Help! No start problem on 84

[JohnGrawcock]

The other day My 84 suddenly decided it didn't want to start after running just fine earlier in the day. Now it cranks but won't start.

By watching in injectors during cranking no know I'm getting no fuel. I also do not hear the fuel pump running at key on.

I checked the fuel pump fuse. It is good.

I applied 12v to terminal G of ALCL. Still don't hear fuel pump or the click of a relay engaging it. This may not be conclusive because I never hear the pump running on my 82 either and I know it's working. However, I should hear the relay.

In checking the fuel pump circuit, I noticed that the check engine light is not coming on with the key in the run position. Now I'm thinking no power to ECM.

The manual shows a Cold Start Module that is on 84 only. Apparently this module deliberately blows the ECM fuse after some fixed number of operating hours. Unfortunately, I can't find the fuse to check it. All the fuses in the fuse panel are good. Is there a separate ECM fuse located elsewhere like the 82?

Anyone have suggestions?

 

[gmjunkie]

The other day My 84 suddenly decided it didn't want to start after running just fine earlier in the day. Now it cranks but won't start.

By watching in injectors during cranking no know I'm getting no fuel. I also do not hear the fuel pump running at key on.

I checked the fuel pump fuse. It is good.

I applied 12v to terminal G of ALCL. Still don't hear fuel pump or the click of a relay engaging it. This may not be conclusive because I never hear the pump running on my 82 either and I know it's working. However, I should hear the relay.

In checking the fuel pump circuit, I noticed that the check engine light is not coming on with the key in the run position. Now I'm thinking no power to ECM.

The manual shows a Cold Start Module that is on 84 only. Apparently this module deliberately blows the ECM fuse after some fixed number of operating hours. Unfortunately, I can't find the fuse to check it. All the fuses in the fuse panel are good. Is there a separate ECM fuse located elsewhere like the 82?

Anyone have suggestions?

Check the fusible links behind the battery,also I believe there may be 1-2 on the starter of a 84 too!!
PS The fuel pump relay may also be the problem!!
Sorry,I don't mess with Crossfires much!!

 

[JohnGrawcock]

I checked the fusible links. I found 3 behind battery. All were good.

I'm looking at the voltage at the fuel pump connector now. With the key on the red center wire is hot. The black wire reads low resistance to ground and the third wire is a much higher resistance to ground. The voltage on the red wire goes to zero with the key off. This seems to imply the relay is working.

I'm really thinking the lack of check engine light is the key here. I just wish I had a better schematic to know where to poke. The crap manual I have mentions this cold start module but doesn't show where it is. The schematics also don't include the power path to the ECM. Don't you love it when your flying blind?

 

[badglas]

No check engine light

This is the procedure to determine the no check engine light problem. You need to start here. Post your findings and I'll try to help from there. I can provide the schematic you will need based on these tests. I am a Cross-Fire specialist and will do what I can to help you find the problem.

Ron Kane
Benchmark Corvette Service

1. With ignition on and engine off, connect test lamp between white ECM connector pin 20 and 12 volt power source.
2. If test lamp lights, inspect ``Check Engine'' light bulb and replace if necessary. If bulb is satisfactory, check circuits 1 and 419 for an open and repair as necessary.
3. If test lamp does not light, connect test lamp between white ECM connector pin 16 and ground. If lamp does not light, check circuit 439 for open or short and repair as necessary.
4. If test lamp lights, connect lamp between white ECM connector pin 10 or 15 and ground. If test lamp does not light, check continuous battery circuit for an open or short and repair as necessary.
5. If test lamp at pin 10 or 15 lights, check ECM engine ground circuits 450 and 450R for an open or short and repair as necessary. If circuits are satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary. Before replacing ECM, measure resistance between solenoid terminals of canister purge, air switch and air divert solenoids. Replace any solenoid which measures less than 20 ohms resistance.

 

[badglas]

cold start module location

 

[badglas]

cold start module location

The Cold Start Module / Elapsed Time Sensor is located behind center of I/P, taped to the I/P harness.

Hope this helps.

Ron Kane
Benchmark Corvette Service

 

[badglas]

Flying blind

Hope these help to shed some light to fly by.

Ron

 

[JohnGrawcock]

Red X's

I'm getting red X's rather than the posted diagrams. What the heck was the setting to correct that? I don't remember.

 

[JohnGrawcock]

This is the procedure to determine the no check engine light problem. You need to start here. Post your findings and I'll try to help from there. I can provide the schematic you will need based on these tests. I am a Cross-Fire specialist and will do what I can to help you find the problem.

Ron Kane

Benchmark Corvette Service

1. With ignition on and engine off, connect test lamp between white ECM connector pin 20 and 12 volt power source.
2. If test lamp lights, inspect ``Check Engine'' light bulb and replace if necessary. If bulb is satisfactory, check circuits 1 and 419 for an open and repair as necessary.
3. If test lamp does not light, connect test lamp between white ECM connector pin 16 and ground. If lamp does not light, check circuit 439 for open or short and repair as necessary.
4. If test lamp lights, connect lamp between white ECM connector pin 10 or 15 and ground. If test lamp does not light, check continuous battery circuit for an open or short and repair as necessary.
5. If test lamp at pin 10 or 15 lights, check ECM engine ground circuits 450 and 450R for an open or short and repair as necessary. If circuits are satisfactory, fault is in ECM or ECM connector. Repair or replace as necessary. Before replacing ECM, measure resistance between solenoid terminals of canister purge, air switch and air divert solenoids. Replace any solenoid which measures less than 20 ohms resistance.

Thanks for posting Ron. I completed these steps and found no power at the battery inputs. Can you give me the circuit path from the battery to white ECM connector pins 10 and 15?

 

[hdcwagsvette]

Had this problem last month and replaced the ignition module. Starts every time now.

 

[badglas]

Power path

Pins 10 and 15 are both fed from circuit 340 which is a battery fed fusible link. It will be a red #2 wire. I am unsure of the location of this fusible link. It will be behind the battery or at the starter. I will check the book in the morning and post a location if it is given.

I suspect you may have a shorted oil pressure switch, which is part of circuit 340. That would explain the fusible link burning.

Ron

 

[badglas]

Fusible Link

According to the 84 electrical supplement this fusible link comes off the battery at or behind the battery. From the illustration it uses a weather pack connector at C341. Check the connector for corrosion if the link tests good.

Ron Kane
Benchmark Corvette Service
217-726-3840

 

[JohnGrawcock]

It's fixed


I fixed the problem the other day so I thought I'd close this out.

I had an open circuit in the continuous battery supply to the ECM. This was correctly identified following the procedure posted by Ron Kane.

As mentioned previously in this thread there are three fusible links behind the battery in an 84. The two red links go to the bulkhead connector. The one that feeds this circuit is orange. It comes off a pigtail on the positive battery cable and loops under the master cylinder and into a small conduit where it meets the heavier orange wire that carries it to the ECM connector. My problem turned out to be corrosion at the connector that that tied the fusible link to the battery cable pigtail.​