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2001 Ford f 150 4.2 V6 p0300 p0306 misfire

Model: 2001 Ford F-150 Fault Code: P0300 Posted: 2014-02-27 01:08

2001 Ford f 150 4.2 V6 with P00303 and P00306 misfire codes, 178,000 miles, well maintained. In the beginning there were also P00171 and P00174 codes, (too lean bank 1 and 2). I cleaned the MAF, checked all vacuum lines and cleaned the air intake body. P00171 and P00174 codes are gone. The P00300 and P00306 codes and the actual missing on #3 and #6 persist. I have replaced the plugs, wires, coil pack and fuel filter. I disconnected the EGR, (I plugged the vac line) with no change in the #3 and #6 miss. This engine has not had the new style isolator bolt and valve cover upgrade, (it will get that next week). as well as get the EGR ports cleaned. The bolt and cover upgrade is more in relation to the air/fuel mixture, after all sensors, causing a lean mixture. However, I still can not identify the cause of the miss. The O2 sensors being bad would cause a "random" misfire, as would a clogged catalytic converter, so I don't think they are at fault. The plugs have less than 100 miles on them and are gapped properly,(the miss was there before they were changed, the same for the wires, coil pack and fuel filter). The injectors have been removed and cleaned. Fuel pressure is good. No vacuum leaks that I can hear, or find. No plug wires arcing. All wire boots secure at coil pack and plug ends. Compression is 92+ on all 6 cylinders. I am out of ideas. One item of interest. A few days before this became an issue, I bought gas at a different station. When the issue first began, I attributed it to "bad gas". I filled up with premium gas and added a can of SeaFoam fuel treatment. The truck does run better, but the miss is still there and on the same cylinders, #3 and #6. Any thoughts, or ideas would really be appreciated.

Related fault codes
P0300P0306
Comments (14)
Anonymous 2014-02-27 08:22

vacuum leaks are hard to find sometimes......before i bought a smoke machine i used propane.....i took a small tank used for sweating copper plumbing and unscrewed tip and attached a rubber vacuum line and turned on and ran along intake gaskets and listened for a rpm change.....i also did this later while monitoring the 02 voltage to see go rich high voltage....could backprobe 02 signal wire with multimeter or just listen for rpm change.

Anonymous 2014-02-27 14:19

Autojoe. Thank you for the suggestion. Have checked for vac leaks, all vac lines, intake to heads, plenum to intake, plenum, air intake to plenum. Everything is sealed. (vac leak test done with 100% ether. Normally instant results). O2 sensor would cause random misfire. Put known good O2 sensor in and no change...

Anonymous 2014-02-27 15:41

have you done a fuel pressure leak down test? gauge do not guess. A easy test, easier said than done- might wnat to swap injectors 3 and 6 to other cylinders, see if code follows.. What is the fuel trim looking like?

Anonymous 2014-02-27 16:18

Kev2. Thanks for the idea. I have cleaned and swapped the injectors and the miss stays the same. I have NOT tried a leak-down test and will try that this evening. The vehicle starts very easy and shows no other symptoms of anything, other than the miss and the P00303 and P00306 codes. I pulled the plugs on # 3 and 6 and they are nice and even light grey/brown. I pulled #2 and 5 for comparison and #3 and 6 are just slightly darker. #2 and 5 look perfect. #3 and 6 have the look of a recently replaced plug, but not new. All have less than 100 miles on them. All of this started with what I thought was bad gas.

Anonymous 2014-02-27 17:29

as autojoe mentioned VACUUM leaks, that 2piece manifold not an easy access for checking. ANYWAY I will throw out some ideas.. >check FPR - I think it gets vascuum from rear of manifold.. >that leak down test- KOEO a inj wiriing issue would show. >fuel trims - PS: what plugs used?

Anonymous 2014-02-28 05:20

Fuel Pressure: I am averaging 43 PSI at idle and maintaining a "hold" of 5.1 PSI. So my Fuel pressure is good... I am assuming that this means my FPR is good. I have checked the plenum, intake, and all vac lines with ether and can find no leaks. (Trust me, I've soaked the engine in ether!). When I changed the plugs I was running stock Motorcraft, PT. # 5308-05048426, gapped at .44.(The engine was missing on #3 and #6 with the stock plugs). I replaces the plugs with Motorcraft PT. #5308-05048432, gapped at .54, which is supposed to be a little "hotter" plug, since I thought this was bad gas and still had about 1/2 a tank. Please correct me if I am wrong. Excluding the plenum to intake seal, (each cylinder is separate), if I had a vacuum leak, on a vacuum line, causing a miss, would that not be a random miss? Same with the O2 sensors? I could understand a consistent miss on any given cylinder for the plenum to intake O rings, or even a bad plenum seal, leaking in just one spot. Also, I would think that such a leak would cause the cylinder to run lean and if it were running lean enough to cause a miss, I would have P00171 and/or P00174 codes, like I did before I cleaned the MAF. This is a very pronounced miss, as in it is almost like the cylinders are not firing at all, (they are firing). I will be doing the Isolator bolt upgrade this weekend, which it is supposed to have and was planned anyway. That should take care of any vacuum leaks from the intake, up. The miss is #3, Back left and # 6, back right, where of course the plugs are harder to get to... like everything else. What are the odds of a bad intake gasket on both sides, on the back of the motor? How would I do a KOEO check on the injectors? What voltage should they have when the triger? I don't have a noid, but a DVOM should work, yes? Thanks for all of the suggestions

Anonymous 2014-02-28 06:51

Fuel Pressure Specs: KOEO: 35-45 psi Idle: 28-45 psi

Anonymous 2014-02-28 08:31

run engine observe fuel pressure - turn off engine move key to run - observe fuel pressure- POst the results - drops to x in @5 min .... that post of yours listed "maintaining a "hold" of 5.1 PSI". is suspect..do the test ask mentioned above

Anonymous 2014-02-28 22:58

Fuel pressure is at between 42 and 44 PSI, (slight vibration in the gauge), at idle. Engine off after 5 minutes is 5 PSI. Turn key on and it goes back into the 40's. Key back off for over 30 minutes, PSI drops to 5, key back on, right back into the 40's...

Anonymous 2014-03-01 09:36

sounds like excessive drop, check the FPR - there should be NO fuel in Vac line.

Anonymous 2014-03-02 00:11

Kev2. No fuel in the line. Friend of mine has the same truck. We checked his pressure. Almost exact at idle, 46 PSI. Key off wait 5 minutes, 7 PSI. Key back on, back to high 40's. Key off over an hour, 4 PSI. Key back on, back to high 40's. Start, drop to 31 PSI, then back to high 40's. Checked mine at start, Key on, mid 40's, start, drop to 28, then back to 44 PSI. Revved engine to 3000 RPM, no load, #3 and #6 missing, fuel pressure drooped for a split second to what looked like about 42 PSI, so fast I couldn't really read it, before it came back up. I'm doing the isolator bolt up grade tomorrow, will swap #3 and #6 injectors with #1 and #4 and see if the miss moves. I was sort of thinking that there might be a fuel flow issue and if there is I think that it is going to be in the injectors. I am beginning to suspect that my thought of bad gas may just be coincidental with when this started and that I may have had a bad coil pack and the new one may have issues. I am going to try and find the coil spec.s tomorrow and test it.

Anonymous 2014-03-02 10:45

yse swap the inj- my bad I ASSUMED when they were removed to clean (original post) they did not return to same cylinder. OHM the injectors while they are accessible.

Anonymous 2014-03-03 01:41

When I cleaned the injectors, I pulled the injector clips & fuel rails. then did the injectors 1 by 1, so that I only had one open hole at a time. I used ether and a tooth brush to clean the face, (nozzle) and body of the injector. I put a light coat of O ring grease on the O rings and put them back in. Before I removed the injectors. I used hot water and cleaned the intake/injector area. (I keep my engine very clean, just light dust to wash off, no leak marks anywhere). I used compressed air to blow dry the engine, didn't want water in the injector holes... I didn't mention this before. I am a mechanic by trade, but not little engines. I am a reciprocating diesel engine mechanic, 30,000 HP and up, (ocean going cargo ships). I have mechanical ability, but know next to nothing about this type of engine. Needles to say, I can put about 4 of my truck in one cylinder of what I normally work on. Plus we have an entirely different type of emissions system. So I am really at a loss on any small gas engine and I really appreciate the ideas and information. I assume the injector voltage is 12 V DC. Can I open the injector with an extended pulse and flush it backwards?

Anonymous 2015-03-10 18:32

Hey Max5101, how'd it go?