4th gear WOT weirdness
 

So here's the deal:

Sometimes I hear a noise from the intake around 5k rpms when I'm at wot in 4th gear. It's hard to describe exactly, kind of a vibration/stutter type noise (loud) and usually accompanied by a noticeable hesitation. If I ease off the throttle it goes away (both the noise and the hesitation). It doesn't happen if I go through the rpm range at partial throttle and it hasn't happened in any other gear. Could it be my afm acting up somehow?

Here's a little background info:

90 na, bonez intake, custom airbox, rp catback, and just swapped in an engine w/approx 20k on it (short block) with all new gaskets/hoses and cleaned injectors. I don't remember this happening with the old engine.

Any ideas?

Dave

Sounds like detonation to me....odd for an N/A.

detonation ..
 

yeah, I thought the same after doing some searches. Can't find much about detonation on an N/A though (with stock ports anyways) .. suppose I could jump up to 89 (fuel) and see if that helps.?

Dave

That would be the first thing I do. Do you use oxygenated gas? I have had many more detonation problems with oxygenated gas than with regular gas, regardless of grade. Another thing you can do is check the timing...it might be overly advanced.

regular unleaded .. 87 octane
 

is what I have used since owning the car (3 years). I just filled up this morning so I think I'll grab some octane booster tonight. We set the timing when the engine was swapped (CAS was initially misaligned) so it should be okay. Will definitely check it again though. Thanks man, I just got her back on the road .. don't even want to think about another dead engine! :)

That's about where the intake VDI opens - you can hear the intake in 4th at WOT? Man, all I hear is exhaust.

I'm sure your headers have nothing to do with that. ;)

The RP system sounds good (ie louder than stock), but this noise is definitely audible. Which is a good thing if it really is detonation.

4th gear at 5k RPMs? I can sure as hell hear my intake. Makes a nice swooshing sound, sometimes passengers say "are you SURE this is not a turbo?" :D

I checked the plugs and wires this morning and all appears to be okay there. They're in good shape and the wires are hooked up correctly.

Anyone else have ideas? Could a bad afm play any role in this (I don't think mine's bad but just trying to cover all bases)?

I have the same problem with my 94's RX_7 in fourth gear?????? at around 4K at WOT in fourth gear, sometime I can heard a strange bbbrrrruuuuuppppppp.........

This also happens to me sometimes. I've noticed it in 3rd gear at WOT. If I let off the gas when I hear it and step on it again, the sound is gone.

Heres info on my car:
'87 n/a. Intake, headers + presilencer, exhaust, lightened flywheel, wire open actuators.

I hope someone can tell us what causes this sound/loss of power.

Mine made a strange sound like that when i had the 6 ports wired open.

Yea ive noticed that somewhat also. It happens when im in fourth and it sounds like a rattle coming from the transmission, could it be detenation?? The peddle can be pushed down over 1/2 way and it'll do it but I dont notice any hesitation. It sounds like somethings loose, im not sure. Ive been wondering if my cars been detonating for about 2 weeks now. it makes an odd pop corn popping noise at idle (which some would describe as a tell tale sign) but it also might be from the exhaust, which is leaking everywhere.

anyone?

update
 

I'm positive that what I experienced was detonation. I gave my old (blown) engine to a friend to tear down, and he said he has seen signs of detonation on that one as well. Not good. However, I've not experienced it again. Since that time I have:

reset the timing (it was slightly advanced .. like a degree or two), jumped to 89 octane gasoline, run injector cleaner (techron concentrate) with a full tank of gas, and I'm about to change the plugs.

Detonation is far more common on turbo cars, but I am positive its something we n/a guys have to watch out for as well. I am not about to lose another engine so the little extra expense for 89 octane is worth it. I also have a suspicion that my AFM is to blame and once I find another one at a decent price (anybody willing to help me out? ;) ) I'll swap that in.

I'll keep you guys posted but definitely check it out before it gets too late. Better to spend a little more now than a lot more later!

Dave

PS My car 'pops' at idle as well, but this is not the same as the detonation I've experienced. I believe its merely the car running rich and backfiring (quite common with our cars).

My car pulls a little to the right and makes a bit of a whistling noise when im going over 130, has anyone else noticed this problem??? :D

My convertible did that until I had the TPS replaced and the full 60K mile service/tuneup.