Should I have 2 coolant temp sensors on an 88 2.8 mpfi

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CorvetteBeretta
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Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby CorvetteBeretta » Sat Jan 17, 2015 6:42 pm

I found a solo wire not connected to anything it comes from the harness that runs to the rear of my plenum its green and white
could this be the reason im throwing a coolant temp senor code I have replaced the sensor and harness under the thermostat housing and I'm still getting a code

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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby JeffD » Sat Jan 17, 2015 10:56 pm

I'm pretty certain my 2.8 had only one... I'd have to check the wiring diagrams. Did you pull apart the conduit around the harness to search for the other end? I'd look around a bit more. You should also check the wiring color to the temp sensor.

Hook up your multimeter and see if it is carrying voltage.



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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby Asylum » Sat Jan 17, 2015 11:29 pm

The only grn/wht wires I can find on the Haynes wiring diagrams for the 1990 and earlier 2.8 engines are for the IAC motor control, and the Fan relay.

For what that may be worth.


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby CorvetteBeretta » Sun Jan 18, 2015 1:45 am

Thanks guys for the input I'm going to dig around in the wire loom and see what I uncover

Another question I have is about removing AC what should I do with the sensors/plugs do I leave the sensors on or remove them? do I have to jump anything? I have had it out for ages and just have the plugs there no sensors.


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby CorvetteBeretta » Sun Jan 18, 2015 5:47 pm

So I unwrapped the harness and followed that wire (also found a solid drk green wire same length cut off) and they both lead into the drivers side firewall connection I see no other cut off wires heading the other way this is as far as I got until house boss called.. LOL

I'm starting to wonder if this harness may be from another car


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby JeffD » Sun Jan 18, 2015 8:27 pm

Just remove the ac lines and dryer, condenser, evaporator, and compressor. I would install the AC delete pulley as I cannot promise that you can just use a shorter belt. To prevent corrosion of the connectors I would use heat shrink on the connector ends.



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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby JeffD » Sun Jan 18, 2015 8:40 pm

The harness you are talking about more than likely leads directly to the ECM. I will check alldata tomorrow at work to see if I can figure out where those wires go.



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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby Asylum » Sun Jan 18, 2015 8:46 pm

Your belt sizes are 61.5" without AC. (No delete pulley.)
70.5" with AC and a 100 Amp alternator.
71" with AC and a 105 Amp alternator.

There is not a lot of water pump contact with the non-AC belt, but I have run it without issue.
Just keep an eye on it.


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby CorvetteBeretta » Sun Jan 18, 2015 8:49 pm

JeffD wrote:The harness you are talking about more than likely leads directly to the ECM. I will check alldata tomorrow at work to see if I can figure out where those wires go.


Thanks man. I just want to drive this F(*^^NG thing again I'm throwing a code for coolant temp sensor and my rad fan runs all the time.. I'm trying to figure this out its driving me crazy.


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby CorvetteBeretta » Sun Jan 18, 2015 8:54 pm

Asylum wrote:Your belt sizes are 61.5" without AC. (No delete pulley.)
70.5" with AC and a 100 Amp alternator.
71" with AC and a 105 Amp alternator.

There is not a lot of water pump contact with the non-AC belt, but I have run it without issue.
Just keep an eye on it.


I have been running with no AC for almost 5 years with some damn belt I cant remember from what with no problems


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby Cliff8928 » Mon Jan 19, 2015 12:16 am

To answer the original question...

If you have an analog cluster, you'll have two sensors. A single-wire sensor in the rear head for the gauge, and the two wire sensor near the thermostat for the ECM.

If you have a digital cluster, you'll have one sensor. Only the two-wire sensor near the thermostat is present because the coolant temperature is passed from the ECM to the cluster via serial data.


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby CorvetteBeretta » Mon Jan 19, 2015 11:12 am

Cliff8928 wrote:To answer the original question...

If you have an analog cluster, you'll have two sensors. A single-wire sensor in the rear head for the gauge, and the two wire sensor near the thermostat for the ECM.

If you have a digital cluster, you'll have one sensor. Only the two-wire sensor near the thermostat is present because the coolant temperature is passed from the ECM to the cluster via serial data.


Thanks I thought so because the heads I got from a cavi had that additional sensor on them


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby JeffD » Mon Jan 19, 2015 12:54 pm

I found the same thing as Asylum. The only green/white wire I can find according to the service manual is for IAC coil A low driver and the ground "control" circuit of the fan control relay. That's probably what your wire goes to, the other end is more than likely shorted to ground somewhere. The solid green wire looks like it's for the fuel pump relay command circuit to the relay, it's the only dark green wire in the whole diagram.

Is it possible that someone removed your relays for the fan and fuel pump and just hooked them up to an ignition circuit? Does your car have a few relays bolted up to the firewall? Disconnect your fan and listen for constant fuel pump noise from the tank, it should last longer than the regular 2 seconds.

As far as the coolant temp sensor codes go, check for ground on the grey/black wire and voltage on the grey wire. The coolant temp sensor shares it's ground path with the MAF sensor, are you getting a MAF code too?



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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby CorvetteBeretta » Mon Jan 19, 2015 1:43 pm

I can actually see the green and whit wire going to the fuel pump relay and yes all the relays are on the fire wall
The green wire for the iac and the green and white for fan relay both are intact I trace them from the sensor/relay directly into the passenger side firewall plug these two other wires run into the drivers side firewall plug

I remember now I deleted my cruise control many years ago I wonder if I cut the connector and just ran the wires in the loom I can't remember if I did that

I'm only throwing a code for coolant temp sensor as of now I will check those wires tonight I'm assuming I have to do it with it running or at least my ignition on?


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Re: Should I have 2 coolant temp sensors on an 88 2.8 mpfi

Postby ronaconda » Tue Jan 20, 2015 1:40 pm

I have a grooved pulley and bolt that will mount to the stub that is intended for an idler pulley on models that are equipped from the factory without A/C if you're interested

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