89 Bronco II. Severe stumbles and then drives great?

Wife was driving our BII the other day and had the same problem I had hit her.


Okay, short history:

2.9 engine. Had an flacked out pigtail to the TFI so that got swapped out last month (problem: engine died after starting. Found if wiggle the TFI connection it would stall out. Did same test last night and problem did not repeat)

Recent repair done: Replaced the power brake booster. Press the brake and it sounded like a wind tunnel under the dash and the RPM would go ZOOOOOM!! Issue resolved and engine no longer goes ZOOOOOM when the brake is pressed.

We have good injectors installed (truck runs like a beast down the highway now) Fuel pressure at idle with the vacuum line unhooked is 41PSI. Hooked up the pressure is 31. Hold RPM at 2500 and it maintains same. (stupid manual only states KOEO fuel pressure...pump won't fully prime in a couple of seconds)

Yesterday the engine just "turned off". As if the key got turn off. We attempted to repeat the same issue we found with the TFI cable, and it was rock solid.

The other day we drove it to my dr's appt. About 15 minutes into the trip pulling away from a stop the engine just started to cough and sputter badly for a few seconds. Then it took off like a bat outta he&& and ran great the rest of the day.

Saturday the wife takes it around town, and it did the same thing after about 10 minutes or so. She pulled out of a parking lot and it started sputtering and coughing badly. Then it took off and ran fine the rest of her trip home.

Kinda stumped on this one. Pretty much everything under the hood's been replaced at one point or another. Had an idea that the converter might be getting plugged (this thing got 'steam cleaned' when the coolant was being shoved into the exhaust) However the exhaust flow out the tail pipe at different RPM's seems quick and the engine has good response with higher RPM and snap throttle test. So I'm on the fence with that.

Injectors
FPR
Complete wiring harness (granted from a pick and pull, but in A+ condition like the injectors)
Repaired the issue of the intake leaking coolant into the cylinder last year.
IAC motor
TPS
No more vacuum leaks, the booster took care of that.
Coil got replaced last year.
Did a basic test light along each spark plug wire and boot to see if I could recreate any arc's to ground. (thanks to ETCG for that tip, along with scannerdanner) Tests came back fine, no voltage leaks.
Cap/Rotor about 8 months old, should be still fine (didn't remove to look, as that's in a PITA location)

Side issue I'll need to consult the body guys would be the typical right side into the cab leak. We had about an inch of ice on the passenger side floor board. It's melted off now. (I did inspect the ECU, and it does not appear to have gotten soaked.)

I'm going to hook up the pressure gauge later today and see if I can get it to recreate the stall it did. Need to remove fuel as a possible issue....


Anyone got ideas in the mean while feel free to chime in! Just very odd the truck runs fantastic, and then all the sudden goes into a coughing fit..and stalled out just doing it's idle.

S-

Does this have a black colored stator inside the distributor, the TFI module plugs into this. They were good for getting soft like a chocolate bar in your pocket causing this type of problem. Or the TFI itself good be acting up.

Also

mycobrars said:

Does this have a black colored stator inside the distributor, the TFI module plugs into this. They were good for getting soft like a chocolate bar in your pocket causing this type of problem. Or the TFI itself good be acting up.

Click to expand...

Check fuel pump ground. Should be under the hood somewhere. Many are on the drivers inside fender. Take it off and do a good sanding of the area and the wire end itself and reinstall with some battery goop on it to prevent corrosion in the future.

Big Jim

Then again if it is electrical you MAY have a backfire when it re-fires. If it ain't doing that then look more closely at fuel delivery. Usually clogged filters show themselves at big load and then disappear until another big load. A pressure check will NOT find slightly bad filters.

Big Jim

Had a few free moments this afternoon. Decided to see if maybe some water got into the electrics causing miss fires or whatnots. Let it idle and frankly soaked the ignition system, injectors, disty. Pretty much the upper half of the engine got a bath.

Didn't even flinch. Ran smooth as butter. So to dry it out we took it around town, and then on a 40 mile trip up to the next town up and back. Ran good as gold.

Things got dried out pretty quick with that trip. I'm left to wonder if I got a tank of rotten fuel last time I filled the ol' girl up and it sucked in a gulp of water? I hate issues that do not present themselves. It's like the waiting game.

S-

I had a similar problem with my 2.9 hesitating especially when cold and upon acceleration. It finally wouldn't start. I found the fuel pump relay connectors were full of corrosion not providing enough power to the fuel pump. I replaced the relay (original 28 years old) and cleaned the plug in. Runs perfect now.

Yes, I would say an interruption of the fuel supply first...it's the only thing that I found with my carbed version of the 2.3...other things would cause other symptoms...fuel almost always bucking...plugged jets = specific lack of power on either high end or low end depending on what side (of a 2bbl) was plugged...