Crank but no start..

Hello all,

So i recently got my car back together after finding out that when i bought the car the timing belt was off on the rear, so i got everything fixed and buttoned up to take it down the road. Car drove good and i had my first chance to actually get on it, second pull the car cuts off in the upper rpm range and i coast back down to my driveway. Get stopped and car will crank but not start, so i get out look around, see nothing, get back in the car and it starts, so i drive it up to my garage. Since then the car will not start at all, i've tried to do all the diagnosing i know and am now looking for help.

Here's what i've done so far: (my car is a 91 5spd, stock except i/h/e)
-fuel pressure check, not getting any pressure when cranking
-replace main relay
-check voltage at resistor (nothing)
-jumper wired the yellow wire to blk/yellow on fuel pump relay and i could hear pump come on
-checked voltage at the wires at main relay, all get voltage except blk/white, service manual says replace fuse #7 but i replaced it and didn't fix it

I can't hear any of the relays clicking on or the fuel pump but don't know where to go from here.

Sounds like ignition switch failure. This is as common as the main FI relay failure.

Is there a way to test it? I didn't figure it would crank if it was the switch

Maybe change your fuel filter...could be clogged.

Filter is brand new. It's definitely an electrical problem

The #7 fuse and the black/white wire to the Main relay only get power when the starter motor is engaged. So, unless you were cranking the engine, you should not expect to see 12 v on the Blk/wh wire. If you were cranking the engine and you did not have 12 v on the blk/wh wire, then you have a bad connection or broken wire somewhere. The engine definitely will not start unless there is 12v on the blk/wh wire at the main relay during the cranking process. The #7 fuse also powers up the bulb check circuit in the gauge cluster. Is the bulb check operational?

Ahh gotcha, didn't check it during cranking just "on" position. The dash lights and bulbs work fine. I ordered a new fuel pump relay, will be here in a few days

When my ignition switch failed, the car would crank and fire, then stall when I let go of the key. In other words, it was the "on" position that failed; "start" was still working.

elijahcole92 said:

Ahh gotcha, didn't check it during cranking just "on" position. The dash lights and bulbs work fine. I ordered a new fuel pump relay, will be here in a few days

Click to expand...

Why did you order a new fuel pump relay? The car should start just fine without the fuel pump relay. The purpose of the fuel pump relay is to short circuit the fuel pump resistor at high engine load. The actual switching of the fuel pump is done by the main relay.



View attachment 124501

When you jumpered the yellow to the blk/yel on the fuel pump relay, you applied 12 v to the supply side of the pump resistor causing the pump to power up, so you know that the resistor and pump are OK. Since your FI relay is new and presumably OK, I would, as cmthomson suggests, go and test the operation of your ignition switch as per the procedure set out in the service manual and hope that's the problem as the alternatives are potentially worse!

Gotcha, didn't know that before hand. I pulled the switch and cleaned the contacts, still not starting and the fuel pump isn't coming on at all unless i use a jumper wire on the relay pins, but it still doesn't crank then. Is there any way to test the ecu to see if it's getting power or working correctly?

Old Guy said:

Why did you order a new fuel pump relay? The car should start just fine without the fuel pump relay. The purpose of the fuel pump relay is to short circuit the fuel pump resistor at high engine load. The actual switching of the fuel pump is done by the main relay.



View attachment 124501

When you jumpered the yellow to the blk/yel on the fuel pump relay, you applied 12 v to the supply side of the pump resistor causing the pump to power up, so you know that the resistor and pump are OK. Since your FI relay is new and presumably OK, I would, as cmthomson suggests, go and test the operation of your ignition switch as per the procedure set out in the service manual and hope that's the problem as the alternatives are potentially worse!

Click to expand...

Just to confirm, from your first post I gather the starter motor is engaging and turning the engine? If not, then time to check the security system interlock and the clutch interlock switch.

Do you have an aftermarket security system that could be killing power to the main FI relay?

Check the yel/blu terminal on the main relay. You should have 12 v there all the time (it is un switched). If you don't, check the #18 fuse.

There are three blk/yel wires connected to the main relay (always helpful)! Rather than try to describe it, I have attached the test procedure for the main relay. It describes the pin numbers on the relay that you want to test for voltage and the procedure and what to check if you don't get voltage.

As a quick check. The main FI relay has two relays inside it. One relay is switched on by the key and powers up the ECU. The second relay powers up the fuel pump when it gets a ground signal from the ECU; however, the ECU has to be powered up for that to occur. Have someone listen to the main relay when you turn the ignition switch just to the run position. You will have to listen very carefully in a low noise environment as the relays are not particularly noisy (at least mine aren't). If you hear a click; but, the fuel pump does not engage, then the first relay may be energizing; but, the second relay may not be getting the ground signal from the ECU. If you hear absolutely no sound from the relay, then the first relay is not powering up and I think you may have a bad connection someplace or a faulty main relay. You will have to go through the complete relay test procedure to track it down.


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If the relay test procedure confirms that the main relay is good and most importantly the connections to the main relay are good, then it is time to look at the connections to the ECU.

Yes it is cranking and turning the engine. No aftermarket system. I did the tests for the main relay connectors and they all got voltage correctly, i checked the fuses it mentioned as well but they're all fine. I have not tested the main relay itself as it is literallly brand new, bought it when i first started having this problem. Yes yel/blu has 12v as well

Old Guy said:

Just to confirm, from your first post I gather the starter motor is engaging and turning the engine? If not, then time to check the security system interlock and the clutch interlock switch.

Do you have an aftermarket security system that could be killing power to the main FI relay?

Check the yel/blu terminal on the main relay. You should have 12 v there all the time (it is un switched). If you don't, check the #18 fuse.

There are three blk/yel wires connected to the main relay (always helpful)! Rather than try to describe it, I have attached the test procedure for the main relay. It describes the pin numbers on the relay that you want to test for voltage and the procedure and what to check if you don't get voltage.


View attachment 124601

View attachment 124600

If the relay test procedure confirms that the main relay is good and the connections to the main relay are good, then it is time to look at the connections to the ECU.

Click to expand...

elijahcole92 said:

Yes it is cranking and turning the engine. No aftermarket system. I did the tests for the main relay connectors and they all got voltage correctly, i checked the fuses it mentioned as well but they're all fine. I have not tested the main relay itself as it is literallly brand new, bought it when i first started having this problem. Yes yel/blu has 12v as well

Click to expand...

OK

The next is a bit of a pain. With the ignition switch in the run position, check that you are getting 12v on the yel/blk wire on the #3 terminal of the relay. This is the 12v power out to the ECU. If that seems to work out, if you want, you could confirm the ECU is getting power by pulling one of the coils and spark plugs and doing a visual check for spark while cranking the engine with the plug ground held against the block.

If you are not getting any spark, first make sure that you are getting 12v on each of the black yellow wires that supplies each coil. If you have 12v there, then the ECU or ignitor is not switching the coils. If you were getting 12 v on the #3 terminal on the main relay, you are going to have to trace that to the ECU and make sure that it is getting the 12v. Could be a bad connection someplace. If you are getting 12 v to the ECU; but, you are not getting any spark, time to start considering that you might have an ECU problem.

Assuming that you get spark, the next test is to put the voltmeter on the green/black wire on the main relay. Should be terminal 8. When you first switch the ignition switch to the run position, the voltage on this terminal should go to zero for about 2 seconds (ECU is priming the fuel pump) and then returns to 12 volts. The green/blk wire goes to the ECU and the ECU connects it to ground to complete the circuit that energizes the fuel pump portion of the relay. If you are not getting this momentary ground on ECU power up, you have a bad connection to the ECU or there is a problem with the ECU. If you are getting this momentary ground, but, the pump is not powering up, the ECU is probably good and you have a problem with your main relay or the wiring in the main relay socket.

Okay so with it in run position and relay disconnected i got this:
yel/blk #3 9v
blk/yel #6 12v
yel/blue 12v
blk/yel #7 0v

Green/black #8 stays at 10v with main relay disconnected, no drop.

My spark tester doesn't fit well on the nsx coil and i didn't have anyone to watch so i didn't try cranking it to see for spark. But i don't hear any clicking at all when i turn the key on.

You have 12 v on pin #6 when the ignition switch is turned to run. If the ground on pin #2 is good (use the resistance setting on your multimeter to confirm that pin #2 has a good connection to ground), the primary relay in the main relay which energizes the ECU should be operating (if the relay is good). In order to get an accurate measurement of the voltage on pin #3 which powers up the ECU, the relay needs to be in the socket. In order to get the voltage measurement with the relay in the socket, you will have to back probe the socket on pin #3 . This requires the use of something stiff like a straightened paper clip which you can stick into the back of the socket on pin #3 and take a voltage measurement.

With the relay in the socket, switch the ignition to run. If you have 12 v on pin #6 and the pin #2 ground is good, the relay should energize and you should get 12v on pin #3 . If you don't then the relay is dead or the socket is defective.

Only if you are getting 12 v on pin #3 should you go to this next test of the fuel pump control. If you are not getting 12 v on pin #3 there is no point since the ECU is not getting a power up signal. In order to test the operation of the fuel pump control by the ECU (the grn/blk wire) you will again need to have the relay in the socket. You will again have to back probe pin #8 (grn/blk wire) to get the voltage measurement. With the back probe in place, turn the ignition key to run and you should see the voltage drop to zero when the ECU provides a ground to the fuel pump relay. After about 2 seconds the voltage should jump up to around 12v when the ECU removes the ground connection and the relay floats back up to 12 v.

Old Guy said:

You have 12 v on pin #6 when the ignition switch is turned to run. If the ground on pin #2 is good (use the resistance setting on your multimeter to confirm that pin #2 has a good connection to ground), the primary relay in the main relay which energizes the ECU should be operating (if the relay is good). In order to get an accurate measurement of the voltage on pin #3 which powers up the ECU, the relay needs to be in the socket. In order to get the voltage measurement with the relay in the socket, you will have to back probe the socket on pin #3 . This requires the use of something stiff like a straightened paper clip which you can stick into the back of the socket on pin #3 and take a voltage measurement.

With the relay in the socket, switch the ignition to run. If you have 12 v on pin #6 and the pin #2 ground is good, the relay should energize and you should get 12v on pin #3 . If you don't then the relay is dead or the socket is defective.

Only if you are getting 12 v on pin #3 should you go to this next test of the fuel pump control. If you are not getting 12 v on pin #3 there is no point since the ECU is not getting a power up signal. In order to test the operation of the fuel pump control by the ECU (the grn/blk wire) you will again need to have the relay in the socket. You will again have to back probe pin #8 (grn/blk wire) to get the voltage measurement. With the back probe in place, turn the ignition key to run and you should see the voltage drop to zero when the ECU provides a ground to the fuel pump relay. After about 2 seconds the voltage should jump up to around 12v when the ECU removes the ground connection and the relay floats back up to 12 v.

Click to expand...

Okay. So just tested it and 3 is getting power with relay plugged up. Geeen /blk is getting power with key on but it doesn't drop at all just stays at 10v (think my battery is weak)

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Actually pin 3 is only getting 9v. What reading should I get if the ground is good? On pin 2

elijahcole92 said:

Okay. So just tested it and 3 is getting power with relay plugged up. Geeen /blk is getting power with key on but it doesn't drop at all just stays at 10v (think my battery is weak)

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Actually pin 3 is only getting 9v. What reading should I get if the ground is good? On pin 2

Click to expand...

Pin 1 on the relay is the yel/blu wire and you said that you were getting 12 v on it when you tested it. When the relay gets energized, pin #3 gets connected to pin #1 . If when you switch the ignition to run, you still have 12 v on pin#1 and 9 v on pin #3 , you have an internal problem with the relay. There should next to no voltage difference between pin #1 and pin #3 .

I am thinking that the ECU should still be able to operate with an input voltage of 9 v. Most digital electronics operate at 5 v at the device level. That said, if you have 12 v on pin #1 and 9v on pin #3 at the same time, you have a relay problem.

If pin #8 is not momentarily dropping to 0v when you first switch the ignition switch to run (it only goes to 0v for about 2 sec), then one of the following is at play:

the wire between pin #8 on the relay and the ECU terminal is broken,
the ECU is faulty, or
the ECU is not powering up because of the low voltage problem on pin #3 of the main relay.

Pin #2 should have no voltage at all on it. If you are measuring any voltage on pin #2 , its connection is faulty. Short the leads on your tester and measure the resistance of the test leads and then check the resistance between pin #2 and the body ground. The two values should be less than 1 ohm difference.

So if theres a difference between 1 and 3 the main relay is bad, even though i just bought it last week? lol

Pin #2 doesn't have voltage, but it reads various numbers much higher than when i short the multimeter

Old Guy said:

Pin 1 on the relay is the yel/blu wire and you said that you were getting 12 v on it when you tested it. When the relay gets energized, pin #3 gets connected to pin #1 . If when you switch the ignition to run, you still have 12 v on pin#1 and 9 v on pin #3 , you have an internal problem with the relay. There should next to no voltage difference between pin #1 and pin #3 .

I am thinking that the ECU should still be able to operate with an input voltage of 9 v. Most digital electronics operate at 5 v at the device level. That said, if you have 12 v on pin #1 and 9v on pin #3 at the same time, you have a relay problem.

If pin #8 is not momentarily dropping to 0v when you first switch the ignition switch to run (it only goes to 0v for about 2 sec), then one of the following is at play:

the wire between pin #8 on the relay and the ECU terminal is broken,
the ECU is faulty, or
the ECU is not powering up because of the low voltage problem on pin #3 of the main relay.

Pin [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=2]#2 [/URL] should have no voltage at all on it. If you are measuring any voltage on pin [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=2]#2 [/URL] , its connection is faulty. Short the leads on your tester and measure the resistance of the test leads and then check the resistance between pin [URL=http://www.nsxprime.com/forum/usertag.php?do=list&action=hash&hash=2]#2 [/URL] and the body ground. The two values should be less than 1 ohm difference.

Click to expand...

elijahcole92 said:

So if theres a difference between 1 and 3 the main relay is bad, even though i just bought it last week? lol

Pin #2 doesn't have voltage, but it reads various numbers much higher than when i short the multimeter

Click to expand...

If you look at the internal diagram of the main relay that is shown on page 11-103 of the test procedure I attached, you can see that pin 1 is connected to pin 3 through the relay contacts. When the relay operates and the contacts close, pin 1 should be solidly connected to pin 3 and the voltage on pin 3 should be the same as on pin 1. If the voltages are not the same, then the contacts are faulty or some of the internal solder connections in the relay have failed (not uncommon according to anecdotal evidence here on Prime).

Carefully check the relay socket for damage and to make sure the connectors are seating properly. Having your existing relay and a new relay fail in exactly the same manner would be a pretty low probability event. If you are still getting 9 v on pin 3 when the ignition is on and you have 12 v on pin #1 , try taking an external jumper to connect pin 1 and 3 at the back of the socket. This should give you 12v on pin 3. Then try a start on your car. I think that when you hit start the fuel pump should power up if the ECU is working and you should get a start. Don't leave the jumper in because you won't be able to turn the engine off if you do. And of course, be careful to make sure you jumper the right pins.

It is really hard to get an accurate measurement of a low resistance connection using a hand held meter. The touch resistance of the meter probe on metal changes with the probe pressure that you apply. What is important is that it is more like 1 or 2 ohms and not like 10 or 20 ohms.

Old Guy said:

If you look at the internal diagram of the main relay that is shown on page 11-103 of the test procedure I attached, you can see that pin 1 is connected to pin 3 through the relay contacts. When the relay operates and the contacts close, pin 1 should be solidly connected to pin 3 and the voltage on pin 3 should be the same as on pin 1. If the voltages are not the same, then the contacts are faulty or some of the internal solder connections in the relay have failed (not uncommon according to anecdotal evidence here on Prime).

Carefully check the relay socket for damage and to make sure the connectors are seating properly. Having your existing relay and a new relay fail in exactly the same manner would be a pretty low probability event. If you are still getting 9 v on pin 3 when the ignition is on and you have 12 v on pin #1 , try taking an external jumper to connect pin 1 and 3 at the back of the socket. This should give you 12v on pin 3. Then try a start on your car. I think that when you hit start the fuel pump should power up if the ECU is working and you should get a start. Don't leave the jumper in because you won't be able to turn the engine off if you do. And of course, be careful to make sure you jumper the right pins.

It is really hard to get an accurate measurement of a low resistance connection using a hand held meter. The touch resistance of the meter probe on metal changes with the probe pressure that you apply. What is important is that it is more like 1 or 2 ohms and not like 10 or 20 ohms.

Click to expand...

It was showing a good amount of ohms, a lot highe er than when I shorted the multimeter. What grounds should I check on the car?

elijahcole92 said:

It was showing a good amount of ohms, a lot highe er than when I shorted the multimeter. What grounds should I check on the car?

Click to expand...

I don't know where specifically pin #2 is grounded. The NSX has a bunch of designated ground points. The easiest way to find it may be to trace the wire bundle. If you down-load the Electrical section of the service manual (you can get links on the Prime Wiki page), there should be a section in there which describes all the locations of the ground connectors and I believe describes what is grounded where.

Before you go off on a quest for the perfect ground, make sure your testing method isn't screwing you up. Take your tester and connect one probe to the point that you have been using for testing the ground and find another suitable spot for connecting to ground. If you get a 1-2 ohm reading, then your testing point is probably OK. If you get a high reading then you are getting bad measurements because of contact resistance. As an observation, using what appears to be a bare metal bolt head on the NSX as a ground point may not work. A lot (all?) of the bolts on the NSX that bolt into the aluminum superstructure of the car are dacrotized to prevent corrosion. The dacrotized treatment may make for a poor electrical connection. That is why the NSX was designed with very specific ground connectors and connection points in the car. If you are going to check for ground continuity it would be best to use one of those ground points for doing the measurements.

Did you confirm that your second relay was also faulty and the car is now working? If the relay is switching and you are getting 12v on pin #3 the ground on pin #2 is likely acceptable (otherwise the relay would not be switching).

I haven't has time to mess with the car. Will check those pins tomorrow. Just a thought, could a bad cam or crank sensor cause this?

So just checked. Still getting 9v at 3 and 12 at 1. I jumpers a wire and no start still. No fuel pressure at all.

Using the ground behind the drivers seat beside the main relay. I got 6.00 when using the 20k ohm setting. I was getting .04 when putting the leads one the tester together.

Also my cel light is not illuminating when I turn the key to the on position if that matters.

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Old Guy said:

I don't know where specifically pin #2 is grounded. The NSX has a bunch of designated ground points. The easiest way to find it may be to trace the wire bundle. If you down-load the Electrical section of the service manual (you can get links on the Prime Wiki page), there should be a section in there which describes all the locations of the ground connectors and I believe describes what is grounded where.

Before you go off on a quest for the perfect ground, make sure your testing method isn't screwing you up. Take your tester and connect one probe to the point that you have been using for testing the ground and find another suitable spot for connecting to ground. If you get a 1-2 ohm reading, then your testing point is probably OK. If you get a high reading then you are getting bad measurements because of contact resistance. As an observation, using what appears to be a bare metal bolt head on the NSX as a ground point may not work. A lot (all?) of the bolts on the NSX that bolt into the aluminum superstructure of the car are dacrotized to prevent corrosion. The dacrotized treatment may make for a poor electrical connection. That is why the NSX was designed with very specific ground connectors and connection points in the car. If you are going to check for ground continuity it would be best to use one of those ground points for doing the measurements.

Did you confirm that your second relay was also faulty and the car is now working? If the relay is switching and you are getting 12v on pin #3 the ground on pin #2 is likely acceptable (otherwise the relay would not be switching).

Click to expand...

k. Could a bad cam or crank sensor cause this you think?

elijahcole92 said:

So just checked. Still getting 9v at 3 and 12 at 1. I jumpers a wire and no start still. No fuel pressure at all.

Using the ground behind the drivers seat beside the main relay. I got 6.00 when using the 20k ohm setting. I was getting .04 when putting the leads one the tester together.

Also my cel light is not illuminating when I turn the key to the on position if that matters.

- - - Updated - - -



k. Could a bad cam or crank sensor cause this you think?

Click to expand...

As I understand it, you jumpered pin #1 to #3 (you should have had 12 v at pin #3 ) and then with the jumper connected attempted to start the car and nothing worked (the relay needs to be in the socket while you are doing this)? The CEL may not be lighting up because the ECU is not getting the power-up signal from the main relay or it may not be lighting up because the ECU is dead.

It could be a dead cam angle sensor. It could also be 100 other things. Eliminate the obvious stuff first. I am not really familiar with pre OBD II cars; however, if the ECU was OK I think a bad cam angle sensor would cause an error code. I can't see a bad cam angle sensor stopping a fuel pump from operating during the start cycle.

Old Guy said:

As I understand it, you jumpered pin #1 to #3 (you should have had 12 v at pin #3 ) and then with the jumper connected attempted to start the car and nothing worked (the relay needs to be in the socket while you are doing this)? The CEL may not be lighting up because the ECU is not getting the power-up signal from the main relay or it may not be lighting up because the ECU is dead.

It could be a dead cam angle sensor. It could also be 100 other things. Eliminate the obvious stuff first. I am not really familiar with pre OBD II cars; however, if the ECU was OK I think a bad cam angle sensor would cause an error code. I can't see a bad cam angle sensor stopping a fuel pump from operating during the start cycle.

Click to expand...

Yes. With it jumpers I checked to make sure 3 was getting 12v with relay in socket with key on. Yeah I figured either one of those sensors would deal mainly with ignition and not the no fuel problem I'm having. Though I still don't know if it's getting ignition or not when trying to start