Mystery problem still there -took a break, now Im at it again

[1987stangman]

So it's week 3 with this problem and I am running out of ideas with the exception of exploring into the engine.

To refresh your memory. What I have is a 96' GT that out of the blue started to miss. The miss is on all B2 cyls and there is no CK engine light for the miss BUT there is a rich B2 code (P0175). The car is down on power and at times idles like my 87' GT with an H/C/I.

I'm not usually the one to throw parts at a car to find the issue but rather step by step diagnose it BUT I am so stumped on this that I installed new coil packs, plugs, and wires and 2 brand new o2 sensors with NO change. It's like the more you mess with it, the worse it gets.

My wife's brother owns a auto repair shop and I brought the car to him and we went over it again. Smoked it for vac leaks. none. Looking at the computer with a scanner the PCM is trying to pull fuel away and the 02's are reading full rich. Even he can't find a solution or explanation.

Over this weekend I pulled the engine's main harness and omhed out every wire back the to PCM and I also ohmed out the O2's harness for both the front and rear O2's. I also checked compression one again with matching 160 on each cyl on that bank. I guess I could do a leak down, but since the compression numbers look good suggest no valve issues.

I guess at this point the only thing I could try is

1) a new PCM, though it's a pretty expensive item for not being 100% sure it's the problem here, but I don't think so.
2) Lash adjuster issue? Seems like I would heard some valve train noise?
3) Physically pull the front cover and verify cam timing though unless something with the guides failed and it jump a few teeth I can't see it being an issue.
4) Sell it and move on. I have seriously never had such a frustrating issue in all my life working on Ford's and my wife is starting to think I'm nuts.

Any extra help or ideas would be great.

 

[trombonedemon]

Is anything obstructing your Mass Airflow Senor, start there.

 

[wmburns]

Is P0175 the ONLY DTC? Tell us about recent work done to the car. Any wiring changes? O2 sensors switched from side to side?

What kind of air flow rates is the MAF telling the PCM at idle? How many lbs/min? IMO, this is a long shot because a MAF problem should affect both banks.

What are the results of a cylinder leak down test? Regarding your point about the compression test ruling out a valve issue, it's not true. A leaky exhaust valve can give reasonable static compression numbers whereas the dymanic compression stinks. Check out the following thread. The problem turned out to be a leaky exhaust valve:

http://www.stangnet.com/mustang-for...ire-p0302-p0316-compression-test-results.html

IMO, it's a low chance item as there should be other indications such as misfire. But thought it's worth mentioning.

What have you done to rule out a fuel injector problem? Has the fuel injector signal return lines been tested for ground fault? Good work on Ohming out the signal wires.

I could see a case where a single mechanically stuck open injector could cause this. One injector is flooding the exhaust with unburnt fuel. This causes the PCM to pull fuel from the entire bank. Now 3 cylinders are LEAN while one cylinder is RICH.

From previous threads, this motor did have a fuel injector problem on #4. Explain?

What if #4 ran rich and 1-3 ran lean. Now the valves have been burnt as a result of the 1st failure.

Consider an injector cleaning/flow test service such as injectorrx.com. Once cleaned and tested, the injectors are as good as new. Cheaper than new.

IMO, it not reasonable to look at the cam timing issue unless:

• This is a new build.
• adjustable cam timing gear was used.
• IF the timing did slip a tooth or two, it would show up in the compression or with PTV contact.
• It is possible for the cam to be 180 degrees out of phase. It's not reasonable for it to slip 180 degrees
• Any noise from the timing chains?
• any metal bits in the oil filter?

1-I don't think this is a PCM problem. In anycase, it's too soon.

2-Lash adjuster. Seems like a long shot. But 4 bad at the same time? IMO, more likely to be an oil pressure issue affecting bank 2.

3-Don't disconunt what inspecting the oil filter can do for you. Inspecting the timing cover can give important information. Yea it's work but it's still a matter of making your best guess and go from there.

4-Keep the faith. Have a beer. Take your Wife out to dinner. Tell her that you love her and her support is important. Remember, this is susposed to be fun.

 

[1987stangman]

Is P0175 the ONLY DTC? Tell us about recent work done to the car. Any wiring changes? O2 sensors switched from side to side?

What kind of air flow rates is the MAF telling the PCM at idle? How many lbs/min? IMO, this is a long shot because a MAF problem should affect both banks.

What are the results of a cylinder leak down test? Regarding your point about the compression test ruling out a valve issue, it's not true. A leaky exhaust valve can give reasonable static compression numbers whereas the dymanic compression stinks. Check out the following thread. The problem turned out to be a leaky exhaust valve:

http://www.stangnet.com/mustang-for...ire-p0302-p0316-compression-test-results.html

IMO, it's a low chance item as there should be other indications such as misfire. But thought it's worth mentioning.

What have you done to rule out a fuel injector problem? Has the fuel injector signal return lines been tested for ground fault? Good work on Ohming out the signal wires.

I could see a case where a single mechanically stuck open injector could cause this. One injector is flooding the exhaust with unburnt fuel. This causes the PCM to pull fuel from the entire bank. Now 3 cylinders are LEAN while one cylinder is RICH.

From previous threads, this motor did have a fuel injector problem on #4. Explain?

What if #4 ran rich and 1-3 ran lean. Now the valves have been burnt as a result of the 1st failure.

Consider an injector cleaning/flow test service such as injectorrx.com. Once cleaned and tested, the injectors are as good as new. Cheaper than new.

IMO, it not reasonable to look at the cam timing issue unless:

• This is a new build.
• adjustable cam timing gear was used.
• IF the timing did slip a tooth or two, it would show up in the compression or with PTV contact.
• It is possible for the cam to be 180 degrees out of phase. It's not reasonable for it to slip 180 degrees
• Any noise from the timing chains?
• any metal bits in the oil filter?

1-I don't think this is a PCM problem. In anycase, it's too soon.

2-Lash adjuster. Seems like a long shot. But 4 bad at the same time? IMO, more likely to be an oil pressure issue affecting bank 2.

3-Don't disconunt was inspecting the oil filter can do for you. Inspecting the timing cover can give important information. Yea it's work but it's still a matter of making your best guess and go from there.

4-Keep the faith. Have a beer. Take your Wife out to dinner. Tell her that you love her and her support is important. Remember, this is susposed to be fun.

I have not inspected the oil filter. I will do that tonight.

Ok, let me try to answer some of you questions/ideas.

No recent work done to the car other than in Feb when it got the PI engine with 65k miles.
Fuel injectors are rules out because I have tried 2 sets, one new, one used for about 3 months. The affected, or what I thought was the affected injector was on bank 1. Counted my chickens before they hatched i guess.
Mass air meter sensor it self is new. I did check for any obstructions in the filter housing and the stock inlet tube after the MAF.

Right now I'm working with live link for data, not sure what or how to check the air flow rate to the PCM.

I have been reading that thread on his leaky valve issue. I will do a leak down. In my recent experience, I had a 3.0L V6 Ranger with a bad valve seat and was getting 0 comp. That's why I sorta figured that a comp test would seemingly rule that out in this case.


As far as ground to the injectors, would using a noid light be better. If I remember right the injectors return through the PCM? I also ohmed out the side if the injectors through the square (20 pin?) harness on the passenger side of the motor.

There is no unusual noice coming from the motor.

Please emphasize on dynamic vrs static compression results?

 

[wmburns]

Ok, I have had some time to think about this. Sometimes the most important clues are the clues NOT present. Specifically, no misfires.

For all indications, the motor is mechanically sound. But one entire bank is rich. The usual causes have been ruled out. What else remains that can cause an entire bank to run rich?

We feel the O2 sensors are good. We also know the wires are likely good.

If there were an electrical problem with the fuel injectors, one would expect to see misfires as well. There are none.

Sooooo.....What if the PCM has a bad Analog to digital converter for the left hand O2 sensor? Such that the PCM is not seeing any change from the left O2 sensor.

For a test, monitor the front O2 values with an ODB2 scanner. They should be changing at a rapid rate. If the right is changing and the left is not (or stuck in a narrow range), this offers a clue and a possible theory.

Next, disconnect the front left hand O2 sensor and see what happens. The PCM should go to "open loop" and ignore the O2 sensors. If it runs better, this offers another clue.

Live link should be able to monitor most any PID.

Dymanic compression is higher than static compression because gas vapors generate much more than 160 PSI while burning.

 

[1987stangman]

Ok, I have had some time to think about this. Sometimes the most important clues are the clues NOT present. Specifically, no misfires.

For all indications, the motor is mechanically sound. But one entire bank is rich. The usual causes have been ruled out. What else remains that can cause an entire bank to run rich?

We feel the O2 sensors are good. We also know the wires are likely good.

If there were an electrical problem with the fuel injectors, one would expect to see misfires as well. There are none.

Sooooo.....What if the PCM has a bad Analog to digital converter for the left hand O2 sensor? Such that the PCM is not seeing any change from the left O2 sensor.

For a test, monitor the front O2 values with an ODB2 scanner. They should be changing at a rapid rate. If the right is changing and the left is not (or stuck in a narrow range), this offers a clue and a possible theory.

Next, disconnect the front left hand O2 sensor and see what happens. The PCM should go to "open loop" and ignore the O2 sensors. If it runs better, this offers another clue.

Live link should be able to monitor most any PID.

Dymanic compression is higher than static compression because gas vapors generate much more than 160 PSI while burning.

That's the part I don't get about this car. There are random misfires in bank2, which is the idle and drive ability issue is. In live link if you pull up all 8 cyls under the misfire monitor PID's you can see them. STFT is pulling fuel but it's still running rich. There are not enough of them to throw a miss-code but they are def there.

I forgot to mention that I pulled the plugs again last night and they don't really indicate rich, they in fact looked good considering the fact that it's running rich enough to have the stench of it in your clothes.

I'm taking notes on this and will try it out later this evening after work if the rain holds.

Again, thanks for all your help.

 

[wmburns]

What I know about using an ODB2 scanner.

Chapter 1.

Don't pay any attention to Short term fuel trims (STFT). They change too much to be of any real value except to the PCM.

Look instead at how the long term fuel trim (LTFT) is acting. Pay attention to how LTFT change from idle to load. It makes a difference if LTFT remains steady, adds fuel, or subtracts fuel. Look for any imbalance between bank1 and bank2. That's where the clues are.

ALL of the details can be important. Each may be the clue needed to solve the mystery.

Regarding the plugs. Consider that if a cylinder is dead, the plugs will not show signs of running rich.

 

[1987stangman]

What I know about using an ODB2 scanner.

Chapter 1.

Don't pay any attention to Short term fuel trims (STFT). They change too much to be of any real value except to the PCM.

Look instead at how the long term fuel trim (LTFT) is acting. Pay attention to how LTFT change from idle to load. It makes a difference if LTFT remains steady, adds fuel, or subtracts fuel. Look for any imbalance between bank1 and bank2. That's where the clues are.

ALL of the details can be important. Each may be the clue needed to solve the mystery.

Regarding the plugs. Consider that if a cylinder is dead, the plugs will not show signs of running rich.

I will record the LTFT tomorrow. What clues can I get from an imbalance between B2 and B1?

Also, today I bought a noid light set and all the injector plugs are getting a pulse from the PCM. Also, I noticed that the car (at idle) seems normal with no noticable miss or signs of running rich (obvious smell) until it warms up a bit (Open loop vrs closed loop?), clue?

 

[1987stangman]

What I know about using an ODB2 scanner.

Chapter 1.

Don't pay any attention to Short term fuel trims (STFT). They change too much to be of any real value except to the PCM.

Look instead at how the long term fuel trim (LTFT) is acting. Pay attention to how LTFT change from idle to load. It makes a difference if LTFT remains steady, adds fuel, or subtracts fuel. Look for any imbalance between bank1 and bank2. That's where the clues are.

ALL of the details can be important. Each may be the clue needed to solve the mystery.

Regarding the plugs. Consider that if a cylinder is dead, the plugs will not show signs of running rich.

Burns,

I have not added to this thread in a while. Been busy as heck but this week I had partial vacation and I had some time to get working on this Mustang of mine.

First I pulled the lower intake and examined it for any cracks or possible bad gaskets even though the gaskets were new, but you never know. I found nothing of concern so I put it all back together with the same results. I also bought a new handheld scanner that does live data and is easier than hooking up live link. Here is the data I have found.

Since the car had sat with the battery disconnected for a week, I use the scan tool right after I started it up and LTFT's were dead zero until throttle was applied in which case it would give data but come down to zero at idle. I figured this could be the fact that since the PCM had no power for 2 weeks it was still learning??? (is there a need to school me on this?) SO I drove the car for a few miles and checked for codes and no pending or MIL codes have showed up. During the first drive cycle STFT trims on bank 1 looked normal but bank 2 was running around -12.5 to as high as -16.00 at idle and would come down to -8.0 when driving or throttle was applied in park.

It was not until I parked it and came back to check it again that I got the below readings.

At idle:
STFT bank 1 2.8
STFT bank 2 -3.1

LTFT bank 1 4.7
LTFT bank 2 -11.7

At a 2000 RPM hold:
STFT bank 1 2.3
STFT bank 2 -1.6

LTFT bank 1 1.6
LTFT bank 2 -10.9

I drove the car after recording the above info while watching the scan tool and it seemed that STFT trims looked better, tho bank 2 still was running in the neg and LTFT was still -11.0 to -15.00 on bank 2.

Also as you requested I did a leak down on all the cyls. There is no more than 20% leak down in each. The guage I have has a green/yellow/red shades indicating the amount of leakdown along with %'s. I did this on a warm engine with each cyl at TDC on the compression stroke.

I also bought a vac guage. I tested at the manifold. Vac is perfect with no abnormal sweeps in the needle.

Anything come to mind with this data?

EDIT: I took the car on the road today. I dropped 100 bucks on 2 brand new upstream O2'2. Had the scan tool on live data the entire time. STFT on both banks looks good. LTFT on bank 2 stays high at -15.00% and drops a bit at WOT but at idle it's high. I can still smell rich exh. and there is still a lack of power. No codes as of yet with the exception of rear O2 codes (no cats,stock tune). :END OF EDIT

 

[evolucion311]

For the purpose of posterity, WMBurns, I did have a leaky exhaust valve but my issue remains. 1987Stangman remain in the same position. Now the misfire has jumped to the other bank of the engine.

I'm beginning to think this is a PCM issue, possibly for both of us.

 

[1987stangman]

For the purpose of posterity, WMBurns, I did have a leaky exhaust valve but my issue remains. 1987Stangman remain in the same position. Now the misfire has jumped to the other bank of the engine.

I'm beginning to think this is a PCM issue, possibly for both of us.

Evo, sorry I have not had a chance to continue this thread, I spent an unexpected 8 days in the hospital and just got out Monday.

Anyway, I was starting to suspect the PCM as well, however since my issue was a rich code only on bank 2 and everything I had done to find the problem with no results lead me to pull off B2 cam cover to inspect the springs, followers, and lash adjusters. What I found was a piece of timing chain tensioner that had lodged it's self under the cam just behind the cam sprocket on the head and using a shop light I could see the guide laying, or more like jammed on the side of the front cover. I removed the front cover and spent what seemed like forever rotating the engine to get everything to line up again and it looks as though B2 was off by a single tooth. This would explain the rich condition and the fact that B2 had random miss fires that were not enough for the PCM to pick up on. Near as i can tell, there must have been enough slack in the chain to cause it skip and I guess I'm pretty lucky it did not skip any more.

I bought new chains, guides, and tensioners and had it all installed before my little trip to the hospital and at this point my energy level sucks so I have been putting it back together very slow. At this point All I have left is the A/C compressor, power steering pump and the ALT and I will be able to see if this is going to finally be behind me. It would be nice to get back to driving the car again.

 

[1987stangman]

Mystery Problem solved!

Well today I felt good enough to get out in the shop and finish up putting the car back together. Did one last check under the hood and then turned the key and it fired right up and ran. I gave it a bit to warm up and checked for any leaks, etc and then hooked up my scan tool to check live data. It was apparent that just by the sound of the engine it was running perfect. STFT and LTFT on both banks are right where they needs to be and no more rich exhaust.

I took the car for 30 mile run and it's got all it's power back. Thanks to all that have helped me out on this. I hope that in the future someone else can use this info.

I would like to point out that I am probably very lucky that the cam timming did not skip time anymore than the one tooth or the out come could have been worse than it was.