I was driving the car back home yesterday, when I felt a noticable "thud", that shock the vehicle. I would accelerate in hopes to clear what I thought was the problem. It seemed to work for the time being. I started it back up, let it run in park, and then neutral, but no sound. When I had it in drive (not moving mind you) it took a minute or so and that lovely "thud"/shaking of vehicle returned. It is intermitent, not continuous. I bring the vehicle up to 3,000 RPMs and no thud for a period of time. I feel like its part of the intake, but not sure. My buddy seems to think its the timing, that one of the cyclinders is firing to early, or late and it's "pushing" exhaust out. I am wondering if one of the spark plugs could be bad and it's not firing as it should. Any thoughts? I have been trying to look at the repair manual, and the RAVE, but not having a lot of success. Any thoughts?

 

CEL? Codes? It could be your drive shaft about to explode, your trans about to fall out or a dirty air filter. Give everyone some info about your truck and what kind of service has been done to it.

 

def need more information... but for future note, if you ever encounter a strange thud, thumb, vibration etc...never speed up or punch the throttle!!! gas off and roll to the shoulder and check the undercarriage, your driveshafts might be on thier way out, lose, debris suck under the car, or a piece of suspension etc... speeding up will only serve to make whatever it was FAR worse... even more so if its an engine related thud, more rpm = more energy = more stress = more problems.

 

Quit reading the Rave and get under the truck and hook to see what you can find.
Do Not start or drive it and send me your number, I'll call you in the morning.

 

Your problem is more likely under the vehicle if no codes. Things like misfires (bad plugs and wires) throw codes like beer cans on South Tryon. A careful inspection from below with a flash light, and engine off (we want you to live to tell us about it) is a good idea.

 

No codes what so ever. I had climbed under the vehicle while it was off, and everything seemed solid. I have had a transmission replaced because a u-joint gave way and snapped into the transmission. I have had a manifold gasket replaced, and replaced the power steering pump. I have not replaced the spark plugs. When it thuds, I can something at the intake manifold, near the throttle body that sounds like a pop. This sound only happens when it's in drive.

 

Well, sounds like you already had the big thud with the prop shaft taking the transmission out already. Did they replace the entire thing or just a new u-joint? Where was it fixed? Not to many things to make a real "thud" in the intake. This only does it in drive, correct? If you just rev with the hood open you don't hear anything?
If that is the case, it very well could be something transmission related. The only other thing I could think that would make a thud sound would be maybe a broken motor mount.
If there is a way to safely take a video so we could hear it, that could be helpful.

 

Perhaps a motor mount that was released to swap the transmission. If that is still under warranty, might have supplier check it. Also, you can inspect the rear motor mounts - see attached. A missing bolt could make things shift at a certain torque.

If happens underway, perhaps flex coupling at end of rear prop shaft (usually shows up as noise from rear).

The secondary air insection system has vac operated valves that allow air to be injected into the exhaust manifold system, at various conditions. Some of these parts are near the throttle body. Sorta works like an after burner to ignite the unburned fuel and keep EPA inspectors from sucking the tail pipe. But usually SAI problems are called a "tick". There is also a tick that can happen from the flex plate betwen tranny and flywheel (new tranny should have caught that also).

 

I am horrible at explain things. In the airintake manifold, you can hear a "tick", similar to an electric charge jumping from one post to another. This happens at the thud. I don't hear a thud. I feel it transmitted through the vehicle. I am going back under to look at the motor mounts, jack the vehcile up (putting it on stands, safety first) and going to put it in neutral and see if I can rotate the tires to feel anything. If it is the clutch plate, it would (probably not the right term) be slipping a bit, or allowing something to pass or skip by when it should be a smooth transition. This thud that I am feeling is happening when it is in gear, and stationary.

If it is the SAI system, would a late firing, to burn fuel, cause a "thud". The place that I hear the "tick" though is near the throttle/air intake. Does that make sense?

 

Perhaps you mean a backfire. That could make things shake. The tick sound could be bad plug wires allowing a spark to jump and cause a misfire. Try looking under hood at night, when totally dark, wih engine running, and see if you see any small sparks along the wires, coils. Would suspect check engine light would be on and codes stored for this.

The flex plate is not a clutch. It connects flywheel to transmission. You can search our forum for cracked flex plate and see photos. It can cause a tick, even while not moving, as engine is turning transmission.