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Old 07-09-2009, 11:29 PM   #1
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no injector pulse

i just bought another s10 after my last one was totalled. its a 94 4.3 TBI. the motor was ceased so I swapped another 4.3 tbi into it. the fuel pump didnt work, so I checked relays and everything under the sun. then i pulled the bed and fed power to it and it runs. so with me just feeding the pump power and getting pressure up to the throttle body and cranking the motor over, i have no fuel. so i went and checked the injectors electrically by slipping on a noidlite to see if i get an injector pulse. i have none. i have tried everything i can think of to figure it out. remind you that the fuel pump still doesnt work when hooked up to the truck. i dont know what to do anymore on this thing. after the heartbreak of what happened to my first s10 i was wanting to get this one up and running. but it isnt working out. i have the front already bagged as well as the back. and i haved i have the three link setup i want to change out on the back and all the valves and plumbing and everything. please help, any suggestions will help. i was thinking about trying a new ECM. sorry for the all the writing, I'm kinda drunk, due to this epic fail of a truck. i used to think i was a pretty damn good wrench, being that I've built numbers of cars and motors, and my crown jewel, my Camaro, but this thing has me really doubting my capabilities.
Old 07-10-2009, 10:13 AM   #2
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Re: no injector pulse

wow, that was one hell of a post. anyways skip thru all of the bullshit, and you see that I have no injector pulse. I was hoping someone had an idea as to what it is. I was thinking an ECM because both my fuel pump wiring and the injector wiring is messed up?
Old 07-10-2009, 10:22 AM   #3
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Re: no injector pulse

im assuming you checked the fuel pump relay? that wont give you an injector pulse, but its a start..... injector pulse usually comes from either the pcm, or a cam/crank sensor
Old 07-10-2009, 01:22 PM   #4
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Re: no injector pulse

ok cool thanks. im assuming that since i have a 1994 that what you are calling a PCM, that I really have a ECM? or are they different? where is the crank/cam sensor? i know some came with a timing chain sensor, mine did not and the new(new to me) motor doesn't ethier. is that what your talking about, or is that something different too? i have a sensor that goes into the intake near the water neck housing, is that the cam sensor? and also i had a hard time finding what/where the fuel pump relay is. on a 1994 i know that its different than the rest. they are not in the glovebox, and they are not on the inner fender. i have three relays up in the engine bay on the passenger side just underneath the wiper cowl, but I dont think any of them go to the fuel pump. so i found underneath my dash, forward of the center console, i removed the platic shroud and found a spot for relays. there are 3 spots for some to plug in. one doesnt have any wires tapped into it, like just to hold for a spare relay. and out of the other two, only one relay was in. the relay there has three prongs in a row close together going one way, and then 2 more spun 90 degrees the other way. could that be it? pepboys says its special order for $20. should i get two and plug both in?
Old 07-10-2009, 01:40 PM   #5
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Re: no injector pulse

so now im really leaning to a bad relay or no relay hooked up. i was wondering if there should be another relay right next to the fuel pump relay so I can get one of those too. i have read that the relay gives fuel pump power as well as an injector pulse. god i hope this is the problem. if not, im guessing I should try a new ECM. how much do they go for?
Old 07-10-2009, 04:48 PM   #6
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Re: no injector pulse

this is where the relays are. i bought a new and plugged it in on the left side. the fuel pump still didnt kick on but my fuel gauge now works. its showing 3/4 tank. which is weird cuz when i supply 12v to it, it still pumps. should i replace the other one? another question i have is the other picture of my fuse panel. the two empty slots on the left side dont have fuses. i see in the haynes manual that they special metal casing fuses that go in there. but i dont think they have to do with anything im having trouble with. they are labeled PWR ACCY and PWR WDO. can someone please help? oh and still no injector pulse when i crank the motor over.
Attached Thumbnails
no injector pulse-0710091608.jpg   no injector pulse-0710091628.jpg  

Last edited by 6ftdwn57; 07-10-2009 at 04:50 PM.
Old 07-10-2009, 04:53 PM   #7
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Re: no injector pulse

here is my fuse panel
Old 07-10-2009, 05:14 PM   #8
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Re: no injector pulse

sounds like there might be positive feed issue to the pump and computer,
maybe the injectors also. check fusible links.

also, those "metal cased fuses" are actually circuit breakers,
and typically used for the mentioned power accy/wdo slots.
Old 07-11-2009, 10:51 PM   #9
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Re: no injector pulse

FP relay should be under hood on that animal. If it isnt engaging and no injector pulse make sure your ECM has power to it (check BOTH ECM fuses.)

Also should be a single wire hanging from the firewall that has a female spade connector on it (is fuel pump prime/test connector)

Fuel pump will be activated by either the oil pressure sender (enough cranking will build oil pressure and engage that switch, or ECM will engage FP relay momentairily to prime system.)

Sounds like ECM is not being powered, ECM fuses will be 10A IIRC. Should be 12v on one side of injectors (ign switch on - might test switch), the other side will get grounded by the ECM to fire the injector.

Last edited by lesterl; 07-11-2009 at 10:58 PM.
Old 07-12-2009, 09:20 AM   #10
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Re: no injector pulse

ok thanks lesterl. I was hoping that you would reply, I have done alot of searching and i have seen that you know your stuff when it comes to this. Im still not quite sure if it was the FP relay that I swapped a new in on. This picture is of the relay I changed. Of the two, I put a new one in on the left. All it did was give me an accurate reading on the fuel gauge, but no fuel pump prime. This picture is from under the dash, forward of the center console, that is where Haynes said it should be on a 1994, which they said is different from the other years. http://www.s10forum.com/forum/attach...0710091608.jpg
I have seen the three switches under the hood, but I didnt think they went to it. I have been checking those 2 ECM fuses religously, and they are good. When I crank the motor, oil pressure comes right up, so I would of thought that would of engaged the FP, but it hasn't. I have a noidlite on the injectors, but I havent checked for the 12v on one side like you said. I will try that and post back. If I dont have 12v, would it be safe to say my ECM is fried, since my fuses are good?

Last edited by 6ftdwn57; 07-12-2009 at 09:26 AM.
Old 07-12-2009, 01:44 PM   #11
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Re: no injector pulse

Quote: Originally Posted by 6ftdwn57
ok thanks lesterl. I was hoping that you would reply, I have done alot of searching and i have seen that you know your stuff when it comes to this. Im still not quite sure if it was the FP relay that I swapped a new in on. This picture is of the relay I changed. Of the two, I put a new one in on the left. All it did was give me an accurate reading on the fuel gauge, but no fuel pump prime. This picture is from under the dash, forward of the center console, that is where Haynes said it should be on a 1994, which they said is different from the other years. http://www.s10forum.com/forum/attach...0710091608.jpg
I have seen the three switches under the hood, but I didnt think they went to it. I have been checking those 2 ECM fuses religously, and they are good. When I crank the motor, oil pressure comes right up, so I would of thought that would of engaged the FP, but it hasn't. I have a noidlite on the injectors, but I havent checked for the 12v on one side like you said. I will try that and post back. If I dont have 12v, would it be safe to say my ECM is fried, since my fuses are good?
Yeah, thats something I dont remember seeing. I am used to the First gens too much I guess.

The Injector 12v SHOULD be fed from a fuse in the fuse block, might be the same fuse that feeds the 12v to the coil/ ICM (hence no injector pulse with noid lite or spark) I take it it didnt fire up with the carb cleaner either?

The ECM drives the other side of the injector to ground (same as ICM does to coil- the power is fed to the other side of either device and the electronics just ground the other line to activate- keeps shorts safe, i.e. short the power side blows fuse, short the drive side to ground activates device -doesnt blow up the electronics!) To test the actual drive to ground, hook one side of the noid lite to battery + (thru a fuse ~ 5-10A of course), hook the other side up to the ECM feed to the injector or ICM feed to the coil.

I will try to check for a wiring diagram in the mean time to get more specific.
Old 07-12-2009, 02:00 PM   #12
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Re: no injector pulse

Ok, found a diagram for a 1993 VCM, RED and WHITE on Injectors are the 12v Feed, Blue and Green are the VCM side (side that gets pulled to ground). 10A ECM/IGN fuse feeds Power to the injectors.

Fuel pump: Orange wire on oil pressure switch should have 12v ALL THE TIME. Fused thru 15A ECM/BAT fuse on fuse block. Fuel pump relay socket should also have an orange wire, grey wire, black/white wire, and dark green/white wire. Orange of course is also supposed to be hot at all times.

There is also another 10A ECM fuse that just feeds the computer.

Do some voltage checks at the injector harness, the coil, and the oil pressure switch.

Also did you have any luck with the carb cleaner in the intake? We need to determine if it is a fuel delivery only issue or if you have fuel and ignition issues or only ignition.

With the breather assembly off do you see fuel being injected?

Use a meter to check between battery ground and engine block for DC voltage. If you have any voltage present between the two you have a bad ground, would be good to have ignition on when checking.
Old 07-12-2009, 06:44 PM   #13
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Re: no injector pulse

i am not sure if 94 is the same as a 92, but the fuel pump relay is a square thing on the driver side fire wall, very top by the quarter panel, on a slide on holder. that is a good start to replace, just bought one at advance 10.00. if that doesn't do it, your ignition control module in the distributor is shot. that is what pulses the injectors. just bought one of those too, 36.00 at advance for the cheap one. those are the two fuel related cut off points. good luck.
Old 07-12-2009, 07:19 PM   #14
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Re: no injector pulse

hey guys, thanks so much for all the help and input. the engine will fire and run when i pour gas into the TB. Yes I have the breather off and absolutely no fuel. Even no fuel when I feed 12v source to run the FP, and have fuel up to the TB. I will check out those specific wires you have described for voltage. I switched the ignition control module from the old blown motor to this one, but still no go. The ICM is the flat plastic piece on the dizzy under the cap right? It has two little screws and a two wire hookup. I have those 3 relays on the passenger side firewall you were talking about, do you know what they go to? One of them clicks when I turn the ignition key forward. Im guessing another one goes to the A/C? Thanks again for finding those specific wires and colors.
Old 07-12-2009, 07:22 PM   #15
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Re: no injector pulse

oh and when you talk about checking the coil, you mean the actual coil that mounts on the intake and runs to the dist?
Old 07-12-2009, 07:27 PM   #16
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Re: no injector pulse

oh, and what a great idea to test the ECM with the noid lite!, i feel stupid now. that will help me determine if i need a new one i guess. at least I have some light peaking through this long dark tunnel now lol. thanks again
Old 07-12-2009, 11:57 PM   #17
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Re: no injector pulse

Quote: Originally Posted by red 92
i am not sure if 94 is the same as a 92, but the fuel pump relay is a square thing on the driver side fire wall, very top by the quarter panel, on a slide on holder. that is a good start to replace, just bought one at advance 10.00. if that doesn't do it, your ignition control module in the distributor is shot. that is what pulses the injectors. just bought one of those too, 36.00 at advance for the cheap one. those are the two fuel related cut off points. good luck.
THE ECM pulses the injectors, the ICM reports to the ECM the crankshaft position.
Old 07-13-2009, 12:02 AM   #18
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Re: no injector pulse

Dont worry about testing the coil, if it runs with an external fuel source.

The relay that clicks, does it click off after 4 seconds? If so that is FP relay.

Check for 12v on injectors on the wires I labeld for ya, the red and the white. IF they dont have 12v the noid light wont lite up. Take your meter and ohm the red/ white wires to ground if you dont have 12v to check for a short. Might be able to hook one up to 12v thru a 5-10A fuse and crank it over to see if it sprays fuel.

Dont replace the ICM, like I said before it reports TO the ECM and the ECM fires the injectors. It runs with fuel poured down the throttle body so it is either ECM, Injectors, fuel pressure, or wiring in between.

Check back when you get more info. :-)

Did you try to pull codes?
Old 07-13-2009, 12:31 PM   #19
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Re: no injector pulse

ok so I checked for 12v on the injector wires and they have power. so then i plugged the noid light into the grounding ECC side and supplied 12v to the hot side of the injector harness, I had no light with the ignition turned on. so then i cranked the motor over for good measure and didnt have a pulse either. I checked to see if I replaced the right relay for the FP with the wire colors you gave me, and I did replace the right one. I checked again for spark at the plugs and I still do. All the while checking those two ECM fuses, and they have stayed good. I havent checked the oil pressure switch for 12v, but doesnt that only deal with the FP? I'm guessing that a quick guess would be that my ECC is not grounding my injectors, and could also be messing up for my fuel pump to kick on?
Old 07-13-2009, 05:00 PM   #20
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Re: no injector pulse

so this truck is f****ed. i took some more pictures to see if you have any ideas what is going on with this shit. this kid really messed with shit, and its killing me.

here is a picture of under my steering column. there is some damn black box that says AutoCommand on it, with wires coming out of it into some plug then those wires going over to the other side under the dash. but some of them are just snipped and hanging. and then there is more wires coming out of the bottom of it with connectors coming off going to more wires. all the while im seeing the dark green/white wire in there with them.







this is a picture of the wires coming out of the autocommand that are snipped. also there is some kind of relay dangling too. and heavy red wire with a inline 30amp fuse. oh and some mini switch with a pink and black wires that came unconnected





and here is some hot wires running to my inner fender on some kind of mount. it looks stock, but doesnt seem like it should be. there is a f***ing wire coming off of it with a connector(the only one with a connector) that has a f***ing paper clip stuck in it!




and now when i turn my ignition key forward i am blowing my 20amp fuse that goes to my guages. i have no idea why

Last edited by 6ftdwn57; 07-13-2009 at 05:04 PM.
Old 07-13-2009, 10:52 PM   #21
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Re: no injector pulse

The paper clip wire looks like your prime connector for the fuel pump.

The Auto Command looks like a remote start rig.

I bet the little sucker cut the wires feeding 12v to the ECM. Might check for power AT the ECM. Look for an orange wire feed (should be 12v constant), Pink/ Black should be 12v in run/start, check for power and go from there, might check out Autozones website:

start at www.autozone.com and sign up, might set up a 1993 S10 and go to the REPAIR GUIDE, CHASSIS ELECTRICAL, WIRING DIAGRAMS, the last 2 are identical as far as I can tell. #25 and #26 but those are the two to look at, also check into where the fuse for the guages hook upto.

Wish you lived closer, I love to troubleshoot wiring. (well not really, but I do enjoy wiring.)

Last edited by lesterl; 07-13-2009 at 10:56 PM.
Old 07-15-2009, 02:05 PM   #22
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Re: no injector pulse

well thanks so much for the help. my internet has been down so i havent been able to get on. thats what i am hoping that wire with the paper clip goes to. as far as checking for 12v at the ECM, I just pull the connector that has the orange wire, along with all the other wires it holds, and check for 12 v? or should i just cut the orange wire and test it there? if this is the case, i wonder where/how i run that hot wire to the ECM. I guess I should ttry to look for the other cut end of the paper clip wire, but I'm pretty sure it isnt there. Thanks again for all the help

Last edited by 6ftdwn57; 07-15-2009 at 02:07 PM.
Old 07-15-2009, 02:42 PM   #23
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Re: no injector pulse

yes the icm does fire the injectors. which is why it will fire with fuel dumped in the tbi. the ecm is an adjuster for the proper running of the engine, taking in all input from the sensors. i didn,t read if you replaced the fuel pump relay or not. but for 50 bucks replacing both is a safe way to go. i tried an old icm that i had when my last one was slowly going south. and it for some reason didn't work now, even though it did before.
get a chiltons manual, good book to have, good wire diagrams.

Last edited by red 92; 07-15-2009 at 02:44 PM.
Old 07-15-2009, 03:13 PM   #24
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Re: no injector pulse

i put 12v to that paper clip wire and boom, fuel pump kicked on by itself. then i turned the motor over and still no fuel out of the injectors. so i put the noid light and got nothing. so then i plugged the noid light into the hot side of the injector harness clip and grounded the other side and the light came on! i guess im still not getting the ground from the ECM, but this is huge progress!
Old 07-15-2009, 08:11 PM   #25
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Re: no injector pulse

Well, the orange wire to the ECM should have 12v ALL THE TIME on it (thru the fuse in the block that has power all the time on both sides if the orange line is dead at the ECM, you could wire a wire back to the fuse block (pull fuse to determine which side you need).

The other wire pink/black should be hot when you are starting and running. If it is dead at the ECM with the ignition on then you will want to track it back to its appropriate fuse in the block, same deal there.

Let us know how it turns out.
Old 07-16-2009, 12:41 PM   #26
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Re: no injector pulse

yea youre right cuz now the FP is always on no matter if the ignition is on or off. so that wire needs to be hooked up into the fuse block. and i will try to figure out what is going on with that orange wire. i do have 12v at the injector harness now, but it just wont pulse
Old 07-16-2009, 02:13 PM   #27
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Re: no injector pulse

i called the guy i bought the truck from and asked if there was an alarm, there was and im taking it that the AutoCommand box is it. now there has been stock wires that have been spliced into wires that go to the alarm box. and also some of the wires coming out of the box have been cut, with no other end to see where they used to go. an orange wire has been spliced into and a white wire running off of it going into what looks like the fuse box. i checked the fuse box and the orange wire fuse is always hot. and then the ignition fuse is only hot when the key is forward, which is correct. im dying here. would a disabled alarm, or whatever is going on with this one cut the power to the ECM? there is so many jumbled up wires underneath this dash, i get overwhelmed. this sucks. i had the old motor out along with the tranny and the new one in, in two days. now its been a month trying to figure out this crap hack job.
Old 07-16-2009, 02:15 PM   #28
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Re: no injector pulse

im also guessing that the relay running from it, is like an ignition bypass setup or something?
Old 07-16-2009, 05:30 PM   #29
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Re: no injector pulse

ok so quick update. i completely pulled the alarm system. then rewired everything back to stock. before wiring it back up I checked for voltage at the wires. with the ignition off, i have voltage on the two heavy red wires that were spliced into for the alarm. then with ignition on, i have voltage at the infamous orange wire. so now with that pain out of the way, and fuses getting power when they should, all signs point to no power to or from ECM. oh yea, the wire with the paper clip shoved into the spade connector is just a fuel pump prime test wire. that is why the fuel pump stays on all the time. so i will disconnect that from the hot wire bar.
Old 07-16-2009, 09:30 PM   #30
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Re: no injector pulse

ok so i also pulled the connectors off of the ECM and tested the orange wire for voltage. since there was a couple i tested both. no power to either. the one orange wire just loops down around near the EMC with a connector. I tried both sides of the connector. here are some pictures to show.





Old 07-16-2009, 11:39 PM   #31
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Re: no injector pulse

Quote: Originally Posted by 6ftdwn57
ok so quick update. i completely pulled the alarm system. then rewired everything back to stock. before wiring it back up I checked for voltage at the wires. with the ignition off, i have voltage on the two heavy red wires that were spliced into for the alarm. then with ignition on, i have voltage at the infamous orange wire. so now with that pain out of the way, and fuses getting power when they should, all signs point to no power to or from ECM. oh yea, the wire with the paper clip shoved into the spade connector is just a fuel pump prime test wire. that is why the fuel pump stays on all the time. so i will disconnect that from the hot wire bar.
Sorry I didnt make that more clear.... Glad ya figured it out.

Also the 2 large red wires to the ign switch are battery feeds to the switch.
The other wires (white, orange, brown, blue, yellow) are power feeds to fuseblock/starter.
The orange wire we are concened with is a lighter guage wire, like 18 guage or so.

Trace that wire down, just FYI, on these GM's orange and red are ALMOST always power feeds of some kind. Supplying power (thru a 10-15A fuse) to this line may make it start. Could be something to try. If the fuse pops, might clip it just before it gets to the ECM and supply power agian to the ECM that way.

Did you happen to find a Pink/Black wire that should be hot with ign on (also durring cranking), was it hot then?

Last edited by lesterl; 07-16-2009 at 11:46 PM.
Old 07-17-2009, 12:01 AM   #32
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Re: no injector pulse

yea i found the pink/black wire but didnt check it for voltage. i was thinking about supplying power to the orange wire that plugged into the computer, fusing it of course, like you said. so that orange wire(the one in the second picture) is the one were talking about? if it is, then i will just tap 12v into it and see what happens i guess. i wonder how power isnt getting to it? i mean im getting power everywhere else that I should be.

Last edited by 6ftdwn57; 07-17-2009 at 12:03 AM.
Old 07-17-2009, 12:05 AM   #33
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Re: no injector pulse

The little SOB who did the hack job may have cut it or who knows....

Try the fused (uses a 15A fuse for that circuit.) feed for that line, check the pink/ black - if it aint powered with the ign on it aint gonna run. (use a 10A fuse for the pink/black circuit.
Old 07-17-2009, 12:11 AM   #34
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Re: no injector pulse

ok cool thanks, i will try that tom after work and report back. if it works, i guess i could just leave it hooked up that way? i mean it would be fused and all.
Old 07-17-2009, 12:13 AM   #35
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Re: no injector pulse

Yeah, could I guess, I would probably just run 2 new wires to fuse block and snip the wires between leaving my new wiring in place of the old.

Keep in mind the orange from the fuse block feeds the ECM AND the Fuel pump relay socket, but give 'er a whirl and see.

Didja ever figure out the blown 20A guage fuse?
Old 07-17-2009, 12:25 AM   #36
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Re: no injector pulse

oh yeah I forgot the orange wire feeds the FP relay. which is weird that it works there, but not to the ECM. when I connect the FP test wire, the fuel pump runs though. I totally forgot about that.

and haha no I didn't figure out the ever blowing 20A dilemma lol. I have just left it out for now
Old 07-17-2009, 12:36 AM   #37
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Re: no injector pulse

So you actually have 12v on the orange wire in the FP relay socket? The prime wire is hardwired to the NC contact on the FP relay and should be dead unless you provide power to it, when relay is activated it should close the NO contact that will have the orange wire to the COM grey wire that feed the pump.

The Oil Pressure Switch should also have a tap off this orange wire to it and a grey wire tapped into the same grey wire feeding the fuel pump (to bypass the relay should it fail and the oil switch will activate over 4 psi oil pressure - usually when FP relay goes bad you have longer cranking times.)

Since it never starts I am going to assume that the orange wire to the switch and relay are also dead as you never mentioned the pump running on its own.

Just some extra info and as complete as I can get tonight- you will want to include both the relay and switch in your bypass since they will need power also.
Old 07-19-2009, 12:52 AM   #38
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Re: no injector pulse

hey. i forgot to post yesterday, but I got it running! the ECM wasnt getting power so I supplyed 12v volts to it like you said. the fuel pump came on and primed for 4 seconds, then turned the ignition on and has pulses. so i plugged the harness back in and got fuel. got it pretty close on timing and the bitch started right up. the motors looks to run real strong so far! i have power all thru the wiring harness on the orange wire. i dont know where im dropping voltage. so tom im gonna just run a new wire from the last spot it was hot into the ECM. thanks so much for your help, i really appreciate it.
Old 07-19-2009, 04:08 PM   #39
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Re: no injector pulse

No problem man, glad ya found it runs! :-)
Old 07-19-2009, 10:59 PM   #40
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Re: no injector pulse

yup, wired it for good today. Starts up all on its own. Well except for an auxillery battery(jumper cables) setup cuz I dont have inner fenders lol. With that out of the way, I got the sawzall and grinder out and ripped off this bag over axle system. Got my C-notches mocked up, and the holes all drilled out. Cant wait to get it done.
Old 07-19-2009, 11:48 PM   #41
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Re: no injector pulse

WooHoo!
Old 12-06-2012, 08:24 PM   #42
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Re: no injector pulse

I have the same problem except my 4.3 tbi will run when not at idle. Injectors pulse when engine is in high idle and ass soon as you let of throttle it will die. I dnt know what to do
Old 12-06-2012, 10:20 PM   #43
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Re: no injector pulse

you can start by creating your own thread with specific details like what have you tried, year of your truck, etc.
Old 12-06-2012, 10:47 PM   #44
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Re: no injector pulse

FP relay should be under hood on that animal.

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