We've got a puzzle - 1986 Bronco II --- UPDATE

[pasusan]

This is not about our RV tow vehicle, but it actually does tow a utility trailer once in a while....

We've got a 1986 Bronco II that is missing badly and we don't know what is wrong. If anyone has any ideas, we're all ears.

It has a 2.9 liter engine with electronic fuel injection and a rudimentary computer (not like today's vehicles).

It sat most of the winter (we don't drive it in the snow and salt).

Our first use of it this spring it ran really rough - engine shaking, exhaust coming out in stinky puffs. But then it cleared up and we took it to Lowes to pick up some lumber in our trailer. All the while it was running perfectly fine.

A couple of weeks later... We started it up and it ran really rough again. This time it did not clear up and actually conked on the side of the road and then wouldn't start. I know - I shouldn't have taken it out of the driveway, but I was 90% sure it would clear up like last time. Checking the oil dipstick - we smelled gas.

We had it towed to our local garage and asked them to diagnose it. They told us the fuel pressure was good and they think that it was condensation in the distributor cap and to do a complete tune up - as the plugs were totally fouled. Oh - and then the mechanic mentioned that it might just be the ACT (Air Charge Temperature) sensor that was giving a wrong reading causing a big fuel feed (like an automatic choke).

Anyway - we did the tune up and it still ran rough. We replaced the ACT sensor and it still runs rough. At least it starts right up with the new clean plugs! But we don't want to run it long and foul up the new plugs.

So... What could be wrong - it cleared itself up once and now it won't. Any ideas?

[zigzagrv]

I had a similar problem on my 95 Tracker. Turned out to be one of the injectors was shorted to 12v....open all the time causing excessive gas to that cylinder. Ran rough at idle and up to higher RPMs with lots of smoke. Should be easy to check. With key on,measure voltage at each injector till you find the one with 12v on it all the time.

[Dakota98]

If the mechanic was right & there was condensation in the distributor cap, then what are the chances that there is water in the fuel system ? Are you still on the same tank of gas that was in it during storage? If so, I'm leaning towards what donn0128 mentioned. Might drain the fuel tank, inspect the plugs once again & clean if needed & fill with fresh gas.

[The_Texan]

Get some straight Seafoam into the fuel delivery(carb or throttle body) system and then let it set for 48 hours. It sounds like your older fuel system is varnished and the Seafoam will clean it. Once you get it running fairly smooth again, use Lucas every other tank and then when you store it for the winter, use Seafoam again, drive it for 30-40 miles to ensure it is in the fuel delivery system and you should be good from then on. I have let 3 different vehicles set for 16 months recently, with Seafoam in them and they started and ran fine after the 16 months. Ethanol is a very POOR fuel, especially if you let it set for months, it will form moisture and varnish.

[newman_fulltime]

It does not like todays fuels run Lucas in the fuel and use only supreme.My truck hates the cheaper gas does the same thing

[donn0128]

Water in the fuel will kill injectors in a hurry.