hotrod351

well it in the 100s here again and my 90 f150 4.9 giving me the same problems it seems to do every year, that is when it gets above 105 it starts really really hard, almost like its either out of gas or flooded, once it starts its fine and runs great, idles great, only in the afternoon when its hot out. got code 51 so i checked the ect and found it out of tolerance so i had one laying around and replaced it, the new one reads good but same problem. im at a loss. 51 is the only code i got, engine running, or key on engine not running.

aquadobie12

it could be possible that if your running higher octane during the summer (89, 93) or anything higher the gas in the intake and lines could be expanding flooding it or pressuring the intake to above normal conditions

hotrod351

im running the cheap gas that ive been getting at our maverick gas station for years. its the one with the least octane. i just did a fuel pressure test and its all good. its something thats being affected by the hot outside temps. im trying to think what would be affected by outside temps. even if i drive uptown and try to restart after 15 minutes it will start hard. yet in the morning it will restart fine. everything is fine until temps get upwards 105 and better. and then its just the starting that is hard, idle and driving is perfect. the only thing i havent tried yet is to go out and crack the gas cap and see if that helps. maybe its not venting, but i have two tanks and find it hard to beleive that both of them are messed up. unless the gas pressure vents somewhere else. all and all it has to do with high outside temps affecting something.

hotrod351

well i went outside, 117 degrees, and this time i opened the front gas cap to relieve pressure then screwed it back on. my truck started right up, no problems at all. im thinking that pressure must be building up inside the tank with the temps being so high. how do the tanks release pressure ?

qdeezie

May be a bad fuel vapor/charcoal canister.

Warlockk

How does it crank when it won't start? Slow crank then start or full speed for a long time then finally catches? Does it missfire or false start/ stumble?

hotrod351

cranks perfect. i checked the hose going to the canister and it doesnt seem clogged. canister doesnt seem clogged.

hotrod351

well i checked the fuel pressure the other day and it was right on, key on and key on engine running, and it also held pressure. when i did this it did the hard start to me, shaking all over and running like it was flooded, but cleared up. i let it sit for a couple of hours and went out and turned the front gas cap, thats the tank it was on, to the let to release the pressure. i didnt really hear anything but did it anyway. well my truck started right up, perfect. so i let it sit for another couple hours and same thing, started right up, perfect. next day the same thing, started up perfect. i checked the charcoal canister and its not clogged, i traced the line that comes off it back to the tanks and no pinched areas. so i figure it might be the vapor valves in the top of the gas tanks. problem is finding them, the ones i have look just like this one that the bronco grave yard sell for up to 87 bronco, but my trucks a 90. anyway unless it just a freak thing that my truck starts now with gas cap vented or thats really the problem i dont know. guess i could tighten them again and see it it starts hard again. but why doesnt checker or autozone show the vapor valve that i have, could it be that my truck is a canada sold truck that makes the valve different ?