My Engine is Misfiring?

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
When the CEL comes on, the lean running condition would be compensated by the ECM so there is actually no real harm to the engine.
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
CLOROX.BLEACH
  • MEMBER
  • 17 POSTS
Even with all the******** and rough idling its doing? It drive's fine, just that it idling rough and the******** I get when I let of the gas pedal.
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
If you haqve not cleaned the throttle body and IAC, get them cleaned and retest. Sometime poor idling would cause a lean condition.
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
TYNDALL
  • MEMBER
  • 8 POSTS
  • 2000 NISSAN ALTIMA
  • 2.4L
  • 4 CYL
  • FWD
  • MANUAL
  • 115,000 MILES
Engine has number one cylinder misfire, bad shake. Trouble codes showing are po 301, 180, 1464, and a few others. I have narrowed it down to the number one cylinder fuel injector wiring. No click or strong click from injector, but I have switched known good injectors and still missfires. All the injectors show approx, 8.7 ohms of resistance. I have replaced the connector, no luck. The wiring has 12+ volts on the supply side and 12+ volts on the signal side, while the others show minimal voltage on the signal side with key on. Could this be a possible short? Checked all wiring from injector to computer, it looks fine I ran a continuity test on the number one harness wires which show continuity. Could it be shorting from one of the bad sensors? I am stumped. Any ideas? Thanks
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
You need to be using a noid light for this test as to not harm the computer and get an accurate test of whether the signal is arriving or not. If you can confirm this injector is not getting a signal, you might try locating that wire at the PCM and maybe cutting it off to test if you have a good signal coming out of the computer. If you do, then try cutting that wire off at the injector plug and splicing in an overlay wire to see if that resolves the issue. If so, you can clean it up to make it a more permanent repair.
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
TYNDALL
  • MEMBER
  • 8 POSTS
Hi, thanks for the prompt reply. I was thinking of doing something along that line. I actually took that wire off at the harness and did a continuity check at the computer harness, but I believe I was getting a continuity bleep on two wires. What is suppose to be the voltage or signal strength coming off of that computer signal wire terminal? Would any other codes have anything to do with this issue? Such as fuel temperature sensor? Thanks again for your help.
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
The computer sends out a pulsing ground signal to operate the injector. You cannot check continuity because that will not tell you if it is shorted. You are better off to cut it off at both ends before doing any testing. The grounding transistor in the computer are very sensitive so you have to be careful not to send any voltage down that line. This is why your testing needs to be done with a noid light or lab scope.

https://www.2carpros.com/images/external/1Noidlightpair__.jpg
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
TYNDALL
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  • 8 POSTS
Hi, I cutoff the original signal wire at the PCM and at the harness. No difference. Injector is still not firing. I checked the voltage off of the cut wire and it is still producing 12 Volts at the computer terminal and at the harness with the spliced wire. All the other injectors have no real voltage present off the signal wire with the ignition on. I sure hope it is not the PCM. Any thoughts? Thanks again, Mike
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
Could be. You are going to need some in depth diagnostics to get to the bottom of this. I would look over the harness very carefully for any burnt or pinched spots.
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
TYNDALL
  • MEMBER
  • 8 POSTS
I have replaced the connector with others twice already. Is that correct that I should not have any voltage on that signal wire? If I check it directly off the computer terminal and it reads twelve volts would that not mean an internal computer problem?
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
You should only see voltage if it is plugged into the injector and the key is on. You will read the power supply through the injector. That should go away with the injector unplugged.
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Thursday, January 21st, 2021 AT 10:52 AM (Merged)
Tiny
TYNDALL
  • MEMBER
  • 8 POSTS
I am reading twelve volts when the signal wire is not connected to the injector. I am even reading twelve volts off the ECM terminal with the wiring harness disconnected. I guess I have to bite the bullet and take it into the shop.
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 46,594 POSTS
It sounds like you have an injector driver inside the PCM that has one bad, so the computer will need to be replaced.

Please let us know what you find so it will help others.

Best, Ken
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)
Tiny
TYNDALL
  • MEMBER
  • 8 POSTS
Hi guys. Thanks for all your help. I believe I have found the problem. I noticed a little rust at the bottom case of the ECM where it sits on the console floor near the fire wall. I decided to open up the ecu case and found corrosion on the circuit board. One terminal for sure was almost eaten away. I cleaned it up with a soft brush and tried to re-solder it. I will put it all together and try and fire it up tomorrow My fingers are crossed.
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 46,594 POSTS
Great work! Please let us know how it goes.

Best, Ken
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)
Tiny
TYNDALL
  • MEMBER
  • 8 POSTS
Hi Guys, well, bad news I fired it up today with the reworked computer still has the miss and all the codes. I guess the PCM was too far gone. I will try and look for a used one from the wrecker. Will that work as long as the tag matches? I guess I will have to take it to the dealership to have it flashed.
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 46,594 POSTS
Yes, it sounds like the water damage got it. Try for a used one if not it is off to the dealer for a new one.
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)
Tiny
TYNDALL
  • MEMBER
  • 8 POSTS
Thanks for all your help guys, much appreciated. Great site with fast responses awesome! Mike
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 46,594 POSTS
Please use 2CarPros anytime, we are here to help and tell a friend.

Best, Ken
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Thursday, January 21st, 2021 AT 10:53 AM (Merged)

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