3" blow through setup, idle problems

[Ludachris]

So, as some of you may know I just put a new motor in the car. It's a 2.3L with cams, 3" MAF-MAFT/blow through, 56 trim turbo, 850cc injectors, S-AFC, yadda yadda yadda. Obviously, this being a completely new setup, I was expecting some issues to begin with anyway - no biggie. I can't keep it from stalling.

It starts up fine and idles at 900 or so when warm. However, when I free rev it and let off it dies. If it's been running a while, I can't get it to start up again to hold idle. I have to let it cool for a while then start it up again and the same thing happens. I checked the resistance on the ISC coils and they're fine. And the fact that the idle speed adjusted as the car warmed up tells me that the motor itself isn't bad. I've checked all the vaccuum lines. I'm wondering if it has to do with the breather on the valve cover...

Also, while I had it idling, I saw that the O2 trim at 1k were pretty lean so I adjusted the IDLE knob up 2 clicks to get the O2 trim near 100%. However, revving it to 2k shows the O2 trims drop down to about 50%. I'm thinking I'll have to richen up the idle and lean out the base? Oh well, I just want to get it to not stall first.

I know 850cc injectors are pretty big and the cams will add to the problem, but I wanted to know if this was a common issue with 3" blow-through systems (with big injectors and cams) or not. These are my cam specs:

Lift: .391 - .379
Duration: .258 - .255
@ .050
Separation: 106

Any help would be appreciated.

 

[psychlow]

Might sound basic, but have you pressurized the intake to check for leaks? A small leak can wreak havok on tuning and idle quality.

 

[Ludachris]

Might sound basic, but have you pressurized the intake to check for leaks? A small leak can wreak havok on tuning and idle quality.

Well, I haven't checked for boost leaks yet, but I have tightened down all connections between the MAF and the throttle body pretty damned tight. I plan on making a new pressure test tool tomorrow. The old one I have isn't the right size anymore.

Besides, I've had leaks before and they didn't cause consistent stalling like this. I'm thinking it would take a pretty bad leak to cause constant stalling - am I wrong?

 

[Ludachris]

Just checked for leaks - I found a tiny leak at the BISS screw, so I replaced the o-ring. That did help a little bit, as the car only stalls when I let of the throttle coming to a stop. At least I've been able to get it to idle a couple times by feathering it ever so slightly - I couldn't even do that before. But it still dies about 99% of the time even after getting rid of the tiny leaks.

Any other suggestions? I know there are other people out there running bigger cams than me that don't have this problem - what is it you guys had to do? I've checked the BISS, the ISC, and leaks. What do I check next?

 

[L2RTSiAWD]

Have you tried getting the idle straight with the MAFT zeroed out so your just relying on the AFC.

 

[Ludachris]

Have you tried getting the idle straight with the MAFT zeroed out so your just relying on the AFC.

I'll see if that makes a difference today.

 

[Ludachris]

Have you tried getting the idle straight with the MAFT zeroed out so your just relying on the AFC.

Didn't seem to help keep the car from dying when coming to a stop.

 

[Budget90GST]

The PCV has something to do with it. Normally the air coming in through the valve cover would have been metered by the stock MAS and now it's going into your intake manifold unaccounted for since you moved your MAF. Just try plugging the intake manifold fitting from the PCV temporarily and see if it helps. If it does then look into running both lines from the valve cover in to a catch can.

 

[DSMJim]

If you have a big cam, your just simply going to have to turn up your idle. If the car is chugging at a 900rpm idle while it's sitting there then it's gonna die when you let off. You'll have to put your idle up to 1000 or 1100rpm so that it holds when you let off.

Unfortunately unless you have some fancy tuning tools, larger lift cams will wanna stall at low RPM. Remember the big ass lumpy cam sound from V8's? Your now experiencing the same problems they had.

 

[lord_gufi]

adjust your biss... or your isc is out.

My 2.3 was doing the same. The cams you have probably aren't even as bad as it would be with the 2.0. 2.3 will idle Much better/stock sounding compared to a 2.0 because of better vaccume.

imo your biss needs to be adjusted

 

[Ludachris]

adjust your biss... or your isc is out.

My 2.3 was doing the same. The cams you have probably aren't even as bad as it would be with the 2.0. 2.3 will idle Much better/stock sounding compared to a 2.0 because of better vaccume.

imo your biss needs to be adjusted

I´ve messed with the BISS and ISC. The cams aren´t that big, but I guess they may be causing problems. Unfortunately, the chip I got from Jeff O. is programed for 900rpm. I figured that would be high enough... guess not.

 

[psychlow]

I know you already checked for leaks and stuff, but to followup:

Besides, I've had leaks before and they didn't cause consistent stalling like this. I'm thinking it would take a pretty bad leak to cause constant stalling - am I wrong?

You're right, sorta. Leaks between the turbo and the T/B will hardly be noticable, especially if they're small. Even a small leak between the T/B and the head can screw with idle incredibly because it's not only a boost leak, it's now also a vacuum leak. Vacuum is the only way the engine has to suck in air and fuel when it's idling and before boost hits. If you're pulling air in that's not going past your MAF, your A/F's will get screwy and vacuum will decrease as a result. This leads to crappy idle.

If you have huge cams, this problem gets multiplited.

Leaks prior to the T/B do also have an effect, just not as much because the air can't get past the T/B plate easily when it's closed. After-TB leaks are like throttling up your car without the intake hose attached - there's no valve to control the flow into the engine.

 

[awdsm drft]

Did you have the capacitors redone when you socketed your eprom?

If not thats a long shot but you never know.

 

[psychlow]

Did you have the capacitors redone when you socketed your eprom?

If not thats a long shot but you never know.

This is a good call.

Chris, have you tried another known good ECU?

 

[Ludachris]

This is a good call.

Chris, have you tried another known good ECU?

The capacitors were replaced. I don't have another ECU handy. I'll doublecheck for leaks yet again and will go from there. I checked between the TB and the MAF pretty good, but who knows, maybe I missed something....

Should I try plumbing the valve cover breather back in somewhere? It seems to me that's sucking in unmetered air and could be causing problems as well.

 

[ChicagoGSX]

The capacitors were replaced. I don't have another ECU handy. I'll doublecheck for leaks yet again and will go from there. I checked between the TB and the MAF pretty good, but who knows, maybe I missed something....

Should I try plumbing the valve cover breather back in somewhere? It seems to me that's sucking in unmetered air and could be causing problems as well.

My vc breather doesn't suck in any air at idle, that doesn't sound right.

 

[Ludachris]

Okay, so Mike at Full Throttle brought up a good point - I have an ACT Xact Flywheel. It's dropping revs faster than stock and the ECU isn't compensating for it correctly. He suggested opening the throttle blade a little and resetting the TPS.

 

[psychlow]

Does it only die after you rev it, then? Will it hold idle otherwise?

Should I try plumbing the valve cover breather back in somewhere? It seems to me that's sucking in unmetered air and could be causing problems as well.

As long as you have the grommet on the intake manifold plugged, this shouldn't be an issue. The valve cover and crankcase is sealed from the combustion chamber by the piston rings. It can't get unmetered air in unless it goes past the rings (and all that oil) somehow.

 

[Ludachris]

Does it only die after you rev it, then? Will it hold idle otherwise?

It idles fine until I rev it.

As long as you have the grommet on the intake manifold plugged, this shouldn't be an issue. The valve cover and crankcase is sealed from the combustion chamber by the piston rings. It can't get unmetered air in unless it goes past the rings (and all that oil) somehow.

Cool.

 

[psychlow]

It idles fine until I rev it.

OK - then as long as you don't have any sort of hesitation or anything like that and it revs freely, it's probably not A/F related. The flywheel could indeed be your culprit....

 

[CYCLONE]

I'm a little confused, do you have a pcv valve on the car right now?
Because I tried running wit out one and had the same problems.
I know of a couple guys that have the valves connected to the manifold
only, and they don't have any idle problems.

Also to get my car to idle right I had to get my low fuel trim up to about
115-120. My chip is set at 850rpm for idle and that's where it will stay
but only with the low setting at 115+

Also do you have a wide band meter?
Because my reads about 13.5-14a/f even though my fuel trims are set lean.

 

[1fast97gsx]

my car was doing the same thing ... adjusted the biss and it stopped. ( built 2.0 with scm 61 )

 

[Maglin]

Yeah if you have a lightweiight flywheel and BS elim. and even the lightweight crank pully you are proably being effected bu tje ECU as it's not opening up the ISC fast enought to catch the quick decell the engine now has for it to maintain a idle. I'm sure Jeff O. will have it figured out in a few days to a week.

 

[Ludachris]

Just an update - I'm waiting to hear back from Jeff at DSMchips to see if he can do a mod so that the ECU can compensate with the ISC to catch the RPMs before it stalls. If he can't then I'll throw the stock flywheel back in and be done with it.

 

[Maglin]

I wouldn't worry. I'm sure Jeff will have this sorted out very shortly. I usually always follow his threads along with Kyle's and Carl's on the ECU board. It's in the works and you can be assured that this can and will be fixed. Just have to do some testing which is the hardest thing to do if you don't have a test car on hand.