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MG MGB Technical - Fuel pump problem

Hi,

I think I'm having an issue with the fuel pump on my '78 B.

It was replaced late last year with a new electric pump after my old one suddenly failed. They suggested it was caused by dirty fuel, so they added a filter between the tank and the pump to help prevent a recurrence.

The other day I tried to start it and it took a while to get started. Wasn't surprised because I hadn't run it for 2 days and it was sitting in very cold conditions in Katoomba, Blue Mountains (not quite cold enough for ice/snow).

It started eventually but died shortly afterwards. It was like it had run out of fuel. I checked the filter under the bonnet and it was empty. Noticed the pump wasn't making the usual clicking noise. I thought maybe all the luggage I had in the trunk had knocked something out of place, so I removed everything and disconnected/reconnected the lead. I checked with a multimeter and there was constant power to the pump when the ignition is on.

I noticed when I disconnected/reconnected the power lead the pump would start clicking for a few seconds then stop. I did this 3 or 4 times until the filter under the bonnet was filled with fuel. Started the car and it ran okay for a few minutes then died again. Same problem. Repeated everything and got it going again.

Did this another 2 times and eventually it seemed to be okay for long enough that I risked driving back to Sydney from the mountains. Made it all the way home without an issue, so I guessed it was just something due to the cold or the car sitting for 2 days without starting.

Next day I left for work. Made it about 3-4 kilometres and same problem happened as I was driving up a steep hill. BTW the tank is at least half full so I know I'm not running out of fuel.

Instead of disconnecting/reconnecting the power, I simply turned the ignition off and waited a few seconds then switched it back on again. Pump clicked for a little while and stopped. I started the car and it got me another couple of hundred metres before it died again. This happened 3 more times and I turned around to attempt limping the car home. Managed to get it home without it dying again.

Sitting in my driveway I tried to check everything. Pump clicks long enough to barely half-fill the filter under the bonnet. The extra filter between the tank and the pump appears to have almost no fuel inside even when the one under the bonnet appears to be getting filled.

I could get the car started and leave it running for a few minutes (anything up to 7-8 minutes I guess, I didn't time it). Then it would die and I could see the filter under the bonnet is empty again. Without touching anything I checked the power lead on the pump and it has power. Disconnected/reconnected it and it pumps for a few seconds then stops.

Is this just a case of Lucas Prince of Darkness haunting me, or is there something I'm just not seeing?

Any help/advice would be appreciated.

Cheers,
David
D O'Brien

I had the same symptoms recently; do a search for the thread under:fuel starvation. Do you have SU HIF4 carbs? My problem was that the carbs were flooding. Somehow this cause the fuel pump to stop working and the filter to empty out. Take the carbs off and check the float height.
willieL.

David - See my article, Fuel Delivery Troubleshooting Guide at: http://www.custompistols.com/cars/dave/ddFuelDeliveryTroubleshooting.htm
with particular attention to the check that puts a hose from the pump inlet into a can of fuel and see if it pumps fuel then. If it does, then you have a clog on the inlet side of the of the pump. Unless the tanks down under are very dirty, it is not likely that you are having a problem with dirty fuel in this day and age and if the fuel is dirty, it would have to have fairly good sized rocks in it to not pass through the pumps internal filter. Most of the time, debris in the fuel comes from a rusted fuel tank. Putting a modern, high efficiency filter between the tank and the pump to correct this kind of a problem is going to result in an all electronic pump failing completely. If the filter clogs to the point where it won't pass fuel, the pump will stall in a current on condition and if power is left on for any length of time when this condition exists (such as when troubleshooting) the internal swamping resistor inside the coil housing will burn out. With an all electronic pump, the circuit board also become scorched. The bottom line, once the resistor burns out and the circuit board becomes scorched, the pump quits working all together.

From your description, my guess is that you have a clog on the either the inlet or the outlet side of the pump, that is not yet completely shutting off fuel flow, but severly restricting the flow and causing the pump to stall. I would bet the inlet side of the pump due to the fact that by turning the ignition on and off, you can get enough fuel pumped to get the car started. You need to determine where the problem is. Thinking about the problem while I write this, I would suggest removing both inlet and outlet lines from the pump, turn on the ignition and see if the pump runs. If it does, then proceed with the other tests (being sure to turn the ignition off between tests to keep the pump from overheating if the inlet side is clogged).

Let me know what you come up with and I'll try to help you find the problem. Cheers - Dave

David DuBois

Do you have the same problem if the gas cap is off? Is the vent clogged?
Kimberly

I replaced the filter between the tank and the pump. Blew through the old filter and it seemed to be okay. So at this point I'm thinking I've just replaced a perfectly good filter and the problem won't be fixed.
Correct. Still got the problem. At least the new filter only cost a $5.

So I pulled the line off the carbie and ran it into a bucket. Turned on the ignition and watched it slowly pump fuel into the bucket. I'm not totally sure, but it did appear to be pumping a bit slow. It wasn't spluttering and the stream was steady, so maybe it's just my imagination.

Anyway, I decided to look in the float bowls of the carbies. I noticed I could not see the oil inside which is normally up to the bottom of the threads inside the top of the bowls. I accidently stripped the threads on the screw cap for the front carbie so it popped out of the carbie as soon as I applied any throttle. This made the engine run a bit rough, but I was surprised it somehow let me get all the way home without any further fuel problems.

I checked under the bonnet when I got home and the filter still appeared to be almost empty. Left the engine running, expecting it to die shortly. It just kept running.

I topped up the oil in the float bowls and applied some Threadlock to keep the screw cap in. Ran the engine for about 10 minutes without a problem. Drove to the shops and back. The filter under the bonnet still appears low (I'm sure it used to be almost full when the car was running before all these problems). Either way, it seems to be working anyway.

Now I just have to figure out a new problem. The clutch suddenly went funny on me. No other way to describe it. It's not completely gone, but I have a feeling it's about to. That's another story for another post I think.
D O'Brien

the azx1307en fully electronic fuel pumps break down a lot more than the azx1307 which has points but will last a long time
ste
Ste Brown

Mine tick until it build up pressure then stops until I start the car.

I had a similar problem to yours, it ran for a while then stopped.

I found out that the vented pertol cap was not venting and the tank was building up a vacuum, the engine ran while emptying the float bowls in the carb then would stop.

You can tell by opening the cap after it stalls and listening for a whoosh when the air rushes back in.

Liam
Liam H

Sounds like the points are iffy, mine did that for a short while before packing up altogether.

The SU pump should deliver *at least* one Imperial pint per minute, with negligible bubbles.

I also had a Moprod 'pointless' pump on the other car and that started playing up - short stroking and causing fuel delivery, and the problem with electronic pumps is that when they *do* start playing up you are stuffed, short of replacement. At least with points pumps you stand a chance of getting them going again. I'd refurbished the points on the pump off the roadster and kept it to hand, put that on the V8 in place of the electronic, and it has been fine ever since. I'd never have another electronic pump.

Fuel starvation from a blocked vent should only happen after several miles of running. Vented filler caps generally have a valve in the cap to prevent leakage in a roll-over, and on mine at least I get a small 'sigh' when removing the cap after running a while. Don't confuse this with the much larger 'GASP' of a completely blocked vent.
Paul Hunt 2

I remember the first time it happened I removed the fuel cap to check if I actually had fuel in the tank. There was no sudden release of pressure.

Replacing the filter between tank and pump didn't fix anything.

Stripping the thread on the screw cap on top of the front carbie meant it was sitting loose all the way home. No idea how, but that seemed to do the trick. Aside from the problem with the clutch that happened just as I got home, everything seemed fine.

The filter under the bonnet still appeared to be low, even though the engine was running without any signs of dying like before. I checked the oil level in the carbie dampers and filled them up to just below the threads. Added some Threadlock to the one I'd stripped and started the car again. After a few minutes the filter under the bonnet filled up almost complete and the engine continued to run without a problem.

I'm wondering if my problem all along was the carbies flooding as suggested by willieL.

Now I've just got to sort out the clutch problem. I think I'm going to need a new one. :(
D O'Brien

Just for the record, the AZX 1300 series pumps should provide just over 2 Imperial pints per minute. Cheers - Dave
David DuBois

Mine gave up working on the Westgate bridge (worked everywhere else). I used to work on the other side of the West gate bridge, of course.
The pump from a carby' subaru (I used one from an 82), honda etc may be tucked out of sight into the top rear passenger side corner of the engine compartment. I just wrapped a bit of foam around it and pushed it out of sight. The location and the the fuel line holds it securely in place. Takes about half an hour to fit, including bypassing the old SU with a bit of fuel line.
It even makes the same SU noises, but works better & cheaper.
Just a thought.
Peter

David,

It sounds like you have the same exact problem I was having with a B, of same vintage, I was JUST helping a friend with!! It was a 1977 or 1978 US Spec B that kept running out of fuel,or at least acted in that manner. When I pulled the fuel line from the carb, that had been changed from our factory supplied Zeinth to the current Weber, I do not recall getting any more than a couple drops of gas. May be none!! I took the cover off the pump and gave it a couple good hits and it appeared to start pumping so I went for a ride. However, it wasn't long that it again acted like it had NO fuel again. Back to the house after it seemed to recover and let it sit for a couple days. The next time I went to start it, no noise from the pump what so ever. Again, I gave the pump a couple shots but nothing this time. So with brand new electronic pump in hand I proceeded to change out the pump. However, I noticed(coming to the climax) when I was removing the pump that the black ground wire going to the body seemed loose. Okay, hook the pump up directly to the battery charger and pumping as good as a new one. My solution was to tighten the factory ground wire on the pump, that is grounded behind the lience plate braket(on US cars) and run a second ground inside the trunk that I terminated to the one of the fuel pump cover screws. I also checked the ground wire behind the liecne plate braket for good/clean ground. The pump is pumping like crazy now and all of the running problems are GONE!! The new electronic pump is back on the shelf for the next user.

If this information was provided in one of the previous responses . . . Sorry, I overlooked. Otherwise HTH. It sure did in my situation. You already checked the other items I would have mentioned.

Again, HTH

Fred
Fred Wright

Well I thought I had it fixed, but I was wrong.

After the clutch went and I spent $1000 getting a new master cylinder and clutch installed I picked up the car and spent a day getting used to the new clutch. Everything seemed to be good (except I'm still getting used to a new clutch).

This morning heading to work, same problem with the fuel as before. I've worked out that it happens when I'm going up a hill.

It doesn't have to be steep, just a gentle upward incline. If I drive more than 100 metres it starts to run out of fuel. If I drive up a shorter hill it gets me to the other side and then it almost dies on the way down the other side, but manages to come good before it totally dies.

I've unplugged the hose from the carbie and turned the ignition on so the pump would activate. It pumps continually, half filling a standard size bucket in about 10 minutes (sorry I'm not sure how many litres/gallons the bucket is).

My father says it almost definitely sounds like the carbies are the problem. He thinks maybe something stuck under the needle and it gets blocked when I'm going up hill because of the different load on the engine and something about how the carbies work under different loads (uphill or downhill).

I've checked the damper oil in the carbies, but I'm not sure about the float level. Is float level the same thing as the damper oil?
D O'Brien

Or maybe the pick up in the tank has fractured?
Stan Best

If the pickup in the tank was fractured would it still be able to pump through continually when I disconnect it at the carbies?

I also just tried running a clean hose from the outlet of the pump into a bucket. It pumped continually the same as at the carbie end, although it was a little bit faster. It wasn't much faster so I don't think there's a blockage between the pump and the carbies, but just in case I did the next step.

Disconnected the hose at the carbies and blew back into the line to see if it was clear all the way back to where it was still disconnected from the pump outlet. It didn't seem too hard to blow through, so I'm assuming no blockages there.

I reconnected everything except for the hose at the carbies. Turned on the ignition again and watched it pump continually into the bucket again. I put my finger over the end of the hose and it stopped pumping immediately and the filter drained empty within a few seconds. Removed my finger but it didn't start pumping again until I turned the ignition off/on. Each time I blocked the hose it stopped it until I turned the ignition back off and on again. As long as I didn't block the hose it continued to pump until my bucket was almost full (it's a 5 litre bucket I found out).

I stopped the ignition. Reconnected the hose to the carbies. Turned on the ignition. Pump gave about 3 or 4 clicks and stopped. The fuel inside the filter barely touches the bottom of the filter material. Turning the ignition off/on restarts the pump but it only gives 1 or 2 clicks each time now.

Disconnected the hose from the carbie. Connected a clean hose and tried blowing through it. Not sure if I'm supposed to be able to blow air through the carbies or not. Either way I couldn't blow anything through at all. Tried opening the throttle and manually lifting up the piston inside the carbies. Removed the dampers. Nothing. I can't blow anything through those carbies.
D O'Brien

I decided to test the "uphill" factor by jacking up the front of the car.

Disconnected the hose at the carbies. Turned on the ignition. It pumped for about 30 seconds then stopped.

Now I'm wondering what the heck is going on. It sure doesn't look like the carbies anymore.

Going to wait until tomorrow and work out a way to remove the back wheel (so I can access the hoses at the pump) as well as having the front of the car jacked up high enough that it's on a reasonable incline.
Then I'll see if the pump runs continually with it disconnected at the outlet side of the pump.

For now, dinner and sleep.
D O'Brien

It seems that you have a faulty fuel pump here. The pump is capable of pumping fuel when there is no resistance (into a bucket) but as soon as some resistance is felt it stops which would be normal in any case. What it cannot do is to pick up pumping again once the resistance has been removed and needs the impulse of an ignition switch off and back on again to get going. If you measure the current draw during this condition you will find that the pump is actually stalled and drawing excess current over and above the run current. The only sure answer is to replace the pump.
Iain MacKintosh

David,

Have you tried removing your vent/overflow tube from the side of your carb. May be your vent isn't venting which will not allow fuel to enter the fuel bowl. Would be easily determined by simply removing the pipe(s) and seeing if your problem continues. Not clear how that works going up hill and such but may be worth a try.

Fred
Fred Wright

I spent ages messing around with that SU fuel pump. Took it to bits, replaced points, adjusted armatures endlessly. Got well soaked in petrol. I suspect that the solinoid, main coil, in the body was faulty. You need a powerful press to get that in and out.
Essentially the 30 year old pump had worn out.
I put in the Subaru one(had one availiable) in a hurry one day as a quick fix to get to work and left it there until I did the V8 conversion a year or two later. The power for the fuel pump is a white wire bullet connection just south of the main fuse box. I wrapped a bit of foam rubber around the pump and pushed it onto that hole at the passenger side rear of the engine compartment. The location and fuel lines kept it secure.
It worked perfectly, cost nothing, sounded the same and did not have to be screwed in place.

It might be a case of just replacing the points (David D is very expert on SU pumps by the way) and if you don't mind spending time and $ on it, it is worth a shot. I seem to recollect paying way too much for a set of points by the way.
If it is the points, an indicator is that the pump can be made to fire by hitting it hard, which is what you generaly feel like doing in these instances so that's a plus.
If you are in a hurry to get the car reliably on the road, go buy a new pump. If you are thrifty, go get a subaru pump (or honda civic) from a wrecker. The subaru pumps are located in the top passenger side of the engine compartment and are easy to get at.
Peter

PS- subaru pumps should have a filter prior to the pump. So I ended up with two filters, one prior and one post. It was easier that way (I was late for work and in a hurry)
Peter

Definitely sounds as though your pump is failing.

It is even struggling to pump the fuel uphill.
Dave O'Neill 2

Sounds like a points problem - they will close again ready for the next stroke with little resistance to fuel flow i.e. a raopid return of the diaphragm, but with resistance i.e. your finger over the end and the consequential slower return will not make contact. This could be the contact surfaces, or very marginal adjustment of the points mechanism. This should be set such that one turns the diaphragm one way or the other until when manually operated the points just throw over, then screw the diaphragm into the points trunnion another four holes.
Paul Hunt 2

This thread was discussed between 13/06/2007 and 22/06/2007

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