Fooled by a worn Transfer case

[Joe Marconi]

We had a 2005 GMC Yukon in the other day for a bucking problem under a load, particularly up hills. It felt like a misfire, but the engine had all the power in the world. Our initial thoughts were problems with a coil, plugs, wires, injectors, etc. But a scan of the computer showed no codes and the data looked normal. In fact, when the bucking occurred, the O2 sensors and fuel trim looked normal too. We checked fuel pressure and induced propane while the bucking occurred to rule out a lean condition, but the bucking did not change.

 

When you applied the brake while cruising the bucking would get a little worse, but with the vehicle stopped, you could not duplicate the bucking by applying the brake and applying the gas.

 

We road tested the truck again. When the bucking started we put the truck in Full Time 4X4 and the bucking stopped. Could it be something in the driveline? After driving the vehicle we could not get the truck to buck again, in or out of 4X4. The fluid in the transfer looked like mud and we suggested we replace it, which we did.

 

Has anyone ever seen or heard of something like this? Remember, even though the bucking felt like a misfire, the engine did not seem to falter. And, all data looked normal with no codes.

[DUFRESNES]

We had a 2005 GMC Yukon in the other day for a bucking problem under a load, particularly up hills. It felt like a misfire, but the engine had all the power in the world. Our initial thoughts were problems with a coil, plugs, wires, injectors, etc. But a scan of the computer showed no codes and the data looked normal. In fact, when the bucking occurred, the O2 sensors and fuel trim looked normal too. We checked fuel pressure and induced propane while the bucking occurred to rule out a lean condition, but the bucking did not change.

 

When you applied the brake while cruising the bucking would get a little worse, but with the vehicle stopped, you could not duplicate the bucking by applying the brake and applying the gas.

 

We road tested the truck again. When the bucking started we put the truck in Full Time 4X4 and the bucking stopped. Could it be something in the driveline? After driving the vehicle we could not get the truck to buck again, in or out of 4X4. The fluid in the transfer looked like mud and we suggested we replace it, which we did.

 

Has anyone ever seen or heard of something like this? Remember, even though the bucking felt like a misfire, the engine did not seem to falter. And, all data looked normal with no codes.

[DUFRESNES]

We also had 2005 GMC Yukon. When it came in it was making a horrible noise, scanned computer and retrieved PO300 random multiple misfires. Live data showed intermittent misfires on 4 & 5 &6 pulled plugs, wires corrosion on the wires, rec: plugs and wires, vehicle was very salt corroded. Engine oil full and proper, oil pressure was good. Engine noise was consistant with RPM and gear change. Best guess was flexplate is cracked. We would have to disassemble to be sure. After repairs it was nice and quite with 2 mounting ears on the bell housing cracked and broken due to rust and may have previous work, no codes and none pending. He stopped by about a month later. It was making some noises. We suggested he take it to our Trasmission shop, we use. He did and the owner called us and said the the flex plate was broken again. He did the repair and we paid him. When I went and picked up the flex plate to turn into for a defective part, it was a disaster cracked all over and broken. No one here had ever seen anything like it except for racing or reving up and dropping it into gear. The transmission shop said they could not find anything we had done improperly. He said there had been an updated one from the dealer. I feel it is going to happen again, don't know.

[CollinsAutomotive]

We also had 2005 GMC Yukon. When it came in it was making a horrible noise, scanned computer and retrieved PO300 random multiple misfires. Live data showed intermittent misfires on 4 & 5 &6 pulled plugs, wires corrosion on the wires, rec: plugs and wires, vehicle was very salt corroded. Engine oil full and proper, oil pressure was good. Engine noise was consistant with RPM and gear change. Best guess was flexplate is cracked. We would have to disassemble to be sure. After repairs it was nice and quite with 2 mounting ears on the bell housing cracked and broken due to rust and may have previous work, no codes and none pending. He stopped by about a month later. It was making some noises. We suggested he take it to our Trasmission shop, we use. He did and the owner called us and said the the flex plate was broken again. He did the repair and we paid him. When I went and picked up the flex plate to turn into for a defective part, it was a disaster cracked all over and broken. No one here had ever seen anything like it except for racing or reving up and dropping it into gear. The transmission shop said they could not find anything we had done improperly. He said there had been an updated one from the dealer. I feel it is going to happen again, don't know.

 

 

TQ converter problem more then likely.