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Username Post: Hot and cold cylinders?        (Topic#351907)
Xray Tedd 
Silver Supporting Member
Posts: 85
Xray Tedd
Age: 34
Loc: Missouri
Reg: 12-20-14
07-06-18 06:32 PM - Post#2739234    

As you may have seen, I have the TPI swapped 87 K5 blazer. I'm still trying to iron things out. One of my issues is (based off the header tube colors) I may have a hot cylinder on #3 and a cold cylinder on #5. I've pulled both plugs and they both look identical in coloring. Both are what I would consider an ideal brownish/tan.
Anyone have any thoughts on this?


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Shepherd 
Frequent Contributor
Posts: 1509

Loc: Lake George, NY
Reg: 11-11-15
07-07-18 08:05 AM - Post#2739272    
    In response to Xray Tedd

Check the tube temps with a infrared thermometer, compare the suspect cylinders to the others, see what you have.



 
gchemist 
Senior Chevytalk Moderator
Posts: 24503
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-08-18 10:38 AM - Post#2739355    
    In response to Shepherd

I agree. Use an infrared thermometer and check each cylinder. If they are within a few degrees, the problem is header coating. All the header will eventually turn that color. I went with ceramic coated headers on my ZZ4.

Are you using stock spark plugs? What's the gap size?

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
Xray Tedd 
Silver Supporting Member
Posts: 85
Xray Tedd
Age: 34
Loc: Missouri
Reg: 12-20-14
07-09-18 06:24 AM - Post#2739439    
    In response to gchemist

The plugs are the Accel R45TS. I have them gapped to .045. I'll have to pick up an IR reader. What temp range should I be looking for? Lowe's has one for $25 but it only goes up to 600*. Would that be high enough?



 
gchemist 
Senior Chevytalk Moderator
Posts: 24503
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
07-09-18 07:26 AM - Post#2739443    
    In response to Xray Tedd

I'm not sure. Let me move your post to the Performance Section. Performance Board users can provide better information.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles


 
Junkyardwarrior 
Contributor
Posts: 331

Loc: Yuma AZ
Reg: 02-25-15
07-09-18 07:33 AM - Post#2739445    
    In response to Xray Tedd

Last time I hit my headers with IR I was looking at about 730 on a small block.

"8 cylinders of why the f&@% not" - me


 
Shepherd 
Frequent Contributor
Posts: 1509

Loc: Lake George, NY
Reg: 11-11-15
07-09-18 09:14 AM - Post#2739456    
    In response to Xray Tedd

The actual temp is not point when it comes to looking for a dead cylinder, it is the comparison to the others. Say 6 of the exhaust header temps read at the same point on the pipe are 350, and the other 2 are, say, 250 or lower, that's a problem. Btw, the 600 IR is fine.



Edited by Shepherd on 07-09-18 09:15 AM. Reason for edit: No reason given.

 
Xray Tedd 
Silver Supporting Member
Posts: 85
Xray Tedd
Age: 34
Loc: Missouri
Reg: 12-20-14
07-09-18 09:27 AM - Post#2739461    
    In response to Shepherd

Awesome! Thanks guys. I'll pick a reader and report back with my findings. I did take it for a 20 min spin this weekend and then pulled the #1, #2, and #3 plugs. They appear to have leaned out more than I'd like but all three are still consistent in appearance. I got my fuel pressure gauge for my fuel rails in the mail Saturday. I'll get that put on and bump my pressure up a little. Before I was renting the pressure gauge from the Auto Parts store @ $134. So I was always trying to get it returned as quick as possible. I can mount my GoPro under the hood and do a live feed to my phone. That will tell me my fuel pressure while under a load in normal driving conditions.



 
Rick_L 
Honored Member
Posts: 27501
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
07-09-18 03:22 PM - Post#2739485    
    In response to Xray Tedd

Why do you want to bump the fuel pressure? On a TPI, it should be 43 psi. The ecm calibration is based on that. Don't vary it. If you are using the O2 sensors, bumping the pressure won't richen it anyway except at WOT, because the ecm controls that in real time using the O2 sensors.

Some variation in exhaust temperature, especially at idle, is pretty normal. A dead cylinder will show up quickly.



 
aghaga 
"4th Year" Silver Supporting Member
Posts: 2169
aghaga
Age: 64
Loc: Altavista, Va.
Reg: 07-05-08
07-09-18 05:59 PM - Post#2739504    
    In response to Xray Tedd

Where is your PCV hose hooked to? Carb or intake manifold?




 
Xray Tedd 
Silver Supporting Member
Posts: 85
Xray Tedd
Age: 34
Loc: Missouri
Reg: 12-20-14
07-10-18 11:21 AM - Post#2739573    
    In response to Rick_L

  • Rick_L Said:
Why do you want to bump the fuel pressure? On a TPI, it should be 43 psi. The ecm calibration is based on that. Don't vary it. If you are using the O2 sensors, bumping the pressure won't richen it anyway except at WOT, because the ecm controls that in real time using the O2 sensors.

Some variation in exhaust temperature, especially at idle, is pretty normal. A dead cylinder will show up quickly.



I needed to bump the pressure back up to 43. It was set around 40. Can you elaborate a little more on the dead cylinder?




 
Xray Tedd 
Silver Supporting Member
Posts: 85
Xray Tedd
Age: 34
Loc: Missouri
Reg: 12-20-14
07-10-18 11:23 AM - Post#2739574    
    In response to aghaga

  • aghaga Said:
Where is your PCV hose hooked to? Carb or intake manifold?




The PCV is connected into the intake manifold. The CCV is hooked to the throttle body.



 
aghaga 
"4th Year" Silver Supporting Member
Posts: 2169
aghaga
Age: 64
Loc: Altavista, Va.
Reg: 07-05-08
07-10-18 05:44 PM - Post#2739618    
    In response to Xray Tedd

Connecting the PCV directly into the intake manifold will cause a lean condition in the port that it is connect to.



 
Rick_L 
Honored Member
Posts: 27501
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
07-10-18 06:44 PM - Post#2739628    
    In response to aghaga

TPI should have a port in the plenum to connect the pcv which won't affect individual cylinders.

What I meant by the "dead cylinder" is that it will be really cold compared to others.




 
Xray Tedd 
Silver Supporting Member
Posts: 85
Xray Tedd
Age: 34
Loc: Missouri
Reg: 12-20-14
07-10-18 07:35 PM - Post#2739638    
    In response to Rick_L

The only vacuum port on the lower manifold had the PCV plugged into it from the factory. Should I change that? My brake booster is plugged into the back of the plenum. I have an IR gun in the mail. It'll be here Thursday so I'll get some readings then.

I really appreciate all the input. Thank you guys!



 
Xray Tedd 
Silver Supporting Member
Posts: 85
Xray Tedd
Age: 34
Loc: Missouri
Reg: 12-20-14
07-13-18 10:00 AM - Post#2739864    
    In response to Xray Tedd

I got a chance to get some readings last night. The weather has been a scorcher here in the Ozarks lately. So #s 2,4,6,& 8 are all +/- 10* of each other about 395*-410*. #1 and #7 fall in that range as well. #3 was reading 445* and #5 was reading 388*. So I guess they aren't as far off as they appear in color. I'm wondering if #3 got hot during break in and has since toned down while fine tuning was being done. I don't know how much it matters that there is an inconsistency in those 2 cylinders, but I feel better that it's not as bad as I was imagining.

Is this as good as it's gonna get, or is there anything else I can do/check to get them closer?

I do have what I believe to be a slight vacuum leak. But my brake booster has gone bad since I broke in the engine. The vacuum gauge reads a few lbs less than ideal and there's a very slight idol surge. I'll check the vacuum again once I get the booster replaced.



 
Rick_L 
Honored Member
Posts: 27501
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
07-13-18 12:17 PM - Post#2739876    
    In response to Xray Tedd

The temperatures may change once you fix your vacuum leak but the range of temperatures you posted is closer together than most engines.

I'm sure these temperatures were measured at idle, which also makes them kind of meaningless in the big picture. They really need to be checked at a higher rpm under load. About the only way to do that is on a dyno.

Checking at idle does tell you if you have a dead cylinder but you don't really need a temp gun for that.




 




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