89 F150 5.8L C6

Truck burning a lot of gas. Im gettin about 5mpg on the highway right now. Truck has an intermittent surge every once in awhile. It was a constant thing but after i put new plugs, wires, cleaned the IAC and fixed the vacuum modulator from allowing tranny fluid into the vacuum lines it hasnt been bad. I did however find that the Y pipe is cracked all the way around the o2 sensor today. I was wonderin if because that o2 sensor may be gettin ambient air as well as o2 readings in the exhaust it might cause the truck to run rich. The truck has a CAT on it so I dont think the gas smell should be as stong as it is.

 

You should not be smelling gas, it sounds to me like you could have a leak in the fuel delivery system.

You should figure this out and fix it ASAP as gasoline leaks on hot engines are never good things:

Truck burning:
‪Windsor truck fire‬‏ - YouTube
Another view of it:
‪Downtown Windsor Truck Fire‬‏ - YouTube
Aftermath of it:
‪Aftermath of Windsor Truck Fire‬‏ - YouTube

 

Its not leaking anywhere

 

Yes, an exhaust leak upstream or very near the O2 sensor can make the PCM think the truck is running lean therefore it dumps in more fuel. An overly rich or lean condition will kill a catalytic converter in a very short time.

Another common problem on these EFI trucks is a leaking diaphragm in the Fuel Pressure Regulator. Pull off the vacuum line leading to the FPR inspect for signs of fuel by sight and smell. Replace it if it shows any signs of fuel. A faulty, but non-leaking, FPR can also cause a lean or rich condition. Check the fuel pressure at the rail with a fuel pressure gauge.

 

Glad to know that you got the vacuum modulator fixed on the tranny! I remember posting on another thread you had started. As previouly mentioned, that Y-pipe cracked is gonna give you erroneous reading to the O2 sensor and check to ensure that the FPR diaphram isn't ruptured.

 

brand new FPR guys and i double checked it the other day and i was pegged at around 38-39 psi at idle

 

An vacuum leak can create a similar condition. Have you checked the PCV valve? It will be in the passenger side valve cover, near the firewall. It's a metering air leak design, that if it not opening and closing properly, it can cause a range of problems. Cheap PCV valve's create a similar condition since they aren't designed to such OEM tolerances.

If you can get access to the valve, remove it from the valve cover with the engine running and cover the end of the PCV valve with a sheet of paper and see if the engine runs any better. If you do a search under my screen name, I have several Post's with useful info concerning problems with a Rich condition. If you can get you hands on a DVOM, preferably a good one, no cheap ones, you can probe the O2 sensor wiring harness (Not the O2 sensor pigtail itself).

 

Havent checked the PCV yet but I will do that later on. I also need to post some pics of some vacuum lines i have some questions about. Im not sure they are routed correctly but thats the way they were when i bought the truck. Its a 3 nipple cluster on the passenger side firewall. Nothings on my schematic about it. off the top of my head the far left line runs to the A/C, middle runs to the vacuum modulator and the far right runs directly to the upper intake manifold. Any insight?

 

Sounds correct. There should be a check valve in that "cluster". Posting pics of your engine and any questions you have about certain areas of unknown would be really Great! Let us know how it goes!

 

Get your Y pipe welded up should fix the issue based on everything else you have done or checked already.

 

 

these are the lines I was wonderin about

 

That is just a T-like device. You have one vacuum source that's getting distributed (shared out to) two other hoses, that's all. No magic there, the order of connections doesn't matter.

Only trucks with AC have that.