1996 F250 Codes issue

A while back I posted about the F250 I bought for my son. It was running extremely rich (blowing black smoke, carboned up spark plugs) but the engine codes were showing that it was running lean. I couldn't figure it out and I brought it to one shop that I had been having pretty good luck with. They replaced the O2 sensor but it was still running the exact same way - they claimed they looked for vacuum leaks and couldn't find any - I couldn't either. Their opinion was it needed the cats put back on the truck to make it run right. I knew that wasn't it because the sensors on this truck were all upstream from the cats - no sensors after the exhaust went through the cats.

Brought it to another shop where the guy "specialized" on Fords. He found 3 vacuum leaks - one of them being a huge leak that powered the climate control (reason for the lean codes). Then he found the fuel regulator was leaking a lot of fuel into the vacuum system (reason why it was running rich). The owner previous told me the truck had running issues when I bought it but he couldn't figure it out. I had replaced the IAC and that had made it run and start a lot better hadn't figure out why the code conflicted with how it actually ran. MPG went from 4 to 14 (5.8 w/auto) before and after his repair. His price was $215 to actually fix the truck as apposed to "working" on the truck.

Great!! I hate it when people throw parts at stuff and guess. Why in the world would anyone want to put a cat converter back ON? (unless for smog test I guess)

How do you go about finding vac leaks if not obvious? I am curious as I got a 99 F250 that surges a little then backs off running down the road seems worse with cruise control and I got a feeling it is a vac leak causing it.

Take care of that guy. Not many that honest and that good. And that reasonable.

Some shops have a machine that pressures the system with smoke to help find leaks.

Any vacuum leak, even a leak between the throttle body and the MAF sensor, will nearly always set a "lean cylinder" code.

Usually a visual and listening inspection will find them. Common places to look are the air plenum having a split down in the pleats or not installed properly, the PCV hose sucked in and leaking on the undeside, out of sight, or any other vacuum hoses.

We used an acetylene torch but a propane torch will work. Open the gas and run the tip around areas of the intake / hoses/sensors. The unlit gas will usually cause the engine speed to increase(RPM), when you take the gas away the engine speed decreases..this usually tells you where you have a leak...intake manifold,hose etc...its worth a try

Had a similar issue on 2004 F150. Truck running rich, gassy exhaust and stalling due to overly rich condition. Basically, an FI, ECM vehicle flooding; which I though was impossible.

Pulled code and set lean on left bank. Cleared code and fixed...for a while. Pulled coded again and lean on right bank.

Just FYI any lean troble code set by the ECM will trim the fuel as rich as the ECM program allows. Thus it can run rich if you have slight vacuum leaks.

A new hose between the plenum and throttle body plus going back to factory air intake/filter fixed it for good.

I plan on it. I was told he would actually diagnose the issue and he did exactly what I wanted done. If the vacuum leaks hadn't been found his next step (after he called me to OK the price) would be to actually start reading the electronic returns from sensors to see if a wire was shorted.

That sounds like a throttle position sensor to me .Check it with an ohm meter and see if it changes smoothly. I can tell just by driving it.

I 2nd the the TPS. Had the same issue with 92 F150. $20 TPS and 15 minutes fixed it.