What does it mean when one or two headers tubes are hotter than the others?

[greeneon01]

I recently changed out my engine (with a used low mileage motor from a salvage yard). It runs good but still doesn't seem quite right. Still seems to have a little miss/vibration I can't pin down. Also I noticed my new headers are discoloring unevenly. One tube has turned almost brown, one is yellowish and the other two are still chrome. I haven't taken a temp gun to them. To make sure it wasn't just a cheap header issue and not really a temp issue....i quickly touched them by hand(with gloves on lol)..the brown tube is much hotter than the rest.

What's causing that? Vacuum leak? Bad injector?

[CyborgGT]

A miss could give you a "dead" cylinder, and therefore not fire into that header tube. Could be a weak or no spark cause by a bad plug wire or dizzy cap contact for that cylinder. Looking at your plugs would also tell you if a cylinder is running noticeably more rich or lean.

https://www.ngksparkplugs.com/about-...d-a-spark-plug

Injectors are less likely to be a problem, but a failure there could still definitely happen on an old engine. No fuel means no ignition and no hot exhaust. You could try putting a simple injector cleaner fluid into your gas tank to see if there's even a slight improvement from that.

[lbus9168]

Let me guess, it's the two outer tubes?

They discolouration due to oils from your hands.

Run your hands over the center ones. You'll get even discolouration.

[CyborgGT]

Wouldn't that show up as obvious finger/hand prints though?

[lbus9168]

I remember reading about it somewhere. If I can find the article I'll post it here, it's basically to do with the exhaust manifold itself being unclean, causing a higher rate of colour change which is due to oils that come from hands as well as manufacturing.

[deevergote]

Pictures would probably help a great deal.
Stainless steel header discoloration is common, and it is usually due to the metal having oils from your hands on it, as lbus9168 said. I have never heard of any instances where the individual runners discolored unevenly due only excessive heat from their respective cylinders... but I can't say that it would be impossible. If your engine seems to be running properly, and your spark plugs show no sign of a problem (white, flaky tips from detonation, or black, fouled tips from improper ignition) then it's likely just the oils on the tubes causing discoloration. It's irreversible, unfortunately (to my knowledge, anyway), but it's harmless.
If the plugs show signs of trouble, then it could potentially be due to excessive heat or a lack of ignition in a cylinder or two. That would PROBABLY be noticeable, though. Even for someone that isn't terribly experienced with cars, I'd think.

[greeneon01]

I apologize for sounding dumb....but not sure how to load pics on here. Don't have a pc....and not sure how to load a pic from my phone.

I do know that oils aid in the discoloration, but the respective cylinders reflect their temperature. The darkest color is by far the hottest. The ones that are most chrome colored still are the coolest. I havent taken temp readings but I will tomorrow.

Ive checked spark on all cylinders with an inline tester and everything was good. Also has new ngk plugs and fairly new wires,cap, rotor (about 5-8k miles on them). I did pull the plugs the other day. The two hot cylinders were a little white, while the cooler cylinders did have a very slight black buildup starting. Btw....hot cylinder is #3,#4 is second hottest,then #2 and #1 being the coolest.

The motor is used but I did pull it all apart besides the short block and check and re gasket everything.

It's timed right, starts up easy. Seems to have good throttle response. Have driven it around a small parking lot with no issues. Doesn't seem to bog down any but just doesn't idle or sound quite like it used too. Feels like a miss or something. It also has older gas in it which I know makes a difference but with the exhaust temps like they were it has me worried a little.

[greeneon01]

Ok checked the temps today with an infared temp gun. Temps are as follows:

#1: 116 degrees
#2: 118 degrees
#3: 243 degrees
#4: 215 degrees

Are #3 and 4 ok...and just dead #1 and 2 cylinders?

[lbus9168]

Wow, is that in Fahrenheit? And how long had the car been running for before?

It could be that the thickness/quality of metal used in your headers are different sizes if it's just a cheap eBay knockoff. It could be alot of things. If it runs perfectly then I'm still not sure it's actually an issue.

Edit: could be head gasket, if two are significantly colder you could be running coolant through that.

[greeneon01]

Yes thats Fahrenheit. Car had been running almost 10 mins.

It doesn't run perfect at all. Pulled number one plug wire off and barely made a change in engine. Pulled number 2 and made a little more difference but still ran fairly close to what's its been....on 2 cylinders. But I know I have fire to those cylinders....so I'm either not getting fuel to the cylinders or they are low compression...I think?

Gonna check compression tomorrow and see.

Head gasket is Brand new and oil is nice and clean still.

[lbus9168]

Let us know the compression results. Maybe you have blocked injectors, if you're getting spark.

[GhostAccord]

Interested to know what you are getting for compression numbers.

What do your spark plugs look like?

[greeneon01]

Plugs are new. The colder cylinders do have a very slight black build up. The other two look normal maybe just a little white. I'll post the compression readings tomorrow

[greeneon01]

And the plot thickens...

Compression test was great. All cylinders between 148-150psi.

Checked resistance on all the injectors and they are good. 2.1 ohms on all four.

Checked resistance on plug wires. They're good. Between 6-9k ohms....under the 25k ohms specs in the repair

Rechecked spark plug gap....good at 0.40

Only thing I can think of is clogged fuel filter or fuel rail not feeding enough fuel to the end cylinders(#1and #2)??????

[lbus9168]

Maybe it's time to get the injectors flow tested, if you haven't already. That's pretty confusing. At the very least it looks like the issue doesn't mean needing to pull the motor apart again!