We made the purchase in 2014 and according to the contract it says that it is a 6 cylinder. So I am going by the purchase agreement.
You didn't answer my question about what you're trying to achieve.
Arguably, you might have a valid claim for fraud/misrepresentation. In order to succeed, you would have to prove the following:
1. A false statement regarding an issue of material fact.
2. Actual or constructive knowledge that the statement was fault (i.e., the person making the statement knew or should have known it was false.
3. The defendant's intent that the plaintiff rely on the statement.
4. Justifiable reliance by the plaintiff.
5. Damages.
You apparently would have no problem proving the first two elements (except as noted below). I haven't read any Illinois case authority, but I assume the third element would be presumed.
The third element is where you start to run into problems. I do not agree that you had any obligation to investigate the status of the vehicle independently (by googling the VIN or otherwise). However, I find your statement that you "are going by the purchase agreement" a bit perplexing. If there was no representation regarding 6-cyl vs. 8-cyl until you got to the point that someone put a contract under your nose, then this probably wasn't an important issue for you. If you really cared about this distinction, one would expect that you would have noted the number of cylinders on the window sticker and/or asked the sales person. If I were representing the dealer, I would argue that, if you are relying solely on the contract, then you didn't really care, so this wasn't a material issue for you.
You also would have a potential problem with damages. As one of the prior responses mentioned, where a vehicle comes in both 6 and 8-cyl models, the 8-cyl version is typically more expensive. Therefore, you may have gotten an 8-cyl vehicle for a 6-cyl price, which would mean you suffered no detriment. On the other hand, 8-cyl vehicles typically get worse gas mileage and are more expensive to maintain, so this could offset that.
The other problem you have is the statute of limitations. According to a quick google search, the SOL for fraud in Illinois is two years, which likely starts when you did or should have discovered the fraud. Arguably, this should have happened no later than when you took the vehicle for its first oil change, which presumably was more than two years ago.
