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1,2 and 4 running rich

H

HappyDog

NAXJA Forum User
Location
CA
I had dragged another thread off-topic by asking about my problem of several cylinders running rich. Here's the history so far, and the following posts are new information.

Thanks to everyone for their help.

cruiser54 said:
Which spark plugs are you using?
Click to expand...
Champion
Talyn said:
Replace them with NGK. 00+ engine really like the NGKs better.
Click to expand...
I didn't know whether the engine controller looked at the Bank 1 O2 to adjust the fuel/air ratio of cylinders 1-3 and the Bank 2 O2 sensor for cylinders 4-6, or just lumped them together to adjust the ratio for the whole engine.

Talyn said:
On teh cali emission package with 4 O2 sensors they trim the banks based on the O2 sensors for each bank.
Click to expand...

After I wrote the question I also thought I should check the coil pack because the rich-running cylinders are adjacent to one another.

Talyn said:
thats not how the coil pack works. The coils aren't firing plugs next to each other. One coil fires 1 & 6 at the same time, 2&5 at the same time and 3&4 at the same time. If they are adjacent to each other its probably the O2 sensor or something fuel related.
Click to expand...
 
How "rich"?

Are you getting any codes?

Driveability issues?
 
Note: I have a 2001 Cherokee with the 4.0L I6 and automatic transmission. It has two precat O2 sensors, and a coil rail instead of distributor, coil, and individual spark plug wires. It has 108K miles on it, and the only things the previous owner did to the engine is change the oil, change the serpentine belt, and replace the battery. I chased down several bad vacuum leaks, one of which was the vacuum reservoir itself which had been punctured.

I have re-checked which cylinders are running rich by looking at the previous set of spark plugs as well as the current set.

The plugs are in order, with #1 on the left. The following two pictures are of the previous set, which have about 8,000 miles on them.

You see the base of the metal shell is quite sooty for plugs 1, 2, and 4.Also the insulators are sooty from the level of the base of the metal shell all the way into the far reaches of these plugs. The soot is dry, not wet, so I don't think it's oil. Plugs 3, 5, and 6 are quite clean.

KlA6b.jpg

2WBOl.jpg


The following set of three pictures is of the current set, which have about 1,300 miles on them. These are hardly sooted up at all, but still the base of the metal shell on plugs 1, 2, and 4 have soot that 3, 5, and 6 do not.

PK4dO.jpg


HAMKn.jpg


nTnSP.jpg


My understanding is that the Bank 1 precat O2 sensor sets the fuel level for cylinders 1, 2, and 3, while the Bank 2 precat O2 sensor sets the fuel level for cylinders 4, 5, and 6.

It is also my understanding that
Coil pack A sparks cylinders 1 and 6
Coil pack B sparks cylinders 2 and 5
Coil pack C sparks cylinders 3 and 4

If it were a coil pack problem, I should see problems with #6 if #1 has a problem, #5 if #2 has a problem, and #3 if #4 has a problem, but I don't.

If it were an O2 sensor problem, I should see a problem with #3 if #1 and #2 have a problem, but I don't.

Ideas?

I'm thinking it's time to replace the O2 sensors anyway -- the way it's running now they should be pretty well sooted up even if they were otherwise OK.

BTW, the tip of the exhaust pipe has a rim of dry soot.

There is no "soot cloud" when the engine is started or accelerated, but the mileage has been dropping for the past year, and is now about 15-16 mpg.
 
I connected my OBD II scanner and took some live readings.

One that surprised me is a MAP reading of 11.8 in Hg at idle (730 rpm).

Isn't that unusually low?
 
In case it helps, here are the measurements reported by my scanner:

Jan 4, 2013

2001 Cherokee 4.0L Auto 108K miles

Code: 
Live Data
DTC_CNT          0
FUELSYS1        CL
FUELSYS2        CL
LOAD_PCT       5.1

ECT (*F)       217
SHRTFT1(%)     1.6
LONGFT1(%)     4.7
SHRTFT2(%)    -1.6

LONGFT2(%)     3.1
MAP(inHg)     11.5
RPM(/min)      702
VSS(mph)         0

SPARKADV(*)      7
IAT(*F)        174
TP(%)         14.5
O2SLOC B1S12-B2S12--

O2B1S1(V)    0.560
SHRTFTB1S1(%)  1.6
O2B1S2(V)    0.300
O2B2S1(V)    0.780

SHRTFTB2S1(%)  0.0
O2B2S2(V)    0.260
OBDSUP       OBDII



Since DTCs Cleared
MIL Status      OFF
Misfire Monitor  OK
Fuel System Mon  OK
Comp. Component  OK

Catalyst Mon    INC
Htd Catalyst    N/A
EVAP System Mon INC
Sec Air System  N/A

A/C Refrig Mon  N/A
Oxygen Sens Mon  OK
Oxygen Sens Htr  OK
EGR System      N/A
 
I suspect a fuel injector problem.

Your long term fuel trims are showing that the PCM is adding fuel to compensate for a lean condition (Long Term Fuel Trim positive numbers). The PCM sees a lean condition and is adding fuel to compensate. Cylinders/injectors 1, 2, and 4 may be the normal injectors but are victims of the rich compensation of cylinders/injectors 3, 5, and 6 running lean. I would suspect that the injectors for 3, 5, and 6 are restricted somehow.

With the engine running at idle, use a stethoscope to listen to each injector operating. You should hear a clicking common to each injector. A lazy injector may be quieter than the others, or mis a beat or two.

You may want to identify which cylinder each injector is plugged into currently and switch out 3, 5, and 6 with 1, 2, and 4 and with clean plugs installed in the 1, 2, and 4 positions, run the engine for awhile and see if the 'sooty' condtions have followed the suspected injector. But before this, measure the resistance of each injector with an Ohmeter (pin to pin in the injector). They should be around 12 Ohms at room temperature. When the you have the injectors out, examine the nozzle ends for contamination.

My two cents worth...:cheers:
 
In my 26 year experience, O2s always tend to bias lean as they get old. In that I mean they report a lean mixture to the PCM causing the fuel trim to go rich.
Change the upstream O2 sensors and it looks to me all will be well again.


Also, a little known factoid is that late model Chrysler PCMs also use downstream O2 for fine tuning the fuel trim. So, changing out the post cat O2 sensors wouldn't be a bad idea either.
 
Sidewinder CC said:
I suspect a fuel injector problem.

Your long term fuel trims are showing that the PCM is adding fuel to compensate for a lean condition (Long Term Fuel Trim positive numbers). The PCM sees a lean condition and is adding fuel to compensate. Cylinders/injectors 1, 2, and 4 may be the normal injectors but are victims of the rich compensation of cylinders/injectors 3, 5, and 6 running lean. I would suspect that the injectors for 3, 5, and 6 are restricted somehow.

With the engine running at idle, use a stethoscope to listen to each injector operating. You should hear a clicking common to each injector. A lazy injector may be quieter than the others, or mis a beat or two.
Click to expand...
I followed your instructions and listened to each injector with a stethoscope, but did not hear any differences among them. Each one clicked without miss and with equal volume, even though the engine was missing. So they appear to be working electrically, but may be partially plugged or otherwise restricted.

Sidewinder CC said:
You may want to identify which cylinder each injector is plugged into currently and switch out 3, 5, and 6 with 1, 2, and 4 and with clean plugs installed in the 1, 2, and 4 positions, run the engine for awhile and see if the 'sooty' condtions have followed the suspected injector. But before this, measure the resistance of each injector with an Ohmeter (pin to pin in the injector). They should be around 12 Ohms at room temperature. When the you have the injectors out, examine the nozzle ends for contamination.
Click to expand...

I did a little Googling and Youtube research, and it seems like it would be faster to get a pressure gauge and connect it to the fuel rail. Then turn on the key but don't start the engine to pressure the rail. Turn off the key then activate one injector and note how quickly the fuel rail pressure drops. Do the same for the other injectors -- if there is a gross blockage the rail will depressurize more slowly. One concern I have is the amount of fuel that would be in the manifold when the engine is started after such a test.

If the blockage is more subtle, I guess the best way of testing the injectors is to measure how much fuel they emit per unit time when wide open. I don't have any good ideas about how to do that quickly and cheaply.

Before I pull the injectors I need to get replacement o-rings, so it will be a few days before I do that.
 
Put your good set of plugs back in.

Move the injectors from the "lean" running cylinders to the "rich" running cylinders.

Drive the vehicle.

Pull plugs and inspect--did the problem follow the injectors? If so, replace those three at a minimum.
 
Digger87xj said:
In my 26 year experience, O2s always tend to bias lean as they get old. In that I mean they report a lean mixture to the PCM causing the fuel trim to go rich.
Click to expand...
I'm sure you're right after seeing how sooty and caked-up some of the O2 sensors on Youtube videos are.
Digger87xj said:
Change the upstream O2 sensors and it looks to me all will be well again.
Click to expand...
I'm not so sure of this -- my worry is that there is something other than the O2 sensors causing 1, 2, and 4 to get more fuel than 3, 5, and 6. And that will quickly soot up the new precat sensors.

If the problem were due to B1S1 reporting more lean than B1S2, then I would expect plug #3 to be as sooty as plugs #1 and #2, but it's not. And I would expect plug #4 to be as clean as plugs #5 and #6, but it's not.

I agree with you it is time to replace the precat O2 sensors, but I want to fix the cause of 1, 2, and 4 running rich before I put in the new O2 sensors.
 
joe_peters said:
Put your good set of plugs back in.

Move the injectors from the "lean" running cylinders to the "rich" running cylinders.

Drive the vehicle.

Pull plugs and inspect--did the problem follow the injectors? If so, replace those three at a minimum.
Click to expand...
Swapping the injectors is quick and easy, but I really don't want to run through about 100 gallons of gas before I have the answer. The "good set" only lightly show the problem and have 1300 miles on them, which corresponds to roughly 90 gallons of gas.

I would like to resolve the problem more quickly than that. If I fix it now, I will burn 23 less gallons of gas in that 1300 miles saving over $80.
 
Sidewinder CC said:
Your long term fuel trims are showing that the PCM is adding fuel to compensate for a lean condition (Long Term Fuel Trim positive numbers). The PCM sees a lean condition and is adding fuel to compensate.
Click to expand...
Thank you for showing me how to interpret the numbers. I purposely noted them because SHRTFT1 and SHRTFT2 were of opposite sign, and I thought that was odd.

I was also puzzled by the MAP reading of 11.5, which I thought was low. So I got out my vacuum gauge and hooked it up and got a reading of 16-17 inHg at idle. How could that be? It became obvious once I discovered that MAP stands for "Manifold Absolute Pressure", not "Manifold Air Pressure" which I took for "vacuum". Duhhhh! As a result, to convert from MAP readings to vacuum gauge readings, I need to use the following formula:
vacuum gauge reading = 30 - MAP
​
because the air pressure here (I'm pretty close to sea level) is 29.97 inHg.

But I did see something new that puzzles me: the vacuum gauge reads 16-17 inHg at idle (roughly 700 rpm), but 20 inHg at 1200 rpm (no load, just sitting in the driveway with the throttle cracked open a bit). I thought the greatest steady-speed vacuum occurred at idle. Is there something wrong, or is it just that my memory is wrong?

TIA
 
HappyDog said:
Thank you for showing me how to interpret the numbers. I purposely noted them because SHRTFT1 and SHRTFT2 were of opposite sign, and I thought that was odd.

I was also puzzled by the MAP reading of 11.5, which I thought was low. So I got out my vacuum gauge and hooked it up and got a reading of 16-17 inHg at idle. How could that be? It became obvious once I discovered that MAP stands for "Manifold Absolute Pressure", not "Manifold Air Pressure" which I took for "vacuum". Duhhhh! As a result, to convert from MAP readings to vacuum gauge readings, I need to use the following formula:
vacuum gauge reading = 30 - MAP
​
because the air pressure here (I'm pretty close to sea level) is 29.97 inHg.

But I did see something new that puzzles me: the vacuum gauge reads 16-17 inHg at idle (roughly 700 rpm), but 20 inHg at 1200 rpm (no load, just sitting in the driveway with the throttle cracked open a bit). I thought the greatest steady-speed vacuum occurred at idle. Is there something wrong, or is it just that my memory is wrong?

TIA
Click to expand...

The vacuum will increase with RPM. What you describe is normal.

Did you measure the resistance of each injector? 12 +/- 1.2 Ohms @68*F.

A quick check of a vacuum leak at those lean cylinders is to dribble some water around the fuel injector where it enters the intake manifold while the engine is idling. Defective injector o-ring will allow air to be sucked (pushed) past the o-ring, causing a lean air/fuel mixture. The water would temporarily seal the leak.
 
HappyDog said:
I did a little Googling and Youtube research, and it seems like it would be faster to get a pressure gauge and connect it to the fuel rail. Then turn on the key but don't start the engine to pressure the rail. Turn off the key then activate one injector and note how quickly the fuel rail pressure drops. Do the same for the other injectors -- if there is a gross blockage the rail will depressurize more slowly. One concern I have is the amount of fuel that would be in the manifold when the engine is started after such a test.

If the blockage is more subtle, I guess the best way of testing the injectors is to measure how much fuel they emit per unit time when wide open. I don't have any good ideas about how to do that quickly and cheaply.

Before I pull the injectors I need to get replacement o-rings, so it will be a few days before I do that.
Click to expand...

Pull the fuel rail and run that test. Don't let all that gas in the engine!!!!

The injectors will open with jumper wires / power from a 9 volt battery.
 
Sidewinder CC said:
A quick check of a vacuum leak at those lean cylinders is to dribble some water around the fuel injector where it enters the intake manifold while the engine is idling. Defective injector o-ring will allow air to be sucked (pushed) past the o-ring, causing a lean air/fuel mixture. The water would temporarily seal the leak.
Click to expand...

Interesting. I would have a hard time believing such a vacuum leak would not be noisy or obvious during combustion? But I guess I have seen stranger things.

That same test should be run at the intake manifold right? Except maybe run with propane gas or carb fluid spray.
 
HappyDog said:
Thank you for showing me how to interpret the numbers. I purposely noted them because SHRTFT1 and SHRTFT2 were of opposite sign, and I thought that was odd.

I was also puzzled by the MAP reading of 11.5, which I thought was low. So I got out my vacuum gauge and hooked it up and got a reading of 16-17 inHg at idle. How could that be? It became obvious once I discovered that MAP stands for "Manifold Absolute Pressure", not "Manifold Air Pressure" which I took for "vacuum". Duhhhh! As a result, to convert from MAP readings to vacuum gauge readings, I need to use the following formula:
vacuum gauge reading = 30 - MAP
​
because the air pressure here (I'm pretty close to sea level) is 29.97 inHg.
Click to expand...

Not many people ever figure that out!!!! :yelclap:
 
Sidewinder CC said:
Did you measure the resistance of each injector? 12 +/- 1.2 Ohms @68*F.
Click to expand...
Yes, they measured 11.4, 11.2, 11.4, 11.3, 11.4, and 11.3

Sidewinder CC said:
A quick check of a vacuum leak at those lean cylinders is to dribble some water around the fuel injector where it enters the intake manifold while the engine is idling. Defective injector o-ring will allow air to be sucked (pushed) past the o-ring, causing a lean air/fuel mixture. The water would temporarily seal the leak.
Click to expand...

I tried that and there was no change. So I guess there's no air leak around the o-rings.

Thanks for the suggestions!
 
I noticed on one of the Youtube videos about O2 sensors that one in good condition will respond quickly enough that at idle speed one can see the effect of each cylinder as it's exhaust valve opens. So I thought this would be a good way of testing whether the richness was due to the injectors or something else. I used my pocket oscilloscope to look at the output of the B1S1 O2 sensor and was amazed that even with this old sensor I could see the effect of the lean cylinder, even though I could not see the rich cylinders individually.

I also used the oscilloscope to look at the injector drive, and each one looked good in the sense that the pulse came down very close to ground for each injector. So I'm pretty confident the injector wiring and PCM grounds are good.

I plan to combine joe_peters's and Sidewinder CC's comments about swapping injectors and determining which cylinders are lean by swapping injectors 3 (lean) and 4(rich), which will put all the rich injectors in bank 1 and the lean injectors in bank 2. I will again view the oscilloscope traces and see if swapping the injectors changed the patterns -- if so, the problem is the injectors.

If the patterns are unchanged after swapping the injectors then something else is amiss, either with the the spark or the cylinder itself. For instance, Dcoy1283 (http://www.naxja.org/forum/showpost.php?p=245752303&postcount=17) found his misfires were due to the valves not closing well and the misfires went away when he replaced the valve springs.

The injector swap test will have to wait until I get replacement o-rings for the injectors. I'll post the results when I have them.
 
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