unequal exhaust temps

[adiabatic]

My truck sounds rough at idle. It sounds like one cylinder is doing all the work of idling. So I got an infrared thermometer from NAPA and looked at each exhaust port in turn. Right before the gas enters the manifold.
#2 reads 94C, #5 reads 85C and the rest are at about 90C. Is this typical or do I have a pump problem? It is a reman pump BTW.
Then I raised rpm to 1500 or so, for a minute or two and rechecked. All were at about 91C. So any imbalance is worse at idle. Maybe the pump gurus can comment?

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1997 4x4 CC 5spd, CPL1553 pump, Horton fan, Sport headlamps, Optima RedTops, 98 shift levers and console, RS5000 shocks, Yaesu VHF radio, and BCT7 scanner in the overhead console... N7DAL.

 

[HEMI®Dart]

In TDR issue # 25 Scott Dalgleish mounted an EGT probe in each cylinder head exhaust port on his '98 12 valve truck. He was comparing the OE intake to the Banks TwinRam. He says that the engine was run at a constant RPM. What RPM is not stated. It must be up there. Here were his findings in degrees F:

Banks TwinRam:

Cylinder # 1-1264°
# 2-1248°
# 3-1216°
# 4-1216°
# 5-1248°
# 6-1216°

Stock:

Cylinder # 1-1296°
# 2-1272°
# 3-1216°
# 4-1248°
# 5-1264°
# 6-1232°

... ... The test results indicate that the stock setup has an 80° difference between the high & low cylinder temperatures. The TwinRam shows only 48° between the high and low, a decrease of roughly 60% in temperature differential. Morever, note that three of the cylinders are operating at 1216°, two at 1248°. Cylinder number one continues to slightly hotter (1264°) due to an accessory casting in the port of the head which causes a restriction of air flow to that cylinder... ... .....

adiabatic,

Although these are not idle exhaust temps, I'd say your numbers are not bad. Scott's # 2 Cylinder was hot like yours.


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Bill R
94 2500 SLT 4x4 5 Speed, 3. 54 LS, JRE 4" exhaust, Autometer Pyro, Boost & Water temp gauges, Bosch 215 HP injectors, Timing @ 14. 7º, JRE Stage III #4 plate 270/675, AFC spring kit, Scotty Air, Bully Dog Propane Injection, Roadmaster Active Suspension, Optima Red Tops, Geno's Exhaust Blanket, Espar Heater (won it!), Synthetic lubes throughout.



[This message has been edited by HEMI®Dart (edited 02-17-2001). ]

 

[illflem]

Could it be you aren't getting enough pressure from the lift pump at idle due to a bad pump or overflow valve?My fuel pressure at the IP reads 22# at idle and only changes with a load uphill or coasting down.

 

[Joseph Donnelly]

It is common for the injection pump to deliver slightly different amounts of fuel to the various cylinders at idle (and at full power for that matter)--slight imbalance. Airflow to the cylinders differs somewhat too. If you have a bad injector, cracking the line nut 1/2 turn will show which cylinder sin't doing its job. Be careful not to let the fuel spray onto you. The high pressure can inject it right under the skin and cause blood poisoning.