underpsi68

I just tried to do the IAC valve test on the scanner. I went from 0-100% duty and the rpm did not change at all. Than after a few seconds the scanner said "can not execute test due to PCM hardware or engine component fault".

The connector and wires were in great shape.

I removed the IAC and the value was not resting on the seat. Is this the normal power off position? That would explain my idle raising up some rpm. (the gasket was in great shape/clean/no leaks. I also blew in the IAC hose from the TB and no restriction.

BUP

iTrader: (9)

like I said in a past post # 10 ---- guardian mode (4247 rpm showing 89 % power) and rpm exceeded that - overspeed / max rpm exceeded fault set as that was your solid horn after the 2 beeps warning. Good guess on my part

I would reset your throttle plate to the correct position and make sure your throttle cable is adjusted correctly as well. I would rerun the engine making sure idle speed is correct and engine fully warmed up. The I would watch the PWM of the IAC for a fully warmed up engine with correct idle at needs to 26 % theu 35 % PWM best is 30 % spot on at idle.

IMO you need a brand new IAC as well installed.

underpsi68

I just installed a new IAC and ran on the hose. The alarm seems to have stopped and the IAC duty cycle is down around 20% now. It was starting to rain so I had to stop for the night. I will adjust the throttle stop to get 30% at a 650rpm idle.

THANKS for the help John!!!!

I have another question if you don't mind: At a 650rpm idle the timing is showing 0 to negative 9 degrees. Is that correct or do I have something else going on? Knock sensor maybe???

Ryan00TJ

iTrader: (8)

Timing going negative at idle is normal with this application. I've also tried the IAC test with my scan tool with no success. Maybe John can tell us what's going on. Sounds like you have her fixed! Good job. The $$ spent on the scan tool will pay for itself in the long run.

underpsi68

Yes the scanner was definitely a good buy. It gives a lot of good info. I also found out my engine has less hours than the hour meter shows.

I'm thinking the low timing at idle might have something to do with emissions.

On the IAC test there was a slight increase and decrease in rpm, maybe 50rpm if I remember correctly. I'll check again this weekend.

BUP

iTrader: (9)

Timing is all over the place at idle normal depending and based how the engine runs and then accelerates. A basic answer here but more info.

Also your scan will show knock sensor faults if they took place plus will show in history of the scan. Knock sensor 1 and 2 fault code(s) number 10 fault code for knock sensor 1 and fault code 11 for knock sensor 2.

Not to get into a full story book of whats going on but a jist of how this ignition works so maybe see whats going on.

The triple nickle as we call it = PCM 555 - it controls ALL ignition events and system operating functions from start up to idling to when the throttle(s) are advancing . It constantly adjusts dwell and spark timing as it uses engine speed and position(s) outputs from the crank sensor and the cam position sensor to control the sequence and dwell and timing of the spark. Do not forget the PCM also monitors other sensors in the system for its information like MAP, ECT, TPS, Knock, MAT, IAC and so on all at the same time and very quickly at that to say the least.

With that said back to the ignition side - PCM 555 has 8 ignition coil drivers or some call them EST outputs (EST = Electronic Spark Timing). They are used to control the ignition driver modules located in each coil themselves. The signals are sent by the PCM to each coil to have the modules open the ground path for the coil primary winding which causes the coil to fire. Anyways basically how it all works in a nut shell.

underpsi68

Great info.

Thanks everyone!!!!!

underpsi68

Ryan I tried the IAC test again today. Going from -100 to +100 the rpm moved maybe 50-75rpm. It was very subtle but you could see it on the scanner display

BUP

iTrader: (9)

So what are you adjusting ?