I took on a job for a friend of getting his 94 ford f-150 running. And i'm stuck. It has a 5.0L with an odometer reading of 165,000miles.
At first it wouldn't even start, which is no surprise becuase it's been sitting for almost 2 years.
Then I got it to crank and ocassonaly fire. And even got it to run when I feathered the throttle. However when I hold steady on the throttle, it will idle up and down from 1200 Rpm to about 3500.
So..I do some checking under the hood. The only code was a 334, EGR closed, high voltage. I omhed out the EVP and it was bad, as well as when I checked the IAC. Just really carboned up, and incorrect ohms and voltage. So I replaced them. But I still have the 334 code.
Then I came to notice that when I unplug the Mass Air Flow sensor, the pickup will run and idle with no throttle, it still surges slightly from 750 rpms to 1000 or so.I droveit, and it didn't seem to lack any power. When I pulled back up I looked under the pickup and the Cats looked like they where getting ready to melt, I could nearly see through them. and when its running and I plug the MAF back in it starts reving up and down and eventulally it chokes out the engine.
But if anyone has seen this problem or can point me in the right dirrection, it would sure help
Thanks
-kuzy

 

With the cats that hot, it's definately lean. Could be a vacuum leak. These engines are known to occassionally develop a vacuum leak between the plenum and intake manifold. It could cause the irratic idle you describe. It would also tend to run leaner than normal. Insufficient fuel supply would cause a lean condition also. When you pulled the plug on the MAF sensor, it went into limp home mode and ran off of the set tables programmed into the ECU for when things do go wrong.

Greg B

 

I'd try hitting that MAF with some MAF cleaner. They have it at Autozone.

 

Deffinatly some sort of a vacume problem, the brake booster isnt working. I was told by the guy that was supposed to work on it (I used to work for him) that it was the upper and lower intake manifold gaskets. He also said that they are kinda known for it. I just really didn't want to believe it. But then a again, I'm a heavy equipment mechanic...kinda retired from working on gas burners and pickups (at the ripe old age of 20). Any other sign or test that I can do to be sure it is the gaskets?

 

MAF is good, I tested it with one I know is good.

 

I guess you could always throw a vacuum guage on the system, and see if it is reading within spec. Or, you could spray small amounts of starting fluid near the suspected areas, and see if the engine picks up a bit.

I think that you might be better off just replacing those gaskets, just so you know what you are dealing with down there.

 

I forget I'm workin on a pickup gas engine, On a truck or tractor you can hear the turbo leaking off instead of pushing air into the engine. I just gotta step back and remember what I'm working on.

 

It's funny how that is. Being able to take a step back is a valuable thing.

I spent the first several years of my odd career as a mechanic in a rental yard, working on everything from wall paper steamers to excavators.

Over the next 14 years I was a parts guy for John Deere, Caterpillar, and Case. Mostly construction, forestry, and over the road truck engines. With a couple of years in automotive aftermarket parts thrown in.

In the last 10 years, I have been a computer systems administrator, and hobbyist programmer.

It's amazing the number of things that one forgets, and the strange little oddities that persist no matter how much time passes.

 

Yeah, I'm working for Caterpillar as a tech. I'm finishing up the 'think big' Cat program in Okmulgee, Ok. (I work in Wichita Falls Texas). Mainly equipment...and not a whole lot of engine work. Hydraulics and a lot of grunt work for now. But i'm enjoying it. I worked for a guy in highschool (and the two summers before that) working on mainly pickups, cars small tractors, lawn mowers...you name it. Thought i'd speacialize in heavy diesel equipment.