Hey there guys, think i can probably guess the answer to this one, but never hurts to ask. Trying to help out a college kid i work with, he has a 90 F150 2wd 4spd, his main transport. About 500 miles ago, everything was fine, then out of nowhere, it sheared the rollpin in the distributor drivegear. He had a shop put a new duraspark on, and 200 miles later did the same thing. Had another shop put another DS on, and SAME THING 200 miles later. The pickup now is sitting at another shop, with a new dizzy, but is really low on power, can only do about 35-40mph and the shop claims there is metal in the oil. They have put a lot of money into this thing trying to make it reliable, computer, fuel pumps, new cat and egr among other things to the tune of about 2500 dollars.

Ive found him a known good engine on craigslist, its a carbureted 300 from an 86 bronco. Will the efi play nice with the carbed engine? I know the cams and some other things are different between them, but i wondered since the 6 was avialable with EFI that year if it would work. I understand we would have to change manifolds, and maybe valve cover, as well as sensors probably.

If you guys could provide some input, we would both appreciate it, and if anyone has any guesses on the distributor thing, im curious. Racked my brain about it, and i cant think of any reason why besides excessive play in the camshaft, or possibly a failing oil pump, which while possible, ive never heard of it actually happening.

 

Trying to retrofit a carbed engine with EFI is going to be problematic. The combustion chambers in the carbed head burn slower, requiring more spark advance.
There is no provision for mounting a knock sensor.
The head has fewer mounting bolt bosses for the two-piece exhaust manifolds.
You may have to convert from Vee drive to PolyVee drive accessories.

I'm sure I'm leaving other stuff out, but it is not a simple bolt-in deal.

 

Well damn, those arent the issues i thought i would run into, but i was pretty sure i would run into issues. Thought maybe we would get lucky since both were options that year, didnt know if the engines were the same, and just different fuel delivery. Thank you very much for your help.

 

EFI started in 1987. There was no EFI prior to 1987. 1986 had a feedback carb with vacuum zone controlled fuel and spark delivery. It was somewhat complicated and trouble prone system, but it eliminated many problems associated with carbs when it was correctly maintained.

 

As FTF said, they did not have EFI and carb'd in the same year.

However, if you're lucky, since the engine is an '86, there may already be drilled out locations for the equipment that the EFI was going to get. I've seen a few '86 carb'd heads that had the 3 extra bolt holes already drilled in them that the EFI heads were going to get.

To me, though, it sounds like you're running into one of two problems, or both.

Cheap distributors with pot metal roll pins or a dying oil pump.
The camshaft spins the distributor gear, and the distributor spins the oil pump. So if the oil pump is failing, it'll put a LOT of load on the distributor gear, and eventually cause the pin to shear off. If it keeps happening, this would be my main guess.
Unfortunately, though, unless you're a crafty mechanic, changing out the oil pump usually requires the full removal of the engine. But, that would give you the chance to inspect everything else.

I also don't buy that you're losing power due to metal in the oil. That's a lot of metal, and a sheared roll pin (even a few of them) isn't going to do that.
I flattened a lobe on a cam a number of years back (that's a lot of metal) and while it had some serious performance issues, it still had a lot of power.

Why was all of this other stuff, like the computer, replaced? Were there engine codes that it was throwing?

 

I agree with the suspicion regarding the failing oil pump - and would personally try replacing that (with a new distributor gear / shaft) before trying a whole new engine. It looks like you can get the oil pan off and pump out without totally removing the engine, but the service manual does state that the radiator and starter need to be removed. See the screenshot below (let me know if it doesn't show up, and I can type up the instructions).

 

On my engines with high volume pumps and hi-lift roller cams I replace the roll pin in the gear with a piece of 1/8 steel welding rod. I melt a ball on to each end to prevent it walking out.

 

The computer did need replaced, it was running erratically and dying, wouldnt idle. Replaced carb fixed that, they replaced the fuel pumps before the computer. The cat was replaced by the shop due to the low power. My third-hand information isnt real good. At this point, he just needs to be able to drive it, digging into the an engine that may or (more likely) ,may not be good is not in the picture. Cant find a used efi engine under 700, but we did find an 88 xl single cab 2wd with a bad trans for 500. Think he may go that route, pull engine, part the easy stuff and scrap it for 200-300.

 

To be sure, the 88 and 91 engines should be identical?

 

I can't remember if the 300 had a knock sensor added at some point or if it had it the whole EFI run. Otherwise yes, an 88 & 91 are going to be virtually the same.