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Ron, ASE Certified Technician
Category: Ford
Satisfied Customers: 23821
Experience:  23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
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2008 Ford F-250 SD FX4 Crew Cab CREW CAB PICKUP 4-DR, 5.4L

Customer Question

2008 Ford F-250 SD FX4 Crew Cab CREW CAB PICKUP 4-DR, 5.4L V8 SOHC 16V
Intermittent misfire on #1 and #8 AFTER Ford dealer replaced all spark plugs and all ignition coil packs. Swapping plugs or coil packs from other locations does not change it. It is always 1 or 8 misfire, always when going up hill or under heavy accel or under trailer load. Cam phaser and throttle body are not the issue (swapped throttle body as well), Never happens when cold or cold days, only warm and under load. IT is acting like the timing is not advancing at all under heavier load. Could it be knock sensor is bad? Note: Truck either runs perfect or missfires at specific times, not in between.
Submitted: 9 months ago.
Category: Ford
Expert:  Jared D replied 9 months ago.

It's unusual to have misfires on only cylinder 1 and 8. Normally when we see timing issues they affect one bank at a time. Since that is the case I would probably suspect a fuel injector issue rather than a timing issue.

Also, have you already ruled out an exhaust restriction? No lean or rich codes are stored during the misfire right?

Customer: replied 9 months ago.
no other codes.. typically it is 1 or 8, rarely at the same time. This was after fuel injectors were cleaned and running high or low octane makes no difference. No O2 issues either.
Expert:  Jared D replied 9 months ago.

Strange. Do you have a scan tool to monitor fuel trims while the vehicle is running?

Customer: replied 9 months ago.
I do, but don't know typical values
Expert:  Jared D replied 9 months ago.

You shouldn't see more than 10 plus or minus on either bank of the engine for more than a few seconds. If the computer runs positive higher than 10 for more than a few seconds that means it is running lean. If it runs at -10 or lower for more than a few seconds then the system is rich. A rich condition means an injector is leaking or a spark plug is not burning all the way. A lean condition means the injector isn't firing or there is an air leak somewhere.

Customer: replied 9 months ago.
I am not used to the scan tool I have, maybe you can tell me, this is cold start up just now:
TP_R(%) 3.9
ATT(F) 41
TP_B(%) 20.4
APP_D(%) 21.2
APP_E(%) 31.4
APP_F(%) 20.0
TAC_PCT(%) 5.9
LOAD_PCT(%) 23.9
ECT(F) 98
rpm 901
IAT(F) 51
MAF(LB/S) 0.02
O2B1S1(V) 0.730
O2B1S2(V)0.060O2B2S1(V) 0.125
FRP(PSI) 39.5
FLI(%) 90.6
VPWR(V) 14.296
EQ_RAT 0.999
Customer: replied 9 months ago.
Here is a full data dump cold startup after mayby 5 minutes idle time. But I need ot load it with a trailer to get the issue to show up.
LOAD_PCT(%) 19.6
ECT(°F) 176
SHRTFT1(%) 0
LONGFT1(%) 1.6
SHRTFT2(%) 2.3
LONGFT2(%) 1.6
RPM(rpm) 642
VSS(mph) 0
SPARKADV(°) 12.5
IAT(°F) 59
MAF(lb/s) 0.01
TP(%) 15.3
O2SLOC B1S12--B2S12--
O2B1S1(V) 0.7
O2B1S2(V) 0.765
O2B2S1(V) 0.23
SHRTFTB2S1(%) 3.9
O2B2S2(V) 0.425
SHRTFTB2S2(%) 99.2
RUNTM(sec) 963
MIL_DIST(miles) 0
FRP(psi) 39.6
FLI(%) 90.6
CLR_DIST(miles) 11
EVAP_VP(inH2o) -0.206
BARO(psi) 15.1
CATEMP11(°F) 740
CATEMP21(°F) 740
VPWR(V) 14.169
LOAD_ABS(%) 16.1
EQ_RAT 0.999
TP_R(%) 2.7
AAT(°F) 41
TP_B(%) 18
APP_D(%) 21.2
APP_E(%) 31.4
APP_F(%) 20
Expert:  Jared D replied 9 months ago.

This number looks a little weird:

Expert:  Jared D replied 9 months ago.

99.2% fuel trim on bank 2 means that the computer thinks bank 2 is running really lean. I would suspect either a faulty oxygen sensor on bank 2 or a dead fuel injector.

Expert:  Jared D replied 9 months ago.

Probably injector #8 since that is the one that keeps misfiring. You might swap it with another cylinder or just replace it and see what kind of numbers come up.

Customer: replied 9 months ago.
that number never changed. it was pegged high. Woudn't that mean faulty o2 sensor? in which case, why not have an o2 sensor fault?
which o2 sensor would I change? I drove the truck hard as hell today and it never skipped a beet once, but it was much colder than it has been and it never messes up in the cold.