nickgost

My 92 vette is having a bad studder/ miss above 4,000rpm. Its like the entire car is turning on and off. While its doing this the tach is jumping around a bit. The icm, coil, and plug wires are less than a year old, and the opti was about 2 weeks old when the issue first occurred. Anybody got any ideas to what it could be? I just now thought fuel filter, but that may be new as well... Ill have to check on that one.

The problem got slightly better when i changed a really bad battery out.... which leads me to believe it stems from an electrical system.

Thanks in advance for any ideas!

bogus

hm... sorry to hear this... hope you find the car...

ok... this is bad... you have thrown a ton of parts at it, and the problem still exists.

First off, there is a junction block behind the battery that does lots of things, make sure it's clean and tight.

What brand parts did you use? Cheap **** will catch you in the end, seriously...

A bad tach filter will cause the tach to jump, but not the miss fire.

Vacuum leaks? Age/condition of the O2 sensors? What is the overall mileage? You don't mention a code check, please check the engine codes and report them back.

This is why one does not throw parts at a problem... it's an expensive way of doing diagnostics...

nickgost

Well these parts weren't all thrown at this problem haha. Its been one problem after another with my lovely pain in the ***. This is a new issue that just didn't seem like the usual bad opti symptoms.

Being that I'm at work I cant run codes but before I leave I will check that junction box, I know for sure that I have an amplifier positive cable running off of that block.

For your other questions:
Car was garbage when I bought it about 2 years ago, and its been a slow uphill climb from there.
Vacuum leaks- maybe small, slowly replacing lines as I'm working around worn ones
O2 sensors - No idea of age, they looked healthy when I put my new exhaust up about a year ago
Mileage - over 120,000

This Saturday I am going to tear into her to change the fuel filter. I'm thinking this might help because I had a really bad battery. Like useless battery in the car, and since I changed it has gotten better. So fuel pressure may have been low. Even if its not the problem I don't know if its ever been changed!

bogus

Also check the condition of the cats... if you have been having misfires, they will dump raw fuel into hot cats, causing them to melt down. Real bad.

nickgost

I will check them as well. I suspect they will be ok, they are brand new hi-flows. And if they aren't oh well, they were just restriction anyway.

aDigitalPhantom

This makes me wonder if you got a bad replacement opti

nickgost

Well this is like opti #4 in 2 years so yeah that could be my problem...... Reallyyyyyy don't want to do that job again... And no i do not wash the motor and my water pump does not leak. Last opti was dry as a bone when it came out.

Ozzstar

What brand or brands of Opti's have you been using? Where are you purchasing from, ebay? used?

nickgost

All of them have been new. The last two have been Cardone (advance auto parts lifetime warrenty)

bogus

that might just be the problem. The remans are junk.

Try MSD... they are expensive, but they do work better.

nickgost

Well to put it plainly. I'm 20, work for a large cooperation that doesn't like to give me hours, and will not promote me to the technician job that I already do the work of..... Sooo MSD prices are very far out of the question.

Also, did some work on the car today. All the electrical connections are good. Going to tackle the fuel filter and a few other things tomorrow.
For no reason that I can tell the car has been acting much better,l. It still has a hard time at the higher rpm's, but it's performing much better.

skyhawk50

Did you ohm check the fuel injectors. I went through all that you replaced last fall. The very last items I replaced were the fuel injectors and that solved the problems. Also, make sure all the drivers side plug wires are carefully routed. I had one rub through on pulley and had some arcing.

cudamax

I am going to tear into her to change the fuel filter. I'm thinking this might help because I had a really bad battery.
That don't make Sense

cudamax

Since ur throwing **** at it Its well over due for an injector clean The kind u hook up to the rails and pinch or pull the power to the pump and run the motor on the can at 2000 rpm also chevy small blocks need to have some att to the wires. Firing order is 1-8-4-3-6-5-7-2 The spark plugs wires on 4 & 3 and 5 & 6 from the dist cap to the spark plugs they should not touch or cross anywhere. lay them out nice and get a lot of those wire separators

81c3

On an LT-1 with an optispark distributor, its almost impossible to have the odd and even side plug wires touch in any way...

lt4obsesses

So, if I'm reading correctly, it onl;y studders/misses above 4,000K? Meaning that it runs satisfactorily under normal driving conditions? It's just on hard acceleration, high demand situations it does this? Is the car throwing codes at you, (MIL light on? Flashing?)

I would take a long hard look at your fuel system if this is the case. First check the fuel pressure regulator, this is a common part, often overlooked, and will produce this symptom. You could have a clogged filter, or your pump may be getting ready to retire. If the FPR is good get a fuel pressure gauge and go from there.

As far as checking the ignition, get a spark tester and check spark from coil at coil, from coil at the opti, and from opti at plugs.

If it's setting off the MIL, there will be codes that will help lead you where you need to look.

nickgost

Going out to work on her right now.

I believe it is fuel related. It sounds like a "fuel cutoff" when it happens. And yes it is only occurring durring high RPM high throttle conditions.

There are no lights on when it occurs. I will be pulling codes now.

What should my injectors read?

nickgost

No fuel from valve on fuel rail after about 24 hours of not moving the car.... Is this normal?

nickgost

Ok so I pretty much have 0 fuel pressure with the ignition on and the car off. With the car on it sprays a tiny bit. I do not have a fuel pressure guage, but will have one tomorrow

lt4obsesses

Do you hear your fuel pump buzz when you turn the key?