Running Rich - ?'s about the FPR

For the past few months I've been smelling gas but never thought much of it, over the past 3 tanks of gas I've notice a massive loss in MPG all of the sudden, from about 18-19mpg down to 12-14mpg per tank (combination on/off highway) and I can't figure it out, but I'm associating the loss of MPG with running rich as the smell of gas is getting worse. Most noticeable on start up, which by seems like it's getting harder and harder, almost like a dry start.

It's throwing no codes, I've cleaned the MAF, TPS, PCV is new, plugs have about 1k miles on them, wires about 5k. I just got done replacing the fuel pump because it died on me last month, all the fuel lines from the filter back appeared to be in good condition for how old they are.. the pump itself is making good pressure (I can't remember if 30 or 60psi is acceptable for the '96 OHV, but it was on par when i checked it) And if it matters I've noticed more loss on the highway, the same route to go to school that would normally give me 19mpg is now giving me 12mpg (according to ScanGuageII) I also ran some injector cleaner through the last tank of gas, no difference.

I've read over on the F150 forums that a 'Fuel Pressure Regulator diaphragm' may be the cause of the fuel smell and loss of MPG while throwing no codes. However, the smell seems like it's coming out of the tailpipes not the engine bay. They say there is a vacuum line attached to it and that it should be inspected for leaks/faults. I'm not too familiar with this, does the '96 OHV have this diaphragm and could this be an issue? If so, where is it located? Can't find it in the Hayne's manual.

Also suggested over there was "..the MAP sensor, Engine coolant temperature (ECT) sensor or Air Charge temperature (ACT) sensor.."

Could this be associated with my problem?
Any thoughts on what else this could be would be greatly appreciated, I've reached the end of my ideas..

-Brandon

24 hour bump because I got 12.4 MPG @ 55mph on my way to class today.

I'm not sure about the OHV, but on the later model 4.0 SOHC there is no FPR, but there is a "fuel dampener" on the back of the fuel rail on the driver's side, which is supposed to soften "water hammer" type noise I guess. The FPR on mine is essentially a check valve attached to the fuel pump inside the tank. Yours is probably on the fuel rail somewhere. In any case, if you have a FPR under the hood, you can pull the vacuum line and look for raw fuel. If so, then the diaphragm is shot.

A lot of things can cause a rich setting though and the smell of unburned fuel from the tail pipe. That could be MAF or TPS problems or an issue with the PCM, leaking injector, misfiring plugs...where to begin really...

Are you getting some rough idling, fast idle, bogging down when you open the throttle, loss of power, misfires?

Your so called dry start might in fact be injectors that are leaking down. You need to check fuel hold pressure 5 minutes after turning the truck off. If it drops significantly, you have leaking injectors.

Fireside3 said:

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First off, I appreciate the response.

I'll definitely look over the fuel rail again, possibly I overlooked the FPR. Also, while I had the fuel pump assembly off I KNEW I saw some bracketry above the fuel pump itself where it looked like something was missing... maybe Ford was preparing for the SOHC on my '96 when it came out in '97?? who knows.

Anyhow, I do have an unsteady idle, but it was greatly improved when I replaced the IAC valve, however it's still not a constant clean idle, but it doesn't actually struggle to hold an idle. As for power loss / misfiring / bogging down... none that I can tell, however I do have a tiny bit of surging under very light load.

I'll check the fuel pressure after turning the truck off tomorrow between classes, would it also be smart to just turn the key on to let the fuel pump prime, a check it to see how long it will hold pressure as well?

On all Ford trucks before model year 1999, the fuel system had a return line back to the tank, a fuel rail mounted vacuum controlled fuel pressure regulator, and an operating pressure in the range of 30-45 psi, 30 being the pressure at startup[System prime] and high vacuum conditions...

In model year 1999, Ford changed the trucks to a returnless fuel system which has no return line to the tank, no fuel rail mounted fuel pressure regulator, and an operating pressure in the 65-72 psi range...This systems pressure does not vary like the earlier system and there are 2 major differences here...First the fuel pressure regulator is still installed but is mounted on the fuel pump/sending unit assembly in the tank...The FPR is not vacuum controlled and it will bypass fuel from the fuel rail if the pressure gets over 80 psi...Second, there is a fuel damper mounted on the fuel rail which is there to smooth out the fuel pulsations before they enter the injectors...This unit is part of the fuel rail yst it will not vary the fuel pressure seen at the schrader valve...

Now with that being said on your 1996 truck I would look for the presence of liquid in the vacuum line leading to the FPR...I would also check the fuel pressure to see if it is higher than the nominal pressure listed above...You can also get a fuel odor from the vapor canister and the emission piping back to the canister which is under the spare tire and the lines run from the drivers front of the truck back to the canister...

I would also pull the dipstick to see if the oil smells like fuel or look at the tailpipe to see if there is a black sooty build up on it...Both will tell you that the engine is running richer than it should and that you need to start investigating the control systems to see if excess pressure, leaking FPR, super rich fuel mixture, etc. are causing your fuel smell and the drop in economy...

ok, update.

My dipstick smells like fuel and my tail pipes are starting to build up black crap like you say.

I found and checked the FPR, it's located on the front of the fuel rail, tucked under cover and intake hose. There was no fuel in the vacuum line and when I turned the key forward just to prime the engine it hit 10psi and held for a while, with the engine running it fluctuated between 28-30 PSI, and with the engine off it cranked up to 35psi for just a few seconds, then dropped to 32psi and thats where it stayed for about 5 minutes.. I then had to go to class.

My buddy says there could be a check valve or something in the FPR that could be holding the fuel pressure in the gauge.. but not to quote him because he's only see very few cars that do have it.

So, my FPR seems to be in working order?

Since you have a Scangauge II...

Use it to see what your ECT and IAT sensors are reading..The ECT sensor acts like a choke to enrichen the fuel misture on a cold engine at startup...If this sensor is sending an abnormally cold readingto the PCM the fuel system will go full rich... Likewise the IAT monitors intake air temp and if the sensor is reading high air temps it will go into an enrichen mode to help cool the engine as well..

I would also scan the PCM for any codes...If there are any there, I would start to run those down and correct them...

Your FPR seems to be working within design parameters and the check valve your friend referred to is in the top of the fuel pump, not the fpr...It is there to help reduce vapor lock and hard starts when hot...Keeps liquid fuel in the fuel rail while the engine is off...Stops the fuel in the rail from turning into vapor from latent engine heat...

Something is making your engine run rich...It is time to find it...

ranger7ltr said:

Use it to see what your ECT and IAT sensors are reading..

I would also scan the PCM for any codes...If there are any there, I would start to run those down and correct them...

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I'm going to let the truck sit all day while I'm at work today, when I go to start it up I'll set the ScanGuageII to monitor the ECT and IAT, when I start it up they should be within a degree or two of each other correct? I'm assuming the ECT would be the same as water temp, thats the option the scanguage gives you.

Also, how do I scan the PCM for codes? If you mean CEL, there are none, and haven't been any

i think we're on to something here... just drove to work, my temp on the console was telling me 51 degrees the whole trip scanguage told me the IAT sensor was at 73 or 76 the whole trip... but this was the second time i drove this morning so im going to let it sit all day before checking it again...

The ECT and IAT temps, depending on the outdoor ambient, will probably be close to ambient at startup...If they are different don't worry...But if either shows either -40F or 255F the sensors are not outputting properly...

Honestly I replace mine more often than most people...When I bought my (( Sport in 2008 I replaced the ECT sensor and when I replaced the engine I replaced it again...The IAT, on my truck, is integral to the MAF sensor and fortunately has not failed...Your truck, assuming it is a 96 year model, has the IAT either in the air tube leading to the throttle body or screwed into the intake...

The ECT will rise as the coolant temp riese and should stabilize around the opening temp of the thermostat...The IAT temp should start around ambient and then will increase to a level dependent on outside air temps and the underhood air temps...I would monitor both and see where they go temperature-wise as you drive...If either temperature reading seems really high or really low then I would replace that sensor...

Or you could just replace them and then monitor temps but what fun would that be?

And I can't remember how to scan for pending codes with the Scangauge as i got rid of mine when my 300C went bye-bye but I do believe it can be done... Pending codes are just codes that the PCM is looking for a repeat occurence to happen before it turns on the CEL...

Let us know what you find out...

Brandon96 said:

i think we're on to something here... just drove to work, my temp on the console was telling me 51 degrees the whole trip scanguage told me the IAT sensor was at 76 or 76 the whole trip... but this was the second time i drove this morning so im going to let it sit all day before checking it again...

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What is the ECT temperature output? The IAT temp of 76F is not that unusual...What does the underhood air temperature feel like? If you have an infrared thermometer, you can verify the underhood temp at the IAT sensor...I would be more concerned if the IAT temp was listed at -40F or 300F or higher..

Check these links for more info on how these 2 sensors work...
http://www.fordfuelinjection.com/?p=28
http://www.fordfuelinjection.com/?p=29

While driving, my engine temp seems to stabilize at about 182 degrees, according to scanguage, but the needle on my dash stabilizes as follows:

(I do have a K&N Intake, and dual 2.5" Exhaust)

I'll check all start up temps tomorrow I suppose

What temp thermostat are you running?

If you are running a 180F thermostat, that temp is accurate on the scangauge... If you are running a 195F[oem] thermostat, then it is stuck open since engine temps should be around 192-197 F..

I'm not sure, I'll crack it open today before I start it and get a part number..

It's brand new though.

Ok, part #13958 from Advance Auto, 180 degree thermostat. It's my fault, thought they were all the same..

I checked all the temps on start up this evening, it was 51 degrees outside, 51 at the intake in the engine bay, Scanguage said both sensors were reading 48 degrees, I started it up and everything checked out, the water temperature rose like it should have and the IAT stayed about the same until the hood started to warm up, then it boosted to about 58 by the time I shut the truck off.

ranger7ltr said:

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Would the 180 degree thermostat kill my gas mileage like that?

Also, if not; Do you remember how you checked pending PCM codes with your ScanGuage? I'm going to keep looking through online, if that's not it, alls I can think of would be O2 sensors, but I thought they threw codes..

If I can't get to the bottom of this it's all good since we ruled out the EFI system / sensors, I'm going to need those in a few weeks for my christmas present from the 'rents

...but that's another thread in a couple weeks :shifty_ey

I know higher coolant temp[to a point] the PCM will operate leaner since that is more like the OEM parameters that the PCM is programmed for originally...And the 180 F thermostat is a recommendation for running an engine richer...

Since I also have a scanner I believe I used it to check for pending codes instead of using my Scangauge II so I unfortunately cannot be of any help on that front...

But I do have another quick question; What does your air filter look like? Can you see daylight through it if you hold it up to the sun or a lightbulb?

You have verified the fuel pump pressure is within Ford spec, the FPR is not leaking and it is regulating the fuel properly, the ECT and IAT sensors do appear to be within Ford spec as well, and the engine coolant is running temperature wise within spec as well...

This picture is the lower intake with the coolant gauge sensor on the left and the ECT sensor on the right both on the front of the lower intake...The one to measure is the one with the 2 leads...

I can only think of 2 items left; If you look at the charts for the ECT and IAT sensors they output a voltage dependent on the engine temperatures...With a voltmeter I would verify that the voltage they are outputting is proportional to the temperature they are seeing...If those both pass, then look for a restriction in the airflow system starting with a really dirty air filter...

And you are correct that the o2 sensors would have to be really dead to force the PCM as rich as your engine is running and that would trigger an engine code...

ranger7ltr said:

...I can only think of 2 items left; If you look at the charts for the ECT and IAT sensors they output a voltage dependent on the engine temperatures...With a voltmeter I would verify that the voltage they are outputting is proportional to the temperature they are seeing...If those both pass, then look for a restriction in the airflow system starting with a really dirty air filter...

Click to expand...

EUREKA!!

I got a little confused pulling up some threads to research a little more info on the sensors after what you said, but, to my understanding there are two ECT sensors on the motor, one to send temp to the PCM, another to send the info to the instrument cluster. Obviously ScanGauge uses the one that is sent to the instrument cluster.

With power on it, the ECT to PCM sensor was putting out just under a volt, when it should have been putting out somewhere around 3.2v at 50 degrees.
(according to FordFuelInjection)

I have a K&N oiled air filter, so that was the first thing I thought killed my MAF sensor which in turn killed my MPG's, but voltage wise it checks out as well, however.. the filter itself has been through 3-4 wheeling trips in the dust, so maybe it is time to clean and reoil it..

I'm hoping this is it, thanks a lot for the help man!

You just need to drain some of the coolant to change it...

I am glad you found the problem...When you change the ECT sensor, the engine should notice the change immediately...

And I think that was why I bought the code scanner instead of using my Scangauge...It works well, don't get me wrong, but I wanted more information than it could provide...

After you change the sensor let us know if the engine runs any better...And you are welcome...If I can assist someone getting their truck running properly then I am just paying back all the info I have gotten in the past...

Ok, got it replaced and everything put back together over the weekend. I immediately got a few MPG's back, but the engine didn't take kindly to the new sensor I don't think.. I left the battery unplugged for about 10 hours, in hopes of reseting the PCM for the new sensor. Got about 75 miles on the last 5 or 6 gallons of gas, however much a 1/4 tank is. 14.4mpg combined.

I didn't like that too much, but it is my understanding that some PCMs take a few tanks of gas to crunch the numbers?

I filled up on midgrade and put in some lucas injector cleaner to see if that will clean out any fuel injections clogs I may or may not still have... and now my cat rattles on the new tank o gas