1989 Ford Bronco Engine runs like S***

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

Lean Condition may sometimes appear because of a bad Differential Pressure Sensor (DPFE). This sensor monitors EGR flow, and is located on the engine near the EGR valve. There are two hoses that connect the sensor to the tube that runs from the exhaust manifold to the EGR valve. The sensor misreads EGR flow and the computer increases EGR which has a leaning effect on the fuel mixture. The fix is to replace the DPFE sensor.

There's no MAF sensor-check the idle speed control air bypass solenoid, Did he do a vacuum leak check?

Hook up a vacuum gauge to the intake manifold make sure its full vacuum not ported/venturi vacuum

When was the last tune-up?

Wanted to check the ignition system he's probably going after the coil hinting it might be weak. While he's there have check the engine compression

He never mentioned the coil, it was something in the dist. Don't recall the name. It could be the distributor pick-up coil/stator or the thick film integrated ignition module he's talking about.

I've checked in the Mit1 maybe wrong info and yes they are normally place where you stated dull looking gray square box with 2 pigtails with a bunch of wires coming out of it. This one has to be grounded properly to function correctly or its on its way out-could be it

Recheck the ISC solenoid

Vacuum fluctuating at 8-13 inch points to weak valve springs or late valve timing

The vac. Is 13-14 at idle, checked at the ports in the intake horn just behind the throttle boby

Sounds like you have an intake leak. Might wanna check the valve and ignition timing if its lined proeprly.

Using the propane method is a good idea.

Propane can also be used in conjunction with an exhaust analyzer (do NOT use carburetor cleaner or you may damage your analyzer!). Engine vacuum leaks almost always cause fluctuating HC readings, so an infrared exhaust analyzer can (1) tell you if there is indeed a leak, and (2) where the leak is using the propane procedure.

Two types of vacuum leaks can be diagnosed with an analyzer. The first kind is a general vacuum leak (PCV hose, brake booster, etc.) That leans out the mixture and causes a very low CO reading and only a slightly higher fluctuating HC reading. The O2 reading will also be high. The second kind of vacuum leak is a "point" leak that affects only one or two cylinders (a leaky manifold gasket or a crack or porosity leak in one of the manifold runners). This will be indicated by a normal or low CO reading combined with high fluctuating HC readings. O2 will again be high.

To find a leak, feed propane at suspected leak points until you note an improvement in idle quality and/or a change in the HC/CO/O2 readings. When you have found the leak, the idle should smooth out, HC and O2 should drop and CO rise.

It is important to note that an overly lean idle mixture will also cause a fluctuating HC reading the same as a vacuum leak. To tell one from the other, there is a simple "trick" you can use. Momentarily enrich the idle mixture to 1.5 to 2.0% CO by placing a clean shop rag over the top of the carburetor. If the engine smooths out and HC drops and remains stable, the problem is a lean idle mixture adjustment. If HC still fluctuates, however, the engine is still too lean in one or more cylinders indicating a vacuum leak

No, the other thing to check is exhuast restrictions, either the converter bed broke up and pieces are wedged in the pipes or muffler, or a pipe or muff is crushed?