wheelieking71

so, preface: my rig "big-whitey" has ran perfectly predictable every day i have hit the key. except once, that was totaly my fault. i put a high pressure lift pump in front of a VE, and it pushed the front seal out of the pump. my bad. that is loooong fixed though, and he has ran perfect since. untill today. today, i noticed a few very fain "stumbles". then it happened. i eased in the throttle from a red light pretty hard, and the engine just cut out repeatedly. it was very fast, and it probly cut out 6 times. it fely like the FSS was on a toggle switch, and somebody else flipped it off/on 6 times, on .5sec intervals. then ran fine, BUT! the "wait to start" light came on. yea, weird. my grid heaters have been unhooked for over a year. as soon as i cycled the key to off, then back on. the light went out, and he ran fine the rest of the 20 miles home. anybody got any ideas?

Brian.B

i had the same problem about a month ago,,i thought it was a clogged filter ,,my truck started acting like it was running out of fuel but it was just instant then it would be running again,and finally it just started cutting in and out real fast,,come to find out it was the wire on the fuel selenoid it was off and just barely making connection but when i gave it fuel it would lose the connection,,,hope this helps

Onemoparnut

Like Brian said check the wire on the fss.

wheelieking71

i have already soldered new terminals on those wires, and they are high quality with a good grip on the spade. pretty sure thats not it. what controls the "wait to start" light? and will that cut power to the FSS?

sooty

temp switch on head with blk/red and blk/lt blue wires is monitored by the pcm on the i/c trucks, earlier trucks sensor wires are blk and lt blue wires, a air heater relay and controller operate the grid, sounds like your system lost power intermittantly, posibly a bad battery connection/fuse link?

wheelieking71

fusable links have been handled properly:



they all have their own dedicated fuses now. no blown fuses. battery terminals are good. it just did it to me again on the way to work. same exact scenario. tipped into the throttle hard and fast, and, it cut out 5 or 6 times at really quick intervals, and the wait to start light came on? this is just one more reason for me to phase the computer out completely.

wheelieking71

okay, just studied the available wiring diagrams in the sticky. i can see that the computer turns on the "wait to start" light. but i cant find where the power for the FSS comes from. i thought it came from the ignition switch. but the cutting out, and "wait to start" light have to somehow be related. because every time this happens, the light comes on, and stays on until i cycle the key.

wheelieking71

just went out to the truck, started it up, and unplugged both temp sensors one at a time. the rear sensor did nothing. the front sensor (both wires light blue w/blk trace) made the "wait to start" light start flashing. but the engine stayed running.

j_martin

What's common to all that is the A21 (Ignition run) circuit from the ignition switch. It directly powers the FSS, and it powers the ASD relay, which would cycle the PCM, causing the wait to start lights to light for a few seconds (power on test)

The only fusing on that circuit is the fusible link, or in your case a fairly heavy fuse. One of the lighter gauge wires in that A21 circuit, which goes to durned near everything, touching ground might blink things out without blowing the fuse.

To test the theory, rig a small lamp to any one of the dark blue wires under the hood (FSS, heater relays, ASD, etc.) and see if it blinks when you're having trouble.

j_martin

oops, double post

G1625S

Or maybe the ignition switch itself?

wheelieking71

yea, i just went on an errand for work, and it was doing it. if i take off easy i can feel very faint stumbles. never really noticed it before, but was never paying as much attention either. the harder i step on it the worse it is. but! it only seems to do it from a dead stop? once rolling it goes down the road just fine. when it does it it feels just like somebody is killing the power to the FSS repeatedly. i hate electrical gremlins! i like doing wiring. and im even pretty good at putting it together. but im no good at troubleshooting problems.

wheelieking71

ohh, and thanks for the very informative reply j_martin! that helps alot! although its not very encouraging LOL. now i have to look for that needle in the haystack!

i tried every scenario i could on my way home from work just now. the only way i can get it to cut out and the "wait to start" light to come on, is from a dead stop. once its rolling, it will stumble lightly with throttle, but no cut out, or light. oh, and when the light comes on, its the only one. no brake, or water in fuel, or whatever else is there. just wait to start.

j_martin

Just for grins and giggles, swap the ASD relay with one of the others. See if the bug moves with the relay.

Also, look at the wiring near the intake manifold, especially that dark blue one. Might be rubbing when the engine is rocking, and it smooths out once yer rolling.

That circuit feeds the power to the OD solenoid if you have one. More opportunity to get wacked by brush or something.

Systematic, as I would do it.
1. swap the relay as I suggested.
2. rig the light as I suggested. If it blinks, ya got trouble in the ignition switch or grounding as I suggested.

Another suggestion would be to hot wire the FSS and see if the bug goes away. If it doesn't ya got fuel problems.


BTW, I'm assuming that by pressure gauge or something, you're dead sure it's not just starving for fuel.

wheelieking71

well, i am within a couple pages of you LOL. just came in from looking at every wire on, near, around, related to the engine/circuit you mentioned that i could find. nothing obvious jumped out at me. gave everything a good shake to see if i could maybe "move" the culprit (if its electrical). went for a ride, still did it. thats when i decided, im gonna hot-wire the FSS. like you said, then i will know for sure if its electrical. but ever time it does it that "wait to start" light comes on without fail. and stays on till i cycle the key. and no, i am not sure its not starving for fuel. while i was out going over the wires i noticed my fuel filter has a nasty leak.