Isuzu SUV Forum banner
1 - 20 of 27 Posts

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #1 ·
1995 Trooper 4x4 with 2000 3.5L drivetrain 5 speed manual

I am having an issue with my fuel trims. So I just replaced the B1S1 O2 sensor as there was a code, and verified it not working on the live data. But I noticed my LTFT Bank 1 was at around Negative 12 at idle and bank 2 was around Negative14 at idle, and did not change much with the rpm increase. The STFT trims were around Negative 3 and Negative 0.8 fluctuating a bit. I Thought The O2 sensor would help but it did not. It also does not seem to idle correctly, with a hiccup every little bit once it's warmed up and the idle drops. I also noticed the trooper jerking every so often while driving as well. I've checked the spark plugs and they all looked good, re gapped them as well. Tested the injectors to see if there is one pulsing wrong. (did not remove them though). Checked the TP sensor for a dead spot throughout its travel. There are no other codes set. It's manual so it only has one cat. Does anyone have any thoughts as to what to check?
 

·
Registered
Joined
·
12,347 Posts
Negative LTFT indicates the PCM is reducing fuel, suggesting the air fuel ratio way too "rich". You may have leaky injectors. I think Negative 14 is almost the maximum amount of correction available on a manual transmission setup.
 
  • Like
Reactions: scalla

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #3 ·
Negative LTFT indicates the PCM is reducing fuel, suggesting the air fuel ratio way too "rich". You may have leaky injectors. I think Negative 14 is almost the maximum amount of correction available on a manual transmission setup.
Thanks buster, yeah the negative is quite a bit, you really think it could be leaky injectors if both banks are almost the same? I mean for them all to be bad? I noticed that when I raised the rpm around 2000 the numbers got substantially better at around negative 9 and negative 7. I was thinking maybe a bad cat, but then the O2 sensors are showing ok after the cat... MAF Is reading between 5-7 g/s which is in range at idle.
 

·
Registered
Joined
·
868 Posts
I do know the 3.2s are known for having IAC issues, especially causing high and/or rough idle. Maybe pull it out and lubricate it to make sure it moves in and out smoothly.
 

·
Registered
Joined
·
12,347 Posts
I do know the 3.2s are known for having IAC issues, especially causing high and/or rough idle. Maybe pull it out and lubricate it to make sure it moves in and out smoothly.
The vehicle apparently has a 2000 3.5L engine installed which does not have an IAC
 

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #6 · (Edited)
The vehicle apparently has a 2000 3.5L engine installed which does not have an IAC
Correct. Today I took it for a drive and hooked up my scanner and recorded the live data.

I noticed it said CL for most the trip but it did show OL driver a couple of times. Still, no codes set tho.

I also noticed this failed test in mode 6 data (pictures attached). Does anyone know how find out what component this is?

It also did not jerk once during the trip...
Communication Device Gadget Finger Font Gas

Communication Device Gadget Telephony Output device Font
 

·
Registered
Joined
·
868 Posts
The vehicle apparently has a 2000 3.5L engine installed which does not have an IAC
My bad, I auto-piloted the 3.5 to be 3.2.
 

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #9 ·
I am reasonably sure Mode 6 Test ID $07 is Exhaust Gas Recirculation (EGR) Readiness Monitor

View attachment 124590
Thank you that is helping me a little better, where did you find the mode 6 data? I can't find it anywhere online, must be a secret 😂. I also got a new code today :
Light Gadget Output device Material property Communication Device

From my understanding is this sensor is only used when starting the car and does not it while running? I was able to get the connector off and test the wiring and it all checked out ok. I can't figure out a way to get the One 10mm bolt out without taking the intake off😳 am I overthinking it or is there a better way to get to it since it's on the back driver's side head on the inside. Thanks again 👍🏻
 

·
Registered
Joined
·
12,347 Posts
The Camshaft Position Sensor (CPS) is used to determine the first cylinder to fire on startup, the engine will run OK without a functional CPS it just takes a few more rotations the get running on startup.
Btw, the CPS function is built into the Ion Sensing Ignition module. Does your engine have Ion Sensing Ignition and an electrically controlled ("Drive by Wire") throttle valve? These were installed starting in 2000?
 
  • Like
Reactions: stahle

·
Registered
Joined
·
35 Posts
...where did you find the mode 6 data? I can't find it anywhere online, must be a secret 😂.
Here is the full GM mode $06 document. The "J1850/Class2" (yellow band) document is the one your vehicle uses. The other document is the GM mode $06 for CAN vehicles, which are newer.
 

Attachments

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #13 ·
The Camshaft Position Sensor (CPS) is used to determine the first cylinder to fire on startup, the engine will run OK without a functional CPS it just takes a few more rotations the get running on startup.
Btw, the CPS function is built into the Ion Sensing Ignition module. Does your engine have Ion Sensing Ignition and an electrically controlled ("Drive by Wire") throttle valve? These were installed starting in 2000?
that's what I figured, no mine still has the cable-driven Throttle
 

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #14 ·
Here is the full GM mode $06 document. The "J1850/Class2" (yellow band) document is the one your vehicle uses. The other document is the GM mode $06 for CAN vehicles, which are newer.
Thank you so much for this!
ok so I have a Failure in Test id $07 and then I am assuming the Id is $0D but in the chart, the limit shows -45 to + 45. Mine is showing a max limit of 2048 and my test value was 63270. something does not make sense to me. maybe I am reading it wrong?
Communication Device Gadget Portable communications device Font Telephony
 

·
Registered
Joined
·
35 Posts
You mentioned previously that your MAF reading is 5-7 g/s, which is about what it should be at idle (2.85-6.65 g/s), so that sounds pretty good for the $07 $0D 1-Low test. Note that there are two $07 $0D tests. The 1-Low test mentions MAF reading as 0-255 gm/cyl, which you stated your MAF appears to show as 5-7 g/s, so that $07 $0D test should be good.

The other test is $07 $0D 0-High, which references a decimal range of -45.000 to 44.99863 kPa, which is units of kilopascals, which is a unit of pressure. 45 kPa is about 13.2885 inches of Mercury, or 6.5267 PSI. The MAP sensor measures the manifold pressure in units of kPa. I don't know the specific criteria for running that test but the MAP sensor is the only sensor (other than the fuel tank vapor pressure sensor) that measures PRESSURE.

While there are many things that can contribute to low or high manifold vacuum, including EGR flow, it is also a possibility that the MAP sensor is failing or giving an incorrect reading. You should be able to see what the scan tool is showing in live data for the MAP voltage and kPa. Check the live data and see if it is reading roughly in the 23-40 kilopascal range, or .65-1.32 volts at idle.

Your MAF should be reading in the 2.85-6.65 g/s area. A reading of 7 g/s would be reading too high at idle.

The attached file is an extract from the 6VE1 (3.5 L) 2002 Axiom manual, which gives typical values for all the data at idle and 2500 RPM. You should be looking at MAP, Barometric pressure, MAF, and EGR values. Also, look at the Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) values. Heck, look at EVERY data readout and make sure it is within specs. ;)

Note the test conditions: Engine running, lower radiator hose hot, transmission in park or neutral, closed loop, accessories off, brake not applied and air conditioning off.
 

Attachments

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #16 ·
You mentioned previously that your MAF reading is 5-7 g/s, which is about what it should be at idle (2.85-6.65 g/s), so that sounds pretty good for the $07 $0D 1-Low test. Note that there are two $07 $0D tests. The 1-Low test mentions MAF reading as 0-255 gm/cyl, which you stated your MAF appears to show as 5-7 g/s, so that $07 $0D test should be good.

The other test is $07 $0D 0-High, which references a decimal range of -45.000 to 44.99863 kPa, which is units of kilopascals, which is a unit of pressure. 45 kPa is about 13.2885 inches of Mercury, or 6.5267 PSI. The MAP sensor measures the manifold pressure in units of kPa. I don't know the specific criteria for running that test but the MAP sensor is the only sensor (other than the fuel tank vapor pressure sensor) that measures PRESSURE.

While there are many things that can contribute to low or high manifold vacuum, including EGR flow, it is also a possibility that the MAP sensor is failing or giving an incorrect reading. You should be able to see what the scan tool is showing in live data for the MAP voltage and kPa. Check the live data and see if it is reading roughly in the 23-40 kilopascal range, or .65-1.32 volts at idle.

Your MAF should be reading in the 2.85-6.65 g/s area. A reading of 7 g/s would be reading too high at idle.

The attached file is an extract from the 6VE1 (3.5 L) 2002 Axiom manual, which gives typical values for all the data at idle and 2500 RPM. You should be looking at MAP, Barometric pressure, MAF, and EGR values. Also, look at the Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) values. Heck, look at EVERY data readout and make sure it is within specs. ;)

Note the test conditions: Engine running, lower radiator hose hot, transmission in park or neutral, closed loop, accessories off, brake not applied and air conditioning off.
Thank you again for this.
I don't have all these specs on my limited scanner. But every checks out goo except the TP % It says it should be between 8-12 % but mine is at 0 and does go up when I move the throttle so its working.

Also Spark advance says to be between 15-22 degrees but mine is 14.5 degrees

MAP & MAF both check out within the limits
 

·
Registered
Joined
·
35 Posts
The injector pulse width at idle should be around 2.2 ms like my known good 3.5 is, which is how much time the injector stays open. If the injector pulse width is less than 2.2 ms at idle fully warmed up, and the trims are still negative, that indicates the fuel pressure is too high (or leaking or stuck injectors) or the air mass is too low (or oxygen content too low from inappropriately added EGR) compared to what the MAF is reading, either of which will make for a rich mixture, which will then be detected by the O2 sensors, telling the PCM to reduce fuel, causing the trims to be negative and lower injector pulse width.

If you have a way of measuring the fuel pressure by hooking up a gauge to the fuel rail valve I would check fuel pressure next.

I wouldn't worry too much about the advance being 14.5, but I would question why the TPS is reading 0%. Mine does not read 0%.

I have included a section of the manual for you to test the fuel pressure, EGR, MAP, and the EVAP purge valve.

If it was mine I would verify with the scan tool that the injector pulse width is correct, and then check the fuel pressure according to the attached procedures. It even states in paragraph 17 that high fuel pressure can cause a rich condition. Fuel pressure testers are pretty cheap and are a good tool to have even if it doesn't turn out to be the problem. If you don't have a fuel pressure tester I would advise you to get one. They are a necessary tool to have as a diagnostician. ;)
 

Attachments

·
Registered
Joined
·
35 Posts
Pay attention to this statement in the EGR section:

Circuit Description A properly operation exhaust gas recirculation (EGR) system will directly affect the air/fuel requirements of the engine. Since the exhaust gas introduced into the air/fuel mixture is an inert gas (contains very little or no oxygen), less fuel is required to maintain a correct air/fuel ratio. Introducing exhaust gas into the combustion chamber lowers combustion temperatures and reduces the formation of oxides of nitrogen (NOx) in the exhaust gas. Lower combustion temperatures also prevent detonation. If the EGR pintle were to stay closed, the inert exhaust gas would be replaced with air and the air/fuel mixture would be leaner. The powertrain control module (PCM) would compensate for the lean condition by adding fuel, resulting in higher long term fuel trim values.


It very well could be a dirty or faulty EGR valve that is not closing properly, causing the negative trims because less fuel is required for the (improperly) added exhaust gas. Pulling the EGR valve to check it and clean it will require a new gasket to reinstall it after cleaning. Pick up a new gasket while you're picking up a fuel pressure tester. That is the next thing on the agenda. ;)
 

·
Registered
1995 Trooper 4x4 with 3.5l
Joined
·
19 Posts
Discussion Starter · #19 ·
The injector pulse width at idle should be around 2.2 ms like my known good 3.5 is, which is how much time the injector stays open. If the injector pulse width is less than 2.2 ms at idle fully warmed up, and the trims are still negative, that indicates the fuel pressure is too high (or leaking or stuck injectors) or the air mass is too low (or oxygen content too low from inappropriately added EGR) compared to what the MAF is reading, either of which will make for a rich mixture, which will then be detected by the O2 sensors, telling the PCM to reduce fuel, causing the trims to be negative and lower injector pulse width.

If you have a way of measuring the fuel pressure by hooking up a gauge to the fuel rail valve I would check fuel pressure next.

I wouldn't worry too much about the advance being 14.5, but I would question why the TPS is reading 0%. Mine does not read 0%.

I have included a section of the manual for you to test the fuel pressure, EGR, MAP, and the EVAP purge valve.

If it was mine I would verify with the scan tool that the injector pulse width is correct, and then check the fuel pressure according to the attached procedures. It even states in paragraph 17 that high fuel pressure can cause a rich condition. Fuel pressure testers are pretty cheap and are a good tool to have even if it doesn't turn out to be the problem. If you don't have a fuel pressure tester I would advise you to get one. They are a necessary tool to have as a diagnostician. ;)
thank you for all this info I really appreciate it! I am in Costa Rica right now, so it's a little hard to find parts or tools 🤣
 

·
Registered
Joined
·
35 Posts
thank you for all this info I really appreciate it! I am in Costa Rica right now, so it's a little hard to find parts or tools 🤣
Glad I can help. Unfortunately, knowledge alone won't fix a vehicle, it requires tools and parts, read $$$.

If I had to bet I would bet it was a malfunctioning/dirty EGR valve causing the negative trims. It is very easy to get to and remove. You can try removing it, cleaning it, and reinstalling it without a new gasket, but that might create more of a problem if after reinstalling it the gasket leaks. The EGR gasket is a very common inexpensive part which is interchangeable with many different GM vehicles. If you can acquire one it would be great.
 
1 - 20 of 27 Posts
Top