Hey there, this is my first post. I've searched the for quite a while on ford forum and could not find my same scenario. So, here it is. As the title says I have a 1988 Ford F250 351 5.8 EFI manual 4 speed granny trans. I'll list the new parts and then give problem. I've replaced the TPS, IAC, MAP, Fuel tank, in fuel tank pump, Coolant Temperature Sensor, Alternator, water pump, starter solenoid, starter, battery and other things that are not related to the issue. The truck has a MSD Distro cap and is clean with newish plugs and wires. I've ran a bottle of sea foam through the master break hose leading to the throttle body and a bottle in the gas tank (not all once but over time). I cleaned the inside of the throttle body as best I could when I replaced the IAC. Ok, shew . . . Now the issue, the truck was running rough on cold idle and worse when hot. It would start fine but idle rough then when hot it would idle so low it would stall out. It had lots of backfires and some that were deep sounding. I had a friend set the timing and seemed to run sweet and perfect (it was a short drive home) that was yesterday. Today on the way to work it was running great till half way here. When I came to a stop sign I down shifted and got the deep backfires back and the idle was high at a 1k or so. Any help would be great thank you all

 

I would say your timing is off just from my own experience.I go to local shop for $50 and they time it right there.we have had alot of ford's on farm that would do samething.a half a degree off makes alot of difference.

 

Thanks Ill go today if can and let yall know.

 

Just out of curiosity , they had a lot of emission stuff on those engines. Is any of it still on there or has it been removed partially or fully ?

 

So I just got the truck back from the shop and it seems to run a lot better. I did notice that even with the timing set right now it still idles a little low when hot on a restart but not stalling out so thank God. Hanky, I'm not too sure about the emissions stuff but I know that the truck has straight pipes off the headers . . . and there are some or at least one pipe that was cut off. Ill send some pics soon of the engine and the pipe im speaking of. KIds are going nutz so ill get back

 

The reason I asked about the emission stuff is because there were diverter and bypass valves and an air pump and check valves to prevent backfire on coast/deceleration and most folks not understanding their purpose removed them, many times creating other problems.

 

Well I think I must have all that removed as this is the most back fierying truck ive ever heard. I guess that will be my next step in fixing this truck. I got the truck really cheap and it is my daily driver.

 

Did you look for possible vacuum leaks ?
There are several possible reasons for backfire which can come from 2 possible causes and they are an over rich mixture getting into the exhaust and a lean mixture where the fuel doesn't burn completely and the mixture gets into the hot exhaust. There are some good videos, if you Google in "What causes engine backfire" , they are somewhat lengthy and easier to comprehend than if written out here.

There is always the possibility of other mechanical problems AND we don't know what the former owner "re-engineered ".

 

Sorry it's been so long . . . I have now gotten a long block remanufactured engine in the truck. Just to recap I have replaced the : TPS, IAC, MAP, ICM, EGR, plugs and wires, front fuel tank, in tank fuel pump, high pressure fuel pump in line with the rail, fuel filter, injectors, fuel pressure regulator, bypassed rear tank and selector "valve", had smog pump removed as I have straight pipes and no cat or muff, Coolant Temperature Sensor, Alternator, water pump, starter solenoid, starter, battery. Shew, I basically have a new truck now. My last issue is this dang idle. When the truck is cold it idles perfect when it gets hot it idles up and down from 800rmp to 1100rpm. Any ideas ? LOL . . .

 

Did you check the oxygen sensors?