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Old 04-30-2013, 04:57 PM
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Cylinder contribution test

I was playing with my otc scanner today. Did injector buzz test and everything passed. Then I did a cylinder contribution test and got code p0281. The truck runs fine have not noticed any kind of problems. I am ordering stage ones this week. Is this an injector issue or something more major?
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Old 05-01-2013, 08:25 AM
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Since it passed the buzz test I am going to assume that the coil on top of the injector #7 and the wiring to it are good. The PCM is reporting that when it gives the signal (or more when it removes the signal) to cylinder 7 to stop firing there is no difference to the idle. Meaning the test is to see how much more the other cylinders have to work when the PCM kills one of the cylinders. The more the other cylinders have to make up for the dead cylinder the more that dead cylinder was contributing to the overall performance of the truck. If the cylinder was dead the whole time (or so weak that at idle it really wasn't doing anything) the PCM will set a code for the particular cylinder that when killed showed no change in idle quality.

What this all means, since it passed the buzz test the wiring _should_ be fine. The injector itself may be weak or dirty, not just dead. Pull the right valve cover and watch the injector while the motor is running. Is there oil coming from the injector exhaust port (injector opening issue)? Is there oil coming up from base of the injector at the head (injector o-ring issue)? Pull the connector off the injector, did the idle change (electrical issue)? Pulling your own injectors is not hard just messy and time consuming. Does the truck drive fine (dirty nozzle issue)?

Last edited by BigFuel; 05-01-2013 at 08:48 AM.
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Old 05-01-2013, 08:27 AM
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That is exactly what happens when I run a cyl cont test, but I get a different code iirc, guess its time for sticks?
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Old 05-01-2013, 08:44 AM
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Sorry the d-rail this thread but while u guys are on the topic. I try to run a cly cont test with my aeroforce interceptor gauge but i keep pulling a code that says my ac or heat is on(witch there off) and It wont run the test is there anything else that i have to turn off to run the test. I know the eot has to be at opperating temp. The gauge will do the buzz test fine. Any ideas ? Iv used a snapp on scaner in the past and it ran the test just fine.
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Old 05-01-2013, 08:59 AM
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What code is it? Being a 95 (I don't know if it is an early or late 95 you have) your PCM would have needed to be flashed for proper OBD II port reporting from the PCM. First thought is that your gauge just isn't syncing to the PCM well. This might be fixed by going to Ford and having the PCM flashed again. But if the Snap-On is running fine Then I would tend to think that the issue is the gauge itself not communicating correctly with the '95 PCM. Did the gauge ever work correctly in performing this test? I don't know why it would report that if the heater was on it would affect the test but if the A/C or Defroster was on yes that would drag on the engine when the PCM dropped the cylinder. Possibly stalling the motor durring the test. About the only thing I see happening is that there might be a short to ground on the A/C clutch connection and the PCM thinks the A/C system is on. Disconnect the connector on the compressor and try again.
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Old 05-01-2013, 10:36 AM
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Ill run the test again tonight if i have time and get the code #. Im leaning towrd the gauge being the culprit bc i did un hook the ac compressor connector but same code was spit out. to turn the defroster off its as simple as putting the dial to off right ??
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Old 05-01-2013, 10:36 AM
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If the HVAC control is set to anything but the upright OFF position, the HVAC fan runs. IIRC, if it's set to the windshield defrost position it will run the AC compressor.
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Old 05-01-2013, 04:57 PM
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Quote:
Originally Posted by BigFuel View Post
Since it passed the buzz test I am going to assume that the coil on top of the injector #7 and the wiring to it are good. The PCM is reporting that when it gives the signal (or more when it removes the signal) to cylinder 7 to stop firing there is no difference to the idle. Meaning the test is to see how much more the other cylinders have to work when the PCM kills one of the cylinders. The more the other cylinders have to make up for the dead cylinder the more that dead cylinder was contributing to the overall performance of the truck. If the cylinder was dead the whole time (or so weak that at idle it really wasn't doing anything) the PCM will set a code for the particular cylinder that when killed showed no change in idle quality.

What this all means, since it passed the buzz test the wiring _should_ be fine. The injector itself may be weak or dirty, not just dead. Pull the right valve cover and watch the injector while the motor is running. Is there oil coming from the injector exhaust port (injector opening issue)? Is there oil coming up from base of the injector at the head (injector o-ring issue)? Pull the connector off the injector, did the idle change (electrical issue)? Pulling your own injectors is not hard just messy and time consuming. Does the truck drive fine (dirty nozzle issue)?
The truck runs great. I have not had any weird driveability concerns. That being said the truck does have 225k on it. I bought it with 170k on it and can only assume that the injectors are original. I have stage ones on order just need to get the chip pulled and have it changed.
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Old 05-01-2013, 08:04 PM
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Mine starts putting pretty hard during test, I finally tested after running it a while and getting oil and coolant to temp, throws code p0281 after its putts a bit at end of test
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Old 05-02-2013, 07:53 AM
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Quote:
Originally Posted by toad View Post
The truck runs great. I have not had any weird driveability concerns. That being said the truck does have 225k on it. I bought it with 170k on it and can only assume that the injectors are original. I have stage ones on order just need to get the chip pulled and have it changed.
Well, there may not be anything wrong with injectors. Kris confirms that the same thing happens to him too. Pull the fuel bowl cover and check the cleanliness of the fuel (should be clear with a hint of blue cloudiness if the sky is clear), pull the dipstick and see if the oil is "off" (Feels really thin, smell like fuel or coolant), look in the degas bottle and make sure the coolant is clean and not smelling of fuel.

With your coming stage I's, do consider also doing the injector cups at the same time. With 225k miles on the stock cups I'd hate to see you swap injectors and then have to go back in to replace cups in a few thousand miles. Get it done at the same time.
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