# Mazda runs rough **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** b4000, mazda\ **Created:** [January 12, 2010, 7:45pm UTC](https://community.cartalk.com/t/mazda-runs-rough/42384 "2010-01-12T19:45:19Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![sanblascamper](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@sanblascamper](https://community.cartalk.com/u/sanblascamper)\ **Post date:** [January 12, 2010, 7:45pm UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/1 "2010-01-12T19:45:19Z")
Truck idles smoothly but runs really rough when gears engaged. Have changed fuel filter, plugs/wires, fuel pressure. Injectors are new. Check engine light is NOT on. ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [January 12, 2010, 9:00pm UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/2 "2010-01-12T21:00:19Z")
How did the old plugs look? ---
**Author:** ![sanblascamper](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@sanblascamper](https://community.cartalk.com/u/sanblascamper)\ **Post date:** [January 12, 2010, 9:17pm UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/3 "2010-01-12T21:17:28Z")
All 6 plugs were clean with little wear and no deposits. I have also cleaned the MAF and checked for vacuum leaks, did not find any. ---
**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\ **Post date:** [January 13, 2010, 1:09am UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/4 "2010-01-13T01:09:04Z")
How about valve adjustment? Maybe a compression test is in order. ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [January 13, 2010, 2:36am UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/5 "2010-01-13T02:36:15Z")
Automatic or manual? ---
**Author:** ![sanblascamper](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@sanblascamper](https://community.cartalk.com/u/sanblascamper)\ **Post date:** [January 13, 2010, 7:52am UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/6 "2010-01-13T07:52:48Z")
Can have that done–installed new motor less than 5000 miles ago. Original engine damaged due to oil pump failure. ---
**Author:** ![sanblascamper](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@sanblascamper](https://community.cartalk.com/u/sanblascamper)\ **Post date:** [January 13, 2010, 7:54am UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/7 "2010-01-13T07:54:16Z")
Automatic ---
**Author:** ![hellokit](https://avatars.discourse-cdn.com/v4/letter/h/6a8cbe/32.png) [@hellokit](https://community.cartalk.com/u/hellokit)\ **Post date:** [January 13, 2010, 11:58am UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/8 "2010-01-13T11:58:02Z")
When you say, “Have changed…fuel pressure…”, do you mean you have measured fuel pressure with the engine under load;, or, do you mean that you ONLY checked fuel pressure at idle, or with the engine off? Whether, you did say that, or not, you need to. If you changed 6 spark plugs, the engine must be a 6 cylinder engine. Probably a V six, no? Is this correct? And the model year of your Mazda B400? ---
**Author:** ![sanblascamper](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@sanblascamper](https://community.cartalk.com/u/sanblascamper)\ **Post date:** [January 13, 2010, 12:57pm UTC](https://community.cartalk.com/t/mazda-runs-rough/42384/9 "2010-01-13T12:57:19Z")
Fuel pressure measured at idle with engine on