Re: Isolating the Computer, ESC, and Distrib Module

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"John Alt" wrote


Have a look again at your wiring diagram. Like I said, the one that I'm looking at for a 1988 S-10 shows the oil pressure switch in "parallel" with the fuel pump relay. If you can tell me how an open switch in "parallel" with the relay would shut the engine off, that would be great. In "series" I could see it....

I don't see a "grey" wire, the orange wire is 12 volts to the relay, the "tan-white" wire is the wire that goes to the fuel pump and then branches off to become a "prime" wire. Which means you can power up the "tan-white" wire and bypass the relay and apply 12 volts directly to the fuel pump. Meanwhile, the orange wire to relay has a splice that leads off to the pressure switch and the "tan-white" wire also has a splice that leads off to the pressure switch. If you take the pressure switch right out of the equation (open).....that will not affect the orange power wire to the relay, nor the "tan-white" wire from the relay to the pump.
I'm looking at Mitchell on Demand wiring diagrams....I'll have to dig up some factory manuals, but I'd be surprised if there is any difference.
Ian
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Ian, Your diagrams seem to agree with mine. Hank, Yea my degrees are in electrical engineering. More pertinent to this activity is that I also have a 2 year AAS-EET degree in electrical technology. Most of engineering school is all mathematical - so there is some truth in the engineers having very little 'technical' skills for hands-on tasks. But I'm here working on this stuff - so even though you may choose to find fault in my fault isolation skills, I do have them. There are careful ways to proceed and less careful ways - and I have worked on TVs and Tube based amplifiers, etc. The advice someone offered about using a little wire rather than the charger to avoid over-jucing the computer was good - and accepted. The most important engineering skill I know is to not be affraid to stop, think, and accept inputs from others. The most common problem solution in the engineering community comes from the cold observer who says something simple without really looking at the problem at hand (i.e.: "did you measure the ground", etc.). Elliott
shiden_Kai wrote:

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You know, I am sorry I made that comment, You seem to be genuinely trying to either answer the question to the best of your ability or to make the best educated guess. I can appreciate that. What you do to your own stuff is your business, just be careful answering queries on this group. I am a grasshopper too.
--
hank
2004 Chev Z71
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snipped-for-privacy@hotmail.com says...

Well, lets all go to the same diagram. This one will do
http://www.smpcorp.com/download/view/Tt3Q00.PDF
Scroll down to diagram 6. This is a later model with a hot fuel handling module, but it will do. The relay is shown "power off", or NO position. The connection between terminal C and E allows the fuel pump test point to operate. When the relay is energized, connection is made between terminals A and E, and this, as we agree, is in parallel with the oil pressure switch.
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.
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"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
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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'

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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 someone who had paid $200 for it and they couln't figure out how to get it running - I told him how but the battery was dead. Anyway... the parallel circuit seems the common, diagram-reinforced, realistic interpretation of the information. John and Ian's interpretation of the PCM's control of it seem logical too. Elliott
TranSurgeon wrote:

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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

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handling
position.
point
oil
supplied
sec
after
fuel
20
back
would
mentioned
far
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John, The diagram looks equivlant... Arranged quite differently, but as I look it over it seems to connect similarly. The one thing I didn't realize that it illuminates is that the Fuel Pump Prime goes to the OBD1 connector. Anybody know which OBD1 pin is a hot-wire, or better a pin-out list/diagram for the OBD1??? Seems a small jumper in the OBD1 would be a reasonable way to prime the pump - though I may still need to hot the ORG wire for the ESC module (My number 1 speculation at this pint is the ignition switch). Anybody want to buy this truck? It's in MD and I'd make a good deal. It's $200/mo for a parking space in LI, and my wife doesn't want to drive my other truck - seems we'll be buying something else. I think with an ignition SW and some check-out this truck will be very deascent for what it is - though I haven't seen it move under it's own power yet. Comes with another engine (carb'd) and manual tranny, etc. $1K asking price. Thanks, Elliott
John Alt wrote:

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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.
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"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
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snipped-for-privacy@hotmail.com says...

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

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snipped-for-privacy@comcast.net says...

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.
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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.

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Dear God......................
Doc
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John, I'm not sure it was clear... the Celeca described previously had a problem (in the Fuel Pump Relay circuit). The oil pump switch did over-ride the circuit - by cranking the starter long enough to get oil pressure. It was truly a $1 car. Elliott
says...

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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 3/18) - it took too long this time). Elliott
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