1986 F150 302 EFI.

My concern is the truck is running rich and fuel is getting into the crankcase. (Dipstick smells like gas.) I've checked fuel pressure (not running, just turning key on and then off) and it stayed solid at 38 lbs for probably an hour before I disconnected it. (I didn't check it running.) I don't think the injectors are leaking. They were replaced about 10 years ago with 24 lb injectors.

My question is would 24 lb fuel injectors (stock is 19) be enough to cause it to run so rich?

 

Yes. You have to realize you have one of the first fuel injected engines Ford put in a truck. They had fuel injection in various things for just a few years. These older fuel injection systems are what is called "speed density" systems. They set the engine up from the factory a certain way, with certain components, certain camshafts, etc. They are then programmed for those components, and the computer can only change things just a little bit to compensate for normal wear and normal things that happen when the system ages.

A big change like the injectors means it will run very rich when it is cold, since it is too cold to look at the O2 sensor(open loop). So it looks up in the memory tables how to fuel the engine. The memory tables are not programmed for the larger injectors, so it runs rich. Then when it warms up, the O2 sensor wakes up (if it's not fouled with fuel) and then the computer goes into closed loop and see's that it is way too rich. It tries to shorten the injector pulse as much as it can to reduce the fuel, but it can only adjust it so much. It will then give an error code "running too rich" and then go back to open loop, and we know what happens in open loop.

That is why these older engines are very difficult to hop up. Later on they came out with Mass air added to the computer system, and that made the computer a little more flexible when changing things. But still only within limits.

 

Thanks for your detailed answer. It explains why when my truck got warm it would do better for a while, and then run rich again..

Do you have recommendations for fuel injectors for this truck? Motorcraft are running around $140x8, which is more than I want to spend!

 

Looks like Motorcraft is out. But here are some Bosch injectors that fit.


You can do some searching, but I am hearing Bosch is who makes motorcraft injectors.

 

Thanks. I can't seem to find the Bosch injectors on Amazon. (The link went to an off-brand injector.)

 

$140 for 8 injectors, from Motorcraft, which is OEM...?

https://www.napaonline.com/en/search...ors&referer=v2

 

Here's from a google search for that NAPA

# https://www.google.com/search?q=FUel...t=gws-wiz-serp

 

It's around $140 per injector. 8 injectors is well over $1K.

 

Then $400 from NAPA looks pretty good, plus you know they will work. Buy from your local auto parts store. I find my local NAPA has the same employees working there some 13 years later. Support a local business and people. They stand behind the parts and can get replacements in most cases in 2 hours if needed.

 

Agreed. The NAPA near me is the regional distribution center, so they stock a lot of stuff that the smaller stores might not have.

These injectors come with a 3 year 36K mile warranty. (I don't put anywhere near that kind of mileage on this truck.) I haven't seen anything else with that good a warranty.

Thanks for your help!

 

Another option would be to snag eight OEM injectors from the U-pull. Get a wiring connector while there so you can power them open on the bench and spray cleaner through them. For $15 you can get a rebuild kit for the set (see tip below). New seals and screens.

OEM injectors are the best and can be found in dozens of Ford models up to about 2003. To find these models go to Rock Auto. Select INFO for any injector listed for your truck > click highlighted part number in box at upper right > a list of all models using the injectors will appear.

Tip: The stiffer black o-rings injector seals are a better choice than the softer blue ones.

Much pricier now than when I had mine refurbished, Scott at the Injector Shop does a great job.

 

Thanks diggerrigger! Lot's of great advice in your post, and I definitely appreciate it!

I might be able to find the original injectors from this truck...they're somewhere in my garage...