What does fuel pressure have to do with MPG? If the pressure were too high, too low, or intermittently haywire, the problems would manifest as blown fuel lines or joints, or engine shutting off at inopportune moments. If injectors are "leaking" too much fuel into combustion, that might be a consequence of "too much" fuel pressure. I can't speak from experience, but that seems most improbable.

In any event, an excessively rich combustion mix would be detectable at the exhaust pipe, but for the catalytic converter "band aid" which covers up vital diagnostic information. On the other hand, I would expect the O2 sensor that lies before catalytic combustion to offer some clues.

Are you flunking a smog test? Years ago, I flunked; tailpipe emissions were too rich, and the fault was eventually traced to a bad throttle position sensor.

How is your compression? Are you burning oil? Is compression leaking from spark plug seals?

How HEAVY is you vehicle?

 

High fuel pressure will cause a rich condition, bad mileage.

 

OK, conceded. But that would have to be fuel pressure after regulation, not the fuel pressure in the feed lines from the gasoline tank. At least in my van, regulation appears to occur physically close to the injectors.

 

Wow,

You guys are really batting this problem around!

Okay. . .I have to change the oil tomorrow morning. . .I'll pull codes, just to make sure everything is okay.

I'll hang a vacuum guage on it, too.

If time allows, I'll pull the plugs to clean and re-gap them.

No, even tho we (turborich and myself) think our Bronco IIs were built on a Monday, or a Friday - I'm not burning any oil (I'm leaking it. . .)

I actually have to take it in for a smog test sometime in the next few weeks. I'll post the results.

If the truck fails the smog test, what would be the next step?

How can a rich fuel mixture be adjusted????

S.

 

John,

The fuel pressure regulator is on the fuel rail, if it not functioning properly or the return line is clogged you would have high pressure at the injectors.

switzee,

The rich condition could be due to high fuel pressure, malfunctioning sensorS, exhaust leaks near the O2 sensor are the main ones.

 

There can be many causes of overly rich operating condition. A catalytic converter can mask the issue, making it difficult to detect at the tailpipe. However, if you pull your sparkplugs, they will tell you plenty. If they're black from carbon, that is overwhelming evidence of excess fuel consumption. That can harm your cylinder walls, too, because excess fuel conflicts with the lubrication merits of your oil; the gasoline cuts the lubricant.
Conversely, if your plugs' electrodes are "dusted white," then that implies leanness. Overly lean condition will hasten the demise of your valves. The hot, oxygen-rich atmosphere will attack the iron, attempting to oxidize anything that has electrons to donate.
I once had a bad throttle position sensor, on a 1984 Mercury Topaz, which caused all sorts of overly-rich operation. So you must find the faulty item(s).

 

Ken,

Thanks for the rich condition symptoms. I appreciate it.

I've actually replaced all of the sensors (yep, every one) and I did not see an exhust leak near the O2 sensor when I replaced it about 5k ago.

Maybe a new sensor that I've replaced could be acting up. . .You know what N.E.W stands for? Never Ever Worked

I guess I'll have to run codes. . .I'll post the numbers, when I get 'em.

Thanks again,

S.

 

why wouldnt you use bosch plugs? i have them in my b2 and it runs fine.

 

Switzee,
Don't just clean and re-gap the spark plugs. Observe them carefully...I'm sure you have. But you have not reported in this thread, what the electrodes of your used plugs look like. Are they black? Is the black thick? That would imply profound richness.
Your plugs will speak volumes.
Let us know.

 

Okay, here are the codes. . .

I got a hard fault of 89

And 14, 18, & 33 were stored in the memory code.

14 & 18 were address a few months back, when I found insulation missing from the wiring harness back there.

33 was the EGR control system, which I replaced.

The hard fault of 89 is the only thing I have not address, as of yet.

I guess I have to drop the tranny pan for that (ugh!)

I was also reading a steady 18 inches from a standard vacuum guage.

JohnPeter - thanks for the info on the plugs!

Believe it or not, I popped one of them out, and it looks like new.

Electrode looks untouched, and the porcelain looks bright white. (after 5k)

I figured there was no need to pull the rest.


Hope this helps,

Thanks.

S.

 

I am getting 20 + in my B2 with 2.9, M/T. Bosch platinums ( I have been using these in all my cars for the last 17 years), K&N filter, and Mobile 1 syn oil. Seems to help.

Greg

 

These so called "old" codes that you say have been addressed. Did you clear those codes after making any repairs? Are you certain they have been adequately addressed if you didn't clear the codes and they are still there. One of the first things I might do is clear those codes, drive it, and make sure CM comes back 11 before assuming those codes have been fully addressed.

As for the KOEO 89, you don't "have" to drop the pan, unless you determine that the circuit fault is inside the transmission. 1st thing to do is make sure the wiring outside the transmission is intact, that it's plugged into the transmission, and that the solenoid is getting power. All of this can be done without undoing any fasteners.

 

Unless you have a spark knock at 10, leave the timing there. Lower actually costs you mileage.

 

Okay,

I will clear the codes in the computer first. . .then check the wires, and connection going to the transmission. I hope you're right, mrshorty!! I reeeeelly don't feel like dropping the pan again.

I'm surpised to hear my timing adjustment will actually lower milage, tvulcan.
The truck (appears) to be "working" a lot less than it did when I had it set to 10.

Maybe I'm just going nuts. . . I'll set it back to 10, and keep you posted.

Now that I think about it. . . the truck will occasionally "hunt" on cold start-up.

It'll rev between 1100 and 1500 with the choke. . . then, once it was warm, it would settle down to around 800 rpm.

RPM's courtesy of my "cheeziod" 20 dollar tachometer.

Thanks again,

S.

 

Iam glad that others have the same prob also my 89's get 20+ 87gets 15 up or down hill but when we plow the all run out about the same time so i just live with it anymore but i think i will pull codes and play with them during the summer. Now iam just pressure washing and painting under sides to slow rust down.