No noid light pulses
Thread Starter
Intermediate
Joined: Nov 2016
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No noid light pulses
have a 1985 Corvette with a 1990 engine except for the intake manifold and runners which were swapped from my original 1985 engine when the dealership installed the new engine in 1990. This past year, my engine began running worse and worse with each startup. I checked typical causes like plugs, cap and rotor to no avail. Eventually the engine refused to start. I found that the 5amp fuse protecting the right bank of injectors was blown so I replaced it and still no start. I checked the resistance on the GM multitech injectors and the values were all over the spectrum. I spoke with Jon at FIC and he said to replace them with Delphi injectors along with a new fuel pressure diaphragm. I removed the multechs and tested them. Out of the 8 just the cold start and two others were functional. The others were either stuck open or did not open. I installed the 8 Delphi injectors, new diaphragm, and intake gaskets and expected the engine to fire up with the first crank. To say that I was disappointed with the no start is an understatement. The first second of each attempt to start the engine resulted in a brief start followed by just cranking. After five or 6 attempts I noticed I had raw gas leaking out of one muffler. I changed the diluted oil and filter and pulled the plugs and injected Marvel Mystery oil into each cylinder to hopefully prevent further cylinder scoring. I pulled the injector and fuel pump fuses and squirted some starting fluid into the intake. The engine started right up and ran for a couple of seconds. I removed the injector electrical connectors and with the key on, I grounded each injector harness contact. On the passenger side, one pin of each injector harness showed 12 volts to ground. The other pin showed zero. Same result with the connectors on the drivers side. This result makes sense to me and to Jon at FIC but the FSM says both pins should show voltage to ground. When I connected a noid light to each injector on the passenger side, cranking showed pulses as expected. On the drivers side, no pulses when cranking except for the cold start injector. If all 8 injectors fire at the same time, I figure I must have a short or open circuit on the drivers side. I checked for continuity between each injector harness pin and one pin in all 9 connectors show continuity with ground. I have no idea where to look next and hope that one of you electrical circuit sleuths can offer advice. Sorry for the long post but I did not want to waste your time with not offering sufficient information regarding history, diagnostic tests and results.
Drifting
Joined: Aug 2019
Posts: 1,339
Likes: 225
One pin for each injector should have 12 volts. The ECM provides the ground on the other pin. If you don't have power, you must have a short, as indicated by your blown fuse. You need to back track all of the power wires to each injector to check where the power open or short is located. If it's a bank fired system, if one branch is shorted, it will take out the whole bank. Let's hope the short didn't take out the driver in the ECM. Test before you replace anything else.
Team Owner
Joined: Jul 2004
Posts: 28,475
Likes: 3,291
From: Hartford WI
My problem was that the driver side valve cover cut the wires and shorted out that bank and it does exactly as you had. Check the harness at that dead side and see if something is broke. The injectors are bank fired. IOW, right side fires and then left side, etc, etc. It isn't all 8 but 4. Change the fuse and disconnect all but the first one. I think it should show 12V on one of the pins. Connect it and go to the next and so on. Maybe that will tell you if there is something wrong?
Thread Starter
Intermediate
Joined: Nov 2016
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Likes: 3
No noid lightnpulses
One pin for each injector should have 12 volts. The ECM provides the ground on the other pin. If you don't have power, you must have a short, as indicated by your blown fuse. You need to back track all of the power wires to each injector to check where the power open or short is located. If it's a bank fired system, if one branch is shorted, it will take out the whole bank. Let's hope the short didn't take out the driver in the ECM. Test before you replace anything else.
Thanks for the help! The aspect of this problem that does not make sense to me is when the key is in the on position, I get 12 volts from one pin on each injector harness. Not just the injectors on the passenger’s side but those on the driver’s side as well. How could this be possible with a short or open circuit? I did unplug both the 24 and 32 pin connectors from ECM and performed a continuity test between the ground pins in those connectors and a good grounding point on the engine. I verified that the ECM is well-grounded. The wiring schematic shows that injector circuits 467 and 468 have a factory splice. Do you know where that splice is located? Are there any fusible links that I need to check?
Thread Starter
Intermediate
Joined: Nov 2016
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Good suggestion. I will check the firewall side of the engine for any exposed or cut wires. I guess I will need to remove the distributor cap and plug wires to clear out the mess of tubes and wires back there.
Thread Starter
Intermediate
Joined: Nov 2016
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Thanks! Yes, both sides get power with key on but noid light shows no pulses on driver’s side injectors during cranking. Is there any relationship between the presence or absence of pulses and the 4 pin and 6 pin connectors attached to the distributor?
Oil Producer
Joined: Apr 2014
Posts: 9,375
Likes: 2,737
my understanding is that the reference pulse travels from the distributor, through the icm, to the ecu, back to the icm, which controls timing to the plugs. i may be wrong.
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Melting Slicks
Joined: Feb 2003
Posts: 2,677
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From: Saskatoon Sask.
Thanks for the help! The aspect of this problem that does not make sense to me is when the key is in the on position, I get 12 volts from one pin on each injector harness. Not just the injectors on the passenger’s side but those on the driver’s side as well. How could this be possible with a short or open circuit? I did unplug both the 24 and 32 pin connectors from ECM and performed a continuity test between the ground pins in those connectors and a good grounding point on the engine. I verified that the ECM is well-grounded. The wiring schematic shows that injector circuits 467 and 468 have a factory splice. Do you know where that splice is located? Are there any fusible links that I need to check?
Thread Starter
Intermediate
Joined: Nov 2016
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To find the open wire, I am thinking of conducting a continuity test between pins D15 and D 16 of the electrical connector plugged into my ECM and each of the connectors on the injector harness. If all check out, is there any way of checking the injector driver other than replacing the ECM?
Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.
To find the open wire, I am thinking of conducting a continuity test between pins D15 and D 16 of the electrical connector plugged into my ECM and each of the connectors on the injector harness. If all check out, is there any way of checking the injector driver other than replacing the ECM?
I don't have a schematic but I am going to assume that D15 and D16 go 1 to each side. You say that the passenger side works so don't mix up the two wires when checking continuity. As far as checking the drivers, I can't tell you that. Maybe an electronics guru will chime in.
Thread Starter
Intermediate
Joined: Nov 2016
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Thanks. I await any help Forum readers can offer. I’ve been a shade tree mechanic for 60 years and learned early on that exhaustive testing is a far better route than trial and error replacement of parts. I will replace the ECM as a last resort.
Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.
To find the open wire, I am thinking of conducting a continuity test between pins D15 and D 16 of the electrical connector plugged into my ECM and each of the connectors on the injector harness. If all check out, is there any way of checking the injector driver other than replacing the ECM?
Thread Starter
Intermediate
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No mood pulses
Thanks for the information. I will check those web sites to see what they offer.
Drifting
Joined: Aug 2019
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One method to determine if the ECM driver is bad is to hook a noid light to 12 volts, then hook the other end to the ECM terminal directly. If the noid light doesn't flash then the ECM driver is bad.
If it does flash, then you have a wiring/connector problem. Just curious, have you used a scan tool to get any data? I don't like continuity tests, because all they'll tell you is if there's an open. You need to determine wire/connector integrity by doing a voltage drop test(no more than 1/2 volt). If you decide to get a new ecm, just make sure they're reputable. Some do a "spray and pray" job without any testing.
If it does flash, then you have a wiring/connector problem. Just curious, have you used a scan tool to get any data? I don't like continuity tests, because all they'll tell you is if there's an open. You need to determine wire/connector integrity by doing a voltage drop test(no more than 1/2 volt). If you decide to get a new ecm, just make sure they're reputable. Some do a "spray and pray" job without any testing.
Thread Starter
Intermediate
Joined: Nov 2016
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I like your idea and I actually thought about eliminating the wire harnesses from the equation by checking for noid light pulses coming directly out of the ECM but I have yet to figure out how to go about doing it. If I disconnect the 32 pin connector from the ECM to directly attach the noid light to terminal D15 or D16 the ECM won’t be powered up and won’t show any pulses at all. If I leave the harnesses connected I would have to puncture wire insulation to tap the wires leaving the ECM connector in order to attach the noid light and I hate compromising the integrity of those wires. No, I do not have access to a scan tool for my OBD1 terminal. What do you recommend I purchase?
Melting Slicks
Joined: Feb 2003
Posts: 2,677
Likes: 812
From: Saskatoon Sask.
I like your idea and I actually thought about eliminating the wire harnesses from the equation by checking for noid light pulses coming directly out of the ECM but I have yet to figure out how to go about doing it. If I disconnect the 32 pin connector from the ECM to directly attach the noid light to terminal D15 or D16 the ECM won’t be powered up and won’t show any pulses at all. If I leave the harnesses connected I would have to puncture wire insulation to tap the wires leaving the ECM connector in order to attach the noid light and I hate compromising the integrity of those wires. No, I do not have access to a scan tool for my OBD1 terminal. What do you recommend I purchase?
I don't recall how the connector is manufactured. Are you not able to back-probe right at the connection?
Drifting
Joined: Aug 2019
Posts: 1,339
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I like your idea and I actually thought about eliminating the wire harnesses from the equation by checking for noid light pulses coming directly out of the ECM but I have yet to figure out how to go about doing it. If I disconnect the 32 pin connector from the ECM to directly attach the noid light to terminal D15 or D16 the ECM won’t be powered up and won’t show any pulses at all. If I leave the harnesses connected I would have to puncture wire insulation to tap the wires leaving the ECM connector in order to attach the noid light and I hate compromising the integrity of those wires. No, I do not have access to a scan tool for my OBD1 terminal. What do you recommend I purchase?