Welcome to our resource for MG Car Information.
MG Midget and Sprite Technical - Fuel delivery prob. New pump?
|I have an ongoing fuel delivery problem. The car is fine most of the time, but at sustained high revs, or WOT passing other cars or going flat out uphill the engine starts to flutter and misfire. If I back out of the throttle it comes back and I can continue, but if I boot it again it repeats the misfire.|
I've checked the clamps on the tank to pump pipe, ie upstream of the pump and there doesn't seem to be any air leaks. The pump is an electronic version of the original SU one although it is not made by SU. When first switched on before starting the engine the pump runs all the time as opposed to priming the carb and then stopping. It's a problem I've had for a while now, so I was thinking about getting a Facet pump. If I do, which one would be the correct one for my car? 1133cc. HIF44 carb with a BDL needle.
Thanks as always.
|Hi Bernie I wasted about 6mths to a year trying to find out what my fuel problem was. Eventually I found out it was the tank inner filter was almost blocked. !!!!!|
|Robert (Bob) Midget Turbo|
I had a similar problem earlier in the year. I had an aftermarket fuel pump which was quite new. I replaced it with an original SU from Burlen and the problem went away.
|Bernie - Disconnect the fuel line from the carburetors and direct it into a container marked at the 1 pint level. Turn the ignition on and see how long it takes to pump 1 pint - should be less than 30 seconds and not be full of bubbles. Bubbles indicate an air leak on the inlet side of the pump - either in the line from the tank, the pickup tube inside the tank or the pump itself. For more troubleshooting tips, see the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ Cheers - Dave|
|One reason why I took so long to find my problem was that I tried something similar to that suggested by David. The pump would have run all day and all night delivering fuel so I thought it must be something else. However I think that test was flawed and in reality what was happening was that when the car was travelling dirt and debris would be swishing around in the tank and ould be captured by the filter thus bloking it when travelling. Wasted a years pleasure!!|
|Robert (Bob) Midget Turbo|
either the pump has too low of a flow rate, or there's a clog in the intake line
with an aftermarket pump, insufficient flow rate would be my first guess, as that is what happened with my car, and went away after fitting an SU instead
but, with any old car, it is also a pretty good idea to check out Bob's suggestion too though, as clogging is way cheaper to fix!
|Check the bottom of the tank for debris and sediment.|
I had this years ago, and never resolved it until the tank rusted and I changed it. When I looked in the tank I was amazed at how much crap was in there. Befor that I kept trying all kinds of solutions.
Obviously it's fuel starvation, you just have to work out why.
Drop the tank and take a look. It's only time your wasting if it's not the cause.
|Thanks for all the varying input chaps. The tanks is the original one, but I cleaned it out thoroughly during the restoration.|
Bob. The blocked filter theory has been nagging me, but I was trying to avoid dropping the tank, but as Lawrence suggests, I may have to do it.
PJ and Norm. Your solution is why I was asking about the Facet pump. I have been thinking that the aftermarket pump I bought was of unknown quality, ie. just because it's new doesn't make it good.
Dave. That's a great site. I'll be reading it in depth.
With regard to the Facet pump, if it does turn out that the pump I've got is at fault, which model Facet should I get?
|I've just been reading Dave Dubois's website from the above link and I'm starting to think maybe I should avoid the Facet pump and go for an electronic SU. What do others think?|
|Bernie - While I am a great proponent of using SU fuel pumps, in all fairness, I have state that there is nothing wrong with the Facet pumps (other than their rather loud and continuous chatter). The Facet pump is a piston style pump rather than a diaphragm pump like the SU. Unlike the SU pumps, the Facet employes a bypass valve in the piston that establishes the output pressure, which leads to two situations that I find less desirable than the SU pumps, where the output pressure is determined by a volute spring. The use of the bypass valve causes the Facet pump to chatter away continuously regardless of fuel flow being stopped by a full float chamber or a clogged inlet or outlet. The result of this action, is that one means of troubleshooting (the MK I ear) is denied to the user. The SU pump stops clicking whenever the float bowl is full or the outlet side of the pump is clogged, which is a good thing foe determining what is happening with the fuel flow. The pump stalling in these two situations is not harmful as the pump is stalled in a current off condition. On the opposite side of the coin, a clog on the inlet side of the pump also stalls the pump (indicating a problem), but does so in a current on condition, which can cause damage to the pump is it is left with the power on for a long period of time (for instance, while troubleshooting). The Facet pump, as stated above, with its bypass valve continues to chatter away, with only a slight change in tone to indicate that it is not actually moving fuel. On the plus side, the Facet pump is not damaged by a clog on either side of the pump.|
The proper Facet pump will work fine in any MG, other than transmitting a lot of noise into the passenger compartment, which can be eliminated by mounting it on a pair of sound isolation mounts (which, if I remember correctly are also used as mounts for the exhaust pipe on a midget). The Facet P/N for the Cube style pump that can be used on MGs where the pump is mounted under the car, near the fuel tank is 40178, 40217, 40241 or 40254 (all of these have an output pressure of 4psi or less. The differences are in the lead termination and/or the inlet/outlet fittings). The newer, Posi-Flow style Facet pump P/N that is usable in MGs is 60104. Cheers - Dave
|Dave. Thanks for the detailed info on Facets and the pros and cons involved.|
I did a test from a can mounted at the same height as the tank and the pump continued to run even when the float chamber was full. I then disconnected the pipe at the carb end and directed the pipe into a 1 pint container. I'd still be there now waiting for it to fill the container, so it looks like the pump is faulty. It must have been just about keeping up with the engine at cruising speed and when I booted it the float chamber gave the required fuel until it got ahead of the pump, at which time the misfire occured. So, new pump it is. I would have expected a bit more than three years and approx 5000 miles out of a brand new pump. Still, at least I've managed(with help) to solve the problem,............I think.
Thanks to all, especially Dave for his in depth postings. I'll get back on here when I've fitted whatever pump I decide on and let you know the result.
|Right. Job done. I eventually went for a Quinton Hazel equivalent to the SU. It seems that anything with the SU logo on it demands a higher price (£103). Anyway I have used Q.H. products before and found them to be of high quality, so that's it, £50 and the problem has gone away.|
|Wow, only 3 years. What's happened to the quality of the SU pumps then.|
Mine had been pumping for 20 or so years. And the one before that was the original.
Are you going to strip the faulty one, and figure out what's wrong with it?
At 103 quid each new, it might be an easy and worthwhile fix.
Then you have a spare. Or you could sell it and get some or all of the money back for the QH replecement.
|Lawrence - Bernie stated in is first post that the pump was a SU clone.|
Bernie - What was the brand of pump that failed on your car? By the way, the QH pump you purchased is a Hardi, a German clone of the SU. It is (or used to be) a really good pump other than the fact that repair parts are not available for them. Cheers - Dave
|Ah Thanks David, lazy reading on my part.|
Glad to know the originals are still good items then. :)
|The pump I took off is called ECCO (Pic attached)
|I've never heard of this make before I bought it as a direct contactless substitute for an SU. It was pretty cheap (Ebay), so I guess you get what you pay for. I think the problem was that one of the non-return valves was stuck because I did the suck test and it wouldn't hold on my tongue. so I blew very hard into the outlet hole, tried again and it worked, so maybe there was a bit of crud holding the valve half open so that some but not all the fuel was to-ing and fro-ing in the pipe. It seems to have cleared now so I'll keep it as a spare, or maybe I could find a use for it on the bench. |
I only finished fitting the new pump at 5pm yesterday and the roads were a bit crowded, so I couldn't do a proper test run, but it's a glorious day today so I'll be going for a good blast this afternoon. I can't seem to upload another pic, but the pump is the same diameter as an SU but somewhat shorter.
|Lawrence. With regard to stripping the old pump, you can pop out the two pipe spigots but you can't get any further and you can't get at where the diaphrgm is. The top seems to be sealed to the body. I guess it must be a disposable pump. |
|Here's the other pic.
|Bernie - The ECCO pump is being made by Fuel Flow in New Zealand. It is basically a remake of the old AutoPump or MoProd pumps. The old style pumps had a nasty habit of developing cracks, but I have been assured by the managing director of the company that this is no longer a problem. If that proves to be true, these should be a good aftermarket pump to be used, although new, they are not real inexpensive. I would suggest setting the pump on the bench and pumping mineral spirits through it for awhile to insure that you have cleared the obstruction in it. If it continues to pump well, it would be worthwhile carrying as a backup pump. Since it is a solid state pump, you don't have to worry about points filming over from disuse. Cheers - Dave|
This thread was discussed between 24/09/2011 and 27/09/2011
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.