# Mis-firing cylinder **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** chevrolet, 1500\ **Created:** [December 20, 2009, 7:14pm UTC](https://community.cartalk.com/t/mis-firing-cylinder/41048 "2009-12-20T19:14:07Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![JonSchmitz](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@JonSchmitz](https://community.cartalk.com/u/JonSchmitz)\ **Post date:** [December 20, 2009, 7:14pm UTC](https://community.cartalk.com/t/mis-firing-cylinder/41048/1 "2009-12-20T19:14:07Z")
Feb 11, 2009 - replaced intake gasket and water pump due to antifreeze leak Feb 14, 2009 - travel 220 miles round trip - notice motor missing (when going down hill only). Check engine light on Feb 17, 2009 - #3 cyl missing - replace all plugs, wires, distributor cap and fuel filter Continues to miss #3 cyl.(only when going down hill). Check engine light on intermitently. Mechanics baffled, problem ongoing for months. Twice replaced #3 plug only to fowl again Nov 4, 2009 - replace fuel injector #3 cyl. Continues to miss on #3 when going downhill typically @70-80mph steeper grade more noticable. Nov 11, 2009 - replace all fuel injectors. No change ---
**Author:** ![UncleTurbo](https://avatars.discourse-cdn.com/v4/letter/u/e9a140/32.png) [@UncleTurbo](https://community.cartalk.com/u/UncleTurbo)\ **Post date:** [December 20, 2009, 7:18pm UTC](https://community.cartalk.com/t/mis-firing-cylinder/41048/2 "2009-12-20T19:18:38Z")
Was a compression check done on cylinder #3? Is it fouled with gas, or oil? I think you have bad rings that is letting oil blow by the rings into the combustion chamber when the motor is providing engine braking as you go downhill. ---
**Author:** ![JonSchmitz](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@JonSchmitz](https://community.cartalk.com/u/JonSchmitz)\ **Post date:** [December 20, 2009, 7:20pm UTC](https://community.cartalk.com/t/mis-firing-cylinder/41048/3 "2009-12-20T19:20:27Z")
fuel - compression is good ---
**Author:** ![UncleTurbo](https://avatars.discourse-cdn.com/v4/letter/u/e9a140/32.png) [@UncleTurbo](https://community.cartalk.com/u/UncleTurbo)\ **Post date:** [December 20, 2009, 7:34pm UTC](https://community.cartalk.com/t/mis-firing-cylinder/41048/4 "2009-12-20T19:34:32Z")
When coasting down a hill the fuel to the injector should be shut off. No fuel should be getting to the cylinder at all. Just guessing now, since new injectors isn’t taking care for this so it must be the fuel management system is telling that injector to feed gas. Can you try a different known good main computer to see if it is your trucks computer? Otherwise you may have a wiring fault, bad connector or bad ground for that injector. ---
**Author:** ![oldschool](https://avatars.discourse-cdn.com/v4/letter/o/e19adc/32.png) [@oldschool](https://community.cartalk.com/u/oldschool)\ **Post date:** [December 21, 2009, 1:40am UTC](https://community.cartalk.com/t/mis-firing-cylinder/41048/5 "2009-12-21T01:40:50Z")
I read of a knew to me cause of a misfire, it happens when ALL the EGR gases are dumped into one cylinder, this can happen when passeges are plugged. Not saying this is the cause for you, but it was interesting. ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [December 21, 2009, 1:55am UTC](https://community.cartalk.com/t/mis-firing-cylinder/41048/6 "2009-12-21T01:55:35Z")
What did the fouled spark plug look like? Did it look like one of these? [http://www.ngksparkplugs.com/tech\_support/spark\_plugs/faqs/faqread.asp](http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp) WHAT are the trouble codes? P0303, etc?