poor acceleration,
 

My 93 6 speed, 55000 miles, has a problem If the throttle is nursed it runs ok, but if I step on the gas to about 1/3 throttle, it bogs down and there is some pre-ignition pinging. It still goes forwardbut at a greatly reduced rate of acceleration. So far I have replaced the fuel filter, plugs, half the wires (the passenger (easy to do) side) and cleaned the MAF. A fuel pressure test shows 39 lbs fuel pressure idling and 45 while driving. A vacuum test to the fuel pressure regulator showed immediate drop in pressure and the manual said replace, which I did. The ignition module also showed faulty so it was replaced. There is a slight miss when idling and the problem seems to get worse as the motor warms up. The bogging down is also more pronounced in the higher gears. The service engine light does not come on. I have a new opti-spark and water pump but I am hesitant to do major surgery just to find out that isn't the problem. At any rate, I'm tired of stimulating the economy by buying parts that are supposed to be bad but the replacements don't help, either. Any suggestions? Thanks for the advice in advance.

O2 sensors??? Dave

We put the OBD 1 on it. There were no codes but the readouts said the MAP sensor was marginal. Nothing else tested bad. I think that included the O2 sensors. Replaced the MAP. No go. All the injectors are well within tolerance. Put on a new coil. Once again, no help. I did discover for sure, though, that it runs fine until it gets to operating temperature. Then it pings and is real sluggish accelerating. Backing off on the throttle and just idling down the road it runs ok, but step on the throttle and BLAAAAAAH ping ping ping. Since winter is setting in, I don't think I'm going to be using it more than once or twice before it's put away. If it doesn't get too cold, I may at least tear it apart this fall and put it back together next spring. Or maybe wait. I'm really getting sick of it, actually. Nobody around here knows a thing about LT-1s anyway. But thanks for the suggestion.

Yeah, the problem is in o2 sensors.

poor acceleration
 

Thanks for the inputs. The car is put to bed for the winter, but I will certainly change the O2 sensors and see what happens. It does make sense now that I think about it.

Check the operation of the EGR valve. if the valve is not opening, it will cause detonation, which will cause the ECM to retard timing to compensate.

poor acceleration
 

Hey, Mech, I was waiting for your input. How do I check the EGR valve?

pinging is a symptom of low octain fuel or high compression or timing advancde very high, 02 sensors normally cause a poping much like a backfire . mine was poping & surging on ocassion but never showed a code about two months ago it started doing this all the time replaced the 02 sensor & have not had a problem since & went from 325- 350 miles to the tank to 450-500 miles to the tank

1st, does your EGR have a wiring connector or a vacuum hose going to it. More than likely it has a vacuum hose. You can use a hand vacuum pump to open it while engine is idling and if it causes the engine to die or almost die it is working, also the vacuum pump will hold vacuum. The EGR with the wiring connector is a linear valve and will set a code.

poor acceleration
 

poor car... maybe the one who did it dude is mad at you.

You can also put a vacuum gauge on manifold vacuum to check for a clogged converter. Measure vacuum @ idle, then throttle up to about 2000 rpm and if the gauge does not return to near what it was @ idle, you have an exhaust restriction.

poor acceleration
 

HUH?? Your reply makes no sense whatsoever!

Hey, Mech 259, I was responding to Bederocobby as your last message didn't show up until later. Threr is no exhaust restriction. Car runs GREAT until it gets to operating temperature. Isn't that when the O2 sensor kicks in? At any rate, nothing will happen around here until next spring as it is about -5 degrees until about April.

Check the operation of the coolant sensor and the O2. You will need a scan tool to see if the coolant sensor is reporting the right temp to the PCM. You can tap into the O2 wire if it is a one wire sensor or if it has a heater you need to determine which one is the signal to the PCM. On a warmed up engine, it should be cycling between around .2v to .8v, and when you snap the throttle, should go to almost a volt. If it stays pretty much constant, test by unplugging vacuum hose to brake booster to see if it drops lean (low volts) momentarily.

poor acceleration
 

It's a one wire O2 on the passenger side exhaust. Tough to get at though. The noise it makes when it isn't running right is kind of a knock and BLAAAAHHH. I'll test the O2 sensor come spring time, which, if you believe the climate change "experts", should be any day now. But I'll bet on late April anyhow.

That's the "green" crowd Dems :-(, the only thing green is the money that will be flowing out of your wallet.

poor acceleration
 

You got that right!

Changed the O2 sensors today. It runs worse now than before. I'm going to check the EGR valve later today. Anybody wanna buy a car?

Was wondering if you weere able to fix it. I have a 90 and when I step on the throttle it just goes BLAAAAH too. Dont have the pinging just BLAAAAAH.

poor acceleration
 

Pinging (or knocking like timing is off or low octane gas used to do when engines didn't have all the sensors etc and a guy could usually fix the car himself) and BLAHHH only worse than before I replaced the O2 sensors. I'm going to take it out today because the weather is half way decent and we'll see what happens.

poor acceleration
 

Well, after almost all summer of trying this and trying that, the miss and knock and BLAAHH was really getting bad so I finally broke down and took the car to BRAD"S AUTO CLINIC, Duluth MN 218 722-7762 (Little plug for ol' Brad there). They happen to have a Sun 450 Engine Analyzer and a very knowledgable staff. The car was hooked up and inside of 30 seconds the problme was deduced. #1 and #8 spark plugs were not firing and #4 was intermittent. Problem? Bad distributor (just as I feared!). Five hours later and a new distributor and water pump (which were purchased 2 years ago for just such an eventuality) I was back on the road and the car runs fine. I would recommend to anyone that if they have access to use an analyzer. It would have saved me lots of time, aggravation, and $$$ for parts I didn't need if I had done so originally. Happy Motoring!!!

I know this is a old post, I just wanted to know if the O2 sensors finally fixed the problem on your Corvette because I am having the same problem now in 2018 on my 1986 Corvette.

Welcome to the forum.
If you read the previous post, you would know that he fixed it by replacing the distributor. He previously said that the O2 sensor did not fix the problem.

Thank you
 

Yes I found your solution once I signed up THANK YOU, I replace the cap and car runs great again! One last question - after you fixed your car, did the new O2 sensor noticeably improve your gas millage?

He didn't say.