[GUIDE] Diagnosing starting issues - fuel wiring, pump, injectors, ignition & spark..
05-09-14, 09:54 AM
#1
[GUIDE] Diagnosing starting issues - fuel wiring, pump, injectors, ignition & spark..
I don't post here these days, but after chasing an issue yesterday I thought I post the info for anyone who might be searching for these keywords in the future. Hopefully this saves people time when diagnosing no-start issues.
I'm about to fire up a new motor in my car and I made a few other changes at the same time including a new turbo setup, new (used) engine harness, etc. This is an auto-to-manual converted car (done before I purchased it) so I had a lot to look at to finally figure out my problem.
Yesterday, I tried to turn over the new motor but it wouldn't fire...long story short, my fuel injectors weren't getting power. Somehow the engine harness had one bad wire in it - the wire that gives all of them power (not the individual signal wires). After much diagnosis, and finding that was the problem, I ran a new wire along the engine harness from ECU pin 1B (on the second largest yellow connector that plugs into the ECU) to the engine bay, and tapped each of the injector's power into that.
Here are some of the steps I took to diagnose this...you should be able to solve other no-start issues with this checklist:
1) Check EGI fuse & relay. Fuse should not be blown, and EGI relay should "click" when you turn the key forward. If it's too loud to listen, you can feel the "click" by holding the relay while someone else turns the key forward. If either are bad: replace. NOTE: If you have a PowerFC, the commander will not power-on & light-up if the EGI relay/fuse are bad.
2a) Pull a plug wire, connect an extra spark plug (ground out the side of the plug on something) and crank the car to check for spark. If you don't have spark, got to 2b.
2b) If you don't have spark, check that the coil packs are all connected and that the harness is grounded (some versions of the harness do no have a ring-terminal ground). Check the coil packs to make sure there is no corrosion inside where the plug wires insert. Ensure the plug wires are fully inserted into the coil packs. Repeat step 2a to check for spark. If you have an HKS twin power (or similar) disconnect it and repeat step 2a. If still no spark, you may want to check your ignitor unit (refer to the FSM, section "G - Engine Electrical").
2c) Check that you have the crank angle sensors connected properly (white clip connects to the top one, grey to the bottom one). Also make sure the small bracket that holds them in place isn't flipped upside-down (yes, it's possible to do this, especially if you have an aftermarket (e.g. FullFunction) trigger bracket. It dosn't hurt to check the pickups with a multimeter (again, refer to the FSM, section "G - Engine Electrical").
3a) Check for fuel flow (i.e. that the fuel pump is functioning). If you don't have a fuel pressure gauge, you can do a few things: turn the key forward and listen for flow, pull off the feed line (at the firewall) then insert it into an empty bottle and then turn the key forward for a moment to see if fuel comes out, etc.
3b) If you don't have fuel flow, the first thing to check is at the fuel pump bulkhead connector. You can also use a multimeter to probe the power wire (with the car key turned forward) to make sure the fuel pump is getting power. If it is getting power, the problem could be the in-tank wiring or the fuel pump itself - open the fuel tank and inspect both. With the pump removed from the tank, you can apply power to the positive & negative terminals to make sure it's not seized (careful, it may spray fuel that's still inside it...).
3c) If you are getting power at the fuel pump bulkhead connector, check the fuel pump relay (similar to how you checked the EGI relay). You can also remove the relay from the socket and make sure it is getting power at the base terminals. You can also test the relay outside of the car with a power source and multimeter: If the relay is bad, you should replace it. In a pinch, https://www.rx7club.com/3rd-generation-specific-1993-2002-16/bypassing-fuel-pump-relay-334320/#post3335738. After doing so, check again to see if you have power at the fuel pump bulkhead connector (you should, but if you don't then your body harness might have bad wiring between the relay & the bulkhead connector - if that's the case, you might want to try step 4d).
4d) If you're still having problems getting power to the fuel pump, you can always rewire the fuel pump with an aftermarket relay. This method also allows you to get constant voltage to the pump. There are a few guides (search). I'm also attaching a diagram I made, and here are pics of how I did it.
5a) Check that the injectors are getting power/signal. The easiest way is to use a noid light. You can get these at harbor freight for $40. If you don't have them, you can use a multimeter: pull off each injector clip and probe the BLACK wire with your multimeter's RED probe (yes, this black wire is power, not ground as you might assume). With the key turned forward you should see voltage to the black wires on the injector connectors. If you don't have power (this was my problem) and you've already checked everything above, your problem could be a bad wire on the engine harness (this was my problem) or the ECU itself (see step 5c). If that's the case, you need to either repair/replace your engine harness ($$$) or do what I did and run a new wire along the engine harness from ECU pin 1B (on the second largest yellow connector that plugs into the ECU) to the engine bay, and tapped each of the injector's power into that.
5b) If your injectors are getting power, you should check signal for each individual injector. You'll need to probe each of the 4 wires coming out of the ECU: pins 4W, 4X, 4Y, and 4Z with one multimeter probe, and then put the other multimeter probe into the corresponding injector clip's signal wire. Here is a video tutorial for checking wire connectivity: If any of those wires don't ohm they could be broken somewhere along the engine harness. Again, you can either repair/replace the engine harness, or run a wire from the connector that plugs into the ECU to the corresponding injector clip.
5c) If the the wires test fine for connectivity, you might want to check your ECU. You can use a multimeter to check voltage by probing the wires that go into the back of the ECU connector while the connector is plugged into the ECU and the key is turned forward to the "run" position. In order to see injector pulse on ECU pins 4W, 4X, 4Y, & 4Z, you will need to turn the key forward to "start" to engage the starter / crank the motor. Make sure you probe these wires with the black probe of your multimeter (since it is a ground signal) and probe a 12v source with the red probe. Also, check ECU pin 1B with the red probe, and put the black probe to a ground.
Of course, there are other things to check, but I think these are some of the most important things to check when diagnosing a no-start issue. Of course, this diagnosis assumes the starter will actually crank. If you can't even get the car to crank...well that's another story. Things to check for no-crank: car battery, factory security relay, the starter itself / interlock switch (MT) / neutral safety switch (AT), and the ignition switch (where you put the key in).
Other helpful resources:
3rd Gen RX-7 PDF Technical Manuals
FD Annotated Harnesses (Front, Instrument, Dash, Rear, & Floor) + *Index*
Front Harness with connector labels
Engine Harnes with connector labels
Battery Harness with connector labels (starter, alternator, etc.)
1993 FD3S Touring Trim Electrical FSM Index/Supplement (Connector list with pin #s and wire colors)
Hope this helps someone...I spent way too much time chasing one wire yesterday...
I'm about to fire up a new motor in my car and I made a few other changes at the same time including a new turbo setup, new (used) engine harness, etc. This is an auto-to-manual converted car (done before I purchased it) so I had a lot to look at to finally figure out my problem.
Yesterday, I tried to turn over the new motor but it wouldn't fire...long story short, my fuel injectors weren't getting power. Somehow the engine harness had one bad wire in it - the wire that gives all of them power (not the individual signal wires). After much diagnosis, and finding that was the problem, I ran a new wire along the engine harness from ECU pin 1B (on the second largest yellow connector that plugs into the ECU) to the engine bay, and tapped each of the injector's power into that.
Here are some of the steps I took to diagnose this...you should be able to solve other no-start issues with this checklist:
1) Check EGI fuse & relay. Fuse should not be blown, and EGI relay should "click" when you turn the key forward. If it's too loud to listen, you can feel the "click" by holding the relay while someone else turns the key forward. If either are bad: replace. NOTE: If you have a PowerFC, the commander will not power-on & light-up if the EGI relay/fuse are bad.
2a) Pull a plug wire, connect an extra spark plug (ground out the side of the plug on something) and crank the car to check for spark. If you don't have spark, got to 2b.
2b) If you don't have spark, check that the coil packs are all connected and that the harness is grounded (some versions of the harness do no have a ring-terminal ground). Check the coil packs to make sure there is no corrosion inside where the plug wires insert. Ensure the plug wires are fully inserted into the coil packs. Repeat step 2a to check for spark. If you have an HKS twin power (or similar) disconnect it and repeat step 2a. If still no spark, you may want to check your ignitor unit (refer to the FSM, section "G - Engine Electrical").
2c) Check that you have the crank angle sensors connected properly (white clip connects to the top one, grey to the bottom one). Also make sure the small bracket that holds them in place isn't flipped upside-down (yes, it's possible to do this, especially if you have an aftermarket (e.g. FullFunction) trigger bracket. It dosn't hurt to check the pickups with a multimeter (again, refer to the FSM, section "G - Engine Electrical").
3a) Check for fuel flow (i.e. that the fuel pump is functioning). If you don't have a fuel pressure gauge, you can do a few things: turn the key forward and listen for flow, pull off the feed line (at the firewall) then insert it into an empty bottle and then turn the key forward for a moment to see if fuel comes out, etc.
3b) If you don't have fuel flow, the first thing to check is at the fuel pump bulkhead connector. You can also use a multimeter to probe the power wire (with the car key turned forward) to make sure the fuel pump is getting power. If it is getting power, the problem could be the in-tank wiring or the fuel pump itself - open the fuel tank and inspect both. With the pump removed from the tank, you can apply power to the positive & negative terminals to make sure it's not seized (careful, it may spray fuel that's still inside it...).
3c) If you are getting power at the fuel pump bulkhead connector, check the fuel pump relay (similar to how you checked the EGI relay). You can also remove the relay from the socket and make sure it is getting power at the base terminals. You can also test the relay outside of the car with a power source and multimeter: If the relay is bad, you should replace it. In a pinch, https://www.rx7club.com/3rd-generation-specific-1993-2002-16/bypassing-fuel-pump-relay-334320/#post3335738. After doing so, check again to see if you have power at the fuel pump bulkhead connector (you should, but if you don't then your body harness might have bad wiring between the relay & the bulkhead connector - if that's the case, you might want to try step 4d).
4d) If you're still having problems getting power to the fuel pump, you can always rewire the fuel pump with an aftermarket relay. This method also allows you to get constant voltage to the pump. There are a few guides (search). I'm also attaching a diagram I made, and here are pics of how I did it.
5a) Check that the injectors are getting power/signal. The easiest way is to use a noid light. You can get these at harbor freight for $40. If you don't have them, you can use a multimeter: pull off each injector clip and probe the BLACK wire with your multimeter's RED probe (yes, this black wire is power, not ground as you might assume). With the key turned forward you should see voltage to the black wires on the injector connectors. If you don't have power (this was my problem) and you've already checked everything above, your problem could be a bad wire on the engine harness (this was my problem) or the ECU itself (see step 5c). If that's the case, you need to either repair/replace your engine harness ($$$) or do what I did and run a new wire along the engine harness from ECU pin 1B (on the second largest yellow connector that plugs into the ECU) to the engine bay, and tapped each of the injector's power into that.
5b) If your injectors are getting power, you should check signal for each individual injector. You'll need to probe each of the 4 wires coming out of the ECU: pins 4W, 4X, 4Y, and 4Z with one multimeter probe, and then put the other multimeter probe into the corresponding injector clip's signal wire. Here is a video tutorial for checking wire connectivity: If any of those wires don't ohm they could be broken somewhere along the engine harness. Again, you can either repair/replace the engine harness, or run a wire from the connector that plugs into the ECU to the corresponding injector clip.
5c) If the the wires test fine for connectivity, you might want to check your ECU. You can use a multimeter to check voltage by probing the wires that go into the back of the ECU connector while the connector is plugged into the ECU and the key is turned forward to the "run" position. In order to see injector pulse on ECU pins 4W, 4X, 4Y, & 4Z, you will need to turn the key forward to "start" to engage the starter / crank the motor. Make sure you probe these wires with the black probe of your multimeter (since it is a ground signal) and probe a 12v source with the red probe. Also, check ECU pin 1B with the red probe, and put the black probe to a ground.
Of course, there are other things to check, but I think these are some of the most important things to check when diagnosing a no-start issue. Of course, this diagnosis assumes the starter will actually crank. If you can't even get the car to crank...well that's another story. Things to check for no-crank: car battery, factory security relay, the starter itself / interlock switch (MT) / neutral safety switch (AT), and the ignition switch (where you put the key in).
Other helpful resources:
3rd Gen RX-7 PDF Technical Manuals
FD Annotated Harnesses (Front, Instrument, Dash, Rear, & Floor) + *Index*
Front Harness with connector labels
Engine Harnes with connector labels
Battery Harness with connector labels (starter, alternator, etc.)
1993 FD3S Touring Trim Electrical FSM Index/Supplement (Connector list with pin #s and wire colors)
Hope this helps someone...I spent way too much time chasing one wire yesterday...
The following users liked this post:
FL 93 RX7 (11-19-19)
05-12-14, 12:30 PM
#6
Just wanted to add one more bit of info to this. There are a few other systems that can prevent the car from starting. I experienced another one over the weekend...
Map Sensor - The map sensor is critical in allowing the motor to run. If the map sensor dies, or if the wiring (power/ground/signal) is damaged, the car won't be able to start/run. Also, aside from completely dying, the sensor can start to "go bad" and cause incorrect voltage on the signal wire, which will also throw off the map and cause the car to run poorly.
(I believe the reason for this is because the map sensor tells the ECU what part of the map to use for fuel injection / ignition, so if the car is trying to run in the "boost" area of the map when the car is just at idle, the injectors can flood the motor with too much fuel. This is a problem I've had before.)
Just for reference, the three wires on the Map sensor are:
A: 5volt power, supplied by the ECU. Brown with a white stripe.
B: Ground. Black wire with a Light Green stripe.
C: Signal, 0-5volt to ECU. Green with a yellow stripe.
You can test the power & ground wires very easily using a multimeter: With the car key turned forward to "run", the brown wire should read 5v. If it doesn't read 5v, the sensor isn't getting power and won't function. As a simple fix, you can actually tap into the 5v power for the TPS sensor. To test the sensor itself, refer to the FSM (Section F, Page 181) - it tells you exactly how to test the sensor using a multimeter, and the voltages you should get by probing the terminals.
I actually had the wiring go bad for my map sensor. The signal wire (labeled as "C" on the sensor/connector, green wire with a yellow stripe) was good, but the sensor wasn't getting 5v power and the ground wire (labeled as "B", black wire with a light green stripe) wasn't actually grounded. I didn't feel like spending tons of time taking the harness apart to figure out where the wire was damaged, so I simply tapped into the Throttle Position Sensor (TPS) harness, which is located only a couple of inches away. I checked the wiring diagrams, and the TPS and Map sensor both share a 5v power source, so I really wasn't changing anything. After I tapped into the TPS 5v (brown with a white stripe) with a new wire, then grounded the Black wire to the bolt that attaches the map sensor bracket to the firewall. That did the trick, and my map sensor was then reading the correct pressure.
Throttle Position Sensor (TPS) - This is another critical sensor. I've seen cases where a bad TPS has prevented the car from starting at all. Personally, I once had a problem where the TPS connector was corroded and preventing a good connection -- as a result, the car would start & idle, but wouldn't rev past ~3k rpm. Cleaning the connector pins and reinstalling with dielectric grease solved this problem.
To test the TPS, refer to the FSM (Section F, Page 182)
Hope this stuff helps someone.
Map Sensor - The map sensor is critical in allowing the motor to run. If the map sensor dies, or if the wiring (power/ground/signal) is damaged, the car won't be able to start/run. Also, aside from completely dying, the sensor can start to "go bad" and cause incorrect voltage on the signal wire, which will also throw off the map and cause the car to run poorly.
(I believe the reason for this is because the map sensor tells the ECU what part of the map to use for fuel injection / ignition, so if the car is trying to run in the "boost" area of the map when the car is just at idle, the injectors can flood the motor with too much fuel. This is a problem I've had before.)
Just for reference, the three wires on the Map sensor are:
A: 5volt power, supplied by the ECU. Brown with a white stripe.
B: Ground. Black wire with a Light Green stripe.
C: Signal, 0-5volt to ECU. Green with a yellow stripe.
You can test the power & ground wires very easily using a multimeter: With the car key turned forward to "run", the brown wire should read 5v. If it doesn't read 5v, the sensor isn't getting power and won't function. As a simple fix, you can actually tap into the 5v power for the TPS sensor. To test the sensor itself, refer to the FSM (Section F, Page 181) - it tells you exactly how to test the sensor using a multimeter, and the voltages you should get by probing the terminals.
I actually had the wiring go bad for my map sensor. The signal wire (labeled as "C" on the sensor/connector, green wire with a yellow stripe) was good, but the sensor wasn't getting 5v power and the ground wire (labeled as "B", black wire with a light green stripe) wasn't actually grounded. I didn't feel like spending tons of time taking the harness apart to figure out where the wire was damaged, so I simply tapped into the Throttle Position Sensor (TPS) harness, which is located only a couple of inches away. I checked the wiring diagrams, and the TPS and Map sensor both share a 5v power source, so I really wasn't changing anything. After I tapped into the TPS 5v (brown with a white stripe) with a new wire, then grounded the Black wire to the bolt that attaches the map sensor bracket to the firewall. That did the trick, and my map sensor was then reading the correct pressure.
Throttle Position Sensor (TPS) - This is another critical sensor. I've seen cases where a bad TPS has prevented the car from starting at all. Personally, I once had a problem where the TPS connector was corroded and preventing a good connection -- as a result, the car would start & idle, but wouldn't rev past ~3k rpm. Cleaning the connector pins and reinstalling with dielectric grease solved this problem.
To test the TPS, refer to the FSM (Section F, Page 182)
Hope this stuff helps someone.
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10-25-14, 11:53 PM
#8
Bumping this up in case someone sees this thread and not my thread that started with a different issue.
https://www.rx7club.com/3rd-generati...start-1072905/
Im somewhere between the 5b and 5c in the above original post. I have 12volts at the injector but not getting the ground signal. I spliced in a new ground signal wire about 2" out of the ecu from Connector 4Y directly to the ground wire at the rear primary injector, then cranked the car. Still no signal to the noid light plugged into that connector.
I was originally having a no click, no start issue. I bypassed the starter relay and ran a push button start straight form the battery to the starter signal wire. This still requires me to have the key in the on position for the car to start. I'm wondering if whatever was causing my no click, no start issue is also causing me to get no ground signal to the injectors. CAS are fine and I am getting spark. Car starts with starting fluid, injectors are not firing because they are not getting a signal.
Any help appreciated.
Thanks,
https://www.rx7club.com/3rd-generati...start-1072905/
Im somewhere between the 5b and 5c in the above original post. I have 12volts at the injector but not getting the ground signal. I spliced in a new ground signal wire about 2" out of the ecu from Connector 4Y directly to the ground wire at the rear primary injector, then cranked the car. Still no signal to the noid light plugged into that connector.
I was originally having a no click, no start issue. I bypassed the starter relay and ran a push button start straight form the battery to the starter signal wire. This still requires me to have the key in the on position for the car to start. I'm wondering if whatever was causing my no click, no start issue is also causing me to get no ground signal to the injectors. CAS are fine and I am getting spark. Car starts with starting fluid, injectors are not firing because they are not getting a signal.
Any help appreciated.
Thanks,
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