justindenton

OK, I bought a 92 Civic that someone cut out the Main Relay and put in 2 Flip Switches, Didn't like that as it wasn't very reliable so I put back the main relay and wired correctly. Although I've got the symptoms of a Main Relay bad but its brand new. The car cranks, I've verified spark, although I don't hear the fuel pump kick on. I've checked power between the leads for the fuel pump on the relay and power is sent through when the key is on.

So I'm about 90% sure its the fuel pump, but I wanted to hot wire the fuel pump just to be on the safe side before I drop the cash.

I see there is 4 wires going into the fuel pump yellow/black. yellow/green and two black ones, I think one is straight black with some gray spots and the other is black with a red line on it.

Anyhow have a wiring diagram or know what these do just want to send power directly to the fuel pump and see if it will kick on.

Thanks,

Justin

Former User

Is fuse 31 (hood), 24, or 18 blown?

Does the fuel pump connector get battery voltage?

The Yel/Grn wire and Black wire are power and ground, respectively, for the fuel pump.

justindenton

Well I know this sounds wierd.. But I jumped the black with yellow and the yellow with green stripe and it kicked on the Fuel Pump. Which showed the fuel pump was good.

Then I plugged the relay back in and nothing. The fuel pump won't kick on.
So I jumped the black/yellow and yellow/green with a flip switch and turn the switch on and the car starts right up, the fuel pump kicks right now. Everything works.

Is there something screwed up with the relay for not kicking power back to the Fuel Pump? And me having to manually jump the relay to send power back?

Former User

Is the CEL on?

Are you sure that the main relay is getting power from all three wires protected by fuses 31, 24, and 18? If so, the main relay power wires ground on the ECU. If these ground wires or the ECU is bad, then the main relay won't work.

justindenton

It must not, or something. It started that one day, then I tried yesterday and it seemed to start ok. But today. Nada.. It cranks like a bad relay again. I can force the Fuel pump to kick on by jumping the wires, but if I don't jump the wires the fuel pump won't turn on.

I checked every fuse in the system and they all are ok. Now unless this fuse isn't labeled or something, everything checked out ok. Or if its been pulled, but per the label on the fuse boxes all the fuses that are supposed to be there are there.

Wierd that the person cut the Relay complete out and put 2 flip switches in. That worked occasionally but still not reliable. Guess I'm banging my head against the wall now.

justindenton

Just saw your post on the ECu / Ground. I'll check out the ground to the ECU, is there specific wires going into the Relay that should show up as Ground from the ECU? -

Also I did check the ECU to the MAP Sensor Voltage for 5v and that checked out ok. But I take it other "things" can cause the ECU to go bad.

Former User

Do you also lack spark?

Does the CEL remain on steady both with and without the service connector jumped?

justindenton

Well the wierd thing is the Check Engine light doesn't stay on. It goes through the normal init phase when you turn the key and then the light goes out. Is there a pin out on the Relay and I can test to make sure there is ground. - I think I got a Diagram somewhere.

But I've went through all the fuses in the fuse panels and none of them are blown, and non look out of place.

justindenton

As for spark, I believe I'm good, I shot I know.. not supposed to but for a quick try some Starting fluid into the intake and it would attempt to fire up. So I'm assuming good spark. Im going to test it out better in the AM.

justindenton

OK here's what I've got. Atleast I have it 100% down to being able to start the car. I'm thinking MAP Sensor replacement. I must not have tested the MAP sensor out correctly, I am getting 5v from the ECU, I take it there is a pin out from the MAP to translate back the 5v to the ECU for the reading.

Anyhow, I can jump the fuel pump to make it kick on, then I can unplug the MAP Sensor, turn on the ignition wait for the Check Engine Light to go out. Takes about a minute or so this way, then I can push in the clutch and it fires right up. Every time I repeat this scenario it works. If I plug back in the MAP Sensor Nada won't start.

All in favor of the MAP Sensor being bad say "I"..

Former User

The MAP sensor may be bad, but it's puzzling that a MAP sensor CEL code was not thrown. Therefore, you should test whether a MAP sensor wire or the ECU may be bad.

The diagram below shows the unplugged wire harness connector to the MAP sensor. The extreme right and left terminals are hot (5V) whereas the middle terminal is ground. With the key in ON(II), do you measure 5V for the right or left terminal when the middle terminal is used as ground?

justindenton

I'll take a reading using the Middle Ground. - I know when I did my reading that I pulled it from those pins but I used the Ground off the battery.

It only throws the Check Engine light when I unplug the MAP Sensor, which like you said makes this sound odd, that it doesn't toss it before.

But with the MAP sensor plugged in, it won't start, but if I unplug the Map Sensor and jump the Main Relay to kick on the Fuel Pump I can start it without a problem. Although I'll check the readouts on the MAP sensor using the middle pin as ground this afternoon.

Former User

I do understand your focus on the MAP sensor based on your test result. Nonetheless, I think your car possibly starts because unplugging the MAP sensor throws the ECU into pre-programmed limp mode, which may complicate interpretation of the test result. For example, limp mode may compensate for a variety of sensor, ECU, and wire malfunctions. Still, troubleshooting the MAP sensor circuit is definitely worthwhile given that faults in this important sensor can cause a no-start problem.

justindenton

Well I checked the voltage on the lines going to the MAP Sensor. Using the Middle Wire as ground and what is marked as "V" in the wire harness as positive I read 5v. The other wire gives a small reading of around .05 volts something negligible. Also I was blessed with a log of the maintenance the previous owner had on the car. And I found that they replaced the ECU once around 110k miles, and they've replaced the Main Relay twice, and then eventually cut out the Main Relay. and replaced it with two flip switches, which wasn't documented in the little book that came with the car.

I didn't find anything about replacing the MAP Sensor, although I went to the local J-Yard over lunch and bought a used Map Sensor, looks pretty clean. And hooked it up to the car. But technically it doesn't cause the Fuel Pump to kick on its own. I still have to flip the switch I wired into the car to turn on the fuel pump. But it seems to start, but that could be because I unplugged the other relay.. I'm going to let the car sit for a while and go back out and see if it fires up consistently.

Former User

I think you found the problem. Did you do the voltage tests on the MAP sensor connector with it unplugged? If so, did the white wire give the low voltage (~0.05V) using the middle wire as ground?

justindenton

ehh.. No Actually had the wire harness disconnected from the MAP Sensor. I'll plug it in and check that wire again just to double check. Only take a few seconds.

Former User

You did the test correctly the first time -- with the MAP sensor connector unplugged. If the white wire terminal only showed 0.05V, then that's the problem. It should have 5V. Either the white wire has a short or open or the ECU is bad.

justindenton

oh ok.. Thats cool. Now dumb question but what is an "open"? I'm taking it that the wires isn't making contact. - but wanted to double check.

Thanks,

Justin

Former User

Your next troubleshooting steps (checking for a short or open in the white wire) require a digital multimeter. Do you have one?

An open in a wire is a break that causes a loss of continuity (infinitely high resistance).

A short in a wire is damage that causes abnormal grounding.

4drint3gr4

bump! let me know how u solve this problem if u do!

justindenton

Yeah I've got a multimeter. I'll test out for shorts and opens in the connections tonight when I get home from work.

And I'll make sure I keep this updated.

I'm going to check out the MAP sensor this morning to see if the car starts like normal. Although regardless, I'm thinking that something is up regardless because the fuel pump isn't kicking on like normal, I'm forcing it to with a jump in the wire.

Former User

If the white wire has no short or open, then you likely have a bad ECU.

Former User

The problem is most certainly the lack of voltage to the white wire in the MAP sensor connector rather than the MAP sensor itself.

justindenton

Yeah definitely because the MAP sensor i tested with from the J-Yard keeps the Check Engine Light on all the time where as the one that was in the car did not. I'll trace out the White Wire shortly and find out. I take it dependant on results I'm looking at a need for another ECU. Looks like the ECU was replaced some 60k miles ago, but its a J-Yard ECU. Definitely not a new one. So I'll do some tracing of the wires find out and go from there. I'll report back.

thanks
Justin

justindenton

Ok so I pulled out the ECU, checked the wiring harness basically the three wires that go back to the MAP Sensor.

The Green with Blue Stripe as Ground
The Yellow with Green Stripe - Shows 5volts
The White Wire Shows like .6 to .8 volts, it varies.

So I'm taking it that this would conclude that the ECU has gone bad?

thanks,
Justin