Hi. My Miniram is off and the Super ram on. I did not adjust my lower VE tables at all and the car starts and idles fine with IAC counts of 40 and, KPA of 50 and BLM/INT of 128. This is exactly the same as the Miniram. The thing is thast I have what sounds liek a vacuum leak in the intake. But I have the same vacuum level as before and the BLM and INT are the same. I'm thinking I'm just not used to the sound of the Super ram yet. With the MAF, if you had a vacuum leak, it would usually show up with a very high BLM value at idle. Does speed density follow the same path? The car runs great. I probed the intake with propane and didn't notice anything. I was really careful about sealing when I installed. Thanks
JAson

 

Jason,
What kind of Cam do you have? That will tell the story if your KPA is high enough and if you have a vacumm leak.

 

Different intakes on a given engine can sound very different. The closer you get to an independent runner setup (no plenum, one butterfly per cylinder) , the louder it gets.

Did you have to change the butterfly opening?. Some engines with a real small butterfly openings will actually whistle at idle. Retarding the timing, can allow a slightly large butterfly opening, and get rid of it. Or advancing the timng, and closing them more. Both just move around when it whistles.

All EFIs react the same to vac leaks.

You can have a vac leak on the bottom side of the manifold (into the lifter valley), and propane won't find that.

 

Grump, no change was required to the butterlies (58mm tb) and my IAC counts are the same. I guess that would mean I have no leaks. Leirch, my cam is the same I ran with the miniram. 220/229 duration .550/.550lift.

 

Hmmm, It sounds like your KPA should be around 55-60 at idle. This same question/coversation has just come up with Kevin in another post. He noticed that his throttle blades were completely closed and when he opened them it seemed to raise the load value up to where it should be.
I don't know if this is relating to your problem but it sounds like a place to start.


Brendan

 

Read my post again. I don't have a problem.

 

I realize that it is running the same. I was just wondering about the KPA value at idle.. it sounded a little low.

 

You think? Trax's car idles at 70KPA. My car pulls a rock steady 14 inches at ilde.

Jason

 

While comparing KPA values, trax's is at 70-+ , mine is at 55-+, yours is at 50+-? That sure doesn't sound correct. Maybe I'm just seeing something that isn't there. I have the LPE 219/219 cam, yours is a little bigger than mine and a little smaller than Trax's so I'd imagine yours would be around 60+-.

Brendan

[This message has been edited by leirch (edited September 03, 2001).]

 

Remember Leirch that I higher KPA value means a lower vacuum. With your cam, I would maybe expect a little lower value than mine. Bigger cam = higher KPA at idle.

Jason

 

Remember guys ... my cam is 230/245. That's hella bigger than 219.

Tim

------------------
TRAXION's 1990 IROC-Z
Best Time = 12.244 @ 112.51mph (1.778 60' / 7.819@88.32mph in the 1/8)
All Natural. No Force. No Drugs. Stock Bottom End. Stock Body Panels.
Gunning for NA 11's with bigger cam, bigger stall, and bigger exhaust.
-=ICON Motorsports=-
Moderator: PROM board at thirdgen.org

 

Jason, Tim,
Thats exactly what I have been saying, Jason's seems a little lower than mine(and shouldn't be). Tim's is alot higher than mine and it should be.

Brendan

 

The tune can play a big role in this.
Lots of timing adds to vac., but raises idle speed (no other changes). Lean will drop idle some (all other things being equal).
I could get my Comp cam 270 355 to idle from 45 to 55 K/Pa. Best idle quality for My combo was at the 55 area.

Took adding restrictors for the brake booster PCV etc to get the 45 number.

 

Another factor to consider is your elevation. I am noticing that at higher elevations my KPAs at idle are lower than at sea level.

You cannot directly correlate the Vacuum to the MAP sensors KPAs without correcting for elevation. At sea level, where your max KPA is 102 if you turn off the engine but leave the scan tool connected to the ECM. If you are getting MAP values of 50, this indicates a vacuum of 52 kpas. If you do the same reading at a higher elevation, your kpa at idle (and also if you measure the MAP sensor by turning off the engine) will be reduced accordingly.

Lastly, it is not a direct 1:1 relationship either as air pressure differences change as you increase in elevation. At sea level, you loose about 1 kpa for every 300 feet but as you increase in elevation, the ratio is different.

I'm just trying to make sure people don't try and use the MAP sensor as a means of compariing vacuum's of cams at idle as the MAP sensor is dependent on elevation, while vacuum is not (well, not as much...though it is too, but differently due to less dense air).

 

Ahhh, I understand now. Very good points.
Its all good now.

 

I know this is an ancient thread, but I'm trying to understand if/why a speed density system (mine is 7747) would care about a vacuum leak. Seems to me having a big gaping hole in the intake manifold would be no different than pressing down on the throttle. Unlike a MAF system, the sensors would all say the right thing, you'd just be operating in a different MAP/RPM cell than you would be without the leak. Am I missing something? I'm chasing a high BLM at idle problem. I'll look for a vac leak if I should, but I can't understand why that makes sense. Thanks.

 

Yikes ! This IS an ancient thread!!! You dug this puppy up 10 years later almost to the day. I still have this car and I still am running the SD ECM. I can't remember the SR whistling or if I had to go in there and fix it.

 

The IAC motor itself is essentially a controlled vacuum leak. Since the speed density system doesn't directly measure air flow (like a MAF system), a vacuum leak wouldn't cause your problem on a speed density car.

What would happen is that, if the leak is small, the IAC motor will close a little to compensate for the increased air flow from the leak. If the leak is so big that the IAC motor runs out of adjustment, you'd see an increase in idle speed.

Nevertheless, a vacuum leak wouldn't cause high BLM's.

 

can I just use the IACmotor to tune my car at an idle through 1600 rpm? im in 7727 pcm but using a 7730.

was thinking of pulling out the chip, stick in an idle at 700rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle at 800rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle at 900rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle a 1000rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle a 1100rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle a 1200rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle a 1300rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle o 1400rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle o 1500rpm, get a int/blm reading.
pulling out chip, adjusting, putting in an idle o 1600rpm, get a int/blm reading.

.. i have a 58mm tb. and there is no one way in heck i can control throttle through the first 1600rpms or so, it gets easier to get readings on tunerpro after about 1600rpm... or to do an averaging function.

 

You can't tune BLMs with the IAC motor. The total air flow into the engine is the sum of all the air coming in- i.e., throttle blades, IAC, PCV valve, any vacuum leaks... On a MAP car, the computer doesn't care where the air is coming from. It's simply going to look at the resulting manifold air pressure and throw in an amount of fuel that corresponds to what you have in the VE table (notwithstanding any other malfunctions).

 

That makes sense to me. The one thought I had was if the leak was kind of big and the IAC closed up, might fuel start condensing on the throttle blades? This would result in less useful fuel to the engine and cause the closed loop system to ask for more. Just a theory.

I changed my PCV valve and I think things might be improved. It's hard to tell. I had the PCV from my carb application and I bought the one for a TBI application. They were different part numbers, not sure how much it matters.