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  #11  
Old 03-12-2020, 08:01 PM
Duncan Duncan is offline
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OK, with a needle in A24 and a ground clamped onto the negative terminal of the battery, I was able to get a trace.

The idle trace looks pretty ugly, but the 2000RPM trace looks really, really good, with 4 crosscounts a second, in a regular pattern. I've attached the files I pulled off the MODIS.

So then... the O2 sensor is working really well. In light of that, what else can I look at to figure out why the power and mileage are down, and the exhaust has that "engine warming up and the cat is working hard" smell??
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  #12  
Old 03-13-2020, 10:52 AM
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Hey there, by any chance have you checked the back pressure on the exhaust system before the cat??

To rule out a clogged/faulty cat.. I would remove the pre 02 sensor and make a hollowed out old 02 sensor and attach and vacuum/pressure gauge. And measure the pressure.
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Old 03-13-2020, 08:03 PM
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The only thing I'm aware of that can make the exhaust smell "sweet" is the very occasional fuel additive, but more often and very common is antifreeze. The almost imperceptible odour from fuel additives is virtually undetectable and is usually only evident when the fuel additive container is close by and has just been introduced.
It's old enough for gasketing problems. Antifreeze will destroy O2 sensors and contaminate CATs as well.
See if you can find some case studies on antifreeze screwing up O2 sensors and compare the traces.
If the power and fuel mileage is down, and the exhaust smells sweet, and the O2 sensors look horrible....what is the ROOT CAUSE-?
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Old 03-13-2020, 09:23 PM
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Quote:
Originally Posted by tech25 View Post
Hey there, by any chance have you checked the back pressure on the exhaust system before the cat??

To rule out a clogged/faulty cat.. I would remove the pre 02 sensor and make a hollowed out old 02 sensor and attach and vacuum/pressure gauge. And measure the pressure.
I've been thinking I should indeed be doing this next. I will hollow out a spark plug though, as I have a ton of them available but I don't have a pile of old O2 sensors to destroy! How much pressure should I be seeing? Ideally pretty close to zero, I'd imagine... A clogged cat would indeed cause poor mileage and low power, but I can't think how it would cause the OBDII O2 signal to look so much slower than the signal straight off the sensor itself. The backpressure test is a very good idea, but I'm wondering if there's still a problem with wiring or the PCM since the upstream O2 sensor has such great trace!

I should have time to make that adapter tomorrow.
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Old 03-13-2020, 09:25 PM
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Quote:
Originally Posted by Crusty View Post
The only thing I'm aware of that can make the exhaust smell "sweet" is the very occasional fuel additive, but more often and very common is antifreeze. The almost imperceptible odour from fuel additives is virtually undetectable and is usually only evident when the fuel additive container is close by and has just been introduced.
It's old enough for gasketing problems. Antifreeze will destroy O2 sensors and contaminate CATs as well.
See if you can find some case studies on antifreeze screwing up O2 sensors and compare the traces.
If the power and fuel mileage is down, and the exhaust smells sweet, and the O2 sensors look horrible....what is the ROOT CAUSE-?
Thanks for your ideas Crusty. I am having trouble explaining the smell of the exhaust, but it is NOT the smell of antifreeze in the exhaust, luckily. I'm familiar with this smell. I remember back when I had a carb'ed vehicle and my friend had an early EFI Toyota, his often smelled like this too.
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Old 03-14-2020, 03:59 PM
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Remember, the O2's are the tattletales. The post cat should be cycling the same as the front O2, but just until the cat gets hot and starts working. This has to reach at least 600 degrees-F. Running in the shop it is almost impossible to get the cat working properly even when raising the RPM.
Take it for a normal drive for about 20 minutes.
Monitor both the pre-cat and the post-cat sensors right from cold start.
Also monitor the STFT an the LTFT.
Coolant, TPS & MAP as well.
Near the end of the road test, go to a very quick large throttle opening for a few seconds, then back off the throttle for an extended decel. The O2 responses should be quick, but unless you use a scope it would be hard to see a 100-ms response time, but you might depending on the number of frames per second the scanner is capable of.
The front O2 is the primary fuel control feedback with the post-cat the monitoring sensor for CAT capability. SOME Chryslers will also use the post-cat for fuel control to "try" to protect the cat so careful observation of the O2 sensors activities under varying throttle & load commands can tell you a lot.
As for back pressure, at idle it should be 0 to at most 0.5 psi. At a park or neutral steady 2000 rpm, it shouldn't be anything more than 2.0-psi MAX, and I mean MAX. Most healthy unrestricted cats are only 1.0, 1.25, 1.5 psi at 2000 rpm.

A vehicle that adds 8% fuel is a lot. Yes it's a long way from 25% where it would code but most vehicles will be running just under, or subtracting on the LTFT. That's provided it's not running bilge wash for fuel.
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Old 03-16-2020, 04:40 PM
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Your video shows you looking at scanner PID values. I would use the lab scope to see the raw data. PIDs are the PCMs version of what it is seeing.
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Old 03-16-2020, 05:27 PM
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Your video shows you looking at scanner PID values. I would use the lab scope to see the raw data. PIDs are the PCMs version of what it is seeing.
Thanks for the suggestion Skip, and you're right, I did post the PIDs in the video. Then, after learning it was a good idea to scope the O2 directly, I also posted two pictures of the scope traces later on. Those two photos show that once the engine is off idle, the brand-new O2 sensor is switching rapidly, with 4 crosscounts per second. Whew!

Today I had the time to make an O2-bung adapter to hook up a pressure gauge. The pressure is well below 1psi at idle, and it doesn't rise as I rev the engine to 2,000RPM or so. Now, I tested the gauge by blowing into it, and I was able to get about 4psi by blowing as hard as I could, so I'm sure the gauge is registering something! I was only able to get the pressure to rear higher than 1 or 2 by blipping the throttle, but it only shot up and then fell immediately down.

I also took the gauge off the pressure line and ran the engine. I was easily able to hold the pressure in the line with my thumb.

So, I have to conclude the cat is fine, and the O2 sensor is also fine. Hmmmm... is there anything else that seems wrong with the video I took of the PIDs? For instance, is it normal for the O2 trace to be so different in the PIDs than it is in the Scope Trace, or does the difference between the two readings suggest another problem somewhere? I'm ready to do more testing! I'n learning a lot, even though I haven't solved the problem yet.
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  #19  
Old 03-17-2020, 11:38 AM
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Hello, I will try to explain very simply about the difference between your raw 02 reading, and your scan tool.

when you are reading a 02 sensor, that is a analog signal, which means its varies in voltage, unlike digital, which is on/off signal or a square wave.

computers are unable to use analog signals, they only work in digital signals, which get converted into binary, then decimal, and then hexadecimal maybe. Now, when the computer gets a analog signal, it first amplifies the signal, then it goes through a analog to digital converter ( a/d converter ) which turns the sign wave into a square wave.

note. ( this depends on the computer, if its a 8 bit computer, that means there is only 8 spaces ( bits ) available for the 1 and 0s to make a byte, only so many combinations. 8 bit computers have 256 combinations. so imagine your flywheel is a piece of pizza and you slice it into 256 pieces... that is how "big" the computer sees the flywheel by the crank sensor, now 16 bit, 32 bit. obviously more spaces and greater "resolution "

Since its now in digital format. The computer does its calculations, slowly I might add, 56 MHz processor is considered fast.

Finally, your scan tool,which has lowest priority as far as the ECM goes. In my simple picture, is of a CAN signal, 0 bit has priority, so if the Trans, scan tool, and cluster are requesting coolant temp. at the same time. the scan tool will be last because it has last priority.

And also the diagnostic speed is at best 41k kilo byte, as cars from 2007 use CAN which is 500k kilo byte. ( which is somewhat considered real time )

HUGE difference is data speed.

So you can see, seeing the sensor in real time, as apposed to all the stuff the ECM has to do to get it to the scan tool is night and day.
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  #20  
Old 03-26-2020, 06:26 PM
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Have you looked into the minor changes on this engine? Maybe you still have the old core?

It shows 91-95 then 96-01

According to Wikki, Small changes were made to the cylinder head for the 1995 model year. In 1996, the engine block was redesigned for greater strength. The new block had more webbing and a stud girdle for added rigidity of the crankshaft main bearings.

There is also a difference in the RPM and power ratings...

1987-90: 177 hp (132 kW; 179 PS) at 4500 rpm and 224 lb⋅ft (304 N⋅m) at 2500 rpm
1991-95: 190 hp (142 kW; 193 PS) at 4750 rpm and 225 lb⋅ft (305 N⋅m) at 4000 rpm
1996-01: 190 hp (142 kW; 193 PS) at 4600 rpm and 225 lb⋅ft (305 N⋅m) at 3000 rpm
2001-06: 190 hp (142 kW; 193 PS) at 4600 rpm and 235 lb⋅ft (319 N⋅m) at 3200 rpm
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