'90 GT- atypical high idle and epic smog failure
09-26-2013, 08:54 PM
#47
Nordschleife Master
a leak past the cats should have no real effect on the numbers.
When the leads were changed, were the plugs?
What plugs are you running?
When was the O2 last changed again?
When the leads were changed, were the plugs?
What plugs are you running?
When was the O2 last changed again?
09-26-2013, 08:57 PM
#48
Instructor
Their test rig is certainly one of the variables, which is why I tried to go elsewhere for attempt #3, but I certainly don't think it's deliberate.
I considered E85 BTW. Virginia only has a single station selling it and I didn't want to take the risk of any rubber or plastic parts reacting badly to it, even diluted. I would prefer to identify a root cause and fix it properly.
I'm glad your car passed even under marginal conditions but Rob started this thread just over two weeks ago, so it's hardly been the epic tome you suggest.
09-26-2013, 09:00 PM
#49
Instructor
Plugs are WR7DC Super Plus. New in April. All look good and have been re-gapped down to the narrow end of the range (.028"). I do have a new spare set but saw no reason to put them in when I changed the wires.
O2 is ~5k miles old. It's another one of the suspects, we'll be checking its voltage trace this weekend. Temp2, MAF, O2 are all on the list.
09-26-2013, 09:31 PM
#50
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It just seems that everything has been changed and we have this problem. The engine control system is not that complicated. It seems that we are not seeing something or being told something. The computer controls the idle. end stop. if it is above the stated idle it is because the computer cannot regulate it lower. THAT is a big sign. Fix that problem and concentrate on it until it is. Then test and reevaluate.
Try pulling the hose off the ICV and plugging it. (I think you can get to it when you remove the maf) That should bring the idle down possibly to the point of stalling, but bring it down nonetheless. Then figure out why the ISV is not working properly.
My GT has 235k km's and uses a lot of oil and once the cats warmed up, it passed the test here in Ontario (no dyno, just rpm). The idle ALWAYS controls down to the right value.
Try pulling the hose off the ICV and plugging it. (I think you can get to it when you remove the maf) That should bring the idle down possibly to the point of stalling, but bring it down nonetheless. Then figure out why the ISV is not working properly.
My GT has 235k km's and uses a lot of oil and once the cats warmed up, it passed the test here in Ontario (no dyno, just rpm). The idle ALWAYS controls down to the right value.
09-26-2013, 10:13 PM
#51
Nordschleife Master
Given it passed in California, first I'd be carefully looking at whats changed since that smog test.
To my mind, the spark plugs are a prime candidate at this stage - you've mentioned they were replaced in April - new doesn't always mean "not faulty" so I'd swap out for another set. If one is faulty (cracked electrode, loose screw cap etc.) and causing a misfire that will read as heavily rich due to unburned fuel entering the exhaust system.
Has anything else changed since the California smog test?
After that change, I'd be asking other basics about the assumed setup:
Are the ECU chips and injectors stock?
Is it running the stock fuel pumps?
Is the vacuum system hooked up to the correct ports on the throttle body, and leak-free?
Is it the original ECU, or is it a rebuilt ECU? (I had wildly rich symptoms trying to pass emissions with a failing LH ecu - until the 6th(!) test visit in as many months, when it failed completely with clicking injector sounds immediately after it passed, and had to be pushed out of the test center!)
Then start with the other basics - following the Workshop Manuals test-plans (measuring sensor outputs, fuel pressure, etc.).
It'll seem daunting, but these cars aren't magic, and although experience may help faster, methodical will still get there every time!
To my mind, the spark plugs are a prime candidate at this stage - you've mentioned they were replaced in April - new doesn't always mean "not faulty" so I'd swap out for another set. If one is faulty (cracked electrode, loose screw cap etc.) and causing a misfire that will read as heavily rich due to unburned fuel entering the exhaust system.
Has anything else changed since the California smog test?
After that change, I'd be asking other basics about the assumed setup:
Are the ECU chips and injectors stock?
Is it running the stock fuel pumps?
Is the vacuum system hooked up to the correct ports on the throttle body, and leak-free?
Is it the original ECU, or is it a rebuilt ECU? (I had wildly rich symptoms trying to pass emissions with a failing LH ecu - until the 6th(!) test visit in as many months, when it failed completely with clicking injector sounds immediately after it passed, and had to be pushed out of the test center!)
Then start with the other basics - following the Workshop Manuals test-plans (measuring sensor outputs, fuel pressure, etc.).
It'll seem daunting, but these cars aren't magic, and although experience may help faster, methodical will still get there every time!
09-26-2013, 11:39 PM
#52
Instructor
Mechanically the car is totally stock other than the Porkensioner.
The ECUs were re-tiled during Rob's ownership, so a few years ago (I have all the records but can't remember everything yet)
Agreed the new plugs could still have a bad egg. I have inspected the tips visually and they all look the same but I recognize that's not a guarantee.
AFAIK the vacuum system is plumbed correctly and not grossly leaking. However if it were the tendency would be for HC and CO to go down, not up, so I'd have an even worse problem if that were the case.
Rob did a full intake R&R, TB/WP, updated various hoses, clamps, fluids, and other miscellany, all subsequent to the last California smog test. So clearly this is his fault but we haven't figured out exactly how yet
It is worth re-stating that the high idle predated all these tests and has persisted, unchanged, through two complete intake refreshes and various other troubleshooting steps Rob performed. The ISV has been refreshed, the MAF has been rebuilt and recalibrated, the injectors have been cleaned and balanced. Fuel pumps, filters, etc are all stock. All the other sensors are no more than 7k miles old, many are younger than 5k. Again, that doesn't guarantee anything, which is why we'll check them individually using the scope.
The poor emissions results I'm getting are therefore a separate issue from the high idle. Whether or not they share a root cause is TBD. I would like to add the little tiny fuel pressure gauge as a checksum, since I don't believe the data is otherwise available.
I am keen to understand the problem because I want the car to work right. I know I could cheat or otherwise band-aid the problem but given the effort Rob put into keeping it stock and pristine, and the fact that I bought the car for precisely that reason, it seems like easy math to pursue it.
The ECUs were re-tiled during Rob's ownership, so a few years ago (I have all the records but can't remember everything yet)
Agreed the new plugs could still have a bad egg. I have inspected the tips visually and they all look the same but I recognize that's not a guarantee.
AFAIK the vacuum system is plumbed correctly and not grossly leaking. However if it were the tendency would be for HC and CO to go down, not up, so I'd have an even worse problem if that were the case.
Rob did a full intake R&R, TB/WP, updated various hoses, clamps, fluids, and other miscellany, all subsequent to the last California smog test. So clearly this is his fault but we haven't figured out exactly how yet
It is worth re-stating that the high idle predated all these tests and has persisted, unchanged, through two complete intake refreshes and various other troubleshooting steps Rob performed. The ISV has been refreshed, the MAF has been rebuilt and recalibrated, the injectors have been cleaned and balanced. Fuel pumps, filters, etc are all stock. All the other sensors are no more than 7k miles old, many are younger than 5k. Again, that doesn't guarantee anything, which is why we'll check them individually using the scope.
The poor emissions results I'm getting are therefore a separate issue from the high idle. Whether or not they share a root cause is TBD. I would like to add the little tiny fuel pressure gauge as a checksum, since I don't believe the data is otherwise available.
I am keen to understand the problem because I want the car to work right. I know I could cheat or otherwise band-aid the problem but given the effort Rob put into keeping it stock and pristine, and the fact that I bought the car for precisely that reason, it seems like easy math to pursue it.
09-28-2013, 10:36 PM
#53
Instructor
After some troubleshooting at Frenzy today, we did indeed learn more about the issue on the car. Thank you again to Fraggle for diving in and helping diagnose the problem, and to Kevin, Greg, and the OC for making the test equipment available.
The readers digest version is that the LH appears to be sending +3VDC down the *input* line which is meant to take 0-1V from the oxygen sensor signal.
We first looked on Theo's software and confirmed that, as suspected, the car was running very very rich. But when we disconnected the 3-wire plug to take the O2 sensor out of the picture, the software didn't report any change at all. We checked the voltage off the sensor line directly and it was pegged at +1VDC unless I blipped the throttle, at which point it would briefly drop before climbing back up.
So we then checked the voltage on the other side of that plug, and that's when we found +3VDC.
So taking my LH out of the car and putting it into Fraggle's, we saw the same wire produce +3VDC in his car too with my LH installed. With his LH, the line gave a reference voltage of 0.5VDC, which seemed reasonable given it's the mean level for the expected output on the sensor.
My LH was serviced by John Speake in 2007 so I've reached out to him to see what he might know about the issue and/or suggest a way forward.
I am confident this will probably lead to a resolution of the emissions testing problem, but whether it's the last remaining issue or there's another one lurking is TBD.
More to come!
The readers digest version is that the LH appears to be sending +3VDC down the *input* line which is meant to take 0-1V from the oxygen sensor signal.
We first looked on Theo's software and confirmed that, as suspected, the car was running very very rich. But when we disconnected the 3-wire plug to take the O2 sensor out of the picture, the software didn't report any change at all. We checked the voltage off the sensor line directly and it was pegged at +1VDC unless I blipped the throttle, at which point it would briefly drop before climbing back up.
So we then checked the voltage on the other side of that plug, and that's when we found +3VDC.
So taking my LH out of the car and putting it into Fraggle's, we saw the same wire produce +3VDC in his car too with my LH installed. With his LH, the line gave a reference voltage of 0.5VDC, which seemed reasonable given it's the mean level for the expected output on the sensor.
My LH was serviced by John Speake in 2007 so I've reached out to him to see what he might know about the issue and/or suggest a way forward.
I am confident this will probably lead to a resolution of the emissions testing problem, but whether it's the last remaining issue or there's another one lurking is TBD.
More to come!
10-06-2013, 09:40 PM
#55
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I've been following this thread since the first page. But, I haven't had anything to contribute since; Folks have jumped-in with all the correct diagnostic advice.
However, this last development triggered my noggin' as I too have a (customer) car on which we've been chasing a high idle for a while. This weekend, I swapped in a known-good LH and it solved my high idle problem. The JDS rebuild on this '91 S4 is causing it to idle ~175 rpm higher (but it isn't sending a too high reference voltage.)
Has anyone heard back from John or Louie on this issue?
However, this last development triggered my noggin' as I too have a (customer) car on which we've been chasing a high idle for a while. This weekend, I swapped in a known-good LH and it solved my high idle problem. The JDS rebuild on this '91 S4 is causing it to idle ~175 rpm higher (but it isn't sending a too high reference voltage.)
Has anyone heard back from John or Louie on this issue?
10-06-2013, 09:52 PM
#56
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Cardinal has been in touch with Louie and John, they're sending out another rebuilt LH to see whether that's the problem. Big thanks to Fraggle for the electron-wrangling at Frenzy, I can safely say I never would have figured this out. (Obviously....)
10-06-2013, 10:25 PM
#57
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Cool. I'll poke them.
10-06-2013, 10:40 PM
#58
Instructor
The emissions failure, as noted earlier in the thread, is a much more recent phenomenon, and I remain optimistic the swapped unit will fix it. We'll know later this week when I get it back.
10-06-2013, 10:54 PM
#60
Instructor
I'll keep you posted.
What's your going rate for helping with an intake R&R job? No water bridge or cam covers, but inclusive of a TB service, needle bearings, etc.
I can offer pizza, beer, and the unending affection of my less-than-credible dogs.
If we rope in Kevin and others I figure we could knock it out in, what, half an hour?
(and yes, I've read Dwayne's writeup...)
What's your going rate for helping with an intake R&R job? No water bridge or cam covers, but inclusive of a TB service, needle bearings, etc.
I can offer pizza, beer, and the unending affection of my less-than-credible dogs.
If we rope in Kevin and others I figure we could knock it out in, what, half an hour?
(and yes, I've read Dwayne's writeup...)