Low fuel pressure causing a P0171 and P0174 trouble code

all right it's actually a field trip day here at Rosedale Tech I have my class with me we're at one of the garages I work for it got six of my students with me and we're working on a 1999 Mercury Mountaineer and the complaint is a check engine light and some lean exhaust trouble code so we have the scanner hooked up and the first thing I'm going to do is I'm going to zoom you in on this on the screen here and we're going to get some trouble codes out of this alright so my codes menu already one of the things you got to remember about Ford's Ford's Arcada goofy as far as our code memory and what they run on what they'll have is a key on engine off self-test which what that does is is the computer will do checks on itself with the key on engine off it's basically a functional test same thing with the key on engine run but the key on engine runs going to do things that it can't do with the engine off things like EGR Flow oxygen sensor activity and things like that I'm not worried about that on this year on this year we're going to go right after the memory codes click memory codes and continue and we have an issue obviously two different codes Pio 171 Pio 174 and that's bank one to lean bank two to lean now there's one other thing that's a concern any time you're in the field when you see a P 1000 code that's unique to Ford's remember p1 codes our manufacturer specific P 1000 means somebody was in here and cleared these trouble codes so what I need to make sure I'm doing with this vehicle is make it clear that the only two codes I'm addressing is the to lean exhaust codes it is it is possible that this vehicle has other failures that aren't showing right now because if we didn't do the drive cycle yet which is what this P 1000 code means that not all of the monitors which is the tests have run yet there is potential for other faults here very important that you document your repair order in this case we're attacking the P o 171 and 174 trouble codes the next thing we want to do with these codes is we want to go to our freeze-frame down notice on the Ford menu that there's no way to access freeze frame data so what you'd have to do is makes it all the way back out of this vehicle and enter it as an obd2 car to get the freeze-frame because it was mandatory freeze frame data is supposed to be an obd2 well the nice thing now that snap one has allowed us is a generic functions feature so what this is is a window into obd2 where I can instead of exiting all the way back out I can access my freeze frame data within that generic functions section here's my freeze frame and what we want to pay attention to anytime you have a lean condition is you want to pay attention to whether or not this is an idle lean condition or an under load lean condition and if you look at these data parameters first of all you look at your to long term numbers is that visible in there all of that in there yes okay you look at these two long-term numbers and you see we're almost at 30 percent positive fuel trim on both long term fuel trim Bank 1 and Bank 2 so definitely have a lean condition take note of this we're 1800 RPM with a 30 mile per hour speed and a 62% calculated engine load so here's what we look at right away with this we're trying to narrow down the type of lean condition we have when I see something like that to me this is an under load lean condition this is not an idle lean condition so I'm not worried about a vacuum leak on this car there's going to be two areas we're going to check for this under load lean condition one's going to be the mass airflow being dirty and the other one's going to be a fuel pressure issue so that's where we're going next to address the mass airflow I'm going to exit out of here go go to my this is om data now it's still my Mountaineer so I'm out of global mode I'm back in the manufacturer mode go to data display on Ford's go under drivability what we're looking for is Baro frequency Baro Hz I know we haven't talked about this yet but this number right here of 152 Hertz Baro eight Z 152 Hertz the way barometric pressure is calculated on this vehicle is it's done from the mass airflow sensor and there is no separate Barrow sensor so the mass airflow senses the barometric pressure at wide open throttle when you're driving this thing wide open it's going to update this Barrow reading right if you think about wide open throttle there's no vacuum in the engine full atmospheric pressure that's where the Barrow gets updated okay so if you have a dirty mass airflow that doesn't anticipate the same amount of airflow so there's more airflow than what it's showing your Barrow frequency will be lower because it thinks you're driving at a higher altitude that being said when you have dirty mass air flows on a Ford you're gonna have under 150 Hertz 140 I've seen them as low as 137 Hertz and that's a red flag you have a dirty mass airflow sea level reading maximum you'll see here is 160 Hertz here in Pittsburgh we generally run about 154 to 156 reigns on the mass air flow for a Barrow calculation we're at 152 and so what that's telling me I'm not going after the mass airflow next I'm going after fuel pressure so our next step is going to be fuel pressure alright so we're going to do fuel pressure it helps to have a spec and this is a nice feature of the Varys that you have two tools in one what I'm going to do is hit the home button and I'm going to go to my component test meter and the component test meter of the verus is basically the vantage prep so what you're accessing is a front door or scope data is what the component test meter does but what's nice about the component test meter is it has all kind of specs for this vehicle and this is unique to this vehicle and a nice thing about this is look I'm looking for fuel pressure there it is and there is a press respect already pre-loaded into this tool that makes it wonderful now this isn't the greatest spec in the world but I gotta tell you I checked Mitchell too and it says the same thing and it's given me a really wide range of thirty to sixty five psi key on engine off then break underneath that it says fuel pressure spec again normal raids fifty-five to sixty five key on engine off so which one is it we checked Mitchell it was the same thing thirty to sixty five psi key on engine off now with my experience with these and this is what helps that they generally run around sixty pounds of pressure with the car running now I'm not a hundred percent sure on that number but you see our range pretty wide thirty to sixty five all right let's take a look at what the pressure looks like now okay looking at fuel pressure nice afford to give us a Schrader valve to adapt to just going to turn the key on watch the games he's off right now turn the key back on that gauge sort of pumps a little bit they move it on very smart so you see our key on engine off pressure is about thirty-three psi now is that a good number or not I mean if it's if the spec is thirty to sixty five that could be a good number from my experience it should be higher on this vehicle but here's the key I don't care if it's thirty I don't care if it's forty fifty sixty doesn't matter the key is going to be doing this fuel pressure check on a snap throttle under load and notice the spec didn't tell you to do that what we want to do is get the injectors to open very wide and make sure pressure doesn't drop on a snap okay so we're going to do this engine running snap throttle watch the fuel pressure now before I do it this is a vacuum type fuel pressure regulator so it is normal to have a higher idling pressure than it is sorry backwards it is normal to have a higher wide-open throttle pressure with no vacuum than it is at idle generally about an 8 psi swing from idle to wide-open throttle so what I want to see on this system let me double check what I'm saying here about this having a having a regulator on the rail what I'm looking for on this fuel rail is a pressure line and a return line okay I lied to you this is not a return type system this does not have a fuel pressure regulator on the rail here's how I know it let me show you all right this is important for what I was about to tell you talking about the vacuum assister is identifying the system type there is only one fuel line running under this fuel rail on running underneath the intake manifold if you look down on the frame you see that one one fuel pressure line there is no other line on this system and so what that means is the regulator for this is in the tank and there is only one set pressure on this car whatever you have at idle is going to be the same pressure you should have wide open throttle there are not two different readings one pressure this is we're doing fuel pressure testing is important that you understand that when you do fuel pressure checks just key on engine off is not good enough I don't care if that's the right spec the injectors aren't spraying you can have a weak pump keep up when the injectors aren't sprayed so can you start the car for me and we're gonna do some snap throttle tests that pressure drop oh that's coming back if you caught that or not let me move this gate to a different spot without a glare all right that's a little better I don't know if you caught that on an initial startup but it had a real slow climb in fuel pressure we can plead that off and catch it again but I don't want gas borne everywhere but here's the key one set pressure on this system which I believe should be about 60 psi for my experience on other explorers at least the 4 liter engine I know runs 60 pounds of pressure this is the 5 liter so I'm not sure if it's different but the key is is when I snap the throttle fuel pressure should not drop under load watch it we okay alright let's try that again do a snap draw to watch fuel pressure gauge farm in the layers okay depression job almost went down at 20 pounds of pressure watch it again this is a confirmed week fuel pump so far off turn the key back on okay let me rephrase that this is a confirmed problem we have a fuel delivery issue if you think about that you match that with our freeze frame data lean exhaust under load driving the car when the injectors are spraying heavy fuel pressure is dropping and that's where our lean condition is coming from is this a bad pump could be cars got or trucks got 180 set or 187 thousand miles on it could this be a plugged up filter yes could be either one at this point with this kind of mileage our recommendation is going to be put a filter in it retest it or do them both pump and filter there's one last thing that we need to address before we do that and that's our pump power and ground now unfortunately we are in a shot that does not have a rack over here so I really don't want to climb underneath the vehicle to do a power and ground check on this pump a pour ground can give us low pump volume a poor power feed can give us low pump volume and I don't want to do that unless I have to so what I'm going to do is an amperage measurement at one of the feed wires to the pump and see what kind of amperage I have and that will tell me whether or not I need to crawl underneath this vehicle so amperage measurement on the fuel pump is next all right I apologize for the shakiness of the camera but I want you to see where we're at we're going after the inertia switch which is under the passenger floor kick panel area and the reason we're going after the inertia switch is it carries the main feed that goes to the fuel pump and I don't and I won't have to crawl underneath the vehicle to access it and give you an idea what it looks like that's it right there there's a three pin connector on it most of them have two this one has three because if the inertia switch trips on this one it actually has an indicator light that comes on the dash but the heavy pink and black wire and the heavy green and yellow that's coming in and going out to the pump either one of those wires will be sufficient for a fuel pump current measurement and that's what we're going to do I'm using my Pico scope to do it using my low amp probe and my aunt probe is set on a 20-amp scale if you were not using a scope that had the conversions in it it would be a hundred millivolts equals one amp if you were using a voltmeter so these same amp probes work with volt meters to clipping that around the wire this is polarity sensitive so worst case scenario is I have to flip it around this way put it back on if my patterns upside down but being I've already done this that is the correct polarity right there all right we're going to the scope screen next which is my laptop all right using the Pico 4000 and my laptop and I'm going to click on the icon on my desktop for Pico 6 and what I'm going to do is set my scales here let me zoom you in on on this you see what scales I'm using for this amperage measurement for the pump and goat NOAA and I'm going to set this because I'm using a calibrated tool already so we have calibrated scales for it I'm going to set this probe to a 60 amp current clamp in the 20 amp mode and when we look at our scales now you see that these are amperage scales I'm going to go minus 5 to 10 amp which is a pretty good scale for doing a pump and you definitely would want to zero your amp probe which I've already done so that line we're looking at right there is zero amps and can we go ahead and start what do you guys start the car for me please here the long crank time little pop in the intake I don't know if you heard it but those are all symptoms of a lean condition in our case that's symptomatic of a fuel pressure problem the long crank time and how long that took to build but what you're looking at here is an amperage number so these are are actually the elect this is the electric motor spinning the fuel pump is actually spinning in the tank and each of these up/down a kind of sawtooth pattern is a representation of a commutator segment on a DC electric motor not to much concerned about fuel pump speed and RPM although we can't calculate that and I guess I can show you that but my main thing that I'm I'm concerned about was my amperage because truthfully what I said was I don't want to crawl underneath this vehicle and check the power and ground and the fact that I have an average of five and a half amps of current flow traveling to this fuel pump tells me I don't need to crawl underneath this vehicle and check my power and ground now if this amperage was real low to be a hundred percent accurate on what we're calling which is low fuel pressure and calling a pump we would want to check powers and grounds I'm comfortable with this test we're done this car needs a fuel pump and/or has a plugged up fuel filter and again no way to know about the filter without replacing it I mean you could Tia gauge in before the filter and Tia gauge in after the filter but by the time you were done doing that you should have just changed the filter it would have been a lot quicker so change the filter if this is your own car change the filter and retest everything if this is a customer's car in a shop you got to leave that up to them on what they want to do but you have to warn them that the potential here is the fuel pump is on its way out too

Channel: ScannerDanner

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Keywords: lean exhaust, auto tech training, how-to, auto repair, DIY auto repair, training, Paul Danner, Auto Tech, freeze frame data, fuel trim diagnosis, scannerdanner, Engine Performance Diagnostics, P0174, P0171, Rosedale Tech Pittsburgh, fuel pressure testing, mechanic school, car repair, how to test fuel pressure, how to measure fuel pump current, picoscope, low fuel pressure

Id: nYN-RoFVwAA

Length: 17min 51sec (1071 seconds)

Published: Fri Feb 03 2012