Fuel Issue Perhaps

ox1969 · Feb 25, 2016

So here is the scenario, bronco II starts fine, runs fine for the most part. Once in a while the engine will lose power, sputter, backfire for like a minute or so, then will regain power and run fine for awhile, then do it again. Did it to me twice this morning on my way to work, only 5 miles.

I did notice on one occasion it happened after I hit a bump, but other than that seem pretty random. So my thought is a loss of fuel pressure. I did put fuel cleaner in my tank the fill up prior so not sure if I jarred some debris lose or what. Was going to change the fuel filters again over the weekend and see if that help.

Was just curious if anyone had any other thoughts on this, electrical or something perhaps.

1986 Bronco II, XLT 2.9, Manual transmission, 4X4.

Thanks

OX

RonD · Feb 25, 2016

Change fuel pump relay, and check it's wires under the socket/base.
The "bump" you mentioned leans toward a physical issue, and a relay is a moving part so could be jarred into opening if it is going bad, loose wire is as well.

It will be with 2 or 3 other relays on the inner fender
Green base = Fuel pump relay
Brown base = EEC Relay, powers EEC(computer) but also fuel injectors and spark system
Black base = WOT Relay, turns off AC compressor when you are at Wide Open Throttle(WOT)

All 3 relays are the same part number and are interchangeable, so if you have WOT relay swap it with Fuel Pump relay.
I wouldn't swap EEC relay because if it is a bad relay truck will die if it opens while driving.

In the passenger footwell is the Inertia Switch, if you are in an accident or roll over this switch will cut power to the fuel pump, would be very uncommon for it to reset itself, but a "bump" can cause it to cut power to the fuel pump, it has a button on the top to reset it.

Common issue on older rangers with TFI spark system is the TFI module starts to go out, usually this happens after engine and TFI module warm up.
Good read here on that: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

ox1969 · Feb 26, 2016

Thanks for the info, I was leaning toward the relay. I did try to swap them this morning, but they do not appear to be the same. The EEC and WOT relay are the same, but the fuel pump relay did not look the same at all.

Going to see about picking up a new relay today, and an new plug. The plug looks burnt and the wires are terrible. Hopefully this will fix the issue. Just got the Bronco II going last week, so I am sure there will be some other issues along the way. When I bought it, it ran ok, but the wiring in this thing looks like it was done by a 2 year old.

Thanks again for the info.

ox1969 · Feb 27, 2016

Swapped the relay and the connector, apparently did not wire correctly. Started fine, ran for a min or so then something popped (Smoked) and it died. Check the wiring diagram (which I should have done to begin with) the orange wire I connected was actually supposed to be tan. Anyway, rewired and it started again and ran for about 5 min.

Shut the hood and was going for a drive, it died as soon as I shut the hood. Swapped relays around all it does it crank now, and does not start. It appears the pump is running, audible anyway.

Could the short have fried something else besides the relay? Now the truck is dead and will not start. I guess I could get another relay and try that, but figured swapping them would have ruled that out. I did check the voltage at the harness. 12v Yellow, hot all the time, key on, red 12v, tan nothing.

Just to note, when tan colored wires gets old, they appear orange lol.

Any ideas where to start on this and thanks for the help

RonD · Feb 27, 2016

1986 used fusible links instead of fuses, so one could have burned out a separated.

There is one between Red wire out of EEC relay to the Fuel injectors, so with key on check if any fuel injector has 12volts on it's Red wire, they all share the same wire.
If not then that fusible link is blown and engine would not start or run.

If the yellow wire still has voltage on either EEC relay or FP relay then that fusible link is still OK

ox1969 · Feb 28, 2016

So it was the fuse-able ink that was blow from the solenoid to the EEC relay. Got that all fixed, now it is running rich. Disconnected the battery to reset the computer just in case, but would not think changing a relay would effect that. But worth a shot. Any other ideas on the running rich. Hoping I didn't smoke the EEC when It blew the fuse-able link.

Fuel Issue Perhaps

ox1969

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