Fuel flow issue
Discussion
My 280i cuts out intermittently and after installing a fuel pressure gauge I see that the pressure drops as the engine cuts out.
Previously I just replaced the inj pump due to its death by ingesting gasket material (sticking out of its dead mouth when removed). To solve this problem I installed an in line screen filter - approx 40 micron, just ahead of the pump.
I continue to have fuel flow issues! Drained tanks and inspected new filter. Small black particles in screen. Now tearing everything out, sealing tanks, replacing hoses and rusty swirl pot.... What a fun project.
Question: might I have actually induced another issue by adding the in line screen filter? Could it aerate the fuel with the high flow, much like the screen aerator on our water faucets??
Or can the pump stall with bits as small as 40 micron??
thanks for any thoughts,
Scotty
Previously I just replaced the inj pump due to its death by ingesting gasket material (sticking out of its dead mouth when removed). To solve this problem I installed an in line screen filter - approx 40 micron, just ahead of the pump.
I continue to have fuel flow issues! Drained tanks and inspected new filter. Small black particles in screen. Now tearing everything out, sealing tanks, replacing hoses and rusty swirl pot.... What a fun project.
Question: might I have actually induced another issue by adding the in line screen filter? Could it aerate the fuel with the high flow, much like the screen aerator on our water faucets??
Or can the pump stall with bits as small as 40 micron??
thanks for any thoughts,
Scotty
Hi the swirl pot should have a pre filter built in, but these can come loose, so if you get a new one, it should be ok not to have the pre-filter.
Also you should have a filter after the pump, this is a very fine filter, you can pump dirty fuel on one end and it will come out clear the other. so is very fine. is this is not working as it should your going to get blocked injectors.
The fuel pumps can handle a small about of debries tho, with it will cause them to pack up.
as long as your getting the right pressure at the fuel rail at 3-4000 RPM then you should not have to worry about if the filer is a problem or not. If you have not got a real fuel presure gauge then you can rig up a foot pump.
Also you should have a filter after the pump, this is a very fine filter, you can pump dirty fuel on one end and it will come out clear the other. so is very fine. is this is not working as it should your going to get blocked injectors.
The fuel pumps can handle a small about of debries tho, with it will cause them to pack up.
as long as your getting the right pressure at the fuel rail at 3-4000 RPM then you should not have to worry about if the filer is a problem or not. If you have not got a real fuel presure gauge then you can rig up a foot pump.
Thanks for your response!
Yup, thanks to you guys I am now aware of the screen in the swirl pot - mine is loose. Thus the new fabrication now underway.
I would rather keep an external pre-filter so I can inspect & clean if necessary. BUT, if it is inducing aeration (as it is only a couple of inches from the pump), this could be the new cause the fuel pressure drop???
I am aware of the large canister post-pump filter. It was replaced.
There is a proper electronic high pressure gauge now installed - that's how I know the pressure is dropping as the engine cuts out.
Yup, thanks to you guys I am now aware of the screen in the swirl pot - mine is loose. Thus the new fabrication now underway.
I would rather keep an external pre-filter so I can inspect & clean if necessary. BUT, if it is inducing aeration (as it is only a couple of inches from the pump), this could be the new cause the fuel pressure drop???
I am aware of the large canister post-pump filter. It was replaced.
There is a proper electronic high pressure gauge now installed - that's how I know the pressure is dropping as the engine cuts out.
The pre filter may be too restrictive, as the pump is gravety feed from the tanks, and only pushes fuel, so need a good steady flow.
I Know my filter is loose, and don't have a 2nd pre-filter, I do have a new swirl pot on order, but for now running no pre-filters, the tanks have been emptyed so know there is not too much sh1t in them.
so it would not do any harm to try it yourself with no filters just in case.
I can see the Am I mad posts about not running a pre filter. but the old one I took apart had holes in it, plus did not seem to have any debrits on it. and I've done 40 miles, and ran it about 30 mins on / off while doing some fixing.
So should not be a problem giving it a quick try.
other option swirl pot may be a bit blocked, if your taking it off back wash it with a garden hose, and then let it dry.
I'm surprized it not leeking, or is it a Ali or stainless one.
Good luck,
I Know my filter is loose, and don't have a 2nd pre-filter, I do have a new swirl pot on order, but for now running no pre-filters, the tanks have been emptyed so know there is not too much sh1t in them.
so it would not do any harm to try it yourself with no filters just in case.
I can see the Am I mad posts about not running a pre filter. but the old one I took apart had holes in it, plus did not seem to have any debrits on it. and I've done 40 miles, and ran it about 30 mins on / off while doing some fixing.
So should not be a problem giving it a quick try.
other option swirl pot may be a bit blocked, if your taking it off back wash it with a garden hose, and then let it dry.
I'm surprized it not leeking, or is it a Ali or stainless one.
Good luck,
It is the stock steel bit from TVR - rusty but no leaks.
I figured the internal screen has pretty large holes in it - have you actually torn yours apart and/or seen the internal screen?
I already did the water thing and it flowed very well.
It probably doesn't take much to stop the pump - the tolerances are quite small and there are a number of steel cylinder "plugs" that rotate in a slotted wheel - like bearings in a carrier. Any debris is going to score the walls, even if it doesn't totally stall. Luckily this pump (higher pressure than the V8 pump) was used in all of the Mercedes 350SL, 400, 450, 480.... Not cheap, but readily available. Unfortunately I will be ditching it when I swap in the 4.0L which uses a lower pressure system, like the Rover.
I figured the internal screen has pretty large holes in it - have you actually torn yours apart and/or seen the internal screen?
I already did the water thing and it flowed very well.
It probably doesn't take much to stop the pump - the tolerances are quite small and there are a number of steel cylinder "plugs" that rotate in a slotted wheel - like bearings in a carrier. Any debris is going to score the walls, even if it doesn't totally stall. Luckily this pump (higher pressure than the V8 pump) was used in all of the Mercedes 350SL, 400, 450, 480.... Not cheap, but readily available. Unfortunately I will be ditching it when I swap in the 4.0L which uses a lower pressure system, like the Rover.
EFI pumps tend to be very vulnerable to restrictions on the intake side, they will cavitate if there is too much restriction. Perhaps this is what has happened in your case. Can you measure the pressure downstream of the pre-filter and see if you are getting a significant drop? If so perhaps you need to fit a bigger pre-filter (or perhaps a coarser one) to reduce the restriction.
Thanks for more thoughts.
I am also concerned with the restriction causing cavitation. I'll likely either do away with the pre-screen or put in something much coarser (that's why I'd like to know what the stock pre-screen looks like in the pot). Unfortunately there's a slight delay now that the tanks are out. Experiments are a pain, what with draining all the fuel out between runs... That's why I am collecting ideas now in order to get the biggest bang for my buck - thanks for the brainstorming!
The electrical cause is possible. I traced all of the wiring to the fuel pump relay (actually an electronic module to cut out the pump in case the engine stalls) so i could sub in a standard relay. I developed a conversion diagram if anyone is interested - the 5 prong output of the module IS NOT THE SAME AS THE RELAYS. I checked the fuse too at that time. This doesn't mean it isn't an electrical problem, however, and it was my plan to run a wire from the pump to a meter in the cab so I could monitor, but I haven't done this yet. I will do this if the fuel system cleaning, new swirl pot and what ever screen i use doesn't succeed.
Oh, I did discover something when converting the pump module to a relay. The wires were coming out of the connectors at the module end and the other mid-connector end (5 inches of wire from module quick-disconnects and another connector to the larger wire harness on my car - an '86). Apparently pliers were used to crimp - NOT PROPER CRIMPERS (i know the difference, being an electrical engineer). Not even soldering to compensate for the crappy crimp! Any one of these wires would have caused a voltage supply issue to the pump - but NO - that wasn't the problem either. That would have been too easy.....
Scotty
I am also concerned with the restriction causing cavitation. I'll likely either do away with the pre-screen or put in something much coarser (that's why I'd like to know what the stock pre-screen looks like in the pot). Unfortunately there's a slight delay now that the tanks are out. Experiments are a pain, what with draining all the fuel out between runs... That's why I am collecting ideas now in order to get the biggest bang for my buck - thanks for the brainstorming!
The electrical cause is possible. I traced all of the wiring to the fuel pump relay (actually an electronic module to cut out the pump in case the engine stalls) so i could sub in a standard relay. I developed a conversion diagram if anyone is interested - the 5 prong output of the module IS NOT THE SAME AS THE RELAYS. I checked the fuse too at that time. This doesn't mean it isn't an electrical problem, however, and it was my plan to run a wire from the pump to a meter in the cab so I could monitor, but I haven't done this yet. I will do this if the fuel system cleaning, new swirl pot and what ever screen i use doesn't succeed.
Oh, I did discover something when converting the pump module to a relay. The wires were coming out of the connectors at the module end and the other mid-connector end (5 inches of wire from module quick-disconnects and another connector to the larger wire harness on my car - an '86). Apparently pliers were used to crimp - NOT PROPER CRIMPERS (i know the difference, being an electrical engineer). Not even soldering to compensate for the crappy crimp! Any one of these wires would have caused a voltage supply issue to the pump - but NO - that wasn't the problem either. That would have been too easy.....
Scotty
I discovered this while surfing:
"We learned that the inline fuel pump was cavitating due to the insufficient pre-filter area (top), causing a pressure drop before the pump and thus heating up the fuel. We swapped to a larger filter with a cartridge element. This cured the cavitation problem and made the pump whisper quiet. Note that the larger filter uses a 100 micron filtering element while the smaller is 40 microns."
Their picture of the failing filter is exactly like mine - a 1" filter disc at 40 microns. The good filter is a cartridge type with MANY times the surface area and as they say, 100 micron.
This is what I will switch to. Guess I'll complete the tank cleaning and sealing since I am 1/2 way there already. Planning on swapping rear rubber bushings for poly too - had Marshall ship them the day prior to his flight to Wedge Fest.
By the way, I see my rear tires are wearing holes in the fendors due to suspension movement on acceleration (thus the bushing change). I am told this is common, with the US cars having the worst issue due a different wheelbase?? Anyway - this sucks. So much for copying Lotus.. I am doubting just the poly bushes will fix this. Now I'll have to build some conversion to the newer V8-like lower A arm and pitch the crappy swing arm's (after whacking off the hub carriers for reuse). Soooo many projects and so little time. Good thing it's all fun!
Scotty
"We learned that the inline fuel pump was cavitating due to the insufficient pre-filter area (top), causing a pressure drop before the pump and thus heating up the fuel. We swapped to a larger filter with a cartridge element. This cured the cavitation problem and made the pump whisper quiet. Note that the larger filter uses a 100 micron filtering element while the smaller is 40 microns."
Their picture of the failing filter is exactly like mine - a 1" filter disc at 40 microns. The good filter is a cartridge type with MANY times the surface area and as they say, 100 micron.
This is what I will switch to. Guess I'll complete the tank cleaning and sealing since I am 1/2 way there already. Planning on swapping rear rubber bushings for poly too - had Marshall ship them the day prior to his flight to Wedge Fest.
By the way, I see my rear tires are wearing holes in the fendors due to suspension movement on acceleration (thus the bushing change). I am told this is common, with the US cars having the worst issue due a different wheelbase?? Anyway - this sucks. So much for copying Lotus.. I am doubting just the poly bushes will fix this. Now I'll have to build some conversion to the newer V8-like lower A arm and pitch the crappy swing arm's (after whacking off the hub carriers for reuse). Soooo many projects and so little time. Good thing it's all fun!
Scotty
Thanks Adam! That helps. If I make the mod, I can move the wheel forward a bit, as they are hitting on the very back. I'd move the tire in, but that would require shortening the half shaft; not the end of the world, but yet another bit to mod. The car has only 12K miles on it and it's already more than 1/2 way through!
Is the handling much better with the A arms? I heard that's why they changed... Someone told me they rubbed under acceleration and I am a bit worried that with the 4.0L it can only get worse.
Scotty
Is the handling much better with the A arms? I heard that's why they changed... Someone told me they rubbed under acceleration and I am a bit worried that with the 4.0L it can only get worse.
Scotty
I have a Sytec pre pump filter as well as a Sytec high pressure filter, the pre pump filter has never given me any problems and was fitted due to having a new swirl pot made without the filter inside. When I fitted the filter i checked to see what the flow was like and it was very unrestrictive but I guess at £60 odd pound a throw you would expect that!
Edited by AM400 on Friday 27th July 23:01
WOW!! That is one clean machine! Congratulations and well done.
Yes, I find that's the price I must pay as well for a proper filter. Did you know your setup is on the wrong side? just kidding - I guess it's mine that's not proper (US version). That's interesting; are all of the pumps on the right side for RHD (assuming yours is)? I wonder why they did that..
Hey - on the suspension issue, do you find that your wheels are eating into your fendor well? Perhaps with those fine shocks you found an improvement in this regard?
Scotty
Yes, I find that's the price I must pay as well for a proper filter. Did you know your setup is on the wrong side? just kidding - I guess it's mine that's not proper (US version). That's interesting; are all of the pumps on the right side for RHD (assuming yours is)? I wonder why they did that..
Hey - on the suspension issue, do you find that your wheels are eating into your fendor well? Perhaps with those fine shocks you found an improvement in this regard?
Scotty
If there's any doubt at all about the pump power supply then run that down before you start playing with the pump/filter. The pump is always running flat out so cavitation problems are liable to occur at any time. They may get worse as the fuel heats up and might just be provoked if you get fuel surge etc, but in general it's not something that's likely to cause an intermittent problem.
To start with I'd stick a volt meter on the pump and confirm that the supply voltage is still good when the problem occurs.
To start with I'd stick a volt meter on the pump and confirm that the supply voltage is still good when the problem occurs.
tvrscotty said:
WOW!! That is one clean machine! Congratulations and well done.
Yes, I find that's the price I must pay as well for a proper filter. Did you know your setup is on the wrong side? just kidding - I guess it's mine that's not proper (US version). That's interesting; are all of the pumps on the right side for RHD (assuming yours is)? I wonder why they did that..
Hey - on the suspension issue, do you find that your wheels are eating into your fendor well? Perhaps with those fine shocks you found an improvement in this regard?
Scotty
No problem with the clearance on my car even with the original shocks which have only just been replaced after 19 years! Thanks for the comments on the car by the way.Yes, I find that's the price I must pay as well for a proper filter. Did you know your setup is on the wrong side? just kidding - I guess it's mine that's not proper (US version). That's interesting; are all of the pumps on the right side for RHD (assuming yours is)? I wonder why they did that..
Hey - on the suspension issue, do you find that your wheels are eating into your fendor well? Perhaps with those fine shocks you found an improvement in this regard?
Scotty
Andy
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