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Old 03-28-2010, 02:10 PM   #1
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So confused, Header Temperature

Here is one for the experts!

I have an L98 with AFR 180's, Lingenfelter cam (74216), Accel high flow TPI, and ceramic headers. The car is running very smooth with no known issues. I it is a new rebuild with about 3 hours on the motor. When working on it the other day I noticed the passenger side headers were much cooler than the drivers side. The ceramic coating is better on the passenger side but I do not think that could cause the difference. The temperatures are posted below and reflect 5 minutes of idling. Like I mentioned, everything is running extremely well. All temperatures were taken with an infared heat gun at the beginning of the tube that connects to the head.

What could cause the temperature difference? What should the header temperature be and is a difference between cylinders a problem?

Cylinder 1: 170 F
Cylinder 2: 63 F
Cylinder 3: 240 F
Cylinder 4: 67 F
Cylinder 5 : 214 F
Cylinder 6: 63F
Cylinder 7: 178 F
Cylinder 8: 63 F

Thanks for your help!!!
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Old 03-28-2010, 02:36 PM   #2
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Re: So confused, Header Temperature

Although what the temp reading "should be" will vary from car to car especially since its not stock i cant tell you what it should be. However ide say that the ones that are only reading of 60s F seems too cool. Course ive never owned ceramic coated headers so maybe its actually the other side thats just too hot. What I can say is that one side is not right and my guess is its probably the cooler side as exhaust gasses are pretty hot lol. What would cause a difference in temp? Temperature is related to many things, primarily A/F ratio. Personally I would start by ohming out your injectors because it seems an entire bank of cylinders have issues.
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Old 03-28-2010, 06:37 PM   #3
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Re: So confused, Header Temperature

You might try swapping sides with the injectors or check the injector wiring grounds.
You don't have AIR injection tubes do you? and no exhaust leaks near the heads?

That does seem too cold.
Is the difference still there after a longer period of time?
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Old 03-28-2010, 09:29 PM   #4
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Re: So confused, Header Temperature

Thanks guys!

I do not have air tubes, just headers with the O2 sensor in the driver side header.

Unfortunately, I cannot drive the car as it is getting painted. All I can really do is let it idle.

Should I let it idle for a while (15 - 20 min) and then recheck temperature?

Thanks!
Josh
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Old 03-29-2010, 04:39 AM   #5
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Re: So confused, Header Temperature

I don't think letting it idle any longer is going to make that big of a difference. 5 minutes should've been plenty.
It's time to start looking into that bank of injectors.
My Jet-Hot headers weren't even that cold when I had a dead miss on 2 cylinders.
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Old 03-29-2010, 10:04 AM   #6
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Re: So confused, Header Temperature

Yea I second that, I really dont think letting it idle longer will make much difference. There may be some variations at first but they should heat up relatively uniformly as they did but differing bank to bank.
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Old 03-30-2010, 11:52 AM   #7
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Re: So confused, Header Temperature

Well, I looked into things a little more and the entire passenger side bank is not firing! The injectors are not running. I pulled out a plug and it was dry with very little carbon. Why would the injectors not work? If one injector is bad, will it cause the entire bank not to work?

Thanks for your help!

Josh
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Old 03-30-2010, 03:21 PM   #8
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Re: So confused, Header Temperature

Yes actually, commonly what happens is one injector has an intenal short and because all injectors are wired in parallel it shorts them all out. This can be confirmed by ohming out your injectors.
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Old 04-01-2010, 09:03 AM   #9
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Re: So confused, Header Temperature

The video below is what confused me! This is the engine running with only the driver side cylinders actually firing!

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Old 04-01-2010, 09:50 AM   #10
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Re: So confused, Header Temperature

Even with only 4 cylinders running it's still nearly 3 liters of displacement firing and a lot of momentum. If you drove it however, it would probably be apparently immediately that half your engine had gone missing.

I wonder if I could program an ECU to turn off half the injectors at a highway cruise and save some fuel.

EDIT: Nevermind, GM only managed a 5-7% increase in MPG on the Gen 4 small block with full cylinder deactivation, I doubt not fueling half the cylinders would provide significant gains in MPG.

Last edited by Saabster; 04-01-2010 at 10:00 AM.
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Old 04-01-2010, 12:43 PM   #11
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Re: So confused, Header Temperature

Actually not too uncommon. I had the exact same thing happen last week. We were measuring header temperatures and found a few cylinders that were much colder than the rest. We determined they were not firing. As for the idling, we did that too! I inadvertently left all of the plug wires off on the passenger side and started the car. It idled at 670rpm and sounded fine. I only noticed it when I got out of the car and saw the wires draped over the carb.
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Old 04-01-2010, 12:43 PM
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