Left this morning, got on the highway, and at about 80, I started hearing an awful sound and seemed to lose power. Turned around, went back home while trying different things to see what set off the sound. It turned out that it's entirely speed-related, and the RPMs or which gear I'm in have no effect on it. It's a metallic clanking sound coming from the rear of the car. I took a short video of it to better show how it sounds:


I first thought it might be the u-joints; however, they appear to be fine, and if it was the u-joints I can't see how that'd lead to a loss in power. My second thought was detonation, but that wouldn't explain why it is 100% dependent on speed; I can rev it to 7000 no problem, but once I get up past 60 MPH, that's when the sound starts. And it's over 60 in 3rd, 4th or 5th; again, the gear makes no difference.

Any ideas?

 

1985 RX7
If you don't remember this Important Info about your car,then I can "somehow forget" to post your Thread.
Best to get as much info into your thread so you can get prompt replies to your Problem.

 

It's a 5 speed RX7 GS with 120k miles and the 12a engine.

 

Anyone? This is my daily driver and I don't want to drive it; in fact, I can hardly drive it at all. Once the sound starts, my power just nosedives and I can't really get the car above 60 MPH.

 

id say maybe your fuel pump is acting up maybe, loose under the car, or bad connection. idk, there not much in the rear and nothing would would cause a power loss. besides that. maybe check the relay.

 

sounds like a heat shield, but probably unrelated to the power loss.

I had a driveshaft that would cause a gradual vibration increase until I couldn't take it felt like the car was going to shake itself apart. Your problem occurs suddenly right?

 

I have had a bit of a vibration for a little, but it doesn't get worse when the sound starts or anything, nor has it gotten any worse at all in the year and a half I've had the car. I can't quite track down what's causing it, but it's also not severe enough for me to be too concerned when compared to other things I've had to deal with.

As for the loss in power, I guess it's possible that the sound just spooks me into rolling out of the throttle unintentionally, though I swore I tried to keep the gas in. I'll check the heat shield tomorrow. If it's something that simple, I'll feel equal parts dumb and relieved.

 

Jack the back of the car, throw it on some jack stands and start looking around. (my laptop speakers kinda suck so I can't clearly make out the sound.)

Grab your wheels top and bottom check for play, do the same side to side. check drive shaft bolts, control arm bushings, pinion bearing on diff and drive shaft for looseness and play.

Gotta start looking somewhere.

 

The heat shields are definitely fine. I did find a bit of an exhaust leak; I'll patch it, but I don't think it's the root of my problems.

I also pulled the front trailing spark plug. It looked like this:



It was also wet with gasoline.

I then pulled the front leading plug, which looked like this:



I didn't think what was going on was engine-related, but now I'm not quite sure of that. These plugs are less than a year old, too.

 

I also think you should start at the back of the car. If the noise is speed related, not RPM related, it should come from the wheels. Maybe it has to do something with the brakes, or the differential.

My personal guess is that you have some resonance there with something being loose. I write this, because if you have resonance problem, it is not enough to find the looseness, you also have to find the source of the resonance that is much more difficult.

George

 

I replaced the plugs and the sound stopped. I still don't know why it was speed-related, but I do now know that the sound and lack of power was being caused by detonation. Which is a very bad thing.

On the other hand, at least now there's a video of exactly what detonation sounds like, so if anyone hears something similar in the future and can't figure out what it is.

 

wow. glad you got to the bottom of it all. it probably wouldn't hurt to double-check and make sure both your timings are set correctly.