Overheat at Idle

So using the scanner this morning on my way into work, I can tell that both banks LTFTs are identical. Both fluctuate quite a bit actually pending on or off the throttle, but for the most part the hover around -10%.

I was able to pull up graphs of the O2 sensor readings as well, and they never really hone in on a set value around 2k RPMs. They fluctuate here as well but more or less on the high end as I would imagine since LTFTs are negative.

Well, on to checking the sensors themselves this weekend....

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I got a chance to test the O2 sensors today.

Observation 1: 3 O2 Sensors Tested OK
B1S1 & B2S1 & B2S2 both tested out OK.
Voltage readings at idle were as expected (between 0.1 and 0.9 volts, cycle roughly every second) - although a bit on the high side.
At 2K rpms it still fluctuate a bit as I originally saw on DashCommand, on the high side.
All grounds tested at a little above 1 ohm, and the heater wire showed full 14 volts.

Observation 2: 1 O2 sensor behaving differently.
I noticed though that B1S2 behaved somewhat differently.
Although I got a voltage reading similar to the other 3, I couldn't get the heater wire to register any power and none of the grounds measured any resitance.
I don't know what effect this has, being it that it's a post mini-cat O2 sensor.
I also don't know how I could have measured any voltage on the sensor reading itself if none of the grounds measured any resitance.

But, my overall belief is that the O2 sensors are OK, especially since replaced within the last year.

Back to the Cooling System Condition
I have noticed within the last few days, that my cooling system is behaving "better".
If I get stuck in traffic like today in 85-90 weather, it will creep up to 220 after a few minutes but as soon as the aux fan comes on it cools back down to 215-216 within another few minutes.
Other than that, it's at 210 while moving slow or fast - no higher.
Although it seems to behave "better", I'm still convinced it's not up to snuff.

I'll keep checking things out...fuel pressure, vacuum leaks, exhaust system & manifold leaks etc.....stuff that I believe may be throwing off the O2 sensor readings as they keep reflecting a rich system with very negative LTFT's.



Question for all:

As I mentioned before, I added roughly a few months ago 6 new reman Bosch 4-pin hole FI's. I don't know what the flow rate is or any of the specs. I bought them on eBay, I believe I had found this seller through someone else's post on NAXJA. Would this for some reason throw my ECU off, thinking it's running rich (because they are 4 versus 1-pin hole, or maybe because flow rate is potentially higher)? Just a thought.
 
Injectors: 4 hole is better than one hole. Reman is questionable, not new.
Bosch brand does not tell us the part number, interchange or lbs per hour(?) of capacity to know if it is the OEM spec for fuel rates.

Observation 2: 1 O2 sensor behaving differently.
I noticed though that B1S2 behaved somewhat differently.
Although I got a voltage reading similar to the other 3, I couldn't get the heater wire to register any power and none of the grounds measured any resitance.
I don't know what effect this has, being it that it's a post mini-cat O2 sensor.
Click to expand...

Not sure what you mean by ground wires not measuring any resistance? Do you mean infinite? Above the test range the meter was set for? Out of range???? Sounds like a bad ground wire.

No power the heater in the sensor is huge problem at idle!!!!!
 
Ecomike said:
Injectors: 4 hole is better than one hole. Reman is questionable, not new.
Bosch brand does not tell us the part number, interchange or lbs per hour(?) of capacity to know if it is the OEM spec for fuel rates.



Not sure what you mean by ground wires not measuring any resistance? Do you mean infinite? Above the test range the meter was set for? Out of range???? Sounds like a bad ground wire.

No power the heater in the sensor is huge problem at idle!!!!!
Click to expand...

Below is a link to the injectors I bought.

http://www.ebay.com/itm/Lifetime-Wa...njector-Set-/281075415650?hash=item4171667a62

Here's the number on the part itself - 0280155823.
According to the webs, it's rated at 19#/hr @ 43.5psi.
And I believe that even at the '01s 49psi rated rail, I don't think this injector type is going to work well....what are your thoughts?
I can't believe I didn't look up these specs before installing, I took the eBay sellers word for it :doh:

And as for the O2 sensor resistance, I do mean infinite. Sorry.
 
Then you have a wiring problem at that O2 sensor that is making it run lean. Focus on it for now!!!!! That ground is bad, that is a big issue, and the missing 12-14 volts to the heater is also an issue. Look for damaged wires first where the wires get close to the exhaust or a moving part. The heater is only for idling!!!!!!

The older jeeps, like mine are 21 lbs at 39 psi. Not sure what yours is. We need help on that question folks!!!
 
I found some equivalency calculator online through Witch Hunter performance.

This would equate my current injectors to a flow rate of 20.2lbs/hr. It's a difference from OEM spec by 2lbs/hr, but I'm not sure if this would have any role in my engine running lean? Or running at a mixture other than stoich?

I'll check the wiring of the B1S2 sensor tonight as well as its ground path. Fingers crossed I find the smoking gun.

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It could be both, but at idle the PCM should use the O2 data to compensate for the smaller injector flow and increase the open time of the injectors. But if the O2 sensor is passing bad data (no power to the heater, no ground), the computer may be using a default data table and or the bad data O2 data and making it run lean. I would think the only issue with the smaller injector might be top end power but not sure.
 
You have injectors that flow ~10% less than the stock ones yet the LTFTs are pulling 10%+ fuel=you have a major o2 sensor malfunction or fuel injector leak or exhaust leak. You should be seeing +10% fuel trims not -10%.


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Last edited:
gradon said:
You have injectors that flow ~10% less than the stock ones yet the LTFTs are pulling 10%+ fuel=you have a major o2 sensor malfunction or fuel injector leak or exhaust leak. You should be seeing +10% fuel trims not -10%.


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Click to expand...
Good point.

An exhaust leak would trick the O2's to think the system is running lean, correct?

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You said your ltfts were both similar, so i don't think it's an exhaust leak or else the ltfts would be positive for adding fuel. Disregard exhaust leak. It's either bad o2 data from both banks, fuel injectors on both banks leaking, bad map sensor, or you actually have 10% larger injectors. Did this problem start after the injector swap?


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Last edited:
That's the unfortunate thing, I honestly don't remember exactly when this started. Although I don't ever remember it happening before the injector swap.

I also had my exhaust system re-done 2 months ago. Cat added back in with stock Walker muffler. I doubt the cat would add that much back pressure, especially if it's parts of the stock setup but it's worth mentioning.

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TheSloMoShow said:
Good point.

An exhaust leak would trick the O2's to think the system is running lean, correct?

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Click to expand...

No, just the opposite.
 
So I traced the grounds and overall wiring path for the B1S2 O2 Sensor. The grounds look OK at G101. I freshened them up anyways.

I then proceeded to follow the wiring to the PCM. Found this.

31cd3922a76dcbbc7f47209cd1b2761e.jpg


It looked like it was rubbing on my intake. So I pulled back the loom and used electrical tape to seal it off. After putting it all back together and resetting the PCM I tested for ground on the B1S2 O2 sensor. Both heater and signal ground tested at ~ 1ohm. So OK.

I then reset the PCM and went for a test drive.

Maybe placebo, but on/Off throttle and overall acceleration felt smoother. I checked LTFT's when I got back, it dropped from 10.5% to 7.0%. I was thinking it might drop more if the ground path was truly fixed for the O2, but maybe it'll take a few cycles for the O2 sensor t get back to norm? Maybe there's still another issue present.

Checked Fuel Rail Pressure tonight too.
46-50psi at idle, 48psi when around 2k rpms. After 30 min, pressure dropped 28lbs. So I think Fuel pressure checks out OK when engine is running, but check valve is bad. I don't think a bad check valve plays any role in engine operating temp so I'm going to ignore that part for now.
 
The fuel pressure drop could be a leaking fuel injector(s)!!!! Instead of the check valve. If one is leaking it might be making the PCM run the other cylinders a little lean. Congrats on finding the wiring issue. Yes you fixed the grounds (right?) but Do you have power to the O2 sensor heater yet?
 
Yep - I neglected to mention that, but B1S2 is functioning properly according to the multimeter (heater and signal OK, both grounds tested OK - varying swing in voltage at idle).

I'm starting to think you may be on to something with the injectors.

I'm going to check all spark plugs tomorrow and run compression/leak down test on all 6 cylinders to determine if I've already blown my head gasket (I should have done this by now), to determine my true fate lol.
Blackstone labs also should have results back to me by end of this week which should solidify whether or not my head is cracked.

Granted these two results/tests give me good feedback, I'll probably look at testing/replacing the injectors next.

I think purchasing reman off eBay may have been a not so good idea.... :nono:
 
With the fuel clips on the injectors and fuel rail so they do get launched, LOL, just cycling the ign switch to run and off, will prime the fuel line and show if any of the injectors, new or used are leaking at the tip just before install :-)

Also I guess a partly plugged injector with a bad spray pattern could leave unburned and unused O2 in the exhaust and confuse an O2 sensor too, or deliver too little fuel making that cyl run lean. A bit more trouble to check the spray pattern, but jumper wires and a 9 volt battery will trigger the injectors.
 
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One of the old timers here once told me that he delayed dealing with a stuck partly open injector on a long trip home, and by the time he got home the cyl wall and piston was trashed. We take injectors for granted way too much. I had a stuck open carburetor needle/seat combo and drained 3 batteries trying to start it, debugging it, before I discover a gallon of gasoline in the oil :(

Lost the oil pump soon after, later the entire engine-bearings.
 
Ecomike said:
With the fuel clips on the injectors and fuel rail so they do get launched, LOL, just cycling the ign switch to run and off, will prime the fuel line and show if any of the injectors, new or used are leaking at the tip just before install :-)
Click to expand...

I see how you would check for a leak at the rail/top o-ring, but how would you check for an injector leaking at the spray tip? This was my assumption as I don't recall seeing any leak by the rail.

I can't think of any way to test for leak there, or for a clog. Maybe just have to try your luck out and replace?

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