Been playing around with my truck for god knows how.many hours trying to fix code 173. So far have replaced throttle ps, egr valve, egr tube, o2 itself, coolant temp sensor, map sensor, had the drivers side manifild surfaced, absolutely no exhaust leaks before the sensor and used up 2-3 cans of brake cleaner looking for vacum leaks.it had thrown random codes such as a.bad map sensor and a bad egr valve and also the tranny has started acting funny like its slippin.into every gear. But that stoos as soon as i unplug the battery. Fuel oressure is fine ive checked and rechecked it. Probably into thisis thing 300+ dollars in parts and would like to get it stopped. It is a 1995 with a 460. Air filter is clean, and i also noticed today that the air system isnt coming out if the cold mode?? If thags what you call it? But if i manually apply vacum to the valve it will change over...and lastly i know the tranny and o2 are in the same wirebundle thing so think it might be a wiring issue?

 

Sorry in advance for all the the spelling errors im typing from my phone. Also when i unplug the o2 it throws the exact same code and runs the exact same way making me think that the wiring might be bad to it somewhere. And it a live code lkke when i start er up it dosent come on but when it goes into the ?closed? Loop when it warms up then it comes on. And last piece i let it idle in the drive way for 45 min and the light never came on...so what do i do guys thats every ounce of information i can give you

 

If your getting weird codes and then different codes, I'm gonna suspect the PCM. You've replaced dozen of parts and that has been expensive, with no solution yet. Pull the PCM and check for damaged pins in the harness it is connected to and also inspect the main board of the PCM for leaking, bulging capacitors.

 

The ECT sensor you replaced did it have one or two wires on it? The new one may also be bad.

How about the IAT sensor, have you checked it?

Have you checked for fuel in the vacuum line to the FPR?

This engine very seldom goes into closed loop except going down hill.

Does it also get the 173 code in KOER or is it just in CM?

 

The truck will only go into closed loop when it's at normal operating temp, the O2's are switching properly and the truck is out of park, or on the road, if you unplug your O2 and your in closed loop there is a problem. If you not familiar with open or closed loop, open loop means the truck is running on a predetermined program by the ECM, When the truck enters closed loop its is know taking information from all these sensors and making adjustments based on what the sensors are saying. If the O2 is lean it the ECM will increase pulse width PW to allow more fuel to whichever bank is lean and just the opposite. The ECM in closed loop tries to keep the air/fuel ratio at ideal 14.7 to 1. Do you have heated O2's 4 wire, or just regular 1 wire, do you have 2 or do you have 4 of them, can you read live data on your scan tool? It sounds like a bad ground to the ECM or a bad ECM, Have you checked the sensors for the 5 volt reference, most sensors 3 wire and up have it, take your voltmeter turn your key on unplug the TPS and probe each pin 1 should have the 5 volt signal.
It is time to stop wasting money and diagnose this properly. What are the trouble codes, that you didnt cause. when you have the key on and unplug the tps for this test you are going to set a code for TPS open. get back to me.

 

I too think he may have a bad PCM Computer.
What David7.3 says is true about closed and open loop for most engines but not for the 1995 7.5L that very seldom goes into closed loop except for going down hill.
I know I have one and others report the same thing and it is backed up by reading the program code that the 1995 7.5L engine runs on.

 

Boy that's silly I guess with the big block and the trucks GVW they skirted the emissions requirement for 95, So this makes it much easier than you can basically unplug most of the crap and she will still run. pull the SES bulb and have a nice day. But seriously there is some thing in the ECM that is causing the problems, cant hurt to check the wiring and connectors, the grounds as well. If he takes the ECM apart there might be an obvious sign of a problem and that way we would know for sure.

 

kyle95, Isn't this the same problem we discussed from before and are you still experiencing an exhaust leak? (173s are ambiguous to chase, often lead to computer, harness issues but I'm still of the belief the exhaust leak is throwing mix off)

(Quote:
Originally Posted by kylek95 View Post
Just trying to get as mich information out there as possible for you guys to help me, i redid the exhaust manifolds a while back. One of them has a gasket on it and the other one i took and had it milled down. But it still has a hair of a leak on the side with the gasket. Do you guys think that could be casuing this, maybe air coming in through there and hitting the 02 and then making it run richer?
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Sounds like you have bad fuel pressure and the leak in your exhaust is also allowing ambient air (via a Venturi effect) to mix with hot exhaust. The ambient air brings higher oxygen content raising the overall exhaust gas oxygen content proportionally to the size of the leak----the oxygen sensor will react accordingly and send erroneous feedback to the computer throwing mix off.

Other results include incomplete NOX reductions which can affect your emissions test, carbon build up and reduced fuel economy.

With that leak your exhaust velocity is also dropping keeping the exhaust valves in constant contact with hot exhaust gases -- those exhaust valves won't cool entirely through contact with the cylinder head and will eventually burn up........

 

I would also check the PCM Computer numbers and see if it is the right one for the truck.

 

Yes same problem as ^ but there is now no more exhaust leak and that is not the problem so instead if rrposting to that one i figured i would start a new one. Also no gas in the fpr line when i take it off and fuel pressure jumps to 40 when i unplugthe the line. Where should i check for the wires on the ecm/pcm? For the o2 and there is only one of them on the truck and i will check to see how many wires it has.

 

Where/how never messed around with that before

 

The numbers or on the plug of the PCM computer.
Check the number with the calibration parts list for your calibration number on the door post.