Sudden loss of power: P0132, P0138, and a bang!

Well, I guess it was my turn


1997 Jeep Wrangler TJ 2.5L – sudden complete loss of power under load + P0132/P0138


Today I was driving on the highway towing a trailer at around 50 mph / 80 km/h. After a fairly long uphill pull, the Jeep gradually started losing power. It got worse and worse until I basically had no power at all and had to pull over, even with the throttle to the floor. At first I actually thought something had happened to the diff.


I let the engine idle for a bit. Then suddenly there were two pretty loud bangs from the rear/exhaust, and I briefly saw the red engine light before shutting it off.


Waited a little and restarted it. It ran slightly rough at first, but quickly cleared up. I then drove another 40 km / 25 miles with completely normal power and no further issues.


OBD showed two confirmed codes:

• P0132 – O2 B1S1 High Voltage
• P0138 – O2 B1S2 High Voltage

I screen-recorded about 11 minutes of live data while driving after the incident. During that time the Jeep ran completely normally.


What I could see:

• Coolant around 79–82°C / 174–180°F
• LTFT mostly around 0 to -1.5%
• STFT moving normally, roughly -6 to +6%
• B1S1 moving from around 0.06 to 1.0V and appearing responsive
• B1S2 generally steadier/higher, around 0.74–0.92V
• MAP around 20 kPa on decel/high vacuum, 30–45 kPa cruising, 55–65 kPa under load and up to around 80 kPa with more throttle
• TPS/MAP appeared to respond normally to engine load
• No obviously abnormal fuel trims on the drive home

My first thought was a collapsed catalytic converter, because when I hit the exhaust with a rubber mallet I can hear what sounds like loose stones/rattling inside.


However, after inspecting it and talking to two mechanics, the catalytic converter appears to have been opened/modded and gutted by a previous owner, so there may not actually be any catalyst material left inside to collapse.


The rattling seems to come from inside the muffler near the catalytic converter inlet, so one theory is a loose/collapsed internal baffle that could move and restrict exhaust flow under high load.


One mechanic also suggested that the engine may have suddenly gone extremely rich under load, for example from an injector temporarily sticking open. According to GPT, that could potentially explain both O2 high-voltage codes, the loss of power and the two bangs in the exhaust.


MAF was also mentioned, but this engine uses MAP, not MAF, so MAF can be ruled out.


Current plan:

• Pull all four spark plugs and compare them for signs of one unusually rich/wet cylinder
• Inspect the muffler more closely for loose internals/restriction
• Possibly test the injectors/fuel pressure
• Monitor MAP/O2/fuel trims if the problem happens again

The engine is currently running completely normally.


Anyone want to take a shot at this one?

macleanflood said:

Might want to do a compression test since you're pulling the plugs.

Your diagnosis seems plausible.

Do they let you do LS swaps in Norway?

-Mac

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Great minds!! I Stopped at the norwegian version of o’reilly’s and picked up a compression test kit on my way home since i am also waiting for a green light to put a SC on the little engine that could. “So why not check health now” was my thinking.

Im planning on the 5.3 from a Tahoe. We can do them, but the paperwork is rough.

Zorba said:

That's because he's a European. Only in America do people think they need gargantuan engines to do anything, much less tow something. With that said, I'm sure it was small/light - but I'd say the same thing about the 6 cyl.

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Ive been pulling restaurant kitchen supplies and food ( couple of hundred kg’s) , no issues. Note: i am 5.13 geared

RMETeeJay said:

With those coolant temperatures, your thermostat is likely stuck open, leading to a rich running condition. 195-220 is the normal range.

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Wrong thermostat put in by last owner. I have a 194f ready to go! :0)

Chris said:

Your suspicions about a collapsed muffler baffle sound plausible. Even with the cat gutted, if the exhaust flow is disrupted by loose parts in the muffler, that could cause significant back pressure, resulting in loss of power. It’s definitely worth a thorough inspection.

The high voltage on both O2 sensors could suggest an overly rich condition, which aligns with the injector issues you mentioned. An injector sticking open could flood the engine, triggering the codes you saw. Checking the spark plugs is a solid plan. If one is wet or shows signs of excessive carbon buildup, that might indicate trouble with that particular cylinder. A compression test sounds like it is in order to me.

Monitoring fuel pressure could also provide insight. If the pressure fluctuates dramatically under load or during idle, it might suggest a failing fuel pump or issue with the regulator, which could lead to erratic behavior in the injectors.

Since your system uses the MAP sensor, just ensure that it’s functioning correctly and that all related vacuum lines are intact. A leak could cause strange readings and rich conditions.

Given that it's running well now, if it happens again, keep a close eye on the live data you recorded, especially under load. Any spikes or unusual behavior in O2 sensor voltages, MAP readings, or fuel trims could give clues.

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Im making a day out of it!
The tj is my son’s project. Im just making it come to life ( he is 7 btw ), he decides on all mods, i just buy, install and mostly enjoy them.

My grand dad and uncle are old volvo/ volvo truck/ bmw mechanics. They are both coming over to help me, help my son do most of the work.

Plan:
Get the tj up to temp ( thats a me job)
Remove fuel pump relay ( also me job)
Let the engine run until it stalls
Disconnect ignition coil ( me again )
Remove all four spark plugs
Photograph/inspect the plugs
Compression test cylinders 1–4 with the throttle fully open.
Put it all back together

Repoet back here. Go from there.

So i checked plugs. Attached for your judgments

Compression was good according to GPT, went trough them twice

1: 175
2: 165/167
3: 170
4 175

Going to scope the muffler next. Anything im missing?

macleanflood said:

Numbers look great. Plugs look great. Good work. Keep digging!

-Mac

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Thanks!
I see the numbers are a bit high compared to the manual, so asked GPT. ( i have the jeep as a project in there with all info on it, works great!) chat came with theories but also saying the same as you about the numbers ( for the future Supercharger project after i get out of this rabbit hole


Gpt

1. The compression gauge may be reading a little high. Inexpensive compression testers can vary quite a bit in accuracy.
2. Carbon buildup in the combustion chambers can reduce chamber volume and increase cranking pressure.
3. The cylinder head may have been resurfaced/milled at some point, which would increase the actual compression ratio compared with stock.
4. The engine may have been rebuilt or modified previously, potentially changing the compression ratio.
5. Test conditions and cranking speed can also affect the readings. A strong battery and faster starter speed can result in higher measured compression.

In todays episode of FAFO, i have a spare manifold laying around, with tb, rail and injectors mounted. Well now i know i have 4 spare injectors that work!

This weeks mission: test the ones mounted in the jeep!

Also while am at it:
Diff fluid change 75w140 ls ( castrol)
Tranny fluid change ( redline mt-90)
Sway bar disconnects
New tie rod and drag link ball joint ends

macleanflood said:

I've never argued about high compression numbers.

Low ones worry me...

View attachment 706746

-Mac

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I did some more testing today to try to narrow down what happened during the original loss-of-power event and also to figure out what is going on with the catalytic converter/downstream O2 sensor. Today I did another approximately 10-minute drive while recording only the PIDs I was most interested in:

• B1S1 voltage
• B1S2 voltage
• STFT
• MAP
• RPM
• coolant temperature

The engine was already fully warm. I recorded approximately one minute at idle first, then normal cruising, acceleration/deceleration where traffic allowed, and finished with a fairly hard uphill pull at higher RPM. The Jeep behaved completely normally throughout the test.

B1S1 (upstream O2):
It was actively switching, roughly between 0.06 V and 0.8–1.0 V, depending on operating conditions. It responded quickly to throttle/load changes and looked like a functioning narrowband upstream sensor.

B1S2 (downstream O2):
This sensor was also quite active rather than remaining relatively steady. It moved through a substantial part of the same voltage range, roughly 0.1–0.8/0.9 V during different portions of the drive.
What caught my attention was that B1S2 often appeared to follow the same general rich/lean movement as B1S1, but more slowly and with some damping/delay.

In other words, B1S2 did not simply sit at a relatively stable voltage behind the converter. There were several periods where changes in B1S1 appeared to be reflected downstream shortly afterward. That is particularly interesting because this 1997 2.5L has one catalytic converter only: B1S1 is before it and B1S2 is after it.


STFT:
Generally remained within approximately -6% to +6%, and for much of the recording the corrections were considerably smaller than that. There was no sustained large positive or negative correction suggesting that the engine was continuously running excessively rich or lean during this test.

MAP:
The readings continued to look plausible for engine load:

• approximately 20 kPa during high-vacuum/deceleration conditions
• approximately 30–45 kPa during normal cruising
• approximately 55–65 kPa under moderate load
• approaching approximately 80 kPa with heavier throttle/load

MAP followed changes in throttle/load normally. I didn’t see anything during the recording that immediately made the MAP sensor look faulty.

Coolant temperature:
Approximately 79–82°C / 174–180°F once warm. The Jeep currently has what appears to be an 80°C/176°F thermostat, rather than the factory-temperature thermostat, which is another thing I’m investigating.

For comparison, the previous 11-minute recording taken after the original failure showed very similar normal-running behaviour:

• LTFT approximately 0 to -1.5%
• STFT approximately -6 to +6%
• B1S1 approximately 0.06–1.0 V
• B1S2 generally around 0.74–0.92 V during much of that recording
• MAP approximately 20–80 kPa, depending on load

So I now have two separate OBD recordings after the incident where the engine behaves normally and the fuel trims/MAP don’t show an obvious ongoing fault.


The unusual part remains the relationship between the two O2 sensors. During today’s more focused recording, the downstream sensor was clearly active and at times appeared to reproduce the upstream rich/lean behaviour, only somewhat damped and delayed as stated above.

If the converter is working properly, I would expect the downstream signal to be considerably more stable than the upstream signal. If the converter is gutted/ineffective, i should expect B1S2 to resemble B1S1 much more closely ?!

Catalytic converter temperature test
Immediately after the drive I also measured the converter with an IR thermometer. After stopping I held the engine at higher RPM for approximately one minute and then let it idle while taking several measurements from both ends.

Engine/inlet side

• 233°C
• 227°C
• 231°C

Average: approximately 230°C / 446°F

Outlet/muffler side:

• 245°C
• 248°C
• 238°C

Average: approximately 244°C / 471°F

So the outlet was only about 14°C / 25°F hotter than the inlet. I had also done an earlier measurement after driving and got essentially no meaningful temperature difference across the converter. So far I am not seeing a large temperature rise across it.

I took some close-up pictures of the downstream B1S2 installation.


It looks suspiciously like the downstream sensor may be installed through an O2 spacer/extender rather than directly into a normal bung. I have not removed it yet, so I don’t want to state that as fact. My next step will be to remove B1S2 and see exactly what is underneath it. If it is a spacer, that could potentially explain something that has been bothering me throughout this diagnosis:


Why hasn’t an apparently gutted/ineffective catalytic converter generated a catalyst-efficiency code?

The original P0132 + P0138 event is still unexplained, though. Both sensors simultaneously reporting high voltage during the actual loss-of-power event still makes me wonder whether the engine genuinely went extremely rich at that moment rather than both O2 sensors independently failing.

There is also still a very obvious “small rocks inside a can” rattle from inside the muffler, close to the catalytic-converter inlet. That keeps the collapsed/loose muffler-baffle theory on the table. A loose internal piece potentially moving under high exhaust flow and temporarily restricting the exhaust would fit the fact that the failure occurred only after a long uphill pull while towing, then disappeared completely afterward.

So my current suspects are roughly:

1. Intermittent exhaust restriction from the potentially internally damaged/rattling muffler
2. Intermittent rich event – injector/fueling/ignition related
3. Something else capable of producing both O2 high-voltage codes during the event
4. Injector. But i am leaning further away from this. But there will be testing

Next step will be to try to b.scope the muffler , test injectors, check «bung» and check wire looms ( injectors and o2’s)

For ya’ll who like to look at numbers, i have uploaded a screen recording of my values from obd, its 12 minutes of 1minute idle at temp, driving steady load, breaking under engine load and finishes up a hill in second close to 3000rpm.
View: %5BURL%5Dhttps://youtu.be/fJHoMWoLLlY?is=O0BWc6q-VoLmCXjE[/URL]

tr21triton said:

You need to change your thermostat to a 195 1st. Man can I bring a lawn chair and 6-pack when you change those o2 sensors out ? Looks like might be fun to watch and might learn a few new curse words . I'd start spraying them now if you plan on changing them next year !

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I have one sitting on the wrench bench ( with burp hole) . Its going in the same day as I flush the heater core ( did a mini flush last year with good results, but still not sauna hot). Looking like i need to start a build thread. I have access to grown up money and last weeks shopping list shows it

New control arms
Sway bar links ( disconnects)
Tie rod ends
Drag link end
Dana 35 gasket
75/140 castrol ls
New catalytic converter

Bring a chair, throw me a beer and i’ll make you a norwegian curse word champion

tr21triton said:

You need to change your thermostat to a 195 1st. Man can I bring a lawn chair and 6-pack when you change those o2 sensors out ? Looks like might be fun to watch and might learn a few new curse words . I'd start spraying them now if you plan on changing them next year !

Click to expand...

Done and done!
Surprised over how straight forward it was.
Bolts out, off with the housing.
Out with old.
Some razor blade action combined with break cleaner.
RTF+ paper gasket
Figured ill make it easier on my self and loosened serpentine
In with the new
Boltes up
Torqued to 20nm ( first 10-15-18-20)
tighten belt
Coolant

Fired up, engine warmed , heater on, hooked up OBD, watched ECT climb. opened at 91 , down to 82 before it went up again. No leaks (thus far)

Waiting for it to cool down so I can check coolant lvl and top off/burp it.

Rabbit hole update – strange Open Loop / Closed Loop behavior after thermostat replacement
I found something interesting during the last two warm-up tests and wanted to add it to the thread

First test – yesterday
The engine was partially warm when started, around 35°C/95°F ECT.
For most of the warm-up the scanner reported:
Open loop due to system failure
The progression looked roughly like this:

• 35°C / 95°F: Open Loop due to system failure – STFT 0%, LTFT 0%
• 53°C / 127°F: still OL system failure – B1S1 ~0.10V, B1S2 ~0.28V
• 70°C / 158°F: still OL system failure – B1S1 ~0.04V, B1S2 ~0.12V
• 84°C / 183°F: still OL system failure – STFT/LTFT still 0%, B1S1 briefly ~1.0V, B1S2 ~0.10V
• At approximately 89°C / 192°F, it suddenly switched to Closed Loop

At 90°C/194°F immediately after entering closed loop:

• STFT: +2.34%
• LTFT: +1.56%
• MAP: 38 kPa
• Idle: 811 rpm
• B1S1: ~0.70V at that instant
• B1S2: ~0.10V

Fuel trims immediately became active once CL was established. The thermostat then opened and ECT dropped back down to approximately 83°C/181°F, but importantly, the PCM remained in Closed Loop. That made me question whether ~89°C was actually some sort of JTEC closed-loop temperature threshold. After doing some reading, that didn’t really make sense. Google says: These engines should normally enter closed loop much earlier once the heated upstream O2 sensor is active and the other enable conditions are satisfied. ( timer included, but the test took 12 minutes)

So this morning I repeated the test properly from a completely cold engine.
A true cold start. Ambient temperature was approximately 10°C/50°F according to the thermometer outside the house.

Before starting, OBD showed approximately:

• ECT: 12°C / 54°F
• IAT: 12°C / 54°F

So both sensors agreed very closely with actual ambient temperature, which makes the ECT reading itself look believable.

This time the PCM initially showed the normal:
Open loop due to insufficient engine temperature.
And then, completely unlike yesterday, it went into Closed Loop very early, while ECT was only around 20–25°C / 68–77°F.

Once it entered CL, the upstream O2 became active and fuel trims started working normally. At around 25°C I saw approximately:

• B1S1: ~0.14V at that particular instant
• STFT: +3.13%
• LTFT: +6.25%
• Fuel System: Closed Loop

It then remained in Closed Loop throughout the rest of the warm-up.

So we now have two very different warm-up events:

Current theory
This pretty much rules out the idea that the JTEC PCM simply requires ~89°C before entering Closed Loop. Today’s true cold start proves that it can enter CL at a very low coolant temperature.

It also makes me less suspicious of a permanently bad upstream O2 sensor/heater than I was after yesterday’s test. If the heater or sensor were simply dead, I wouldn’t expect today’s completely cold engine to enter CL so quickly and then regulate normally. The strange part therefore remains why yesterday’s PCM status specifically said “Open loop due to system failure” all the way from 35°C to ~89°C, rather than normal temperature-related open loop.

A few possibilities I’m considering:

• Some temporary condition following the thermostat/cooling-system work.
• A transient O2/heater/signal problem that was present yesterday but not today.
• Something related to the previously stored P0132 (B1S1 high voltage) and P0138 (B1S2 high voltage) event.
• Some JTEC adaptive/reset/startup behavior, although I don’t believe the PCM actually has to “learn” a new thermostat.
• Possibly an OBD scanner/app interpretation issue, although the fact that STFT remained exactly 0% during the OL-system-failure period and immediately became active in CL suggests the PCM really wasn’t using O2 feedback. ( cheap ebay scanner, but i can also check with hptuner m..4)

I’d be very interested if anyone familiar with the early JTEC PCM knows what specific condition makes Fuel System Status report “Open loop due to system failure,” and why that condition could disappear completely on the next cold start.