Intermittent Problem

[J-Mech]

I've got a complicated one for someone out there. I'm working on a 1990 chevrolet C1500 350TBI in with an intermittent die/no start condition. Ive narrowed it down to an ign module problem. When i took my Snap-On Modis and used the graphing feature and graphed out the wire that runs from the ign mdle to the ECM, when it thro's its fit the voltage goes from a positive wave form to a positive/ negative wave then dies off altogether. When you try to restart it no longer shoes good waveform. By connecting a test light to the positive battery post and touching to that wire it fires the injectors and resets the problem and i can restart the engine. (that test is as specified in the troubleshooter in the modis) Now here is the catch the distributer is new along with the cap, rotor, wires, plugs, pickup coil. Im not saying that the module isn't bad but why the reverse wave? Is it possible that the wires in the harness are picking up "noise" because that wire loom is rotted away and wires are routed messily? I'm going to put a new module on unless someone has another idea.opcorn:

[67malibu]

Places like AutoZone can test the module (out of the truck) and tell you quickly if it's frying. They will do really strange stuff when they start to go but mostly when they heat up.

[J-Mech]

I have a Module testor

[2000CAYukon]

Did you fix this yet?

Check the vacuum hose from the MAP to TBI. On my 90 K1500, the glue would get hot and then it would not hold a vacuum. I did not find this until I used a vacuum pump on the hose. Give it a try. If the leak is bad enough, it can cause the truck to die.

//2000CAYukon

[J-Mech]

Hey! Got it fixed. The ign module that we put in with the new dist was bad. Found it by graphing the wire from the module to the ecm (Purple with white stripe, injestor signal wire) on a graphing multimeter. after a while the signal would shift half pos half neg. Replaced module. FIXED!