error 51 showed up on the code reader, referring to the coolant sensor on the manifold, this is the temp gauge sensor...correct?
chiltons stated that it controls idle speed; fuel mixture and purge canister control...I find it hard to believe that an $8 sensor can throw the engine into running rich and hard starts and puffing black smoke at startup...any ideas or thoughts...

Thanks

 

Sounds right to me, if the sensor is bad, it will think the motor is cold, cause it to run rich, which explains the black smoke.

 

Correctamundo, Its about closed loop and Open loop, and if an EFI motor doesnt get the right signal from one of those sensors it reacts accordingly....

Isnt it amazing how picky EFI motors are?

 

Hey Kevin, will my 85 throw codes? its EFI too, but hard startin sometimes.

no CEL on that thing.

 

Here's how it works. I don't know what you're driving so I'll answer in a general sense........

*If there is a temp gauge on the dash there should be a sending unit for the gauge and seperate temp sensor for the electronic engine control system. The latter will be of concern, not the coolant temp sender for the gauge. The usual tipoff is the one of interest here will have two wires (don't know what you're driving).

*A cold engine operates in open loop until the engine reaches an established temp per design (maybe around 120 - 140 degrees, depends on what you're driving), then it switches over to closed loop. In open loop, the A/F mixture is based on, among other things, "predefined" settings stored in the ECM (Electronic Control Module, aka 'puter). In closed loop, A/F mixtures will be determined by, among other things, information from the O2 sensor. The O2 sensor must be at a defined design temp before it operates correctly; this is why it stays in open loop for awhile. Rich mixtures burn cool, lean ones burn hot; the O2 sensor makes use of this fact and sends a small voltage back to the ECM. This info, among other info, is used to determine the correct A/F mixture. If the system cannot switch to closed loop (such as when a bad coolant temp sensor is sending bad/false information to the ECM) it will generally run rich, much like a choke being stuck on.

*Depending on what you're driving, the canister purge system does not draw vac through it constantly. I've seen old carbed vehicles run rich because the temp sender had failed; air was constantly being drawn over gas in the carb. I suppose the same might be possible with the fuel in the gas tank.

*If you've got EFI and the system is in open loop (cold engine operation), it's going to increase idle speed just like an old carb will until the engine warms up. This decreases incrementally as temp increases and the engine finally enters closed loop operation.

*If there are other codes besides 51, then we probably have a bit more to talk about before you begin the fix. In particular, there is a sequence that each code must be addressed. Failure to do this can result in , , or .

**Be aware that a code in itself does not automatically mean a bad sensor. In general, a code is flagging a problem in a system of which a sensor(s) is a part of that system. As an example, a few years ago I fixed a problem where the codes (for more fun, more than one ) were pointing to the MAF (mass air flow) sensor. But in the end, the problem turned out to be the the IAC (idle air control) solenoid. WTF, how the hell could it be that, it idles great. I got the job done by using diagnostic flow charts and a digital voltmeter rather than guessing; saved me the cost of a MAF sensor ($90 maybe). Good news in your case is that you're looking at an $8 sensor rather than two of them at about $100 each (spendy guessing on non-returnable parts).

 

Yes Brent, your truck is EEC-IV alhtough a real early form of it, Ive never tested one for codes, but i think it does throw codes

 

ye syou can still get the codes, you just need a mechanical volt meter or test light. Put the + side to battery + and the - side to the STO. Then ground the STI and turn the key on to get the codes. Visit www.fordfuelinjection.com for details.

Cheers,
Tim

 

If he's got EFI he's got a check engine light (CEL). Either the light is burned out or someone *fixed* a problem by removing it. Dirty trick some people play once in awhile and often before selling vehicles. Some people also go to the trouble of getting into the lights and putting a piece of tape on the inside of the surface that reads check engine. The CEL, by design, will illuminate with the key on and engine off. BTW, there are three ways to pull codes on EEC-IV, including using just a jumper and the CEL.

 

The older trucks do not have a check engine light. My '87 (and other folks' '87 trucks on this board) did not have a CEL from the factory. My instrument panel had a place for one, but there was no wire in the harness for it.

Right idea, but the O2 sensor determines A/F ratio by reading the amount of oxygen present in the exhaust stream, not the heat of the exhaust. More oxygen means a leaner mixture, and less oxygen means a richer mixture.

 

A rich mixture is one in which there is insufficient oxygen for total combustion; a lean mixture has an excess of oxygen and may produce excess NOX. Generally, an O2 sensor operates via a chemical reaction to detect the amount of oxygen in the exhaust stream. Such chemical reaction generates a small voltage of which the ECM uses to determine the correct fuel required for a given operating condition (throttle position, vehicle speed, etc).

 

Awesome information; the truck I drive is a 88 Ford F150 4x4 that has been aptly named by my wife as "grumpy's money pit"...did change the sensor and it seems to be ok...but you never know?

Thanks
here are some of the truck pics...
https://www.ford-trucks.com/user_gal...&albumid=15527