Recently bought an 86 f150 2wd SB. The truck was built with a 4bbl inline 6 cyl and a previous owner dropped either a 302 or 351. Question: How do you tell the difference between a 302 and 351 without an engine ID plate?

Today I replaced the spark plugs and wires (distributor looks as if it is pretty new). I went through the motions just like I always have...changed the plugs one at a time and replaced the wires one at a time. When i started the engine it was idling rough and sputtering really hard. I checked all of the connections and tried it again but still a rough idle. I consulted my handy dandy Haynes Manual and checked the firing order. When 1-5-4-2-6-3-7-8 didnt work I tried the Windsor order of 1-3-7-2-6-5-4-8 and it wasnt working either... Questions questions questions...

Is using a penetrating lubricant a bad idea for dislodging seized spark plugs and would the penetrating lubricant cause the rough idle? Also, i made sure not to get any Anti-Seize compound near the electrodes on the plugs but would that cause a rough idle? I also tried the "shifting" of the wires leaving the distributor (moving each wire to the right one spot, in correct firing order).

Also, the guy I bought the truck from, he removed the Inertia Switch to the fuel pump and jerry-rigged an ON/OFF switch under the steering column. Now that I have changed the spark plugs and made whatever mistake I made, the truck runs at a fine idle with the fuel pump in the OFF position! I'm clueless... She sputters and spits with the fuel pump running and runs like a champ with the fuel pump not running.

 

Dave will come on here in a few min's and give you a drawing of the diff between a 302 and a 351. He seems to keep that one in his back pocket. But, IIRC the distance across the intake manifold is ~9" for a 302 and ~11" for a 351W.

But, it doesn't sound like you have done anything wrong in the ignition itself, but more likely in the wiring that goes to the pump. If this engine doesn't have a mechanical pump on the engine it cannot run w/o the in-tank pump running - unless the truck is sitting nose-down on a steep hill. So something has gone wrong with the wiring to the pump. Can you verify that there is/isn't power to the pump when the toggle switch is on/off? Maybe by hearing it run or measuring the voltage or using a test light? And, does it just idle like a champ with the pump off or does it drive like a champ?

As for the penetrating oil and anti-seize, if the truck runs fine at some point then the plugs are fine. It has to be a fuel problem causing it to sputter.

 

I've had DOA plugs before. Return the firing order to the way you found it and with it running disconnect and reconnect each plug wire. When you disconnect a good cylinder it'll run worse. When you disconnect a bad cylinder the idle will change very little. Isolate the cylinder(s) that are bad and change those plugs. It that doesn't work then backtrack.

Is the engine carbureted? I thought most of those didn't have an electric fuel pump. Could it be he added one to replace a broken mechanical one? I'll never understand why people do that.

Also, they way I look for a 351 vs 302 is where the water pump bolts to the block. If the cylinder head parting line is right on top of the water pump it's a 302. If it's about 1" higher then it's a 351.

 

Just a thought.
I have a 94 explorer 4.0 as well. I was told that those motors were very picky with plugs and to use only motorcraft or autolite. Is it possible thid applies here? Maybe different heat range?

I dont know much so dont take what im offering as advice. Just a suggestion/question.

 

From Franklin2's images:

 

First item, check the 8th character of your VIN, that will confirm what the truck was built with. If you have an inertia switch, I will almost bet money the original engine was a 302 EFI. Ford never built a 6 cyl. with a 4 barrel from the factory, Chrysler did with the old 225 hyper-pack in Valiant's and Lancers and Pontiac did with the Sprint in the Tempest and Firebird (it was OHC also).

If your truck was a 302 EFI, it has either 2 or 3 fuel pumps depending on how many tanks you have. There is a high pressure pump on the frame and a medium pressure pump(s) in the tank(s). There is a small reservoir on the frame just behind the high pressure pump. Depending on number of tanks it will have 4 or 6 lines.

If you have a carburetor and try to feed it with 40+ psi it really doesn't like it.

 

The Pontiarc OHC was a glorified Stove Bolt, but it could run.

As for the fuel pressure, why didn't I think of that! That would explain a bunch of things. No needle and seat is gonna like 40 psi and there will be gas flooding into the engine. Good job, Bill!

 

Yes it would, but lord help you if you had to do a valve job on one, getting everything right took a bunch of special tools.

 

Thanks all for the replies and the info on the displacement differences. Very useful. I'm in for the night so I'll be checking it tomorrow and checking the fuel pump. How can you tell the diff between mechanical and electric. It has the distinct hum when turned on.

The fuel pump def turns on. I can hear the hum for sure. I used my dads Matco spark tester ( i dont know the exact name, it looks like a fuel filter, you plug it to the boot and the wire and it shows if its sparking or not). I checked all eight plugs and all were sparking. I removed all of the plugs and inspected...all were covered in soot and even had soot on the porcelain insulators above the threads (the white area). Is this odd being that the engine wasnt running for more than thirty seconds four or five times? Would the plugs get covered that quick? I bought bosch plugs that were pre-gapped. they have four prongs and I didnt even think about heat range. I'm going to buy Motorcraft plugs tomorrow and gap them myself and maybe get new wires. (Haynes says the wires should be less than 5000 ohms per inch and maybe I have too much resistance?)

Im positive the fuel pump works. She died when I was driving and shut it off, and hesitated when I gave it gas to accelerate. I replaced the fuel filter about three weeks ago and ran some chemtool b12 through the system. Whoever owned this beauty in previous years either didnt know much about mechanical systems or was too busy smokin crack. Maybe both.

It now has an EFI V8, Ill be checking the displacement tomorrow. I decoded the VIN and it was built with a 300 inline 6 4bbl. How long ago the swap took place I have no clue.

It WAS idling like a champ with the pump off. Not doing it anymore, or atleast the last time I let my pops hear it run. With the pump on, she sputters and "misses" at around 1000 rpms when it usually idles at approx. 1400. And when I turned the pump off to kill it it would idle normal without sputtering and missing until I turned the key off.

 

sorry about that. 1 barrel carb was the original setup.

 

Several things. Again, it did not come with a 300 six and a 4bbl as Ford didn't put a 4bbl on that engine. Second, you said it now has an EFI V8. That means it has a computer, so you should see what the computer thinks the problem is. Third, a mechanical pump will be on the block on the driver's side right near the front, down by the steering linkage. Last, if the plugs are all sooty then you are getting way too much gas into the engine. Last plus one - 1400 RPM isn't idle. It should idle at ~650 RPM.

 

If he used the ford setup for that year then there will be a tank pump and a frame pump. If you have dual tanks then there will be two tank pumps. It will run with just the tank pumps but won't rev much before it runs out of fuel pressure. Could it be that the on-off switch is on the front pump?

Also, pull the vacuum line off the fuel pressure regulator and make sure it's not wet. The diaphragm inside sometimes ruptures and excess fuel goes through the vacuum line into the engine and it runs rich.

 

You're right, I misstated. It had a 1bbl, at least according to LMC. 8th VIN number is Y. It idles @ 1400 when in park. When I put it in drive or reverse it drops to about 800. Im thinking that whoever swapped the engines was going for high performance. The gas tank only holds 7 gallons. Im sure Ford would build a truck with a bigger tank than that. You can def tell something was done. Alot of wires aren't connected and the engine bay looks empty compared to what i see in others. The entire AC setup has been stripped. Somebody either didnt know what he/she was doing or this thing was a beast at one point in time or another!

This thing has mucho issues but thats good for me, I like to learn and I need something positive to occupy my time and money.

 

Thanks Dave. All of you guys have been nothing but helpful so far. Wish I could track down the "mechanic" that did the swap!

 

Look for Ham Phist, or Shayde Tree, I'm sure it was one of them. If you go to my website, under downloads (left side, middle) the fuel pump circuit for the 86 EFI is on there. Maybe that will help. Some pictures might help also.

Back to post #4, I only use Motorcraft plugs in my Fords, under no circumstance use Bosch platinum plugs, they will misfire unbelievably in a Ford.