20 Most Recent 1996 Chevrolet Express Questions & Answers

This is most definitely ignition related or fuel injector related.

with the ignition in the "off" position get a test light and touch one wire at a time while cycling the ignition switch to the "on" position, When you see that the test light goes off when the ignition switch is in the off position then you found the hot wire, make sure you dont hook it up to the "alway hot " wire or you might drain the battery hope this helps.

It is under the hood on this truck.

No, the catalytic convertor does NOT sound right.
Normally with a random misfire a tune up takes care of it. What has also caused a misfire on those early motors is the popet injectors. They were prone to having problems and have been updated back around 2000 or so. But usually its a cyclinder or two or three or... misfire. All popets going bad is unlikely.
Might try changing the fuel filter and maybe checking pressure. Just the key on pressure should be 60-66psi. While running it may be around 60 and a snap of the throttle will make it rise to 65 or so.

Hi, black smoke means your fuel mixture is running rich. You need to fix the fuel mixture if this is a carburetor engine you need to adjust or replace the carburetor. If this is fuel injected you must check the O2 sensors, fuel pressure, and computer sensors to fix the problem

Just the upper in take will have to come off,

You should find it on the engine side of the fire wall, passenger [RH] side down low near the bottom of the wall. Usually it's a small, short open ended hose about 3" long. Can be difficult to see and is most likely plugged with debris which can cause water to drip on the passenger side floor when the a/c is on.

to find the draw Switch off all electrical loads such as lights, radio equipment, auxiliary equipment and make sure the vehicle ignition system is turned off. Remove all ground paths from the negative battery terminals. Connect a jumper lead from theground cable to the negative battery terminalYou are now feeding the electrical current requirements of the entire vehicle through the jumper lead. Do not activate any other electrical equipment while the jumper lead is supplying the vehicle current. Wait five minutes to allow all electrical devices to shut down and go to standby mode. While waiting for the vehicle electronics to go to sleep, set up a digital ammeter, such as the Fluke 88to read amps (automatic scale) and make sure the test leads are plugged in to the correct connectors to read amps (COM and A). Connect the COM ammeter lead to the negative battery stud and the positive lead to the connected ground cable After five minutes with the jumper and the ammeter connected in parallel, remove the jumper lead from the three connected cables to the negative battery stud as shown in Figure 3. The vehicles entire current requirements (parasitic load) will now be going through the ammeter. Read the current flow in milliamps. Remember that 1000 milliamps is equal to 1 amp. If the readout has ma after the reading youre measuring milliamps, if the readout has A after the reading youre measuring amps. If at any time during this process the current flow is interrupted (a connector falls off) you must begin again with the jumper connected for five minutes before attempting to remove it leaving the ammeter passing all current and measuring the parasitic load, Under normal conditions, while parked, a vehicle equipped with a standard electronics package should be drawing less than 50 milliamps. If the parasitic load is more than this the vehicles battery storage life will be shortened. If excessive current draw is observed, remove the fuses one at a time until a significant current drop is noted. Do not pull and reinstall the fuses as this may wake up some circuits and cause excessive surge current through the meter. Make note of fuse locations as they are pulled so they can be reinstalled in the proper fuse panel location when testing is complete. When high current draw devices are isolated consider relocating their power feed from a power source that is inactive when the ignition switch is turned to OFF. Sorry So long but hope it helps

sounds like you need a brake job