URGENT Tech HELP needed- Bronco II dies after running 30 min.

[RICHARDG]

Hi all,
My Bronco II has the same engine, wiring & drivetrain parts as the 1989-90 Ranger... So I thought I would post it here.

Here's the problem: Bronco II dies after running (or idleing) for EXACTLY 25-30min. Runs like a top (NO engine firing/"missing") with good idle & acceleration for 25-30 mins. then engine "lugs"/chugs (like spark or fuel starvation) & just dies. Does NOT blow any smoke, leak any oil. engine temperature is NORMAL. "check engine" light comes on after ~ 20min at idle, just before it dies 5 -10 min later at the 25 - 30 min mark.
IF I disconnect the vacuum hose that runs between the air filter & intake manifold then the "check engine" light DOES NOT come on BUT the engine still dies at the 25 - 30 min mark.

History & tech specs:
> 1990 Bronco II 2.9L fuel injected. 76K ORIGINAL miles
Engine DOES NOT have a MAF or EGR sensor.
Truck was garaged for ~ 10 yrs.
> New parts installed:
Fuel pump, fuel filter, FPR (fuel pressure regulator), air filter, plugs, plug wires, TFI (distributer ignition module) thermostat.

> Troubleshooting procedures & maintenance checks performed:
ACT sensor cleaned & resistance checked OK.
IAC cleaned
PCV cleaned & checked OK
TPS checked OK
Throttle body cleaned
Coil resistance checked & spark jump checked OK ( ~ 1"" + )
Distributer cap & rotor checked OK
Alternator voltage output IS STEADY ( DCv) checked OK @ ~ 13DCv at idle RPM. (output voltage DOES NOT INCREASE with higher RPM )

>Possible causes issues/& other miscellaneous symptoms identified so far:
Base Idle Adjustment - Cant set/get the engine to idle below ~ 1000 - 1,100 RPM ( factory spec is ~ 850 - 950RPM)

?? - RF headlight "dims" with right turn signal engaged (NO other light/turn signal dimming, NO engine RPM decrease/ dying)
??? - Alternator gets very warm (hot?) the longer the engine runs.

SOoooooo...... the question is...
Whats causing the engine to die ?
?? MAP sensor is bad ?
??? ECM malfunctioning ?
???? other ?

Any comments/help appreciated
Thanks
richard

 

[kimcrwbr1]

http://www.autozone.com/autozone/pa...N-iu39lZ9n80t?itemIdentifier=118646_967354_0_
Sounds like the classic ICM getting hot it is mounted on the distributor. You can get the special tool at most any part store. Have it tested but have them test it three times in a row so it has time to get hot. As far as the lighting issue sounds like a short somewhere thats a whole other ball of wax.

 

[RonD]

Yes most likely TFI ignition system, they have a 100% failure rate because of their age now.
Good info here: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

But heat is the issue so all tests can come back OK when things are cold, but when heated up spark stops, you can use a hair dryer(blow dryer, or heat gun) to heat up components while testing.
ICM and coil are the main components effected by heat


One other thing to try.............loosen the gas cap.
The EVAP system sucks air from the gas tank to prevent fuel vapor from polluting the air, the gas tank will either have a vent gas cap or a vent hose to relieve the negative pressure.
If the EVAP system runs for awhile and there is no working vent the fuel pump simply can not pull enough fuel out of the tank to keep engine running, vacuum lock in the gas tank.


Ignition problem or EVAP problem will both turn on CEL.

Getting the Code Number would help you ID the problem better.
Good info here on getting those: http://www.therangerstation.com/tech_library/OBD_I.shtml


Cold engine idle should be 1,100-1,200rpm depends on outside temp.
The computer uses an ECT(engine coolant temp) sensor on the intake manifold to read coolant temperature, this is a 2 wire SENSOR, not to be confused with the 1 wire SENDER used for the dashboard temp gauge.
When you first turn on the key the computer checks the ECT sensor, if engine is cold computer sets Choke Mode, this sets a higher idle and a richer fuel/air mix.
As ECT sensor warms up the computer will start to lean fuel/air mix and lower the idle, after 5 minutes or so engine should be up to minimum operating temp, 195degF, and the computer then uses MAP and O2 sensors to set fuel/air mix and will drop idle to target warm engine idle, 700 manual trans, 800 automatic.

Idle is controlled by the computer using the IAC(idle air control) Valve, if engine is warmed up and idling, unplug the IAC Valve connector, engine idle should drop to 500rpms or engine may stall, either means IAC Valve is working, so higher than normal idle would be a problem with computer, could be it is getting bad engine temp info, or engine temp is too low, i.e. stuck open t-stat or wrong t-stat, Ford t-stat should be 192deg or 195deg model.
Ford temp gauges usually have 210-220degF as the half-way point, so after warm up needle should be just below 1/2, if your temp gauge is showing 1/4 or so when warmed up, then replace T-stat.

If idle doesn't change when IAC Valve is unhooked then you probably have a vacuum leak, computer has closed the IAC valve all the way, and 1,000rpms is the lowest it can go.
Or IAC valve isn't working at all, but if engine idles higher when cold then idle drops as engine warms up the IAC Valve is working.

 

[black_demon69]

might also check fuel pressure when it dies pump could be going bad and when it gets hot it dies and pressure drops like a stone. had a problem with my fuel pump took me months to track it down because it was random and never happened when i had tools to diagnose it also fuel pump had just been replaced from lot i got truck from so i didn't even consider it.....

 

[Spott]

Yes, this is the correct website. We support all "Ranger-Based Vehicles" such as Bronco 2's, Mazda B-series trucks, and Explorers.

Uhm, before you dig any deeper into the problem... What error codes are you getting from the computer? That should be the first thing you check whenever the Check Engine Light comes on.

Also, (and this is probably a side problem, but you never know) your alternator should be producing (nominally) 13.8v when running. A good, fully charged battery should be at 12.6v at rest. I don't like the fact that your alternator output is closer to "just running off the battery" than "what it ought to be".

The fact that your headlight dims when you turn on the blinker might indicate a bad ground. You would be money ahead to clean, apply dielectric grease to, and tighten all your grounds. Then check your alternator output again.

This just might solve your other problem, too. Bad grounds can cause all sorts of tricky electrical gremlins. Even if it doesn't solve the main problem, it will prevent many other obnoxious problems in the coming years.

 

[huh?]

just a shot in the dark- every few minutes between start up and vehicle shutting itself down, take a stroll to the tail pipe and see if the flow of the exhaust starts to diminish.

my truck has taken to shutting down after being driven to normal running temp and coming to a stop unless i fart with the accelerator to keep her going. this started at the same time as discovering muffler is muffling not only exhaust sound but also exhaust flow. last night while standing next to truck to ascertain where new exhaust noises were emanating i glanced at tailpipe and noticed lack of smoke puffing out. put hand on tailpipe and felt some suction. using biological testing equipment(hands), it turned out the (intermediate?) pipe between converter and muffler was getting real warm but the muffler remained the same as the ambient air temp.

as asserted above, just a shot in the dark and the two symptoms showing up at the same time is probably purely coincidental, but unless there's some inclement weather going on, it's an easy check to do.

girlfriend's done work at 12 tonight so i think i'm gonna pull fuel filler cap drive on down there and pull codes in walmart parking lot, and call my friend randy to ask him if i can borrow his fuel pressure tester. i also have the tfi testing protocol printed out so i can review that, too. thanks to all the replies from the gentlemen who responded before me and...

good luck to you, RICHARDG