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code 17 + 51....need a solution and advice

809 Views 13 Replies 2 Participants Last post by  NAJ
code 17: coolant not getting up to operating temperature....possible thermostat ......or .....possible coolant temp sensor failure

Code 51: Engine running lean.....oxygen sensor malfunction
.....but also possible map sensor malfunction and oxygen sensor compensates

My question is.......how do i diagnose (test) for accurate failure.....i dont just want to throw parts at this thing. i want to figure out exactly what is causing these problems......is it the map, oxygen, coolant, or thermostat?

will i fix one and it take care of the other one or are they un related

Gas mileage doesnt seem bad.....car does have a bad exhaust leak at the muffler but is not sputtering and doesnt seem to affect back pressure

stumbles at idle when cold and had to crank it twice when its cold to get it to start but ran fine.......check engine light isnt on

voltage references and electric testing procedures will help either way.
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What are we working on?
Need to know to give you more info on the Code 51.
Anything that will cause a Lean Condition or a Misfire will set a Code 51, also a faulty O2 that failed below .450 volts will set the code.

99% of the time Code 17 is a stuck open thermostat.
This will not set a Code 51, a colder engine will run richer.
92 dodge spirit non turbo

so i check voltage at the 02 and if below .450 volts then its bad.....

could it be a weak ground to the o2
2.5L or 3.0L?
do you have copies of the nf tests
I am on my way out, I can scan and post some of the tests tomorrow morning.
You are going to need at least a digital multi-meter and vacuum gauge, fuel pressure gauge and timing light.

I would replace the thermostat and clear the codes before diagnosing the Code 51.
i have everything i need.....will try to clear code 17 and then see what happens
by replacing thermostat

just for my reference
engine vacuum should be 18-22
timing should be 12bdc when warm
fuel pressure should be 39......no port for gauge.....
should replace the coolant temp sensor because its cheap.....probably the original...making it 20 years old....for the cost of $9.00...why bother even testing it with the back probes.....when i said i didnt want to throw parts at it...i didnt mean parts that cheap....

i should test it just for the practice .....the spec on that should be around 2.50 at 190 degrees......i saw another thread where you went in depth on testing it....ill go by that.the one where you tested your and your sons 3.0.....that should work for me as well.....then ill look into the code 51.....
Fuel pressure on the TBI is 14-16 PSI.(AN Body TBI is 39 PSI)
They make an adapter hose that would go between the fuel inlet and TBI that has a service valve on it to attach the gauge.
Engine vacuum at a manifold source and at the Map Sensor @ idle should be 16-20" HG and steady.

When looking for the causes of Code 51 look at all of your basics first and verify the O2 sensor is not at fault.
The average life of a HO2S is 60K.
1)Physically inspect the wiring to be sure it is not damaged causing a short.
2)Backprobe the O2 signal line at the O2 connector BK/DG wire(do not confuse with the DG/BK) and read the voltage.
A properly operating system O2 voltage will constantly cross above/below .450 volts.
With your Code 51 voltage should be latched below .450 volts.
3)If this is the case create a rich condition by goosing the throttle several times and see if voltage increases above .450 volts, if it does not replace the O2 sensor.
4)Also be aware that an exhaust leak before the O2 adds additional air to the exhaust stream and causes the O2 to latch below .450 volts.

If the code persists after checking/replacing the O2 other causes and items to check...
1)Cam/Ignition Timing
2)Spark Plugs for wear and fouling
3)Excessive resistance in secondary ignition, Cap, Rotor, Wires
3)PCV System operating properly, hoses not soft/swollen/collapsed/cracked/loose fitting
4)Vacuum System, hoses are tight/secure/NOT cracked/dry rotted/swollen/collapsed.

Of course this is all on the assumption that the engine is in sound mechanical condition.

Your hard start condition when cold may be caused by one of the above conditions and/or a carboned throttle plate and AIS pintle.


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have only replaced the thermostat and cts.....code 17 is still there
car is fixed....timing at distributor was off and the pcv hose was cracked..................after clearing the codes no more showed up.....car runs much better now.....although at idle it still drops down some ...then goes up to normal...then drops down...and so on....it doesnt seem too bad though....my guess was timing threw the engine code 51...the cracked pcv hose was from the pcv valve to the valve cover.....last time i replaced it was recently...it cracked almost right away...so i replaced it with a water line....as for the code 17 it just went away after a good drive and the replacing of the thermostat and cts.

thank you so much for all the information.
If idle is still erratic you may still have a vacuum leak elsewhere or a carboned throttle plate and AIS pintle.
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