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Raidy 03-26-2004 09:17 PM

2.9L Ford Bronco II 1986

I've got this interesting problem with my bronco II. On Warm days (like now :( it will not run for very long. At first, it'll run nice and smooth; and eventually get weak and die on me. It will not restart for 15-20 minutes or so. I've replaced the following components on this truck, and it hasn't helped much. I'm not a mechanic myself, so I'm getting a bit desperate; I like this truck, I just wish it would run better.. Anyways, I've replaced the ignition coil, ignition module, fuel pressure regulator, fuel/oil filters, Throttle Position sensor and I've verified that the engine is not running hot. At first, if you floor the truck (it's a 5 speed) it'll take off like a shot, until it gets warmer. After about 10 minutes or so, if you flooor it; past 4,000rpms, it'll do what I call frog hop. Basically, it'll try to take off and backoff.. A little while after this, it won't run. I can feather the pedal when it gets real weak and keep it crawling for a short distance; but eventually it quits running. and won't start back.

if the weather outside is cold or chilly, the truck will run fine all day and just start frog hopping after 4grand a few hours into running, but otherwise won't die on me.

It's an 86 fuel injected 2.9L with 53000 miles on it. What could be wrong?

mrshorty 03-27-2004 09:55 AM

What you describe sounds a lot loke a bad ignition module (aka TFI module). When you replaced the ignition module, did you put dielectric grease on the backing plate? As I understand it, this is important for heat transfer, to keep the ignition module cool, so it doesn't fail again.
Aside from that, when it stalls, have you verified whether or not the stalling is due to lost spark? or fuel pressure?

Raidy 03-27-2004 10:14 AM

Yep. It still gets spark, and pressure is still on the fuel line. It acts like it wants to run when I try to start it, it just isn't able too. I did put the dieelectric grease on the module when i changed it. Since changing those things, the truck runs smoother over all; but still decides to die when it's warm weather outside. As far as I can tell, it's getting spark and fuel when it plays dead.

BroncII 03-27-2004 02:24 PM

2.9 Ground Problem
I had the same thing happen and I finally traced it to the ground cable from the battery. Mine is an 87, but I suspect they are the same design. The cable consists of three cables attached to the negative battery connector. With age, the two smaller cables finally break and corrode causing poor communication with the computer related parts. Replace the cable. JK Auto parts has one for about 38 bucks. In the mean time cut the two smaller cables off and check to make sure you have good copper showing and add ring terminals so you can temporarily mount to the post terminal bolt. If the problem is the same you won't belive the difference. :-X22

Good luck!

Raidy 03-29-2004 09:49 AM

reply to bronc
I checked for the cables you spoke of. Apparently, Mine doesn't have them. It has one primary ground wire coming from the battery; which mounts to the chassis of the truck, and another smaller ground wire which mounts right behind the radiator bracket. Just to be sure though, I cleaned both contact points with a wire brush. It hasn't made any difference so far.

A person I was speaking with suggested it could be a stopped up catalytic converter; Before I have this replaced I was going to get this forums input... I've smelled the rotten egg smell twice in the last few days, But I can't be sure it was from my truck vs one I was falling in traffic.

Any assistance would be great, thanks!

mrshorty 03-29-2004 11:34 AM

A quick and dirty check for a clogged catalytic converter (or other exhaust component) is by measuring engine vacuum. Hook up vacuum gauge, start engine and note reading at idle. Hold engine steady at about 2000 RPM. Engine vacuum should be the same or higher than it was at idle. If vacuum is lower at higher speeds, then you may have something stopped up in the exhaust.

BroncII 03-29-2004 07:10 PM

Ground Cable
So the connector on that goes to your battery post has two wires coming out of it, one large, one small?

Raidy 03-29-2004 10:01 PM

ground cable 2 ;p
Yep. Two wires. One large fat one, like the positive battery cable; and one very small one coming from the same terminal block on the battery; Both going to ground on the truck frame, essentially.

I've checked wires all over the truck for corrosion, nipped them and rewired any I found that were bad or appeared to be in rough shape. But it doesn't seem to help. The truck is still doing the garbage it's doing.

BroncII 03-30-2004 07:31 PM

How old is the battery? What is the voltage coming off the charging system?

olddave208 03-30-2004 10:36 PM

Usually if you have a bad ground your oil and temerature gages will become very erratic. The gages are quickly affected by bad grounds. If you are seeing this, definately check your ground wires, they may look good on the outside, but may have been consumed on the inside of the insulation. Even a resistance check will not show the problem. Use a jumper cable to ground the battery to the motor to see if it helps.

Raidy 04-03-2004 08:45 PM

sigh.. still no go
Sigh, I've checked ground problem. I took the truck to Advance auto and had them checkout the battery, alt, etc. Everything is fine. The truck once again messed up on the way home; Had one heck of a time getting it to the house...

Someone I spoke with suggested vapor lock as a possible cause. If this is indeed it, how in the world do I fix that? :( Still open to any suggestions.

thanks for your help!

mrshorty 04-04-2004 11:10 AM


Someone I spoke with suggested vapor lock as a possible cause.
It is next to impossible for a fuel injected system to vapor lock in the traditional sense, because the fuel system is under pressure. You said earlier that you had verified the pressure in the fuel rail, so I don't think that's the issue. Out of curiosity, when you verified the fuel pressure, did you use a gauge, or just press on the valve and saw that gas was present?
Another thought, have you ever run the EEC-IV self-tests?

olddave208 04-04-2004 07:21 PM

Fuel Pump?
I ran into this problem a couple years ago with a Bronco II. Ended up being a high pressure fuel pump going south. When it dies check your rail pressure to make sure your getting around 40 lbs. It should be either spark or fuel.

Raidy 04-05-2004 04:22 PM


When I checked fuel in the rail, I pressed the nozzle on it; Gas went everywhere for a brief moment. (I let my finger off of the rail once gas started coming out of it; it)....

If the fuel pump is going bad, why does the truck run when the weather is cold outside, but not when it's warm weather? I've been lucky this week so far; it's quiet cold outside. But it's eventually going to be summertime temps, and my ride isn't going to run very well when it is.

I'm going to try and have the truck fuel pressure checked with a guage sometime this week...

Raidy 04-05-2004 04:25 PM

Side note,

I haven't run any EEC self tests. I'm not even sure what those would be? I did have the old ignition module checked recently; and it turns it it's good. Well, the diagnostic equipment claims it is anyway, so I'm holding onto it as a spare.

I'm basically having this thing checked out as I can find the time after work. So bare with me if my replies are slow. I appreciate the help tho. :)

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