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Old 02-05-2018, 09:39 PM   #1
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Injectors temperature

Here is a question for our fellow mechanic handy TFers.
When making a temp reading of the injectors with a heat gun, should they all show same temp? Of course I know that the reading will not be exactly the same. The question is more what is the acceptable difference? Just curious.

Note: in my case the engine is an old straight 6 cyl naturally aspirated.

L
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Old 02-05-2018, 10:35 PM   #2
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If you're trying to troubleshoot a weak or dead hole you should be looking at the egt. The injector bodies will typically be the same temp as the cylinder head. The max allowable fuel temp for cats is 150*f.
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Old 02-06-2018, 08:55 PM   #3
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Quote:
Originally Posted by BIG CAT View Post
If you're trying to troubleshoot a weak or dead hole you should be looking at the egt. The injector bodies will typically be the same temp as the cylinder head. The max allowable fuel temp for cats is 150*f.
Well in fact not trying to solve any issue just try to educate myself. I mean that let say I measure injectors temp, one is 20 C over other doea this mean something? What about 50C? What if under others? Etc You see what I mean.

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Old 02-06-2018, 11:29 PM   #4
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Quote:
Originally Posted by Lou_tribal View Post
Well in fact not trying to solve any issue just try to educate myself. I mean that let say I measure injectors temp, one is 20 C over other doea this mean something? What about 50C? What if under others? Etc You see what I mean.

L
I don't think you would see any significant variation in temp from one to another. The main injector body is typically seated to the cylinder head and should be close to that temp. The egt is a direct indicator of injector fuel delivery.
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Old 02-07-2018, 01:28 AM   #5
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The most basic injector test is to loosen the fuel supply fittings one cylinder at a time. The engine should slow down and run a little rough, and come right back to normal idle as the fitting is retightened.
If interrupting the fuel supply to a particular injector has no effect, there is a problem with that cylinder, though it is not necessarily a bad injector.
I have never seen a mechanic shoot injector temps as a troubleshooting procedure.
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Old 02-07-2018, 11:56 PM   #6
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I'm just not getting the injector temp thing. I've seen the use of temp data from all sorts of sources, but just don't understand how you'd get an accurate measurement of just an injector or what it would mean. Enlighten me.

I'd think that if there is real concern, setting up egt measurements for each cylinder would be the better check.
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Old 02-08-2018, 03:20 AM   #7
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If injector temps differ, it can be the coolant circulation path. They're fixed tightly to the head, the head is cooled by circulating coolant. All cylinders don't get exactly the same cooling effect. Cooling effects for each cylinder probably were never exactly the same even when the engine was new. Passages between the head and block could be partly blocked or restricted due to corrosion or buildups on the coolant passage surfaces in the head. If you're trying to determine if all cylinders are running evenly, a better place for your heat gun to test is the exhaust ports where they leave the head. In other words, Exhaust Gas Temperatures as BIG CAT suggested.
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Old 02-08-2018, 06:32 AM   #8
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Thank you, injector temp is irrelevant, noted

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Old 02-08-2018, 01:23 PM   #9
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Quote:
Originally Posted by kapnd View Post
The most basic injector test is to loosen the fuel supply fittings one cylinder at a time. The engine should slow down and run a little rough, and come right back to normal idle as the fitting is retightened.
If interrupting the fuel supply to a particular injector has no effect, there is a problem with that cylinder, though it is not necessarily a bad injector.
I have never seen a mechanic shoot injector temps as a troubleshooting procedure.
X2.

When you get into bigger engines we typically will have a egt probe for each cylinder and one before the turbo. Egt is the primary indicator for the cylinders health when compared to the other ones. If you see one that's more than say 75*f more/less than the others it's time to investigate what's happening. Also cutting out one hole may not give you a strong indication on a weak cylinder. If you can cut them out under loaded conditions you will see a much greater change in engine rpm for each cylinder that's cut out. On the bigger stuff I work on. It's not uncommon for us to cut out three or four cylinders on an i6. When you do it that way. It forces the injectors to work much harder than they would if you only cut out one.
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