Dale Earnhardt Jr lasted until lap 52 of 200 in Sunday's Pennsylvania 500 before a combination of cramp in his recently burned leg and a virtually undriveable racecar saw him reluctantly hand the controls of his #8 Budweiser Chevrolet over to relief driver John Andretti.

Earnhardt Jr, who started the 200-lap, 500-mile event around Pocono's unique 2.5-mile triangle shaped layout from 16th position, quickly dropped towards the rear of the pack when the race went green and fell off the lead lap before the first round of green flag pitstops.

Struggling to stay in the top 30 and with his left leg starting to go numb, the decision was made to place Andretti in the car during the races first caution period, which came on lap 52 when Scott Wimmer spun.

With much more time available to them before the pace car completed a full lap under caution, the #8 DEI crew took more than 80 seconds to securely strap Andretti in before sending him on his way, still one lap down to the leaders.

However the handling problem, which had caused Earnhardt Jr's early race slump, was worsening and with zero practice laps in the #8 car all weekend, Andretti was struggling to keep the car off the outside wall. Eventually the problem developed to such an extent that Andretti was unable to maintain the minimum speed mandated by NASCAR and was black-flagged.

Once the team had got the car back to the garage, the crew were able to diagnose the root of the problem as a loose front sway bar and despite losing a further six laps, Andretti was sent back out with a car capable of running at race speeds.

Thanks to Pocono's demanding nature, no less than 17 cars failed to finish Sunday's race, a factor that helped elevate Andretti into 25th position, where he scored 88 points for a disappointed Dale Jr.

"The car wasn't running too well," said a visibly upset Junior as he watched the race unfold from pit wall. "And I thought if we was gonna make a change, we should make it then. I could have run the rest of the way, but the car was so bad there really wasn't any use of me being in there wasting my time.

"(I figured) I should be out of the car trying to get better. I think I'll be able to go to next week's race without any problem."

With the burns on his neck at least looking better, Dale Jr also said that his legs were improving, but not quickly enough to complete 500 miles on what is a very bumpy track.

"The bumps hurt a little bit but my foot was going to sleep," continued Earnhardt Jr, who dropped behind Jeff Gordon to third in the points table as a result. "I haven't been using it a lot -- I haven't been standing on it much and it just goes to sleep and cramps up real easy.

"I'm just really disappointed that things are going like they're going. I wish that this thing would heal up a little faster, but it just takes time, I guess."

Earnhardt Jr also felt bad for Andretti, who was thrown in at the deep end and kept all four corners on the car in a difficult situation.

"We threw John in there and he ain't had a lap this weekend," continued Dale Jr. "The sway bar bolt was missing and the car was rolling over and spinning out on him, and I just hate it for him."

After watching the race for a while on pit road, Earnhardt Jr was then taken to the infield medical centre as a precaution for a check up.

"I hated to put Martin in that situation last weekend (because) I know the car wasn't that great. But I just didn't really have any business trying to run it and hopefully we'll come to Indy and be able to get through it."

"Once the Adrenalin dropped, I think the pain really started to set in and that why they (EMS) got him on the cart and took him out of there," stated team representative Jade Gurss.

"He hasn't complained about pain at all. The reason for the limp is like the muscles in his skin feel like they were tightening up. If you get a bad sunburn, it feels like your skin is shrinking. They (the burns) are healing as expected, but the feel to him is very much a tightness because he's got small burns above and below the knee. It makes it hard for him to flex his knee.

"The doctor feels that with his legs out in the seat, it's really not the position but the muscles going numb. The nerve endings apparently are what the doctor feels aren't getting the blood flow."