86 after sitting for 4yrs.
 

Hey folks,
I'm kind of in the same boat. My 86 sat with a bad motor until recently. I bought a wrecked 1990 almost identical with dual tanks and have swapped the motor into the 86. Before the motor failed in the 86, I was having an issue with the return fuel always going to the front tank, but both tanks worked fine supplying. After the motor swap, the gauge would not register, but finally started working (my guess was bad contacts in the dash switch from sitting).
The problem now seems to be it acts like it's starved for fuel with more demanding acceleration. I've changed the filter and that seemed to help for about 25 miles, but now it's back to starving. Gauge shows 1/2 tank in front and between 1/4 & 1/2 in the rear. The tanks did have some old gas in them, but I was able to get about 11-12 gal in each one.
I do plan on pulling the other filter that has been mentioned, but I'm wondering if anyone knows the differences between the 86 system and the 90. Did they do away with the low pres. pumps in the tanks in the 90 set-up and only have the high pres. on the frame rail? I'm also wondering if I should have swapped the computers on the trucks when I did the motors. (both are 5.0 EFI)
Any help would be appreciated and I'll keep on searching and reading the threads on the site.

Note: I've been driving a Cummins diesel for the last 5 years and I never messed that much with the EFI gassers,,,,,, so please bare with me. :-roll

90 still has the low pressure pumps in the tanks, just has the extra high pressure pump to get the pressure up for the fuel injection. The high pressure pump, mounted on the left frame rail next to the tranny, is not needed for a carburated motor.

Also, if the tank selector valve is going bad it can bleed off pressure through the returns and cause low pressure at the motor, hence causing lack of fuel during high demand. It usually causes one tank to fill up the other, front to back or back to front.

But....the valve operates on fuel pressure from the low pumps, so if the low pumps in the tanks are going bad, they may not provide enough pressure for the valve to operate properly.

Do you think they could have made this system more complicated and problem prone?

Tank selector should not bleed off pressure, that is the function of the fuel pressure regulator on the fuel injector rail.

The valve switches from pressure from the tank low pressure fuel pump of the tank that was not the last one feeding the high pressure pump. Until that valve switches, the high pressure pump would continue to try to suck from the last tank and return fuel will also continue to go back into that tank. The canister stay at the last tank that switched it. Once switched,

Dual tank fords are well known for cross filling tanks when the LP pumps go. I've seen it before.

I finally fixed my fuel problem on my 86. I ended up replacing everything. The proplem that I was having is that the truck ran fine when driven easy. If you hit the gas to pass someone it would stumble. I tried last week to check the fuel press. but the roads where snow covered and it's hard to watch the FP when the truck is sliding all over the road because you have to get on it to make it stuble. Anyway...

I replaced the FPR, Inline Filter, and frame (HP) pump because it sounded very noisy. Got better for a couple days, then back to normal and the new pump was even louder. Roads cleared up and I was able to test the FP. When it was stumbling the FP was under 15psi. The motor would stumble, the pump would catch up, power would return (then stumble, catch up...).

Replaced the Tank pump and canister filter (Pueralator #50126) and it's fixed. Also the frame pump quieted down (ALOT). The canister filter looked like trash. My guess is that the tank pump was junk and the frame pump was doing all the work but it's not designed to, so it ran ok and low speed, but couldn't keep up.

I think the 90 uses only a in-tank pump. Maybe it was 91 I can't remember. But they did change from the tank and booster pumps to a single pump around the same time that they went to 100% EFI. I know an 89 still uses the 2 pumps.

Rattlinram, change the canister filter, but you're probably going to have to do the tank pumps.

86 and 90 EFI motors are both speed density and should be interchangeable. Use the 86 computer in the 86 truck. The pinouts may be different for the 90 computer.

David

Thanks guys,
I'll do some more checking when I get home from work this afternoon and the weather is going to be a little warmer today and then even better this weekend. Virginia weather,,,, if ya don't like it,,,,, wait a day or two and it will change!

Sorry, didn't mean to go against any statement on the cross flowing into tanks. I got pressed for time and had to cut it short, as I have to now. Being such that it has to stop passage one way and allow passage another, just about anything's possible. Got to go for now. Maybe I can get back later and finish where I left off above.

Thanks all you for any input given.
Dale

I didn't get a chance to look at it this afternoon, but I'll get to it this weekend,,, suppose to be up in the 50's.

Thanks David,
I'm using the 86 computer now and everything seems to be OK so far. It does act like the timing is not advancing far enough because I'm getting some spark knock on acceleration (still may be the old gas also even though I have put some octane boost and injector cleaner in it). I'm hoping to get all that stinking gas out of both tanks, check the selector valve out, check the tank pumps and put a temporary fuel pressure gauge on this weekend. Have I read correctly, that I should see 30-35 psi at the schrader valve on the fuel rail? And should this psi stay about the same under a load.
I can help ya out with this kind of info concerning a diesel Cummins,,,,,, but I'm kind of lost with this gas stuff. :-X15 I miss the days when you had screws to turn on a carb,,,,,

Rattlinram, if the ignition is advanced too far you will get a knock. It should be set to 8 deg BTC (before top dead center), but I'd use 10 - 12 deg BTC. When you set the timing remember to pull the SPOUT connector. It's on a wire that comes out of the distributor. It's a jumper that once pulled will keep the computer from changing the timing. Just remember to put it back in.

Fuel pressure specs are 35 - 41 psi with 38 psi being ideal. Just pull the vacuum line off the regulator and the pressure should jump to about 38psi if everything is good. Also the needle on the gauge should be steady.

One point to remember is that just becasue the idle pressure is ok it doesn't mean that the volume is enough. At idle with the regulator connected the FP will be about 25 - 30 psi. Under load it should climb to 38psi, same as when you disconnected the FPR. If it drops you're pumps are bad, or the filters are clogged. Also the FPR could be bad.

So after fixing my truck, here are my thoughts on how to approch this.

* If the fuel pressure gauge jumps around replace the inline or HP filter.
* Replace the canister filter. Ford says it's a lifetime part and there are no service intervals which means that it probably has never been out even if the truck was well cared for.
*If the no load test with the FRP disconnected is less then 35psi and the filters have been replaced, replace the HP frame pump.
*If the Idle test is good, but pressure drops under load, replace the tank pump.
*If your dual system cross feeds tanks, replace the tank pumps.
*If fuel comes out of the vacuum line port on the FPR, replace the FPR.
*If the pressure doesn't change when you disconnect the FRP, verify vacuum at the line, if found replace the FPR.

Hope this helps, and also BTW on the 5.0 and 5.8 you can replace the FPR without removing the rail. You need a 5/32 allen wrench, a small inspection mirror and ALOT of patience.

David

Hey rattlin ram!!!!!! mx261 here-- from the dodge forum! I got an 85 f150 with the same problems, it tends to pressuize the front tank so when I take the cap off I get a shower of gas. My gauge only works when its full and she goes to e in about 10 miles. But for now I just leave it on the rear tank and fill it every other day.

I worked for Ford as a parts manager for a couple of years and I am wanting to think there was a recall on these trucks with dual fuel tanks. I believe it had something to do with fuel going from one tank to the other. You can take your vin # to a dealership and they could tell if the recall has been done.

Hey mx261, :-wink
Trying to get the old truck back on the road for the wife. Before I lost the oil pump in the original engine,,, my tank gauge read correctly for both tanks. Then one day I got the gas shower from the overfilled front tank and found that I could still fill both tanks as long as I used the front one first. I would run it down to 1/4 mark and then switch to the rear tank. When that got down to the 1/4 mark,,, I would switch back to the front tank and it would be back up to 1/2. When it reached the 1/4 mark this time,,,, it was time to fill both tanks again.
The biggest problem now is coming from leaving the truck sit for 4 years until I bought a 1990 donor truck just recently. Letting any vehicle sit outside for that length of time does not help at all. the dampness has even caused stuff inside the cab to rust and oxidate,,, so I imagine the outside stuff is worse. The 90 donor truck is in good shape other than the BIG caved-in place on the driver's side where it got "T-Boned". I'm in the process of finding out just how much stuff can be swapped if needed (fuel pumps and anything else)
It's raining sleet right now and I'm in no need to get it fixed right away because we have plenty of vehicles to drive for now. It ain't gonna hurt the wife to drive that butt-dragging Camaro a little while longer,,,,, at least till the weather is a little more favorable! :-X10 .

stdumas,
Thanks for the tip on the possible recall, I'll check on that.

Rattlin Ram, Man this startin to scare me! You got ctd, I got one, You got 80s ford f150, I gotan 85 (that i got up and runnin for the wife!!) AND you got a camaro?? what year? mines a 87 z28 tpi 305 auto. lol lots in common I guess.

You got any dirt bikes? we could go racin!! lol

camaros like these?

http://img.photobucket.com/albums/v2...randyscars.jpg

http://img.photobucket.com/albums/v2...andyscars4.jpg

http://img.photobucket.com/albums/v2...dyscars002.jpg

they all got scrapped/parted cept the brown one(is in indiana somewhere now)

ive owned many and firebirds too, ive had my 82 trans am since 2000

ive had closer to 200 vehicles since 94

album:
http://smg.photobucket.com/albums/v2...spastvehicles/

i have an 85 f250

have had other '80's ford trucks and some cars too
'70's F100's, '79 monarch
a '69 F100(my first vehicle ever, in 94)

etc

haha

some day this winter i need to scan and upload old and current vehicle pictures, hmm

coincidences are common

good luck

another 86 problem.....
 

i have been battling my fuel?? "engine cutting out problem" for a couple of weeks now! duel tank nightmare!


question is, where is my fuel filter at???? is it in the "pressure switch? i've inspected the whole frame rail. no canister , the only thing there is the tank switch and the fuel pump and 50 ft of fuel line with quick connects everywhere.


thanks for any input

dave