My G35 has around 115,000 miles and it slows down when driving, particularly when driving uphill. RPMs reach 2-3 and car begins to drag with an occasional jerking. I’ve replaced all spark plugs (don’t think I’ve ever replaced them since I bought the car used with 40,000 miles) and I notice one of the coil packs and its spark plug was oily, but then I also notice it was not connecting to the spark plug like the rest the rubber tip was ripped. I replaced the coil pack, but the issue still exist. I just got back from a test drive and this time it doesn’t lose speed so much, but still trembles, especially when going uphill.
Has the fuel filter ever been replaced since you’ve owned the vehicle?
If not, that’s where I’d start.
Tester
Are you the car’s original owner? Was this vehicle subject to the VOLUNTARY RECALL CAMPAIGN for engine sensor (Crankshaft Position Sensor, Camshaft Position Sensors, and in some cases the Variable Timing Control Sensors) replacement?
I see according to a 21 page 12/19/2003 Technical Service Bulletin that 2002-2003 Infinity models, including some (all?) G35 vehicles were involved.
The service was to correct a defect that could result in engine stall or reduced engine power.
CSA
What exactly is the engine doing when you’re at 2-3k rpm? Is it then stumbling and you see the tach drop, or does the tach rise faster than you think it should based on how fast the car is accelerating?
@Tester I’ve never replace the fuel filter. Is that the same as the fuel pump (cause the pump is pretty expensive, $300+) Don’t what to dive that far if it’s not the issue.
@“common sense answer” I am not the original owner, I got the car at 40,000 miles. I’ll look into the recall. Thanks.
@shadowfax When it reaches 2-3k rpm, it starts slowing down and if I push it the car will do rapid jerk, I quickly let go of the gas and it stops.
I spoke to a mechanic yesterday and he tells me based on the information I provided that it could very well be the catalytic converter, but he would have to find out which one. If that’s the case I plan on doing the work myself. I just have to figure out which side. Parts of very expensive on these type of cars, smh.
There’s a cat back pressure test that might confirm if the cat is involved or not. If I suspected a bad cat on my car I’d probably temporarily remove or bypass it and see if that helped or not. That way you’d know for certain if the cat is involved. It certainly could be, based on the symptoms.
When you are driving uphill and accelerating that is causing the engine to take in as much air and fuel as quickly as possible and expel as much exhaust gas through the cat and muffler and out the tailpipe as quickly as possible. So anything in that pipeline slowing the flow could be contributing. I’d be suspicious of that ignition wire problem you note too, and would fix that just to make sure it isn’t contributing. It has to be done anyway if you want a reliable ride.
The only other guess I can come up with is the torque converter lock-up function is malfunctioning. Ask your shop if it is possible to temporily disable that function, might provide a clue.
I agree with the fuel filter suggestion by Tester. After that I’d suspect failing fuel pump or clogged exhaust.
A fuel pressure test could be performed and the easiest way to check for a clogged exhaust is with a vacuum gauge. The latter is cheap and easy.
Fuel filters should be changed regularly as a partially clogged filter can lead to premature pump failure.