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I just bought my 04 srt4 88k miles a week ago and while trying to clean the cobwebs out i ran into a couple discrepancies. First problem I have is that I get like 80-100 miles to a tank around town then like 220 Highway, which seems odd. I have read several posts on here but didn't really get a clear answer as to why. What I was told when I bought it is that it has Seibens 1000cc injectors in it, a 93 performance tune and a punched cat. I know the injectors are for sure seibens, (idr how to spell it off hand) but unsure of the size of them don't know whether or not it has the 93 tune or not and the cat is for sure punched. He claimed 264whp and 304 tq which I also don't know whether hp and tq numbers matter in my case or if it's even true. And, every 30 miles or so the CEL comes on for 02 sensor. My question is, would this cause my terrible city mileage. And it doesn't matter if I'm putting around or hard in the boost around town it's still around the same mileage, 80-100 to the tank Now my second cause for concern is a shudder mainly when I'm in 4th gear under light acceleration no acceleration and deceleration. Once I slow down enough it goes away .Braking in and of itself doesn't change the shudder, but it does go away when I slow down below 30 or so. I have no issue at all with gears or the clutch, no grinding, no pops, all gears shift flawlessly, clutch feels amazing, but at around 30-45 mph or when I shift into 4th gear just cruisin' around I get it and I can only describe it as feeling like I'm on a rough road, fresh grated road or maybe like a flat tire, All my tire pressures are an equal 34 btw and the shudder is through the entire car, but it feels like it originates from the back. Now when I'm hard in the boost I don't notice a vibration/shudder at all through any of the gears. I got it up to 120 today and smooth all the way up and back down. Any help on these would be much appreciated. I don't want to go on a wild goose chase. I don't know where to start and this is the 1st srt4 I have ever owned or even ridden in for that matter. Thanks.
 

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When your gauge shows the fuel is low and you go fill up, how many gallons are going in?
 

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Discussion Starter #5
am i reading 30mph in 4th gear right?

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When I'm just cruisin casually around flat areas in my city, I'll shift into 4th at 30-35 or so. So to answer your question, yes. However I tested it today and the shudder is also there in 3rd as well at 30-45 mph, then goes away. So it seems like it is speed dependent. However In second at 30 mph I'm in the boost and when I'm in the boost, I don't notice it at all.
 

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When I'm just cruisin casually around flat areas in my city, I'll shift into 4th at 30-35 or so. So to answer your question, yes. However I tested it today and the shudder is also there in 3rd as well at 30-45 mph, then goes away. So it seems like it is speed dependent. However In second at 30 mph I'm in the boost and when I'm in the boost, I don't notice it at all.
I would check the cv joints, and associated components, if it does it in all gears then its got to be something in the driveline.

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Welcome,

The cars didnt have great gas mileage stock so adding bigger injectors and power isnt helping that. It still seems low but your highway isnt really that far off. It runs at like 2700 in 5th at 70mph.

First thing I would suggest is buying yourself a handheld DSP for tuning, find a quality tuner, send your tune file in and have them check it out. You also need to figure out exactly what your mods are, especially fuel pump. If you have those injectors then its probably E85 capable or has had E85 at one time. So maybe the tune needs work and you can have it tuned down to 91 which will help you on gas mileage. If you can still contact the seller I would double check w them and ask who tuned it, what other mods it has, what they think the issue could be.

As far as your shudder goes - it could be drivetrain related or tune related. I had a major issue w a sticky brake caliper that I couldnt figure out, it only was noticeable on very smooth roads. Everything pointed to a bad axle. So a few possibilities there.
 
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