neilcase

Hi all,

I bought a 1987 305 TPI with T5 that was sitting under a big redwood tree for 10 years. Lots of corroded wiring. I've gone thru the majority of it but cant get it to start. Here's what I can tell you.

1. Got 12 volts at each injector fuse

2. Got 12 volts at all the hot leads to the ECM excepr for A6 which is ignition but that was not this way until today when I pulled the entire dash out to see about tracking bad grounds. Dont know what I unplugged under there that would cause no voltage at A6.

3. When I jumper an ECM hot pin to both or either of the ECM injector pins (D15 & D16) and test each injector connector I get 11.88 volts both sides of each injector on all the odd side of the engine. But then I get 12.7 volts on one side and 11.7 volts on the other side of every even number injector. Is that normal?

4. I checked all ECM ground pins and they all check out as grounded OK.

The bottom line is that something is preventing 12 volts from running through the ECM to the injectors (not the fuses I checked). Not the ECM I swapped it for a known good one. Not the injector harness as it carries the voltage when the ECM pins are jumped. What am I missing that is preventing the ECM from routing the proper 12 volts to the injectors?

antares57

iTrader: (8)

I am going to assume that the engine cranks, you have spark, but are not getting fuel. Ohm the injectors to see if they are bad. They should all be in the same range. Any under 10 ohms are probably bad and if they are the original it's probably time for a rebuilt or new set. Good luck.

neilcase

Sorry I forgot to add in my post that I DID ohm all the injectors and they ALL came in at pretty much exactly 16 ohms. The problem is that the ECM or some other component is not sending the 12 volts. I know that the 12 volts is supposed to be a constant voltage and the pulse signal is actually a ground signal from the ECM that fires the injector. It's a ground side control but with key on the injectors should be hot at 12 volts at all times and that is not happening. Why?

WhiteBlaze

iTrader: (1)

I had the exact same issue on my LT1. Drove me nuts for awhile. One of commons in the harness were VERY corroded.
Here was my thread https://www.thirdgen.org/forums/ltx-...tation-no.html

neilcase

Unless I'm not thinking about this straight I'm pretty sure its not the harness because as I said, when I jumper an ECM hot pin to both the injector pins at the ECM (pins D15 & D16) and then take a voltage reading I get 11.88 volts on the entire odd number side and 12.7 + 11.7 on the even number injectors. Does this weird voltage on the even side (exactly 1 volt drop from one side of each connector to the other side of each on all of them) give any clue. But the point here is that the harness must be OK because it carries the voltage to the injector connecters when jumpered hot. But as soon as I plug the harness back into the ECM I get zero. Its NOT the ECM cuz I swapped it for a known good one. Its not the ECM grounds because I verified they are all good. Its got to be some related component that is preventing the ECM from sending the 12 volts to the injectors.

What other sensors/ switch/relay etc would stop the ECM from sending the voltage? I suck at reading wiring diagrams but I'm learning slowly. THanks

Six_Shooter

iTrader: (2)

The ECM grounds the injectors. The injectors get their positive voltage from the fuse/ignition directly. To measure this on a DMM an AC setting needs to be used, while running/cranking.

neilcase

At the moment I'm not trying measure or even detect the pulse signal. I'm only trying to GET the initial 12 volts from the ECM to the injectors. Are you saying that cant be measured unless its cranking or running? I was under the impression that the initial 12 volts should be there with just key on?

RBob

iTrader: (1)

As 6-shooter posted, the ECM only provides a ground. The +12 volts to the injectors comes from two fuses. INJ1 and INJ2, in the fuse block under the dash.

Note that D15 and D16 are tied together inside of the ECM. There is only one injector driver in the '7165 ECM. Sounds like some terminals/pins on the ECM may be corroded.

RBob.

neilcase

OK I understand all that (I think) except for this. Based on what you are saying then, there should always be 12 volts at the injectors from the fuses with KEY ON no matter what the ECM is or isn't doing? I understand the PULSE comes from the ECM grounding the circuit. But what I'm getting at is this... where does the initial 12 volts come from? And does it route through the ECM and if so is there some other "trigger" or signal the ECM needs in order to supply the 12 volts to the harness and then on to the injectors. Keep in mind that I know the harness (tested) and ECM (swapped) are both good.

I appreciate all you who have responded, Ive learned a little from you all but still have not found my answer.

eseibel67

No, the 12v that the injectors need is not routed through the ECM. The 12v supply comes from the 2 fuses.

WhiteBlaze

iTrader: (1)

Power comes directly from the fuses. They should have power as long as the key in "on" or "start".

neilcase

Fantastic. Now I got something new I can hunt for. Is it correct to say then that in theory if I yanked the ECM and sat it in the backseat that I should still be getting 12 volts with key on at the injectors? And if so any ideas why I am not?

But.... why would I get the 12 volts when I hot jump the orange (hot) wire at the ECM to either of the injectors pins of the ECM (D15 & D16). Is that just because it essentially completes the circuit? It seems to me that the fuses supply the hot 12 volts but unless that voltage makes it's way around again via the ECM then we have no completed circuit? But that doesn't happen. Am I envisioning this wrong?

Shoulda paid better attention in my electronics classes.

RBob

iTrader: (1)

From what I can tell, two wires (both PNK/BLK) exit the fuse block and go across the dash to the passenger side. Go through connector C221 (near ECM), pins A & D and join up with the EFI harness to go out to the engine.

RBob.

eseibel67

Not sure what the consequences of of applying 12v directly to pins D15 & D16 might be, hopefully you didn't fry the computer. The computer pulses those two pins to ground to complete the circuit and fire the injectors.

neilcase

RBob I traced the small pink wires on both the diagram and physically on the car and found that they do indeed run straight thru the C221 connector and right into the injector harness, bypassing the ECM. Back at the fuse block I see a much heavier pink wire that appears to provide the power to the two fuses. I cant physically trace that wire due to it being concealed too much so I referred to the schematic. I suck at reading schematics and I am at a dead end. Any idea where this terminates based on the snapshot below?

https://www.sugarsync.com/pf/D7039745_708_066283794

RBob

iTrader: (1)

The heavy pink wire originates at the ignition switch. Run & crank positions.

The ignition switch is fed power via a heavy red wire that originates at the fusible links (on starter solenoid). It gets into the interior via the bulk head connector at the fuse block.

RBob.

neilcase

Great, I'm learning this stuff bit by bit and all you guys have been a great help. Just wanted to let you all know that it is appreciated. Hopefully I can pay it forward someday somehow. I'll stay on the forums sharing my experiences and what I've learned.

Anybody know if there is a source that tells a person what and where all the connectors are that are found in the diagrams? For instance I always wondered what and where the C221 was and I finally found it partially by help from here and partially just by snooping through it all. But is there a list somewhere that tells me what and where to find them all? That would be so helpful.

RBob

iTrader: (1)

The factory service manual (FSM) is about the only source. Although sources such as Michell and alldata also has that information. They are subscription services designed for mechanics that work on cars every day.

RBob.

L98_383_Stroker

One comment on measuring the voltage at the injectors with a volt meter. Connect the voltmeter negative lead to the vehicle ground. Connect the voltmeter positive lead to the injector terminal. If you put both leads in the injector plug you will measure zero volts. One injector termila is positive to the injector fuse (as everyone is saying, always 12v). The other is pulsed ground. Many people put a test light across the injector terminals to see if it is pulsing when the engine is turning over.

neilcase

NEW FINDING: Guys tell me what you think of this. Tested for 12 volts at the Inj1 & Inj2 fuse terminals with key in run position. 4 of 5 times it was good at 12 volts but sometimes I got nothing. Next test: While getting the 12 volts at an Inj1 or 2 fuse terminal, I turn key to start and the 12 volts goes away completely and when the key springs back to RUN it stays gone! So..

Question #1 - is it supposed to go away at start position? I wouldn't think so.

Question #2 - if it is supposed to go away at start I certainly wouldn't think it should stay gone when spring back to RUN? How the hell would the car stay running?

MORE: So obviously it appears to be a faulty intermittent Ign switch? At the moment It's giving 12 volts (next time it might not). I was about to write that one Inj was getting 12 volts at C221 and at the injector while the other was only getting 8.5 volts. But before I wrote that I decided to take another look at the fuse box. Decided that the downstream pinch connector on the fuse 1 was sloppy and didnt pinch good anymore. Fiddled with that now I have 12 volts to ALL injectors!!! Finally.

So unless you guys have other thoughts do you think its safe to say that this ghost in the machine is a faulty ignition switch?

Please remember that I'm electronically challenged but learning from all of you. Thanks

WhiteBlaze

iTrader: (1)

Think you found your issue. You need 12 volts in start as well, otherwise you'll never get fuel to start the engine.

neilcase

I hope I found it. I tore half the car apart and took out the entire dash chasing gremlins. Does that also explain why I would measure 12v at the coil pink wire and then that would drop to nothing while cranking? And I think it also explains why I would sometimes hear the fuel pump prime and not at other times (just thought my hearing was bad)

Odd thing is that the key switch feels pretty tight. But when I put a DMM on it and then wiggle it a bit it cuts in and out (mostly out).

Are there any solid definitive tests you can suggest to nail it down to the IGN switch?

Hey do you think I can get in on the big lawsuit against GM for bad IGN switches? Looks like it might go back farther than they are admitting!!

morgsie

iTrader: (1)

I would try adjusting the ignition switch first, if not simply replace it. The new one will need to be adjusted when you install it FYI.