vacuum line off of the fuel pressure regulator to make sure gas isn't getting sucked directly into the manifold. The code 41 can mean that the computer can't lean out the mixture any more and the O2 sensor still reads rich, which would explain your poor fuel mileage - the computer can't lean the mixture to achieve the proper air/fuel mixture. It could also be the O2 sensor itself. When was the last time you replaced it? Generally, O2 sensors should be replaced about every 60000 miles. How many miles are on the engine? It usually takes a few miles on a new engine to get the fuel economy up to the normal level.

 

i just relooked up the code, and i didn't have enough detail, on a website called troublecodes.net, code 41 for cm means "System was lean for 15 seconds or more (no HO2S switching) - Fuel control"

Does this mean that it is my fuel system or o2 sensor, cuz it says no o2 sensor switching, but i don't know what o2 sensor switching is, and my dad is in africa so i can't exactly talk to him right now.The o2 sensor was replaced when i did the engine, which has about 4000 miles on it.

As I said, im a highschool kid working for min wage, and i hate having all my money go to gas. I know that the easiest solution to this would probly be buy an old beater 4-banger, and keep my truck for haulin and muddin, however, my dad won't let me drive anything that weighs less than 6000 pounds until im out of his house so i can't exactly do that.

by the way, i would still like a point in the right direction as to where to find an article on doing the conversion, because it would be fun to do it, not to mention ill be able to actually get gains from performance parts afterwards, and it'll cost next to nothin(except a lot of wrench time on my part).

Thanx for the help.

Nate

 

Nope.

First, there is no such thing as a speed density sensor.

K&N/exhaust won't effect the EFI system.

Code 41 can be caused by many things...all it's telling you is an improper o2 sensor reading. The o2 sensor could be reading the exhaust content perfectly fine, but the exhaust content could be wrong (ie rich or lean).

I'd definitely hold off on any MAF swaps right now. Fix what is wrong with it first.

It sounds like you did the KOEO test (key on engine off)...did you do the KOER (key on engine running) test? That will help indicate if there are any other codes.

 

I did do the KOEO test, because i didn't know that their was a KOER, the website that i found how to do the self-test on didn't say anything about it. Do i do it the same way, but just turn it on?

And if I pull my o2 sensor, is their any way that i can tell by looking at it if it is bad or not, or can NAPA test it or something, cause I really don't want to buy another o2 sensor, because this one is almost brand new.

Sorry for my incorrect terminology, its a speed density what???

And, I would still like someone to point me in the right direction as to where i would find an article on the MAF conversion. I would like to read it and see how hard it is going to be, whether I will end up doing it or not I don't know. But I still want to know how.

I'v also got a couple other questions,
1. what is o2 sensor switching
2. how much can I do to my truck before the EFI is affected(performance wise)
3.How much do you think I could get for a 91 f-250 single cab long bed w/ 4000 miles on the 302, 5-speed manual, new paint job(blue metallic w/ a clear coat), stainless steel side hooks for tying stuff down, stainless bed rail caps, stainless fender trim, and a new chrome bumper?? The odometer reads 70000, but i don't know if its 170000, 270000, or just 70000.

for the last question, I was thinking something in the range of 4k-6k

Thanx

Nate

 

Run the KOEO test, go through the codes and CM codes. See if you get anything, mark what you get. Turn the key off, then start the truck up (make sure no wires are in the way of the fan, etc). It should blink 4 times then it'll initiate the KOER test.

You'll hear solenoids click, you'll hear the idle go up, down, etc. The computer will check all the actuators and sensors while it's running. You should tap the brake while it's doing this. Then you will see a blink, signaling you to snap the throttle. Punch the throttle and when the RPMs go past 2000 let off (just a quick snap) and it'll come back down to idle. Then it should spit codes at you. It gives you 10 seconds to snap the throttle.

These are KOER codes.

If you just replaced it, it's probably fine, but you can check the voltages with a volt meter and paper clips. Any chiltons or Haynes manual will be helpful if you havn't picked one up yet (I highly recommend Haynes over Chiltons).

Speed Density is refering to the type of EFI system your truck has. The other system used with Ford EFI is the MAF (Mass Air Flow) system, which you're looking to possibly convert to.



You can use the search function of this website to look up "MAf conversion" or keywords like that. That topic has been beat to death...

Basically, you can use a $650 Ford conversion kit, or piece it together. You can get a 88-93 mustang a9l or a9p computer and mustang harness. Then put the computer in your truck, and use the mustang harness and your truck harness to make 1 MAF harness by following a wiring schematic and re-wiring your trucks harness, using the mustang harness for parts/plugs.

1. o2 sensor switching is the fact that an o2 sensor doesn't put out a constant voltage. It refers to it's voltages switching up and down. You don't have to be very concerned with it, code 41 is basically telling you the exhaust content isn't right or the o2 isn't working. If you just replaced the o2 sensor, either you got a bad one, there's a problem with the wiring from the o2 to the computer, or your truck is simply lean/rich based on another problem and the bad o2 sensor reading is a side effect (probably the latter).

2. You can do quite a bit, the main concern is switching the camshaft. The K&N doesn't really affect airflow much, and the exhaust is downstream (after the fact) so it doesn't matter.

3. Check NAPA, Kelly blue book, etc. Prices vary by location and quite frankly, it's worth what someone is willing to pay for it. We can't really tell you what it's worth. Look at local vehicles being sold to get an idea of what the market is like.

 

http://bjoern.brembs.net/cars/maf_conversion/

you can use that as a reference for what needs to be done with the wiring. You don't have to do everything on that page (like adapt a lightning throttle body, or change injectors), but it will give you a general idea of what is involved.

The O2 sensor is probably fine, the code 41 is more likely to be a wiring or a fuel delivery problem. I get a 41 if I run with the O2 sensor unplugged, so go over the wiring to make sure there isn't anything broken along the way. There is not really any way to tell if it is bad by looking at it, but you can check the voltage while the engine is running. There are three wires on the sensor, one is 12V, one is ground and the third is the signal wire.

Speed density is the type of EFI these trucks run. The computer uses the engine speed and the air density (manifold pressure) to determine proper fuel and spark requirements.

Definitely start with checking the wiring and checking the fuel pressure and the fuel pressure regulator.