90 GT suddenly running very rough
07-10-2008, 12:14 PM
#18
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Since you have the diagnostic port using it is the quickest way to rule-in or out a bunch of possibilities. It's the first thing I do with an 89+ that is mis-behaving.
07-10-2008, 12:18 PM
#19
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Stan--
You saw on that other thread that the problem was cured by replacing the ignition module. That part is easy to change, so might move up the candidate list if you happen to have a spare from a nearby car to try.
You saw on that other thread that the problem was cured by replacing the ignition module. That part is easy to change, so might move up the candidate list if you happen to have a spare from a nearby car to try.
07-10-2008, 12:29 PM
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I don't have a spare to swap, but I was presuming that if the timing light sees an electric pulse to every cylinder that the ignition module is working ok, right? I think in the other thread he found spark lacking when he tested with a timing light.
07-10-2008, 12:30 PM
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OK. Time to 1) run the car and when running rough see if one or more of the LEDs are lighting up and 2) hook up the software. Or just do #2 because it should tell you if #1 is happening.
Since you have the diagnostic port using it is the quickest way to rule-in or out a bunch of possibilities. It's the first thing I do with an 89+ that is mis-behaving.
Since you have the diagnostic port using it is the quickest way to rule-in or out a bunch of possibilities. It's the first thing I do with an 89+ that is mis-behaving.
07-10-2008, 01:10 PM
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The protection relay prevents half (or all) of the injectors from seeing ground, thereby preventing the injectors from firing. It cuts fuel. The purpose of the relay is to cut fuel if you lose spark. So, if you don't have spark for some other reason in one or more holes, the relay may (eventually) cut fuel. However, just because you have spark doesn't mean the relay isn't cutting fuel. The relay can cut fuel for other reasons not-designed-in. It can fail, an EGTs can go bad, bad 02 sensor, bad MAF, etc.
07-10-2008, 02:28 PM
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The protection relay prevents half (or all) of the injectors from seeing ground, thereby preventing the injectors from firing. It cuts fuel. The purpose of the relay is to cut fuel if you lose spark. So, if you don't have spark for some other reason in one or more holes, the relay may (eventually) cut fuel. However, just because you have spark doesn't mean the relay isn't cutting fuel. The relay can cut fuel for other reasons not-designed-in. It can fail, an EGTs can go bad, bad 02 sensor, bad MAF, etc.
Last edited by Stan.Shaw@Excell.Net; 07-10-2008 at 03:40 PM.
07-10-2008, 02:59 PM
#24
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Just FYI, you can temporarily jumper the ignition monitoring relay plug, terminals A1-A2-87. Note one terminal is labeled AL - don't confuse that with A1.
07-10-2008, 05:01 PM
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So, I did find today that after letting the car run for a just a short time, the green light does come on in the relay. I put the bypass relay in and it does run much better. Now I need to determine what the fault is that is causing the green light.
Jim B. don't be concerned, I will not drive the car with the bypass relay, except for testing purposes. And I do appreciate your warnings
07-10-2008, 06:33 PM
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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.
07-10-2008, 06:51 PM
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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.
07-10-2008, 09:37 PM
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Stan, recently I went through a 'green light episode' on another 90GT. It had a bad MAF and a bad 02. At idle it was running as rich as the LH could go. I can only assume that the mixture was so rich that it was quenching some cylinders some of the time. The protection relay got tripped. Anyway....
... since you have a new 02 sensor bored out of its little zirconium dioxide brain sitting in a box...
... since you have a new 02 sensor bored out of its little zirconium dioxide brain sitting in a box...
07-10-2008, 10:00 PM
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Stan, recently I went through a 'green light episode' on another 90GT. It had a bad MAF and a bad 02. At idle it was running as rich as the LH could go. I can only assume that the mixture was so rich that it was quenching some cylinders some of the time. The protection relay got tripped. Anyway....
... since you have a new 02 sensor bored out of its little zirconium dioxide brain sitting in a box...
... since you have a new 02 sensor bored out of its little zirconium dioxide brain sitting in a box...
I did find some information on checking the exhaust temp sensors and may review that process a bit more. If anyone has a document, let me know.
07-10-2008, 10:31 PM
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