I am getting code 173 in KOER test on my 1996 F250 with the 351w. Its saying that the O2 is reading rich. I have no exhaust leaks. I took off my exhaust and welded it up tight. There are no vac leaks. There is no fuel in the FPR vac line and the fuel pressure is at 35 with vacuum and 40 without. It holds pressure when the truck shuits off. It is still hard to start and stalls a bunch, but in the upper rpms its seems to run fine. What could be causeing this problem? Is the O2 bad?

 

Could be. How many miles are on the o2 sensor? If it's over 50,000 you'll probably want to replace it.

However, have you checked out the IAC valve at all?

 

Not quite sure how many miles are on it. Got the truck for cheap and put the motor and trans in it. Original had 204xxx on the motor and trans. Could be factory, i am not sure.

As for the IAC, i unplugged it and the truck died. Going off of FFI.com that means it is functioning i believe.
Would a bad O2 cause a hard start?

 

No, not very likely. I would suspect a problem with the MAP sensor or perhaps the ECT or ACT sensors. All of them can be removed and tested with a meter, a vacuum source, heat source.

A quick and dirty test is to electrically disconnect the MAP sensor, then try starting the truck. If the starting improves, you are on the right track.

As far as the ECT/ACT you need a heat source and a meter to check their output at different temperatures. You could start at ambient to see if they are in range then increase the temp with a heat gun or oven.

 

Before you go trying to replace your HEGO sensor (O2), with the truck running, stick your hand in the exhaust gas for a few seconds, then smell your hand. If it's running rich, you'll smell gas on your hand. And that's what the code is telling you, so the HEGO sensor is working. HEGO sensors are out of the loop until the engine warms up and switches to closed loop operation, so it doesn't have any effect on cold starting.

I'd check all your spark plugs. A plug with black, sooty deposits will indicate a rich condition in that cylinder (all Haynes manuals have color pictures of what effects various engine conditions have on spark plugs). If you do find a sooty plug, you may have an ignition problem in that cylinder, or the injector may be leaky or clogged (shooting a stream that doesn't burn well instead of a fine spray).

Jason

 

Wouldn't a bad ect or act set a code? I replaced the ect a few weeks ago because it did throw a code. Also, both of these could cause a rich fuel mixture too correct? I'd rather not jump to injectors at the moment! But how would I test the ignition on the truck?

 

The sensor could be registering in range, but not necessarily correct. Therefore no codes will be set.

 

I'll just replace the act/ect just because they are original on a 220k motor and we will see if anything changes. I'll check out the plugs this week and see what they have to tell me.

When I have the timing advanced to 16-18* the truck idles alot better, but the lifters or something start rattling badly and can't do above 45 unloaded without it chattering. Does that tell anyone anything besides it's advanced too far?

 

Those aren't lifters rattling, that's detonation, and too much of it will munch your pistons.

Are you pulling the SPOUT connector when you're setting your timing? Factory timing is 10º BTDC, and some guys can do 12º or so, but I don't know of anyone getting away with 16-18.

Put it at 10º for diagnosis...it's what it was designed for.

Jason

 

We havent driven it much since we advanced it that far. I usually have it set to 10* but it would keep stalling on me so I upped it more until it would stay running. Talk about a band-aid fix!

 

That tells me there is more to the story than your error code 173.

 

That's the only code that comes up on the koeo and koer tests. The exhaust really does not smell like raw fuel like it's running rich...

 

If your engine will not run at 10 BTDC w/spout out then you have a problem. The code 173 is a side effect of something other root cause. Get that engine to run right at the proper timing setting then I suspect the 173 problem will be resolved.

I think you have been down the road of checking for vacuum leaks, good plugs/wires/etc., cleaning the IAC (replaced perhaps) but something is amiss here. Something basic needs to be resolved.

 

The truck has autolite plugs and wires that were put in new when the motor was installed. I have replaced everyvacuum line with a rubber one that fit the nipples good. I have not yet cleaned the IAC but have unplugged it while the truck was running, and it stalled so i thought that meant that it was working as it should.

The motor will run at 10-12* but it stalls alot when idling and slowing down. During the a cold mornig start up i can see that th exhaust is "puffing" instead of a steady stream of steam. Its like it is like the lope of an old muscle car...

 

As suggest you really need to look a ACT, ECT and MAP sensors. Problems with one or more can cause it to run rich. All are used during cold start up to determine fuel mixture.

And yea 16-18* of advance is way to much, idles alot better because increasing timing advance increases vacuum at the same time masking other issues, in your case increased vacuum also = less fuel if everything else is normal.


You said you replaced the ACT and ECT sensors, as stated you gotta test them.


The sensor could be registering in range, but not necessarily correct. Therefore no codes will be set.

Your also going to have to test the map sensor if the ACT and ECT prove to be within spec. Test with engine cold and then when up to running temp.

Those will be easier to test, a meter with a tach function will be needed to test the MAP sensor.

However you can and should use a volt meter to verify 5v reference voltage is present to all three to start with. (Gray-Red wire)