98 Escort, fuel pump not running..

[dllewell]

98 Escort wagon SE, 2.0 L, SOHC
I have Chilton's manual

I had the tank refurbished about a month ago, there were several pinholes in the tank near the filler hose connection. Yesterday morning the car would not start. I noticed immediately that the fuel pump was not coming on when the key was turned to the run position.

So i performed a battery (pun intended) of electrical tests on the fuel pump circuit. Here is what i know:

The battery voltage is 12.6 V when everything is off
With the ignition int he run position the voltage drops to 11.8

There is continunity in the inertia switch (ie. functioning properly).

When i traced the wires to the fuel pump (the harness going into the pump has 6 wires (2 for the guage, 2 for the warning light and 2 for the pump...i assume).

With the ignition switch in the run position, the voltage across this harness (while disconnected from the fuel pump) reads 11.8 and it stays on. However when i connect the fuel pump and try again, the voltage climbs to 7.8 and then drops back to zero. Presumably the 11.8 is 'stray voltage' that disappears once a load is placed on the line. In addition, the 7.8 is the voltage across the pump which is probably too low to run the pump.

Why is it too low? Well based on the wiring diagram, the only 2 faulty parts are the fuel pump itself and the fuel pump driver module (which i assume is somewhere under the dash).

For the next step i measured the resistance across the fuel pump lines which was 1.1 Ohms. This suggests to me that the pump is pooched, (ie. has a short). The resistance across the leads of my multimeter alone is about 0.6, i would have expected the resistance across the pump to be 5 to 10 Ohms.

I am still not positive thet it is the pump though. So my next 2 steps, before pulling the pump out of the tank were going to be 1. measuring the resistance across a new pump and 2. connecting my current pump directly to a 12 V power supply (i was going to use my battery charger set on the 10 Amp setting, with a 5 or 10 Amp fuse in line on the power lead). My thinking is if the pump runs on a direct power source, its probably fine.

I have searched this forum for similar porblems and came up dry. I am wondering if anybody has any more helpful advice, or if there is a flaw in my logic (ie. am i missing something)?

please help,
dllewell

[Selectron]

My Escort is diesel-engined so I can't offer any direct help, but perhaps this page in the Autozone repair guide may be of some assistance if you haven't already seen it:

Escort fuel pump fault-finding

Edit: also, be sure to check out that hidden inertia fuel cut-off switch which they mention. That turned out to be the problem for somebody in a recent thread on here although in that particular case the car was refusing to start following a low-speed impact in a parking lot - the inertia switch had tripped. Not likely to be the fault in your case but still worth a look.

[dllewell]

thanks for the response Selectron, I mentioned the Inertia Switch in my first post, it is fine. I also checked out the link that you attached. It looks like it was taken directly, word-for word, out of the Chilton manual that i have. Note the last 3 sentences:

"Using the scan tool, enter output test mode and turn on the fuel pump circuit.

Using a Digital Volt Ohmmeter (DVOM), check for voltage (approximately 10.5 volts) at the fuel pump electrical connector.

If the pump is getting a good voltage supply, the ground connection is good and the fuel pressure is not within specification, then replace the pump. "

I do not have the scan tool, but it seems to me that turning the ignition switch to run activates the fuel pump circuit (at least for a few seconds). I have done this and, as i mentioned, the voltage was only 7.8 (which is significantly lower than the 10.5 that they mention). The manual does NOT mention what to do if you dont have 'good' voltage.....

I am still suspect of the pump itself due to what i percieve is a low resistance across the pump leads....this implies (to me) that there might be a short in the pump.

However, since i do not have 'good voltage' at the pump, there might be something else wrong in the fuel pump driver module (which is the only thing between the inertia switch and the fuel pump in the wiring diagram). I have no idea where this module is or what it looks like (but i am guessing that it is somewhere under the steering wheel.

any insight is much appreciated,
dllewell

[Selectron]

Ah yes, you did mention the inertia switch - sorry, I missed it twice when I read your initial post.

Speaking as an electronics engineer, I'd say you've made a good series of tests and I would say you're on the right track. Provided that you're sure that you have positively identified the motor DC feed terminals then I think that powering it directly would be a good idea. I've never measured the current into a fuel pump but I'd be surprised if it were to be any more than one amp or so, so I'd use maybe a three or five amp inline fuse for protection during the test. I wouldn't have the charger on the 10 amp setting - I'd select the lowest current setting that you have - I'd guess that a couple of amps would be plenty.

If I knew what the current consumption of the fuel pump was then I'd be keen to connect a dummy load in its place and see how the feed voltage then held up under load. I'd select a suitable low wattage 12V lamp to serve as a dummy load, and illumination of the lamp accompanied by a healthy voltage reading would indicate a faulty pump. Conversely, if the lamp failed to illuminate and the voltage collapsed then it would point to a fault in the driver module. That's a bit academic at this point though because without any knowledge of the fuel pump current consumption it's a bit of a gamble to select a lamp wattage at random. If the current is being fed via relay contacts then it would be safe enough but if the current is fed via a series pass transistor or similar then you could easily exceed the current capabilities of the device and damage it. As I say, it's a bit academic but I'll leave this paragraph in as food for thought in case it triggers any further ideas.

A resistance reading across a known good pump would certainly help but that may not be so easy to obtain eh.

I think then, all things considered, that I'd go for feeding the pump directly from a 12V supply as the next step. If there's any fuel in the vicinity then make the 12Vdc connections to the pump first before applying power to the power supply - that avoids any sparking at the pump terminals. And then when disconnecting power after the test, pull the mains connection first and the low-voltage 12Vdc connections last, again to avoid sparking.

[dllewell]

Ok...now we are getting somewhere

I believe that your assumption about current draw is wrong. For example, the fuel pump circuit is protected with a 20 A fuse. Furthermore, in various places on the internet there is mention of the current draw required for today's high pressure fuel systems (55 to 85 psi according to my manual). These numbers vary but are all in the range of 4 to 9 Amps, with higher draws being associated with higher pressure systems as well as systems that are not operating properly (eg. clogged fuel filter).

I am not sure how measuring the current draw will help me in this case since i dont know what it is supposed to be like.

Thank you muchly about the advice re. hooking up an alternative power supply. Though there is no gas around the pump wiring harness, this is very good advice to follow whenever such a situation arises.

I will start with the charger on the 2 amp setting and will a small fuse in-line. However if this fails, how far do i go (how big a fuse) before i call it quits?

I have found a arts supplier with a new pump in stock, so i think i will purchase it at least to see its resistance. I could also connect it to the fuel circuit (but not install it) and see if turning the ignition to run activates this pump (just for a few seconds).

As an interesting side note, premature pump burn- out is often caused by clogged filter or a clogged or improperly installed in-tank strainer (so i have my suspicions about this as well since my tank was recently refurbished...perhaps the pump/strainer assembly was not properly installed).
Furthermore, when i bought the car, the person i bought it from just happened to have a spare OEM fuel filter that he gave me. Perhaps just a coincidence.... I have put off replacing this filter because it looks like a pain to replace (attached to the firewall behind the engine). But since my fuel system is likely depressurized, i guess now is as good a time as any to do that too! (sorry, off topic a bit and now i am rambling0

dllewell

[Selectron]

Ah, I see - I've been driving only diesels for many years now and I'd no idea that modern petrol (gasoline) engines were fed at such high pressures.

There are two scenarios for feeding the fuel pump from an external supply:

1. If you externally feed your present pump, then it will still be in-situ and still attempting to feed fuel through the system, and thus working against a physical resistance, as normal. Therefore it will run at its regular current rating, so probably you would need to have your charger set to 10 amps.

2. If however you obtain another pump and run it but without actually installing it, then it will not be developing any pressure - i.e. not working against any physical resistance and therefore I would expect the current consumption to be a lot less. In that case I would set the charger to a 2 or 5 amp setting.

What you have said about premature burn-out due to clogging is interesting because that ties in with what I was just saying - the greater the physical resistance that it has to work against then the more strain that will be placed on the pump itself and the more current it will consume and therefore the greater the wattage which it will be dissipating - none of which are particularly good for the pump or the driver circuit.

If you're sure about the current consumption of the pump being probably in the range of 4 to 9 amps then if it were me I would be connecting a lamp as a dummy load, in order to observe what happens to the feed voltage. To achieve a current of, say, 2 amps, just for test purposes, then a lamp wattage of around 24 watts would be required (24 watts divided by 12.6 volts = 1.9 amps). But that of course would only be if you wanted to pursue that route.

[dllewell]

since i dont have any low voltage bulbs laying around (like the MR11/MR16), i am not yet ready to pursue that route...but good information nonetheless.

I am quite interested in measuring the current draw however, unfortunately i do not have a benchmark (ie. i dont know what it should be). Having said that, i think i will measure this current on whatever pump i do manage to get running both before and after i replace the fuel filter...a fun little test!

Wish me luck, going back at it tonite fully armed with a 20A digital multimeter and a fuseable link (With 10 A fuses).

I will post my results tomorrow

dllewell

[Selectron]

One thing which does occur to me is that a bad ground connection for the pump could also cause the symptoms described. The pump will not be grounded physically via its casing, for safety reasons, but instead the ground connection will be achieved via one of the leads coming out of the six-way connector - I'd follow that lead back to its grounding point if possible and unbolt it and make sure it's clean and free from either rust or oxide. Then prior to reassembly I'd apply a coating of what we (in the UK) call petroleum jelly (Vaseline) or similar - whatever you use over there to protect your battery terminals.

The reason for that is: with the pump out-of-circuit, and measuring the voltage on the feed end of the connector, you are reading a healthy 11.8 volts. When you put the connector back in place and take the same measurement with the pump in circuit, the voltage sits at 7.8V and then falls to zero, and that could be explained by a high-resistance connection to ground.

I'll pick that up again in a moment but first I'll need to digress. In the Autozone notes it says:

"Turn the ignition key from the OFF position to the RUN position several times (do not start the engine) and verify that the pump runs briefly each time, (you will here a low humming sound from the fuel tank)."

That suggests to me that it's on a timer of some sort and therefore is designed to switch off and the feed voltage intentionally falls to zero after a few seconds.

So then, let's return to the voltage reading of 7.8 volts. You start out with 11.8 volts (open circuit) which falls to 7.8 volts when the pump is back in circuit, so I'm wondering where the missing 4 volts went to. If you have a near short-circuit within the pump motor then that could be causing it but equally possible is that the 4 volts are being dropped across a high-resistance ground connection at the chassis. The current enters the pump, goes through the motor windings and then makes its way out again via the multi-connector and heads for ground. Let's assume an operating current of around 6 amps. Now then, since voltage = current x resistance, resistance must equal voltage divided by current, so what resistance would it need at that connection to drop 4 volts?

Answer:

resistance = voltage divided by current

resistance = 4 volts divided by 6 amps = 0.67 ohms

So, it would take an oxidised/rusted ground connection of less than 1 ohm resistance to drop 4 volts at the ground connection, and as you said earlier - the remaining 7.8 volts may simply not be enough to power the pump. Therefore I would want to check out the ground connection. It does specifically mention checking that connection in the Autozone notes, and that will be the reason why. Sorry that the explanation is a bit lengthy but you obviously know your way around voltage, current and multimeters so I'm sure you will see what I mean. If I haven't made it clear though, just ask.

Good luck with your next tests, and if anybody following this has any direct knowledge of the vehicle and its fuel pump then please do jump in and comment - I know nothing about the system but my electronics knowledge may be of some help which is why I've joined the thread. Thanks.

[carlos80]

if i were you i would just run a couple of wires directly from the battery(ground and power) to the pump(for testing only) it will only draw what ever amperage it needs(which since it hasn't blown the fuse its under specs). As long as its a 12 to 14 v source it should be fine.

A good idea is to jump the pump relay terminals at the fuse box to keep power going to the pump without having to cycle the key on and off. After doing that connect the harness back to the pump and with an alternate power source backprobe the pump ground you should have less than .5v anything greater would indicate excessive resistance on the ground side. If thats within specs backprobe the power side and you should read power source which should be battey voltage(check the battery to make sure it has good voltage)going into the pump anything less would indicate excessive resistance on the power side of the circuit.

[dllewell]

Thanks again for your suggestions.

Last night i got the fuel pump to work again. Firstly, i took the battery out and put it on a trickel charge (2A) while i replaced the fuel filter. This was a no-brainer since the batter was a little low on voltage after all fo the cranking that i have been doing. As well, the only possible way to access the fuel filter is by removing the battery shelf. The filter was pretty darn hard to get to but once i got my hands on it, the replacement went smoothly. BTW the gas that came out of the pump side of the filter was an opaque brown dirty mess, but performing the blow test (just blowing on the inlet) informed me that it was not clogged....just doing its job i guess!

The battery terminal were quite corroded so i cleaned thes up as well on installation (hoping that a clean, charged battery might be enough to convince the pump into action...not so).

Anyway, then i started checking the voltage at the inertia switch and at the pump wiring harness and got nothing (where there was voltage before). This was a puzzler for a while till i checked the fuel pump fuse located under the engine and found that it had blown...this was odd, it either happened at the end of my previous diagnostics or after i reinstalled the 'refreshed' battery.

Anwyay after replacing the fuse, i performed the same diagnostics as before and wound up witht he same results.

BTW, Selectron, the when in the run position, the fuel pump comes on for a few seconds and then shuts off again until some sensor tells it that the engine is actually spinning (thats why the voltage dropped to zero after hitting 7.8).

My next step was to connect the pump directly to my battery charger (heres where things interesting):

First time through, i had it ont he 2 A setting and the pump activated (could hear the hum) but was definitely not turning. SOunded like a stuck motor (like when an electric drill gets overloaded and cannot spin the drill bit). I activated/ deactivated the charger several times (3 s each time). Then the in-line fuse popped (10 A). Hmm.... not working yet, but getting there.

Then i replaced the in-line fuse, and tried again, this time with the charger on the 10A setting. And what do you know? Off the pump went! Cool!

Then i reconnected the pump to the car, turned the ingntion and off she went. Initially, there was some stuttering but i think this was probably while the filter was filling up etc. I tried it a couple of times and it worked like clockwork...turn the key to run and the pump comes on and then shuts off in seconds, and then she started right up.

I dont think i am out of the woods quite yet though. WHen i tested the voltage at the pump (when in run) now it went up to about 10.5 before dropping to zero. Then i wired the multimeter in series to measure current and found that during that initial few second burst, the pump draws 4.1 A.

It was getting late so i quit at this time, though i think i should have gone 1 step farther and measured the 'running' voltage and current draw (ie. while the engine was actually running).

So now what? Sure the pump runs, but for how long? What caused it to stop working? Was it something mechanical (like a blockage or contaminant inside the pump), or is there something wrong electrically (like is there a 'dead spot' in the pump motor...and will it get stuck again?).

Should i be replacing the pump, or should i take my chances in getting stuck in a parking lot? I was very fortunate to have this failure with the car parked in my semi-warm garage (its -10 C here in Canada), what are my chances of the next failure happening while parked int he garage.

Will the pump work for an hour, day, week or year?

I know that there is probably definitive answer to this but i would like to hear your best guesses based on the synptoms that i have described.

BTW, Selectron, I tested the resiatance of the new, aftermarket pump thaht i bought and it was the same as the current pump 1.1 Ohms.

Thanks so much for your advice, I hope you can take the time to read this last post and make a suggestion on where i should go from here.

dllewell

[12Ounce]

I would be suspicious of your battery, it seems to be dropping quite a bit of voltage for such a low current draw. Low voltage will prevent relays from switching.

[dllewell]

Originally Posted by 12Ounce

I would be suspicous of your battery, it seems to be dropping quite a bit of voltage for such a low current draw. Low voltage will prevent relays from switching.

I am suspicious of my battery, there was quite a bit of corrosion at the negative terminal. Having said that, turning the key to run was enegising the fuel ump circuit, and once i got the pump to run 'remotely' it now runs properly when i turn the key to run.

[Selectron]

That's good news, dllewell - pleased to hear that your efforts were rewarded with success.

Regarding the motor not running when the charger was on the 2A setting - that's obviously because not enough current was available, with the motor then running okay when 10A was available. I would be tempted to say that your problem all along has been the corroded battery terminal - I assume the missing 4V was being dropped across that resistance - however, that doesn't explain why the pump still refused to run, after cleaning the battery terminals. That's a bit of a head-scratcher and it would point towards a dead spot in the pump motor, the spindle of which perhaps rotated slightly (away from the dead spot) when it was physically disturbed during the removal process.

The fact that you now have 10.5V at the pump, where before it was 7.8V would reinforce the belief that the missing voltage was being dropped at the corroded battery terminal.

Regarding the measured current of 4.1A - I assume that was measured with a digital multimeter and I've found that they always read low for current measurements - if I want accuracy then I always use my old moving-coil analogue meter. Therefore I'd say even though you've measured it at 4.1A I'd guess that in reality it would be closer to 5A or 6A (the series resistance which the meter introduces to the circuit accounts for the lower measured current - this series resistance is always lower in an analogue meter for some reason).

If the pump had operated correctly first time, after cleaning the battery terminals, then I'd say you had solved the problem and could leave it at that but unfortunately you are still left with the possibility of a dead spot in the motor. It might take weeks or months before it came to rest on the dead spot once again, and there is the possibility that it could leave you stranded anywhere, anytime, following a long period of apparently reliable operation. Therefore if you have actually purchased the replacement pump which you mentioned than I would fit it for sure, and clean the old one and store it in a dry location as a possible spare for emergency use only.

12Ounce makes a fair point - I'd keep an eye on the state of your battery, although if it's beginning to fail then I would have expected you to be having problems running the starter motor before you had problems running the fuel pump. Do keep an eye on it though.

[dllewell]

thanks yet again Selectron,

Everything you have said has been uber helpful. And i concur fully that if the battery was indeed the problem then the starter motor should be the first thing affected.

your comment about the charger at 2A vs 10A....if there wasnt enough current to run the motor at 2A, why then did i blow a 10A fuse at 2A?

cheers

[Selectron]

I shouldn't pay too much attention to the fuse because I'm sure it would prove to be a red herring and would only cloud matters. I'll ignore it for now and add a footnote by way of what I think is the likely explanation.

Whilst I was cooking dinner, I was thinking about your recent fuel tank repair, and about your fuel filter and pump. Which side of the pump (in terms of direction of fuel flow) does the filter sit on? Is it:

fuel tank -> to filter -> to pump -> to engine

or is it

fuel tank -> to pump -> to filter -> to engine?

The reason why I ask is that if it's the latter arrangement and fuel enters the pump unfiltered, then there exists the possibility that a piece of swarf/debris left in the tank following the repair could have physically jammed the pump. Given the direction of fuel flow and the physical design of the pump inlet port, would that be a realistic possibility?

That's the only further thought that I've had so I'll just finish off with what I think probably happened to your fuse.

I would say the fuse failed because of fatigue (very common), and specifically it was probably a voltage spike which killed it. Whenever you make or break the circuit to an inductive load (in this case the pump windings would possess significant inductance) you generate something called back-emf, where emf is electromotive force, more commonly known as voltage. This voltage can be very high indeed (hundreds or thousands of volts, even when being fed from, say, a 12V source) and can be calculated from the formula e = L x di / dt, where e is the generated voltage, L is the inductance of the device (pump windings), di is the change in current and dt is the time taken for the current to rise (if switching on) or fall (if switching off). Now let's put some figures into that:

L = 1.5 H (I'm taking a guess that the pump has an inductance of 1.5 Henrys - the Henry being the unit of inductance)
di = 2A (that's the change in current - rising from 0A to 2A at switch-on or falling from 2A to 0A at switch off)
dt = 0.01S (that is 0.01 seconds - just a guess at the time it took for the current to rise from zero to 2A - or fall if switching off)

so:

e = 1.5 x 2 / 0.01

e = 3 / 0.01

e = 300V

The figures I've used are just guesswork but a voltage spike of 300V is by no means unreasonable, and probably such a spike just proved to be the last straw for your fuse - even though it was well within its 10A rating, its voltage rating has probably been exceeded once too often by a voltage spike, or back-emf.

That's what causes the bright blue sparking which you will often see when connecting a voltage (even a low voltage) to a load - it's the high-voltage back-emf thereby induced which is capable of jumping the gap between the terminals which are in the process of being connected. You hear it around the house too - a little 'pop' from the speakers of a stereo system perhaps as the fridge or the washing machine or the electric light is switched on or off - the voltage spike travels around the house wiring and enters the stereo system and is able to pass through the elementary mains filtering and into the amplifier audio section, generating the characteristic popping noise from the speakers which you've probably heard before. Well that turned into a long footnote but I would round off by saying that I really would ignore the fuse failure.