Intermittent poor idle in SV6 Auto 5 speed.. EVAP or Oxygen sensors?

[diysv6]

25 June 2014 UPDATE: The fault was the ECU failing to switch on #4 Fuel Injector - Replaced ECU.


In recent weeks my 2004 SV6 5 speed auto, has exhibited a stumbling idle on hot or cold startup, or when hot after driving for some time. I get no messages on the LCD Dash display, so I am in the dark at present.

The idle is rough/loping but the car does not seem to want to stall. It does not feel like a spark plug miss in the idle. There is a slight fluff at the exhaust at idle but not the dead cylinder noise from a dud spark plug at the exhaust. If I speed up the motor the car runs OK. It seems to be about the idle RPM that the problem is evident. Perhaps it is there under driving conditions, but its effect is unnoticeable.

The only maintenance I have recently done is to replace the fuel filter. ( I pulled the fuel relay and its fuse and dropped pressure by engine cranking etc.) The car does accelerate smoothly and better since I replaced the gunked filter.

As part of the fault finding regime, I have now cleaned the MAF/IAT and the throttle body with MAF cleaner. The TB was fairly clean and no sticking etc.. No oil in the inlet tract, and the PCV was working well at idle. The rough idle has occurred since the MAF was cleaned.

Out of about 50/60 starts the idle has been irregular on five occasions. I normally have the a/c on at all times. (SE Qld). On one start, the exhaust was smelling of raw fuel but the irregular idle was not present. It recently occurred when hot, I turned off the air-conditioning and the problem persisted. I removed the engine cover and could not hear the EVAP, the fuel tank's Evaporative Canister Purge solenoid clicking. I bumped the valve a couple of times, it then seemed to start clicking and when I listened to the exhaust the idle was more stable. There are no vacuum leaks that I can find at present, unless the EVAP is not closing off properly. I replaced the EVAP solenoid hose to the inlet manifold about 15 months back. It is in good condition, no perishing/cracking at the elbow etc.

The other thought I have is that the oxygen sensor "disable" circuitry is starting to go on the blink. My understanding is that for some time after start-up, the oxygen sensors are disabled until the engine oxygen sensors gets up to certain status, and then the oxygen sensors are cut in to manage the fuel metering etc.

Would this coincide with the engine sensors settling down and about when the EVAP would start to click?
Can anyone indicate when the EVAP solenoid should cut in after an engine start? Does the a/c being on have any bearing on the EVAP solenoid's operation?
Do oxygen sensors once failed stay failed or can they drift in and out of correct operation?

My fuel economy is about average at this time. Have not done enough Kms to get another tank full.

I would appreciate your advice.

 

[diysv6]

Update:

Last week I had the most interesting driving experience. The car started OK after a short journey of about 3 kms, then whilst driving in a 60Km zone the whole car started shaking like it was on a plate of jelly, almost as though every road wheel was suddenly badly out of balance. I've experienced drive line vibrations in the past, but this shaking was a low speed body shake. Pulled over to the side and the EVAP solenoid was not clicking. I gave it a couple of shakes and bumps. The idle was irregular but not missing a cylinder. Drove home, about 2kms, and the problem cleared on the way. The EVAP was clicking when I arrived home.

I have trialed blocking off the inlet (feed from the canister) to the EVAP solenoid with a rubber chair tip, and under road test conditions it has not occurred. If anything, the engine feels a bit more responsive.

Looked at the DTCs. The disconnection of the fuel pump relay and fuse was logged (changed the fuel filter), then a surprise P0204 - Injector 4 control circuit malfunction. They were reset and I now await the next occurrence.

Reading about EVAPs it could be a bad coil (H/R, O/C or S/C or anywhere in between). Loss of 12V supply to solenoid, loss of "earth wire" back to the ECU, or ECU itself. These conditions should bring up a DTC?

Mechanically the valve could be stuck wide open and not responding to the ECU pulses. Would the O2 sensors normally pick up the lean mixture and adjust the fuel mixture and not give a DTC?

If the #4 Injector was on the blink with the EVAP, maybe I have a common earth return line to the ECU, and the ECU back to the battery negative post. I'm not certain if the same fuse feeds both the fuel injector and the EVAP solenoid. I expect the car would give more varied DTCs if the earth from the ECU to the negative battery post was going bad.

So the fix could be about $90 towards $900 +++ (?) for a new ECU fitted and tuned in by Holden. I'm hoping it's the solenoid.

Any ideas when the EVAP should have been operating (clicking)?

 

[morphix]

The solenoid should only be operating under idle IIRC.

 

[diysv6]

The solenoid should only be operating under idle IIRC.

Thanks Morphix
I located my old vacuum gauge(s) since my last post, and hooked it up to the input side of the EVAP solenoid. Before starting I had zero vacuum present. After about 45 seconds the EVAP started to chatter and the vacuum rose steadily to about 65kpa, about 19" mercury. My other gauge read about 18.5" mercury. I cannot vouch for either gauge's accuracy, but it did confirm that the EVAP did open on idle after a nominal "warm ?" up. (Would this be where the o2 sensors switch into the loop?)

After a couple of minutes idling, the EVAP shut off completely. Then it restarted to chatter again. The chatter rate seemed to be varied when the A/C kicked in, the idle speed being stepped up for the A/C compressor load.

Letting fresh air into the solenoid intake or connecting the charcoal canister line makes no change in the speed or quality of the idle speed. I guess this proves the canister or associated lines are not blocked.

Now have to figure if it "sticks" open on the road and causes the wobbles and bad idle conditions.

 

[diysv6]

Hello again,
An update for the VZ. My title suggests EVAP or Oxygen Sensors problems. It now looks like the ECU or the connector X1 at the ECU. Sorry this is a bit long, but I thought my process was a positive systematic approach to the problem and might help others with similar problems. If you consider I have missed something and am barking up the wrong tree, please let me know.

The car has been intermittent with the bad idle, and varied from a definite #4 cylinder misfire to a slight intermittent failure on #4. It played up badly last Friday, got the car home and measured all the injector coils 12.5 ohms. Depressurised the fuel line. Made up a test battery of 3 x 1.5vAA cells = 4.5volts. Positive to terminal 2 and triggered, for short periods, each injector (2, 4 and 6) on terminals 6, 7 and 8 of X102 located at the rear of the intake plenum. All worked OK with 320mA of current flow. The current reading tended to confirm no shorted turns in any injector. (2 x 1.5V AA cells did not operate the injectors).

Switched on the ignition with the fuel injector connector X102 unplugged. The fuel pump does not run until the "start" action is called by the ignition key. Checked the incoming 12v feeds for the injectors at the connector X102 at the rear of the inlet manifold, both OK. The battery voltage was 12.02V at the battery terminals. Put my digital multimeter DMM over the six female connectors and got 3.52 to 3.55 volts on them except #4 which read 3.45volts.

Started to wriggle the engine wiring harness around the engine and worked towards the ECU. I could change the reading by about 0.02 of a volt on #4. I tested the voltage for injectors 2 and 6 and the voltage reading did not change. Turned off ignition.

Disconnected the negative battery terminal and allowed all circuits to self discharge for about 35 minutes. Used the DMM to check the ohms continuity between the X102 connector (injector harness) and the X1 connector at the ECU. X1 is the lower plug on the ECU. By gentle probing with a pin found the injector 2 control was on terminal 62. Injector 4 was on terminal 45; and injector 6 was on terminal 64.

I felt that the contact pressure on terminal 45 was lower than on 62 and 64. The DMM did show slight variations of 0.1ohms when X1 was manipulated.

Put X1 back in circuit, restored X102, connected up battery. The "system check" on the dash was OK. Stared the car, ran perfectly. Concentrated on wriggling the X1 connector a bit more vigorously, and found I could bring on the engine miss if I lifted the X1 connector up. It improved when I pushed it down. The movement was very little but it made the miss vary from slight to complete failure. Took the car for a shopping run Saturday afternoon. Started perfectly, then varied from a total failure of a cylinder to slight failure during the journey to the shopping centre. Opened the bonnet, pushed down gently on the X1 and the miss has not returned. Used the car today Sunday, no problems.

My observation is that the weight of the engine harness X1 and other wiring harnesses on X2 is pulling at the ECU and perhaps has distorted the X1 connector enough to cause contact damage/misalignment to an already marginal #45 connector. I don't know if the contact pins assembly set into the ECU is damaged and the real culprit is inside the ECU. I have not removed the ECU and taken it to the work bench. Need to get all of my options clear before that step.

So, my questions are:

Can the X1 connector be dismantled and repaired with access to a kit of release probes etc. to allow me or a Holden dealer to remove and perhaps replace contact # 45?

If the X1 is not repairable, then perhaps I am up for a new loom from Holden if still available , or a good used engine wiring harness, anyone with a spare laying around for a 2004 SV6 sedan, Auto 5 speed.

Of course if the ECU is damaged, then the outlay will also be significant. Any good compatible ECUs about?

Thanks in advance for your patience and any further ideas/feedback.

 

[morphix]

Wow some in depth testing.

Just a FYI the ECU for these will set you back around $1200 all up for a brand new ECU and it to be programmed, i had mine completely fail about 2 years back and had that nice outlay.

I too at the moment have a slight poor idle, but i ended up replacing some bits and pieces that were pretty much on their last legs anyway such as all new injectors (mine were really dirty), new o2 sensors (1 had a dent in the outter casing and gave odd readings) & EVAP Solenoid (mine was clicking when it wasn't meant to) all of these improved the way the car run, but still didn't fix the issue.

 

[diysv6]

Hello again.

The Saga of the rough idle has been solved.

The fault was the ECU X1, pin 45 going open circuit. It posted a DTC P0204 for Injector #4. Since my last post, the car has been very good to very bad. Last Sunday, it started with a complete #4 cylinder miss and continued through until Monday. I was able to get at the "full-on' fault condition for long enough to really start to eliminate the various parts of the wiring and the ECU socket. Pressure on the X1 (lower) ECU connector made no difference to the idle. Testing the continuity of the engine wiring harness saw no changes. Earlier I had seen small variations in the resistance, but the repeated homing of the connecter must have removed any tarnish build-up and the engine harness came out as good. See note below.

My final test was to connect the DMM on DC volts and look at the voltage on X102 (Fuel Injector) harness Pin #7 (injector #4) and the ECU earth location.
Switched on the ignition, it read 3.54 volts (like the other injectors had tested), and over a period of about 2-3 seconds, the reading dropped to 0 volts. On prior testing, the voltage would drop to about 2.0v and return to the 3.54 volts, but during these tests I had the engine harness in the test circuit. This sustained drop to 0 volts was the first time it had ever happened. Checked the other fuel injector voltages and they all started at about 3.54 volts and did not drop to zero.

Chased around for second hand ECUs and was advised to keep away from the 2004/2005 build ECUs. The older ECUs have a reputation for failure when removed from a vehicle and set on the bench for more than 2- 3 weeks and then pressed into service. ECUs built in 2006 in the 2006 VZs have been improved so that the internal failure rate is not so frequent.

Bought a new ECU, had it fitted and "linked in" to my car. Took about 45 minutes to load the software and hook up with the BCM etc. The technician used a Tech2 and a laptop loaded with the GM software for my car's VIN specification. (That's how I understand it).

First start no engine miss. Subsequent starts have no miss. Road tested, and the car feels very crisp and responsive. My ECU was built 07/2004. The new one is manufactured by Bosch in the USA, dated 13-05-08. I had to surrender the old ECU assembly, so maybe Bosch are placing new computer assemblies into the old aluminum heat sinks?
Anyhow, 12 months warranty and $990 fixed my problem. Now to enjoy the car again. Hope this helps someone out.

Please note: Probing the very small connectors in the ECU connectors X1 and X2 requires that you use a "probe" less than 0.64mm in diameter. I used some dressmaking pins with a 0.58mm diameter, so no connector damage was done. On the Delphi USA site, they show the irreparable damage that can be done by a 1mm diameter test probe which can be pushed into the connector. The cylindrical shape becomes tapered and conical and then fails as a connector. In passing, the contacts are rated at 7 amps.

So check the diameter of any wires, pins etc used in your fault finding.