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

[amberbrush]

I recently acquired a 1988 Ford Bronco II with the 2.9L engine and auto tranny. I just purchased the vehicle a little over a month ago. The guy I purchased it from was stumped as to the problem it was having as well and gave up so decided to sell. The bronco drives nicely until it warms up to full operating temperature. Once the motor is fully warmed up it has no power. You can't go over 35 mph with it. If you punch the pedal it hesitates badly and cuts out. If you just want to cruise 35 you would never know anything is wrong with it. It idols nicely, no knocking or weird sounds. We figured it would be something fairly easy so we replaced the following to no avail: spark plugs and wires, distributor cap and rotor, ignition coil, map sensor, fuel injectors and both fuel pumps. We checked all the vacum hoses. We then did a compression test and got readings of 150 from 5 cylinders and 120 from the other. The check engine light is not on. One mechanic I asked was positive it was the catalytic converter so we took it off as well and it did nothing. No one else seems to know what it is. Do you have any suggestions?

[Nobody]

I'm going to go with the TFI module on the side of the distributor.

[Joel H]

Have you set the timing with Spout plug removed?

[ran429]

I'm going to go with the TFI module on the side of the distributor.

This could be the problem, also could be a faulty connection on the single wire coming off the dist.
You will need a special tool to take the TFI module off the back of the distributor.
cheap at the auto parts stores.

[Paul]

IAC Cleaning/Testing: (12)



The IAC is usually a cylindrical unit attached to the upper intake manifold. This unit 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.


this might help you too, and you can also check the oxygen sensor

[Paul]

TPS Calibration: (6)



Warm the engine up. Shut engine off, and turn ignition on. With a voltmeter on the appropriate setting, probe the TPS center wire with the (+) probe, and ground the (-) probe. Adjust the throttle plate adjustment screw so the voltmeter’s reading is 0.9 to 1.0V DC.

this could also be a problem

[Paul]

TFI:

The TFI module may be removed, and tested for resistance between terminals to determine complete failure. Often stock TFI modules only partially fail when engine temperatures get warm, and the vehicle runs rough then dies. The vehicle then restarts, and runs for 20 seconds then dies again. This is a defect, which affected ALL TFI modules before 1995, although some do not seem to be very problematic (this often causes codes 14 and 18).

now in agreance with Nobody I would definatly start with the TFI module and if you want to know how to check it well then there is a picture diagram on a site with the different ohm readings from pin to pin and identification of pins on this site ....... and i would advise to print it so you can have it in front of you when testing it, the best thing to do would be to replace it and not worry about testing because heat can create a variance in ohms across sensors ....... the main reason the TFI module was so bad about failiing was due to ecxcessive heat in the engine compartment, and you should check for exhaust leaks .... because they will create the same effect as the TFI if you loose too much back pressure around a manifold before the exhaust gas hits the oxygen sensor.

http://www.broncoii.org/techpages/eeciv ... est:%20(9)

[amberbrush]

I am going to put a new fuel regulator in the Bronco tonight and go from there. When I smell the oil on the dipstick it smells as if fuel is in it. I was told this could be due to a faulty regulator. If that isn't the problem I am going to put in a new TFI module. Are these easy to install? What is the best way to do it? Also, I was told by a mechanic to bypass the catalytic converter. Can you do this and if so what do you do with the oxygen sensor?

[PHROX]

if none of that works, check your valves. I had almost the exact same problem. thought my cat had colapsed and when It warmed up it wouldn't let exhaust thru. I was wrong. it was the valves had come loose under the valve cover and come out of tolerances. so I would probably put that on the list of things to check.

[bower100]

FWIW,

I'm rebuilding a 2.9 with 140k miles on it. My trusty machine shop guy said the valve guides in the heads are pretty slpppy...valves wobble too much. Intake valves all have a excessively wide seat area.

My compression test revealed 110-120 psi across all six cylinders.

( Don't know why yours would be a seemingly healthy 150 psi).

I don't know how much power this motor had...it's a spare I'm redoing, but my 2.9 in the truck, with 185K and similar compression testing results is a REAL dog. Very weak ...as in ... lets say a moped will give it a run from 0-30 mph, and above that I have to really get into the gas petal to achieve 60-65 mph. It's resistant to shift to OD and drops out of it in a mild headwind.

Nuf said.

By the way, I too thought my cat conv. was clogged, so I built a straight -thru pipe to temporarily replace it, ( that was a real task, by the way because of the odd 3-bolt oval inlet flange it has). The temp pipe prooved my cat was unobstructive.

dave

[amberbrush]

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

FWIW,

I'm rebuilding a 2.9 with 140k miles on it. My trusty machine shop guy said the valve guides in the heads are pretty slpppy...valves wobble too much. Intake valves all have a excessively wide seat area.

My compression test revealed 110-120 psi across all six cylinders.

( Don't know why yours would be a seemingly healthy 150 psi).

I don't know how much power this motor had...it's a spare I'm redoing, but my 2.9 in the truck, with 185K and similar compression testing results is a REAL dog. Very weak ...as in ... lets say a moped will give it a run from 0-30 mph, and above that I have to really get into the gas petal to achieve 60-65 mph. It's resistant to shift to OD and drops out of it in a mild headwind.

Nuf said.

By the way, I too thought my cat conv. was clogged, so I built a straight -thru pipe to temporarily replace it, ( that was a real task, by the way because of the odd 3-bolt oval inlet flange it has). The temp pipe prooved my cat was unobstructive.

dave

[DBrown]

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

[amberbrush]

O.k. I put a new fuel regulator and temp sending unit in last night and had no luck. I also had another computer lying around so I hooked it up to make sure my computer wasn't bad and found it isn't that either. I have done some research on the TFI module and everything I read says that your vehicle dies after it warms up and won't start until it is cool again. My bronco II never dies so I am unsure if that is the problem. How do you check the timing? I am beginning to think it is something in the cylinder heads but would like to rule everything else out before tearing apart the engine.

[DBrown]

you need to get a manual for your truck and a timing light if you realy don't know how to set the timing. it is pretty simple but the manual will show you step by step.

[PHROX]

I didn't think you could set timing on a 2.9. I know you can dissconnect the advanced computer thing to check it. but you can't change the timing. the comuter does it all. that's what I thought anyway. let me know if I am wrong