The check engine light came on a few weeks ago. I read the codes with the key on, engine off. The dash light flashed 6 7 6 7. The book says something about a/c, I believe. Does anyone know what this means? And, secondly, what to fix?
I think I might have damaged an emissions valve near the rear of the engine when I hooked up a pipe from the catalytic converter to the hoses near the right side exhaust manifold; I was trying to pass inspection and was told I needed this pipe. Big mistake...it melted the plastic hose connection, and possibly damaged something else.
The truck runs OK, but I want to make sure I won't damage it by not addressing the check engine light.
Randy
1990 F150
V-8, 5-speed

 

Code 67 says that you did not hold the clutch down during the self-test.
You must do this when you have a 300 Cu in I6 4.9L engine.

 

I retested, this time with the clutch in. The codes are 2 2 1 2 2.
That seems to indicate it's an issue with the MAP sensor from what I can tell. Let me know if you agree.
I tried to check the MAP sensor, but couldn't really figure out how. Any suggestions would be appreciated.
Thanks in advance for your assistance.
Randy
1990 F150
V-8, 5-speed

 

Service Code 22 indicates that the Manifold Absolute Pressure (MAP)/Barometric Pressure (BP) sensor is out of Self-Test range. Correct MAP/BP tester range of measurement is typically from 1.4 to 1.6 volts.

Possible causes:

-- MAP/BP SIG circuit open between sensor vehicle harness connector and processor.

-- MAP/BP SIG circuit shorted to VREF, SIG RTN, or GND.

-- Damaged MAP/BP sensor.

-- Vacuum trapped at MAP/BP sensor.

-- High atmospheric pressure.

-- Damaged processor.

-- VREF circuit open at MAP/BP sensor.

-- SIG RTN circuit open at MAP/BP sensor.

You can use either an old hand held tachometer or a frequency counter to test them.

 

I have an Actron tach, model cp7605. I tried using it but didn't seem to know what I was doing...at least I couldn't tell if it was working, or not.
Here's a link to the tach:
Amazon.com: Actron CP7605 Dwell/Tachometer/Voltmeter Analyzer: Automotive
This instrument should work for this, right?
If so, how do I use it check the MAP? Do I probe the MAP, or the MAP connector?
Thanks,
Randy

 

Yes you can use the CP7605 on the 4 CYL position.

KOEO FORD VALUE IS 157 HZ.

Here is the hook up.



On Ford applications, a multimeter that can read
frequency is normally required to check the sensor’s
output. But you can also use an ordinary tachometer
because a tach can display a frequency signal.
Here’s the procedure:

1. Set the tachometer to the four-cylinder scale
(regardless of how many cylinders the engine has).

2. Connect one tachometer lead to the middle terminal
on the MAP sensor and the other tachometer test
lead to ground.

3. Connect the two jumper cables the same as before,
attaching each end terminal on the sensor to its
respective wire in the wiring connector.

4. If you want to measure engine vacuum so you can
correlate it to a specific frequency reading, connect
a vacuum gauge to a source of manifold vacuum
on the engine, or tee the gauge into the MAP
sensor hose.

5. Turn the ignition ON and note the initial reading.
The reading on the tachometer should be about
454 to 464 at sea level, which corresponds to a
frequency output of 152 to 155 Hz.

6. Start the engine and check the reading again.
If the MAP sensor is functioning properly, the
reading should drop to about 290 to 330 on the
tachometer, which corresponds to a frequency
output of about 93 to 98 Hz. No change would
indicate a defective sensor or leaky or plugged
vacuum hose.

 

I used a cheapie DVM I purchased at Harbor Freight. The meter has a Frequency range setting. I back probed the connector like subford illustrated above, then I applied vacuum with a hand held vacuum pump/gauge. I used the values listed here: Ford Fuel Injection » Manifold Absolute Pressure Sensor (MAP)

I will question your test results you mentioned earlier. Are you sure the codes were not 1,1 pause 1,1 separator code 1,1 pause 1,1. That would indicate a system pass in KOEO and CM with a code 11.

 

I was thinking this too.

 

Yes, I think it might be 1, 1 pause 1,1 separator code 1, 1...
I am not used to reading the codes, and this was the first time I've done it.
If the above indicates system pass, why didn't the engine light go off? I disconnected the battery for about twenty minutes, but the light remained on.
If the above indicates system pass, is there anything wrong with the truck? What do I have to do next so the light on the dash goes off?
Thanks for the diagram on the hookup of my tach. I think I'll have time to check this later today. I didn't have it hooked up right before, and wasn't getting any readings.
Big thanks to all for the help.
Randy

 

Do you have a tachometer in the cluster?
You say the light will not go off, so how are you reading the codes?
If you do have a tachometer in the cluster what color is the light that will not go off (red)?
If it is red and you are reading the codes with a yellow light then that red light is the oil pressure and high temp light.
Or are you reading the codes with a VOM?

 

Yes, the engine light that is on is RED, and says ENGINE.
The codes are given in a YELLOW light.
If CLUSTER means the gauges on the dashboard, then yes I have a tachometer in the cluster.
Randy

 

As I said above the red light has nothing to do with codes. It means that you have low oil pressure or the engine temp is too high (hot).

 

OK, that makes sense. So, if I have the red ENGINE light on, how do I fix it? I checked the oil level, and the coolant in the radiator. Both are fine. The truck seems to be running fine, and I am going to take it on another short 5 mile drive right now to see if anything changes.
Thanks in advance for any ideas,
Randy

 

Here is a diagram of it:


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