Need help w/ lean running / cold start issues

[RhinoGT]

Hi everybody. I bought my first fox a couple weeks ago. 90 lx 5.0 hatch auto. The car's only mod was an x303 cam. (YES I KNOW) I didn't put the stupid thing in, lol! Here are my problems:

Right now I am pulling codes 41 and 91. I have been keeping an eye on the plugs and they are now getting white. The car lacks power big time and fuel mileage is between 14 and 16 mpg. When cold the car will not idle unless I feather it. Sometimes even when warm at a stop it will stall out on me. However it usually idles steady at around 1100 once it's warm.

So far I have replaced the coil, cap, rotor, plugs and wires, fuel filter, removed air silencer and dropped a K&N in. I Put the timing @ 12* and I have been running 93 in it. I have cleaned the Iac valve and egr valve. (BOTH were hideous!) And replaced the faulty tps. Tonight I unplugged the FPR vacuum and tripped the fuel pump into running, no fuel leaked out of the FPR. I have not yet gotten a fuel pressure guage so I can't say what the fuel pressure is exactly.

WHERE should I go next?

TFI? Leaking injectors?

I need your help!!

 

[jrichker]

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

Code 41 is a RH side sensor,
Code 91 is the LH side 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. The O2 sensor voltage should switch between .2-.9 volt at idle.

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.

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.

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

Make sure you have the proper 3 wire O2 sensors. Only the 4 cylinder cars used a 4 wire sensor, which is not compatible with the V8 wiring harness.

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

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 so that there is no carbon blocking the free flow of air to both heads.

 

[RhinoGT]

Thanks for the info.

The smog pump is gone, but the pipe is still there. Its just has a rubber cap with a hose clamp covering the end of that valve right now. Is there a way to seal off that valve at the end of the pipe below the air intlet tube? If not, how hard is it to take the pipe off with the motor in the car? If I take the tube off, what can I use to seal the heads off? I am pretty sure there isn't a vacuum leak at the top of the engine as I did the spray test on the vacuum lines and around the intake gaskets. I will try to check the O2 sensors at the pcm but based off the color of the plugs, the motor is running lean like the 02 sensors say.

I also forgot to mention, I did a compression test last week and came up 150psi on all 8 cylinders.

 

[RhinoGT]

ok, I replaced the TFI yesterday because they had one in stock. Didn't help, but now I have a spare at least. However today on the way home from work I was coming to a red light and put it in neutral to let it coast and it stalled on me. I would start for another 20 minutes or so, which sounds like the TFI again so I am confused on that one. I have yet to check the O2's as the only voltmeter I have access to I can't get to until friday.

Could the PIP cause these problems?

What about the air diverter pipe leaking? Could that cause me to be running lean on all cylinders?

Thanks guys.

 

[jrichker]

A failing PIP sesnor will often set a code 14

Code 14 - Ignition pickup (PIP) was erratic – the hall effect sensor in the distributor is failing. Bad sensor, bad wiring, dirty contacts.

The PIP is a Hall Effect magnetic sensor that triggers the TFI and injectors. There is a shutter wheel alternately covers and uncovers a fixed magnet as it rotates. The change in the magnetic field triggers the sensor. They are often heat sensitive, increasing the failure rate as the temperature increases.

The PIP sensor is mounted in the bottom of the distributor under the shutter wheel. In stock Ford distributors, you have to press the gear off the distributor shaft to get access to it to replace it. Most guys just end up replacing the distributor with a reman unit for about $75 exchange

 

[RhinoGT]

ok, I'll pull the codes again tomorrow to see if it popped up.

 

[riored94cobra]

clean your MAF sensor. The K&N Filter most likely got oil on your sensor causing faulty readings. you PCM calibrates the a/f mixture from the MAF sensor AND the O2 sensors.

Clean it with something like brake cleaner/carb. cleaner.

 

[RhinoGT]

Maf has been cleaned. The symptoms were the same before and after. They were also the same before and after install of the k&n. It actually had one in it already but it was dirty beyond cleaning, couldn't hardly see through it after 3 cleanings.

 

[RhinoGT]

ok, pulled the codes again they are:

33- egr
81- air circuit
96- FUEL PUMP CIRCUIT

41
91

 

[RhinoGT]

ok, I ordered a new dizzy today, should be here tomorrow. Today the car stalled on me and wouldn't restart 3 different times. Each time I had to wait at LEAST 20 minutes before it would fire up again. This is starting to happen more and more frequently. Tested the 02's today, they were within the appropriate range. Now the car will only idle on its own in park or neutral. Even then, it will eventually stall out on me. The brake pedal will sometimes become very firm and hard to depress. When that happens, (usually at slow speeds) it is very hard to slow down. When it does this at a stop it takes maximum effort to keep the car stopped if it is in drive.

The motor is getting replaced in a couple of weeks but I need to make sure that I can get this motor to run better before that so I don't foul up the new one.

 

[jrichker]

ok, I ordered a new dizzy today, should be here tomorrow. Today the car stalled on me and wouldn't restart 3 different times. Each time I had to wait at LEAST 20 minutes before it would fire up again. This is starting to happen more and more frequently. Tested the 02's today, they were within the appropriate range. Now the car will only idle on its own in park or neutral. Even then, it will eventually stall out on me. The brake pedal will sometimes become very firm and hard to depress. When that happens, (usually at slow speeds) it is very hard to slow down. When it does this at a stop it takes maximum effort to keep the car stopped if it is in drive.

The motor is getting replaced in a couple of weeks but I need to make sure that I can get this motor to run better before that so I don't foul up the new one.

The brake pedal problems and the 41/91 code indicate a vacuum leak. Look for broken vacuum connections, damaged vacuum lines and hoses (don't forget the PVC valve and brake booster hoses). Check the brake booster and the rubber grommet that holds the brake booster vacuum check valve for damage and leaks. The brake booster may be the source of the vacuum leak, but don't replace it unless you have eliminated all the other possiblities.

There is no easy way to find vacuum leaks. It is a time consuming job that requires close inspection of each and very hose and connection.

Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much from engine to engine that it may be difficult to detect small leaks. Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure comparison is a reading taken when your car was performing at its best through all the RPM ranges and what it is doing now. Use one of the spare ports on the vacuum tree that is mounted on the firewall near the windshield wiper motor to connect the vacuum gauge.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will change speed.
Avoid using flammable substitutes for the oil such as propane or throttle body cleaner. Flash fires can occur due to the heat and possible electrical sparks. Fire is an excellent hair removal agent, and no eyebrows is not cool...

The vacuum line plumbing is old and brittle on many of these cars, so replacing the lines with new hose is a good plan. The common 1/8” and ¼” vacuum hose works well and isn’t expensive.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[RhinoGT]

Well I went ahead and bought some hose. I will replace them all even though the Idle never changed when I did the spray test before. But I am betting that you are right about the booster. I looked at the hose and grommet and they are pretty loose. If that is the culprit, can I just replace the hose and grommet or do I have to get a whole new booster?

 

[jrichker]

Well I went ahead and bought some hose. I will replace them all even though the Idle never changed when I did the spray test before. But I am betting that you are right about the booster. I looked at the hose and grommet and they are pretty loose. If that is the culprit, can I just replace the hose and grommet or do I have to get a whole new booster?

Do the cheap and easy stuff first - replace the hose & grommet and if that doesn't at least fix the brake problem, then replace the booster.

 

[sdrt]

i also have the brake problem and it hunts for idle when it's cold. i am new to cars anything else i should look for? i don't have a loss of power or anything. thanks

 

[RhinoGT]

where can I get the grommet for that thing? I can't find it.

ALSO, I noticed there is a LOONG vacuum line coming out of the firewall between the brake booster and the DS fender. It is not connected to anything and has a bolt in it. What could this be for? Cruise?

Thanks again guys. (and GALS)

 

[Brian992V]

Thats the hose for the cruise control so if its capped on the tree, no need to worry about it unless you want your cruise to work.

You may have to buy both the fitting and grommet together. Its called a check valve. FYI

 

[RhinoGT]

ok, bought the new check valve and grommet. But before that I RTV'd around them both and bam, it runs so much better now. I will replace it shortly to see if it helps more. The brake problems are gone THANK GOD!

It is still cold blooded though. It also has really long starts when hot. And it does still idle hunt. Coming to a stop it will still want to stall if it is in gear but in neutral it does fine. It also seems like the cam is fighting the torque converter. (it's the stock one) I wonder if replacing the converter would relieve the stalling issue?

I noticed today that there is oil in the TB. I went and bought a new pcv and screen, they had to order the grommet.

I know for sure the Pass. side exhaust manifold is leaking. I wonder if that leak would cause the idle hunting? Im going to go ahead and replace the whole exhaust anyway as im sure the cats are clogged and the catback is pitifully small and crimped.

Anyways, the car is driving better than it was, but I know there is still some work to be done.

Just a couple questions:

1. Should I replace the converter?

2. Will fixing the exhaust manifold leak help my idle?

3. Will the pcv system blowing oil into the intake cause the car to smoke under hard acceleration?

Thanks again guys.

 

[sdrt]

rhino you replaced the line and fitting going into the brake booster? did you get that right from ford,or auto parts store?

 

[RhinoGT]

naw, autozone. I haven't put it in yet though.

It will be in the area of the store where all the grommets and misc. repair items are. The part number on the box says 80189. If you look it up online, it will be under accessories for some reason. Just type the part number in the search box. It DOES come with the grommet.

 

[sdrt]

thanks called autozone this morning they have it,thanks for the help. did this also cure the idle issue? i checked all the other lines and they look ok.