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lt1 injectors not firing???


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i know i post this before, but i cant seem to figure out what the heck is going on with my lt1. it worked before after i pulled out the motor and now after putting it all back in, some of the injectors are not firing again. 1-3-5-7 and 2 injectors are not firing! what causes the injectors to fire anyways? the distributor or ??? it worked before i pulled the engine out, all the connectors have power comming to them, just tested. all the exhaust runners are cool except for 4-6 and 8 are hot, meaning they are firing. a while back i had the same problem if some of you guys remember, but it was a wiring issue. rewired it and it worked then. whats the chances of all my injector going bad at the same time? i know the pink wire on the injector clip goes to ignition hot, where does the other wire lead to. i would hate to do my harness again but i dont think thats the problem. all the fuses are good. everything seems to be on, just this friggin injector not firing is delaying me from driving the car for the first time. let me know what you guys think!

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Well i think you should start with this

 

Get a 9volt battery and hook it up to one of your injectors that you think is not working. If you hear a little "click" then the injector is fine your wiring is wrong. But if you do not get a "click" then your injector is bad and try another one.

 

This should let you know if your injectors are bad, or your wiring is wrong

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Well i think you should start with this

 

Get a 9volt battery and hook it up to one of your injectors that you think is not working. If you hear a little "click" then the injector is fine your wiring is wrong. But if you do not get a "click" then your injector is bad and try another one.

 

This should let you know if your injectors are bad, or your wiring is wrong

 

Ya but that wont tell you if its clogged...

 

How is your engine running off of 3 cylinders is what I want to know!? The PCM controls the ground side of injectors....

FUEL_INJECTOR_CIRCUIT.gif

 

You should have power on the pink wires with the key on and the pcm will ground out the injector that needs to fire.

 

I would ohm out the ground side of each injector to the pcm and check for shorts to power and ground.

 

 

 

Guy

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ill try the 9volt batery deal thing. believe it or not, but it runs on 3 cylnders...i can rev it a little but i dont want to push it. it sounds like its a carb motor at the moment and it sounds crappy.

 

so what your saying is, the ground wire on the injector clip is what fires the injectors correct? i think i might know whats wrong but ill check over and over. one of my ground the the batery did fell off but if thats the problem, they all would of failed since they all have the same ground if i recall. but i could be wrong. thanks for the replies and 80lt1, do you have a bigger pic of that? i can barely read the typing on that image...

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If you save the picture you should be able to zoom in on it with "paint" or other picture viewing software pretty easy.

 

What I'm saying is that the PCM grounds the injector. There is no ground wire running from the injector to the battery or engine. The PCM is grounding the wire internally. If you grounded the injectors they would run fully open all the time(100% duty cycle). That's not what you want.

 

Now with the PCM and injectors disconnected....Check your wires on the ground side of the injectors from each injector to the PCM with and ohm meter, they should read less than 1 ohm(usually .3-.5 ohms). Also check for shorts to power and ground. What you do there is run one wire of your voltmeter to the + side of the battery and take your other lead and run it to the wire, if you have any significate voltage you have a short to ground. Now to check for a short to power, you run one lead of your voltmeter to the - side of the battery and run the other lead to the wire, if you have any significate voltage you have a short to power. If you have either type of a short you will have to trace out the wire and find the pinched or rubbed through wire.

 

Are you sure its an injector? How old is your OPTI? Did you check for spark at the bad cylinders?

 

Guy

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wow, kenai, i thought i was the only one! i know its probably not an injector since it worked the last time i pulled the motor. ill have to redo the wiring harness and put new wires for ground im sure. i remember when in had the harness appart, ther was rubbed areas on couple areas of the ground wire. same to the red, but i fixed the red ign hot already for the fuel injectors. ill have to check the ground side of the injector. i rather have the problem being the injector since i got another set of injectors on my donor lt1. my wiring is wired to the fuse box under the passenger dash and is a PITA to take it off..sliped through from the heater hose hole on the firewall.

 

i dont think its the opti, but i could be wrong. one of the vacumm wasnt hooked up on the opti, but i hoked it up now and it still doesnt work. could the opti went bad because of this? if so, how are the other ones working? now that you mentioned earlier in the post, ill be checking my ground connections. i bet its the ground. i only have one ground to the engine and its the batery cable that goes to the starter/block...

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ok guys, i feel pretty stupid but i guess im only human, still doesnt explain it but all of them work now except for #3 piston. i dont know how the hell this is, but i test it with the 9v batery, yes all the injectors work. i turn the key to on until the fuel gauge was around 40psi, test each injector and psi goes down meaning they work. after a while of testing, my gas went out and i decited to poor in some good old 91 octane. only 2 gallons. and it fired right up with thunder....all works except for #3 piston. how in the hell is that? if its low in gas, why would only 4-6-and 8 work, add 2 more gallons, 4 more works! ok, now im thinking, maybe if i add one more, # 3 will work? how dumb does that sound! hahahaha...who knows, it might just work. ill fill the damn thing all the way to the top of the tank. im use to 4 cly engines and would never thought that a couple of starts would hogg up that much gas in a 5.7ltr..but yeah, im more happy now and should be driving it soon after i get my jtr radiator mounts. thaks to all who has replied...hopefully you find your problem kenai, or may you might need to add some gas! good luck!!!

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Yes a return style fuel system like that on a LT1 will cause miss fires if you are low on gas. I get misses from the air in the gas line when I take a highway clover leaf style off ramp fast and I have less than a quarter tank left. Gets my blood flowing thinking something's wrong every time.:weird:

 

Piston- check your ground straps from your engine to the body and your battery to the body to engine. Install more straps if necessary. LT1's love ground straps, and like to throw fits without them. Make sure and hook up the opt venting tube up correctly also, one to a ported vacuum source and one to the intake nipple before the throttle. Opti's are notorious for going out. I've had to change mine twice already.

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  • 3 weeks later...

does the negative wire on the injector connect to the other injector ground? or does the black wire lead straight to the pcm? i forgot to check when i did my wiring. i think everything fires except injector #3 is not firing cause the exhaust runner is not at hot. if it just grounds to any dround on the wiring, then ill just ghook it up to the neg injector wire next to it like ho i did the pos pink wire.

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when you look at the pcm pinouts, it shows red connector pin 21 is what controls #3 piston. so i would assume if i hook a wire up straight to the pcm pin and connect it to the injector neg, it should fire up right? #3 always had a problem firing but it did fire up at one point. dont know what happened. my wiring always has little problems like this. hopefully it doesnt screw me over on the road far from home someday..ill wire it straight to the pcm pin and see what happens.

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