Purrs with coolant temp sensor unpluggled.

[Amgreppin]

Today while under the hood of my 2.9 b2 I was curious and decided to unplug the coolant temp sensor. The truck instantly idled to 800rpm and purred while giving good throttle response. Truck runs fine with it plugged in but idles at 1000rpm and doesn't sound as good. If running it unplugged richens the mixture, then it shouldn't be a problem considering I live at 10,000 feet above sea level? Any info on if it's bad to run the truck with the coolant temp sensor unplugged, or should I just buy a new one?

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[RonD]

ECT sensor has 2 wires, thats the one computer uses to set Choke Mode(Open Loop) or Run in Closed Loop, warmed up engine.

No it won't hurt anything to leave ECT unhooked but Computer will run engine a bit Richer.

MAP(intake manifold pressure) sensor may be the issue however, since you are at 10,000ft elevation.

When you first turn on the key the MAP sensor will establish air pressure at trucks location, at 10,000ft pressure would be lower so computer would recognize this and lean out the air fuel mix to match.

One of the draw backs of MAP systems(speed density) was that if you started engine at sea level then drove up into the mountains engine could start running rough, or visa versa(drive down from the mountains), but simple shutting key off and turning it back on would reset Starting Pressure for current elevation, i.e. stop for gas and truck runs better afterward.

MAF(mass air flow) system didn't have that problem, lighter air/less pressure is compensated for by hot wire cooling less so less fuel is added, same as warmer air.


I would check the MAP sensor, usually on the firewall behind wiring, and it's vacuum hose to the intake manifold, if hose cracks it will cause issues like you describe.

But no worries on running without ECT connected, may get a CEL(check engine light) if your '88 has one.

 

[Amgreppin]

Cool, thanks, a lot of great info.

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[firehawk618]

RonD is exactly right.

These EECIV rigs do not have dual map sensors. Some speed density rigs have two. One strictly to read barometric pressure and the 2nd one controls fueling / timing.

The most expensive sensor on your truck that will mess with it running is the MAP sensor. A new one is ~$40.

If you don't have a scope to test it I would just replace it. Heck, even if you had means to test it I would just replace it.

The ECT sensor is a dirty cheap part also.

Don't forget there's also an IAT sensor that will also effect how it runs although the coolant ECT has a bigger effect than the IAT does.

The IAT and ECT are easy to test however unless you have a breakout box or want to run some wiring and do some extensive testing it's better to just replace them because they may read the right resistance when you are testing but have bad spots that act up when at other temperatures.