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2000 jimmy rough idle

M

MA87K5

1/2 ton status
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Apr 6, 2000
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Location
Chicopee, Ma 01020
Code reads p0304 for a #4 missfire. I pulled the #4 plug wire while running and no change in engine idle. I just changed the plugs, wires and cap and rotor. Same rough idle before and after new parts. Now I'm leaning toward a bad injector. The resistance are the same for all the injectors though. What could be the problem? Thanks
 
just because the resistance is good doesnt mean the injector isnt bad, your just checking the electrical part of the injector not the mechanical. those poppit injectors were known to be problems, thats why they came out with a whole new setup to replace em. also check compression. if the compression is good and ur getting spark to that cylinder i would have to say it is the injector
 
Ok new problem. Put a new injector in and put everything back together and it wont start. It sounds like the timing is off but that wasn't touched. Any ideas? Thanks
 
make sure everything is plugged in, go over everything u did, u got a scanner, or a way to see if there's any codes? cranks but dont start?
 
yup cranks but doesn't start. I double checked all connections. Have a scanner but doesn't it have to run for the comp to run its tests to pop a code?
 
no, if it notices something wrong it should trigger a code, running or not, u need to go to the basics now see if it has fuel pressure, spark, and injector pulse, see what it has or doesnt have. also does it smell real bad like fuel like u didnt get something sealed, and did u put the injectors back in there right spots? because it does matter.
 
took it all apart again and cleaned the tips of the injectors. Now it runs but #5 and #4 are not firing. #4 is the injector that I changed. Now wtf? I thought it would be a simple job of just changing the injector, man was I wrong. How do I check for injector pulse? Thanks
 
your gonna need a wiring diagram to check injector pulse, i cant get one till monday, but chances are if 4 of them are firing and two of em arnt, it probably wont be that those two arnt getting a pulse, i would lean towards that those two are bad but its just a gut feeling, and it dont make a lot of sense, unless u switched 4 and 5 and because of that they arnt firing at the needed time, but then again i dont think it would be possible to switch those two
 
$266.60 with shipping and bracket at Gmpartsdirect.com. Parts store wants $370 with no bracket. Saving over $100 and being a gm part I think is a good deal. I do think that she is going to keep the jimmy for a while.
 
well u have one power wire pink i think, then u should have 6 wires coming from the computer to trigger em
 
I checked volts at the injector connector. Put the meter at both terminals with key on and to start and got 12 volts also did same to one term and to positive on the bat as well as neg on the bat, did that to both terms. Compared that to a injector that I know was good and came with the same readings. I came to a conclusion that #4 injector and #5 injector are bad. Must of got a bad injector from the parts store. Thanks for your help.
 
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Update
Put the mfi conversion in and #4 is still not firing. How do I check for injector pulse? If no pulse, what would cause it. Thank you very much.
 
are u sure u have spark? did u check the compression on that cylinder, personally i would pull the plug make sure u didnt crack it putting it in, and if u have any doubts replace it cause there not that expensive
 
Have spark but the plug still looks new. Like it just came out of the box. I replaced them along with the wires when I started this project. looks like no fuel is getting to the cylinder.
 
wow u have a really weird case on your hands, i've never heard of a computer not firing a single injector, I think im going to end up at work tomorrow, if i do ill look up a wiring diagram for u, so u can test.
 
I took it apart again and took #4 injector out of the intake and turned the motor over (with fuel lines connected of course) and watched the spray or lack of. More like mouse sneeze instead of a dog sneeze. I did the same to a different injector and got the dog sneeze. How can that be. I thought 12v was 12v. Maybe the injector is getting 6v or so. Or the plug is loose just on #4. I'm pretty much shooting at straws here. Thank you for the diagram offer. I thank you. Hopefully that will help me out. I even totally unplugged the pcm and that didn't change anything. Watch it turn out to be something stupid and easy. I even sprayed carb cleaner down the #4 injector hole thinking it was blocked, not blocked.
 
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