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post #1 of 10 (permalink) Old 04-14-2019, 02:45 PM Thread Starter
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Rich on start up

So my 93 TA M6 has this problem where it starts up crazy rich. Hard to start sometimes windup feathering the throttle but it always starts but stinks to high heaven and run rough/low idle for about 10 seconds. After that runs fine. I was going to just throw a coolant temp sensor and fuel pressure regulator at it. Any other thought?
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post #2 of 10 (permalink) Old 04-15-2019, 07:50 AM
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Put your car on an obd1 scanner that does real time sensor data. See what the sensors say before replacing parts.

Don't have an obd1 scanner you say. Well, theres a free pc based scanner that was made for our lt1 equipped cars. Written by member GaryDoug, Scan9495 reads codes, does running sensor scans, and will log data to a file for playback. Get it at My Files

To use the program, you will need 2 things. (1) a cable to connect aldl to usb port of pc based computer. Get the 12 pin cable @ OBD Diagnostics

Get the newest version of Scan9495 from the lt1 v8 folder.

(2) you will need microsoft dot net framework, version 4.0 or newer. You can get it at same site you download "scan9495" Or get at Microsoft site.

And while getting info, you might as well download the 93 service manual. Get @ www.mediafire.com/?40mfgeoe4ctti

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post #3 of 10 (permalink) Old 04-15-2019, 09:03 AM Thread Starter
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Probably a good place to start was hoping someone more familiar with the lt1 platform may have noticed a common issue. Thank you
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post #4 of 10 (permalink) Old 04-16-2019, 07:26 AM
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Being that your car is26 years old, wiring, connector & ground problems are common. So if you get a code when you scan, know that some codes don't light the check engine light. Use the 93 service manual to look up the code you have. The manual will tell why code sets, what action the ecm takes when code sets. And has troubleshooting procedures.

Manual also has complete wiring diagrams. When doing a running sensor scan see which sensors are not reading in normal range. If you find sensors that read abnormal, don't run out and buy the sensor. Wiring, connectors, & grounds that are bad can cause abnormal readings.

Some of the readings to pay attention to are fuel trims, O2 readings, tps, map. coolant temp that ecm sees. Your temp gauge uses a different sender then ecm coolant temp does. Ecm coolant temp sender is screwed into water pump area. A good pic of it is @ shbox.com

The site has a wealth of lt1 info.

Finally, if you haven't a clue to what sensor data means, PM me with your email address. I'll send you pdf file of "scanner readings and what they mean".
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post #5 of 10 (permalink) Old 04-16-2019, 07:30 AM Thread Starter
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10 4. I'll give it a scan. Wasnt aware a code could be stored without setting off the ses.
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post #6 of 10 (permalink) Old 04-16-2019, 09:45 AM Thread Starter
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Well check for codes. Nothing just keeps blinking the 12. I did however while just looking around find what I believe to be a severely dry rotted and maybe collapsing vacuum connector. Does anyone know that this sensor might be?
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post #7 of 10 (permalink) Old 04-20-2019, 01:44 PM Thread Starter
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Just incase it helps anyone the problem ended up being the cooland temp sensor. It got to the point that the car wouldn't even start just sputter and poor out raw fuel. The first crank with the new sensor fired without hesitation and ran fantastic.
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post #8 of 10 (permalink) Old 04-21-2019, 06:51 AM
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That's why I recommended the running sensor scan. You would have seen that coolant temp that pcm sees was way off. Even if engine won't run, you can still see coolant temp on scan..


So get an obd 1 scanner. Here's a free one called "scan9495" It is a pc based scan program written by our member GaryDoug. It works for our 93-95 lt1 cars and also the 3.4 v6 cars. It reads codes, does running sensor scans, and will log data to a file for playback. Get at
www.mediafire.com/?0elo4c935uc5s


Get the newest version in the lt1 v8 folder. To use scan9495 you will need 2 things. (1) a 12 pin obd 1 cable to connect car's aldl to usb port of pc based computer. Get at OBD Diagnostics

(2) you will ne microsoft dot net framework, version 4.0 or newer. Get this at same site you got scan9495. Or get at microsoft site.

Since you are a lt1 owner, I also suggest buying a pc based oscilloscope. It is the only tool that will 100% diagnose the optispark low & high resolution pulses. Opyi is a sore spot on lt1. Also good to test your 30 hertz fuel enable signal, which without the signal, engine won't run. They cost about $70 on ebay amazon, etc.

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post #9 of 10 (permalink) Old 04-21-2019, 07:07 AM Thread Starter
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Strangely enough I did. I jumped the terminal and all I got was 12 over and over and I even used a good scan tool and for some reason could not get it to communicate with the car. Just kept getting "communication failure."
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post #10 of 10 (permalink) Old 04-21-2019, 01:37 PM
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I'm not talking about reading codes when I suggest a running sensor scan. A good scanner can read sensor data with engine running, or some data with ignition switch on. The coolant temp sensor CTS has a reasing with engine running or with ignition on. The problem with your car was that cts was reading very low compared to actual coolant temp. This was when car was running, but rich.

The low temp reading by cts was causing pcm to add much more fuel, as needed in very cold weather. When cts failed altogether, it read around 0 degrees and engine would not run. You made a good guess changing the cts. But you could have guessed wrong and spent money on a part that didn't need replacing.

The whole purpose of a running sensor scan, is to let you see what data the sensors are displaying under different running conditions. Once you learn what is normal readings for different conditions, seeing data out of spec can help pinpoint trouble area.

Those in the know, still don't rush out and change the part indicated. They check wiring, connectors, grounds, & splices, before assuming the part is defective.

As an example, my 90 3.1 v6 car has a map sensor connector that makes poor contact from time to time. The symptoms are a mis and jumping rpm. This gets worse & worse until engine won't run when trans shifted from park. Taking the connector off the map & reinstalling it solves the problem, until the next time connection gets bad. One day I'll actually change the connector pigtail.

Your car being 26 years old, means that many problems will be electrical, vacuum lines leaking, etc.
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