Help! Bronco II has no power when engine is warm.

bower100 · Post by **bower100** » Thu Jun 28, 2007 11:31 am

Posted: Wed Jun 27, 2007 7:05 pm Post subject:

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Did you hook your O2 sensor to the temp pipe or just let it hang?

The O2 bungholes in the wye-pipe just before the cat pipe section.

QUOTE:
check your timing...I had the same problem and the timing was out.

Ya know, I've done a bunch of stuff to the Bronco, but never actually cheched the timing. Dumb, I guess. I supose I just never figured the P/O would have messed it up. It's electronic and does'nt change unless fiddled with. I'm gonna check it asap.

dave[/quote]

Joel H · Post by **Joel H** » Thu Jun 28, 2007 1:48 pm

To set the timing you need to pull the spout plug out of it's socket. Located on the passengerside of intake. Plug that goes to nothing, just has a Grey cap on it.

Losen the bolt for the distributer. Keep it snug enough that you will be able to start the truck.

Set up timing light and set timing to 12* BTDC. 10 is what the book says but I found it to run better at 12.

Turn dist to set.

Lock Dist back down when your satisfied. Engine off of course

Reinstall spout plug.

restart engine and check base timing again. Should be around 12 still.

Don't ever assume the PO set the timing right. I had the same problem and after a month of checking things somone suggested I check the timing. I did and it still ran like crap. Found out I was missing the spout plug part of setting the timing. Found the spout, set the timing, went for a ride and was grinning ear to ear.

PHROX · Post by **PHROX** » Thu Jun 28, 2007 5:59 pm

thats cool.

Paul · Post by **Paul** » Fri Jun 29, 2007 12:04 am

yes on a 2.9 with a distributor you can adjust the timing, first you disconnect the spout connector, then start the motor, to make sure the initial timing is at 10 degrees BTDC. once set turn off motor, reinstall spout connector, and restrat truck the computer adjusts from there, but the initial must be located at 10 BTDC with spout unhooked for computer to locate it right, it only can be adjusted on the 2.9 because it uses a distributor and not a CPS or crank positioning sensor like the 4.0 Liter uses. iof you check a manual on the 2.9 Liter it does cover the timning adjustment, the spout connector on my 2.9 Liter was a yellow connector plug on the passenger side located in the main wiring harness next to the firewall, it looked like a spade type fuse but was a black rubber plug that just plugged in to a boot with a yellow wirre going in and a yellow wire coming out of it and pulled straight out ...... and on my 4.0 the spout wire is pink..... but it was a 1991 explorer motor.

Paul · Post by **Paul** » Fri Jun 29, 2007 12:10 am

the reason for the spout connector on the 4.0 is to tell if the computer is adjusting the timing for the motor as required, it will also give tell tale signs on timing chain wear, if the CPS shows timing other than 10 BTDC on the 4.0 then either the timing chain is worn or the cam psotitoning sensor or crank positioning sensor one is bad... cam positioning sensor feeds info to the Crank positioniong sensor and Crank positioning sensor feeds info to the computer, which then adjusts timing.......

Paul · Post by **Paul** » Fri Jun 29, 2007 12:21 am

but for future reference and motor with a distributor the timing can be adjusted .......... in the case where there is no distributor the Cam Positiong Sensor normally located unde the intake ..... must be moved to locate the right degree on the motor but the base timing can always be adjusted......... but this shoud be done by a professional who is accostomed to working on that style of vehicle .... preferably a dealer becasue small increments can prevent the vehicle from running at all ....

Paul · Post by **Paul** » Fri Jun 29, 2007 1:03 am

AGAIN ....... i would recommend the IAC becasue it can stick open as well as shut and when the temp warms up on the motor it would cause the motor to run rich which can cause it to run rough, but you should definatly check the timing on the motor as it too can cause a loss of power once the engine warms up. if your not having a problem with engine idle being high or low i would not suggest it to be a vacuum leak... or throttle positioning sensor (TPS) ...... now for the IAC .....

IAC Cleaning/Testing:

The IAC is usually a cylindrical unit attached to the upper intake manifold. This unit is electrically controlled by the computer, and allows air to flow into the intake at idle, bypassing the throttle plate. The extra air is accompanied by extra fuel to bring the idle up to proper speed, and when cold, allows a high idle condition. These units may become dirty, and need cleaning. Many idle and stalling issues tend to be blamed on these units. Cleaning is achieved by removing the electrical connector, and two screws holding it on. Once off of the vehicle, clean with throttle body cleaner (or a good carburetor cleaner). Continue cleaning until unit is clean, like new; reinstall unit. This is also a good time to clean the intake, and EGR ports (if applicable).

Testing may be achieved by bringing the engine to operating temperature, noting the idle speed (should be within spec). Unplug the unit’s electrical connector, and the idle should drop to about 650 RPM. When the unit is reinstalled, it should return to normal idle speed. If the vehicle does not idle at proper RPM (too low), there are no vacuum leaks, and the TPS calibration is correct, than the unit is most likely faulty.

amberbrush · Post by **amberbrush** » Mon Jul 02, 2007 9:42 am

O.k., I timed the bronco II this weekend and no luck. It still runs terrible when it warms up. I am convinced it is internal and have already found a donor engine to swap in. Thanks for everyones suggestions!

BDEUCE · Post by **BDEUCE** » Tue Jul 03, 2007 7:50 pm

holy cow. i have to echo paul in saying that it's a possibility it could in fact be the IAC. check it out, it could be the problem, and be free (besides your time) to fix/clean.

if i may ask a question: why are you convinced it's "internal"? i have bad compression, oil consumption, head gasket leaking coolant into the exhaust, and a collapsed lifter, but throw her into third on the highway and she passes on a hill, man! are you going to swap another 2.9 in? seems exorbitant if you are just inferring an 'internal' problem. ask the experts, take it to a shop - pay a hundred bucks to find out it's a sensor you discounted/overlooked/didn't know about. could be something easy, dude. don't take all this the wrong way, but look at all the angles. me, myself, i'm pulling my 2.9 and sinking a grand into it, because even in it's worst hours, it pulls and hauls and roars like a bad muthafuckka!! i'm putting 31's on this fall, and i know it'll turn 'em fine.

i also understand if you just have your heart set on a bigger motor, though.

p.s., i mean not to sound condescending, or to tell you what to do, just my $0.02 is all...

nate

CraigK · Post by **CraigK** » Wed Jul 04, 2007 4:24 am

Hi amberbrush

I'm with BDEUCE, if the engine runs just fine until it warms up, it's highly unlikely it's an "internal" problem. My understanding is that once the engine is warmed up, and this is sensed by the computer system through the temperature gauge etc., the enrichening mode (lotsa gas) is shut down, and the computer starts to send fuel to the injectors based on readings from all the sensors. Your problem is probably with this system, not the motor "internals". FYI, I spent literally YEARS chasing down a problem on my '87 B2 (it would run fine until warmed up, then it would begin short cycles of sputtering and lost power - drove me crazy) that was instantly fixed when I disconnected the O2 sensor. (Not removed or replaced, just disconnected!)

If you want to swap engines, great, but if you just want to get it running, keep checking those sensors and lines. Good Luck!

CraigK

amberbrush · Post by **amberbrush** » Thu Jul 05, 2007 6:47 am

Thanks for the replies. However, I did clean the IAC unit with no luck. I also already disconnected the O2 sensor when I took off the cat converter. The reason I think it is internal is because there is the possibility that I could have a worn valve spring. My brother had that happen in his car. When the engine warms up the spring gets hot and weak. I also can hear a faint tapping when the motor is running. I just noticed it when we timed the engine. I am unsure what other sensors to check. Yes, I probley should have taken it in to have it hooked to a computer at the Ford dealer but at the time I figured I could figure it out and avoid having to haul it in on a car trailer.

Paul · Post by **Paul** » Thu Jul 05, 2007 12:07 pm

the reason disconnecting the O2 sensor made it run better, is simply the computer only leans out the mixture from the O2 sensors readings and adjusts to predetermined settings in the PC, disconnecting the O2 tells it its extremely lean, allowing to run off base settings without adjustments ...... engine idle at cold temps ....... the richest mixture of fuel it can get for idle is normally the engine idle cold temp setting, this is usually the outcome when an 02 sensor gets clogged, or just goes bad when you disconnect it . . . . .

1 question does your temp guage work right? because if it doesnt send a signal to the ignition system controller (computer) then it will make it run wrong.

Paul · Post by **Paul** » Thu Jul 05, 2007 12:08 pm

the reason disconnecting the O2 sensor made it run better, is simply the computer only leans out the mixture from the O2 sensors readings and adjusts to predetermined settings in the PC, disconnecting the O2 tells it its extremely lean, allowing to run off base settings without adjustments ...... engine idle at cold temps ....... the richest mixture of fuel it can get for idle is normally the engine idle cold temp setting, this is usually the outcome when an 02 sensor gets clogged, or just goes bad when you disconnect it . . . . .

1 question does your temp guage work right? because if it doesnt send a signal to the ignition system controller (computer) then it will make it run wrong.

amberbrush · Post by **amberbrush** » Thu Jul 05, 2007 12:15 pm

Yes, I do believe my temp. guage works right. It normally runs about half way up. I also put in a new temp. sender unit which for some reason makes my guage read higher. After I put the new sender in it reads about 3/4 of the way up. One other thing that I noticed about my Bronco II is that my plugs were very black after they were changed about 150 miles. It appears the engine is running very rich.

PHROX · Post by **PHROX** » Thu Jul 05, 2007 12:21 pm

ok, I think I will say it again. at this point I am pretty sure its something loose in the valves. its not usualy a bad spring or anything. its just something that needs to be tightend down under the valve cover. I had this problem and have met a few other people who have had it to. I caught it too late, the motor was already on the ground. but I would definetly check that before you pull the engine.