97 expy 4.6 random one off misfire 287k

[IMINYOURCHAIR]

so my $400 expy is pushing closer to 300k miles. I have about 12k miles on a new set of plugs/wires. headed home from work I was about 3/10 mile out and at a stop light, after changing songs on the radio I noticed I had missed the light turning green so I get heavy into the throttle to get some quick speed.

when I did this the engine misfired on one cyl for about 10/15 cycles. then it began firing again. I am going to take a proper look at a few things when I get the time but I thought it a good idea to ask if this is a common sign of a failing part. I don't have my android phone to pull the engine data to see which cyl missfired during that time and with my other phone I can only see codes via a bluetooth adapter and the mil is off with no pending codes. otherwise I would already know which cyl to look at.

 

[JUST4FUN]

with that many miles injectors come to mind

 

[IMINYOURCHAIR]

could that cause the truck to present symptoms of trans slip under heavy throttle? this usually happens with the truck hot. this is the first misfire i have noticed since I replaced the plugs and the first one to happen with less than 2 miles into the trip.

when you mention injectors failing what is the typical mileage span?

 

[FordandPolaris]

Did you replace the wires when you did plugs? It sounds like either no spark, or a lean fuel mixture. Clogged fuel filter and failing fuel pump could cause that too. With that mileage, it could be all sorts of things. What do you know has been replaced other than the plugs and non-engine related items like suspension?

 

[IMINYOURCHAIR]

yes, wires were also replaced. coils (two that drive 4 each) look OE.

as far as fuel system goes, I replaced the filter at about 280k and the fuel pump had no receipt showing a replacement, so, I assume it's still original. knowing luck I will have to drop a full 30 gal fuel tank to get that done when it's time...

other parts, the PO seemed to have put the truck under the knife to knock out quite of things at once. some things I had to finish up myself. but I will do the best I can to recall all of it as most parts were visibly done while others had actual receipts.
I will put (po) or (me) to say who installed them.

(po) tstat and water pump replaced
(me) intake gasket and lower metal pipe replaced coolant pitted head/intake. filled with jb weld and sanded flat. no coolant leak since 276k miles. all intake port surfaces were still viable and not repaired.
(po) upper control arms about 1 3/4 years ago, unknown mileage other than my 11k since purchase.
(me) lower ball joints about 5k ago.
(po) front/rear shocks sometime before upper control arms. rear air bags replaced with new ford replacements about a year before purchase.

(po) front/rear brake pads/rotors (incl bearings)
(PO) ac compressor replaced with Bypass pulley
(me) bypass pulley replaced with used compressor from known working system. 330k miles on donor expy ODO. added to my truck at 279k charged and running fine since then

 

[IMINYOURCHAIR]

the trans has not had it's fluid serviced that I am aware of but it does read correct and does not look/smell burnt or otherwise abnormal although the tc does shudder if under right conditions of load/speed and with OD off.

 

[FordandPolaris]

Nice thank you sir. I would check fuel pressure using a FP gauge. You can rent one for free at most auto parts stores. If the fuel pump is original it is very possible the engine gets fuel starved when it's under a big load. I don't know what the pressure range is for the 4.6 but I will try and find it on googel

 

[IMINYOURCHAIR]

I can look that up in the service dvd I have, maybe it will tell

 

[JUST4FUN]

heres what I want you to do , at night take a spray bottle of water and wet down the coils and the wires look for stray spark. ill bet the coils are degrading
https://www.youtube.com/watch?v=5Vcojw0DL3A&list=UUN467fmgLLlk98JddJLL51w

 

[IMINYOURCHAIR]

will do that tonight.

F&P: here is the fuel pressure from the manual
Engine Running kPa (psi) 193-310 (28-45)
Key On Engine Off Kpa (psi) 242-310 (35-45)

 

[IMINYOURCHAIR]

voltage leak test passed. even soaked the engine as if I had pressure washed it (which I have done two times without any misfire issues, once after purchase, again after loosing power steering cap.)

I haven't pulled the coil packs off to look since the truck has been on the road a few times today. I can visually inspect them tomorrow while I have a cold motor bay to work with. monday I can go by an auto parts place to borrow a fuel pressure gauge.

 

[JUST4FUN]

Your headed in the right direction

 

[IMINYOURCHAIR]

automotive diagnostics. both interesting and infuriating at the same time.

 

[IMINYOURCHAIR]

both coil packs are clean...no corrosion in ignition or control ports. no cracks and the grounds look good. the wires are also free of chafing and all are seated properly in the head. no oil or coolant on top of any plug boots.