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dscableguy

Injector Circuit 51 diagnostics

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I have a '95 pathy SE and i got a 51 trouble code "injector circuit" on my CPU. The truck starts and runs great when it is cold but if i take a trip to the store or somewhere, when i start it, the check engine light comes on and it runs rough. If i let it idle for a couple minutes the check engine light goes off and everything is back to normal. Please give me any information that may help me fix this problem.

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I had the exact same issue a couple of months ago.I mean Exact I took a multimeter and checked the ohm readings on my injectors they were all the same but one the number five cyl. was like 35 when the others were between 11 or 12 had a bad injector or one that was ready to go out that is why I believe it would run rough then go back to normal.I replaced with a good injector thanks to a great NPORA friend.And I have had no more trouble since.Have driven around 5000 miles since IOWA to WISCONSIN and back.The only draw back is to check the injectors on fuel rail under plenum you have to remove the plenum.I got lucky and had bad inj. on passenger side was able to replace with little to no trouble at all.Good luck and hope this helps I went through many hours of tests to arrive at this conclusion from checking coil to dist to fuses to cpu ect,ect,ect.......................

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Thank you, i was assuming a bad injector but this will save me alot of time. Sorry you had to go through the trouble, although you should have some good Karma now!

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OK, now this sounds stupid, how do i check the ohm rating on the injectors? I can't seem to remove the cap of the injector to test for ohms.

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Nevermind, i figured it out.... Now, I have discovered that clearly it is the injector closest to the firewall on the passenger side. What a coincidence? would you mind guiding me through the removal of the injector? I can probably figure out the installation given that it's in the reverse order, huh?

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Sure thing sorry it took so long to get back.I used an mutimeter set for circuit testing thats the one that looks like a horseshoe and it does not matter which probe goes on injector plugs either one will work.Good is around 11 or 12 approx.Now to remove you want to use something like pb blaster or similar to loosen injector up loosen screws and you should be able to wiggle it out replace the o rings use a little gas to coat the end of injector and it should go right back in the reverse order.A mechanic gave me that tip he just takes a cup of fuel and dipps the end of the injector in it and viola it popps in easy. Be careful not to force it and mess up the o-ring it has to seat properly or it will leak gas.Sometimes you have to give it a slight twist.You should be able to feel it if it goes in right you know what I mean.Good luck and happy motoring.

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^Yep, exactly. The keys seem to be to lubricate the O-ring and give it a little twisting to assist in the removal/installation. Don't force it though as you will either tear the o-ring (bad) or twist the top cap of the injector injector without the bottom part moving (bad).

 

http://www.nissanpathfinders.net/forum/topic/29686-change-fuel-injector/page__p__563495__hl__+injector%20+removal#entry563495

 

 

 

B

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  • Do you have to release the fuel pressure first ? ... Im thinking pull fuel pump fuse start til stalls, then turn over once or twice to release residual pressure ? .. or is that not necessary ? ... thank you !

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I pulled the fuse on mine cranked it to relive the pressure. Number 5 was bad on my 95 Pathfinder , went to the junk yard paid $5.00 for a used one. When cold my Pathfinder worked fine but drive some were shut it off and get back in would run rough with the check engine light for a few minutes.Checked it with a ohm meter when cold was fine but when it was hot it went past 1m ohms .

Edited by Jimmie

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I had the same problem with 1 injector on our R50. It only acted up when shut off hot and restarted before it cooled. Tested fine cold, failed hot.

 

  • Do you have to release the fuel pressure first ? ... Im thinking pull fuel pump fuse start til stalls, then turn over once or twice to release residual pressure ? .. or is that not necessary ? ... thank you !

Yes, that is the best way to do it AFAIC. You will still have some fuel dump into the cylinder so you might want to blow it clear by cranking it (only if it is safe, obviously).

You are welcome.

 

B

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I understand that there are different colored injectors. Can anyone tell me if there is a "Gray" colored injector? That is what my truck has.

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Yes, there are several color coded injectors and I believe silver is one of them but I'm not sure about grey (seems too close). Could it be a dirty silver? :D

 

Can you post a picture?

 

B

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YES to all the above.And injectors have a small dot of paint on them Blue and Black and Grey or silver if you prefer that anology.They say you have to use the same color and not to mismatch.Or it won't work right.that's just what I hear don't shoot the messenger. On my 95 they were blue replaced with a blue one and no problem's since.

Edited by AzZo

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Thanks to all that helped me on this one... I went to the JY the other day and got a fuel rail with 3 injectors on it. Took one out and replace my Injector #5 with a little elbow grease. Seems to be working great... The only thing i didn't replace the O-ring but doesn't seem to affect anything. Thanks again for the help....

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Ok, forgive my ignorance here. I can't seem to locate the connector where the injector resistance can be tested. I am looking at a 94 Path.

 

Does anyone have a picture of it. Can't believe I'm even posting this......<smh> tired.......zzzzzzzz.

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[url=https://flic.kr/p/BT4ivD][img=https://farm1.staticflickr.com/616/23550272419_2d0efc5591_k.jpg][/url][url=https://flic.kr/p/BT4ivD]photo 2[/url] by [url=https://www.flickr.com/photos/128745873@N07/]Jim Dandy[/url], on Flickr

 

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Here's a few pics of the connectors. Can someone kindly point me in the right direction ?

 

(Had to re-figure how to post from Flickr. Moderator kindly remove previous post.)

 

23550272419_06bab886b0_z.jpg

 

23289912234_5844063172_z.jpg

 

23892032356_7887f76ed6_z.jpg

Edited by JackStraw1

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IIRC it's one of the plugs mounted on the passenger's side valve cover. The EF&EC section of the FSM should show the plug pinout for testing.

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In your second pic, it's one of the 2 on the right. The Service manual will tell you which.

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Thanks guys, I figured it out. it's amazing what a good night's sleep can do. Here's a few labelled pics to help anyone else who is looking to test the resistance of fuel injectors and doesn't want to spend an inordinate amount of time trolling through the wiring diagrams and FSM.

 

This one shows the more common functions of the engine control harness sub connectors and more importantly the numeric labeling of each.

23968462945_57d79b86e1_z.jpg

 

 

This one was pirated from PattiMax and I added the labels showing which connection was which (this was what i was having trouble with when I first looked at it) The green arrows show where to test resistance. Ohms should be between 10 -14 for normal function. Hope this helps someone get it done a little faster :)

 

23860183412_490c4c5aae_z.jpg

 

  • Like 3

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thanks to this I was able to find out which injectors were misbehaving on mine without tearing the intake off!

 

1 = 10 ohms

2 = 14 ohms

3 = 36 ohms (uh oh!)

4 = 12 ohms

5 = 56 ohms (yikes!)

6 = OL/open circuit (probably stuck shut! THAT explains the sputtering!)

 

Luckily there's an injector cleaning shop near me. I talked to him to see if an injector is high resistance whether or not a cleaning will help. He said he can usually clean 'em up good enough and/or unstick the element and get them back into spec again, very few times he's encountered an injector that HAD to be replaced. Good to know for when I tear in and take the plenum off...

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I have a diagnostic code that shows 51.  Check Engine light was on all the time. Cable was lose to ECM. Tightened cable. Cleared codes. Engine light went off and stayed off but only for one short trip. Next day check engine light only comes on during acceleration. Diagnostic code shows 51 again. OHM readings are 11.4 / 11.3 / 14.0 / 10.9 / 14.6 / 14.9. Any ideas? Would appreciate any help.

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Sounds to me like having the harness plug loose at the ECM might have "stretched" the female wire terminals in the connector making a poor connection. One of the tests we did at the dealership in these situations was to do a pin fit test. That required a special tool that is not common. However, you can do a visual examination and see if one or more are spread larger than the others. You are going to want to look at the 6 wires that run from the injectors to the ECU. If they are ok, then you might want to try and do a continuity test on those 6 wires between the ECU connector and injector harness connector where you did your resistance tests to see if a wire is damaged. 

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