94 LT1 starts ok, runs badly, then ok
08-28-2018, 05:27 PM
#1
94 LT1 starts ok, runs badly, then ok
This is a 94, manual. It starts easily, but for the first 30 seconds, it runs horribly, like on 4 cylinders. Then it wakes up and runs fine.
Any ideas?
Any ideas?
08-28-2018, 06:36 PM
#2
Zen Vet Master Level VII
Check your coolant sensor. You symptoms are consistent with your sensor being wonky. A faulty sensor will tell the computer that the engine is hot when it is cold and/or or cold when hot. The fact that the engine (once warm) runs well tells me that when you first start the computer puts the engine into lean situation and starves your engine. Once warm, your engine needs less fuel.
08-28-2018, 10:26 PM
#3
That was my first guess. When it's warm, 190, it reacts the same way, but not as bad. So maybe it doesn't take as long for the second sensor to supersede the first, and the first is just not working at all. Thanks for your help.
08-28-2018, 10:45 PM
#4
Team Owner
There are 2 sensors? I would think that there is only 1 but I don't have that year car. Scan it so you know what the ECM is thinking the temperature is. Check the sensor with an IR Thermometer and they should be fairly close. IF not, change the sensor.
08-30-2018, 04:46 PM
#6
All fixed. Bill was right on, ECT was the problem. I thought I would unplug the ECT and start it to see how it ran. It won't run with out the ECT. When I pulled the plug, I noticed that the cup portion where the latch is, was broken and stuck into the wire part of the plug. The connector came apart easily. After the "unplugged experiment", I stuck the two halves together as best I could considering that they would not latch; the car started perfectly.
I looked on line for a new ECT. I ordered the AC from Advance Auto, 213-4514. The next day, while I was standing with my finger plugging the water hole, I noticed that the new ECT had a much smaller diameter thread than the one I just took out. Back to the store. It seems that their 4514 number is for ZR1s. I bought whatever fat ECT they had in the store. With the new piece installed, the engine started perfectly every time.
Aklim- I had read bits and pieces in the FSM about how the starting system works. I thought I had remembered 2 temp sensors. My new interpretation is that the computer checks the ECT to see how to pulse the injectors depending on the cold temp. When the O2 sensors get up to temp, the computer uses their input to determine the fuel injection. When they came up on line, that is when my car "woke up."
Thanks all. Until next time.
I looked on line for a new ECT. I ordered the AC from Advance Auto, 213-4514. The next day, while I was standing with my finger plugging the water hole, I noticed that the new ECT had a much smaller diameter thread than the one I just took out. Back to the store. It seems that their 4514 number is for ZR1s. I bought whatever fat ECT they had in the store. With the new piece installed, the engine started perfectly every time.
Aklim- I had read bits and pieces in the FSM about how the starting system works. I thought I had remembered 2 temp sensors. My new interpretation is that the computer checks the ECT to see how to pulse the injectors depending on the cold temp. When the O2 sensors get up to temp, the computer uses their input to determine the fuel injection. When they came up on line, that is when my car "woke up."
Thanks all. Until next time.
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cardo0 (08-31-2018)
08-30-2018, 11:52 PM
#7
Team Owner
Aklim- I had read bits and pieces in the FSM about how the starting system works. I thought I had remembered 2 temp sensors. My new interpretation is that the computer checks the ECT to see how to pulse the injectors depending on the cold temp. When the O2 sensors get up to temp, the computer uses their input to determine the fuel injection. When they came up on line, that is when my car "woke up."
Thanks all. Until next time.
Thanks all. Until next time.
Where exactly is this fat sensor you found? IIRC, the one below looks like my sensor and is in the front of the engine under the TB.
Can you tell me the letter of the sensor you are referring to? If it is N5, I understand where the issue is. If it is D, the sensor above should fit.
Whoops. You have an LT1. It is still in the front. Here is a better pic of the gauge one.
This is the one by the opti which is for the ECM.
Last edited by aklim; 08-31-2018 at 12:06 AM.
08-31-2018, 10:26 PM
#8
Intermediate
All fixed. Bill was right on, ECT was the problem. I thought I would unplug the ECT and start it to see how it ran. It won't run with out the ECT. When I pulled the plug, I noticed that the cup portion where the latch is, was broken and stuck into the wire part of the plug. The connector came apart easily. After the "unplugged experiment", I stuck the two halves together as best I could considering that they would not latch; the car started perfectly.
I looked on line for a new ECT. I ordered the AC from Advance Auto, 213-4514. The next day, while I was standing with my finger plugging the water hole, I noticed that the new ECT had a much smaller diameter thread than the one I just took out. Back to the store. It seems that their 4514 number is for ZR1s. I bought whatever fat ECT they had in the store. With the new piece installed, the engine started perfectly every time.
Aklim- I had read bits and pieces in the FSM about how the starting system works. I thought I had remembered 2 temp sensors. My new interpretation is that the computer checks the ECT to see how to pulse the injectors depending on the cold temp. When the O2 sensors get up to temp, the computer uses their input to determine the fuel injection. When they came up on line, that is when my car "woke up."
Thanks all. Until next time.
I looked on line for a new ECT. I ordered the AC from Advance Auto, 213-4514. The next day, while I was standing with my finger plugging the water hole, I noticed that the new ECT had a much smaller diameter thread than the one I just took out. Back to the store. It seems that their 4514 number is for ZR1s. I bought whatever fat ECT they had in the store. With the new piece installed, the engine started perfectly every time.
Aklim- I had read bits and pieces in the FSM about how the starting system works. I thought I had remembered 2 temp sensors. My new interpretation is that the computer checks the ECT to see how to pulse the injectors depending on the cold temp. When the O2 sensors get up to temp, the computer uses their input to determine the fuel injection. When they came up on line, that is when my car "woke up."
Thanks all. Until next time.
09-01-2018, 07:49 AM
#9
Safety Car
It sounds like a vacumn problem or may be a loose wire or maybe o2 sensor we could go on and on. Have it scan for free at aoto zone or oreilys. Then see what direction you should go in.
09-01-2018, 08:36 AM
#10
Aklim, The broken sensor was the one into the waterpump. It looks just like the one in your close up photo, but apparently there are two listed for 94 Vettes. My LT1 uses the one that has about a 5/8 diameter threaded portion. The other one listed for the water pump looks the same except that the threaded portion is about 1/2" in diameter, maybe for the ZR1. The head temp sensor has one wire, and feeds the gauge. I don't think the computer consults this one to control the engine.
With the original sensor with the broken connector, when I started the car, it would barely run and crow hop around the garage for 30 seconds, then it would miraculously flip to smooth idle and run normally. The new sensor fixed it completely. Now I sleep at night.
With the original sensor with the broken connector, when I started the car, it would barely run and crow hop around the garage for 30 seconds, then it would miraculously flip to smooth idle and run normally. The new sensor fixed it completely. Now I sleep at night.
09-01-2018, 11:15 AM
#11
Team Owner
You are going to need a scanner sooner or later so why not today when you need it?