Please confirm my diagnostics

SVX10 · #1 04-06-2010, 10:20 PM

Hey y'all. Some day my SVX will not have any issues. Until that day...

So, it stopped starting. I drove it around all day, then I went to drive it that same night, and it cranked and almost started, but then just lost its will to run. Ever since, it will crank with no problem, but not start. It does start with starter fluid. So, we're looking at fuel.

I disconnected the inlet fuel hose at the fuel filter and turned the key to the on position. No fuel. I cranked the engine. Still no fuel.

I checked the relay. I believe it's bad. Here's the results of the test...
Key off: Yellow to gnd = 12v
Key on: Yellow to gnd = 12v; grn/wht to grnd = 12v; blue to grnd = 0.6mV; voltage @ blue wire @ fuel pump = 0.6mv
Key on, jumper @ relay from yellow to blue: voltage to gnd (both circuit ground and body ground same result) @ blue wire @ fuel pump = 12v. Fuel pump does not run

So, my conclusion is that both the relay and fuel pump are shot. Accurate diagnosis?

I say relay is shot because yellow to blue @ on should be 12v
I say pump is shot because even with 12v @ the blue wire @ the pump, it doesn't do anything.

Trevor · #2 04-07-2010, 12:01 AM

Quote:

Originally Posted by SVX10

Hey y'all. Some day my SVX will not have any issues. Until that day...

So, it stopped starting. I drove it around all day, then I went to drive it that same night, and it cranked and almost started, but then just lost its will to run. Ever since, it will crank with no problem, but not start. It does start with starter fluid. So, we're looking at fuel.

I disconnected the inlet fuel hose at the fuel filter and turned the key to the on position. No fuel. I cranked the engine. Still no fuel.

I checked the relay. I believe it's bad. Here's the results of the test...
Key off: Yellow to gnd = 12v
Key on: Yellow to gnd = 12v; grn/wht to grnd = 12v; blue to grnd = 0.6mV; voltage @ blue wire @ fuel pump = 0.6mv
Key on, jumper @ relay from yellow to blue: voltage to gnd (both circuit ground and body ground same result) @ blue wire @ fuel pump = 12v. Fuel pump does not run

So, my conclusion is that both the relay and fuel pump are shot. Accurate diagnosis?

I say relay is shot because yellow to blue @ on should be 12v
I say pump is shot because even with 12v @ the blue wire @ the pump, it doesn't do anything.

1) With the ignition off there should be no voltage at yellow.

2) With the ignition on you appear to have 12 volts at yellow, i.e. the input to the relay contacts, which is correct.

3) When yellow and blue are bridged, this is equivalent to closing the relay and with the ignition on the pump should run.

4) Ignition on, Blue to ground should register approx. 12 volts to ground, switched by the relay from yellow. No voltage here will indicate a faulty relay.

4) 12 volts at the fuel pump does not make sense in view of (3) & (4).

If there is 12 volts at the fuel pump and it does not run, either the pump or the resistor which should ground the pump, is faulty.

It would appear that your tests are somehow haywire.

SVX10 · #3 04-07-2010, 12:23 PM

1) Hmmm...depends which wiring diagram you look at. The fuel system specific diagram indicates that 12V is continuously applied to the grn/black wire through fuse #2, while the yellow wire is powered by the ignition through fuse #16. However, functionally, 12V to the grn/black causes the relay to close, so this setup would cause the relay to always be closed. The wiring diagram covering the entire electrical system is reversed. Yellow wire goes directly to 12V through fuse #2, and the grn/black gets 12V @ key on through fuse #16. This matches the function of the relay, and explains 12V @ yellow @ key off.

2) Yes, I have 12V to yellow at ignition on. I also have 12V to between green/black and black, showing that that portion of the relay is functioning fine. The 12V between grn/black and black should be closing the relay, causing 12V between blue and ground. However, blue to ground is basically 0V (as you can see in #4)

3) When I jump yellow to blue, I do get 12V at the fuel pump connector, but the fuel pump does not run. Conclusion...bad fuel pump or bad fuel pump ground.
3a) To check fuel pump ground, I read voltage between the blue wire terminal and black wire terminal at the fuel pump connector (blue = 12V source, black = circuit ground). Doing this, it read 12V. Conclusion...fuel pump ground is OK.

4) With ignition on, yellow to ground is 12V, but blue to ground = 0.6mV. Conclusion...relay is bad (already ordered a new one)

5) The 12V at the pump is only when the jumper is in place.

I just want to make sure that this is the proper conclusion, rather than some fuse somewhere, or some ignition kill switch or something.

Mat

kwren · #4 04-07-2010, 02:11 PM

Fuel pump is bad... unless you are just out of gas!

Keith

Trevor · #5 04-07-2010, 02:13 PM

Kia ora Mat,

1) Hmmmmm --- I note there is confusion over the colour codes. I am using the MPFI system diagram on page 6 - 3 - 44, Fig. 38 - 1, US Electrical Manual.

2) Your reference to a black wire is confusing. Black normally indicates a negative or ground wire. I must presume you are referring to black/white as black.

3) My manual shows the coil of the relay as black/white(black) and green/black. B/W(B) to fuse 16, G/B to MPFI unit, where a ground connection will operate/control the relay. With 12 volts confirmed at B/W(B), grounding G/B should operate the relay. The relay is controlled via the negative leg.

3a) N.B. The fuel pump has no ground as such. The pump is controlled via a negative ground connection through the modulator. You appear to have things mixed up, in respect of the control circuit involving the blue and B/W(B) wires.

4) However, blue should supply 12 volts to the pump via yellow when the relay closes. As you have concluded, no voltage here indicates a faulty relay.

5) You previously advised “ Key on, jumper @ relay from yellow to blue: voltage to gnd (both circuit ground and body ground same result) @ blue wire @ fuel pump = 12v. Fuel pump does not run”

You now advise. “The 12V at the pump is only when the jumper is in place”. I remain confused, even after having spent a lot of time sorting things out.

SVX10 · #6 04-07-2010, 05:54 PM

1) OK. We'll stick to the MPFI diagram. I'm not sure what page it is...I'm just pulling it from the online PDF file.

2) Yes, my apologies. It was dark under the column and tough to maneuver. I suppose I could've pulled the black/white from the diagrams, though.

3) My assumption was that the GB is just a ground, and that the operation of the relay was dependent upon 12V being supplied to the relay via ignition switch being closed. I see how it could work the other way, though, with the 12V continuously applied and the GB being open until grounding @ ignition on. Just for my own learning, I will verify its function tonight w/voltmeter @ ignition on and off.

3a) understood about the modulator. Re-evaluating the wiring diagram, i guess I need to ensure that the yellow wire @ the fuel pump connector is grounded.

4) We agree! Hooray!

5) This one is simple, to me anyway, let me try to explain better.
The purpose of the relay is to connect yellow and blue sending 12V to the fuel pump, correct?

However, my relay isn't working, so 12V never gets to the pump. How can I tell if the pump is working or not? Somehow, I need to send 12V to the pump.

So, what I did was create a jumper wire...3" of 14 or 16ga wire...and I physically connected yellow to blue.

Testing at the fuel pump connector, I verified that this sends 12V to the blue wire at the fuel pump.

IF the fuel pump grounding circuit through the modulator is functioning properly, this 12V should cause the pump to run, correct?

I'll sit down with the wiring diagram, my voltmeter, and the SVX again tonight and verify whether or not the pump operates. I know the relay is bad, so it's just time to verify the pump function.

Trevor · #7 04-07-2010, 08:47 PM

3) GB is not just a ground.

3a) The yellow wire at the fuel pump is not permanently grounded. You have only to ensure that it becomes grounded as the means of control.

5) Spot on. Therefore bridging yellow and blue should energise the fuel pump, and even if the modulator is faulty, the pump should run at slow speed via the resistor.

As I keep trying to tell kwren/Keith, who continually messes up technical threads, and wastes space, a $2 test lamp is better than a voltmeter for checking for voltage in auto work. Unlike a meter, substantial current is involved in energising a lamp. Refer the confusion regarding the 0.6 Mv mentioned in your original post. All you were reading was an induced voltage, rather than a battery voltage.

SVX10 · #8 04-07-2010, 10:02 PM

1) I definitely have 12V to ground at the yellow wire with key off
3) Either way...relay isn't working. New one ordered.
3a) OK, I think I finally get this. I tested blue to yellow at the pump tonight and saw that it's not a simple 12V to ground. With the bad relay, key on, there is a -5.3V reading from blue(+) to yellow (-) at the pump. With my jumper in place at the relay, thus sending 12v to the pump, the blue (+) to yellow (-) reading at the pump is 6.7. The difference between the two is 12v, meaning the modulator is providing 5.3V on the "back end" so to speak while a good relay provides 12V on the "front end." So, I assume this means that the pump runs off of 6.7V @ start up idle when all is working as designed. The ECU then screws with the "Back end" voltage to allow the pump to operate at different levels while getting a constant 12V from the "front end" relay side.
5) Nothing from the fuel pump no matter what I do. Time to order a new one?

SVX10 · #9 04-17-2010, 01:28 AM

I installed a new fuel pump and fuel pump relay tonight. Good and bad news...

Good news is that the old fuel pump was bad, and the new one works

Bad news is that the relay isn't working still. It works if I make a jumper from Grn/blk to ground. So, the grn/blk isn't grounded, so the relay isn't closing, and 12V isn't going to the fuel pump.

Any ideas how to find the bad ground?

Thanks!

Mat

SVX10 · #10 04-17-2010, 04:03 PM

Checked various pin voltages @ the ECU per the Owner's manual, and 2 of the ones related to my issue were not reading correct voltages. Since nothing had actually changed as far as wiring goes, I suspected the ECU. Put in my spare, and it fired right up.

So, here's to hoping whatever killed my ECU was fixed between the relay and fuel pump replacement