90 GT suddenly running very rough
07-14-2008, 10:24 PM
#91
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Last test was with the bypass in place, so it never triggered, but just ran bad. While idling well with the MAF disconnected, I then plugged the MAF in, and it almost immediately (if not immediately) started running bad. I unplugged the MAF and it smoothed out.
07-14-2008, 10:31 PM
#92
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What does the car do if you disconnect the 02 sensor?
07-14-2008, 10:48 PM
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07-15-2008, 12:58 AM
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Found more tests to do from above, thanks to John:
http://www.jdsporsche.com/faq.html
I find there is power to the MAF, @ battery voltage between 2 & 4 of the harness
I find both MAFs are @400ohm resistance for to show the idle mixture pot is right, between pins 3 & 6.
But maybe I found a problem, which is probably unrelated to my current problem. The harness does not have a metal clip in the #6 connector. Maybe this normal, but doesn't seem right. Maybe this has something to do with my slight surge at idle problem that started after the intake refresh?
http://www.jdsporsche.com/faq.html
I find there is power to the MAF, @ battery voltage between 2 & 4 of the harness
I find both MAFs are @400ohm resistance for to show the idle mixture pot is right, between pins 3 & 6.
But maybe I found a problem, which is probably unrelated to my current problem. The harness does not have a metal clip in the #6 connector. Maybe this normal, but doesn't seem right. Maybe this has something to do with my slight surge at idle problem that started after the intake refresh?
07-15-2008, 12:02 PM
#95
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There is no connection to pin 6 on the MAF connector - I've had two MAFs that don't have it.
I've been e-mailing with the good doctor Mr. David Lloyd about my intermittent problem, and here's what he had to say:
To confirm "limp home", remove the carpeting from the P-side footwell. You'll notice a clear-ish plastic cover over a device mounted to the outside wall. There a two LEDs, a red and a green. Go for a drive. When she starts misbehaving, one of those lights should come on.
Red is the right bank (P-side) distributor being shut down, Green is the left. Could be as simple as the coil wire or one of the 4 plug wires going to the indicated distributor, or it could be a bad knock sensor or, a failing cylinder head temp sensor - I think your car has it.
Again, mine seems to be going into limp-home mode randomly (I have not confirmed that it really is going into limp-home by the lights, though), and it has twice reset itself back to normal on restarting. I am now suspicious that it's the same problem I had late last year, which appeared to have been fixed by replacing the MAF.
Stan, I am expecting a used MAF in the mail this week. If you are going to be at or can make it to the PCA DE at LRP on Saturday, I can lend it to you for diagnostic purposes.
I've been e-mailing with the good doctor Mr. David Lloyd about my intermittent problem, and here's what he had to say:
To confirm "limp home", remove the carpeting from the P-side footwell. You'll notice a clear-ish plastic cover over a device mounted to the outside wall. There a two LEDs, a red and a green. Go for a drive. When she starts misbehaving, one of those lights should come on.
Red is the right bank (P-side) distributor being shut down, Green is the left. Could be as simple as the coil wire or one of the 4 plug wires going to the indicated distributor, or it could be a bad knock sensor or, a failing cylinder head temp sensor - I think your car has it.
Again, mine seems to be going into limp-home mode randomly (I have not confirmed that it really is going into limp-home by the lights, though), and it has twice reset itself back to normal on restarting. I am now suspicious that it's the same problem I had late last year, which appeared to have been fixed by replacing the MAF.
Stan, I am expecting a used MAF in the mail this week. If you are going to be at or can make it to the PCA DE at LRP on Saturday, I can lend it to you for diagnostic purposes.
07-15-2008, 12:11 PM
#96
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Hello Stan,
What you have is correct. Pin 6 is the idle CO pot which isn't needed for your cat car. Idle CO setting is autotmatic using the O2 loop.
What you have is correct. Pin 6 is the idle CO pot which isn't needed for your cat car. Idle CO setting is autotmatic using the O2 loop.
07-15-2008, 12:16 PM
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There is no connection to pin 6 on the MAF connector - I've had two MAFs that don't have it.
I've been e-mailing with the good doctor Mr. David Lloyd about my intermittent problem, and here's what he had to say:
To confirm "limp home", remove the carpeting from the P-side footwell. You'll notice a clear-ish plastic cover over a device mounted to the outside wall. There a two LEDs, a red and a green. Go for a drive. When she starts misbehaving, one of those lights should come on.
Red is the right bank (P-side) distributor being shut down, Green is the left. Could be as simple as the coil wire or one of the 4 plug wires going to the indicated distributor, or it could be a bad knock sensor or, a failing cylinder head temp sensor - I think your car has it.
Again, mine seems to be going into limp-home mode randomly (I have not confirmed that it really is going into limp-home by the lights, though), and it has twice reset itself back to normal on restarting. I am now suspicious that it's the same problem I had late last year, which appeared to have been fixed by replacing the MAF.
Stan, I am expecting a used MAF in the mail this week. If you are going to be at or can make it to the PCA DE at LRP on Saturday, I can lend it to you for diagnostic purposes.
I've been e-mailing with the good doctor Mr. David Lloyd about my intermittent problem, and here's what he had to say:
To confirm "limp home", remove the carpeting from the P-side footwell. You'll notice a clear-ish plastic cover over a device mounted to the outside wall. There a two LEDs, a red and a green. Go for a drive. When she starts misbehaving, one of those lights should come on.
Red is the right bank (P-side) distributor being shut down, Green is the left. Could be as simple as the coil wire or one of the 4 plug wires going to the indicated distributor, or it could be a bad knock sensor or, a failing cylinder head temp sensor - I think your car has it.
Again, mine seems to be going into limp-home mode randomly (I have not confirmed that it really is going into limp-home by the lights, though), and it has twice reset itself back to normal on restarting. I am now suspicious that it's the same problem I had late last year, which appeared to have been fixed by replacing the MAF.
Stan, I am expecting a used MAF in the mail this week. If you are going to be at or can make it to the PCA DE at LRP on Saturday, I can lend it to you for diagnostic purposes.
Thanks for confirming the wiring. I have done all of that testing, mine is definitely not that simple nor likely to be ignition related.
I don't think I will need the MAF as I can test the ones I have here. If they are bad I will send them off to be fixed. I think it is unlikely as neither was bad recently.
07-15-2008, 12:16 PM
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07-18-2008, 01:24 PM
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I am cautiously optimistic.
I replaced the oxygen sensor and with the MAF connected it started and eventually reached an idle, after perhaps a minute. The battery was discharged while it was on jack stands (an alarm issue I think) so perhaps the LH was learning the new O2 sensor?
I also put my RMB on, but it is leaning against the rear bumper cover cutout, so I did not want to run it long enough to find out more. I am hoping this can be adjusted, as my rear muffler was adjusted properly before this swap.
I replaced the oxygen sensor and with the MAF connected it started and eventually reached an idle, after perhaps a minute. The battery was discharged while it was on jack stands (an alarm issue I think) so perhaps the LH was learning the new O2 sensor?
I also put my RMB on, but it is leaning against the rear bumper cover cutout, so I did not want to run it long enough to find out more. I am hoping this can be adjusted, as my rear muffler was adjusted properly before this swap.
07-18-2008, 01:30 PM
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Sounds like you may be making some progress Stan.
Hope to see you and the GT at the BBQ in August.
Hope to see you and the GT at the BBQ in August.
07-18-2008, 01:45 PM
#102
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Funny, George Suennen's car started "green-lighting" last week. We cannot account for it after checking spark plugs for spark and exhaust temps at the manifolds. It trips about a half minute after the car starts. The car runs MUCH worse after it trips and actually seems fine before it trips. So, we care calling it a false alarm, but he is having other problems, specifically low vacuum at idle (12 inches), so we are going to pop off the intake manifold to see if his very high-boost supercharger blew something apart under there. Perhaps that can create conditions that will trip the monitoring system. We don't know yet.
BTW, David Lloyd uses the term "limp home mode" in reference to tripping the ignition monitoring system in the quote posted previously. I think it has been mentioned that term refers to the LH operation when the MAF signal is out of range. Our generic reference for the tripping of the ignition monitoring system is usually "4 cylinder mode".
07-18-2008, 02:08 PM
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Maybe not relevant to the case at hand but of interest - We pulled George's intake and found one injector lower o-ring deformed and cut, on cylinder 3. This can happen when the rails are reinstalled if the o-rings are not well-lubed (I usually use silicone grease). The lower o-rings can get pinched and not seat properly inside the manifold leading to a vacuum leak and lean condition on that cylinder. We found nothing else wrong, although it is possible the flappy vacuum source was detached too. Not sure if it came off during removal or was that way before. Anyway, we fixed those 2 things, and the car now idles OK with good vacuum and the ignition monitoring relay no longer trips.
BTW, David Lloyd uses the term "limp home mode" in reference to tripping the ignition monitoring system in the quote posted previously. I think it has been mentioned that term refers to the LH operation when the MAF signal is out of range. Our generic reference for the tripping of the ignition monitoring system is usually "4 cylinder mode".
BTW, David Lloyd uses the term "limp home mode" in reference to tripping the ignition monitoring system in the quote posted previously. I think it has been mentioned that term refers to the LH operation when the MAF signal is out of range. Our generic reference for the tripping of the ignition monitoring system is usually "4 cylinder mode".
Hi Bill,
Thanks for the thoughts. In my case the car ran well enough for a couple of thousand miles after the injectors, etc. work. Do you think it is a problem that could show up later on? Also, up to this point disconnecting the MAF has made a huge difference, do you think that would be true with the injector o-ring was an issue?
I definitely feel a bit more knowledge and understand the difference between the MAF disconnect limp home mode and the IMR LED 4 cylinder mode. The second has the potential negative consequences of vibration leading to TT failures, right?
07-18-2008, 02:08 PM
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07-20-2008, 12:31 PM
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My 4-cylinder-mode problem was kind to me yesterday - in its way. I made it through my first DE at Lime Rock yesterday without a problem, but then the moment I pulled out of the park, it kicked into 4-cyl mode! I pulled over and checked for LEDs, and sure enough I had a green light on - left bank.
I shut down and restarted to make sure I was looking at the right light, then about 15 seconds later it switched into ugly mode and the green light came on. I had to deal with it the whole way home... running rich and burning up $8.75/gallon 110 octane race gas at single-digit mpg the whole way!So the O2 sensor reads the exhaust temperature? Stan, which bank was giving you problems? Did you replace the O2 sensor on the same side?