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No power at fuel pump

DansGreyMj

DansGreyMj

NAXJA Forum User
Location
Nuevo, Ca
The relay turns on, I even switched them around, I tested the pump outside and it works, but there is no power at the pump and the truck just cranks. If it matters it matters it does not have a ballast resistor.
 
Oh btw, this is on an 87 Renix. I've switched relays around and nothing changed. Where is the fuse located I couldn't find it in the panel? I'm going to check the ground at the taillight tomorrow.
 
Good idea on the ground wire near the taillight.

But, have you seen the 1" by 3" white ceramic resistor mounted on your driver's side inner fendere well? That's the fuel pump ballast resistor. If it's bad, no power to fuel pump.
 
It doesn't have a resistor.
 
The 87 doesn't have a ballast resistor and is wired a little different than the 88-90.

Turn the key to the run position, the fuel pump should power up for a few seconds to prime the fuel rail. Then when the key is in the start position the fuel pump relay should close again as soon as the ECU gets a pulse signal from the CPS.

Check for spark while it is cranking, no spark or fuel and it is likely to be the CPS.

The main power for the fuel pump relay is from a fusible link. If a fusible link goes out, it is likely to affect more than just the fuel system. Fusible links are like master fuses and when they blow will shut down multilpe sub system

If I remember correctly the ground for the pump is near the pump and a sheet metal screw through the floor pan. I may be wrong, but I do remember the ground is nearby.

The power between the fuel pump relay and the pump goes through a couple of splices and connectors. And the wire changes color from orange to orange with a stripe and pink with a stripe.
 
the fuel pump ground on the mj is that ring terminal behind the driver's side tail light. i remember a guy who was completely confused as to why the truck wouldn't start after he removed the bed. :confused1
 
8Mud said:
The 87 doesn't have a ballast resistor and is wired a little different than the 88-90.

Turn the key to the run position, the fuel pump should power up for a few seconds to prime the fuel rail. Then when the key is in the start position the fuel pump relay should close again as soon as the ECU gets a pulse signal from the CPS.

Check for spark while it is cranking, no spark or fuel and it is likely to be the CPS.

The main power for the fuel pump relay is from a fusible link. If a fusible link goes out, it is likely to affect more than just the fuel system. Fusible links are like master fuses and when they blow will shut down multilpe sub system

If I remember correctly the ground for the pump is near the pump and a sheet metal screw through the floor pan. I may be wrong, but I do remember the ground is nearby.

The power between the fuel pump relay and the pump goes through a couple of splices and connectors. And the wire changes color from orange to orange with a stripe and pink with a stripe.
Click to expand...

True that the 87s came without the ballast resistor but there was a TSB on installing the resistor and associated wiring if a customer complained about fuel pump noise.
 
I didn't get the chance today, I will check the grounds and I have a spare CPS I can swap in. This sucks because it ran totally fine 30 min prior to doing this.
 
What exactly did happen? Running and died or not starting after you turned off the ignition and tried to start it 30 minutes later. I assume the latter since you mention the 30 minutes.
 
I t drove fine all day, got back in 30 mins later after a stop and never started again.
 
Check your CPS.

Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
　
Revised 11-29-2011
 
The clutch is fairly new, so it could have some debris from break in. Would a bad cps cause no power to the fuel pump?
 
Note from DJ
I am not familiar with the wiring on your 87MJ but on my 88 4.0 XJ I have 2 Yellow caped diagnostic connectors located behind, or firewall side of the relay center, if I take the cap off the smaller 6 pin connector while leaning over the passenger side front fender I have 4 female connectors and 2 blank spots in side.

If I take a jumper wire and place it between numbers 5&6, which are the two connectors on the engine side. #6 is the one closest to the firewall and is a direct feed to the fuel pump, (it is a direct diagnostic connection to see if you are getting battery voltage transmitted to the fuel pump), now if you take the other end of the jumper wire and insert it into the connector forward but still on the engine side which is connector #5 [that is a constant battery + voltage supply] the fuel pump will run for ever, if it and the wiring to the fuel pump are OK.

NOTE: this jumper wire test is best none with fused jumper wire in case there is a short in your wiring, because you don’t want to burn up your wiring if there is a short in the wiring.
 
I had a chance to check the spark, it was orange and looked very weak, I checked it at the coil and plug.
 
Try this then:

Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner.
Squeeze the springy contacts closer together with some needlenose pliers. Apply some dielectric grease to the contacts and bolt the coil back on to the ICU.
While you’re right there unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier. Apply dielectric grease to the connectors and plug them back in.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 11-29-2011
 
I cleaned all the contacts and the CPS, the spark seems stronger, but mono of it changes the fact that I am still not getting power at the pump. The diagnostic port thing did nothing.
 
It kinda fires with fuel in the throttle body.
 
So you have checked power at the pump, like a couple inches from the unit? And you're checking voltage between the power wire and ground wire? And getting a reading of zero when the key is cycled on by someone else while you're underneath watching the meter?

And FYI, testing a pump outside the vehicle is a no-no. Can blow up in your face.
 
JohnX said:
So you have checked power at the pump, like a couple inches from the unit? And you're checking voltage between the power wire and ground wire? And getting a reading of zero when the key is cycled on by someone else while you're underneath watching the meter?

And FYI, testing a pump outside the vehicle is a no-no. Can blow up in your face.
Click to expand...

Good advice here^^.
 
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