I need some help with this one...

My Bronco is having a cold idle problem that has had me stumped for some time, and I'm tired of chasing it. WHen the engine is below operating temp, it runs like crap. I don't know if it's getting too much fuel, or not enough, but there is a loud ticking sound from the area of the #5 injector area. I have pulled all 8 injectors and bench tested them, all good. I have replaced the spark plugs with Autolite Copper plugs to help determine the problem. Once the engine is at operating temperature, the engine smoothes out, as if someone hit a switch. I have removed the throttle body and scrubbed it, and cleaned out the upper intake. There are no intake leaks or vacuum leaks. I thought it may be a lifter ticking and going bad, but that wouldn't go away with the engine warming up. I'm leaning toward the theory that whatever the problem is, it's temperature related.

 

A temp sensor?

 

Good guess...and I think you may be right. I just checked the resistance on it and got nothing, indicating an open. It's a $20 gamble.

 

Ford Fuel Injection » Engine Coolant Temperature Sensor (ECT) Make sure that this is the sensor you are testing and not the temp gauge sender.

 

I'm checking the right one. The resistance was off compared to a new one, but it didn't fix the problem. Ignition timing is right at 10 degrees, where it should be. I'm two steps away from unplugging everything noncritical and start from there.

 

Air charge/Intake Air temp Sensor. Another sensor that acts like an ECT sensor, and can cause similar problems. It should be located on the manifold. As for the ticking, a lifter can tick for sometime, usually until the motor warms up. Another thought would be the PCV valve. If it's stuck open, then it will create a vac leak that make the truck run like crap as well. Take a sheet of paper and cover the end of the valve after removing it from the valve cover. If the truck idles smoother, I'd say it's time to clean the one you have or purchase a new one. Stay away from NON-OEM PCV valve's. Just spend $8 for a Motorcraft one and all will be fine.

 

I cleaned the PCV last week whn I had the upper intake off. It was fairly clean, but I cleaned it anyway just to be sure. I'll check that ACT sensor. Do you know the resistance specs on it?

 

Same specs as the ECT sender. As you stated that you cleaned the PCV, next step is to check that it hasn't worn a groove around in the housing allowing for more unmetered air to enter the intake. Try the sheet of paper trick and go from there. Also is the PCV hard rubber line cracked? If it is, this problem could just be a vac leak from the line itself. It may be time to relocate the PCV line to the center of the Vac Tree on the plenum and route the brake booster line to the rear of the plenum.

 

Man do I love my '79 bronc. I had a '94 that was giving me the same fits. I scraped it and never looked back. Wish you the best of luck with that EFI.

 

No, I don't have any cracked vacuum lines, rubber, plastic, or otherwise, none that I can see.

 

Ford Fuel Injection » How To Run a Self-Test Maybe check for trouble codes as described in this link (even if no light on).

 

It spit out some codes, something it's never done. 113, 118, 126...all for the ACT and ECT being out of range (cooled down engine), but I got a 327 DPFE/EVP below .2V. I'll mess with it more later...sun's right overhead and it's about 105+. Time for a nap.

 

I think you have found the cause if it also showed the ACT out of range. If these codes were stored and not codes that were spit out while running, it's a sure bet.

 

Nah..."out of range" means it couldn't be tested because it was cold, or below operating temperature, which it was. If it were to spit that out with a hot engine, then yeah, that would be my problem.

 

Have you checked on the IAC, cleaned, or run a test on it?
Ford Fuel Injection » Idle Air Bypass (IAB)