Re: Isolating the Computer, ESC, and Distrib Module

NH rules. And they just abolished the need for a permit to carry concealed... yay.

~KJ~

Well, lets all go to the same diagram. This one will do

Now, I think the problem we are running into is when is power supplied to the green/white wire to operate the relay. This is the 2 to 10 sec prime signal, sent by the computer. Correct me if I'm wrong, but after the prime signal is done, the green/white goes low. The fuel pump relay is only on when the truck primes. The only path to power the fuel pump is through the oil switch, since the E to A connection is gone. Well, in the case of this diagram, the hot fuel module will power it 20 secs longer to help with vapor lock/hot start issues.

As this article and diagram mention, the grey wire I was referring to can also be either tan or tan/white. My truck is grey.

"John Alt" wrote

I think that you are incorrect about the fuel pump relay only working for the two second prime. It only is switched on for two seconds if it doesn't see a "running" engine. Once the engine is running/cranking, it's back on again. I know for a fact that I've never encountered a GM vehicle that wouldn't run because the oil pressure switch isn't working. In some ways, it would not be a bad idea, probably save some engines, but with the high rate of sending unit failures, it would probably just irritate the customer un-necessarily.

Anyway, this is not my area of expertise, but I've heard this mentioned so often on the newsgroups, ie: oil pressure switch will shut off the fuel pump if it's not working, and I think it's incorrect, at least as far as GM vehicles go. I'll do some more digging and see if I can come up with a definitive answer...or perhaps some more knowledgable "driveability" tech can chime in.

Ian

running/cranking,

the pump is switched on by the ECM during the prime mode, and then again when the ECM 'sees' ignition pulses

this is to insure that a lack of ignition does not cause the catalytic converter to fill up with unburned fuel

watch the voltage with a meter, as soon as you start cranking, it goes back 'high'

I once had a celeca with a bad Fuel Pump Relay (or some related circuit)... To start it I had to crank it for about 30 seconds - long enough to build up oil pressure. Then it ran fine. Since I only paid $1 for the car, and had 2 other trucks plus a car, I ran it that way as a winter-beater (abusing the %^&* out of the starter/flywheel). So I sold it for $2 to a friend who sold it for $4 who sold it for $8, and they they got greedy

- I later met some>

That diagram shows it pretty well. The connector is shown from a front view, with the attachment ears facing up. Look at your connector, and see which side is up, as it changed on various models. The fuel pump test point is the red wire, terminal G. Again, refer to the connector diagram.

I could swear that I read the relay drops out after the prime, but since Ian and Gary both say no, I'd believe them. I'll have to look it up again. Damn, I feel stupid. But putting a system in parallel like that is stupid in the first place. It might be something GM thought better about and changed the computer's EPROM, rather than change thousands of pre-built wiring harnesses.

You mentioned the celica needing oil pump pressure. The ford system is the same, also. That one I know from working on a Taurus a friend changed the oil in and forgot to add oil after draining. Damn, I'll never let him live that one down.

"John Alt" wrote

I talked with some of the more knowledgeable guys in our shop about the oil switch/fuel pump issue. Apparently, when GM first came out with the electric fuel pumps, there were some vehicles that did use the oil pressure switch as part of the pump circuit...ie: these vehicles would quit if the oil switch went open, or you lost oil pressure. They haven't done this for a while now.

Ian

I'd bet the Astro Van was one of them. My first conversion used an Astro wiring harness, motor, and transmission. Most of my research was in the Astro manual. I only have the wiring diagrams I photo-copied from the factory manual left. Well, I only feel half stupid now. But it's Friday, so there's still hope to achieve total stupidity by 2 am.

The Chevy Monzas and Vegas were wired that way. As far as I know none of the fuel injected cars were though. Bob

Progress but not there yet... Hotted the ornge wire (via a piece of that old ornge extension cord). That gets the fuel pumping and it starts - for a moment. Gets up to about 1500 RPM and shuts down. Doesn't seem to be timing related (timing bolt is still loose - tried everything that would make it start). Best I can figure is that the computer is sutting it down for some reason... Would the oil-pressure switch be a possible reason? Should I just short the leads that plug into it? Thanks for the help so far. Elliott

TranSurgeon, Per your comment: "the pump is switched on by the ECM during the prime mode, and then again when the ECM 'sees' ignition pulses"; How does the ECM 'see' the ignition pulses? Seems my system is shutting down within about 2 seconds of startup - could be related - ideas? Thanks, Elliott

Now it's more fustrating... Maybe I broke something... Hotting the ornge wire brings the fuel pump to life. And earlier today it would start for about 2 seconds and then shut itself off. Now nothing. The pump is on (can hear it), but no gas at the injectors like there was earlier - and it is getting a spark but it doesn't even seem to be trying to start now. Maybe just that I'm out of starter fluid. :( And the fuel like I didn't replace (the return line) has now sprung a leak. One of the tranny lines is still leaking, the ignition switch seems blown (hotting the ornge), and now something else (it seems). This project has turned really sour. I hate to take it somewhere arround here - that would be hundreds. And I don't see a use to having it in LI. Maybe it's time to sell it for a dollar. Elliott

FFFFFFFFFIIIIIIIIINNNNNNNNNNNAAAAAAAAAALLLLLLLLLLLLLLLLLLYYYYYYYYYYY It's Running!!!!!!!!!!!!!!!!!!!!!!!!!!!! Sounding Great!!! So to get it going I have:

1. Hotted the ornge wire to the fuel pump
2. Shorted across the oil-pressure-switch connector
3. Shorted OBD1 pins A&B (puts it into diagnostic mode). Surprisingly it's not setting any codes. I'm gonna let it run for quite a while now. Thanks for the suggestions guys!!!!!!!!!!!!!!!!! Elliott PS: OK maybe I'll keep it now. May even decide to part with the 96 Sonoma instead of this one.

It's getting frustrating because you are throwing jumpers in and doing other half-ass things to solve the problem, rather than looking for the root.

You have no power at the ECM B fuse. Find out why. Note the names of those 2 fuses: ECM B and ECM I. Those stand for Battery and Ignition. The ECM B fuse is ALWAYS hot. The Orange wire, therefore, is always hot. The orange wire has nothing, repeat nothing in common with the ignition switch. Well, about as much as the dome light, but still....

That same orange wire powers the computer. The computer isn't firing the injectors. There is a clue located somewhere in those last 2 sentences. Stop jumpering and use the old thinking cap. If you have a tone generator, break it out and chase down that wire break. If not, hook up the VOM at the fuse holder and work out from there until you lose continuity.

As a footnote, the injectors are powered from (In order) ECM I fuse (pink/black) to white wire injector 2, red wire injector 1, and then out green and blue to the computer, where the computer grounds them in pulses to fire the injectors. If your pink/black didn't have power, there would be no spark, since the computer would be off. So fix the orange wire. Oh, you might want to trace out the orange wire too, and fix it.

When you have 12 volts on all the orange wire, try and start it. Don't bother until you do. If it still wont start after that, then post back.

It's been running for a couple of hours now --- Thank GOD! And thanks NG! Is the computer fried??? If I pull the AB jumper it dies instantly. I have the oil pressure switch bypassed (and it doesn't make a difference - the connection isn't so good, but no diff (though that may be a test-mode thing)). The idle is too low- rigged a hose clamp to increase it (there's no idle screw on this one). So to pass inspection and drive it...

1. Headlights (install 2nd)
2. Turnsignals/B-Lights (non operating - one bulb comes on)
3. Gas leak (replace return line)
4. Tranny line (either slowing or burning off on the Y-pipe)
5. Ignition Switch (hotting the ONG sucks).
6. Computer ??? (test mode only)
7. Tighten up the timing adjust bolt. AAAAAAAAAAHHHHHHHHHH - so much more encouraging with it finally running - the list doesn't seem so terrible now. This was the one with the home-sanded heads (posted

And YES I'M HAVING A BEER NOW!!!!!