Disappearing fuel pressure!

fpm

I have a Manta with LE-jetronic injection, but thats not so critical to my problem, hopefully some of you out there will be able to help me...sorry for the long post, but I want to give as much info as I can.

The car occassionally loses fuel pressure. I could be driving along, or the car could be idling,she'll start to splutter, and then die. Won't restart unless left for 10 minutes or so. It seems like the problem occurs on hot days, and has happened after idling, after 10 minutes driving, and after 90 minutes driving. When she dies, the fuel pump (mounted in a bracket underneath the car, more or less under the back seat), feels hot, and she won't run again until it cools down. Will run for another few miles/minutes, before heating up and dying again.

What I've checked so far:
1) Return lines to the tank - all clear, no blockages.

2) Fuel pump relay - output line to fuel pump is around 13v constant, even when she's spluttering and dying. Theres a connection in the line to the pump, made in the passeneger footwell, just with a spade connector,
and I've also got 13V here. Only about 5-6 feet of cable between here and the pump.

3) Pump Ground - Made to body, and ground is good.

4) Voltage across fuel pump - Normally 13V-ish, but as she starts to splutter, the voltage is slowly dropping, and eventually when it gets to around 10V, she stops. Although strangely when the car is started first, you have to give it a bit of a rev to get the alternator to kick in (she's always been like this). Before it starts charging, the fuel pump is getting around 10V, and car is running quite OK.

5) I've used an ammeter to measure the amps being pulled, and the pump is pulling a pretty constant 3amps.

6) Resistance across contacts on fuel pump is around 2ohm, cold or 'hot'.
(Now points 4,5, and 6 don't add up to me - V=RI?)

7) Fuel filter - old one was quite dirty, replaced with new item, problem persists. No idea if the old fuel filter was 12 months or 12 years old though.

8) Running a separate ground cable to the battery, or running a separate +ve feed, problem persists. Interestingly, after I'd run the separate live feed, she refused to turn over, like it had emptied the battery. Needed a jump start to get it to start, but didn't require the battery to be charged.

My only conclusion is that the fuel pump itself is somehow bad, I can't think of what else to try now. The fact that its getting hot can't be a good sign, also that the (after-pump) fuel filter was dirty, means that the fuel pump could be quite dirty too. Although the fact that the amps being pulled stay constant, even as the voltage across the terminals is dropping, doesn't add up.
Anyone any suggestions?
Thanks in advance.
F

BeardyGit

Depending on the type of fuel pump you may be able to strip it - A Facet Interruptor can be stripped and cleaned and then reassembled with a new filter. Parts, and whole pumps here:

http://www.demon-tweeks.co.uk/Motorsport/Fuel_System/Fuel_Pumps/1542

Double check whether you need a blue/silver/redtop if you're tempted to go for one - They each pump at a different pressure. They're very reliable. Don't know about the solid state, but the Interruptor's a good unit.

While you're at it, it might be worth fitting a filter before the injector rail, if you don't have one already.

I'd agree though that a dirty filter post fuel pump isn't a good sign, nor is the pump feeling 'hot'. But you could also have a fuel pressure loss due to other things, like pipework or a fault injector. Did it seem to be running rich before this started occurring?

fpm

Thanks for the reply...

Didn't seem to be running rich, but I haven't actually checked with a meter. It drives 100% fine, right up until the point it starts to splutter and die...

I've checked the pipework for leaks and all seems OK. Why do you say a faulty injector? Thinking an injector might stick open, and drop the pressure by flooding a cylinder?

Current pump is a Lucas item, I've found an instruction on how to disassemble on the web, but I'm pretty sure its an irreversible process, more of a 'pull apart to see the insides', than a strip and clean, since the pump housing has to 'uncrimped' to get the motor out. I can get an equivalent replacement from Sytec. I will be putting in a pre-pump filter when I get the chance.

I will get a pump if needs be, I just don't want to waste money on one if thats not the culprit - interetsed to hear other opinions before I spend money on a pump, and then find out I've missed something else!

BeardyGit

fpm wrote: »

Thanks for the reply...
I've checked the pipework for leaks and all seems OK. Why do you say a faulty injector? Thinking an injector might stick open, and drop the pressure by flooding a cylinder?

That was my line of thinking....yeah.

kasper

hi i may be going in the wrong direction here but there is almost certainly a filter on the petrol pick up pipe in the tank and when they get blocked can have more or less the same effect , cure is just to push it into the tank with a brazing rod or such , or take the tank out .

Anan1

I had a very similar thing a while back, finally decided the fuel pump was on the way out and temporarily seizing when it got hot. Replaced it and the problem disappeared.

ikb

I'd try to confirm no blockage,sludge, water in fuel tank first. Then tackle the pump- Mostlikely is possible to strip it ok. A new one is possibly 70/80 quid??
Then strip the old one and keep it for spares.
(If the pump is running while dry- impellers will heat up and possibly seize)

fpm

Thanks guys...regarding sludge, or a tank filter being blocked, I would have expected that to be the case all the time, just not every now and then? Although I guess theres a chance that a lump could be sucked up once in a while, causing a blockage and leaving the pump to run a bit dry and get hot. Hmmm...sounds possible.

@Kasper: Don't want to take the tank out if I can help it, you say it'd be OK just to push it back into the tank? Could it not be picked up again and lodge somewhere?

I still can't understand why the voltage seems to drop across the pump terminals though...that beats me.

kasper

if you push the filter off it is a cup shaped cap that fits on over the pick up pipe , i would think in every instance i have done it that it would just roll around the bottom of the tank and should be out of reach of the pick up pipe , the **** that gets dragged up can be put through an external in line filter that can be changed when need be , the pick up pipe in the tank doesnt is not touching the bottom of the tank