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Update after installing rebuilt AMM Posted by huxley99 [Email]  (#2339) [Profile/Gallery]
(more from huxley99) on Sat, 22 Oct 2022 11:45:35
In Reply to: Saabina, Thank you for the information, Awesome., Rociero  [Profile/Gallery]
, Sun, 4 Sep 2022 00:38:22
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I wanted to update this thread now that I have a rebuilt AMM and have done some more troubleshooting. As a reminder, I have a 86 9000T that would repeatedly stall when cold, and disconnecting the AMM would improve the cold staring. Here is an update if what I have checked since early September:
-- I had the AMM rebuilt by Injection Labs.
-- I checked the spark plugs and they definitely suggested the car is running rich -- they were black and sooty. They are relatively new NGK BCPR6EGP spark plugs which I believe are an acceptable replacement for the original spec BCP6ES or BCP7ES, but I might be wrong. I cleaned the plugs and set the gap to 0.6-0.7 mm.
-- I looked for vacuum leaks and as far as I can tell did not find any.
-- I confirmed the fuel pressure regulator (FPR) holds vacuum and fuel does not come out of the FPR vacuum hose.
-- With the rebuilt AMM installed and set to 380 ohms the car would still stall when cold, but it would do less of the idle-speed hunting than before (prior to when the AMM was rebuilt the idle would increase to 2000+ RPM before stalling when the engine was cold. With the rebuilt AMM the idle holds at ~1000 for a few seconds before stalling during a cold start). After restarting about 12 times the car would hold idle at around 850-1000 RPM, but after a few minutes of steady idle without stalling, black smoke starts pouring out the exhaust. I checked the output of the O2 sensor and it was swinging between ~100 mV and ~900 mV, which from what I understand is appropriate. But the black smoke coming out of the exhaust suggests the car is running really rich.
-- I then adjusted the AMM down to 150 ohms, which from what I understand should make the car run leaner. After starting and stalling a few times it would hold idle at around 850-1000 RPM, but again after a few minutes black smoke started to pour out the exhaust. I checked the O2 sensor and it was stuck at ~115 mV (i.e., not swinging between lower and higher voltage), which from my understanding would indicate the car is running lean, but the black smoke coming out of the exhaust indicates otherwise.
-- I have not had a chance to try running the car with a higher ohms setting on the AMM.
So it seems that once the engine is warm enough to not stall, it does not appear to run rich based on the exhaust, but after a few minutes it seems to run really rich. The timing of when black smoke appears would seem to coincide with when the O2 sensor starts to influence fuel flow. But once black smoke starts to appear the output of the O2 sensor does not suggest the car is running rich (i.e., it isn't stuck at ~900 mV).
Any advice on next steps? Thank you --
, Sun, 28 Aug 2022 05:21:55, Sun, 28 Aug 2022 10:10:32, Mon, 29 Aug 2022 06:24:27, Sat, 3 Sep 2022 16:03:16
, Mon, 5 Sep 2022 11:13:54, Sat, 3 Sep 2022 17:03:10, Sun, 4 Sep 2022 00:38:22, Sat, 22 Oct 2022 11:45:35 <-- Viewing This Message
, Fri, 28 Oct 2022 02:24:04, Sun, 27 Nov 2022 05:20:34
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