Noisy IAC, No start; fuel, IAC, or?

[nimrod.sixty9]

Was easier to just swap throttle bodies. Noise stayed and issue stayed with Yukon. Had to call it quits before I could do another round of testing spark due to millions of blood sucking mosquitoes. Another day...

 

[nimrod.sixty9]

Well turns out the stupid spark plug tester was a waste of money.

So tons of wasted attempts. So just decided to grab another plug and use jumper cables. Sparked without issue. And I just knew it would leave me on a hanger so I immediately decided to hook the wire back up and it fired right up! AHHHHHHH!

Cranked instantly next 10 times and runs perfectly... fkn figures. So now I have no idea if it was a valid test.

Lets assume its an intermittent no spark on start; what would cause this?

FYI, now we do know that the FP tests are the same either running or not.

 

[SunlitComet]

either the crank sensor was not putting out signal as needed because of fault or power supply issue, pcm was not functioning correctly, icm is faulting in the same way as sensor or the coil is screwy or maybe even a ground issue somewhere.

 

[nimrod.sixty9]

either the crank sensor was not putting out signal as needed because of fault or power supply issue, pcm was not functioning correctly, icm is faulting in the same way as sensor or the coil is screwy or maybe even a ground issue somewhere.

CPS is new and ICM /coil was switched between Tahoe and Yukon. What about CAM Sensor?

Could you explain power supply issue and PCM? Why so damned intermittent? It's either perfect or nothing. And for the most part the issue only seems to be at starting; if it turns on, it runs and runs great. Only died on the road twice and that may have not been related to this issue.

Also, I just thought about this; remember way back I did have a short under the dash that kept popping the big ass starter fuse. I don't think anything else was on that circuit and that was a long time between that and this issue. Just throwing it out there.

 

[SunlitComet]

supposed to be able to start with a bum cam sensor but i code would post about it. power supply as in the wiring and fuse that supplies the crank sensor with power could be goofed somewhere. the pink wire on either cam or crank sensor should supply system voltage during run and start. crank fused thru ecm-1 cam fused thru eng-1. both under the hood. pcm receives three voltage feeds. constant hot on pcm "clear" connector pin 21 orange wire. hot in run and start "black" connector pin 18 pink wire. hot in run only "black" pin 13 brown wire. fed from ecm-b, ecm-1 and #18 brake fuses respectively. use gf for help probing as needed. unlike other pcm's the factory does not give a list of what can happen when a certain wire into the pcm is dead.

hmm, does tranny indicator still light? if not check "trans" fuse in the cab. if no system voltage on either of the fuses contacts there is a feed problem from the ignition switch perhaps or further back. however if it does actually crank then the power supply to the switch should be good and the switch itself might be at fault. those last couple of circuits are fused separately outbound of switch but fed inbound to switch with only one wire. take a moment and soak it in. now start probing.

 

[nimrod.sixty9]

supposed to be able to start with a bum cam sensor but i code would post about it. power supply as in the wiring and fuse that supplies the crank sensor with power could be goofed somewhere. the pink wire on either cam or crank sensor should supply system voltage during run and start. crank fused thru ecm-1 cam fused thru eng-1. both under the hood. pcm receives three voltage feeds. constant hot on pcm "clear" connector pin 21 orange wire. hot in run and start "black" connector pin 18 pink wire. hot in run only "black" pin 13 brown wire. fed from ecm-b, ecm-1 and #18 brake fuses respectively. use gf for help probing as needed. unlike other pcm's the factory does not give a list of what can happen when a certain wire into the pcm is dead.

hmm, does tranny indicator still light? if not check "trans" fuse in the cab. if no system voltage on either of the fuses contacts there is a feed problem from the ignition switch perhaps or further back. however if it does actually crank then the power supply to the switch should be good and the switch itself might be at fault. those last couple of circuits are fused separately outbound of switch but fed inbound to switch with only one wire. take a moment and soak it in. now start probing.

Not sure what you mean by tranny indicator. Do explain.

So the switch has two output circuits; one is crank which is working fine and another that is 'run' which could be the problem?

Or a couple of wires coming from the PCM to CAM, ICM/Coil, and CPS?

Could a bad relay of some sort cause this? Still curious about all that noise...

 

[SunlitComet]

gear selection indicator foo.

switch actually has two inputs and five outputs. just the ones i mentioned just happen to branch off the same input line.

the power to pcm can be tested with the pcm connectors off and tun the key as needed to check the power voltage the sensor ones can be tested at sensor connectors.

so looking at the video again it does not seem to be tied to fuel flow after all. it can only be the iac that is doing it as it is the only servo device around there engine with the exception of egr. if i recall correctly mine does the same. part in oe. i have a spare because i believed that it is faulting and choking the engine and won't let it start every few weeks. strange part is when it happens i have to turn key off and literally open and close my door. i am looking into the issue which started after the 0411 pcm upgrade. i am not fully equipment enough just yet to get fast data or easy answers and i know the program on it has some altered specs that are really messing up tranny shift when i floor it while already moving a bit. i thought it would be the iac doing it but when running it seems to react as it should and quickly as well. i had a one time egr fault qwerk that never came back before he pcm change and for some reason the fuel input got so bad i would be sometimes at 8mpg till i shut down. would floor it and make it look it was puffing diesel smoke particles. could restart and then maybe 15mpg say 30 minutes later. only happened once on on trip to come home. am looking into several other things tied to it. seem to be normal since then. have not touch the egr as it seems to be working correctly now. until i equip myself enough i think i am looking at a power supply issue somewhere myself. i have a fluke 289 with a gazillion probes and infrared thermos but still do not have a fast enough laptop to get 4 samples per second of the entire data output of pcm at the same time. instead it can one sample every three seconds. it is really making it difficult right now to catch a intermittent data glitch.

do what you can and let me know what happens. i will stop rambling till the next post.

 

[nimrod.sixty9]

gear selection indicator foo.

switch actually has two inputs and five outputs. just the ones i mentioned just happen to branch off the same input line.

the power to pcm can be tested with the pcm connectors off and tun the key as needed to check the power voltage the sensor ones can be tested at sensor connectors.

so looking at the video again it does not seem to be tied to fuel flow after all. it can only be the iac that is doing it as it is the only servo device around there engine with the exception of egr. if i recall correctly mine does the same. part in oe. i have a spare because i believed that it is faulting and choking the engine and won't let it start every few weeks. strange part is when it happens i have to turn key off and literally open and close my door. i am looking into the issue which started after the 0411 pcm upgrade. i am not fully equipment enough just yet to get fast data or easy answers and i know the program on it has some altered specs that are really messing up tranny shift when i floor it while already moving a bit. i thought it would be the iac doing it but when running it seems to react as it should and quickly as well. i had a one time egr fault qwerk that never came back before he pcm change and for some reason the fuel input got so bad i would be sometimes at 8mpg till i shut down. would floor it and make it look it was puffing diesel smoke particles. could restart and then maybe 15mpg say 30 minutes later. only happened once on on trip to come home. am looking into several other things tied to it. seem to be normal since then. have not touch the egr as it seems to be working correctly now. until i equip myself enough i think i am looking at a power supply issue somewhere myself. i have a fluke 289 with a gazillion probes and infrared thermos but still do not have a fast enough laptop to get 4 samples per second of the entire data output of pcm at the same time. instead it can one sample every three seconds. it is really making it difficult right now to catch a intermittent data glitch.

do what you can and let me know what happens. i will stop rambling till the next post.

Hell this is getting confusing. Being intermittent isnt going to help either
Im going do another test on spark when I get home.

I never noticed if the gear light was on, but looking at the first video, seems good to go.

Also, I really dont think the IAC is making the noise. I swapped the entire TB between vehicles; so including the IAC and TPS. Noise stayed with the Yukon and Tahoe quite as can be.

 

[SunlitComet]

that only other device that can make a noise like that is possibly the egr. it is also servo drive type. every other sensor is not motor driven. you want to try the egr?

 

[nimrod.sixty9]

that only other device that can make a noise like that is possibly the egr. it is also servo drive type. every other sensor is not motor driven. you want to try the egr?

Maybe so, Im going to try and get a better recording. Wonder if it could cause a no start if it's stuck wide open or being told to stay wide open.

Also, whats the specs on your laptop? Maybe I can help you out.