Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Ok 05 F250 with 5.4 variable timing 3 valve engine. I get lean codes that set at 1500 rpm so I am not really looking at vacuum leak .After changing the plugs yesterday I saw the biggest ever negative short terms of about -15 and thought it was fixed but still have steady 12.5 long terms at hot idle.It is the worst at flat land cruse at 1500 rpm range with 16 LTB1 and 14 LTB2 fuel trims. The crazy thing is that climbing the mountain under 2500 rpm so as to stay in closed loop the trims come down somewhat so that steers me away from fuel pressure/injector issues. Does that make sense to anybody?
Did you reset the fuel trims after changing the plugs? If not (what it looks like because of the neg. stft) you may have to wait a while until everything balances out if the the new plugs were the cure.....it doesn´t hurt to check fuel pressure, volume and injector drop anyway.
Otherwise you may want to reset the trims/adaptives and watch from scratch what´s happening then.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
just now reset the KAM again so LT,s went back to 0 and the short terms add a bunch until they get the LT,s back up to around 12.5.at idle. The reason I reset it was to see if would change my reading of what the scanner calls "short term fuel trim bank 1 sensor 2 and short term fuel trim bank 2 sensor 2". They are always 99%. Is that telling me anything? Also my MAF is reading only 4.6 grams per second at 650 rpm. Is that reason enough to change it? It graphs along with the TPS but may be under reporting. The baro is good. Thanks for your response.
the scanner says fuel pressure is 39-42 most always and KOEO it looses less than 5% in 5 mins. It has no regulator or return line or test port. Not sure how to check the injectors but I did spray carb cleaner through them and they ohm out about the same. I am about to change the injectors on one bank to see if that helps because the spray pattern did not look good to me and that would be easier than making a way to really test fuel pressure
The post cat O2 sensors do have some authority on fuel trims on some cars out there. When the pcm does not regard these post cat sensors for fuel trim you´ll usuallly see this 99% reading in generic OBD2 data, nothing to worry about..
A low MAF reading may be an/the issue with your car, although often times they deviate more at higher rpm and load.
No, you shouldn´t change the MAF sensor yet. You may want to pull it and have a look at it. At times they are dirty and some of them are actualy cleanable.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
I did a compression test today because that was all I could think to do and all were real close to 200 psi. I ohmed out the coils and all were 5.15-5.25 except one and it was 5.8 ohms accrross the secondary. Is that reason enough to change it? My ALLDATAdyi subscription does not tell me I will have to get an incadesent test light tomorrow to see if the sprk jumps real good or maybe just see if it jumps ground You said to check fuel volume.Are you talking about disconnecting at the rail and pumping into a jar ? If so , what rate am I looking for?
The resistance difference in the coil´s secondary is a minor one, I don´t see a problem there.
Regarding fuel volume: the numbers I want to see are close to half a gallon (2 liters) in 30 seconds on BIG V6 or V8 engines (like yours) and everything super/turbocharged. On smaller 4 cylinder engines without turbo I look for half a gallon per minute. A quick and dirty test is to open the bleeder valve on your pressure gauge while idling: the engine should not stall.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
No test port for me. Thanks Ford. Will disconnect the filter and pump gas into a bucket and check volume and for air today. Maybe braze a Schrader valve onto the filter or fuel rail or something Do you have any ideas how I can get a valve on here to test it? Freeze frame data from a while back said the lean code set at 32 psi and it almost always stays at 39-41 psi even at snap throttle so something fishy there.
If you had à fuel pressure gauge with a quick release you could tee-in just at any accessible point in the feed line. Don't like the idea of "braze"too much that close to gasoline.enviroment if you wasn't to pull the rail out of the car while doing this.Though teeing in would still be easier and quicker.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Using an ohm meter to test coils is not a reliable test. You can have perfect ohm readings and have a bad secondary winding. Scope waveform is the best test.
From reviewing your data I don't see why you're getting codes. Positive 12+ long term with neg 15 short term give you neg 3 overall. That would not set a code. What codes are you getting P0xxx you have not said.
What was the reason for the spark plug change?
I believe Juergen is pointing you in the correct direction. Clean the MAF and don't clear memory. See if it starts to correct trims. May take a drive cycle to see change. Test light is not a test to rule out bad spark. Spark outside the cylinder is different than inside. Scope ignition waveforms is best but not everyone has these tools.
Not criticizing your methods but giving you food for thought and I'm applying what results you come up with to my diagnostic knowledge.
Keep posting so we see the final fix.
"an open mind let's knowledge flow in and wisdom flow out for a man who has neither never listens to those who have both".
Being wrong doesn't bother me, it's being right and not understanding why that does
Always get the p0171 lean bank one after long terms get past 20+. I increase rpm in park and short terms do not go down so along with my smoke tests cold and blocking off brake booster and all make me think I do not have a vacuum leak.. Before testing fuel pressure today I watched my short terms go negative all the way to town about 10 miles. On the way back home they went positive. That has to be a clue but I don,t know what to make of it. I dont have a scope but am feeling good about my coils because pulled one today and saw spark jump almost an inch onto a hammer. I changed the plugs because the rebuilt engine has 50k on it and I wanted to check compression. I did clean the MAF and it does under report some at 650 rpm and 4.5 grams per second but it doubles with rpm and graphs along with the tps. I never get p0174 lean bank2 but it is always close
so what does everybody think about me teeing into the fuel line at the filter and getting 30 psi at idle and my IPC Injector pressure sensor on the rail telling the scanner that I have 40 psi I took the filter out for the test. It has no Schrader valve or return 2005 Ford 5.4 3valve engine
Last edit: 3 years 9 months ago by craig anderson. Reason: added info
so what does everybody think about me teeing into the fuel line at the filter and getting 30 psi at idle and my Injector pressure sensor on the rail telling the scanner that I have 40 psi P I took the filter out for the test.
This is completely NORMAL on this product. While the gauge is referenced to atmospheric pressure the fuel pressure sensor is not: it refers to absolute pressure:) .
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Thanks That really did help me a lot . I am glad that I did not try to splice into the fuel line close to the manifold to check pressure. I think I will redo my fuel volume test . This time I will open the pressure relief valve on my gauge while it is running like you said. Did not really like cranking for 30 seconds and did not get any fuel with KOEO like I expected. If it does not keep running that should tell a lot
Watched just long term trims on my 3rd trip to town and back about 20 miles each trip. they hovered from 7 to 13 not too bad and out of nowhere hit 20 and then back down in about 2 mins without any change in load or rpm. So some kind of an intermittent failure I think. Bank 1 is usually a little higher than bank 2 so I will switch the injectors from one side to the other. If that changes things it should tell me something. Also will flush the fuel rail because I could have pieces of O rings or something in there.Does it sound like I am on the right track?
My ALLDATA dyi says there is a TSB for my truck about P0171 and P0174 with or without driveability concerns. They are to smoke test etc. and if ok, reprogram the PCM Has anybody seen this condition I describe here? Watching just LT trim on one bank on a 100 mile round trip all I can. Stays between 7 and 15 positive 95% of the way but sometimes goes to 2 to 18 positive w no big difference in load or rpm. It is gentile hills all the way. Is this normal?
Issue no longer intermittent Trims go way positive when the truck sees 18-22 grams per second on the MAF reading Before or after that not too bad. What does that say ?
Topic Author
