HELP!!!
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Senior User
Joined: Jan 2010
Posts: 161
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From: Independence
HELP!!!
I have an 86 F150 300i6 with less then 150 miles on the rebuild. My problem is, when cruising down the highway my truck will hesitate real hard at different speeds and start backfiring when I let off of the gas. The truck runs smooth at idle. When we dropped it in, we didn't hook up any of the vacuum lines and it ran fine. I had the carb idled real high and it got ****ty gas mileage, but it ran fine. It didn't start hesitating until after I hooked up the vacuum lines yesterday.
Cargo Master
Joined: Sep 2007
Posts: 2,095
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From: Wahpeton ND
DId you have the lines blocked off? Did you have your vaccum advance disconected? If the vaccum advance was disconected you need to re-time your ignition. If the problom presists you have a vaccum leak somewhere.
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Senior User
Joined: Jan 2010
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From: Independence
I didn't put the vacuum block that bolts to the valve cover on till yesterday either. Before that, everything that should have had a vacuum line was plugged. I used rubber fuel line to run the vacuum lines because the plastic ones snapped when I was taking the engine apart. My distributor isn't a vacuum advance distributor. It has an electronic control module. Like I said, it ran pretty darn good until I hooked the vacuum up, but, it got terrible gas mileage. I'm talking a half tank used in two days and I don't drive more than 50 miles a day.
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
I dont understand how you dont have a vaccum advance on a carbed engine. However it sounds like your timing is retarded and needs to bee advanced a bit. Ford had a vaccum advance on all the carbed engines and did not go without untill they installed fuel injection. If you installed one of theese distributors without the propper ecm to back it it will not advance the spark propperly for a given load or rpm.
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Joined: Dec 2007
Posts: 7,987
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From: Boise, Idaho
The 84 - 86 300s had computer controlled timing advance with the feedback carb setup.
That feedback carb setup sets your advance based on signals it's getting from the engine, so if you don't have everything hooked up correctly, it's getting mixed signals and not setting your engine as it should. That's the one setup (feedback carb) where everything has to be in place and working.
That feedback carb setup sets your advance based on signals it's getting from the engine, so if you don't have everything hooked up correctly, it's getting mixed signals and not setting your engine as it should. That's the one setup (feedback carb) where everything has to be in place and working.
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Senior User
Joined: Jan 2010
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From: Independence
I ran everything according to what it says on the vacuum diagram sticker on my core support. What is OBD III?
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Joined: Dec 2007
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From: Boise, Idaho
OBD is On Board Diagnostics. It's the ability to have the computer tell what's wrong with the engine.
I think your year would be ODB-I, since before that, they didn't have any computers.
FORD 1983-1995 OBD1 Decoder
You might be able to see if the computer's throwing any error codes. It could be that even though everything is hooked up right, a component that the computer relied on has just bought the farm due to the engine's age.
Honestly though, the feedback carb setup runs great when it's all in working order, but that's rarely the case. Many of the components and electronics are too old to work correctly, and since it was only used on the 300 for 3 years, they can get very expensive to replace.
Most people do a DuraSpark II swap, which is pulling out all of the feedback carb stuff, and installing a control module, distributor, and carb from a pre-feedback engine. They're much simpler, inexpensive, and work just as well.
I think your year would be ODB-I, since before that, they didn't have any computers.
FORD 1983-1995 OBD1 Decoder
You might be able to see if the computer's throwing any error codes. It could be that even though everything is hooked up right, a component that the computer relied on has just bought the farm due to the engine's age.
Honestly though, the feedback carb setup runs great when it's all in working order, but that's rarely the case. Many of the components and electronics are too old to work correctly, and since it was only used on the 300 for 3 years, they can get very expensive to replace.
Most people do a DuraSpark II swap, which is pulling out all of the feedback carb stuff, and installing a control module, distributor, and carb from a pre-feedback engine. They're much simpler, inexpensive, and work just as well.
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Joined: Dec 2007
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From: Boise, Idaho
https://www.ford-trucks.com/forums/9...questions.html
There's a bit of good info in that thread. Also, just using the search function for "duraspark swap" will pull up a lot of good info. Use the advanced options to select just the 300 I6 forum for more fine tuned searches.
There's a bit of good info in that thread. Also, just using the search function for "duraspark swap" will pull up a lot of good info. Use the advanced options to select just the 300 I6 forum for more fine tuned searches.
Cargo Master
Joined: Sep 2007
Posts: 2,095
Likes: 2
From: Wahpeton ND
Fords Early emissions control and engine managment system are notoriously hard and expensive to work on. Like abandoned said they only used it for three years. There was a reason for that. When they run (I have seen one) the run great. Otherwise the standard procedure is to throw all this stuff into the trash and simplify with a duraspark and non computerized carb.
Duraspark was Fords first mass used electronic ignition system and is still ranked highly today for its relability, simplicity, and nice hot spark. The moduals are about $30 and a reman distributor with rotor and cap will set you back about $140 without a core.
This should be a plug and play operation as I belive the wiring is nearly identical.
DO NOT DO THIS IF YOU HAVE TO PASS SMOG INSPECTION!
Duraspark was Fords first mass used electronic ignition system and is still ranked highly today for its relability, simplicity, and nice hot spark. The moduals are about $30 and a reman distributor with rotor and cap will set you back about $140 without a core.
This should be a plug and play operation as I belive the wiring is nearly identical.
DO NOT DO THIS IF YOU HAVE TO PASS SMOG INSPECTION!