94 chevy pick up 1500 5.7. starts and stalls with the 5v bypass timing pluged in. have changed distributer,coil,ignition module and computer and prom.

Could be a bad coil, bad Ignition Control Module (what controls the ignition coil as commanded by the engine computer), or a bad crank position sensor, or cam position sensor. Or the wiring and circuits to all the ignition parts.
Often it is the crank sensor (CKP sensor)-The pcm must have this information from the crank sensor to determine spark timing. If no good signal from the crank sensor, there will be no spark.

If you have power to the coil but no spark, did you replace the coil? You may have an intermittent wiring problem inside the coil (common).

There is the possibility that the ignition coil is faulty and first check to see if full battery voltage is getting to the "Pos" (+) positive side of the ignition coil when the key is in the "Run" position, and also that full battery voltage is getting through the "Pos" (+) or positive side of the ignition coil and over to the distributor ignition module, dis-connect the wire connector from the ignition module and if battery voltage is not present at the connector to the ignition module with the key in the "Run" position but it is present at the "Pos" side of the ignition coil, then the ignition coil is faulty. If battery voltage is present then check the ohms between the high tension terminal (where the coil wire goes on the ignition coil) and the "Pos" terminal on the ignition coil by first dis-connecting the wires from the ignition coil and then test with the "Neg" lead from the ohm meter in the high tension terminal on the ignition coil, and the "Pos" lead from the ohm meter to the the "Pos" terminal on the ignition coil, and the ohm reading should be between 6,000 and 30,000 ohms and if not replace the ignition coil. A faulty ignition coil can also damage the ignition module.

The ignition module and the pick-up coil/stator located inside of the distributor is what generates the signal that the ECM (Engine Control Module) uses to time and fire the fuel injectors, as well as the signal to run the fuel pump and the dwell signal timing to fire the ignition coil. A faulty ignition module can cause any one of these systems to malfunction.

That does sound like a malfunction with the ignition module inside of the distributor, and you can remove the ignition module and have it tested for free at most auto part stores. If the ignition module does test out alright then the problem could still be in the pick-up coil/stator, (it can be tested using an ohm meter by dis-connecting the wire connector from the pick-up coil/stator and the ohm reading between the two wires from the pick-up coil/stator should be between 500 and 1500 ohm's, and both of the wires from the pick-up coil/stator should show an open loop or an infinite reading between each wire and ground) and if the pick-up coil/stator is found to be faulty then replace the entire distributor, or the distributor will have to be dis-assembled to install a new pick-up coil/stator.

If you do purchase a new ignition module be sure that it does come with a silicone grease or a die-electric compound because it is a heat sink and the ignition module will burn up without it.

To install the new ignition module first clean out the mounting surface inside of the distributor. Then completely coat the metal contact surface under the ignition module with a thick coat the silicone grease or die-electric compound and do not leave any of the metal contact surface of the ignition module un-coated with the silicone grease or die-electric compound, and be very careful not to over-tighten the ignition module or it will be damaged.

What I see the most often is a stalled engine with a loss of spark when driving. Once the engine cools off it will sometimes start and run fine for a short while then do the same thing again. Often, but not always, the pickup up coil or ignition module [both are under the distributor cap] have to heat up quite a bit before they will act up. I replace about 10 ignition modules for every one pickup coil but either one can cause the same identical stalling problem. I keep a few known good modules around as test units so I can just replace a suspected bad module and road test it to see if it works. Another thing that can go wrong in these distributors are the magnets built into the pole piece. A weak or cracked magnet can cause all kinds of odd problems such as stalling when placed in reverse, misfires over 1,000 rpm, etc. Worn bushings in the distributor can also cause problems. As far as a specific test you can do to see which part is failing? I wish there was a relaible one. I've tried using a lab scope and module testers to diganose the culprit but you have to catch the problem as it's happening for those tests to be accurate.

the way i would check this is too use timing light or a spark tester on the coil wire run motor until it stalls check for spark @ ignition coil if the pickup coil is failing you wont have any spark bare in mind the ignition module can do the same thing so can the ignition coil. the part in the distubutor is called the pickup coil there is couple ways to test this. there are wires going to the coil that come from distubutor one wire pulse fires the coil there is a wire by the coil its a tach test lead you hook up a 12 volt test light to battery positive and check for pulses after the stall ocurrs. also test before stalls so you know what to exspect.if the pulse trigger stop its either the pickup coil or the ignition module.hope this helps Thunderboltz

Connect a voltmeter set on ac volts to the pickup coil wires (disconnected from the module) and crank the engine.

2. The pick-up coil output should be more than 0.7v AC. If not, replace the pick up coil and distributor shaft.

3. Visually inspect the condition of the magnet on top of the distributor shaft to be in good condition. If not, replace the distributor

1. Disconnect the set timing connector or ground the Tan/Black bypass wire.

2. The check engine light should come on and code 42 should set.

3. If the engine stops stalling, disconnect the pick up coil connector at the Ignition Control Module (ICM).

4. Check acv output from the pick up coil while cranking the engine at a normal cranking speed.

5. If output is less than 700 mv replace the distributor shaft with a new one.

Have u changed out ur Ignition module ? Needle nose pliers to take off retainer clip.Detach negative battery terminal,remove Dist cap nd rotor. Detach pick up coil leads from module.

speed control sensor [email protected]

I had the same problem with a 94 Caravan, turns out the main computer was Dead, went to the junk yeard picked up a 50doller one, and was back in action.

Well.... I do not see the ignition module listed, which is mounted inside the distributor mentioned yet. Have you replaced it and just not listed it? The crank sensor could be too.....I just can't imagine having to cut a wiring harness. Never had to before... keep trying other things.