fuel injector?

High RPM Miiss: The most common source of a high RPM miss on a warm engine is a bad TFI module.


Leaking fuel injector: Fuel injector seal kits with 2 O rings and a pintle cap (Borg-Warner P/N 274081) are available at Pep Boys auto parts. Cost is about $2.74 per kit.. The following are listed at the Borg-Warner site ( http://www.borg-warner.com ) as being resellers of Borg-Warner parts:

http://www.partsplus.com/ or http://www.autovalue.com/ or http://www.pepboys.com/ or http://www.federatedautoparts.com/

Most of the links above have store locators for find a store in your area.

Use motor oil on the O rings when you re-assemble them & everything will slide into place. The gasoline will wash away any excess oil that gets in the wrong places and it will burn up in the combustion chamber.

The pintle caps fit either injectors with a pin sticking out the injector end or 4 with more tiny holes in the injector end

Place the new pintle caps in some boiling water prior to trying to install them. It makes them soften up and easier to install.


Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.

Code 41 RH O2 Sensor
Code 91 LH O2 Sensor

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Testing the O2 sensors
Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.

Testing the O2 sensor wiring harness
Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts.


If you get only code 41 and have changed the sensor, look for vacuum leaks. This is especially true
if you are having idle problems. The small plastic tubing is very brittle after many years of the
heating it receives. Replace the tubing and check the PVC and the hoses connected to it.
A secondary problem with only a code 41 is for cars with an intact smog pump and cats. If the tube
on the back of the heads clogs up the driver’s side, all the air from the smog pump gets dumped
into one side. This excess air upsets the O2 sensor calibration and can set a false code 41. The cure
is to remove the crossover tube and thoroughly clean the insides to that there is no carbon blocking
the free flow of air to both heads.

redfox91 said:

Ok I have a problem. It seems to have a miss under a load in the 4000 rpm and up range. I have a leaking fuel injector and I did just replace the o-rings and pintle caps thinking that would fix the problem? I moved the leaking injector to another spot on the fuel rail as well and it still leaks. It seams to be coming from where it mounts to the rail. I have pulled codes both koeo and koer and did a cylinder balance test. The only code that came up was a 91. Everything else came out fine. Injector clogged or cracked??? If I replace it should it fix my issues????? I am not driving it with the leaking injector anymore as I don't want to burn down my car!

Click to expand...

How do you know the injector is leaking?
Is the leak internal or external?

A 'frozen' injector could cause the lean issue. Try moving the suspect injector to the other bank, clear the KAM, and run the motor a little, then run KOEO/KOER again.
If the problem is with that injector, then code 91 should disappear and be replaced with code 41...

Code 91 could also be from a vac leak or a leaking header gasket.


Hope that gives you something to work with

Run a cylinder balance test and see which cylinder comes up short if any. Lets say cylinder 5 came up as weak, swap that injector with one from the other bank of the motor and see what another balance test shows. If the lean code moves from one side of the motor to the other and the weak cylinder shows up as the one you swapped you have a bad injector. You can also check on the injector to see if the pintle cap is seated all the way, even soaking them in hot hot water they snapped on not all that easily. As suggested earlier motor oil on the o-rings is a must and seating all the injectors evenly and not at to severe an angle(in the case of aftermarket rails)should keep you free from leaks.

Good luck!

Matt

The TFI module is mounted on the distributor of 86-93 5.0 Mustangs.



Most auto parts stores can test the TFI module. However, I recomend that you bring a hair dryer along to heat the module as you have it tested. The modules are most prone to failure when they get hot.

redfox91 said:

Gotcha, the ignition module. I replaced this not to long ago but that makes sense. I replaced that and the distributor at the same 6 months ago. I am going to put a new injector in it today to see if I get rid of the leak. I noticed that it doesnt hold pressure that long as well, that must be caused by the leak?

Click to expand...

That or an aftermarket fuel pressure regulator will lose pressure alot faster than stock. Also if the leak was taking from the pressure it would be shooting out and would smell like raw fuel.