← Back to list

2005 F-150 5.4L Open Loop misfire

Model: 2005 F-150 5.4L Fault Code: P0300 Posted: 2019-03-15 07:12

2005 F-150 5.4L w/180k miles: Symptoms: At EVERY cold start it will misfire until warmed or settles down in closed loop. When it does throw codes, I get vaying combinations of P0304, P0308, P0300. Sometimes P0316. On RARE occasion I get P0172 (probably because of the EXTREMELY high fuel trims. LTFT B1 likes to idle around +15 and bank two idles around +25 It is not uncommon to see LT and ST add up to well over +30 or more. Fuel economy is averaging about 13MPG (this is likely also affected by having to let it warm completely up before driving (10-15 minutes each start -twice daily) When problems first came up, I assume it just needed some TLC and tune-up. I did the following: New plugs, COPS, injectors, fuel filter, top engine cleaner. Did smoke test - inconclusive. I removed and ran without O2 sensors to see if too much back pressure - no difference Went buddy mechanic and scanned/trouble shot - found lose connections to runner controller (once connected got stuck open code) - throttle body died here (replaced). Again, found no evidence of vacuum lean, not exhaust leak. Replaced runner control and due to some previous "back yard modifications" and suspect gaskets I also replaced intake manifold. The only thing I haven't done yet is a compression test. I've avoided this because I feel it runs pretty good after warm. But could this be the root of my problem? So fat EVRYTHING I havce done has made it better, but the misfire is like clock work. I'd willingly bet a year's salary that it will misfire any given morning!

Related fault codes

P0300P0301

Comments (16)

Anonymous 2019-03-15 09:27

Do fuel trims come down if you hold rpms up at 3000 for 30 sec or so?

Anonymous 2019-03-15 10:38

ALL trims are Positive: RPM LTB1 LTB2 STB1 & 2 (they ALWAYS are in step and bouncing) 550 13.3 18.0 3.0 to 7.8 1500 4.7 14.8 3.1 to 14.0 2000 3.1 18.0 3.9 to 10.2 3000 3.1 17.2 7.0 to 14.8 I failed to mention that I did replace the MAF sensor.

Anonymous 2019-03-15 11:43

Question: STB1 and STB2 are both reading the same? 3 to 7.8 or is B1 3 and B2 7.8?

Anonymous 2019-03-15 11:46

yes, they mirror each other all of the time. one leads the other by like a quarter of a second but always to the same figure SOrry, I was unclear.

Anonymous 2019-03-15 12:11

Regarding the fuel trims at different RPMs, if you hold the RPM up at each level for a least 30 sec does this change the readings from what you have posted ? If you can, set the scan tool to read only fuel trims for more accurate reading. OK, these trims at operating temp i assume? Bank1 high but corrects somewhat at higher RPM Bank 2 should be close to setting a too lean P0174 since trims all RPMs are 25+. So suspect lack of fuel. Need to verify fuel pressure first, if good then check injector contribution. No other codes associated with bank 2 O2 sensor? Have you tried clearing code to see what error codes return and when, according to freeze frame data?

Anonymous 2019-03-15 12:31

Each was sustained for a minimum of 20 up to at least 30 seconds with engine at normal operating temp. I can graph, but LT readings were steady with exception of ST which ALWAYS bounce around. Yes, I have cleared codes and always the same ones come back. I only RARELY get a P0174. So ALWAYS have only misfire codes mostly 308 sometimes with 304 and lesser with 300 and or 316. Ok, I guess I have to go buy fuel pressure kit for it... the ford geniuses got rid of the schrader vavle! The OBD2 system always reports good pressure... I can't recall what it is, but I know it was within range when I checked. I believe that may even point to a potential (I can't remember the name of it) failing module back under the bed. I'd have to take to a shop for the injector contribution... would that go back to PCM if bad? I had the same issue with old and new injectors. Thanks!

Anonymous 2019-03-15 12:51

One thing you can do to verify fuel delivery. The pre-cat O2 sensors should read high around 1 v at high engine loads. So at say 80% engine load if both sensors stay high it indicates good fuel flow.If not then as fuel trims seem to indicate there is a lack of fuel. Note that fuel pressure and fuel volume are a bit different. If OBD reports good pressure could be volume is lacking. Volume can be measured by specific fuel pressure/volume tester. Lets see what the O2s do at high engine load.

Anonymous 2019-03-15 13:25

Ok... Using "calculated load value" pid 80-90%.... O2 Sensors get up to .8V and stay there (takes a few seconds to level out).

Anonymous 2019-03-15 14:42

Ok, u replaced MAF does it read normal? Around 5-6 g/s at idle up to maybe 160 g/s 80% engine load. If so then kind of exhausted the easy tests. Time for the shop visit. "I'd have to take to a shop for the injector contribution... would that go back to PCM if bad? I had the same issue with old and new injectors." If PCM/injector wiring were at fault should set error code. Could be with hard cylinder misfire that PCM programed to cut fuel to that cylinder causing O2 sensor to go lean. If so then a cause of misfire needs to be found. Best i can do. Let us know what shop comes up with. Let them do their own diagnoses/repair so they can make good on any misdiagnoses.

Anonymous 2019-03-15 14:46

While misfiring is 6gps then once clears is 4gps. I’ll check what it is a 80% load. I appreciate your effort!

Anonymous 2019-03-15 15:46

Fordtechmakuloco.com has good youtube info on the 5.4. Ford IDS software can quickly check compression/injector fuel contribution/misfires etc. In your situation i would find a shop that can do IDS non invasive tests. Good luck

Anonymous 2019-03-15 18:37

Thanks for all your time and help. Yes, I’ve seen his videos, unfortunately the only one that comes close to my problem ends up being an obstructed air inlet. I take it you don’t see a need to compression test based on what I’ve been able to tell you?

Anonymous 2019-03-15 19:12

Compression check is done quickly on all cylinders with IDS software. Misfire can be caused by abnormal compression so i wouldn't pass it up. From what i gather fix misfire first and fuel trims may come in line. Do your misfires cause check engine light to flash?

Anonymous 2019-03-15 19:27

I’d say about half the time. There have been occasions when I thought I may have dodged it only to have it start once I was on my way and not only would light up the CEL, but it would flash. But if left at idle and sets the light, then no flashing. I definitely think the misfires and high trims are symptoms of the same cause.

Anonymous 2019-03-15 21:55

As you probably know misfire with flashing check engine light shortens cat life. Let us know what the fix turns out to be.

Anonymous 2019-03-20 06:23

SO... I monitored O2 again and have different results (I did it this time on the highway where it was flat). See attached picture. Also this morning it was kind of jerking while in OD when I accelerated just slightly. I'm going to focus on fuel delivery (pump and fuel module) - Just need to get kit to check fuel pressure with gauge and do some research on what my fuel volume should be.