I have a mid to high rpm mis that I was wondering if it could be caused by not running premium or higher octane fuel? I also seem to have an issue with where my shift point is and it may all be related, which is why I ask.

Short story here is I recently picked the car up and it had some questionable mods: 3.73 gears that make noise (says they are "hard" gears, that's why...doubt that for some reason) originally was 3.23, Electric Mazier (sp?)water pump, MSD plug wires, no PROM tune that I know of. With the lack of tune in mind, can that cause these running/shifting issues as the car is not aware of the different gears? Chance of messing up the opti by getting it wet when changing the water pump (would it still idle fine and run decent for the most part unless hitting higher rpms?) The speedo does read about 10 mph higher than actual speed at 60.

 

if the speedo is off than you probably do have diff gears, however they shouldnt "wine" if thats what your explaining

 

Yea, I would say it is bad bearings, but it is only under steady speed load...under accel and decel, nothing, only when I hold a steady speed. The other thing I was thinking is maybe the backlash wasn't set properly and the pinion is riding on the ring gear incorrectly. Anyway, that is just one small issue...the bigger issue being would that 3.73 cause the shift point to be off? Seem like a mis up high but maybe just rev limiter? I'm tempted to go back to all stock parts and start over with the car as I don't 100% trust anything that was previously done to the car...

 

No ideas?

 

The pcm get's it's speed data from the tranny output, so the ONLY problem the lack of tune with gears causes is the speedo, has no impact on the shifting or anything like that.

The gear setup sounds botched, pinion depth is probably off and probably too late to fix it as the wear pattern is likely a done deal. Backlash usually causes a coasting whine.

Depending on what else may have been done to the car a "high rpm miss" is often valvetrain problems, people trust the wrong folks and andup with springs insufficient for the cam.
Might be a good idea to change the cap and rotor though, they are often neglected and are wear items. The MSD cap and rotor kit will convert your opti to be vented which helps long term relibility.

 

As far as the high rpm miss goes, It could be a fuel, spark, or valvetrain issue.
Test your fuel pressure at KOEO, idle, and driving at WOT.
Test your coil.
How old are the plugs and wires?

 

The wires and plugs were replaced semi recently with MSD by the previous owner...maybe 15K miles. The fuel pressures checked good, but I have an issue with it bleeding off as soon as the key is turned off. It runs good pressures through the rpms as long as it's running though, so the check valve in the pump is probably the problem there. It is also pretty intermittent I think, which is why I want to think it is ignition. It is probably the original opti, cap and rotor. I am pretty positive he never got into the valve train or cam/springs/etc. But the car has 117K miles, so it may just be getting old. I was planning on putting a mild cam, springs, lifters, seals, etc. anyway, but wanted to make sure there were no other major issues or driveability issues before dropping that kind of mod/money in the valve train.

 

given you don't know the car history you need to check fuel and ignition systems. After that valve springs or Opti are a common cause of high RPM stumble. If the valve springs are stock...they are tired.

 

I had the understanding that the pcm commanded shifts based on mph, not rpm. Unless I've been misinformed, I don't see how it couldn't affect the shift points.


Agreed! The only way to fix the whine will be a new set of gears that are set up properly to start with. I once ran an old 2nd Gen Camaro for several years with a whine at steady speeds. It held up to weekly trips to the drag strip, but it was annoying as hell on the highway.


I would start with plugs and wires. My car came with a horribile high rpm miss that went away when I tossed the bran new looking champion platinum plugs and went with some plain old autolite 106's.

 

The pcm uses rpm and speed for shifting, either way a gear change wont affect it.

Only reason I did not say wires was because it sounded like the MSDs were fairly fresh, then again someone who leaves gears setup wrong and doesn't tune for them may well have done a bad job looming the wires and one could be fried already.

Autolite 106 seems a little hot to me, I would do a 104 or an NGK TR55 which seems to fall in between the 104 and 106 heat range.

 

From my own personal experience, I went from 2.73 to 3.42 gears. The shift points were very confused until I had it tuned for the new gears. Perhaps because it was a more radical change? At any rate, once it was tuned for the new gearing (and it was the only change to the PCM, btw) everything was fine.
I would strongly suggest that you get Tunercats (I think they have a free 30 day trial or something along those lines) and see what the settings are in your PCM.
AFA the Opti, your car came stock with an unvented Opti. If the waterpump has gotten water into it, you may encounter the miss you are describing. But that is supposition, you will have to get inside to see what is going on.

 

Well, I was planning on building the top end some...mild cam, 1.6 roller rockers, springs, seals, lifters, etc. anyway. While in there I was going to at least look at the opti...put the mechanical water pump back on...and probably replace the wires/plugs since the heads would be off and the top end would be getting worked. Might as well put fresh stuff back in. B ut the kid who had it before me was definitely not a tech wizard...he knew just enough to get himself in trouble I think.

Anyway, I also have to probably replace the fuel pump as I have a bleed off issue there that annoys the hell out of me to say the least...plus it may be part of my high end issue...lean fuel/mis. I will be doing a base line dyno run tomorrow and I will find out then for sure if the car is getting lean up top which would clear up some questions.

I just wanted to make sure I didn't need to replace something in the ignition or opti for sure before doing the other top end work. If replacing the items listed so far is part of upgrading the top end anyway, most of the issue should go away then. I'm just wanting to see if anyone else HAD to get a tune for the re-gear or if that was by main problem here from the sounds of it. I will be getting a tune, just probably not before I do the top end. I might tell the PROM burner what I plan on eventually having and get that tune and either put it in later or run it now until I finish everything.

Sorry for the book here, just a lot to cover on this thing as I just bought it and have plenty of previous owner issues to work out. thanks for the responses...they always help in this diagnosis part. Gives me something to think about I might not have thought about. It is appreciated.