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Mercruiser fuel pump 12-15 psi
Just installed 2 mercruiser gen 4 fuel pumps. Started the engine and the holley carb overflowed with fuel. I tried to adjust the floats..no luck. I installed fuel pressure gauges and I couldn't believe the pressure at idle..12 psi and at 1300 rpms it pinned the gauge to over 15..wow. I have never seen such high pressure from a stock pump.
Has anyone ever seen this. I never had regulators before |
Update... I called Mercury Marine today and told them about the 12 psi at idle.. They said that's alot of pressure but did not say it was a defective pump. He said some run high and it will calm down after it breaks in. They offered me a thicker gasket to put between the pump and the block to change the amount of travel from the plunger riding on the cam. I didn't like that idea so I decided to do the regulators instead.
Is there anyone else who had stock merc pumps with high pressure? |
It is a known issue. For a while we would not sell the OEM pump. If you try and push on the pump arm you will see the spring is really stout. That is what determines the pressure.
It looks like the newest batch have been fixed. |
I installed pressure regulators..I'll know tomorrow..hopefully it will work
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make sure the tygon hose is not clogged it will cause the same 12-13 lb psi check the vent tube hope it hepls.
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Originally Posted by protechcoat
(Post 3669201)
make sure the tygon hose is not clogged it will cause the same 12-13 lb psi check the vent tube hope it hepls.
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Originally Posted by 35fountain
(Post 3669234)
What is a tygon hose ...the vent tube is dry..no leakage
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it makes more pressure than it was designed to. that means it makes more pressure than it was designed to stand up to. i would replace it/them.
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Oh ok..Now I understand..That hose was changed years ago..but not with the brite yellow..These pumps are brand new from mercruiser model # 862049A1. Superceded from 814624A2. Mounted on block 1990-1992
465, 502 mag, 600sc. No regulator ever needed until now. Hopefully the regulator will keep the pressure at 6.5 without bouncing around. Changing the pumps and sending them back to the dealer is a royal pain in the A_ _.. |
same thing with my new fuel pumps. Had 11psi at idle so we put on regulators. my engine builder said this was pretty normal. Mine are sea pump mounted
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Originally Posted by jbraun2828
(Post 3669263)
same thing with my new fuel pumps. Had 11psi at idle so we put on regulators. my engine builder said this was pretty normal. Mine are sea pump mounted
What is the max pressure these pumps can handle before ??. They are supposed to be explosion proof. Where does the pressure go when holding it back with a regulator. Does the vent tube blow?? |
Update, I called mercury marine. They called the dealer where I bought the pumps for a return on the bad pumps..They refunded my money. Apparently they knew of this problem. I bought 2 Holley pumps.
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the pressure will hold diaphragm and arm up off the pump drive cam, it wont keep building pressure.
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the stroke length of any of these mechanical pumps will determine the pressure... so if the eccentric that drives it is slightly different from motor to motor or the boss on the block is machined slightly different then you get different numbers. the thick gasket deal would have been perfectly acceptable presuming the the pump itself truely wasn't bad... which since they noth did it was probably not the case... what this all sounds like is that batch of pumps got designed for and application with a certain x distance from the 0 point on the eccentric to the boss and is now trying to be used in apps where that distance is shorter...
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I don't think the stroke length would change the static pressure much, only to the extent of the change in the force created by the spring due to the different compressions.
It would change the volume for sure. So it is possible that would result in lower pressure if the engines requirements exceed the fuel delivery at a given RPM, just like running too small a pump. But that is not exactly predicable. And most likely would do zip at idle. We did some bench testing on these when we first discovered the problem. If you hold one in your hand you can barely push the pump arm. I cannot remember the part number with the issue, but it was not a random batch. It was all of them from a new vendor. The PN has since been superceded, the new part seems OK. |
Originally Posted by Mbam
(Post 3674990)
I don't think the stroke length would change the static pressure much, only to the extent of the change in the force created by the spring due to the different compressions.
It would change the volume for sure. So it is possible that would result in lower pressure if the engines requirements exceed the fuel delivery at a given RPM, just like running too small a pump. But that is not exactly predicable. And most likely would do zip at idle. We did some bench testing on these when we first discovered the problem. If you hold one in your hand you can barely push the pump arm. I cannot remember the part number with the issue, but it was not a random batch. It was all of them from a new vendor. The PN has since been superceded, the new part seems OK. i had a whole bunch of motors in various catagories that required the use of the std mech pump and adjusting the stroke length by virtue of shims/gaskets allowed me to taylor it quite specifically... if you say these pumps are different inside then thats that... but ive never seen an example of it... |
Steve it took me a while to figure it out way long ago, but take a take a closer look.
In a mechanical fuel pump the displacement of the arm from the at-rest position is the intake/suction stroke. The spring, which is above the diaphragm in the housing returns the arm/diaphragm to "at rest" position. That is the pressure "stroke". The output pressure of the pump is directly related to how hard the spring pushes on the diaphragm. You can actually calculate the pressure it if you measure the spring pressure at the relevant height and divide that by the active area of the diaphragm. So if the diaphragm is 2.5 OD there is about 5 square inches of area, 10 PSI would mean 50 lbs of spring pressure. If it was the other way around the pressure would be only be limited by how strong the components are until something broke. Make sense? |
Originally Posted by Mbam
(Post 3675021)
Steve it took me a while to figure it out way long ago, but take a take a closer look.
In a mechanical fuel pump the displacement of the arm from the at-rest position is the intake/suction stroke. The spring, which is above the diaphragm in the housing returns the arm/diaphragm to "at rest" position. That is the pressure "stroke". The output pressure of the pump is directly related to how hard the spring pushes on the diaphragm. You can actually calculate the pressure it if you measure the spring pressure at the relevant height and divide that by the active area of the diaphragm. So if the diaphragm is 2.5 OD there is about 5 square inches of area, 10 PSI would mean 50 lbs of spring pressure. If it was the other way around the pressure would be only be limited by how strong the components are until something broke. Make sense? sure... but think about it... the total diaphram movement in both verical directions is defined by the arm... if the arm moves a lot, then the diamphram sucks in a lot of fuel but then the pressure spring is also collapsed a like amount so its generated force is higher... f=-kx ... where f is the force k is the spring constant and x is the displacement... and it will be linear.... stroke the dia. 1" get x vol of fuel delivered at y pressure. stroke it 1/2 inch and get 1/2 x volume at 1/2 y pressure... and because of the leverage effects , small stroke changes make big changes to both the total stroke defines both parameters... thats why when you change the cam or the eccentric you have to make sure that the gaskets and spacers are also adjusted to get youy back the volumes and pressures you need. in the case of the merc pump we are talking about ( and again i say i have never cut one up to look inside) i can't imagine that it isn't exactly the same as every other pump on the planet... either way... in this guys case, reinventing the wheel would have been the wrong thing to do anyway... just get the right pump and go home early. |
Merc # 861678A1 was the old part # for the fuel pump that would cause about 12 psi at 700 rms flooding the carb. It seems the year the problem pumps were made in 2010. I thought these mech. fuel pumps were all made by Carter. I knew years ago that was true.
The new fuel pump # is 8M0058164 and the problem has been resolved. At first we checked all of this to try to pinpoint the problem as well. Carb float adjustment - float itself, carb problem, venturi problem. Spring too tight around the diaphram vent hose clogged or fitting clogged too long or changed out fuel pump rod or changed camshaft - and or cam lobe problem these 2 can cause high fuel pressure by overstroked the mech. fuel pump level. possible very high crankcase pressure fuel pump lever arm longer or angle of degree different mounting gasket and or spacer depth different. anyways what I was told - use thicker gasket and or a spacer close to 1/8 inch thick and that did take care of the problem - the pump arm had something different about it and overstroked the pump - hense the higher fuel pressure. I will email back to Merc engineering to see if that answer has change. I dropped the issue because used other pumps and Merc. problem has been resolved. |
Originally Posted by BUP
(Post 3675192)
Merc # 861678A1 was the old part # for the fuel pump that would cause about 12 psi at 700 rms flooding the carb. It seems the year the problem pumps were made in 2010. I thought these mech. fuel pumps were all made by Carter. I knew years ago that was true.
The new fuel pump # is 8M0058164 and the problem has been resolved. At first we checked all of this to try to pinpoint the problem as well. Carb float adjustment - float itself, carb problem, venturi problem. Spring too tight around the diaphram vent hose clogged or fitting clogged too long or changed out fuel pump rod or changed camshaft - and or cam lobe problem these 2 can cause high fuel pressure by overstroked the mech. fuel pump level. possible very high crankcase pressure fuel pump lever arm longer or angle of degree different mounting gasket and or spacer depth different. anyways what I was told - use thicker gasket and or a spacer close to 1/8 inch thick and that did take care of the problem - the pump arm had something different about it and overstroked the pump - hense the higher fuel pressure. I will email back to Merc engineering to see if that answer has change. I dropped the issue because used other pumps and Merc. problem has been resolved. carter has been in the fuel pump business for 100 years... litterally i think... they make a great product... beyond that, if its not too much hassle, an electric with a regulator... all good quality of course is a perfectly good solution... and a better deal all around i would think. but there might be other considerations in your case i am unaware of.. |
I just bought my fuel pumps a couple months ago and had 11psi at idle. So they are either left over from 2010 or they are still making them the same way. I put regulator's on and never thought anything about it.
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I have an extremely stupid question and embarrassed to ask and I'm sure I'll get blasted for being a dumbass but here goes.
The brass looking vent tubes on the side of my mechanical fuel pumps are reasonably plugged with brown dry sludgy looking crap. Should these tubes be cleaned out? Blast away. LOL |
Yes clean it out but IMO these pumps should be changed out every 5 to 10 max anyways. Today fuels are really bad and the internal side of these mech. fuel pumps form very heavy corrosion and or a form of aluminum oxcide. White or lite yellowish power.
I see this all the time and the worst are the 4 bangers - Mercs and Volvos get completely contaminated of the complete fuel system and carb. Why these apps more so than the rest - because these apps do not have water fuel separating filters installed like the V-6 and up apps. Water in the fuel really accelerates this problem by 10 times as fast. Also will add - the problem pumps that Merc had would over stroke causing high fuel pressure, 11 to 15 psi and that is too much for carb apps. They flood / dump especially at idle. We at that time sent these pumps back but to only get another bad pump that did the samething. A thicker mounting gasket brought the psi back down to spec. We still have currently these apps running 100 % fine as we speak. just an FYI. |
Originally Posted by bustag
(Post 4421401)
I have an extremely stupid question and embarrassed to ask and I'm sure I'll get blasted for being a dumbass but here goes.
The brass looking vent tubes on the side of my mechanical fuel pumps are reasonably plugged with brown dry sludgy looking crap. Should these tubes be cleaned out? Blast away. LOL :D:D:D Yep, clean them out. It is the overflow tube in case the pump diaphragm ruptures. The fuel will dump into the tube and up to the carb instead of dumping in the bilge. |
Thanks guys thought they should be clear so I gently cleaned them out hoping I was right. Almost done with the engine room remodel Griff I think you will like it. repainted, wires hidden and loomed, new shiny diamond plate and mirrored stainless, Now if I can figure why the gen wont start I'll be really happy. Arrrrg! See you in June buddy.
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I know this thread is now well dated but I as well am having this same issue. Just put part number 862049a1 for my 502 magnum a week ago, installed it over the weekend and immediately flooding out carb at idle. Replaced needle and seat same issue, adjusted float level same issue. Checked fuel pressure and 11psi at idle. Called dealership that sold fuel pump and they have also instructed me to install the thicker gasket. After doing some research I have found that installing this gasket can create a tapping noise from the fuel pump rod slapping the pump arm. Can anyone confirm this? Most people that experienced this, called Mercruiser and they instructed them to install a Sierra pump. I called Sierra and they don't offer a fuel pump for this application. I really don't want to change this pump again as it was a huge pain in you know what, and I hate hack the stock tube up to install regulators but that might be what has to happen. Does anyone know of a good aftermarket pump that will work to replace this part number? I considered the holley marine pump but they are rated at almost 8 psi and from everything that I've read Quadrajets don't line over 6 psi at the needle and seat. Thanks for all the input if anyone is still following this.
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Originally Posted by mach12450
(Post 4449383)
I know this thread is now well dated but I as well am having this same issue. Just put part number 862049a1 for my 502 magnum a week ago, installed it over the weekend and immediately flooding out carb at idle. Replaced needle and seat same issue, adjusted float level same issue. Checked fuel pressure and 11psi at idle. Called dealership that sold fuel pump and they have also instructed me to install the thicker gasket. After doing some research I have found that installing this gasket can create a tapping noise from the fuel pump rod slapping the pump arm. Can anyone confirm this? Most people that experienced this, called Mercruiser and they instructed them to install a Sierra pump. I called Sierra and they don't offer a fuel pump for this application. I really don't want to change this pump again as it was a huge pain in you know what, and I hate hack the stock tube up to install regulators but that might be what has to happen. Does anyone know of a good aftermarket pump that will work to replace this part number? I considered the holley marine pump but they are rated at almost 8 psi and from everything that I've read Quadrajets don't line over 6 psi at the needle and seat. Thanks for all the input if anyone is still following this.
I too have this same issue. Just had my Q-jet rebuilt and installed the 862049A1 pump from my local merc dealer and surprise..it flooded the carb out. Does the 8M0058164 pump work for the 502's? Looking up the info on it and it states 5.0, 5.7L small blocks only. |
I have done some research and have not found any other pumps that will work for the 90-92 carbed 502 without the sea pump style fuel pump. I called Sierra and they said they don't offer a pump that will supply enough volume for the 502 at high rpm. Everyone else that has had this problem seems to have installed a regulator in line between pump and carb. I haven't had a chance to do anything yet, but later this week I'm going to install the thicker mercruiser gasket that they told me to install and will report. What really sucks is I rebuilt my Q jet and replaced the fuel pumpwith the same part number on my starboard engine 2 years ago and it was a flawless process.
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What gasket are they telling you to use? I would rather try the gasket than install a regulator at the moment.
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I'll get you the part number as soon as I pick it up. It's a mercruiser part number supposed to space the pump out from the block and cause the arm travel to shorten and lower the pump pressure. I'll let you know what the number is and how it works out this week.
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The gasket/spacer is part# 21-431861.
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Originally Posted by RBOT
(Post 4453565)
The gasket/spacer is part# 21-431861.
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Originally Posted by Mbam
(Post 3674990)
I don't think the stroke length would change the static pressure much, only to the extent of the change in the force created by the spring due to the different compressions.
It would change the volume for sure. So it is possible that would result in lower pressure if the engines requirements exceed the fuel delivery at a given RPM, just like running too small a pump. But that is not exactly predicable. And most likely would do zip at idle. We did some bench testing on these when we first discovered the problem. If you hold one in your hand you can barely push the pump arm. I cannot remember the part number with the issue, but it was not a random batch. It was all of them from a new vendor. The PN has since been superceded, the new part seems OK. Spring over the diaphragm will determine pressure. Reducing stroke on the arm will cut volume. So some pinhead(s) at Merc decided to cut volume to cut pressure. Since the spring would require more labor, and they obviously wanted an attempted fix vs sending a fuel pump that works correctly... Mark, I'll bet $100 the supplier was Airtex. They blow goats, and have cost me lots of money at work. Electric pumps - I haven't touched any of their products since, |
Originally Posted by RBOT
(Post 4453713)
sorry should be 27-431861. Just picked it up, we shall see if it works.
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From another site
Bad Mercruiser Fuel Pump May 14th, 2011, 07:50 PM I'm not sure if many people had this problem or not, so I'm going to just give a little story here about an experience with a Mercruiser fuel pump. I have a 1993 Mercruiser 5.0LX 305 V-8 230HP. I was having a problem with fuel making its way into the oil. So, I learned that either the fuel pump needed to be replaced, or, the carburetor need to be rebuilt. Both of these parts were original from 1993. So, I replaced the fuel pump thinking that the ethanol in the fuel must have eaten away at the internal parts of the fuel pump. After replacing the pump with a mercruiser pump, the engine wasn't really running right and the carburetor was beginning to flood out. The carburetor is a Rochester quadrajet. So now that this was happening, I decided to rebuild the carb since it was all original. After rebuilding, the flooding problem in the carb was still occuring. I tried replacing the needle and seat and float again in the carb with it still flooding out. Then I purchased a rebuilt Quadrajet from a carb shop and was told that if this carb floods out then there is a problem with the fuel pump, and the quadrajet can only take 4-6 lbs of pressure and anything more than that would force the needle open. So, I replaced the carb and still had it flooding. Now I called Mercruiser to que them in on the situation. After I explained to them what had been going on, they said to try a thicker gasket, part # 27-431861. After this gasket was installed, the flooding did stop. However, a few minutes after running the engine, a ticking noise presented itself. This had to be the rod that pumps the fuel pump slapping against the pump or the cam inside the engine since the pump was now about 3/16 of an inch further out from the block. Now another phone call to Mercruiser to find out that "if after using gasket 27-431861, the flooding does not stop, or a ticking noise occurs, then you must use an aftermarket fuel pump." So, now I bought a Sierra fuel pump, part # 18-7283, bolted it on, and had no problems since. Just thought I would try to spread the word if anyone else was having this problem. Any questions, please dont hesitate to ask! |
Yes I have read this thread, however no one offers a mechanical pump for a 90-92 mark iv carbed 502 that I'm aware of. They offer ones for carbed 502 mark v blocks that have the fuel pump bolted to the sea pump but I've found none that will fit my application. I'm going to try this gasket before I have to install the regulator. If anyone knows of one that will fit my application I would gladly try it. Thanks!
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It looks like Marc from BAM (earlier in this thread) would be able to get you the right one since it looks like he can recognize the good ones.
A regulator will obviously work too. Just depends on what you want to do. BAM is advertiser and Merc dealer. Very good peep's. |
Originally Posted by SB
(Post 4453748)
It looks like Marc from BAM (earlier in this thread) would be able to get you the right one since it looks like he can recognize the good ones.
A regulator will obviously work too. Just depends on what you want to do. BAM is advertiser and Merc dealer. Very good peep's. Called BAM this morning. Looks like there aren't any decent pumps and he suggested to just run a regulator. |
Ya that's what I figured. I just picked my gasket up huge difference from other one in thickness. Installing friday morning see what happens. Hate to install regulator on one engine when other is perfect without it.
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This whole thing is bullchit.
FU Mercruiser ! |
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