Hot Air Rebuild - Low Engine Vacuum / Zero IAC Reading

[BroadcastENG]

Looking to get a better understanding the what, why, and how (to best proceed) behind low engine vacuum (vacuum break assist related) and IAC readings of zeros after initial engine fire and tune.

New engine build consists of:

• Original iron heads (ported, 3-angle valve job), 409 block, Comp 218/212 cam, 3.65 stroke Eagle crank, Eagle conRods, DSS .020 over 15cc pistons, TA front cover (high flow), Harland Sharp rockers, Johnson lifters (reduced travel), Smith Bros pushrods, RJC deep sump oil pan
• TT chip, MAF Translator, 3" LT1 MAF, Scan Master, Powerlogger, and AEM Wide Band monitor
• 5857 Work Turbo and single nozzle (M15) ally kit

I have performed the IAC reset procedure and set the MAF translator to + 10% fuel at idle. After doing so, I now have a car that starts and run on every single startup.
The car idles at 1050-1150 rpm and when in gear it idles at 825-900 rpm.

Engine Vacuum Issue
I have yet to hit the road due to the fact that my vacuum brake system no longer behaves or reacts as it did prior. The first thing I noticed was that my boost gauge was reading -11 vacuum. My original engine was at -18 vacuum.

Online research came up with an explanation for the decreased engine vacuum. Larger cam = less engine vacuum (cam card image attached)
Q1: This now sounds like common knowledge but wanted to check with the team. Would my particular build explain the lack of engine vacuum?


IAC Idle Reading Zero
I have seen IAC readings (with engine hot)from 160 to 6 and everywhere in between. I've cleaned the IAC sensor, pintle port and replaced the sensor gasket. The car is currently idling and stays running when put into R or D (this wasn't the case for several days). Like I mentioned earlier, running a good as I have been able to get it to since first engine run.

I assume the next step in dialing in IAC, I would work on dialing down the Idle Air Setting counter clockwise to "raise" IAC reading while simultaneously lowing RPM. If I try to reach an idle RPM of 800-850, the car will not stay running. if it does, the engine will not stay running.
Q: What issue should I expect if I don't bring my IAC numbers to between 10-20? Should I make smaller, micro moves (1/4 turns usually) that don't register in PL but then shut the engine off and power back on, in hopes I will see an IAC # move then?


Thanks in advance!


-G

 

[ShaunKris]

What do your BLM's show after it's warmed up?

 

[BroadcastENG]

What do your BLM's show after it's warmed up?

BLM 128

 

[ShaunKris]

The ECM will need a bit of drive time to learn as well.

 

[ShaunKris]

Which translator and chip are you using? (edited)

 

[ShaunKris]

Try resetting the ECM. Maybe open the throttle blade a tiny bit.

 

[BroadcastENG]

Which translator and chip are you using? (edited)

TT 5.7 91 octane / Alky

 

[BroadcastENG]

The ECM will need a bit of drive time to learn as well.

Yes, just bit the bullet on an electric vacuum pump and should be on the road in 4-5 days.

 

[ShaunKris]

Yes, just bit the bullet on an electric vacuum pump and should be on the road in 4-5 days.

I've seen other people run a mechanical vacuum pump. That does work.

 

[pacecarta]

Try resetting the ECM. Maybe open the throttle blade a tiny bit.

opposite actually
low iac indicates the throttle blade is open too much , turn the throttle blade screw out (CCW) to close the throttle blade a little at a time and watch the tps stays around .40-.44v, if it goes to low readjust the tps by loosening screws and rotate slightly
warmed up to op temp in gear the iac should be 20-30 counts, (tps .42-44) adjust untill you get there, rpm will come down and vac will increase

 

[BroadcastENG]

opposite actually
low iac indicates the throttle blade is open too much , turn the throttle blade screw out (CCW) to close the throttle blade a little at a time and watch the tps stays around .40-.44v, if it goes to low readjust the tps by loosening screws and rotate slightly
warmed up to op temp in gear the iac should be 20-30 counts, (tps .42-44) adjust untill you get there, rpm will come down and vac will increase.

opposite actually
low iac indicates the throttle blade is open too much , turn the throttle blade screw out (CCW) to close the throttle blade a little at a time and watch the tps stays around .40-.44v, if it goes to low readjust the tps by loosening screws and rotate slightly
warmed up to op temp in gear the iac should be 20-30 counts, (tps .42-44) adjust untill you get there, rpm will come down and vac will increase

So I'll make CCW moves while the car is running, and should not turn off the engine in-between, correct?

 

[ShaunKris]

opposite actually
low iac indicates the throttle blade is open too much , turn the throttle blade screw out (CCW) to close the throttle blade a little at a time and watch the tps stays around .40-.44v, if it goes to low readjust the tps by loosening screws and rotate slightly
warmed up to op temp in gear the iac should be 20-30 counts, (tps .42-44) adjust untill you get there, rpm will come down and vac will increase

Right, I just said that to keep it runnning so it doesn't stall and maybe keeps a bit more vacuum.

 

[pacecarta]

doesnt need to be running to adjust , scanmaster (with 7148ecm)can be used to check tps volts or you could get a low tps ses code
,but iac numbers wont change until you restart as iac will open (increase) try to get the idle rpm that programmed in the chip
IAC is zerod now because its trying to drop idle rpm by reducing air flow around the throttle blade

if you cant get idle down and iac doesnt go up look for vac leak

 

[BroadcastENG]

opposite actually
low iac indicates the throttle blade is open too much , turn the throttle blade screw out (CCW) to close the throttle blade a little at a time and watch the tps stays around .40-.44v, if it goes to low readjust the tps by loosening screws and rotate slightly
warmed up to op temp in gear the iac should be 20-30 counts, (tps .42-44) adjust untill you get there, rpm will come down and vac will increase

I can get the car to idle at around 900 rpm with no change to IAC reading (0) but now if I put it in gear, the car stalls.

doesnt need to be running to adjust , scanmaster (with 7148ecm)can be used to check tps volts or you could get a low tps ses code
,but iac numbers wont change until you restart as iac will open (increase) try to get the idle rpm that programmed in the chip
IAC is zerod now because its trying to drop idle rpm by reducing air flow around the throttle blade

if you cant get idle down and iac doesnt go up look for vac leak

I understand and have adjusted TPS using my SM G.

To Confirm: Tonight, I will make the necessary adjustments to the idle air adjustment screw (CW) to keep my car running (with the ability to shift in and out of gear) and up to temp. I will then use my SM G to bring down idle down 50-100 points down, while checking TPS, followed by turning off the engine. I will fire up the engine and look for IAC numbers to change. If the numbers don't change or are far from the target number, I will adjust once again (idle air screw CCW) and turn the engine off. Rinse and repeat, correct?