Lean meat: 172 Lean code, checkin all my bases...

[Creager]

Yep she’s running lean, the question is... why?

The last time I rebuilt the top-end of this motor was a few weeks ago, prior to that was January (yeah three months between rebuilds, Hey I’m pretty good at it now). Ill try and explain the sequence of events.

I removed the heads in Jan to chase down a problem with extensive oil and coolant loss. Head was cracked, guides shot. Stock heads were brought in, valves grinded, deck milled, guides replaced with phosphorous bronze guides of similar dimensions (stock Volvo part I believe?). Afterwards I sealed up the top end and she was running great, haven’t lost a drop of oil or coolant since...

A few weeks later I’m driving' home on a 120 mile trip from Boone, NC when the check engine light comes on. At the time I was alarmed, but I couldn’t do much so I just took it easy on her. Then, at some point as I was cruising up and down the mountains she started miss-firing BAD. I guessed she was running on 4 cylinders, and I was right. Removed the spark plugs, plugs that came out of cylinders 2 & 4 were completely melted, no electrode left (surprizingly, the other 4 looked perfect, nice golden color). Threw in some new plugs and limped her home. Cylinder 2 had lost ~30lbs of compression, and cylinder 4 was at zero. Removed those heads, and found a dime sized hole in the exhaust valve on cylinder 4.

Lost for an explanation I went to my machinist. He helped me out, grinded all the exhaust valves for free, replaced the one blown valve for cost, and even kernelled out some of the exhaust guides (fo free!) as he felt he they needed a little more clearance (as he was the one that put them in there). Either way, he felt that it was obvious I had a fueling problem or an air leak.

So I got it all back together and ran the codes,

KOEO test brings up 172 in the memory codes,

KOER test also brings up 172 and only 172.

First things first, fuel pressure...

I hooked up my fuel pressure gauge, and turned the key without starting...

First turn of the key... 12lbs (not really good...)
Second turn of the key... 38lbs (much better)
Third turn of the key... 40lbs (just what I like to see)

Then, I checked the pressure with the engine running

At idle the pressure sits between 32-35lbs.

At WOT, the pressure drops to 28lbs, the lowest I saw it go.

These numbers indicate to me, that I have solid fuel pressure.

But just to make sure, the two cylinders that madly leaned out, got brand new fuel injectors.

On to checking the vacuum...

The lower and upper intakes were just recently sealed with new gaskets and torqued to spec (using the Haynes manual, the instructions Fel-Pro includes with their gaskets, and snip-it’s from the Ford Manuals.) So I know there is no leak here.

So moving forward, I found a can of starting fluid in my hand, and sprayed a mess on every vacuum line I could find... FPR, PCV system, A/C lines, Break booster, cruise control, everything I could think of.

Although the RPM never changed, nor did I see any smoke from the exhaust.

So on to the various sensors and circuits.

TPS is set to ~.965v

MAF cleaned, and swapped with the Factory unit (had a PRO-M on there).

On to the 02 sensor...

First I ran a ground from the computer to the block, to make sure.

The best I could come up with was by using a voltmeter to measure the voltage coming off the 02 sensor. Ford used 4 wires to mate up the engine harness with the sensor. An orange wire, a orange with black stripe, a grey with blue stripe, and a black with a white stripe. One of the orange wires stayed constant 12v, the other orange wire and grey wire would be at .45v with the engine off, while the black one would usually be around nothing.

With the engine running the black wire seemed like the right one (I don’t really know) but it was constantly switching around .45v. The voltage was pretty much all over the place, from .01v-.4v then it would jump .6v-.9v;

There were a few times, after the CEL would illuminate, that the readings would get 'stuck' in a certain range... At one point the readings stayed between .01v-.1v while the engine RPM hovered around 2000. Then another time, the reading didn’t move from .80-.83 while at 2000 RPM. (I figured that would throw a rich code, but it still said 172) My research indicates that a bad 02 sensor could get stuck like this, but it seems like I’m really running lean! I pulled the plug out of cylinder number 4 and it was clean... TOO clean. Whitish, lean... lean meat no good for my beefy engine!

my theory...

From what I understand, when the CEL becomes illuminated the ECM automatically attempts to judge fuel/air mixture by pre-calculated ratios from the factory (?). Now, since I’m running a much different cam, and have serious vacuum getting sucked into this thing, what the computer thought was a safe default setting, may be leaner then normal, especially at RPMs higher then 3000. Which could explain the massive lean out, but the 02 sensor is actually sending the computer a lean code which illuminated the CEL in the first place...

I’m confusing myself!

 

[Glacier991]

As I was reading your post I kept saying to myself as I read down your laundry list... yep, yeah, ok, uh huh.... so If we have similar brains, I think you are on the right track..... my only Q probably comes down to fuel pressure regulator....that and I would LOVE to know the O2 sensor readouts time graphed....not easy on a 1st Gen.

 

[MrShorty]

With your cracked heads and such, were you losing coolant through the combustion chamber (as so often happens with head issues)? Coolant is known to poison O2 sensors. Where you've already checked many of the other easy things to check, and, under this scenario, there's a reasonably good chance the O2 sensor is poisoned. I would be seriously tempted to just replace the O2 sensor and see what happens. If it fixes the problem, then great. If not, then at least you know the sensor itself is good.

 

[Creager]

The crack was actually parellel to one of the intake runners, actually on the opposite side (top side) of the head. It could of been possible i was burning coolant aswell.

It seems pretty logical that i may have poisoned the oxygen sensor, so i did indeed just replace it with a new unit. Although the problem still persists.

Afterwards i tried watching the fuel pressure as closely as possibly. I warmed up the engine, until finally the CEL illuminated. From there i revved between different ranges of RPM and still didnt see the fuel pressure drop below 29lbs (even at WOT). It pretty much sticks between 30-35 while revving, and 35-40 while idle.

Getting time-graphed 02 sensor readings, is there a formal way to do this? I could just sit there and attempt to read off whatever comes off the voltmeter. I heard about some kind of USB voltmeter? Maybe i can write a program that will save all that junk to a file.

At this point I'm not sure where to go. Im going to take another hard look at all the possible places i could be loosing vacuum, but i kind of feel like I'm not going to find anything. Is there a way to see what kind of pulse the computer is sending to the injectors? maybe a bad computer?

 

[MrShorty]

A simple thing: Have you checked the wiring from the sensor to the computer to make sure you didn't pinch/cut/break/etc. the wires to the O2 sensor?

On further thought, your analysis of the spark plugs suggests that the engine is actually running lean, just as the o2 sensor is reporting. Perhaps the issue isn't in the O2 sensor circuit. I would still check to make sure, but the O2 sensor may just be reporting reality.

A bad computer is a possibility. The trouble with diagnosing a bad computer is that it is usually done by process of elimination. Meaning, if every other possible cause of the code checks out ok, then the computer must be at fault. The trouble is that it is difficult to eliminate every other possible cause of a lean code.

A few years ago, I recall hearing about a gadget that was supposed to plug in series with the PCM that would record EEC-IV data for graphing on a computer, but I also recall that it was quite expensive.

I know I've put an oscilloscope on the injector wire and been able to see the injector pulse that way. I've never used it to diagnose anything though. I suppose you might be able to see missed pulse that way.

Going to have to think on this one. Have you been able to get hold of a copy of the pinpoint test from a good manual? If I were in your shoes, that would probably be my next step.

 

[Creager]

As far as i can tell, the wires from the 02 sensor the computer are intact. I havent completely traced them down, but i have traced it from the sensor, past the coil pack and fuel injectors, upto where the engine harness meets the chassis harness. This is where i was getting my readings from. So i know the wires are pretty healthy up to the firewall.

At this point im convinced its actually running lean. It would have to be a pretty big vacuum leak for it to be leaning out like this. I should get a picture of that valve for you guys, its pretty bad.

I'm not aware of the pin-point test? You will have to elaborate on this for me. One thing i havent tried, which i may try is removing/replacing my air filter. It wasnt recently oiled, nor is it showing any signs of being dirty, but maybe, just maybe its screwing with the MAF... making it think less air is comming in then reality. Otherwise im going to start replacing every vacuum line i can find! haha.

 

[MrShorty]

I'm not aware of the pin-point test? You will have to elaborate on this for me.

When the engineers designed the diagnostic system, they put together step by step pinpoint tests for each trouble code the computer could put out. These pinpoint tests (sometimes called circuit tests) are referenced in a good manual. Libraries around here will carry either Motor or Mitchell, and they are usually in the Engine Performance and Driveability manuals (or equivalent). In these manuals, after describing the self-test procedure, they usually have one or more lookup tables. You find your trouble code in the table and it will refer you to a specific circuit "pinpoint" test. You then go to the pinpoint test and you find a step by step procedure of how the engineers intended for you to diagnose that trouble code. I find these to be useful resources, especially when I get stuck to make sure my "seat of the pants" procedure has been reasonable and to make sure I'm not ignoring something.

 

[Turdle]

Was the burned valve before or after the pro-m maf was changed out?

 

[Creager]

yep still chasing this one. Its a better now hah, the 172 code is gone and hasnt returned. I believe this is what tripped the code (for me): I found the hose at the throttle, for the canister purge to have massivily failed (big hole).

Although, my plugs still scare me. I could get a picture, as they are still kinda white, with hints of brown on the bottom side of the electrode and insulator. I've also noticed some fouling (maybe), seems to be on each plug: one side of the electrode will be black, while the other 3 sides are white/Hint-o-brown. I want to think that may be because I've burned up my valve seals with hot, lean valves; which is probably the first thing to go when these things get that lean... causing oil burn at startup.

I think i had the PRO-M on when i burned up the valve, but since then Ive swapped between the Ford unit and the PRO-M with not so much luck at finding out why im lean.

But the problem is not as bad as before, no 172 code. I did get a CM code of 153 (i believe), i do know that the code was for MAF - Low voltage or grounded. So im checking this area at the momment. The code will appear with either the Pro-M or the Ford unit.

This is somethings i did to trouble shoot...

-Looked for leaks between the intake between the MAF and Throttle, aswell as around the manifold.
-Checked the torque on the lower intake
-Bypassed (capped off) the different vaccum-ran systems for testing (cruise control, small A/C line, Fuel pressure regulator, Canister pruge, even the brake-booster for a short amount of time =)
-Fuel pressure regulator: sticks at ~41 PSI from idle to WOT when vaccum is disconnected.

So either i have contaiminated injectors, a bad computer/ground, or maybe an improperly inserted dipstick! I wasnt able to find a complete circut test, i was only able to peice togeather snipits from other manuals and sources.

If you can make sense of what i just wrote, and you have an idea! Post a reply...

 

[Turdle]

Does this engine have a camshaft position sensor?

 

[Creager]

no camshaft sensor, just the oil pump drive.