I just finished repinning my 747 harness to 730 for my TPI swap. WHen I turn the key on , SES light works and there is proper voltage at the various ECM pins. Except for the injector wires. I have tried two different ECMs and two different chips, one that I made and one from a friends car, which I know had VATS removed and the computer was from the same running vehicle. The only thing that is not working are the injectors. fires right up on ether, so spark and timing are pretty good. I tested the voltage with the key "on" and "run" right at the ECM and got nothing at all from the inj wires. I went over my wiring and repinning schematics and everything seems to be in order. Hopefully I described everything enough, eyes are a little fuzzy after looking through over 600 other posts on the subject! I really need my vehicle so I can get back to work when disability is over at the end of the month, and this is driving me nuts! Thank you to anyone who can shed som light on these dark times!

 

Seems to me like the injectors get full power, they are triggered by a ground signal from the computer. The vats deal sends a square wave ground pulse to the computer to verify the system and this allows the computer to pulse the injectors. Might check into putting a jumper to power the injectors and see if it will run, but look into this further, not on just my sayso.

 

Please, someone has to know! I have reached the point of desperation

 

I did jumper the power side of the injectors, and got power through the harness. The ECM refuses to ground them. It is like the injector drivers are nonexistant in the computer. Will have to try out some more things tomorrow. I am about ready to set this thing on fire

 

Have you checked for voltage at the injector? Have you hooked up a noid light? Have you ohm tested the injectors? Have you double checked the pining you did? Is the fuel pump priming? Do you have pressure at the fuel rails? Are the bungs possibly clogged? Have you tried pressing the pedal when you start it? Have you datalogged it?

That should keep you busy.

 

Have done all of that, besides datalog. My ALDL isn't working right, or I am not sure how to do it. I think my ALDL is a little different from the TPI cars, or is it? Injectors seem to have around 16 ohms resistance. THere is no voltage anywhere in the injector crcuit, incluging at the ECM plugs. Applying voltage to the hot side from another switched source, and a test light on the ground shows a complete circuit. Known working distributor module. A voltmeter confirms that the the proper voltage is coming from the EM at all the pins, and I tested all the grounds at the ECM and all are good. I see no reason why this should not work. Would it be a bad idea to put 12v right to each injector and tent them individually just to see if they work so once I get the rest of the system working, I will be sure of the injectors?

 

didn't pull the intake off yet to check, but would anything have happened if i wired the injectors backwards? Just a thought. Would this blow anything out? everything else in the wiring checks out. I used the diagram in Anesthes(sp?) article, the pinout in The TPI Swapper's Guide, as well as the pinouts for the original wiring in the truck 747.......

 

I did not read thru all of this, BUT

When I reinstalled my MSD distributor after installing my stroker motor, the elctronic module in the dizzy was bad. The injectors were not getting grounded out or they were not getting any signal at all due to a bad dizzy. The dizzy was working great when I took it out, and was bad when reinstalled. It sat on a shelf and all by itself went bad. Go Figure.

I installed my 17 year factory dizzy and the engine fired right up. I spent one month on this problem.

 

You can not wire injector wrong. Rule that out. Could be a distributor as said earlier. I don't know how it would be that though? It also sounds like you should look for a replacemnet ecm. I always try to have a spare lying around. No matter what it is.

 

I would look into your ignition module in the distributer and see if your getting a reference pulse to the ecm, the pulse tells the ecm when to fire the injectors if you search theres a few posts about this on here

 

Not sure I'm entirely clear on what you're seeing. The 2 pin injector connector should have +12V on one of the pins when the key is "on". If you don't have that, you'll want to look for a blown fuse or some other interruption in the circuit. From what you wrote above, it doesn't sound like that's what you're seeing....?

I'll try my hand at a little ASCII art to help explain:

+12V -----|Injector Pin 1| |Injector Pin 2|-------|ECM|

As mentioned earlier, it doesn't matter which injector pin has 12 volts. Just make sure one of them does. The other should go back to the ECM. The ECM will ground the circuit when the injector is supposed to fire. If you reconnect the injector connector and disconnect the connector from the ECM, you should measure 12 volts at the injector pin with the key on. If not, the problem is the supply voltage to the injectors.

If you pass this test, you'll next want to make sure your fuel pressure is OK. The fuel pump should run for a few seconds when you first turn the key on. Make sure the problem isn't a bad fuel pump relay. It may be that the injectors are firing with little or no fuel being supplied to the rail.

Other than that, are you sure you have the 4 pin distributor connector securly fastened? That's an easy one to forget since it sits toward the back of the engine.

 

If you have spark and no current at your injectors, it's not your module, that would cut off spark too.
I've seen it happen if your Throttle position sensor fails, it will cut off the juice to the injectors.

 

4BoltMain, you may be on to something here. Should it work with the TPS unplugged? I tried to adjust the TPS and it reads a constant 4.5 volts, no matter where the throttle position is. Is this a autoparts store thing or a dealer thing to replace? Any other way to test it before buying a new one? Thanks again!

 

$15-20 at any parts store. You NEED that for any kind of driveability. So I would say it would be a good idea to repleace that.

 

i agree with the spark modual in the distributor. me and my father had the same problm liek this with a 86 blazer though. the power wires lit up on the injectors, no ground though, it had to either be the spark modual or the ecm. we were getting fuel to the thorttle body but didn't get fuel coming out the injectors. our problem was the ecm though but you said you tried that so i would get the spark modual in the distributor. we didn't get a check engine light, i have a snap on scanner and it was saying no connection. you said your check engine light comes on so your ecm is probably not the problem, i'd try the spark modual

edit: didn't really read all the posts but if the tps doesn't work maybe try this heh

 

Hmm... looks like something happened in the wiring. I was checking the TPS wire at the ECM and I got around 4.5v with engine off and no throttle. So, TPS is bad. Tested the other terminals on the ECM for the TPS signal and ground. Got 4.5 at the ground terminal as well. It got cold so I then went back inside. It has to be a stupid problem like this that is keeping it from running. Hopefully this will be the only one.... Checked everythign else and it seems fine so far. All the injectors tested at 16 ohm, +- 0.5 ohm.... Time to pick apart he wiring again. Just hope I didn't do any damage to the ECM. Only get code 12 when I ground the diag terminal.

 

with the tps unplugged you should be able to get voltage to the tps harness. The way they designed the elcetronics is that if the tps shorts out it cuts off all power to the injectors, because if it does short out it has no idea how far the throttle is open thus killing fuel supply so you don't blow the motor.