Hey all,

i've just brought a s5 rx7 that was converted from auto to manual, drives like a dream, cant even tell the difference, except when slowing down, with no foot on the accelerator, the car will get to about 2k revs and then starts shuddering (bunny hoping almost)....weird?

My little diagnostics points to the clutch or flywheel, because as soon as i put clutch in, it stops.

Another problem i have, is that a weird...high pitched noise coming from what i believe either the gearbox or or god knows what. I dont think these two problems are related because when i got the car, i didnt notice it when i first got the car. my next step to try and find this problem is to get it up on a hoist and have a listen, but this might take some time.

any help or ideas greatly appreciated.

thanks guys/girls
G

 

You sir, have a vacuum leak.

 

lol, thanks for that, anychance for some more info? not that ive had a good look under the car yet, im 100% positive that the high pitched noise is not coming from the engine itself.

also, what part of my post were you refering too?

Thanks
G

 

With a vacuum leak, when you try to decel (let off the gas, in gear, let the engine brake for you), it will "hop" around, or get really figgity, however you want to describe it. It doesn't want to do it! This is because you have unmetered air being pulled in when you should be having vacuum, vacuum being what causes the car to slow down. So you will slow down some, then pull in some air, slow down some, pull in some air, etc...

Generally found around the intake manifolds, needing new gaskets. But really, it can be ANYWHERE before the AFM(towards the engine).

 

hi,

thanks for the great info adrock, i will look into it.
I would of never guessed that it would be caused by a vacuum prob.

G

 

actually some rotarys buck under 2k when coasting. thats just the nature of a rotary, im not exactly sure that it would be a vac leak. there was a thread on how the car bucks under deceleration awhile back.

for example, my car bucks when its colds, other than that its fine.

 

heya bobafc3s,

funny you should say that, i posted my probel on ausrotary, and one of the replies was exactly the same. My s4 never did that,but that was an auto. and havnt owned any other rotaries bar that.

Cheers for the imput everyone : D

G

 

Werd I don't let my car coast with the clutch in below 2,000 rpm. It bucks.

 

I agree with the vacuum diagnosis; the lean surging condition could possibly be caused by a tps mis-adjusted/going out.

Just to make sure none of the noises you hear are related to driveshaft check out this thread: https://www.rx7club.com/2nd-generation-specific-1986-1992-17/noise-deceleration-514397/

 

yeah id definitly agree with the vacume leak as a posibility or the TPS out of adjustment

ive had a couple rx7 that do that bucking, they ARNT posta do that, that means somethings a little out of wack

 

Hey Guys,

have a read of some of the responses on this:

http://ausrotary.dntinternet.com/for...ic.php?t=95989

no one thinks its a vac prob, and i think there reasons why it isnt are valid, but until i've fully checked, i dont know myself. Just not enough hours in the day : (

Cheers
G

 

does your car do this when its fully warmed up or when its cold. a few rotaries i know do this when its cold, but also some do it all the time. not sure my 7's been to the shop for vacuum checks because my intake gasket was broken once and im always paranoid about not being able to start the beast in the morning.

 

Heya bobafc3s,

I always warm the car up before i drive it, so , its when warm. The car drives like a dream except for the bucking, (Only happens under 2k revs when on decel.) And the whining noise (need to put car on jacks to check, think its to do with gearbox). Only

I'm getting an a/m boost gauge this weekend, so i'm going to check what the vacs like and boost.

I will also check all of the vac lines, and proberly replace them all.

From what everyone has been saying on both forums, - this is common. which i personally find strange, but since this is my first manual rotary, i guess i'll just have to accept it if its still there once i've checked all vac lines.

Cheers
G

 

Regarding the bucking we've all experienced below 2000 RPM.

Do you guys think this could be caused by the low torque generated by the motors? Or would it possibly have something to do with the drivetrain?

I'm interested in hearing a little more info on this.

James

EDIT: I'm not talking about the slight surge from when going WOT at such low RPMs, just the slight bucking on decel.

 

Hey spot_skater,


from what i can understand from my posting on the ausrotary forum, it proberly is because of the torque, a post said i never noticed it on my s4 because it was an auto and had a torque converter which was buffering out all the load on the engine at low revs.

G

 

I bet if you watch the tach it starts bucking as soon as it hits 1500rpm. The reason is the when you lift off the gas the injectors are shut off, but they're turned back on when the engine drops to 1500rpm so that the engine can idle. The small amount of fuel injected causes the bucking. It's not a rotary thing, any engine will do this at very low revs but modern EFI systems handke it much better.

EFI is so common now that people have forgotten that carbs used to do this all the time because the fuel flow is constant. To avoid it you simply have to upchange before 1500rpm or push the clutch pedal in.

Most likely the TPS is out of adjustment too, which will make this bucking worse.