94 Z28 stock LT1. It has started shuddering really bad when going up hills under acceleration. Places where I could leave it in 6th gear before now I'm having to downshift to 5th to stop the shuddering/missing. If I let off the gas and shift to a lower gear it seems to run fine. No miss when idleing. Does it in all gears just really noticeable when in the higher gears... Throttle response is really bad. If I'm just cruising along and floor it, it shudders really bad, you can feel the whole car jarring.

 

First things to demand attention are plugs and plug wires.

 

When you lug the engine, cylinder pressures increase dramatically. That causes at least two problems. First, the higher the cylinder pressure, the more voltage it takes to fire the plugs. The ignition system is put to the test, all the way from the coil to the plugs. Each component is suspect. Second problem is detonation caused by extreme cylinder pressure, which will trip the knock retard system, and cost you power. What grade fuel are you running?

Other possibility, after the weak ignition system, is a weak fuel system, but those problems usually show up at high RPM where fuel consumption is much greater.

Just for reference, what RPM are you seeing when you would normally be using 6th gear?

 

This happened to me a long time ago, it’s like back firing and you have absolutely no power on highways. How is when taking off? If it’s same that it’s you cat, your catalytic converter has collapsed and it’s blocking the exhaust to exit. Run the car for a 5 min cycle (idle), crawl under the car and touch the pipe before the cat and after the cat, DON’T GRAB IT!!! This is where that laser temp gauge comes in handy. Temperature of the pipe before the cat, the cat and pipe after the cat have to be the same temp, plus or minus 2-3 degrees. If the pipe after the cat is significantly lower temperature it’s your cat that’s blocking the exhaust and you need to replace it. It would be same with a muffle too…

 

It could be your plug wires those engines do get hot and the wires do get frayed. That could cause enough vibration to set off your knock module. Before i did that i would start small and check all the fluids especially your transmission fluid. Then i would go to the driveshaft and grab and shake it and it should not move. Other than all of this listed along with the other guys ideas it could possibly be the rearend which i have rebuilt one in my day also if it would turn out to be your rearend you could get another real cheap. Just go to hawksthirdgenparts online and they have complet rearends for five hundred dollars with any gear yu would want. Well hope its just low transmission fluid and it very well could be .

 

I don't think low transmission fluid in a T56 would cause those problems.

 

Check your brake light fluid...I agree that the symptoms which you described do not point toward a fluid issue.

It could be a drive shaft but if it was it would have fallen out already. If even one bolt fails on the U joint the entire shaft will slip out.

You would not get the shutter feel from a transmission, however if you did its a transmission failure.

Can you explain a little more in detail what exactly happens, I'm sure we can help you find that little gremlin.

 

"Check your brake light fluid".....

Was that last post a poor attempt at a joke?

The responses to this thread are getting further out in left field with every post.

 

I would first replace the coil wire.My02.

 

Yes unfortunately that was an attempt at a joke because everyone was going way into the left field with this issue. I’ve noticed on few occasion people posting problems but never again posting messages. So were just bickering among each other when we don’t have enough info.

Back to this issue: I would not start investing money into guessing what works and what doesn’t. Find what could be a problem and try isolating it one by one. Test it and test it again. Start with something easy like the temp check and sound checks. Don’t remove anything unless you are sure that it’s a defect part and especially don’t start replacing parts if you don’t know if they are bad, trust me your wallet is going to thank you!

No pun intended to anyone on here I would hate to see anyone start guess in defective parts on their engines.

 

If it was only the coil wire there would be a hesitation but since it shudders broadly; plugs and wires need replacing... these engines cook wires and high voltage makes them short out sooner.

 

I've had the car for a little less than a year now and the guy I bought it from said he replaced the plugs and plug wires about six months before I bought it. So the plugs are roughly a year and a half old. Do they normally need replacing that fast? I did let the car overheat once and it got very hot before I got it shutoff that may have fouled the plugs. It does the shuttering in all gears but it is most noticeable in the higher gears and only when the rpms are low. In 6th gear at 60mph I'm usually at about 1500rpm, I think(just guessing I'll double check it tommorow). I haven't checked the cat-converter but that is a good possibility. It really feels like an electrical misfire though. I don't think it's transmission related. Just had the car serviced at my usual spot and they found no fluids low. Could it be a bad opti? Thanks for all the responses, and my bad for not responding for a couple days been busy..

 

Misfires generally show up when you try and lug the engine in the wrong gear. I'll try asking this question again, since you didn't answer it. At what RPM are you trying to accelerate in 6th gear?

Have you done something as simple as open the hood in the dark, and look for arcing around the ignition components?

 

I'm not trying to accelerate in 6th gear, the car will not maintain its speed at all when climbing even moderatley sloped hills. Inclines that I could easily pull in 6th gear I am now having to downshift. The rpm range that it seems the worst is between 1500-2500rpm. No I have not looked for the ignition arcing in the dark but will do so... The problem also shows up on take off from a dead stop, if I try to accelerate to fast. The more gas I give it the more it misses. But it is most noticeable in the higher gears.

 

Thanks for clarifying that.