Bump while cruising - misfire?

Alright so 2013 Roush, 97k, running 91. Cruising the highway I will get what feels like a bump but from what I can gather it’s a misfire. Only while cruising, doesn’t seem to be an issue while accelerating. No codes, but I only have a cheap scanner. Anyone else had this issue or have any advise on what course of action I should take to remedy this? Read a few misfire threads but nothing quite like this. Would like to avoid dealer if necessary.


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Is this something that has occured since you have owned the truck or something new?

B E N said:

Is this something that has occured since you have owned the truck or something new?

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Fairly new. Maybe 1000 miles.


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Have the plugs ever been changed? You are about due, also check the condition of the coils and boots.

I just had the exact same issue. I did new plugs, wires, and coil packs. Didn't solve it. Got the JDM tune and it disappeared.

I used Mode 6 test in FORScan to determine it was a multiple cylinder misfire usually 2/6 but only occurred at 1423 - 1489 RPMs.

Depending on belt tension, you may be feeling the ac compressor kicking on. I notice it on smooth highway while cruising with my procharged setup. Easy to test by just turning the climate off.

Blacktor said:

Depending on belt tension, you may be feeling the ac compressor kicking on. I notice it on smooth highway while cruising with my procharged setup. Easy to test by just turning the climate off.

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I’ll try this. I looked at the mode 6 data and I wasn’t getting any misfires really. I think the most I had was 4 in one cylinder on about a 45 min drive. From what I’ve read that’s pretty normal. Now thinking about it I do notice it more when I have the ac going.


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After some testing, this “bump” does only occur when the ac is turned on. If anyone else is having a similar feeling, get on the highway and then off the ac for a few minutes, then turn it back on and you should feel the “bump” within a few seconds. As stated above, I’m going to go with the ac compressor clutch engaging and thinking that this has to do with belt tension as my truck is supercharged. My brother has a stock 13’ and his does not do this. Belt was just replaced after I bought the truck so maybe after a while it will stretch a little and this will go away. For now, not worrying about it. Thanks to all who helped.


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I have a 30 mile round trip drive planned for the morning I’ll test the theory. I have noticed my bump came back. Thought it disappeared. Probably did for a while because I had the windows open and no a/c. I may have the wrong sc belt too. I went to a 72mm pulley. Will have to check on that as well.

Only experienced the bump with A/C on at cruise.