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No Prime

keepwishing

NAXJA Forum User
Location
nwflorida
I have a little problem that maybe needs more expertise than I currently hold.
I have no fuel pump prime or turn on. I have worked off and on for a year now trying to figure out way. this is what I have done so far...
New grounds, all plugs have been cleaned and relays checked. I have .17v at the pump but cranking voltage at the spice where the ballast used to be. Found .17v at all plugs in the cab by following the pink w/ black strip wire. Took the computer out and checked connections all looked good.
Checked the B+ and fuel pump relay and all have power. Jumped the fuel pump relay and the darn pump came on. Put everything back together and hit the key and she came alive for 5 sec. Still no prime or pump.
I got curious and splice the terminal 86 on the a/c relay to 86 on the B+ relay and got both pump and prime. Actually drove the beast.
Now I'm not one to leave something rigged so I want to get this fixed. Is this a computer issue? Here in Florida its hard to survive without a/c.
Any thoughts?
 
The yellow wire is power input to the 86 pin on the fuel pump relay and should have power when the key is in run or start.
Same yellow wire that is power input for the ignition module, alternator and other stuff.

If I'm understanding correctly, when you stole power from the B+ relay everything worked?

You likely have an open yellow wire going to the 86 pin of the fuel pump relay. I'd unbolt the relay block, carefully turn it over and look underneath. It can get really dirty and corroded back there. Maybe the yellow wire is open (broken) between the splice and the relay 86 pin or the splice is bad?

The relay gets power into the relay coil side (the side that actuates the contacts) from the yellow wire, from the ignition switch. The ground side of the coil that actuates the relay contacts is grounded and switched through the ECU. In other words this relay is closed and controlled on the ground side, not the power input side.

When the contacts inside the fuel pump relay actuate, they pass the main current from the red wire (30 pin) to the orange wire (87 pin). Orange wire (sometimes orange with a black stripe) is main power to the fuel pump, injector drivers and other stuff.

A little trick that may be helpful, that same orange wire (sometimes a orange wire with a black strip) plugs into the starter relay and is easy to get to. If you jump that orange wire to the red wire lug on the starter relay it is a straight shot, bypassing the relay and other stuff, straight to the fuel pump. A good, quick way to test the fuel pump and the back half of the fuel pump wiring. When starting the vehicle (starter relay actuated) all the normal controls, relays and ballast resistor for the fuel pump circuit are bypassed as long as the starter is in motion. This is to get max available voltage to the pump, while the starter is sucking the voltage down.
 
I may have confused everyone with what I wrote. I have stared at wires so much they all look the same now. Lol.
I actually stole the orange on the Ac 86 relay and put it on the 86 pink on B+. And the jeep ran. I have everything back to original now.
All relays have power and with the B+ hooked up to original factory wiring the relay clicks with key on and off after 3 sec. Fuel pump relay has power to 30 all the time and 87,86 when cranking.
At the starter switch I have battery voltage on input and cranking voltage on the fuel pump wire. Only thing I haven't check is the wire the diagram shows going to the coil. It shows a fuel pump wire ,ground and tach.
My diagram shows 86 going to + on the ecm for both a/c and B+. Is that correct? Just a little weird that the B+ relay will click on and off and get nothing and when stealing 86 from the Ac it runs.
 
The latch relays basic function is to park the stepper motor (IAC) slightly open for the next start (so you have enough air for a start without pushing the gas pedal). And has little or nothing to do with the fuel.

It may be an alternate power source for the ECU, for whatever reason. I'm sure the engineers had a reason (they never shared with me).

If your motor starts without having to push on the gas pedal, your B+ latch relay is likely working as designed.

My brain is old and I have good days and bad days, today is somewhere in between. Maybe list your issues in a list form and I may better understand.

You have a fuel issue?

A spark issue? etc.

You mentioned a no prime? Which is way unusual, if they do nothing else, they usually prime. It may be priming and you are just missing it? It may be priming and loosing the prime because of a check valve? The only way I can think of to know for sure is to release any pressure on the fuel rail, hook up a pressure gauge and see if the needle moves when you turn the key to the run position (try it a few times if nothing happens the first try). Which is a lot safer than, releasing the pressure, holding the schrader valve open with a small screw driver tip and having somebody turn the key to the run position, which is likely to spray fuel all over the intake exhaust, all over you and maybe into your eyes.
 
Good call 8Mud. After looking back over the manual I see what you are saying. I'm just really confused as to why I can steal the a/c 86 and splice it to the power latch 86 and the darn thing runs. I did just find bare wire on the o2 relay 87a. Two orange wires that go to the center of the relay. Don't know if that has anything to do with the power.
But as you asked... I have good spark and the rail is pressurized. No prime or pump. It cranks for 3 to 5 secs and dies. Over and over again.
 
The red wire going to the 30 pin on the fuel relay is the main power input for the fuel pump. Is it possible you have a blown fusible link? No power to the 30 pin, this wire should be hot as long as the battery is connected.

The yellow wire going to the 86 pin is what supplies power to switch the relay closed (on) and comes from the ignition switch.

The 85 pin, orange wire with a stripe, goes to the ECU and ground switches the relay.

The 87 pin is power to the fuel pump, normally through the ballast resistor.

A few minutes with a volt meter or even a trouble light should sort out your problem quick.

A few possibilities I see is an *open circuit going to the fuel pump relay*, either the red or the yellow wire. An open circuit on the relay ground wire going to the ECU, less likely because you said you jumped to the 86 pin and it worked. Or for some odd reason the ECU isn't grounding the relay coil and not allowing the relay to close, also not likely if you did in fact jump power to the 86 pin and the relay worked.

If I'm understanding correctly the most probable issue is power into the 86 pin from the yellow wire?

The orange wires coming from the O2 sensor relay may be an issue. They may have shorted and either blew a fusible link or melted a wire. Depends on which orange wires they are. If they are to the 87a pin (I think) on the O2 sensor relay they are part of the fuel pump wiring and bypass the ballast resistor during full throttle operation to kind of super charge the pump.

You'll need a diagram to sort out the orange wires at the O2 sensor, there are two batches of orange wires for different sub systems there. One spot where trying to follow the wire color codes can screw you up.
 
Just rechecked and here are my findings. ..
Key off= power to 30
Key on= power to 85,86,30
Start= power to 87 voltage drop in 86.
Trying to upload a pic but haven't figured it out yet.
 
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If I'm understanding correctly the most probable issue is power into the 86 pin from the yellow wire?QUOTE]

It was the 86 pin but on the B+ relay one of the two pink wires.
Which has me really confused if it only controls the stepper motor.

I don't know this for a fact, but I've read someplace that it is *also* a power supply for the injector drivers and some other stuff in the ECU. Or maybe a parallel power source to make sure the drivers have a steady (fewer surges, peaks and valleys) power supply. I don't know for sure? It may have more than one function. Very few instances of trouble with this circuit that I can remember. I know I've never had any issues with it.

I've been through around 90% of the circuits in the Renix multiple times, this is one circuit I never had to troubleshoot. Much of it was engineered by the French, it doesn't have to make sense, it just has to work ;).
 
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Those smooth French. .. With their tiny mustaches. I'm going to get to the bottom of this problem sooner or later and will post back with my findings. Thanks, 8Mud
 
8Mud here's a puzzle for you. I traced the pink wires back to the ECU and have voltage on both with key on. Went back to the B+ relay and have key off voltage at 30 and key on voltage at 30,85,86,87. Checked A9And B10 one ECU again and there is voltage to both with key on. My diagram shows A9Being a switch had ground. Could this be a short in the ECU?
 
Here is a segregated view of the B+ Latch relay. As you can see it is a loop or what I call a holding relay. As you can see the 86 and 87 are spliced together.

30 is always hot and comes directly from the battery through a fusible link.

85 is the relay coil ground and can switch the relay open. Many relays in the Renix (and later models) switch on the ground side and not the hot side.

The D2 3 and D2 5 are pins in the diagnostic connector.

I may be full of it but the only way I can see for that relay to close is if the ECU pulses the 86 pin or more likely constant power through a diode.

And the 85 switches the ground to control the relay.

You have three power sources to the ECU, the red which is constant power from the battery through a fusible link, the yellow which in effect turns on the ECU from the ignition switch and the B+ latch circuit. Why? I haven't the faintest idea? Maybe a redundancy, maybe an afterthought when the engineers discovered they had forgotten something in their design (which seems likely).


bilder hochladen kostenlos

Is it possible your red power wire or your yellow switch wire (key on) has no power? Just a wild guess here.

Is it possible the *probable* diode inside the ECU for the pink wire circuit (B+ latch relay) has failed? I'm not sure there is a diode in the ECU for this circuit, but it seem likely.

Just for the heck of it, pull on the back of the wires at your ECU connectors just to make sure a pin isn't trying to back out of the connector. I've seen this before. Gently tug on each wire with a pair of needle nose pliers to make sure the little pin tab is seated and locked into the connector. I've found the pins in this connector not locked properly into the connector and making iffy contact.
 
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Note from DJ
Sorry for the long post but I’m going to offer my 2 cents for consideration hear.

OP keepwishing in your post #8 you posted:
Quote;
“Just rechecked and here are my findings.
Key off= power to 30
Key on= power to 85, 86, 30
Start= power to 87 voltage drop in 86”.
You shouldn’t have power at #85 that is a ground terminal.

In your post #13 you posted:
Quote;
“8Mud here's a puzzle for you. I traced the pink wires back to the ECU and have voltage on both with key on. Went back to the B+ relay and have key off voltage at 30 and key on voltage at 30,85,86,87. Checked A9And B10 one ECU again and there is voltage to both with key on. My diagram shows A9Being a switch had ground. Could this be a short in the ECU”?
Again you shouldn’t have power at #85 or A9 they are ground terminal.

Now here are my thoughts with my limited electronic knowledge; if you have lost the ground path needed to complete these circuits; when you placed your meatier lead on those connections and the other lead on a ground point you were only seeing the voltage that was waiting to be grounded; not a supplied voltage.

Now hear may be quick ground path test for you to try.
Locate the Diagnostic Connector #1 which is the smaller yellow caped 6 pin connector located on passenger side of the engine compartment.

When you remove the cape you will see that only 4 of the 6 connection points are used.

If you are standing at the front of the Jeep this is the connector layout;
Firewall
3 6
X
2 5
X
1 4
Front of Jeep

X’s stands for the two indentations.
# 1 is for the Tachometer signal.
# 3 is for the battery negative voltage.
# 5 is for the battery positive voltage.
# 6 is a directly connected to the fuel pump voltage supply wiring.

With this information with nothing turned on take your meter stick on probe in cavity #3 battery negative connection and touch the other lead to the positive post of your battery and look for battery voltage.
Post what you see.
 
Note from DJ

Thanks for reporting back your findings.

Here's a link to Crusier's Mostly Renix Tips." He was a teck on the floor at Jeep for years, we are super lucky to have this info.>> http://www.cherokeeforum.com/f51/cru...x-tips-153657/

If you don’t have this link book mark it; it is full of good tips on Renix Jeep’s.
If you haven’t done #1 it’s well worth the time spent; it helped me with some of my problems on my 88XJ.
 
After going over every inch of wiring I replaced the ECU and she fired up and is running. The diodes in the ECU that controlled the ground for the B+ relay must have failed and was sending voltage through the ground. Good news is, I know a little more about the renix. Hope to see everyone at the All American Jeep Show this weekend. Should be a good time. Thanks
 
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