Running Rich


May 24, 2005
I have an 87 5.0 with a mass air a9p ecu conversion, cobra intake, 3.73's and full exhaust. Stock tb, stock mass, stock injectors.
I am getting about 160 miles to a tank which is around 13.8 miles a gallon.
The car never had Great gas mileage but it used to get about 220 miles to a tank before the mass conversion and intake.
I have tried to run seafoam thru the intake and oil. With no help. Timing is set at 12 degrees and I run 89 octane gas. Car drives very well idles perfectly, lets out a bit of black smoke usually from the right exhaust pipe when at wot.
I have done a tune up about 4 months ago; plugs were fine except the #4 and 8 which showed white buildup. My tail pipes are black.
I haven’t tried pulling the codes yet, but will try to do it today, so that I can give some feedback. I had a friend who had similar problem; it resulted to a leaky injector. How can I determine which injector is bad if this is my problem?
Originally I though my fpr was not working properly, I had it tested by a mechanic and he stated that it was fine and fuel pressure was good too. I’m open to any opinions, just trying to get this resolved before I take it to the dyno by the end of the month to get base numbers before I do h/c/i. Thanks in advance. \
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See the cylinder balance test for the how to dump codes. Find and fix any
codes prior to doing the cynder balance test. The odds are that your poor
mileage results are due to a failing sensor.

If you have any bad fuel injectors, this will help isolate them.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a
jumper wire or paper clip to put the computer into test mode. Start
the engine and let it go through the normal diagnostic tests, then
quickly press the throttle to the floor. The engine RPM should exceed
2500 RPM's for a brief second. The engine RPM's will increase to about
1450-1600 RPM and hold steady. The engine will shut off power to each
injector, one at a time. When it has sequenced through all 8 injectors,
it will flash 9 for everything OK, or the number of the failing cylinder
such as 2 for cylinder #2. Quickly pressing the throttle again up to
2500 RPM’s will cause the test to re-run with smaller qualifying figures.
Do it a third time, and if the same cylinder shows up, the cylinder is
weak and isn’t putting out power like it should. See the Chilton’s Shop
manual for the complete test procedure

Here's the link to dump the computer codes with only a jumper wire
or paper clip and the check engine light, or test light or voltmeter.
I’ve used it for years, and it works great.



IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

For those who are intimidated by all the wires & connections,
see for what a
typical hand scanner looks like. Normal retail price is about $30 or so
at Walmart.

Or for a nicer scanner see – It has a 3 digit LCD display so that you don’t have to count flashes
or beeps.. Cost is $33.

Do a compression test on all the cylinders.
Take special note of any cylinder that shows up as weak in the cylinder
balance test. Low compression on one of these cylinders rules out the
injectors as being the most likely cause of the problem. Look at cylinders
that fail the cylinder balance test but have good compression. These
cylinders either have a bad injector, bad spark plug or spark plug wire.
Move the wire and then the spark plug to another cylinder and run the
cylinder balance test again. If it follows the moved wire or spark plug,
you have found the problem. If the same cylinder fails the test again,
the injector is bad. If different cylinders fail the cylinder balance test,
you have ignition problems or wiring problems in the 10 pin black &
white electrical connectors located by the EGR.

How to do a compression test:
Only use a compression tester with a screw in adapter for the spark
plug hole. The other type leaks too much to get an accurate reading.
Your local auto parts store may have a compression tester to rent.
If you do mechanic work on your own car on a regular basis, it would
be a good tool to add to your collection.

With the engine warmed up, remove all spark plugs and prop the
throttle wide open, crank the engine until it the gage reading stops
increasing. On a cold engine, it will be hard to tell what's good &
what's not. Some of the recent posts have numbers ranging from
140-170 psi. If the compression is low, squirt some oil in the cylinder
and do it again – if it comes up, the rings are worn. There should be
no more than 10% difference between cylinders. Use a blow down
leak test (puts compressed air inside cylinders) on cylinders that
have more than 10% difference.
Finally had some time today to run the tests, these are my results:

67: Park/Neutral circuit fault - PNP
95: Fuel pump: open, bad ground or always on - Power / Fuel Pump Circuits
94: AIR system inoperative - Air Injection
44: AIR system inoperative - Air Injection
90: Passed balance test

I removed all of the spark plugs...plugs are about 6 months old.
1, 2, 3,5,6,7 looked like this:

4 and 8

Code 67 was triggered because during the first test my car was in gear. When I put it in neutral and tried it again… it didn't show up.
Codes 94, 44 have to do with the valves that are connected to the air pump and thermactors. I knew these codes were going to show up because one of the rubber hoses that connects to the valves has been cut in half and the other has become very brittle.
Code 95 is the only one I am worried about. I also have no idea what to do in order to fix it or if in anyway it can be associated to having bad gas mileage and hesitation.
I also checked the timing, it was set at 14, i brought it down to 11-12 degrees.
Tomorrow im going to clean the mas sensor and replace the thermactor hoses to take care of the 94 and 44 codes.
Thanks for any advise.


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Depending upon how you did your MAF conversion, 95 can come from the conversion (it has to do with the FP monitoring circuit, IIRC).

I dont think you'll pick up a smog code with bad hoses alone. I'd check the TAB and TAD and their vac lines (Jrichker will have a nice synopsis for you). The AIR wiring changes with the conversion too, IIRC.

See this article for assistance with the FP and AIR codes.

Good luck.
The 44/94 codes don't hurt engine performance unless there is a vacuum leak in their vacuum plumbing. For reference, here is the test path...

Codes 94 & 44 - AIR system inoperative - Air Injection. Check vacuum lines for leaks, & cracks. Disconnect the big hose from smog pump: with the engine running you should feel air output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its purpose is to either dump the pump's output to the atmosphere or pass it to the next valve. The next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow changes from one hose to the next.
The two electrical controlled vacuum valves mounted on the rear of the passenger side wheelwell turn the vacuum on & off under computer control. Check to see that both valves have +12 volts on the red wire. Then ground the white/red wire and the first solenoid should open and pass vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open and pass vacuum.

Remember that the computer does not source power for any actuator or relay, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

The computer provides the ground to complete the circuit to power the solenoid valve that turns the vacuum on or off. The computer is located under the passenger side kick panel. Remove the kick panel & the cover over the computer wiring connector pins. Check Pin 38 Solenoid valve #1 that provides vacuum to the first Thermactor control valve for a switch from 12-14 volts to 1 volt or less. Do the same with pin 32 solenoid valve #2 that provides vacuum to the second Thermactor control valve. Starting the engine with the computer jumpered to self test mode will cause all the actuators to toggle on and off. If after doing this and you see no switching of the voltage on and off, you can start testing the wiring for shorts to ground and broken wiring. An Ohm check to ground with the computer connector disconnected & the solenoid valves disconnected should show open circuit between the pin 32 and ground and again on pin 38 and ground. In like manner, there should be less than 1 ohm between pin 32 and solenoid valve #2 and pin 38 & Solenoid valve #1.

If after checking the resistance of the wiring & you are sure that there are no wiring faults, start looking at the solenoid valves. If you disconnect them, you can jumper power & ground to them to verify operation. Power & ground supplied should turn on the vacuum flow, remove either one and the vacuum should stop flowing.
See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)