'99 Random Misfire
 

I started my '99 F250 V10 the other day, and it just ran like crap. It didn't throw a code, but i plugged my reader into it and it gave me a P0300. I have no idea what it could be and all the wires are on the plugs right. There is ZERO power... Any ideas??? Thanks! :)

P0300 is a random misfire.

I bet there's a vacuum leak (the PCV plumbing elbow at the throttle body) or a whole slew of other things. MAF (clean it just to make sure), fuel pressure, you name it.

So where should i start?

Well, I fully agree that the PCV elbow can cause a "random misfire" P300 code. I just bought a 99 SD SC 4x4 V10 and it ran like a bag O crap. Decided to throw a set of plugs and known good coils in it and noticed a crack in that PCV hose.
When I removed it , it had two 1" long cracks in it.. Being sunday and all... I carefully cleaned and taped the hose.Monday I will get a new one from the dealer.
Now the truck runs like a million bucks!!!
BTW I just bought this truck for $2500 and everything works.. ESOF 4x4 and all.

So where do i find the PCV Elbow?

It is the fat hose running from the bottom of the throttle body(front)to the passenger side valve cover PCV valve. The "elbow" is under the front of the throttle body below your throttle linkage setup.

Sorry. If you meant the elbow to buy it, they have them at auto zone for 20 bucks.

OK. I am asking because i don't know where to start. Should i start with plugs? Coils? Plug boots? PCV? I'm not sure. I don't want to spend a lot of money to find out something is not the problem. I'm guessing start with something cheap like plugs? Then boots and so on...?

P0300
 

I had the same issue last year. I decided to replace all the COP's, boots, and plugs. Problem solved. I got the COP's on ebay for around $100 for the set of ten. Supposedly those boots are the cheapest route to go as far as replacement/solutions go, but, i bought my rig used and had no idea what the previous owner(s) had replaced. It also had 80k on it. In some forums i've read that any kind of coolant leak or hard water spray will cause the boots to fail and the COP will somehow arc through the boot occasionally, causing the "random" misfires. Good luck

I bought the boots at car quest and the plugs. Total for everything was about $80.
The rubber PCV hose was $26 at the dealer. I happened to have a set of coils sitting around since i have friends that work in the engine plant where they build the engine. :)
Its easier to change the plugs and boots than I thought it would be except the back 2 on the pass side.
Remember, if your not bleeding, your not working... lol

Mine was running like crap and i cleaned everything i could get to externally. IE new fuel filter, cleaned IAC, MAF, EGR, IAT, and pulled all the boots and checked anddi-electric greased them. One day later the "pending P0300" changed to "P0301 missfire." Replaced cop on number 1 for 32.00 and all is great. All the cleaning took a few hours but cost only 20.00 for the maf cleaner, carb cleaner and di-electric grease. I also checked my pcv elbow first and found it to not be cracked so went on with the cleaning of all those other things. I guess I am saying start with looking at the pcv elbow. You need to remove it to look at it good. Then go on and do MAF, IAC, EGR, and then the boots. Change up the order if you want but that is where I would start. There is my two cents. Out!

My dad's friend is a "Backyard mechanic". But he really knows his S**t. He said that it could have slipped out of time if it is misfiring randomly and also when it starts, it turns over very slow like a car out of time. It cranks almost like the battery is dead. Could this be the problem?

On this engine there is no timing adjustment. I would think that if it 'Slipped' out of time then it would be pcm or timing chain issue.

Ok... Well then i can rule that one out. I think i'm going to check my MAF today and PCV and plugs, boots and i guess if thats not the problem, i will just have it running, and start pulling COP one at a time to see which one doesn't affect how it runs/sounds

Thanks SDV10 for giving me the idea of checking the PCV elbow. I had multiple issues when I bought this 99 F250 with the V10. hard misfire at first. Threw codes P0174, P0340, P0302, P0300. I didn't know the condition of the plugs and saw that 5 of the COPs were aftermarket. I changed all the plugs, boots, springs and COP on #2 (with new dielectric grease). Cleared the codes and test drove. Miss was not as bad but still there between 1300 and 1800 RPM in overdrive. Threw code P0302 and P0300 so I swapped the #2 and #3 injectors. That cleared the P0302, but still had that P0300 code and it still had that miss. Stumped, I logged in here and saw your post and just like you described, I had a hole in the PCV elbow. I wrapped it with electrical tape and 'wallah' the engine runs perfect. Got the elbow on order.