hey everyone. So this project i had in my head as being fairly straight forward is turning into a nightmare. I had this master plan to strip down the wiring harness and get rid of anything i didnt need/use and put everything on switches that i did. (this is a daily driver but its a track car in the works)

the car is a 91 Z28 5.7L T5 swapped

So i have everything stripped down and switches are all hooked up and i get power, but when i go to start the car it just cranks. To give you an insight into what ive done i'll explain the wiring now.

for starters i have done NOTHING with any wires relating to the ECM or the engine sensors. I have a ignition switch that i hooked up to the pink wire from the ignition switch off of the steering column. a push button start hooked straight to the starter a fuel pump switch hooked directly to the pump. and an accessory switch hooked to the brown wire from the ignition switch on the column.

i have 12V going EVERYWHERE i need to when i turn the power on as far as i know. at the ingition coil, at the ICM, at the fuel injectors, the fuel pump runs, theres fuel at the rails, gauges twitch before the starter engages but when i hit the start button it just cranks and cranks and drains the battery fairly quickly which concerns me abit but i have a jump box i'm using now.

ANY ideas would be really appreciated. I'd rather check double check and triple check everything all over again as you all give me some ideas. i'm pulling my hair out trying to figure this out.

I'm wondering if something got removed thats causeing the ECM to not realize the engine is trying to start and its not sending signals to spark or something.

Please and thank you fellow thirdgeners. this site has saved me more times that i can count. i'm hoping it pulls through again.

 

Did you remove the VATS wiring?

 

well elt me explain this. The car had remote start and security(had). i took it out with everything else. they had cut into the yellow wire i followed it up to the module where they ran it through a relay and had a resistor to bypass it.

BUT as i was ripping wires out from under the dash i followed that wire farther up and saw that is had been cut and spliced by the previous owner.

I was under the impression the Vats system read the resistor which in turn activated the starter relay? (in a perfectly wired car) so wouldnt vats be obsolete with having hooked the starter up to a switch directly? or does Vats tell the ECM information that would cause the engine not to fire?

 

VATS tells the ECM 2 things: 1- to crank the starter, and 2- to provide fuel to the engine. It sounds like you have the cranking part ok, but I would bet your ECM is not pulsing the injectors to provide fuel to the engine. You may have 12V to the injectors, but the ECM actually provides the ground path in order to "fire" the injectors. If the ECM is not receiving a signal from the VATS module that the engine is cranking, it won't switch the injectors to ground and they won't fire( pulse).

Take apart the main injector harness connector, and connect a one lead of a multimeter to the pins for the dark green & dark blue wires, and the other lead to a good ground. Turn the meter to the lowest "ohms" or resistance setting and have someone crank the engine while you watch the meter. You should see the reading change, or the needle bounce if it's sn old analog meter. This indicates the ECM is doing its job. You can also run this test with a self-powered test light, connecting those wires to its ground wire. You should see it flash. If neither method works, your ECM is not firing the injectors. There are special sets of test lights called "noid" lights that can do this tool you should be able to rent them cheaply from the major auto parts stores(autozone/advance/etc).

 

i'm abit confused as to what connector i should be probing. just one of the injector 2 wire connectors? or the harness connector at the ecm?

 

also, i cant check spark until tomorrow because i'm by myself and dont have a spark tester or spare plug with me. but i probed the pink wire at the coil and like i said it gets 12v when ign on but i watched the multimeter as i cranked and it drops to 8v during crank.

I know it needs to be at 12v during crank but what can i do to fix this? My Ign switch gets a direct 12v from the battery and it runs right into the same pink wire that was on the old ign switch that haynes says was the pwr during crank wire. from what i comprehended the pink wire i'm connected to is 12v during crank to the ign coil, ecm,and injectors.

 

On top of the engine, the wires for each injector all go back to a single connector before going into the main harness from the ECM. I believe the connector is at the back of the fuel rails, near the distributor, but it's been a while since I looked at one of these so I could be wrong. Just follow the wires from one if the injectors and you'll find it.

 

8V at the coil is not going to be enough to provide a good spark(if any spark at all). The pink wire should be straight from the ignition switch to the coil, with only one splice in it from the factory.

What are the voltage and amperage ratings on the starter button you used?

In your initial post you said:
"I have a ignition switch that i hooked up to the pink wire from the ignition switch off of the steering column. a push button start hooked straight to the starter"

Do you mean that you installed a different ignition switch than the original one in the column? Either as a replacement switch or as a secondary switch?

Also, make sure you have a good connection on the braided wire ground strap that bolts to the rear of the engine & to the body.

 

Alright I will look into that tonight when I get home.

 

What should the one splice be going to? I believe the pink separates to 3 wires 1 to the coil 1 to the ECM fuse and 1 to the in fuses.

I now longer have the keyed ignition switch. I have a single covered toggle switch that I wired up to into the old wires.

And ground is good. I checked it although I didn't touch it.


I'm going to check to make sure ECM still has the direct feed of 12v at all times and take off the pink wires spliced in so the ONLY thing taking power is the coil during crank.

 

Correct, that pink wires feeds the injectors, coil, ECM, and a couple other thugs you want, like the taillights. Don't cut any of those wires, they are the splice I was referring to. Also, if you remove the wire to the ECM, it definitely won't run then because that is the wire that tells the ECM the car is "on".

The ECM already has a constant power source via another wire from the fuse panel.

What is the amp rating on that toggle switch? Odds are it isn't high enough to handle the current that needs to run through the ignition switch wires.

 

The switch is a 20amp switch. Is that not high enough? Also I think the wires I used are a 14 or 12 gauge. Any chance those can't carry the power it needs?

 

alright so here are some new developments. I found an org wire that i had cut out that fed the ECM direct 12 volts. i installed that wire and got it reconnected. After doing that the ECM must not be drawing my power from the switch because i now get good voltage to the coil during crank.i havent seen it drop below 11V. thats the good news.

Bad news is it still wont start. I got a noid light to check injector pulse and it stays solid during crank. so no pulse. which means its def the vats. i'm going through the old remote start system that was here and seeing they put in a new relay for the starter and had a resistor wired into some of the wires. i'm assuming that was the temporary bypass until i put my key in. SO my idea is to use that resistor and wire it back into the car to bypass vats permanently.

Here is where i'm having a problem. If i understand correctly the 2 wires that read the resistance are the black and white and the purple and white. Heres the catch. these 2 wires are looped together. so they dont lead to anything. is that just now causing my issue and do i need to tear those apart and put my resistor in between those?

Am I missing something???

 

alright so after further investigation the 'linked wire' for the 2 vats wires were actually the resistors nicely wrapped in tape. my bad on that one. so now i'm lost again, vats is bypassed, and still no start....

 

Is your VATS module still in the car or have you removed it already? Is the Security light on your gauge cluster staying lit the entire time you're cranking it, or does it go out after the bulb test?

 

20A is on the lighter side of what I would normally recommend for that. I used a 40A switch on my pushbutton start.

Same with using 14 gauge wire. I would recommend using at least 12 gauge wire.

 

i just hooked the gauges back up to check and i dont get any sort of security light or even a check engine light anymore. i will probably swap the switch and wires out before the final install but that shouldnt be whats keeping it from starting should it?

is there anyway i can test the ecm inj pulse thing by giving the ecm a signal to ground. from what i can tell the ground is in the module itself, but is there something i can do to maybe ground the blue wire before the module just as a test?

and if the module is the one ive read about on the firewall somewhere tucked in the dash no i havent. i havent even stumbled across it yet i dont think

 

The VATS module is mounted to the backside of the dash on the passenger side. If you can find the C207 under the passenger side of the dash near the ECM. You can ground the dark blue wire from it to test. The C207 is actually 2 connectors. Make sure you ground pin L on it on the side that goes to the VATS, not the side connected to the ECM. You should be able to pull it down far enough to tell which side is which.

The switch your using shouldn't be the problem since the starter is cranking the engine, unless it's cranking slowly. Using an underrated switch can cause the switch to burn out prematurely. It could also potentially cause a fire, but since it's not "on" very long, that isn't as much of a concern as a switch that has power going through it constantly.

 

Aaallllrighty. So I got a bit side tracked tonight by friends and beer but I did manage to do a few things while I had extra hands. I got the car to fire with starting fluid but as soon as you stop spraying it dies.

I realized the vats module is a terror to get to so I managed to trace the power to wire and found that it did not have power going to it. I played with some wires and got power going to it again.

After all this I put my gages back in and tried to fire it up and still nothing. Though the security light came on and then turned off. So I believe vats is good now??? I didn't get a chance to ground the module though.

I also checked spark to be certain I had it. I unplugged the coil and held it to a ground and saw the arch so spark is reaching the distributor. I hooked a spare plug up to a pulled wire but I didn't see any spark at the plug.

 

I guess tomorrow on my lunch I will run home and probe the injector to see if I have pulse now or not. Didn't think to do that earlier.

 

If your security light is going out after the bulb check, then VATS should be fine.

If it runs on starter fluid, but shuts off after you stop spraying, then your most likely not getting fuel to the engine. Or not enough fuel. I'd definitely recheck pulse with the noid light and see what you get.

 

SHE LIVES! thank you very much TTOP. this problem seemed to be one thing that lead to another. I got off work early today and came home with absolutely no idea what i was going to check, I double checked for pulse and there was none still.

Apparently in the midst of redoing some wires i blew the inline fuse by the battery that powers the ECM and OPSU. I replaced that and it fired up first try. i still have headlights and accessories to wire up but i shouldnt be messing with anything i've already done.

Thanks again!!

 

You're welcome! Glad you got her fired up!