Diagnosing Fuel Pump Issues - Defender Source
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  #1  
Old May 3rd, 2009, 08:56 AM
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Diagnosing Fuel Pump Issues

There are a number of threads related to fuel pumps but usually the pump is mentioned inside of a "won't start" thread. While my truck would qualify as a "won't start" candidate (by the fact it's sitting in my garage and I had to have it towed here ) - I thought I'd try a thread that is specifically around how to determine if the pump is bad or it's something else that controls the pump (wiring, relays, etc.)

Can someone look at this list and let me know if there is anything else I can do to diagnose? My truck is sitting in my garage unloved and unwilling to start at the moment

Summary:

I parked my truck and came out to drive it again an hour later and it wouldn't start up again. I cranks but seems to be choking for gas. I cannot hear the fuel pump humming when I turn the key to the start position. I also don't have fuel pressure (no gas) when I turn it to start and press on the valve near the injectors. There are no codes being thrown and no check engine light.

With those 2 big items it seems that my fuel pump is either dead or that a wire or relay is preventing it from turning on.

I've gone through the forum and tried to consolidate the items that could cause a fuel pump to not function - or at least how to determine if the pump is completely dead. The should be in order of ease:

Fuel Pump Fuse:
I CHECKED THIS AND IT LOOKS FINE
15A fuse in the fuse box under the hood on the driver's side. I checked it and it looks fine.

Inertia Switch:
(snipped from another thread) ...Did you try and reset your inertia fuel switch under the hood, center, near firewall? (Push the button on top). If that doesn't work try, by-passing it with a paperclip in the plug end. (If still no start, you've at least likely eliminated the inertia switch as the culprit.)

Fuel Pump Relay: HOW CAN I DETERMINE IF THIS IS MALFUNCTIONING? Also I opened the box and didn't see it from the top.
From what I understand, in the 1997, unlike the 1995s, the pump is controlled by a special multi-function relay. (NOT one of the 9 relays inside the cab right?) It is located under the hood on the passenger side inside/under the "white box." I'm assuming there isn't much you can do here to test thing right? Here is the item at AB - RELAY - FUEL PUMP - MULTIFUNCTION Item: YWB100820LG Genuine Part
http://www.roverparts.com/Parts/YWB100820LG.cfm

Change Fuel Filter:
Worth a shot. I don't know if a clogged fuel filter would actually prevent the pump from turning on. I'm going to try this later today. For me specifically I changed the fuel filter only 8 months ago. I can/should give that a shot but I can't imagine that's it(?). I hope so.

Fuel Pump Wiring: HOW CAN I SEE THIS WIRING? HOW DO I LOOK AT THE TOP OF THE TANK?
(snipped from another thread) ...figure out if the fuel pump plug end itself is corroded. There are 4 wires that run to the plug connecting to fuel pump: Purple/White is fuel pump power; Green is fuel guage power, and two Black ground wires.

Other Items:
Ensure there aren't any check engine codes, reset the codes with an OBDII reader, disconnect the batter leads for a while then reconnect.

Finally I know that the mass air flow sensor might come into play along with other fuel-related devices. Other items, to me, might prevent the truck from starting or cause it to die a mile down the road but when the truck cranks but won't start AND I can't hear the fuel pump then I have to think it's related purely to the pump and controlling items (above).... right?

Thanks for any advice... I'm especially interested in how the hell to see the wiring on the pump itself without dropping the gas tank. Is this possible?

Hutch
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  #2  
Old May 3rd, 2009, 11:24 AM
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Jason Dempsey
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I had a similar problem and it turned out to be a fuel temp sensor..simple and cheap. I did all the check symptoms, changed fuel filter, changed fuses ect
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Old May 3rd, 2009, 01:21 PM
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In a 1997, I would not be concerned about the relay (never heard of one go bad). If you are getting no gas (ie not even catching a little when cranked) and can't hear the pump, it pretty much has to be the pump or the wiring to the pump. So how full is the tank? Ever drop one before?
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  #4  
Old May 3rd, 2009, 03:22 PM
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Quote:
Originally Posted by evilfij
In a 1997, I would not be concerned about the relay (never heard of one go bad). If you are getting no gas (ie not even catching a little when cranked) and can't hear the pump, it pretty much has to be the pump or the wiring to the pump. So how full is the tank? Ever drop one before?
Good to know about the relay in the 97. I've been stranded by the relays in the 95s going bad - simple fix.

The tank is pretty full actually - just over half I think. I've never dropped one before - uggh. It's been a while since I've pulled the black mat in the tub back but if I recall you can't remove the bottom panel separately. Would have been a good idea to leave an access hatch for that LR!!!

There isn't another way to check the wiring?

I'll have someone try to start the truck while I check the valve just to be sure but I'm pretty confident it's not getting any pressure.

Also - I'm assuming it's not really realistic that a bum fuel filter would prevent the fuel pump from running right?

FYI - Jason - good tip about the temp sensor. I found it in the manual and will locate it and if cheap enough it's worth a shot.

Hutch

Follow-up Post:

Quote:
Originally Posted by jdempsey
I had a similar problem and it turned out to be a fuel temp sensor..simple and cheap. I did all the check symptoms, changed fuel filter, changed fuses ect
Would that prevent the pump from even firing up? I could see it killing it one the sensor goes off (or is bad) but I would assume the pump would start and then be killed. Just a guess.

Found it on AB:
http://www.roverparts.com/Parts/ETC6661.cfm

I feel like each possible component is about 100 bucks. If I bought them all I might as well have taken it to he local LR shop! Eeek.
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  #5  
Old May 3rd, 2009, 03:52 PM
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The wiring does run back there and I believe there is a junction that can go bad, but that might be on a RRC or earlier truck and I honestly don't know.

One other thing to check is the inertia switch which would be an easy fix.
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  #6  
Old May 3rd, 2009, 05:04 PM
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Quote:
Originally Posted by evilfij
The wiring does run back there and I believe there is a junction that can go bad, but that might be on a RRC or earlier truck and I honestly don't know.

One other thing to check is the inertia switch which would be an easy fix.
I *think* I see where the wiring veers off from a thicker bundle of wire but it looks good at the junction point. Regarding the inertia switch - do you just mean reset it by pushing it down? Someone else had mentioned bypassing it using a paperclip but I'm not sure how to pull that off. Just pushing it doesn't have an effect unfortunately.
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Old May 3rd, 2009, 06:32 PM
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You could bypass it, but it is unlikely that it is the cause. Check the junction on the fuel pump wires. Unless someone else has any bright ideas, I would start dropping the tank and run power directlty to the pump to see if it is bad.
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  #8  
Old May 3rd, 2009, 07:12 PM
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J. Michael McCaig
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Are you sure that its not getting fuel? Check for fuel pressure (32-36psi) at the fuel rail. When you first crank the engine the fuel pump should run for only a few seconds to pressurize the system until engine start then it runs continually. If it is doing that then most likely the fuel pump is operating ok and I would look another issue
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Old May 3rd, 2009, 08:24 PM
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Quote:
Originally Posted by LRover
Are you sure that its not getting fuel? Check for fuel pressure (32-36psi) at the fuel rail. When you first crank the engine the fuel pump should run for only a few seconds to pressurize the system until engine start then it runs continually. If it is doing that then most likely the fuel pump is operating ok and I would look another issue
I tried 2 things.

1. I attached a bike pump (!) to it and cranking the engine didn't make the pressure needle jump at all. (Not sure if this is a ridiculous way to test.)

2. I then simply pushed down on the needle on the valve and had someone try to start it - no gas/air coming out of the valve.

I think it's dead or something else is the culprit. Thanks for the idea - any other advice is welcome for sure...

Follow-up Post:

Quote:
Originally Posted by evilfij
You could bypass it, but it is unlikely that it is the cause. Check the junction on the fuel pump wires. Unless someone else has any bright ideas, I would start dropping the tank and run power directly to the pump to see if it is bad.
I'm pretty hands-on but after reading over the workshop manual seems like a job for a couple people and not something to take lightly or just as a quick test. I'm starting to think this has to be it - either wires or dead pump but I'm going to use this as my last resort and probably will have to tow it to the dealer (who has stuck it too me at least once or twice). Any other advice is welcome. I'm hoping for that silver bullet... perhaps a "flux capacitor" at advance auto parts?
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  #10  
Old May 3rd, 2009, 08:39 PM
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You can syphon off most of the gas to make it easy to remove (remove the big filler neck end of the rubber hose and stick the syphon hose in). If yours is a florida truck, it should not be hard to get out, only time consuming.

I am trying to think, the only other thing I can think of that gets power to the fuel pump is the ECU.
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  #11  
Old May 3rd, 2009, 09:09 PM
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Quote:
Originally Posted by evilfij
You can syphon off most of the gas to make it easy to remove (remove the big filler neck end of the rubber hose and stick the syphon hose in). If yours is a florida truck, it should not be hard to get out, only time consuming.

I am trying to think, the only other thing I can think of that gets power to the fuel pump is the ECU.
Regarding the ECU, I checked with an OBDII reader and it isn't throwing codes so I *think* it shouldn't be that.

One thing to note is that it WAS a MD truck for a couple years of its life so there are some - not a lot - rust spots. The one item that does have the most is the damn skid / gas tank cradle. As a matter of fact when putting in shocks/springs last year I snapped the bolts off the sway bars.

I'm assuming if I drop the tank that it would be a good time to replace the skid / fuel tank cradle/guard? I don't mind getting charged labor - assuming I'm not doing this myself - but I'd hate to get killed on the fuel pump and guard at dealer prices. I'd rather walk into the dealer with the parts - or order then next day air once the truck is there. Also the fuel line connectors have a little rust. If it turns out it is the pump does it make sense to replace the lines, fuel tank guard as well as the pump?
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  #12  
Old May 3rd, 2009, 09:45 PM
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just be generous with PB Blaster, my truck was a Fl for 85% of its life, it was in PA for a little while. I havent had any rust issues.
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Old May 3rd, 2009, 10:05 PM
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Quote:
Originally Posted by hutch
Regarding the ECU, I checked with an OBDII reader and it isn't throwing codes so I *think* it shouldn't be that.

One thing to note is that it WAS a MD truck for a couple years of its life so there are some - not a lot - rust spots. The one item that does have the most is the damn skid / gas tank cradle. As a matter of fact when putting in shocks/springs last year I snapped the bolts off the sway bars.

I'm assuming if I drop the tank that it would be a good time to replace the skid / fuel tank cradle/guard? I don't mind getting charged labor - assuming I'm not doing this myself - but I'd hate to get killed on the fuel pump and guard at dealer prices. I'd rather walk into the dealer with the parts - or order then next day air once the truck is there. Also the fuel line connectors have a little rust. If it turns out it is the pump does it make sense to replace the lines, fuel tank guard as well as the pump?

There has to be an independent near you that would change the pump and do a new skid plate for you. ECR has alloy skidplates for $225 on the website, but I don't know if Mike would ship you one.

Ron
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  #14  
Old May 4th, 2009, 08:12 AM
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Quote:
Originally Posted by evilfij
There has to be an independent near you that would change the pump and do a new skid plate for you.
You read my mind. Actually I've worked for a long time with a guy here in the area but Rovers are his passion and don't pay all the bills so it's tough - weekends only really and I don't want to drag this out as it's not a "project" truck . There is a shop literally down the road that I've seen Unimogs and Pinzgauers parked out front. I also have a friend with a lightweight that they've done work on so I'm probably going to give the shop a shot and see if I can build some trust. If anyone knows of a good shop in the Tampa Bay Florida area I'd be interested in knowing in case this doesn't work out.

I'll post the outcome. Thanks for the ideas.

Hutch
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Old May 4th, 2009, 11:20 PM
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I seem to have experienced a similar problem. Please let me know how things go. There is what looks like a plastic hose coming up out of my fuel tank that has been cracked and creased. Not sure if this could have led to or contributed to a fuel pump issue. Having my shop take a look this time as I'm sick of dropping the tank myself and want to get it running again asap. It has been choking out on me occasionally leading up to today. Now it doesn't sound like the pump runs at all. I'll let you know when they find something.

Brandon
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  #16  
Old May 5th, 2009, 12:02 AM
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Quick question before you drop the tank....does the check engine light illuminate when you turn on the ignition (bulb check) and then go out....or is it nonfunctional? The reason I ask is that the main relay on a GEMS motor (located near the ECU under the hood) is a combined relay that energizes both the fuel pump and provides power for the ECU. If your check engine light isn't working at all, it really could be a bad relay. There are a bunch of connectors next to the blower box under the hood. One of these should be a 2 pin connector with a green/black wire (gas gauge) and a white/purple (fuel pump). If you unplug this connector, you can check for power on the white/purple to confirm that the fuse/relay/inertia switch are working as well as ohm check the pump. I recently had a D90 with a random no start problem and the issue was with water in this connector. It is a convenient place to split the system for diagnostic purposes.
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Old May 5th, 2009, 07:56 AM
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Quote:
Originally Posted by Roadsiderob
Quick question before you drop the tank....does the check engine light illuminate when you turn on the ignition (bulb check) and then go out....or is it nonfunctional? The reason I ask is that the main relay on a GEMS motor (located near the ECU under the hood) is a combined relay that energizes both the fuel pump and provides power for the ECU. If your check engine light isn't working at all, it really could be a bad relay. There are a bunch of connectors next to the blower box under the hood. One of these should be a 2 pin connector with a green/black wire (gas gauge) and a white/purple (fuel pump). If you unplug this connector, you can check for power on the white/purple to confirm that the fuse/relay/inertia switch are working as well as ohm check the pump. I recently had a D90 with a random no start problem and the issue was with water in this connector. It is a convenient place to split the system for diagnostic purposes.
I know the mutlti-function relay you are talking about (or I should say I was told about it during this research.) I can see it under the hood buried inside the white box/cover. Yes the check engine light comes on and then goes out as it should. Interesting to know if it didn't that the multi-function relay could have been culprit.

As Ron pointed out while it's possible it's probably pretty unlikely that that is the issue because they don't go bad that often (unlike the little box relays that have left me stranded before in my 95.) In a way I hope that's not it because I will have certainly gone to a lot of trouble just to replace a simple part!

The truck is now in good hands at a nearby shop that has worked on old LRs, Unimogs, etc. They should know something today and I'll post my findings.

Thanks for the input,

Hutch

QUESTION: What is to be expected in labor/parts if the shop needs to drop the tank and replace the pump? I think the pump kit is around $250 from RN and if I need to replace the skid-plate for the tank due to corrosion that's another $250+. Just not sure about the labor. I haven't worked with this shop but a friend has. Just hoping they are fair - doesn't have to be "cheap."
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Old May 5th, 2009, 04:02 PM
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Well as annoying as this is I towed it to the shop only to find that when they tried it the next day it started up and hasn't had the problem since. The shop has been driving it around all day today.

This is really frustrating because the truck had sat OVERNIGHT in my garage and failed to start the next day after trying multiple times (warm and cold.)

I'm going to replace the crankshaft sensor to rule out that as a possibility.

I guess in theory it could be a soon-to-die fuel pump but I thought fuel pumps usually just go and don't usually show signs of "I'm about to die" but I could be wrong.
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Old May 5th, 2009, 04:03 PM
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Don't worry, it will do it again.
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Old May 5th, 2009, 04:19 PM
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Take a look at your Mass Air Flow Sensor and check for debris or a busted up screen. This seems to have caused (at least part of) my issue. The symptoms were the same. As a follow up, these sensors are expensive, can they be repaired? Anyone ever replace the screen on one?
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