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Found cause of misfire, now what???

G

getsum111

Yes I am a Pirate, 200 years too late.
Joined
Apr 5, 2005
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4,188
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Pillaging in Freedom, PA.
Hello again.:laugh: I finally tracked down the misfire problem I have been having since before Thanksgiving. I am not getting a signal for fuel injector #6. My buddy brought over a test kit that uses bulbs that you plug into the fuel injector harness to see if they are getting a signal to open. It did not light up for cyl. #6. What would cause this? I opened the harness next to the fuel rail, and I don't see any obvious breaks. Can someone help me narrow down what I should check next? What would cause the signal to the injector to stop? Thanks again for any and all suggestions.
 
getsum111 said:
.... My buddy brought over a test kit that uses bulbs that you plug into the fuel injector harness to see if they are getting a signal to open. It did not light up for cyl. #6. What would cause this? ....
Click to expand...
Wiring harness issues? Probe the wire for continuity.
 
I really don't want to sound dumb, but how should I do that? I do have a digital multimeter, what is the best way to do this? Not too much experience w/ these yet. Thanks.
 
You know which wire and what color it is at the injector end. Turn multimeter to amps. Put one "pin" on this end and probe the other end of the wire (as far as you can go), and see if there is continuity. If there isn't, keep on "halving" the length until you get continuity. That will tell you where the break is.
 
Now I feel really dumb. By "probe" should I push the red probe INTO the wire while the black touches the end? And should the key be on, as I have the UIM off and the Bank 2 fuel wire harness off the front 3 injectors. Thanks for your understanding.:cool:
 
No, the key is irrelevant, as you aren't testing VOLTAGE.. you are testing whether or not the wire physically stays "whole" all the way down the length of the harness.

If your multimeter has a little "split" on the tip, you can simply place that "split" around the wire and then touch the red probe to the tip(exposed end) of the wire. the "split" is a device that measures current without having to physically mash the probe through the sheathing and in to the wire (which COULD not make good contact, etc) If you DON'T have that option, then you would have to either use a straight edge and peel away a tiny tiny section of sheathing and test, then shrink wrap, etc. or mash the probe through the sheathing as you suspected.
 
For the 1998/1999 SVT, wiring color for Injector 6 is Red/Black(?) and it goes to Pin 94 at the PCM Terminal End of the wiring harness connector. Doing this first should "confirm"(?) if it is the wire or the PCM ($$$$).
 
Pin 94?

Pin 94?

Wow. That's all I can say. I have cofused myself to a new degree.:laugh: I found the connection that is at the bank 1 valve cover. The wire is good to that point. I do not know where the PCM terminal end of the wiring harness is, or where pin 94 is. The Haynes manual's wiring diagrams did little good. Is it where the wires connect to the PCM underneath the power steering resevior, or is it underneath the coil pack? :crazy: I have been in the cold toooo long today w/ too little beer.:laugh: Tony sent you a PM, but decided to post here as well. Thanks all.
 
"I do not know where the PCM terminal end of the wiring harness is.....Is it where the wires connect to the PCM underneath the power steering resevior,"

Correct. The connector below the PS reservoir.

"...where pin 94 is."
Look at the wiring harness connector end. It is 104 pins. Top row left is Pin 1. Top row Right is Pin 26.
Bottom row left is Pin 79. Bottom row right is Pin 104.
From bottom right, count back (towards left) from 104 to 94. That is PIN 94. You should be able to confirm the wire color looking at the wiring side.

1 2 3......24 25 26
o o o......o...o...o
o o o......o...o...o
o o o......o...o...o
o o o......o...o...o
79 80 81......102.103.104



"The Haynes manual's wiring diagrams did little good."
Haynes manual wiring schematic is for 1995. OBDI. Electrical and engine wiring are good through 1997, I think.
 
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Bad PCM?

Bad PCM?

Oh, no! I tested teh wire for the injector. It is good all the way back to the PCM. What does this mean, is the PCM bad?:cry: Is there something else that could cause this? Why would it only affect Cyl. #6 and not the others. Help, please!
 
If you have continuity all the way back to the computer...and both wires for the injector ohm out then yes it is an injector driver inside the computer. Meaning..new ecu for you or you drive a 5 cylinder :)
 
Thanks, Judge. I only tested the red/black wire @ pin 94 per above. Does anyone know which pin the other injector wire (green/brown stripe) is so I can test it. Do I even want to know what a new PCM cost?:nonono:
 
Actually, if you can get a hold of a real time scanner, that is what you should do. With the PIDs or freeze frames, it tells more. In the meantime, you may want to switch out injector 6 with 5. Scan for codes. Reset PCM. And then switch out injector 3 with 2. To ensure it is not a injector 6 or injector 2 issue.

I would hate for you to purchase a new PCM and then find out it is a wiring or injector issue.

Incidentally, I take it you have tested the Spark plugs, SP wires and ignition coil and they are good? If you haven't, do that too. SP gap 0.054 inch.

Edit. Autozone link
http://www.autozone.com/servlet/UiB..._us/0900823d/80/1b/c4/02/0900823d801bc402.jsp
 
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Yes, it has new plugs, and wires. I tested teh coil, it was at the lower end of acceptable. We used a noid light to test the injector harness, but it didn't light for #6. The injectors resistance checks ok, it just isn't getting a signal to fire. What could cause this, besides a bad PCM.

Is a dealer the place to go for a real-time scan? Or independant? General consensus is....? THanks again.
 
getsum111 said:
...Is a dealer the place to go for a real-time scan? Or independant? General consensus is....? THanks again.
Click to expand...
Cost is one hour diagnosis (maybe $100). For a few beers (if you can get a CEGer near you) or a Actron C9145 (about $200), you can do all the real time scans you want.
 
I think you are hearing "driver" and thinking that it means the same thing that it does in the computer world. a file, or code that tells the hardware what to do.

In this case, it is referring to a transistor, or driver.

I don't have anything on hand to look at but I think it is an open collector driver in this instance (IIRC) and the statements above are referencing the fact that this particular component on the PCM could havce burnt out.

IF that is the case, then no.. a reflash is not going to fix the problem.
 
I guess you COULD run a temp wire from the PCM to the injector to completely remove the wiring from question.
 
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