1990 F150 300 i6 EFI 5-spd

I've had a bad misfire for some time. It's less when it's cold. As the engine warms up it gets much worse. I figured it was a slightly bent valve, so I swapped the head out with an EFI same year. After the swap it's much better, but still misfiring.

I've been reading the threads on here. Based on those suggestions will go to O'Reilly and get some codes, test the fuel pressure, get a new fuel filter and air filter, and try swapping out plug wires (distributor, plugs, and coil are all new already).

I wanted to thank the posters on this forum for your expertise. It is much appreciated.

 

I've since purchased a 1976 300-6 for $75 with all wiring. I'm looking to take the EFI off, and put the carb and vacuum advance distributor on. I've read several online forums regarding this, and I had a few questions:

(1) Can I leave the existing computer completely hooked up, and simply unplug the fuel injectors, sensors, and distributor wiring?

(2) Does anyone know if the throttle linkage assemblies fit right up? Or if they require some tweaking?

(3) My father's used after-market air intake filters which are basically large rubber or plastic tubes which pipe over to a filter off to the side of the engine ... does anyone have experience using these on a carb, rather than as an air feed into some kind of plenum?

(4) I've seen YouTube videos where people are hooking up turbos to their 300-6 engines. I would like to do this for additional fuel economy. Has anyone done this here on this forum?

Thank you in advance.

Best regards,
Rick C. Hodgin

 

Looks to me like a lot of work to downgrade to a carb and non-computer controlled ignition.

The computer triggers the fuel pump(s) by sensing the PIP pulses from the distributor. Without those pulses the fuel pump relay will energize for 1-2 seconds then shut off. Leaving the computer in is not going to gain you anything IMHO.

Speaking of fuel pumps that carb'ed engine requires a lot lower fuel pressure so how do you plan to knock down the ~50-60 PSI to something usable like 5-7?

You can adapt most anything for use as an air filter, but in the long run it will not be as efficient as the factory EFI filter system that pulls in cool air from behind the grille.

Adding a turbo is going to very complicated, especially with a carburetor. Even with EFI a basic turbo requires a lot of engineering on your part. Adding a turbo for fuel economy is an oxymoron.

 

How the hell did a thread about a "misfire" become a carb'd engine swap project? Oh, and a turbo addition as well!

Good luck!

 

... x2 on the above replies. you were on the right track with pulling codes and checking fuel pressure. whatever happened with that ?

 

I still plan on getting the codes and checking the pressure. If I can get it to work I won't make the swap. However, I'm not willing to continue throwing money at the truck to try and resolve the issue. I had the ECU replaced, coil, distributor, wires, head swapped out, it had new fuel injectors put on it just before I got it (it's had the issue all the time I've had it).

Switching the head made some difference. But it still runs poorly when the engine's cold. But, when the air temperature outside is cold (30F or lower), and the engine warms up, it runs almost perfectly (if the outside air temp is above 30F, then it misses out, and if it's summer temperatures 80F or higher, it runs as bad as it does in the next sentence). But if I shut it off and start it back up (after long enough to run into a gas station, for example), it runs horribly. It starts backfiring under average to strong acceleration, and I can feel that the power hitting the wheels is going up and down like it's starving for fuel, or the timing is advancing and un-advancing, etc. It continues that way for about 3 to 5 minutes, then begins to just misfire badly unless I'm driving on the Interstate, and then it will gradually smooth out of the next 20 miles.

It's very frustrating. And my thinking is like how much more money do I throw at the truck to try and fix it? I have a $75 solution plus some time that will then guarantee that if I have any problems in the future they'll be low dollar finds.

Best regards,
Rick C. Hodgin

 

From other threads I've read, there are two fuel pumps, one in the tank, and one high pressure pump. The one in the tank is sufficient to provide low-pressure fuel for a carb, and people who have made this conversion have used that. If not, then I'll get an inline electric pump.

I had the idea of running the plastic / rubber piping over from the EFI filter system into the carb, but through the tube which goes across and then 90 degree turns down into the top of the carb.

I was under the impression turbos increased compression and horsepower, and therefore fuel economy. I looked online after reading your post and the posts I read seem to be mixed. Some state that there is never any gain whatsoever under any conditions. Other people cite gains they've seen in their own experience.

As for me, I'll go by example. I'd like to see if someone has made the upgrade to turbo personally, and got it working, and if their mpg increased (many people say they can't keep their foot out of it so the gains are lost in that way, but would be there otherwise).

Regardless of whether it's through a turbo or something else, I've heard of people getting 20mpg or so on carb 300-i6 in F150 pickups ... so I'd like to target something there. If it requires doing a few things to get there I'm content to do it. I like to tinker. :-)

Best regards,
Rick C. Hodgin

 

There's another related thread I started earlier this year:

https://www.ford-trucks.com/forums/1...manifolds.html

Still on the same path.

Best regards,
Rick C. Hodgin

 

That would be true for 1984 through 1989 model year trucks. 1990 and newer use a high pressure pump in each tank.



That should work



More horsepower requires more fuel unless you also increase the efficiency of the engine itself. A turbo on your tractor engine is only going to pump more air therefore it needs more fuel. If you managed to eek out a little more MPGs, remember you are still driving a barn door, the pay back time will probably exceed the cost of the upgrade.

Tinkering is a good thing

Best regards,
Rick C. Hodgin[/QUOTE]

 

Ah! Missed it by a year. :-) Also, I've wondered how the fuel pumps could be so loud when they're low-pressure pumps. Now I have my answer. :-)

Do you have any suggestions? Drop the tanks, pull out the existing pumps and just replace them with a line and filter? My sending unit is not working properly in the rear tank as well. When full it only reads about 7/8, and when empty it reads about 1/8.

I think until I get it all working, I'll probably just use a portable tank from my wood-splitter and an inline electric fuel pump.

Indeed. It gives me something to do which isn't tied to computers now and again.

Best regards,
Rick C. Hodgin

 

The sending units are known to go bad, you can check it with an ohm meter at the tank switch. Should be ~145 ohms full and 22.5 ohms empty.

The problem with removing the pumps is the way the fuel system is tied together there is no electro-mechanical switching valve per se. Each in tank fuel delivery module consists of a pump, sending unit, valves and other pieces. These valves prevent the energized tank from back filling the tank that is not in use. Removing any part of the FDM will result in transferring fuel from one tank to the other unless you put in some type of valve, which does exist for low pressure fuel system like you are contemplating.

A diagram of the Fuel Delivery Module:


courtesy of subford

You could use the basic "top hat" of the FDM, remove the pump and valves then weld in a pick-up tube that would draw fuel from bottom of the tank. I would suggest a filter like the existing one.

Another option is the keep the existing high pressure pumps then use a fuel regulator that returns the bypassed fuel back to the tanks.

 

Front tank's good. I had the thought to compare their ohms.

I had envisioned tubes coming from each tank to a Y-valve, two in, one out, and that would be hooked to the "front/rear" switch on the dash. Then the inline pump would be ahead of that on the single line running up to the carb.

I had that thought as well, or creating a buffer for each tank with a float like a sump pump that turns the high pressure pump off when it reaches a high level, with a vent back into each tank.

Not having the low-pressure pumps in each tank makes it more difficult. I think I'll probably wind up dropping the tanks and removing the high pressure pumps, and then welding the tubes on there as you suggest. I have a TIG welder so it should work well.

Best regards,
Rick C. Hodgin

 

Okay ... I'm to the point where I'm ready to switch out the 1990 EFI 300-6 with the 1976 carb 300-6 I bought. My plan is to do the following:

(1) EFI out
(2) Carb in
(3) Manual temporary hookup to skid tank in the pickup bed.
(4) Get the EFI working in my garage "on the bench" with an after-market computer.
(5) Once it's working, carb out
(6) EFI in

I need a reliable truck to get around in, and that 1976 carb engine should do nicely until I can get the EFI issues resolved.

Any thoughts?

Best regards,
Rick C. Hodgin

 

swapping engines seems excessive to install efi... but ok.. I did weirder stuff when I did mine.

I went and did my fuel tanks first and stuffed the carb on the efi engine and head. the timing remained stock and I guess i should have gave it a better tune as the efi head has fast burn tech. it worked and didn't ping (detonate) so I was happy with the temp solution.

What I used was a Holley By-Pass Regulator 12-803BP to drop the efi fuel system pressure down to low carb pressure. work a charm until the carb failed due to an unrelated JB Weld incident...

The only issue I can see in your efi swap, is you might have to add extra wiring for extra wiz-band stuff, like Wide Band O2 sensor or fully sequential Injectors. Some early ford efi used a batch fire injector setup, where 2 banks of 3 injectors where fired. I didn't notice on the harness I got and had to re-make it for the extra injector wiring.

I would rip out all the wiring and get a custom pre-made harness and mate the two together. start with power distribution sections to power the custom efi harness to keep work to a minimum and remove the rest of the stock efi wiring. Or rip it all out and install new custom ... which depends on what you get in the kit.

 

I decided not to swap out the whole engine yet. Instead, I took the EFI stuff off, and am using the 1976 300i6 carb and Duraspark II for the swap. But, I've run into an issue.

See this thread: https://www.ford-trucks.com/forums/1...l#post16178047

Best regards,
Rick C. Hodgin