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RPMs all over the place and MPGs down?

h0wl0ngcanitbe

h0wl0ngcanitbe

Lifer
So ever since I replaced the CPS im thinkin my HB might be off? I have been getting pretty crappy gas mileage when I normally get really good mileage, at odd speeds im getting a pretty noticeable vibration. And today at cruise at 55MPH the RPMs wouldnt kick down past 2300k? Normally the RPMs drop well below 2k at any kind of highway speeds especially while in cruise.

No codes yet just really temperamental driving conditions. Just wanted to see if any one has experienced this? Its not too bad but just annoying enough for me to wonder what is going on. I hate it too cause just a week ago I got an oil change at a Jiffy Lube and i normally do my own and I know that that has nothing to do with it but its just the first place my brain goes when the same week I get a burning smell in the engine compartment that is now gone but it smelt like belts and not oil?

Thoughts suggestions?

All I got right now is HAI and engine cover delete! Otherwise im stock all around.
 


Its impossible for the HB to be off if unless the keyway was gone and you screwed something up.

It can only go on the crank in 1 spot.

As for the rpms problem, maybe trans related? 4th Gear problem?
 
I was worried about that, would 4th gear issues cause vibrations? I was pretty certain I put the HB back on correctly... As far as I could tell it did not need to be lined up, I didnt mark the location when I pulled it so when it went back on it could have rotated but that shouldn't have been an issue right?
 
The harmonic balancer has a slot in it that fits where the keyway is on the crank, all you had to do what put the hb on and spin it till it fell into place and impacted the bolt on.

You couldnt have messed it up.
 
Well I didnt follow that procedure at all as far as spinning it until it "fell into place" IIRC when putting everything back together I just put the HB back on the bolt and impacted back on the HB bolt. was the HB supposed to spin until it stopped?
 
No, the HB has to line up w/ the key that is on the crankshaft. If you didn't put the HB on the crank and then just rotate the HB by hand until you felt it slip on a bit and lock to the point where you couldn't turn the HB anymore, then you likely just killed the HB and key on the crankshaft when you impacted the HB back on. Hopefully the HB is still good and you can just replace the key on the crankshaft.
 


Fak. So how do figure out if I did what we are thinkin I did. Since the post the car has been driving fine. But im not gonna let a temporary lapse in correct performance sway my thoughts on this.

So my question is, when you have a bad HB what are the symptoms?
 
Ok so is the "Key" your talking about? If so then yes I was able to line it up, IIRC you cant even put the HB bolt back on unless its slid in place but I just cant remember specifically. But yes if the key was just a slot to line up the HB back on the housing to bolt it back on I did do that.

CPS_Key.png
 
MAF is replaced wiring looks good but now im trying to figure out the ABS issue. Light is on but otherwise seems to be working fine. I just had them serviced so im a little confused as to why the light is back on. Between the two I have one functional GP!!!! I kid, they are both operating just being very temperamental.
 
ABS light is probably on due to a bad wheel speed sensor in one of the 4 hubs. Have it scanned w/ a GM Tech II or something that can read the ABS codes and give us the code. Could also check the wire harness conenction at the hubs as sometimes they get ripped out, corroded, etc and throw a code. Worst case you replace the hub.
 


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