jdhuegel1

If you missed the other thread, the only way I can get the car to start is by tapping the injector grounds together.. It's as if there is no signal unless the 2 wires are touching..

Ive:

Ohmed the harness
Checked voltage at injectors during crank
Checked voltage at injectors with key on
Checked grounds
Verified injector function via 9V battery
Verified signal to injectors via noid light
Checked fuses

I've done it all... Still nothing. Car get's no gas. It'll crank, but won't even attempt to start.

If I run a wire between the 2 grounds on the injectors, it fires right up as if there isn't any problem. But the problem is you can't run both primaries off of one (or shared) ground from the ECU, as the pulses will match, and need to be offset with the rotation..

With the wires tapped the car acts COMPLETELY normal.. Why? What do the 2 primary injector grounds share that would only allow them to function when crossed? The CAS? I thought the CAS were good, as when the wires are crossed, the car runs perfect... since the CAS also controls spark I ruled them out.. I'm out of ideas if the ECU isn't at fault (which I doubt)

Something I'm missing?

I've ruled out the ECU, but will still swap it to see if that does it, as it's the only thing I haven't replaced..



Thanks for any other ideas.. No, I'm not trading it for a Supra yet...

dubulup

Sorry man...I haven't looked at the wiring dia. for the fuel system in awhile, so I can't say if the injector require a different GND. I have followed most of your build up on "the other forum" and problems over here...

Why do you say the pulses will be the same if you jump the GND's together? There are two wires from the ECU, I'm guessing a 12V (signal) and a GND for each injector. When an injector is hit with 12V thats when it fires. (At least thats how I found my bunk injector; test off battery) A GND is a GND; 0 VOLTS. I wouldn't think the ECU grounds each injector to make it fire, meaning it ALWAYS would have to have a 12V signal to it; I would think it's the other way around, pulses the 12V. Maybe one of the GNDs on one of the primaries got scored somewhere sometime in the project and now has formed an open circuit. Have you pulled codes off the ECU? Can you with the PFC. [If not,] I'd suggest [plugging in the stocker] ,without the jumper in place, Turn car ON, don't crank. Pull codes, even if you don't see the CEL; then unplug a primary inj and turn car back ON and pull codes again (then again with the other pri unplugged). Then put the jumper in place and pull codes...see what differences there are, if any?!?!

In my mind (and on all the schematics I studied in college) a GND is common throughout the circuit, a component just has to see GND somewhere in the circuit, without it (OPEN CIRCUIT) the 12V signal can't be sent.

sorry if this is rambling or if you knew all this, and know something special I don't about the GND in the fuel sys circuit. Good Luck, but a normal running car with two injectors running off the same GND doesn't sound WAY off to me. But you say you've checked the harness for continuity from ECU to injector...so I'm lost and wrote entirely too long. I'll look at the fuel system again when I get home.

-DUB.

jdhuegel1

Hey dub, thanks a bunch for the response. What you say makes perfect sense. Somewhere in the expanation from the FSM and all the people that have helped me I may have gotten it screwed up.. the reason it confuses me is because of exactly what you state.. GND is a GND.. However, in the FSM it shows the 12V+ as a common wire for all 4 injectors and a seperate GND lead off the ECU for each injector. That's the confusing part.. I still plan on throwing a stock ECU in there, just to settle my brain... but I don't think that's it. I also might throw a few more chassis grounds on the car, as people have had many starting problems due to lack of grounds.. (Although I didn't remove any, and actually added 1 during the rebuild) I guess we'll see tonight. Thanks again!!

dubulup

Ok, so I was wrong about the firing then, sorry. I'll still look at the FSM again, sometimes extra sets of eyes helps more than knowledge itself...

jdhuegel1

Hey no problem. The logic is definately there... Thats why I grounded them together in the first place and got it to work!! Now the only qustion is how!

dubulup

jdhuegel1

I would imagine you can.. I'll find that out tonight as well.

dubulup

reason I ask is, When I had a 4500rpm limp mode due to a sticking sec. inj. the CEL never came on. Some codes get thrown and don't light the CEL. So I take it you have tried to pull codes since the build up???

jdhuegel1

Nope, have not. Reason being is I though the PFC would need to go through the initial learn phase before anything would be correct.. Maybe I'm wrong. It was just what I thought; I don't think I read that anywhere here.

dubulup

I heard the same

try the stocker, and keep us posted

jdhuegel1

I will. Thanks again for the help Dub.

jdhuegel1

Grounds don't work...

I'm on my way to get an ECU and new CAS. If that doesn't work, you can find my car in the for sale section.

Rx7oneluv

Any update on this. I'm having the exact same problem with my PFC. Also I was thinking. I did a NON-Seq conversion for my car, would I be able to use a ground from one of the removed selenoids and splice the ground from my injectors into another plug? Or is that pure stupid logic (im not very knowledged when it comes to curcuits)

rfreeman27

iTrader: (5)

It was the injectors.

Rx7oneluv

they were bad?

rfreeman27

iTrader: (5)

yes

jdhuegel1

Yeah.. The stock 550's were sticking for some reason.. I also added another ground to the battery and it runs fine now..

Of course, the clutch slave took a dive and I can't seem to sort out the surging idle, but hey it still looks nice right? lmao

Rx7oneluv

thanks for the help man.....I got my injectors cleaned and they worked before that....so I'm guessing that bastard wrecked em.....ARGH...now im not confused I'm just pissed

Rx7oneluv

Primary injectors are bad....did the 9volt battery test