My check engine light came on the other week. I got the engine scanned and it came back as bad O2 sensors. I changed all 4 sensors and got it rescanned and the Banks were too lean. I did some research and found out about the rubber elbow on the back of the engine. I checked it and it looked and felt fine. My MAFS looks clean. Any ideas????? My truck has 109,000. Original spark plugs.

 

Anyone?

 

spray004,

A LEAN condition is just that, too much air (for the amount of fuel that the PCM has added).

A "dirty" MAFs allows more air go by than it "reports" to the PCM. So the PCM doesn't add enough fuel. You say "MY MAFS looks clean". A coatong of 1/10,000 of an inch of "crud" can insulate the MAFs filiments enough to cause a lean condition. Spray your MAFs with contact cleaner or brakekleen!

Other "unmetered" air getting into your engine can cause the same problem. So look for vacuum leaks. Check for detached,cracked or deteriorated vacuum lines. And replace that "rubber elbow at the back of the engine". Even if it's not the problem now it could be in the future. Spend the buck 380 it's worth it.

Do the above than reset your PCM. If the code(s) come back check for a cracked intake manifold or bad gasket. If that's not the problem check your fuel pressure and than anything else that could cause low fuel delivery.

Good Luck

 

I dont believe its an intake leak or bad intake gasket. I've had problems on different vehicles before with intake leaks and this doesn't have the same symptoms. Besides the CEL, the only noticeable problem is when i'm idling at a stop light or somewhere for a while after the engine has warmed up, it will idle very rough. Since the O2 sensors are bypassed until exhaust gases reach 600 degrees I believe that also leads me to believe that its not the intake. Driving down the road I don't notice any problems, only at idle. I'm going to clean the MAFS when I get a chance and look for vacuum leaks. I'm also going to change my fuel filter.

 

You have heated o2 sensors that do not rely entirely on exhaust temp. It always amazes me that people prefer to assume the basics are OK and go after the more obscure problems first. It idles rough warm because it is running lean ( Lean misfire ) Try using carb cleaner around the intake manifold and vac. lines while it is running rough. If you hit a spot with a leak it will change the rpm and you have a place to take a closer look at. You have 109k miles. Plenty of simple things to rule out first before you need to get nuts chasing computerized ghosts.

 

109,000 miles on original plugs and wires? How'd you manage that?? Bank 1 too lean ended up being a bad MAF on my truck. No amount of cleaning would help it. It is worth a try to clean it though. I lost my MAF at about 65k.

Get the number of the code, and it'll be easier to figure out what the problem is............

Worst case scenario: Take it to the dealer and have them diagnose it. Then, refuse the repair estimate once they tell you what the troublemaking part(s) are, and replace them yourself. I wish I had done that on my cruise problem. $386 vs half that for the part.,,,,98

 

How did I lose 1100 posts??? I hardly EVER post in the Gen. Disc forum? Sigh!,,,,98

 

I had the same code bank 1 too lean. I cleaned the MAF, and it seemed to help, at least the CEL did not come on. However, I also cleaned the EGR, DPFE, and the IAC shortly after, so I don't know what the actual cure was but it has been 20k since the cleaning, no code for bank 1 too lean. CEL came on about 2k ago, I did have a cyl # 4 misfire, and found a bad plug. Hope this helps, good luck.

 

I have a 5.4L so no worries on the wire situation, but the plugs ive put off changing simply because of the pain in the a$$ it is. The upper O2 sensors were a pain, especially the passenger side one (damn i wish i had midget hands). Dealerships want way too much to change spark plugs ($470 at one place).

I'm going to clean the IAC valve and MAFS. Also gonna change the fuel filter. Is there a cheap way of checking my fuel pressure and what is the optimal fuel pressure for a 5.4L? I know there is a valve on the fuel line to release pressure, is there a cheap gauge that will fit onto that valve to messure the pressure?

 

I've been chasing this code P1131 for a while now and maybe it's the maf Sensor. I'll take my meter to it and clean it to see what that does. It appeared after I changed the plugs and wires that had 112,000 miles on them. 98 F150 4.6L Any other ideas out there?