I changed the plugs and wires, the wires had a lot of cracks in them, also some of the boots were even torn open as well. It runs alot better and smoother now, but if I hit it to drop down into passing gear the motor falls flat, and a second later will take off.

I'm thinking maybe fuel pressure?? Any thoughts???

Pasta mike..

 

What year do you have? Could be fuel related , when is the last time you changed the fuel filter? Could be you have a bad fuel injector too!

 

........... The $64 question is : Was it doing this before you messed with it ? ...... If yes , then proceed with your diagnostics ... if no , then recheck everything you did ... did you drop any of the plugs during the change out ? you may have broken a ceramic insulator ... did you get the firing order right with the new wires ? 5 & 7 are easy to mix up ... How about the cap and rotor ? are the new wires properly seated on to the plugs ? did you use the correct plugs ? did you knock any vacuum hoses off ? Have you checked the timing ? Start with the basics ... sometimes we tend to get all complicated when guessing what is wrong ... use the diagnostic flow charts from the Factory service manual ..........

 

That can be a 2-fold issue...

Stumble.

a. poor exhaust w/high back pressure from a semi stock system and/or plugged cats...


b. fuel pressure flow from a weak pump or plugged filter. Pressure needs to be near 40 key ON, 38 at idle. Fuel pressure should drop instantly as throttle is applied BUT recover instantly. A 'slow' recovery indicates a tired pump thats unable to keep up
with demand...<- very likely to be at least part of this problem.

 

Used ac delco plugs, triple checked fireing order before installing wires. checked for vacuum leaks. I didn't change the optispark after seeing how bad wires were. All that went very well, even changed headlight motor gears and they work perfect now.

Checked fuel pressure and its only at 40lbs, thought hearing and all-data says 55lbs, is this right? Before I go and tear it all apart and replace the water pump, opti, and may as well do the seals too, may do the fuel filter first?

Never tested a injector before?? Oh and its a 96 with 41,000 and change on her..

Thanks for the input..

 

........ Fuel pressure on LT1 is 40-42 psi ......... test injectors by using your digital meter ... disconnect injector plug and Ohm check the two terminals on the injector ... check cold and hot ... should be around 16 ohms ..... I didn't realize you had an LT1 with Optispark on my original post ... focus on ignition with your diagnostics ... Ignition Control Module mounted on the cylinder head with the coil ... these can be tested at the chain parts stores ... spark plug gap is critical ... then look into a new Opti ......... Any codes at all ? .........

 

Only codes when scanned were muliple misfire..

 

stay away from the Opti unless you want to spend $300 and a lot of shop time. When the opti fails its misfiring, burping, chokin and all rouind misbehaving from spark timing..yours does nothing like that...so feel fortunate. Fuel is cheaper to investigate...

 

Your description tells me that this car has not been one of those maticulously maintained exapmles.

Plugs and wires are always a good place to start. The fuel filter is a rather easy one as well.

From your description of the problem, runs fine except stumble at WOT, tells me it may be a vacuum issue. So I would look at this first. There are many posts in here on finding these, try seaching vacuum leak with the search function.

Another possiblity is your fuel pressure regulator. After reving it, pull the vac. hose off the tip and check for fuel in the hose.

PVC valve could be another cause.

Clogged egr could do it too.

Also check the opti air vent system. Do this by pulling the fresh air hose on the drivers(left) side of the air duct behind the MAF. Feel for suction from the hose. If there is no suction then you are not getting air into the opti. Also check at the intake mainfold, it is the hose with the two check valves. This creates the vacuum to pull fresh air into the opti. This could cause this because if the fresh air line is clogged, and the intake is creating a vacuum, this can actually pull the opti cap onto the rotor under heavy load and cause it to misfire.

But I'm betting on a vacuum issue somewhere. I had an old Cougar that ran alright until I went to accelerate, then it would stumble exactly as you described. When I went to look at vac. hoses, one at the manifold had a huge hole in it, and the PVC hoses literally crumbled to dust when I touched them. Fixed these and it ran much smoother.

 

I found one missing vacuum line missing on the pass/side along the intake, theres one elbow empty by the TPS, and to the rear of the intake a square black box with one line in front and a open hole at the rear of it..

Also checked the line for the opti/spark and nothing,no vacume, could it be the two check valves or one of the and how does one test them??

Thanks pastamike..