I would find out what he scared of or what he dislikes about the car. Is it the car itself, the sensation of being closed in, the movement when the car is being driven? Then work on whatever the problem is, with food.
As for food, I use raw duck and vegetables. And I hand-feed all meals, so I never have a problem with not eating/partially eating. I would also recommend hand-feeding for anyone who does have a dog with food issues.
Shredded chicken is good (as long as he doesn't have any reactions). But that and some kibble isn't a balanced meal. You may wish to look into a vitamin supplement, specifically something that has a focus on omega 3 (since chicken is high in omega 6), Vitamin C & the B vitamins (because if all he's eating is chicken and kibble, where is his source of vitamin C and the B vitamins?), zinc & copper (same reasons).
All the best.
EDIT: I just realized this thread is a year old and was bumped by what is almost certainly a bot.
