90 GT suddenly running very rough
07-13-2008, 07:12 PM
#76
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07-13-2008, 07:14 PM
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07-13-2008, 08:24 PM
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Actually, we'd accidentally reversed the exhaust fan. Once the 02 loop kicked in it started spewing fuel. We didn't notice it at first. Then our eyes started melting. Filled up the whole garage with a/f. Good think there were no open flames or it would have been a real Jim_H moment.
07-13-2008, 08:44 PM
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Damn Dave, what kind of trouble you getting yourself into these days!
Maybe would have been cool to put an igniter at the exhaust tip for flames!
Maybe would have been cool to put an igniter at the exhaust tip for flames!
07-14-2008, 12:57 AM
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EGT sensors can fail intermittently. IIRC you can eliminate them from the list of possible issues very simply by unplugging them from the loom (round connectors under the airbox) so that the signals that the IGN monitoring relay receives are guaranteed to be the same - No signal.
07-14-2008, 07:31 AM
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I disagree John. I think that if the over-fueling is massive the lower combustion a/f limit can be reached periodically in one or more cylinders. The mixture is too rich to ignite properly. Even under perfect 'factory' conditions the cylinders will not get exactly the same amount of fuel.
I base my opinion on direct observation, troubleshooting, and repair of a 90GT a few weeks ago. The o2 sensor and MAF were both bad. The motor was running so rich that the protection circuit triggered. The obvious explanation is that the over-rich condition coupled with other uncharacterized non-optimum conditions (such as perhaps bad spray pattern on one or more injectors) quenched one or more cylinders sufficiently to cause a temperature differential between the EGTs.
I base my opinion on direct observation, troubleshooting, and repair of a 90GT a few weeks ago. The o2 sensor and MAF were both bad. The motor was running so rich that the protection circuit triggered. The obvious explanation is that the over-rich condition coupled with other uncharacterized non-optimum conditions (such as perhaps bad spray pattern on one or more injectors) quenched one or more cylinders sufficiently to cause a temperature differential between the EGTs.
07-14-2008, 09:23 AM
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Hmm, I can kind of see them, but think I need much smaller and longer hands to get to them. Anybody dealt the R&R of CGTs that can give me some hints. Looks like a pita job, in which case I will want to replace them, rather than have to shred my hands more than one time dealing with them.
07-14-2008, 09:31 AM
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I haven't gone below yet, as I will be inclined to start too many wyait projects (motor mounts, oil pan gasket, A/C updgrade). I already have two cars on jackstands for a long time, need to prevent getting another one on jack stands....
07-14-2008, 10:14 AM
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I can't ohm them if I can't get at their connectors from above.
I haven't gone below yet, as I will be inclined to start too many wyait projects (motor mounts, oil pan gasket, A/C updgrade). I already have two cars on jackstands for a long time, need to prevent getting another one on jack stands....
I haven't gone below yet, as I will be inclined to start too many wyait projects (motor mounts, oil pan gasket, A/C updgrade). I already have two cars on jackstands for a long time, need to prevent getting another one on jack stands....
But more importantly, in my post #33 I posted some information from Rich Andrade specifying how to test from inside the car at the Ignition Monitoring Relay.
07-14-2008, 08:58 PM
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First off, you can get to the connectors from above. It's not pretty, but it can be done.
But more importantly, in my post #33 I posted some information from Rich Andrade specifying how to test from inside the car at the Ignition Monitoring Relay.
But more importantly, in my post #33 I posted some information from Rich Andrade specifying how to test from inside the car at the Ignition Monitoring Relay.
I should add the with the MAF disconnected it seems to idle as well as it ever has. (I think).
07-14-2008, 09:00 PM
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07-14-2008, 10:18 PM
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Stan, from cold, how long does it take the car to manifest the behavior and trigger the protection relay?
With either of the MAFs, does it run OK from cold for a handful of seconds?
With either of the MAFs, does it run OK from cold for a handful of seconds?
07-14-2008, 10:19 PM
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The first test I found to test the MAFs is the hot wire resistance test. Rich's document says resistance should be 3.6 to 4.1 between terminals 3 & 5 of the MAF.
Assuming I have a clue (questionable) the resistance may be on the high side,
The older MAF shows 4.7, but after subtracting the internal resistance of the multimeter (.7), it is within the above range at 4.0.
The recently rebuilt MAF shows 4.8, so after subtraction is also at the top of the above range 4.1
I will try the hot wire signal test when my son comes over next, as it looks like I need to be in two places at the same time.
Assuming I have a clue (questionable) the resistance may be on the high side,
The older MAF shows 4.7, but after subtracting the internal resistance of the multimeter (.7), it is within the above range at 4.0.
The recently rebuilt MAF shows 4.8, so after subtraction is also at the top of the above range 4.1
I will try the hot wire signal test when my son comes over next, as it looks like I need to be in two places at the same time.