engine trouble and low fuel mileage

[retep88]

I have a bronco II, 89, 2.9L. It's been idling poorly once it's warmed up. The idle will rev up then die down, rev up, then die down. It's been getting really bad gas mileage. Like 8 mpg bad. I don't care how bad I drive, it shouldn't be that bad. I pulled the codes and get an all clear for KOEO, 14 and 41 in the memory, and KOER was 41. 14 is intermittent RPM signal, 41 is the engine running lean. When I changed the spark plugs yesterday they looked a little sooty. My suspicion is that the O2 senors is bad, but I am wanting other people opinion. What other options could it be giving me horrible mileage with the engine running lean.

 

[martin]

punctured diaphram in the fpr.

 

[retep88]

how would that cause low fuel mileage. Wouldn't the return line do it's job and return the fuel to the tank?

 

[country0001]

A lot of people have been having this problem lately, Look in the B2 forum and the 2.9 forum. It could several things or a combination of those things. The ignition module (TFI) on the distributer seems to be where everyone is starting. Good luck and report back w ur findings.

 

[robertc1024]

Coolant Temperature Sensor?

 

[crusin93]

If the FPR is bad, the fuel pressure at the injector will be too high, and allow too much fuel to flow per injection pulse. Hook up a FP gauge to the schrader valve. It should read around 40psi with no vac. If you smell raw gas out of the tailpipe you may have a stuck injector. Noid light test the harness for problems. Usually ground related issue. A bad o2 sensor will cause poor gas mileage. Remove o2 sensor and perform a resistance test. Look at the chiltons manual for acceptable readings. If out of spec simply replace. Not the most likely cause but, the coolant temp sensor can cause all sorts of driveability problems. Check resistance and replace if necessary.
Remember to start simple. Hope this helps!

 

[adsm08]

how would that cause low fuel mileage. Wouldn't the return line do it's job and return the fuel to the tank?

The FPR is vacuum controlled. If the diaphragm punctures that fuel gets sucked up the vac system and makes its way into the engine.

Also, a punctured diaphragm will result in low vacuum, simulating a higher throttle position. That means more pressure in the rail when the injectors open which will push more fuel through the injector when it opens. But given your sooty plugs AND your lean code, I'd guess bad O2.

Pull your FPR line, if there its dry, start the engine and rev it a bit while watching the line and see if any fuel comes out. If not, go get yourself a new O2 sensor.

 

[retep88]

Just an update here. I replaced the O2 sensor. It got rid of the 41 code, it's now a 42. It also has the same idle problems like before. I have yet to test the fuel mileage. I am going to see if a buddy has a fuel pressure tester and check out the fuel pressure regulator. What other places should I be looking to stop the engine from running rich? How hard is it to get rid of the code 14?

 

[adsm08]

What is code 42?

I'd guess the code 14 is probably caused by a bad pickup module. It lives down' under the dis cap and you have to pull the stem apart to get it out.

yank the dis, pound out the roll pin in the drive gear, pull the gear off, pull the shaft out, and then pull the two little screws and bingo, it's out. The hardest part is usually getting the pin out. You need a stupid small punch. I think the last time I did it I actually used a 10 penny nail. That is NOT a recommended procedure.

 

[retep88]

code 42 is "the engine is running rich" KOER. Which makes a lot more sense then 41 which is "the engine is running lean"

 

[adsm08]

That's what I guessed.

41 would make sense if you have a vac leak. engine will run lean, it dumps fuel, runs lean and so on until it can't give it any more fuel and it's still lean. that would be a bigger leak though and I'd think you'd prolly notice it.

If it was the bad sensor causing it it may now have adjusted the fuel trims up so high that its running really rich and it is taking time to get them back down. Try unhooking the battery for 15 minutes to clear the stored fuel tables.