Jas0n

Hey guys, i got a 94 gc that wont start up.
I've checked the fuses and the asd and fuel pump relays.
I've replaced the fuel pump, and Ignition Switch.
I've also recapped the ecu.. Im at my wits end.
When turn the key to the ON position the fuel pump wont prime.
I can start it by providing power directly to the pump.
I'm curious about the orange wire, is it 12 volts constantly or does the asd relay turn it off... Ive read both.
Please help me out.
It makes me feel incompetent because i work on cars and computers every day.

thanks
-jason

nick_n_ii

I'd say your Crank Position Sensor is shot..

When it goes bad the fuel pump won't turn on and you don't get any spark..

MulishaXJman

nick x2222222

Jas0n

it must not be that then, because pouring gas down the tb or running the pump directly from a battery will let it start up.. thanks for the replies tho

Willys55

If you jump out the ASD relay will the fuel pump relay engage?

OverlandZJ

Recently started getting cold in Oregon right.. Try this, doesnt cost anything.

Grab a beer and sit in the Jeep, ignition on, radio off.. this could take awhile. Your waiting to hear a series of clicks coming from the power distribution box. This will be the fuel pump relay. Then you'll hear a whoosh as the pump pressurizes the fuel rail. If you have security system, you'll see the dash light blink a few times. Start the Jeep. Sounds odd right?

Apparently theres a resistor or something in the ECU that takes time to "warm" or something as the ECU ages. This is more prevelant in colder temps. I swear this happens, had the same issue last winter with the wifes ZJ. Did a search and found my answer at www.jeepsunlimited.com.

The fix is a new ECU. Is this an earlier V8 ZJ?

I'll dig up the thread for ya..

Jas0n

I was going to reply last night, but it wouldnt let me... I already tried recapping the ecu. I might have messed it up during the soldering process. I tried the ground test at the relay socket. None of the terminals in either the ASD or the Fuel Pump Relay were grounded. I noticed that the positive wire to the fuel pump was grounded, does that mean the relay wasn't tripped? I also tried cleaning the terminals on the ecu. I ended up ordering a refurbished from autozone for 254.98 with the 87 dollar refund when I turn the old one in. For those that have opened their ecu and fiddled with it don't worry, they didnt care... Even when my mom opened her mouth and told the guy i took it apart trying to fix it.. She even asked me in front of the guy exactly what i did. Shes lucky the guy didnt care....

ET JEEP

When you turn the key to on, the PCM turns on the ASD and Fuel pump relays for a couple of seconds then turns it off until you crank the engine. The fuel pump should run during this period then shut off.

The ASD and FP relays should have constant battery voltage at pin 30 regardless of key position. Pin 87 is the feed when the relay is activated. The ASD feeds the coil, injectors, alternator and ASD sense to the PCM. The FP feeds the fuel pump and the heated oxygen sensor.

Pins 86 and 85 are the relay control pins. When you turn the key to on, pin 86 on both relays should have battery voltage. Pin 85 is controlled by the PCM. The PCM grounds these pins to activate the relays.

My diagram does not show an orange wire. It does show an orange/dark blue tracer. This is the feed from the FP relay to the fuel pump and the heated oxygen sensor.

If you install the ECU and still have a problem, I would look at the heated oxygen sensor. It may be robbing power causing the FP not to turn on.

Jas0n

first off, thanks for the reply

so to simplify this ill write down what you said a different way...

Pin 30- (+) 12v Constant Power Feed from Battery
Pin 87- (+) 12v Wire To Fuel Pump
Pin 86- (+) 12v Power When Key is in the ON Position
Pin 85- (-) ECU Grounds this Pin, Causing the Relay to Send Power to the Fuel Pump via Pin 87

that is how i interpreted it, if that is incorrect, please let me know

so i have a question.... what would cause the positive wire on the fuel pump to become grounded.. would that be from the bad ecu...?

just a note.. a diagram i found on the internet suggests that 86 is the ground wire instead...

thanks,
-jason

OverlandZJ

Heres that thread i promised ya.

http://www.jeepsunlimited.com/forums...&highlight=ecu

ET JEEP

You have it right. Actually it is the socket with the relay removed that you check.

Socket Pin 30 is always hot with 12 volts
Socket pin 87 is the feed when the relay is activated. It feeds the fuel pump and O2 sensor

Sockets for Pins 86 and 85 are not polarity sensitive so they may be wired in reverse. Most diagrams I see have 86 as positive and 85 as ground. It could be wire in reverse and still work. To find out turn the key to on and do a voltage test on each socket. One will have voltage. It should be the same pin on both the ASD and the Fuel pump relay.


Regarding this question,

so i have a question.... what would cause the positive wire on the fuel pump to become grounded.. would that be from the bad ecu...?

Are you talking about the relay pin 30 wire or what?



You can test the relay. Pull the relay out. Do a continuity test between pins 30 and 87; there should not be any continuity. Test for resistance between pins 86 and 85; there should be approximately 75 ohms resistance.

Now, apply battery 12 volts to pin 86 and negative to pin 85. This activates the relay. Now you should have continuity between pins 30 and 87.

Jas0n

im talking about the actual orange/black wire at the fuel pump.

what do i need to do to check the heated o2 sensor?
jumping pin 30 and 87 did not work either...

this may be a weird observation... but pins 85, 86, 30 all had 12 volts.. could a broken o2 sensor cause that?
thanks

72gremlinkid

My father has a 94 zj when he would try to start it nothing would start if you put the key in on position then he jumped the starter witha wrench. Long story short it ended up being the ignition assembly where you would put the key in to turn it a piece broke off inside and wouldnt allow it to start. He took the part off where you put the key and cut corner of a socket off and put it on a 3/8 allen wrench to use as a key to turn the ignition all the way. May not be it but hope it helps

Jas0n

thanks for the reply, ive already replaced the key switch..

ET JEEP

That is a weird setup. The socket for pin 30 should have 12 volts. The sockets for pins 85 and 86 are a problem. One should have voltage and one should be grounded by the PCM. That completes the circuit which then activates the relay. When the relay is acitvated power goes from 30 to 87 and to the pump. The pump should run.

If both 85 and 86 show 12 volts then one is getting power from the PCM. Not sure that is right.

Pins 85 and 86 are the relay control pins. They operate separately from pins 30 and 87.

The 12 volts at 85 and 86 I do not understand.

The o2 sensor would not cause that problem. It just gets fed by pin 87.

Sounds like you have a fault in the wire from 87 to the pump.

I can't find the pump wiring. I will check another source to see if I can find something.

You may have to do a trace on the wire for pin 87. If you can see the color find it at the pump connector. Do a continuity check on it.

The o2 sensor check is a bit complicated. Check to see if you have any codes.