The exhaust manifold temperature on cylinder 1 and 2 (passenger and driver front) appear to be 50 degrees colder than 3-8 (which were measuring about 325F).

Temperature readings were taken after a 15 minute drive using an infrared thermometer. The truck had been idle for a few days prior to starting and I let the truck warm up for a few minutes before driving it.

Do the fronts typically measure colder or is this yet another indication that my injectors (at least 1 & 2) need to be replaced.

Thank you.

 

Two things to consider:

The style of the manifold lends itself to exhaust gasses from "upstream" cylinder exhaust ports to, for lack of a better word, "contaminate" the temperature readings of downstream manifold ports. If the manifolds had more distance between the port mating surface and the "log", then you'd see less variance (hopefully if things are working properly).

How many cylinders are upstream of #1 and #2?

 

Wait, I know this one. Just give me a minute.

Just wondering why you're measuring the front two cylinders on the passenger side, but the front and read cylinders on the driver side? A strange way to compare things.

You should probably run it longer and make sure the engine is up to full operating temps and has been for a few minutes before you take a reading.


What do you mean another? What other indications do you have there is a problem with #1 & #2?

 

If this is a trick question, I'm not knowledgeable enough to understand. As far as I know, I've got a stock exhaust manifold. As far as "upstream", I was measuring the forward most point on the exhaust manifold and calling that #1 or #2. In my mind, there are no ports upstream of 1 & 2.

 

I pointed the infrared thermometer at all 8 points on the exhaust manifold that I thought were associated with exhaust points. My understanding is that all eight exhaust ports should (if all is well) produce the same temperature (although cleatus has me thinking about the "temperature contamination" from upstream ports). I assumed if I found a point on the exhaust manifold with a lower temperature (as I found), the associated injector was not injecting as much fuel into the cylinder as the others.
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Not necessarily just 1 or 2 but I've got noticeable knock (especially when cold) on injectors that I believe have 235,000 original miles.

 

pull the valve covers and retorque everything before they bounce around too much,they can break apart at the tip,if they are tight check for puking oil out of them

 

You could do a cylinder contribution test.
If those two are indeed running cold, it will show up in that test.

 

I have dual EGT gauges, and there has been a see-saw with a temperature drop on one side and the other (they used to match). #7 was reading low (everything is upstream from that one), so I swapped it to the #2 position. The EGT gauges flip-flopped on which was high and low. The difference is about 50 - 75 degrees on the highway, and #2 is about 50 degrees cooler than the other 7 while idling.


I'm not disputing anybody here, I'm just sharing my observations.


I had air in my fuel, and I believe it may have done some small amount of damage to #7. It's not dead, it's just no longer balanced.

 

Why don't you remove the valve covers and watch the oil discharge from each injector when cold? That can tell you if you have injectors that aren't firing right when cold.

And you understood Cody's post correctly. The back end of the manifold is also heated by the upstream cylinders.