Rough idle VY Commodore

[Biggsy]

Got a problem with my car that has always been there since I bought it but haven't bothered to try and fix till now.

Car: VY SS LS1 M6, Stock apart from tune.

Problem:
When in idle, motor has a miss/stumble every few seconds. It doesn't really show in a scan but you sure can feel it.

What I have tried (Not all because of problem):
New Spark Plugs
New Leads
New Coils
New Intake/exhaust gaskets
Std tune, Mod tune, mod tune mafless.
New Battery
New PCM
Checked Earths
Checked for vacuum leaks
Run a cylinder balance check and all are pretty close to each other
Compression check - Good

None of the above made a difference.

If I load the car up, eg A/c on high beams etc, it smooths out the idle a little but nothing to write home about.
Car cruises and accelerates without issue.

The only way I can make it smooth, is to use Bi-Di conrols in the scan tool and command 12.5:1, this makes it idle almost perfect. Wide Band O2 proves it is 12.5:1.

It has me baffled

The only other thing I can think of is maybe blocked injector/s, but I don't want to buy a set and find they are not the problem.

Car has 80,000kms on the clock and has had every service done on time.

Anyone have any ideas?

Cheers,

[JezzaB]

Got a problem with my car that has always been there since I bought it but haven't bothered to try and fix till now.

Car: VY SS LS1 M6, Stock apart from tune.

Problem:
When in idle, motor has a miss/stumble every few seconds. It doesn't really show in a scan but you sure can feel it.

What I have tried (Not all because of problem):
New Spark Plugs
New Leads
New Coils
New Intake/exhaust gaskets
Std tune, Mod tune, mod tune mafless.
New Battery
New PCM
Checked Earths
Checked for vacuum leaks
Run a cylinder balance check and all are pretty close to each other
Compression check - Good

None of the above made a difference.

If I load the car up, eg A/c on high beams etc, it smooths out the idle a little but nothing to write home about.
Car cruises and accelerates without issue.

The only way I can make it smooth, is to use Bi-Di conrols in the scan tool and command 12.5:1, this makes it idle almost perfect. Wide Band O2 proves it is 12.5:1.

It has me baffled

The only other thing I can think of is maybe blocked injector/s, but I don't want to buy a set and find they are not the problem.

Car has 80,000kms on the clock and has had every service done on time.

Anyone have any ideas?

Cheers,

Have you tried changing the commanded base spark idle? If you log it you will probably see when the "miss" appears the timing jumps around alot more. Could try lowering the spark swing (over/under speed correction)

Jez

[Biggsy]

Have you tried changing the commanded base spark idle? If you log it you will probably see when the "miss" appears the timing jumps around alot more. Could try lowering the spark swing (over/under speed correction)

Jez

Yes I did, even when you Bi-Di the spark control to keep it steady, it will still do it.

Even does it with a std tune.

[ntae]

Have you pulled the throttle body & cleaned it ? what are your idle steps ?

[joecar]

Dave, can you run some injector cleaner (the type that attaches to the fuel rail).

[Biggsy]

Have you pulled the throttle body & cleaned it ? what are your idle steps ?

I have not, i'll check the idle steps and clean it 2day.

Lets just assume it is the throttle body.
How come when I command 12.5:1 it idles fine?
How would the throttle body be playing a part in this?

Cheers,

[Biggsy]

Dave, can you run some injector cleaner (the type that attaches to the fuel rail).

I managed to "borrow" a set of injectors off my mates motor, gave them a try last night and it made no difference :confused:

[joecar]

Dave,

- how's your fuel filter...?
- how's your fuel pressure (is it constant when the stumble happens)...?
- can you ohm all the plug leads (noting which ohms go to which leads)...?
- when the problem happens, does batt/alt voltage drop...?
- check voltage drop on all ground wires (i.e. from block to chassis).
- check for small airleak at intake manifold.

[Biggsy]

Dave,

- how's your fuel filter...?
- how's your fuel pressure (is it constant when the stumble happens)...?
- can you ohm all the plug leads (noting which ohms go to which leads)...?
- when the problem happens, does batt/alt voltage drop...?
- check voltage drop on all ground wires (i.e. from block to chassis).
- check for small airleak at intake manifold.

Fuel filter is new

Havent checked pressure

Checked all leads, all equal (brand new aswell)

Problem always happens (except when cold and motor is running richer) and batt volts steady 14.1 even when loaded

Earth wires are all good, checked continuity back to batt on each one

I am did suspect intake leak but could not find one, resealed intake manifold. Checked with squirter bottle.

Definatly acting like an intake leak, explains why when richer is being commanded, it smooths out.

[vxchev8]

have you checked the Idle Air Control (IAC)

So there are no vacuum leaks i.e the PCV valve near throttle body.

Try a reset - PCM/Idle learn here (http://sikls1.v8owners.com.au/index28.html) cost you nothing :grin:

[JezzaB]

have you checked the Idle Air Control (IAC)

So there are no vacuum leaks i.e the PCV valve near throttle body.

Try a reset - PCM/Idle learn here (http://sikls1.v8owners.com.au/index28.html) cost you nothing :grin:

Good point but if your Desired Airflow is good, a good old PCM reset wont do jack. Sorry Les :p

[vxchev8]

come on Jez worked back in 2002 :grin: , Biggsy give your IAC a clean see how that goes.

[joecar]

Dave,

Do you have access to an automotive style oscilloscope (e.g. Pico scope)...?

If you do, you could examine these waveforms:
- crank sensor voltage,
- injector voltage/current,
- coil secondary voltage [capacitive probe],
- fuel pump current.

Any misfire/stumble has to show up on at least one of those.

If you always had this problem, then is must be due to something in the "next layer down".

Post up some logs.

[Biggsy]

come on Jez worked back in 2002 :grin: , Biggsy give your IAC a clean see how that goes.

I have already done that when I resealed the manifold, thanks anyway.

12.5 AFR makes it run fine, this is the biggest clue I have.

[Biggsy]

Dave,

Do you have access to an automotive style oscilloscope (e.g. Pico scope)...?

If you do, you could examine these waveforms:
- crank sensor voltage,
- injector voltage/current,
- coil secondary voltage [capacitive probe],
- fuel pump current.

Any misfire/stumble has to show up on at least one of those.

If you always had this problem, then is must be due to something in the "next layer down".

Post up some logs.


No oscilloscope unfortunately Joe :frown:

Logs do not show anything.
I have a log that I did that shows a straight WBO2 line, straight timing line, straight MAP line and a RPM line which keeps within +/- 15rpm yet I can feel the stumbling and hear it poping in the exhaust.

"AFR 12.5 makes it run fine" keeps repeating in my head. I'm thinking I have one or two cylinders running lean. I have been tuning with this condition so to get the right AFR in the exhaust.

I would have increased the overall fueling to make the AFR average to be stoich @ the O2 sensors.
Now I have 6 or 7 cylinders running richer than stoich and 1 or2 cylinders running leaner that stoich which averages
The motor will run quite fine richer that stoich but doesnt lik running leaner than stoich.
So, when I command 12.5 @ idle, I get 1 or 2 cylinders running @ or above stoich and 6 or 7 well above stoich (>12.5 AFR) which allows it to run smooth.

Having said all that, I have to find the cause of this leaning!
Heads, gaskets, worn cam/rockers/lifters could also be an issue.
Of course, I could be totally wrong.

Might have just justified myself getting a 6lt ls2 or l98 crate motor (getting cheap as now)

"Darling, me and the EFILIVE boys have worked out the motor in my car is worn out and I need to get another one!"

How'd you reckon I'd go?

Cheers,

[joecar]

Dave,

lol... "and I can save money by buying a new motor"... :D

Move the wideband to the other bank and see what it shows.

Do your logs show a variation in rpm...?

Is EVAP, EGR, AIR getting in the way...?

[macca_779]

What are the NB's doing Biggsy. Force it closed loop and log both sides. If you don't trust the sensors you could swap them over too. On the other hand, and I know you don't really want to do it but if its likes 12.5 at idle, give it 12.5.

[ssvolvo]

I'm an auto technician by trade(but not a tuner!). I'll give this a shot. You already know what is happening. It's obvious you have a lean stumble and if you fatten it up the miss goes away. You might try to take away a tiny bit of timing right at that idle RPM. Before I even try that I would try to isolate the cylinder(s) that are causing the problem. Can you change {C5621} misfire idle per cylinder mode and try to get the thing to code by making it very sensitive?
Most GMs that have a misfire problem take an act of congress to set a code, then most VW/Audi products can misfire like twice (really) and set a MIL light....VERY SENSITIVE!
Once you see which hole(s) are acting up then it might be easier to diagnose. Also we use a cylinder leakdown tester in conjunction with a compression tester to verify cylinder leakage (much more accurate). Also a mechanics stethoscope will sense even the tiniest of vacuum leaks near the intake manifold for cheap money!
Your engine should idle fine at stoich, you already know that. A wide band might even "pulse" enough to show a lean cylinder. Might be a tough one but you are already on the right track.


Food for thought, John:Eyecrazy:

[Biggsy]

Dave,

lol... "and I can save money by buying a new motor"... :D

Move the wideband to the other bank and see what it shows.

Do your logs show a variation in rpm...?

Is EVAP, EGR, AIR getting in the way...?


Logs show very little variation

What do you mean EVAP, EGR, AIR "getting in the way"?

[Biggsy]

.......... On the other hand, and I know you don't really want to do it but if its likes 12.5 at idle, give it 12.5.

How do I idle at 12.5 but keep in closed loop for other areas?
It should idle at stoich, every other car does!

[Biggsy]

I'm an auto technician by trade(but not a tuner!). I'll give this a shot. You already know what is happening. It's obvious you have a lean stumble and if you fatten it up the miss goes away. You might try to take away a tiny bit of timing right at that idle RPM. Before I even try that I would try to isolate the cylinder(s) that are causing the problem. Can you change {C5621} misfire idle per cylinder mode and try to get the thing to code by making it very sensitive?
Most GMs that have a misfire problem take an act of congress to set a code, then most VW/Audi products can misfire like twice (really) and set a MIL light....VERY SENSITIVE!
Once you see which hole(s) are acting up then it might be easier to diagnose. Also we use a cylinder leakdown tester in conjunction with a compression tester to verify cylinder leakage (much more accurate). Also a mechanics stethoscope will sense even the tiniest of vacuum leaks near the intake manifold for cheap money!
Your engine should idle fine at stoich, you already know that. A wide band might even "pulse" enough to show a lean cylinder. Might be a tough one but you are already on the right track.


Food for thought, John:Eyecrazy:

Food for thought indeed!

I'm loving your idea about increasing the sensitivity of missfire detection! Something I would normally think of but didn't:shock:

I'll have a play this week.

Thanx for the idea John :cheers:

I'll keep everyone informed.

Cheers,

[macca_779]

How do I idle at 12.5 but keep in closed loop for other areas?
It should idle at stoich, every other car does!

Simple, you use Custom OS3 or 5 and command it. The Semi Open loop nature of OS3/5 means that when you command 14.63 its closed loop.. Anything else and its open loop. Pretty much every cammed car I've tuned with a tightish LSA and over 224 duration I command around 14.2-13.6 as that's what they tend to like in my experience.

[joecar]

What do you mean EVAP, EGR, AIR "getting in the way"?If these are leaking then you would see a stumble at idle...

Each of those has a connection to the intake manifold (the AIR solenoid allows vacuum to open the AIR router)...

Oh, but if those were leaking then you would see it in the wideband AFR, which you don't... I was thinking out loud. :fluffy:

[Biggsy]

Simple, you use Custom OS3 or 5 and command it. The Semi Open loop nature of OS3/5 means that when you command 14.63 its closed loop.. Anything else and its open loop. Pretty much every cammed car I've tuned with a tightish LSA and over 224 duration I command around 14.2-13.6 as that's what they tend to like in my experience.

Thanx for that, I didn't know!

Cheers,

[Sikhabib]

what kind of spark plugs are you running and what did you set the plug gaps?
On my car i run tr6 plugs cause i have turbos. i was having trouble with spark blow out at higher rpm so to fix it i closed the plug gaps down to 0.26 which fixed the higher rpm problem but it then developed an idle miss similar to what your having. i opened my gaps slightly and it idled beautifully again.

maybe something to try??

[Biggsy]

what kind of spark plugs are you running and what did you set the plug gaps?
On my car i run tr6 plugs cause i have turbos. i was having trouble with spark blow out at higher rpm so to fix it i closed the plug gaps down to 0.26 which fixed the higher rpm problem but it then developed an idle miss similar to what your having. i opened my gaps slightly and it idled beautifully again.

maybe something to try??

I run the genuine plugs (Delco I think), can't remember the gap off hand but it was what the OEM Manual said.

I'll try what others have said first because this is the second set of plugs that I have tried. Incidently, all plugs looked healthy and the same when I pulled them out (ie could not see the 1 or 2 cylinders faulty like I am suspecting). Maybe if I let it idle for 1 hour then pull the plugs, they might tell me something.

If I can't find anything else, I will have a try of what you have suggested. Just got to finish work on time 1 day this week so I can try people's suggestions

Cheers,

[joecar]

Dave,

GM have revised the plug gap from 0.060" (1.52mm) to 0.040" (1.01mm).



Ignition System - New Spark Plugs/Gapping

Bulletin No.: 03-06-04-060A

Date: February 12, 2007

INFORMATION

Subject: Information on New Spark Plugs and Gapping

Models:
2004 Buick Rainier
2002-2004 Cadillac Escalade, Escalade EXT
2003-2004 Cadillac Escalade ESV
2004 Cadillac CTS-V
1997-2004 Chevrolet Corvette
1998-2002 Chevrolet Camaro
1999-2004 Chevrolet Silverado
2000-2004 Chevrolet Suburban, Tahoe
2002-2004 Chevrolet Avalanche
2003-2004 Chevrolet Express, TrailBlazer
1999-2004 GMC Sierra
2000-2004 GMC Yukon, Yukon XL
2001-2004 GMC Yukon Denali, Yukon XL Denali
2002-2004 GMC Sierra Denali
2003-2004 GMC Envoy XL
1998-2002 Pontiac Firebird
2004 Pontiac GTO
2003-2004 HUMMER H2

with 4.8L, 5.3L, 5.7L or 6.0L V-8 Engine (VINs V, P, T, Z, G, S, N, U - RPOs LR4, LM4, LM7, L59, LS1, L56, LQ9, LQ4)

Attention: Please disregard the Set Gap Per Vehicle Specification statement on the side of an ACDelco(R) Iridium Spark Plug Box. The statement will be removed from the boxes in the future.

Supercede:

This bulletin is being revised to bring attention to the Set Gap Per Vehicle Specification on the ACDelco(R) Iridium Spark Plug Boxes. Please discard Corporate Bulletin Number 03-06-04-060 (Section 06 - Engine/Propulsion System).

A new spark plug has been released for use in the above vehicles. The new spark plug has an Iridium tip instead of the current Platinum tip. Due to the different tip design, the gap of the spark plug has also changed.

The new spark plug, P/N 12571164 with AC Delco P/N 41-985, is gapped to 1.01 mm (0.040 in) when the spark plug is made.

The spark plug gap is set during manufacturing and should not be changed or damage to the spark plug may result. Any new spark plug found to not be properly gapped should not be used.

[Biggsy]

OK, I set {c5621} values to 1 and still couldn't get it to log a missfire, even when I unplugged an injector! It does not work.

I have uploaded COS3 to run semi-OL, that has given me a temp fix, but can still feel it (but know where near as bad)

The stumble is worse when the ambient outside temp is colder.

NB O2's are switching fine and are similar in both banks.

Cleaned throttle body.

Changed spark plugs again, gapped them as per Joecar's post.

Listened for air leaks with stethascope, could not find one.

Begining to think its just a dud motor and has always been like this from new.

[joecar]

:doh:Oh, I just remembered that failing the MAF prevents the misfire monitor from running...

sorry Dave, I should have thought of that...

[Delco]

The first thing is to clean the injectors and do a cylinder leakage test - no amount of electionic trickery will cure a mechanical problem like a low flo injector or a leaking valve , guides wear pretty badly on a LS1 , I see a lot of engines that have intake valve leakage when doing cam upgrades

[Biggsy]

:doh:Oh, I just remembered that failing the MAF prevents the misfire monitor from running...

sorry Dave, I should have thought of that...

Oh well, poo happens!:)

[Biggsy]

The first thing is to clean the injectors and do a cylinder leakage test - no amount of electionic trickery will cure a mechanical problem like a low flo injector or a leaking valve , guides wear pretty badly on a LS1 , I see a lot of engines that have intake valve leakage when doing cam upgrades

Tried a known good set of injectors (as mentioned earlier), made no difference.

What do I need to do a cylinder leakage test?

If it is a leaky valve, heads will have to come off. If heads have to come off, I'm gonna change the cam!

Cheers,

[Biggsy]

Well, had a leakage test done today, no problem showed up.

I have a set of recon heads that I am putting on this weekend (oh, and a mild cam while I'm at it :angel_innocent:)
Maybe a couple of valve springs have lost pressure? Bent pushrod? Head gasket?
I will soon find out.

There will be nothing left to change after this weekend!

I really hope the problem will be fixed, getting sick of fault finding :wallbash:

[joecar]

Dave, let us know how you go.

[The Alchemist]

Hi Biggsy, I know that miss you are talking about. I see quite a few cars that have "the miss" at idle. I've never bothered spending much time chasing it though and when I have richening up the idle in open loop does seem to smooth it out. If you can live with it I wouldn't loose sleep over it.
Mike

[Biggsy]

Hi Biggsy, I know that miss you are talking about. I see quite a few cars that have "the miss" at idle. I've never bothered spending much time chasing it though and when I have richening up the idle in open loop does seem to smooth it out. If you can live with it I wouldn't loose sleep over it.
Mike

I haven't come accross any out of the 20-30 cars I have driven, but thats only a small % of what is out there.
I have started to pull my car apart and I have found a/the potential problem.
There is a little "U" shaped hose that goes between the manifold (just behind the throttle body) and the valley plate. As I went to pull it off, I noticed a split on the underside of it!

I am hoping this is the problem.

[Scoota]

Dave, I had a VY in the other day that had the same problem you are talking about (running semi Open Loop Mafless).
Just a query, If you run it in full open loop does the stumble go away.

Cheers Scotty.

[joecar]

...
I have started to pull my car apart and I have found a/the potential problem.
There is a little "U" shaped hose that goes between the manifold (just behind the throttle body) and the valley plate. As I went to pull it off, I noticed a split on the underside of it!

I am hoping this is the problem.Is this on the same side as the throttle linkage (the bank 2 side of the motor)...?

That is the PCV hose... your valley plate has the integral PCV valve.

If that hose was split, then air is entering downstream of the throttle blade... an airleak.

[Biggsy]

Dave, I had a VY in the other day that had the same problem you are talking about (running semi Open Loop Mafless).
Just a query, If you run it in full open loop does the stumble go away.

Cheers Scotty.

Running open loop does make it run better.
If I use the scan tool Bi-Di controls to change the AFR, it runs better than if I command the same in the tune.


Cheers,

[Biggsy]

Is this on the same side as the throttle linkage (the bank 2 side of the motor)...?

That is the PCV hose... your valley plate has the integral PCV valve.

If that hose was split, then air is entering downstream of the throttle blade... an airleak.

Yes, the same side as throttle linkage.
I'm used to my old VX which didn't have that there, it had a hose that ran down that side of the motor to the back somewhere.

I kind of guessed it was the PCV but didn't want to say it and be wrong!

The W/Shop manual I am using is for an earlier motor so there are a couple of differences.

What sh%ts me, is that I have had the intake manifold off before but didn't notice the split.
Over the last week or so, I've been getting a stumble even at 12.5 AFR. I guess the split has been getting bigger.

Anyway, just finishing my breakfast off and I'll get out into the cold and keep going with the dismantling. I've bought all the gaskets, springs, cam, heads etc... I'm still going to install them!

Cheers,

[Big Kahuna]

Dave doesnt it shit you to death when the cause of your grief may come down to a 20 cent part?

Down side is you get to have the joy of a cammed motor.

Grant

[Biggsy]

Dave doesnt it shit you to death when the cause of your grief may come down to a 20 cent part?

Down side is you get to have the joy of a cammed motor.

Grant

It does!

UP SIDE is having the joy of a cammed motor.

DOWN SIDE is the grief it is giving me in the install!

Crankshaft balancer bolt that took 2 hrs to remove! :cussing:
Right hand head bolts at back are right near brake booster making it real hard to undo :cussing:
Genuine puller I borrowed off a mechanic mate, broke as I was pulling balancer off :cussing:

[vxchev8]

Glad you sort out the split in the tube. I had the same problem, it's not until you give the tube a squeeze that you see the split / hole in the tube.
I upgraded to a VYII system as holden no longer sell VX system......

It cost me $60 as they don't sell in sections, only the whole thing. :shock:

[joecar]

When you're able, post a pic of the tube.

[Biggsy]

When you're able, post a pic of the tube.
I will when I get a chance!

[Biggsy]

Well, I've finally finished the upgrade!!!! WooHoooo!:fluffy::fluffy::fluffy::fluffy:

Apart from the hose I mentioned earlier, I found loose head bolts on passenger side head (Left side). The head showed signs off cross flowing between number 5 and 7 Cyl. Stupid me forgot to photograph it:doh2:

It was a nervous first key start, but it fired up straight away! Bit of a stumble as the lifters settled, but then it idled (although it was surging due to the different cam)
Played with fuel settings and timing to get it to idle better.

Guess what? The idle missfire is gone!!

If anyone is interested, the baby cam I used is a Crane 216 224 115
I didnt want a monster cam and it will suit my needs.


Thanks for everone's help and advice!

Cheers,

[joecar]

Guess what? The idle missfire is gone!!:banana::cucumber::banana::cucumber::banana:

The leak between #5 and #7 must have been small, so it mattered only at idle.

Had you noticed any change in coolant level...?

Good job Dave. :cheers:

[Biggsy]

The leak between #5 and #7 must have been small, so it mattered only at idle.

Had you noticed any change in coolant level...?

Good job Dave. :cheers:


:cheers:

No change in coolant level but a definated scorch mark between 5 and 7 at the thinnest point between the two. I put a straight edge on the head and it wasnt bent.

It's fixed though :cucumber::cucumber::cucumber:

[ssvolvo]

Glad you got it to run decent. Bottom line is you knew there was a problem and were persistent enough to see it through to the end. Now with all of your new found knowledge you are a better tuner/tech/father/husband BS'r/carguy?/beer drinker....enough said, John:doh2:

[Biggsy]

I don't have the photo of the PCV hose itself but below is where it goes (I stuffed up the top arrow, it connects just below that fitting which is out of view).

Also, you can see in the other photo the 2 cylinders that are at fault.

And thirdly, the old and new cams side by side.



3482

3483

3484

[joecar]

Looks like signs of coolant in 5/7.

[Smets]

Correct me if im wrong, so at the end of the day it was air leak which was the problem?