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If installing a new pigtail, does it matter how the 2 wires are hooked up. The new pig tail has a black, 2-wire lead, ones side is solid black, the other white stripe. When patching this back into the factory EMS, again.. does it really matter how the 2 wires are installed?
-Thanks!
If installing a new pigtail, does it matter how the 2 wires are hooked up. The new pig tail has a black, 2-wire lead, ones side is solid black, the other white stripe. When patching this back into the factory EMS, again.. does it really matter how the 2 wires are installed?
-Thanks!
When I did this in my 93 both wires were the same black wire but what I did do was I connected them the wire spliced went to the same terminal, does it make a difference not sure it's more than likely a pass thru sensor
The short answer from me is that you should keep these 2 wires straight. Don't cross them. The connector is polarized. It only goes in 1 way.
The longer answer is that this sensor is almost certainly wired into the ECM as a voltage divider. I currently don't have access to a wiring diagram or a sensor. But a voltage divider circuit uses a voltage source, a ground, a signal wire and 2 resistors. 1 resistor is a fixed value and the other is a thermistor (resistance varies according to temperature). If both resistors are part of the sensor and the circuit uses the sensor body as a ground, then, you absolutely need to keep the wires straight. If the sensor only contains the thermistor and there's no connection between the pins on the sensor and the sensor body (ground), then you can cross the wires.
If you have access to an ohm meter, you can check for resistance between each pin on the sensor and the sensor body. If there is any resistance, keep the wires straight. If it's an open circuit and there's no continuity between the pins and the body, you should be able to cross the wires.
Voltage divider circuit where R1 is a fixed value and R2 is variable. ECM connector wiring from an 88 Vette. Coolant Temperature Signal wire is C10. It's yellow.
Last edited by C4industries; Apr 3, 2025 at 12:23 AM.
You should probably, to be on the safe side, keep them seperate. I do not have 89 schematics but the ECM is a 7165 and the coolant temp sensor is the same p/n also. The 452 circuit is ECM 5+ return and is shared with the TPS and manifold temp sensor . I only have 86 87 88 schematics, just know that, but they are most likely the same. With all that said, thermistors, as i know them, are not polarized.
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Great info! These are the schematics you need. As I suspected, it's a voltage divider circuit. And according to these schematics, the coolant temp sensor only contains the thermistor and it is not polarized. The fixed value resistor and ground connection in this circuit are part of the ECM. So you CAN swap the leads on the pigtail at the sensor.
Last edited by C4industries; Apr 3, 2025 at 05:59 PM.
Thanks a lot. Mine fires on first try, but after that, it's almost like its missing on 3 cylinders, then 2 seconds later it sound better, then after another 2 seconds, you can hear/feel it operating on all 8 cylinders. It started every single day this past winter, and still continues to. I just thought that possibly wiring in another coolant temperature sensor, correctly, or my guess it was installed correctly, could aid in first starts. It most likely correct, but I'll replace it & see. Again, much gratuity on the help.
I have an AEM UEGO Wideband, as I built a new engine, South Bay adjustable pressure regulator, new diaphragm. South Bay Bosch 3 injectors. I didn't want to go WOT until knowing i was lean. In the morning it crank for 3? 4? seconds then lights, stumbles, shuts off. 2nd start attempt it fires but is missing pretty bad, for two - three seconds, then gains ignition on a couple more cylinders, then! a second later it's on all 8. This is a pretty consistent starting pattern. Once it idles, on all 8. shutting it off. it re-fires fine. It starts full temperature no problem. Driving to work in the morning, is a railroad. IF!!! I get there and a train is rolling through, put her in park, and shut it down. Refires fine. The whole experience is flawless, except for this rough cold first start. I'm running a nice high torque, reduced gear starter, Optima redtop, NAPA alternator. The distributor is 100% new, base fuel pressure has been set, replaced mass airflow sensor, tps, (set correct tps voltage) iac valve, rebuilt throttle body (This enabled a surgical idle), once at operating temp, in gear it idles at 600rpms, solid. No dips, revs. no cats, 2 mufflers, new o2 sensor, replaced all relays. Oh! it only starts odd initially. Once it warms up, i can park it in 20degree weather for 4 hours, and it starts fine. The cold start I'm complaining, concerned about, is after i park it, and it sits overnight. I mean, it sounds like a Black Hawk starting in the morning. Sorry to re-hash the whole scenario 15 different variations.. I have a FSM. Thanks for any further input.
Wires are 1 year old. Put new plugs in (and gapped) Christmas 2024. Every part in the distributor is Brand new from Summit September 2024.
They are stock flow rate injectors. 22lb? When the engine was built, a new hydraulic roller cam and lifters, rockers, guide plates, pushrods were installed. Heads have 3 angle cut, comp cams everything. line bored, ARP main, rod bolts. arp head studs.. mls gaskets.. i did the engine how me and my wallet agreed on.
It's done this since first initial start... and gets worse the colder the weather. I've replaced it all... and still haven't been able to figure it out. new pump, sender assembly. Always 93 octane. And yes, turning key primes pump for 2 seconds. I don't smell fuel. No leaks.
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Why on Earth would I want to spray starting fluid into my engine, and I'd have to remove something, or hack something up to allow starting fluid into the system. I'm installing upper/lower radiator hoses early next week. While that's going on, I'll take some pictures of my fuel injectors..
>>Disconnect the EST wire and see if it starts right up.
what/where is the EST wire?? sorry, i was glancing over each reply and just noticed this...
Why on Earth would I want to spray starting fluid into my engine, and I'd have to remove something, or hack something up to allow starting fluid into the system
Most of us just remove the PCV hose from the intake and spray it in the intake.. And I ask you why would you do that ???????????????????????????????????
Here's a clue ............................ you have a starting issue !!!!!!!!!!!!!!!!!!v If you read the entire post of things given to you you would understand.
Last edited by Vets-Vet; Apr 13, 2025 at 01:45 PM.
Thanks for the clue, and i understand I have a starting issue. But starting fluid is a good way to bend a rod...and you never answered my question???
>>Disconnect the EST wire and see if it starts right up.
It starts on 2nd try... not right. But I'm sort of against loading the intake up w/starting fluid..,.. can't there be some other means of troubleshooting???
I am not saying this is your problem, but it will narrow it down
A lot of members here have had problems with initial cold starting and for most with L98 engines it was the cold start injector which youdo not have, 89 deleted it and used a MEMCAL/ECM routine to spray the 8 injectors in place of the cold start injector. The people that decide to get rid of their cold start injector reprogram their memcal and use the 89's method . I am in over my head talking about MEMCALS and programming, but it is what people here do.
By spraying the inake you find out if it is fuel related. That is a giant leap in narrowing the problem, wouldn't you say so ??
I am not a pro engine man by any stretch of the imagination, but in my years here and watching and learning elsewhere I have never heard of anyone damaging an engine with starting fluid on a healthy engine.
Vets Vet,
No No.. I'm sorry to come off.. arrogant. I grew-up on SBC, and have seen one too many engines (2 or 3??) get damaged from Ether... So yes, indeed I have a starting issue. Now today it was 52F, i turned it over... and it began starting.. stumbling, missing, then!! 2 seconds later it caught.. it seems to be worse (and more noticeable) when temps are low 40's & Below. But, by far. it's not starting correctly, whatsoever. And obviously, I cant sell it.
It still surprises me to this very day.. today i was on an open road coming from a 5mph roll, and i hammered it, trans downshifted, and it took off!!! chirped 2nd gear. The transmission is phenomenal!!! shift points are Very predictable... never slips, misbehaves. Now, I don't beat on it but 1x/wk. mebbe.. it's may have seen 5500rpm.. just an awesome car. I believe it had some trans work.. somewhere, somewhere, sometime.. Oh Well!
>> >>Disconnect the EST wire and see if it starts right up.
Where might this mysterious wire lay??
Last edited by stiggity99; Apr 13, 2025 at 06:47 PM.
Reason: forgot something?!
I would forget disconnect the EST wire, it is just a pickup coil test, that is the least of your worries if you have a new distributor so forget that. I would think a fueling issue for the start up routine would be more apparent when it is cold. That is why gasoline gets an octane boost in the winter. This all points to the start up routine. Others have been down this road for months before this simple test proved it was a fueling issue at start up. But that is your choice,
Good luck.
Most often after stumbling a little first try...second try starts it. What kind of fueling issue do you think i could have. Lets say loading intake with Ether, gets it to fire.. what next?? The behavior is consistent.. which i guess is a good thing. Now that it's getting nicer outside, it starting Easier, but far from correct. And initially it does turn over for 2 or more seconds before lighting...
I appreciate all the help, and will never take this forum for granted, as I've encountered some of the coolest folks...
'89, AT, Coolant temperature sensor.
