bdierks

Hello All! I have a 1978 Ford F250 It has an Inline 300 Six in it. I know that these are fairly basic engines. But I am not a mechanic. Here is what I know.... The truck sat for like 6 years. It got it passed down to me. So I wanted to get it going and drive it. So I took it to a shop and said... Get it running.... And they DID.... Barely... It ran like **** and he said I had one cylinder that had broken rings, and the best thing would be to rebuild the engine. So ok... We talked about it and he said, It would still be fine for dump runs and hauling the occasional load of dirt or rocks. So, I took it home. (Drove it Actually) It was obvious it needed some other things done... I put a new starter on it... New exhaust manifold.. And it still needs an exhaust installed. Also I took the Single barrel carburetor down and had it rebuilt. So now..... I cant get this thing to run.. It turns over a million times.. natta.. Sometimes it will backfire back up the carb. sounds like a shotgun!! LOUD. I thought rebuilding the carb would help. but it seems to be acting the same as before I did anything.
The mechanic said my plugs and wires looked good. They replaced the fuel pump and filter.
Ive double checked the firing order.. Its all good. Its a new battery...

So what else??? Theirs just not much to these engines.. So it has to be something simple. Would the broken ring problem really cause it to act this way? I would think that it should still start up good. And it would just not be running great with the ring situation.
Any thoughts??

Matthew Burr

Its got fuel... if its blowing back out the carb then at least one plug is firing but at the wrong time.
I would pull one plug out at a time and leave the cable on it, then hold it against the block while you turn over the engine, note the color of the spark(do it at night) also check the gap etc.
Let us know what you find out

Also fyi use really well insulated gloves or get one of those plug clips that will hold the plug and clip to the block

Chris_1

iTrader: (1)

Backfiring through the carb could be timing

RLXXI

All internal combustion engines require 3 things to run, Fire, Fuel, and Compression, if you have all 3 then the timing of those items happening is off. If just one is off it may or may not run so in order to better answer your question you need to answer some for me, do you have fire at the ignition system (spark plugs sparking), do you have a fuel supply and is the pressure correct (install a pressure gauge), and what are the compression readings from all cylinders (requires a compression gauge)?

bdierks

Ok Sounds like I need to check the timing.

Since I sent it to a mechanic I figured they checked the "spark" and "fuel" And "Compression". They did replace the fuel pump. And I believe all cylinders where good except for number 1. Which I think was at 50%. Which he told me was do to the bad rings in that one.

So to double check the spark plugs..... I pull them out and hold them close to the block, then turn over engine and see if sparks... Correct? What am I looking for as far as color??

06redlongbed

I never worked on a truck that wasn't OBD II but, my Ranger misfired and acted crazy when the computer went out. Is that a possibility in your case?

bdierks

Well im not sure what OBD is....?? And I dont think my truck has a computer.. Am I wrong???

06redlongbed

OBD = on board diagnostics. And in your case I think you have a computer, lol. I'm not sure dude my oldest ride was a 1996 Explorer. You have a check engine light?

bdierks

Looks like there is an Ignition Control Computer... But thats it. Must be under the dash or something

JayzDaddy

Unless the engine was swapped for a fuel injected engine or a feedback carb system which no one would do there is no computer.

Backfiring through the carb means spark is comming back up through the intake valve. That means timing is off. For a 78 engine, that thing probably has up to 400,000 on it depending what it was used for. Being a 300 its probably never been rebuilt. Depending on your money situation it may be more frugal to drop in a new engine. Ive been told you can find rebuilt long block engines for around $1300 bucks. Ive never looked so i cant say for sure. A rebuild of yours could cost up to about $2000.

If you play with the timing to start it move it a tiny bit at a time. You have to think a full turn is 360*. 2-4* can make a big difference. Once it starts, time it to about 10-12*btdc.