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

[SunlitComet]

mine is noisy. i have a replacement but have not done it yet.

 

[nimrod.sixty9]

I had a weird no-start issue once and this tutorial helped me to find a coil wire that was grounding out on a bracket.

http://easyautodiagnostics.com/gm_misfire_diagnostic/ignition_misfire_tests_1.php

Noisy IAC is strange though.

Before starting ignition testing, I like to verify that fuel pressure is within range. (Either through the Schrader valve pressure test, or by using some starting fluid directly into the throttle body to see if things change.)

Good Luck though ******.sixty9

Took off cap and rotor, both were dirty; cleaned points with a Dremel wire wheel. Fired right up multiple times, told girl she can drive the truck to work the following day. Comes back in in the morning and wakes to tell me it's once again doing the same thing.

Still 100% random...

Does not seem starter or short related. Itll either fire right up, or turn and turn then kick back, or turn and immediate kick back. Never just turns, turns, then starts. Pretty much can immediately tell if it will run or not.

I do need to check FP tho. Cant find my damned gauge... Going to have to rent for now.

Spark testing would be difficult due to the randomness. Already changed coil to my Tahoe and it's been running great for 4 days now. Ive pulled the bracket fairly far away from the coil wire when doing the coil change. If that had been an issue, I cant imagine it would be the problem now. Ill take a visual just to sure and maybe even change them between vehicles.

Maybe I should try the IAC; cant imagine it would cause this hell, but never know I suppose.

Really appreciate the help

0ytpy07

 

[hourang]

sounds like something is stopping the starter from spinning. usually the starter is on a separate circuit from most sensors. This seems like an issue with the ignition switch, ground/wiring issue, starter itself, maybe even neutral safety switch. this is what i would check:
-check battery cables for corrosion, make sure they are really clean and tight.
-check ground to engine
-check wiring to starter
-run a jumper cable from the battery to the starter directly with the key in the on position. this will rule out whether it is a bad switch, solenoid, etc.

 

[SunlitComet]

what bracket?

 

[nimrod.sixty9]

sounds like something is stopping the starter from spinning. usually the starter is on a separate circuit from most sensors. This seems like an issue with the ignition switch, ground/wiring issue, starter itself, maybe even neutral safety switch. this is what i would check:
-check battery cables for corrosion, make sure they are really clean and tight.
-check ground to engine
-check wiring to starter
-run a jumper cable from the battery to the starter directly with the key in the on position. this will rule out whether it is a bad switch, solenoid, etc.

Im still not convinced its the starter because there are times it turns and turns and turns, but the truck never runs. Its either instant start, or nothing.

On the battery one point was a little loose and both were dirty. All good to go with same result.

what bracket?

The one that goes over the pass side of the distro. Holds a wire loom in the rear and bolts to the rear of the head (i think) and to the upper plenum with the coil. Obviously put there by the worlds biggest *******.

 

[SunlitComet]

ok but put there for a reason. isolation of certain components to prevent one from hurting another.

 

[nimrod.sixty9]

ok but put there for a reason. isolation of certain components to prevent one from hurting another.

It's still there sun. Just pushed out of the way.

 

[SunlitComet]

probably won't do any harm moving a tad bit.

 

[nimrod.sixty9]

Finally got fuel pressure tester. Battery to weak to really turn it over but enough to get fuel pressure.
First prime immediately gets 63+/- PSI and stayed after attempting to to start truck.
Again tho, the issue had been random, so whose to say this time it could have been a start scenario.
Will test again when batt is charged.

 

[SunlitComet]

with that pressure it would seem that you have not pump issues. a damaged relay could slow down pressure build up but yours sound like either of those is a none issue. i would test the iac while it is out and inspect its behavior and possible try a used icm/coil if possible to see if you have thermal issues with them.

 

[nimrod.sixty9]

with that pressure it would seem that you have not pump issues. a damaged relay could slow down pressure build up but yours sound like either of those is a none issue. i would test the iac while it is out and inspect its behavior and possible try a used icm/coil if possible to see if you have thermal issues with them.

Well, I switched coil/ICM from my Hoe and the Hoe has been fine (been to Tampa and Palm Beach since).

Going to change the IAC between them and see if any changes (still gotta wait for the charge tho).

 

[SunlitComet]

don't forget to reset it after install.

 

[nimrod.sixty9]

don't forget to reset it after install.

Reset procedure? Link?
Uploading video now...

EDIT: Vid with IAC noise, no start, and putter;
https://www.youtube.com/watch?v=W7XKROSdw68&feature=youtu.be

 

[SunlitComet]

alright that noise i believe is the fuel running thru its manifold and regulator. have you tested for spark when it won't go. you can have no spark from ignition system or fuel injector connections that are poor somewhere or the pcm won't send the reference for spark and fuel because it is not seeing activity from the crank sensor. you can lose the cam sensor and have a long rough start but it should run regardless. try spark testing at least two front cylinders on each side and look for oddities in there pattern.

---------- Post added at 05:31 PM ---------- Previous post was at 05:26 PM ----------

even you previous video has me thinking you are have a crank sensor issue. do you have any crack on the block mounting bosses where the starter go?

i posted this in 2011. kinda fits your problem i think.

SunlitComet
02-19-2011, 12:03 AM
It sound like you are suffering from the tsb below. You said you replaced the crank sensor perhaps you got another bad sensor or something in the wiring is goofed. You can also have a left over symptom listed below that was over looked. One other thing did you perform the crank relearn procedure when you replaced it last? Here is the TSB details:


Engine - No/Hard/Slow Start/Backfire/Kickback


File In Section: 06 - Engine/Propulsion System

Bulletin No.: 00-06-04-014

Date: April, 2000

TECHNICAL
Subject:
No, Hard, or Slow Start, Backfire or "Kickback" During
Crank/Start, "Grinding" or Unusual Noises During Crank, DTC P0338
(Replace Crankshaft Position Sensor)

Models:
1999-2000 Cadillac Escalade
1995-2000 Chevrolet and GMC SIT Models
1996-2000 Chevrolet and GMC C/K, M/L, G, P Models
1996-2000 Oldsmobile Bravada
with 4.3 L, 5.0 L, 5.7 L or 7.4 L Engine
(VINs W, X, M, R, J RPOs L35, LF6, L30, L31, L29)

Condition:
Some customers may comment on one or more of the following conditions:

^ Backfire during crank/start
^ "Kickback" during crank/start
^ "No" start
^ "Slow" or "hard" start/crank
^ "Grinding" or unusual noises during crank/start
^ Cracked or broken engine block at the starter boss
^ Broken starter drive housing
^ Broken starter ring gear on flywheel
^ Any combination of the above

Cause:
A condition may exist that allows the crankshaft position sensor to command up to 50 extra degrees of spark advance during engine cranking only. This in turn exposes the engine to higher than normal cylinder pressures which may result in an inoperative condition to the starter drive housing, the engine flywheel starter ring gear, or the engine block at the outside edge of the starter boss.

Correction:
Inspect for a stored powertrain DTC code P0338. This DTC will NOT illuminate the "Service Engine Soon" light. If this code is stored, the Crankshaft Position Sensor, P/N 10456607, MUST be replaced and the remaining components inspected for damage (engine block at the starter boss, the starter drive housing, and the engine flywheel starter ring gear).

Notice : When DTC code P0338 is set, failure to replace the Crankshaft Position Sensor could result in repeated inoperative conditions of the starter or flywheel.

Important : Some flywheel wear is normal; broken or missing teeth and/or cracks, are not normal.

 

[nimrod.sixty9]

alright that noise i believe is the fuel running thru its manifold and regulator. have you tested for spark when it won't go. you can have no spark from ignition system or fuel injector connections that are poor somewhere or the pcm won't send the reference for spark and fuel because it is not seeing activity from the crank sensor. you can lose the cam sensor and have a long rough start but it should run regardless. try spark testing at least two front cylinders on each side and look for oddities in there pattern.

That noise does not happen on either the Tahoe or Suburban and only started making that noise when I started having the issue. It also already had pressure, cant imagine that much sound if that were the case.

Each time I tested for spark (from coil and random cyl) it was good, but could have also been an actual start scenario; reference the first video to see how one start could be perfect and the next not so much. Also, remember crank sensor is new.

EDIT
I had also pasted that TSB in this thread. Didnt see anything wrong with block, no cracks etc. There are just so many time its runs and starts perfectly. Damned randomness... Think I should try an exchange on the CPS? The scond vid does not show kickback, that noise is two sputters after cranking has stopped.

Just been thinking on this, but would a cross spark on cyl 4 in the cap cause this?

 

[SunlitComet]

i did but would suggest it was running more during each start. and when it is running get a scanner read of rpm and compare it to tach. if they off quite a bit then the crank sensor or wiring has had it. i say the fuel noise because it seem timed to the relay going on and off. regardless that pump can put out more the 70+psi so even tho there is pressure the fuel still moves while regulated to about 60. i was thinking the noise was the sound of fuel rushing past the regulator into the return line. that is always happening. if the return line was blocked you would likely set your cats to melt if not catch fire outright from to much fuel or blowout any seals in the spider. to be sure try this pull the fuel pump relay out and go back to key on a few times if the same noise is still there it has to be the iac.

---------- Post added at 06:03 PM ---------- Previous post was at 05:53 PM ----------

cross sparking can cause it sometimes but in the video last it would have to cross a lot at the same time or just not pass the spark to get what you had. when you can try the rpm readout test . dont do the cps just yet. you will need a high end scanner to case relearn if you do.

 

[nimrod.sixty9]

i did but would suggest it was running more during each start. and when it is running get a scanner read of rpm and compare it to tach. if they off quite a bit then the crank sensor or wiring has had it. i say the fuel noise because it seem timed to the relay going on and off. regardless that pump can put out more the 70+psi so even tho there is pressure the fuel still moves while regulated to about 60. i was thinking the noise was the sound of fuel rushing past the regulator into the return line. that is always happening. if the return line was blocked you would likely set your cats to melt if not catch fire outright from to much fuel or blowout any seals in the spider. to be sure try this pull the fuel pump relay out and go back to key on a few times if the same noise is still there it has to be the iac.

---------- Post added at 06:03 PM ---------- Previous post was at 05:53 PM ----------

cross sparking can cause it sometimes but in the video last it would have to cross a lot at the same time or just not pass the spark to get what you had. when you can try the rpm readout test . dont do the cps just yet. you will need a high end scanner to case relearn if you do.

Err, forgot about return line

I can imagine the RPM comparison is when running, compare via OBD readout to gauge?

Unless I missed it, how do I reset IAC?

Another thing I find weird is that it works fine when it runs. This only happens during start. If it starts its good to go, never stalled (except once awhile ago which may have been gas). That said, I wouldn't think no spark issue would would arise say from coil or cap.

 

[SunlitComet]

yes compare the obd scanner read rpm to the tachometer on dash. iac is start and run for 20 seconds, off for ten then start again. likely, any possibility of active or stored codes on the pcm?

 

[nimrod.sixty9]

yes compare the obd scanner read rpm to the tachometer on dash. iac is start and run for 20 seconds, off for ten then start again. likely, any possibility of active or stored codes on the pcm?

Alright, will test tomorrow.

Only code I had stored was post O2 on one CAT. Nothing else...

How can I reset IAC if I cant get it to run LOL

 

[SunlitComet]

you will have to just try a few times.