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12 replies to this topic

#1 Zborzekofski

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Posted 3 weeks ago

My 93 formula runs great when cold, after about 10 minutes of running the car will shut off. The engine code is saying I have a bad ECT sensor. Has anyone put a new one of those in and solve this issue?

#2 Injuneer

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Posted 3 weeks ago

By “ shut off” do you mean run rough and stall, or do you mean just stop like someone turned off the ignition?

 

The ECM uses the coolant temp sensor (CLT) reading on cold start to set the idle speed, and the degree of cold start A/F ratio enrichment.  If the engine warms up, but the ECM sees a cold temp from the CLT sensor, the engine will be running too rich and may stall.


1994 FIREBIRD FORMULA
FRED

 
381ci all-forged stroker (Callies Stealth, Oliver billet rods, BME 2618-T61 nitrous pistons) - 10.8:1 - CNC LT4 heads/intake - Comp Cams solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74#/HR injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11 Pro-Street gears - AS&M headers - true duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP / 800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117 MPH straight motor
 
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#3 Zborzekofski

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Posted 3 weeks ago

Like someone shut the ignition off while the key is still on

#4 Injuneer

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Posted 3 weeks ago

Do you have DTC 14 (low voltage, high temp), or DTC 15 (high voltage, low temp)?

 

Is is possible you read the SES light flashes incorrectly, and you have DTC 41 for the ignition control module (ICM) open circuit?  That could shut the engine down.



#5 Zborzekofski

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Posted 3 weeks ago

DTC 15

#6 Injuneer

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Posted 3 weeks ago

That code does not shut down the engine. 

 

Will the engine restart immediately after it shuts down?  Or do you have to wait a while until things cool down?  If it won't restart, have the ICM tested.  Make sure they get it good and hot, because heat soak from the aluminum head its mounted on can cause the problem you are experiencing. 

 

http://shbox.com/1/4...tml#ICM_cooling

 

In the meantime, fix the problem with the coolant temp sensor in the water pump housing.  It's an open circuit.  Either the wiring of the sensor.  That causes difficulties with the ECM's ability to switch to closed loop A/F ratio control.

 

Coolant temp sensor troubleshooting guide, from Shoebox:

 

http://shbox.com/1/4..._tech2.html#ect



#7 Zborzekofski

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Posted 3 weeks ago

I have to let it sit. I have put in a new ICM.

#8 Injuneer

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Posted 3 weeks ago

How many miles on the engine?

 

Did you replace the ICM in an attempt to solve this problem?

 

Has the OptiSpark distributor ever been replaced?  If so, when and what brand?

 

Is the engine stock?  If not, what engine mods have been made?

 

Has the fuel pump ever been replaced?.

 

Is this a recent problem, or something that has been going on for a while?

 

The more info you give us about the car, and the more detailed the description of the problem, the better chance we have of coming up with a solution.



#9 ZumpTA

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Posted 3 weeks ago

In addition to what Fred asked, did you use the thermal compound with the new ICM?


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#10 Zborzekofski

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Posted 3 weeks ago

164,000 miles, the distributor was just replaced two weekends ago along with the coil and ICM, the engine is stock, fuel pump was just replaced on Saturday, its a problem that the previous owner had and never messed with due to always being on the road. The thermal compound was replaced with the new ICM.

#11 Injuneer

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Posted 3 weeks ago

One possible way to find the problem is to data log the ECM.  A member here, GaryDoug has written scanning software that accesses the ECM/PCM data in the 1993/1994/1995 LT1. (Yes, it's called Scan9495, but it also works on a 93). By recording the data over a period of time, and exporting the data as a .csv file, it is possible to observe over 50 sensors and PCM parameters.  If you can run a log from startup, through the point where the engine shuts down, it may show up in the data.

 

This is a lot more productive, and less expensive than playing "parts replacement roulette".

 

You would need to download the (free) program to a Windows laptop.  Buy or build a cable to connect the laptop to the DLC connector.  GaryDoug is here to help you with any issues in downloading or setting up the program, and producing the data log.  I (and others) can review the data log to see if we can find the event that is causing the engine to stall.

 

Once the data connection is made, I can give you a guideline on how to start and drive the car to produce the most meaningful results.

 

https://www.firebird...9495-lt1-obd-1/

 

 



#12 sea dog

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Posted 3 weeks ago

May I add, if the opti that was installed on your engine is anything except GM, Delco, or Delphi, it is junk. With a high chance of failure right out of the box. And known to have a high failure rate, if it works  right out of the box, within the 1st thousand miles.

 

For your peace of mind, buy a PC based oscilloscope. Learn how to use it. Then use it to check low & high resolution pulses that opti sends to ECM. Pulses should be a square wave. Scope available on Ebay, Amazon, etc, for around $70



#13 Injuneer

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Posted 3 weeks ago

If I'm reading the description of the problem correctly, it existed before the car was even purchased from the previous owner.  It appears that the multiple parts replacements mentioned, including the Opti, were attempts to solve the problem, but did not help.

 

It would have been useful to have all this info in the first post.






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