Back when at WOT, the car would buck and fall on it butt. Ran scan and came up with muliple misfire. Replaced plugs A/C delco's, and new wires, took off the throttle body and cleaned the thing till it shined in side. Also installed a new plug for the map sensor too.

Car runs smooth and idles great now till I drop the pedal into passing gear and then nothing but a big hesitation and bucks then it will go. Fuel pressure is at 40 and no gas in the vacuum line either..

And corvette is a 96 with 48,000 and change on it, but the old owners really did a bad job as far as maintaining her..



Ran a smoke test, and the starter fluid test and nothing, no change in the motor while running, and no smoke leaking out. Did find no vacuum at the optispark line and also no vacuum at the EGR valve. And on the pass side of the intake, none of the line on that side have any vacuum.

But there is vacuum at the fuel pressure, and on the drivers side I have vacuum where the two check valves are on the side of the intake.

HELPPastamike...

 

Little more info would help
What year ?
What problems?

If you have previously inquired here , would be better to update that original thread so everyone knows what is going on rather than starting a vague new one.

 

Sounds electrical. Try to start it in a real dark place and look at each plug wire to see if they're arcing. I've seen them look like a lightning storm at night. If that doesn't seem to be it and you have no vacuum at the opti line then it may not be getting vented. If it's not got any vacuum there's a good chance that it's got some moisture in it or it may have carbon tracked causing multiple misfires and they will be random.

For some reason this shows up mostly when at a high RPM with a load on it. If it's just some moisture in the Opti then there's a good chance that you can take it apart and clean it to make it good as new. If it's carbon tracking then you'll need a new cap and rotor for the blasted thing. Good Luck

 

Check the fuel pressure when you gas it, pressure should rise. Also check tps for smooth voltage rise as you move the throttle, best checked with analog type gauge good luck!

 

I second watching the engine while revving in the dark.

Watch the hell hole closely. I ended up individually wrapping each wire in plastic conduit where they go through to stop my miss.

 

The line with the two check valves on the driver's side intake, is your opti vacuum line. Probably not your issue, but you can check by pulling the hose before and after each check valve, this will tell you if those chack valves are functioning. Do the same with the all the check valves on the passenger side. If your getting no fresh air to the opti, check that the elbow connector at the intake is not clogged. You can do this by removing it and see if you have suction in the line. If you do not have a flow of air coming in, and there is vacuum on the opti, it can actually pull the cap onto the rotor and cause a misfire on acceleration. But this is among the last of checks in the FSM.

Now, no vacuum at the egr valve. Hmmm. If the egr is open or sticking, upon wot you could be getting too much recirculation of exhuast gas into the chamber at wot, which would cause a stumble or hesitation. Also the egr vacuum solenoid is run off the pcm using info from the MAP, TPS,IAC,VSS, and RPM. If you replace the egr valve, it is a "negative backpressure valve" denoted with an "N" stamped after the part # on the valve. (If the car was not well maintained, it could be clogged)

I just can't help but think you have a vacuum issue somewhere. If the car runs and idles correctly, temps are normal, oil pressure and voltage are normal. Everytime I've had a car that stumbled under sudden heavy load (dropping the go pedal) it turned out vacuum related.

 

I just can't help but think you have a vacuum issue somewhere. If the car runs and idles correctly, temps are normal, oil pressure and voltage are normal. Everytime I've had a car that stumbled under sudden heavy load (dropping the go pedal) it turned out vacuum related.[/QUOTE]

The older couple that owned for years, she did very little to the car, and also I believe now also that at one point in time it was driven very hard too. But I'm not giving up on this vett [B]NOWAY.[B]

As far as any arcing from wires there is none at any point in the wiring.
Now I have found one elbow with nothing comeing from it on the throttle body pass/side, but theres no vacuum there either? Also no hose coming from the charcoal can at all, just the plastic tube at the bottom of the pass fender.

Checked the fuel pressure and was at lbs and dropped to 38 then came back up with just small hit on the throttle. ( shouldn't it be between 41-49 lbs?)..Going to change fuel filter today and recheck fuel pressure.

Sorry for long thread but this is driveing me nuts till i get her right..

Thanks for the input so far..

 

The older couple that owned for years, she did very little to the car, and also I believe now also that at one point in time it was driven very hard too. But I'm not giving up on this vett [B]NOWAY.[B]

As far as any arcing from wires there is none at any point in the wiring.
Now I have found one elbow with nothing comeing from it on the throttle body pass/side, but theres no vacuum there either? Also no hose coming from the charcoal can at all, just the plastic tube at the bottom of the pass fender.

Checked the fuel pressure and was at lbs and dropped to 38 then came back up with just small hit on the throttle. ( shouldn't it be between 41-49 lbs?)..Going to change fuel filter today and recheck fuel pressure.

Sorry for long thread but this is driveing me nuts till i get her right..

Thanks for the input so far..[/QUOTE]

Fuel pressure seems fine, 42 lbs +/- with a slight drop and instant recovery w/ throttle is okay. You might also try some injector cleaner, and make sure you are using 91+ octane. Also, some top end cleaner like Seafoam or GM Top End cleaner might help too. Just thinking that perhaps if prev. owners cheaped out on maintenance they might have cheaped out on gasoline as well and ran the 87 octane. Might have some carbon issues. You said you changed the plugs, what did the old ones look like? Black, crusty, white, oil soaked? Old plugs can tell alot about what's going on in the chambers.

The only reason I mentioned a top end cleaner is if it only stumbles at wot acceleration, the gas is most likely getting there before the air, causing it be too rich and killing the spark until the air catches up. This can be caused by excessive carbon build up around the valves in in the chambers.

 

Plugs weren't that bad at all Sept they weren't all the same. Pas/side rear was A/C delco and the drivers side front plug was A/C delco as well, as for the rest they were NGK's.

Now I took what you posted and found, after finding a vacuum diagram there were two vacuum line's that were crossed. One coming from the EGR valve and the other on coming from the same double line conector.

I put them back to right elbow's and now have vacuum at the EGR valve.
Also one of the check valves was back wards with the blue side facing the front of the motor. I then took a little bit of parts cleaner and sprayed into the hose going to the check valve. And pulled off the vacuum line coming from the op ti and sprayed a little in there also and bingo now have vacuum there also.

Tomorrow going to replace the fuel filter, and see how she does when I put the hammer down..

Ok what about this sea foam where and how should I use it seeing its a good cleaner?

And thanks everyone so far for all the good help..

PastaMike..

 

Seafoam is junk. Elixir. A "Fix-All". Anything that you "can pour in your oil, gas, and intake"....should be seriously questioned. Water will work just as well for your combustion chamber/"top end" cleaner (better, actually) and real injector cleaner will work MUCH better for cleaning injectors. People should know what they're recommending before recommending "magic elixirs"...in this case, oil, naptha, and alcohol. 91 octane doesn't matter either. W/o startind a debate on "what octane should I be running?", octane won't cause the symptoms that you are describing.

FUEL PRESSURE: Dude...you HAVE to check the pressure during the symptom!! Hooking up a gauge and wacking the throttle a couple times doesn't gaurantee that the proper fuel is being supplied under a real load -the load that creates the condition. You have NOT confirmed that your FP is good at this point!!

Once you have confirmed that FP is good (if it turns out to be good), then use your scanning device to observe the low and hi res signals from the distributor, when the symptom is present.

Neither of those tests will cost you a cent (unlike a $10 can of "Seafoam"), and if those don't identify the problem, then I would install a spark tester, such that I could observe spark, while the symptoms are occurring.

 

Hopefully you have found the issue with the Vacuum fixes.

And Tom's right about the 'mechanic in can' items. However, I've never heard of using water as a top end cleaner, I guess 'steam cleaning' would work. I do know that folks have been using Seafoam and top end cleaners for years. I've done it a few times, seems to work. Wouldn't put in my oil or gas tank though.

But if the old plugs didn't have carbon build up, I wouldn't worry about it. I was just thinking that if the prev. owners used a lower grade gas over time it might cause some build up.

And yes, if you have a scanner that displays hi and lo res operation, by all means hook it up and see what it says.

 

OK thanks guys for the info. I'll buy test kit today and tape to the windshield when I go buy the fuel filter after work. Also the hose running down to the charcoal canister then needs to be put back also right, and the elbow with nothing on it.

I'll take a pic to show just what I'm talking about because I'm not sure of the names of these parts grrrrrr. But there is no vacuum at either of the hose connections not even sure theres suppose to be any. ( < dummy.

But at least I'm moving forward with all the help your giving me.. Sorry for all the posting over one dumb problem..

Pastamike..