Jeep 4. 0 - Flashing Engine Light BUT NO MISFIRE?
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Date: 2020-08-05
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Comments and reviews: 10
Rod
I had a similar symptom with a Honda accord. Misfire that got incrementally worse over a years time. Did all the checks, diagnosed it as a bad exhaust valve. Put a head on it (correct diagnosis, the exhaust valve had part of it eroded away in a neat little perfectly round pac man-esque bite. The similarity was when it was done it ran flawlessly. At RPM above 1000 it would flash the money light and set a misfire code, but it was running perfect (as a honda can. For 2 days it drove me nuts, had to walk away and do other payers as i contemplated this bizarre turn of events. The supervising super tech at the company did all the same tests i did, called tech support. No dice. I started exploring EVERY possible data parameter. As i stumbled through every possible menu in the scanner looking for ANYTHING that could help, i find an option buried in the engine side (Snap on scanner) reset engine adaptives. CLICK. THE PROBLEM WAS GONE. I was thinking it was something like that on Eric O's headache. First time i had ever seen that as a menu option.
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I had a similar symptom with a Honda accord. Misfire that got incrementally worse over a years time. Did all the checks, diagnosed it as a bad exhaust valve. Put a head on it (correct diagnosis, the exhaust valve had part of it eroded away in a neat little perfectly round pac man-esque bite. The similarity was when it was done it ran flawlessly. At RPM above 1000 it would flash the money light and set a misfire code, but it was running perfect (as a honda can. For 2 days it drove me nuts, had to walk away and do other payers as i contemplated this bizarre turn of events. The supervising super tech at the company did all the same tests i did, called tech support. No dice. I started exploring EVERY possible data parameter. As i stumbled through every possible menu in the scanner looking for ANYTHING that could help, i find an option buried in the engine side (Snap on scanner) reset engine adaptives. CLICK. THE PROBLEM WAS GONE. I was thinking it was something like that on Eric O's headache. First time i had ever seen that as a menu option.
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GeminiSeven43
Missing Misfire Mystery Solved?
Once again a great video and the fact that you were guessing doesn't worry anyone who know that your guesses are based on a
solid foundation of both knowledge and experience and you can guess on my car any day. By the way I noticed that when you start the video
and show the cam/crank relationship at idle the cam signals are lining up with the fourth crank signal but when you rev up the engine the
cam signal now is lining up on the third crank signal. This might explain why the misfire code are being generated. I notice that after the
crank sensor was replaced the cam signal stays with the fourth crank signal even at higher RPMs. Please check it out and let me know what you think.
Keep up the awesome videos they are teaching me alot and you crack me up with your terminology and the ease and enjoyment that you get when
working on cars. Thanks so much.
reply
Missing Misfire Mystery Solved?
Once again a great video and the fact that you were guessing doesn't worry anyone who know that your guesses are based on a
solid foundation of both knowledge and experience and you can guess on my car any day. By the way I noticed that when you start the video
and show the cam/crank relationship at idle the cam signals are lining up with the fourth crank signal but when you rev up the engine the
cam signal now is lining up on the third crank signal. This might explain why the misfire code are being generated. I notice that after the
crank sensor was replaced the cam signal stays with the fourth crank signal even at higher RPMs. Please check it out and let me know what you think.
Keep up the awesome videos they are teaching me alot and you crack me up with your terminology and the ease and enjoyment that you get when
working on cars. Thanks so much.
reply
JD
Some Engine computers are probably so sensitive, that if they pick up small anomalies, or slightly off-time feedback events from aftermarket electronic parts, that it triggers the check engine light, and limps the car. That happened to me with an 02 Toyota Camry spark plug coil. The original coil was replaced with a China made aftermarket turd coil, because it wasnt firing #2 cylinder, and I was a broke joke back in 2009. It worked well for about 2 months, then the check engine light came on. This time it was a PO302 (Igniter malfunction code, and a limpy car that would shut off if you accelerated too hard on the road. I suspected that the China made coil was culprit, and bought some used original Denso coils from the junk yard, and replaced it. Problem solved. No check engine light, and No more limp.
Never buy aftermarket electronic parts for newer vehicles! Buy original.
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Some Engine computers are probably so sensitive, that if they pick up small anomalies, or slightly off-time feedback events from aftermarket electronic parts, that it triggers the check engine light, and limps the car. That happened to me with an 02 Toyota Camry spark plug coil. The original coil was replaced with a China made aftermarket turd coil, because it wasnt firing #2 cylinder, and I was a broke joke back in 2009. It worked well for about 2 months, then the check engine light came on. This time it was a PO302 (Igniter malfunction code, and a limpy car that would shut off if you accelerated too hard on the road. I suspected that the China made coil was culprit, and bought some used original Denso coils from the junk yard, and replaced it. Problem solved. No check engine light, and No more limp.
Never buy aftermarket electronic parts for newer vehicles! Buy original.
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CentralCoastCamper
Thank you for the fix! I had the same problem with my 1998 Jeep Wrangler 4. 0. Only 3000 miles on a complete reman. longblock, ran like a top but the check engine light came on and I scanned it and the codes showed multiple misfires across all 6 cylinders. It still ran silky smooth. I ran across this thread yesterday and so I removed the newer aftermarket crank sensor and put in a used oem crank sensor I had laying around and it cured it. No more codes. Now I can get this Jeep smog tested tomorrow so I can get it re-registered. One thing I noticed is the magnetic tip on the OEM crank sensor is very strong and can pick up a wrench, but the aftermarket version can bearly pick up a screw. Thank you so much for sharing your technical knowledge, you saved me some money for sure!
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Thank you for the fix! I had the same problem with my 1998 Jeep Wrangler 4. 0. Only 3000 miles on a complete reman. longblock, ran like a top but the check engine light came on and I scanned it and the codes showed multiple misfires across all 6 cylinders. It still ran silky smooth. I ran across this thread yesterday and so I removed the newer aftermarket crank sensor and put in a used oem crank sensor I had laying around and it cured it. No more codes. Now I can get this Jeep smog tested tomorrow so I can get it re-registered. One thing I noticed is the magnetic tip on the OEM crank sensor is very strong and can pick up a wrench, but the aftermarket version can bearly pick up a screw. Thank you so much for sharing your technical knowledge, you saved me some money for sure!
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kenglong
I have a 2001 Wrangler 4. 0L with the same symptoms. CEL comes on at about 3500 rpm under load or sometimes during light deceleration at highway speeds. But, no misfire is felt and engine power feels good. The crank position sensor has been replaced with OEM part several times. Problem still there. Two local shops have used their parts cannons on it. Problem still there. Last shop suggested replacing the ECM. I'm still thinking about it but don't want to pull the trigger until it can be verified. I need to find a good shop in the Albuquerque area that can do a real diagnosis (lab scope, pressure transducers, etc) and verify before hanging parts.
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I have a 2001 Wrangler 4. 0L with the same symptoms. CEL comes on at about 3500 rpm under load or sometimes during light deceleration at highway speeds. But, no misfire is felt and engine power feels good. The crank position sensor has been replaced with OEM part several times. Problem still there. Two local shops have used their parts cannons on it. Problem still there. Last shop suggested replacing the ECM. I'm still thinking about it but don't want to pull the trigger until it can be verified. I need to find a good shop in the Albuquerque area that can do a real diagnosis (lab scope, pressure transducers, etc) and verify before hanging parts.
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Adam
2 micro seconds is a long time when you're going round and round at 3, 000 rpm. Even the slightest delay can make the computer think there's a lag. Remember that electricity travels at 186, 000 miles per second. That means that electricity traveling through that crank signal wire travels 1. 86 miles per microsecond, which is one millionth of a second. Modern computer processors can process 80 billion commands in one second. With speeds that fast, there's plenty of room for error. One microsecond seems like an unimaginable speed to us, but to electricity, it is like waiting for a snail to cross the atlantic ocean.
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2 micro seconds is a long time when you're going round and round at 3, 000 rpm. Even the slightest delay can make the computer think there's a lag. Remember that electricity travels at 186, 000 miles per second. That means that electricity traveling through that crank signal wire travels 1. 86 miles per microsecond, which is one millionth of a second. Modern computer processors can process 80 billion commands in one second. With speeds that fast, there's plenty of room for error. One microsecond seems like an unimaginable speed to us, but to electricity, it is like waiting for a snail to cross the atlantic ocean.
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Alberteezy
Having same issue with a 01 Jeep Wrangler at the shop. At 3K RPM shows ghost misfires. I put an aftermarket sensor and didn't help, guess ill go OEM. I noticed you didn't relearn the misfire counter when installing the new crank sensor. You can see and your scanner it says adaptive learned no. That's why it wasn't showing misfires. I know because when I changed the crank sensor it wasn't misfiring again until it learned the misfire monitor. You fixed it though since the vehicle never returned.
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Having same issue with a 01 Jeep Wrangler at the shop. At 3K RPM shows ghost misfires. I put an aftermarket sensor and didn't help, guess ill go OEM. I noticed you didn't relearn the misfire counter when installing the new crank sensor. You can see and your scanner it says adaptive learned no. That's why it wasn't showing misfires. I know because when I changed the crank sensor it wasn't misfiring again until it learned the misfire monitor. You fixed it though since the vehicle never returned.
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Rod
Thats not a parts cannon, thats not a guess, thats deferring to unofficial tech support with a known good fix for a known problem. When do you hit the bullseye first shot with the parts cannon? never. It is only the parts cannon if you need a second shot or more.
I know several shop owners and technicians in my area, we use each other for unofficial tech support all of the time.
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Thats not a parts cannon, thats not a guess, thats deferring to unofficial tech support with a known good fix for a known problem. When do you hit the bullseye first shot with the parts cannon? never. It is only the parts cannon if you need a second shot or more.
I know several shop owners and technicians in my area, we use each other for unofficial tech support all of the time.
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Dan
2 questions. as a do it myself when possible(the right way) owner.
When the computer was hooked up to it is it possible to disconnect crank sensor and start in a limp mode to test misfire, Is there a limp mode, will it run?
Second, is it faster/easier to remove front drive shaft bolts and slide shaft out of the way to replace sensor?
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2 questions. as a do it myself when possible(the right way) owner.
When the computer was hooked up to it is it possible to disconnect crank sensor and start in a limp mode to test misfire, Is there a limp mode, will it run?
Second, is it faster/easier to remove front drive shaft bolts and slide shaft out of the way to replace sensor?
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Lucky
I'm thinking the extra hole in the bracket = made for more than 1 application = aftermarket. The aftermarket sensor is probably made with a junk magnet so that there's a slight variation in when the voltage is induced as the rotor passes. The ECM then picks up the variation in he crank signal and decides it's due to a misfire
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I'm thinking the extra hole in the bracket = made for more than 1 application = aftermarket. The aftermarket sensor is probably made with a junk magnet so that there's a slight variation in when the voltage is induced as the rotor passes. The ECM then picks up the variation in he crank signal and decides it's due to a misfire
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