md6a, replace lift/feed pump with electric

[farm sail]

my old venerable MD6A has a suspected feed pump issue I have diesel in the oil and fuel starvation problem under load at speed. I am considering bypassing the (expensive and hard to get) Volvo mechanical feed pump with an electric. what if any are the drawbacks or problems with going this route. I realize this will make my engine " electrical dependant " and a total electrical failure would leave me sans engine.

does anyone know the specs or where I can find them as to the fuel pressure and flow of the stock pump.

thanks

[hpeer]

I have used small diesel transfer pumps before, trying to recall the name.

Ah...Walbro. Start here and see if this helps.

Walbro FR-Series Industrial and Marine Fuel Pumps from Fuel-Pumps.net

[gjordan]

I have converted to electric lift pumps on 2 Perkins with zero problems. Simple Napa Auto 12 volt pumps. I also discovered that the Perkins 4-236 (in a tractor) would run fine with just the pressure from the tank being about 12 inches above the injection pump. If you want an electron independent motor, install a small day tank as high above the engine as you can, and use it if you have an electrical failure. I have not yet run my MD7A, but I suspect that the injection pump will also work with very low input pressure. Be very careful of running with fuel leaking into the oil sump. My first Perkins had a RUNAWAY which was a scary experience, and that is what prompted me to put an electric pump. At least with the Volvo, you could pop the compression relief to stop the engine. I could not stop the Perkins. It should be easy for you. Just my 2 cents worth. _____Grant.

[DougR]

The original MD6A fuel feed pump was a Pierburg model PE 15672. It delivered 9.2- 12 psi feed pressure @ 2400 rpm.

The engine consumed just below a gallon /hour at WOT, and figure 10 or 15% return fuel to come up with your total fuel flow.

Another source of fuel in the oil could be the input shaft seal on the high pressure injection pump, but it's unlikely that the seal is so far gone that you would have starvation at high speed/ load.

DougR

[farm sail]

thanks for the input. i bypassed the lift pump with an electric fuel pump and unfortunately saw no improvement. but it sure makes it much easier to bleed the system now.

i guess i need to go back to the beginning to try and figure out my problem.

this is on an md6a in a 9000lb sailboat 29.5 ft long. boat is a recent acquisition so hard to compare performance to the past. on sea trial and shake down cruise engine performed as expected. full throttle in gear gave about 2300rpm negligible smoke no overheating. full throttle in neutral gave just north of 2400 rpm. prop is year old 3 blade 12x12. i am not much of a motor sailor and primarily only use the engine in marinas, restricted areas and approaching my mooring ball. knowing the previous owner used the engine even less than I, i added some seafoam to the tank on the last fill with the though that the system would get a good cleaning the next time i took her out. while transiting from the fuel dock back to the mooring i was running her close to full throttle 21-2200rpm all was good. then the rpms dropped, i thought the engine was dying but before i could throttle down or shut down the rpms stabilized just over 1500. no black smoke, engine sounded "normal" i pulled back the throttle till it started to reduce rpm and then set it right at 1500 i then popped the hatch to check out the engine. all seamed well no evidence of over heating or leaks of any kind. i was close to my mooring so i continued on and secured her till my return as i was needing to catch a ferry and head home. the engine at idle as i was shutting down did not seam as smooth as it had previously but i had only run it a half dozen times or so, so it could have been a mis perception. on my next visit she started just fine and idle like when i had shut her down. she would rev up to 2400 in neutral but still only around 1600 in gear. while reving in neutral it seamed to really smooth out around 1800-2000rpm everyone that heard the engine said she sounded real good but i still felt she was stumbling somewhat at idle and lower rpms both in gear and neutral.

my initial thought with reduced performance and negligible smoke i figured fuel starvation as the problem. with my recent seafoam treatment i suspected i had loosened a bunch of gudge and the filters were plugged. after talking with the old owner he mentioned having recently changed the aftermarket racor but commented it had been a long time since he had changed the engine mounted filter or screen on the lift pump. so i replaced the engine fuel filter and restarted the engine and found no noticeable change. idle sounded the same full rpms in neutral and 1600rpm full throttle tring to tow the mooring. so i shut it down and went to replace the aftermarket racor. as i attacked the racor i noticed the drain cock on the bottom and decided to drain a small amount from the bottom to see if i could see water or other contaminants. to my surprise, instead of fuel dribbling out it sucked a bunch of air bubbles in through the filter housing. this led me to think the racor was blocked and the pump had pulled a vacuum on the fuel line. so i swapped out the racor element and the old filter paper was effeminately dark almost black compared to the amber colored paper on the replacement element. i was feeling pretty confident i had solved my problem and fired up the engine again only to have the same performance. so i decided i would go ahead and motor in from the mooring to the local dock before i continued only to find i had not bled the system sufficiently and the engine died just as i drifted off the mooring. i threw the sails up quickly but the was really no wind and what little there was kept shifting around. i was doing my best to navigate the mine field i mean mooring field when a nearby boat started chatting me up. i guess i must have looked like i had it under control...lol after a few exchanges i asked explained what happened and asked if his dighy had enough umpf to pull me back to my mooring a 100ft away or so. after the adventure of him wanting to drag me backwards "cause we are so close" and me not arguing with free help i got her back on the mooring. at this point i knew i had not bled the system enough and proceeded to get that right. after that and another chat with the old owner i decided to replace all the rubber fuel lines as they were approaching 10yrs old. i replaced all the lines from the tank to the engine and back to the tank. still no joy, then after posting here i bypassed the lift pump with an electric still no joy.

when i bought the boat i knew of the problem with fuel in the oil and expected to deal with that . old owner suspected the injection pump but i was of course hoping it was the lift pump. the injection pump had been rebuilt 10 or 15 years back but we could find no mention of replacing or rebuilding the lift pump in the maintenance records. old owner commented on having tried biodiesle sometime in the past and wondered if that could have caused the leak allowing fuel into the engine oil. i am kinda hoping the leak was in the lift pump and that by bypassing it i have solved that problem. i will be changing oil on my next visit and continuing to try to get back to full power.

i have read and reread the owners and shop manual for the engine and every post i could find here and elsewhere on the net about the md6/7a with similar problems. i have suspected and not addressed the possibility i picked up something on the prop. i will be diving the bottom to check that out next, fingers crossed. i have also heard of similar performance hits due to plugged exhaust particularly at the water injection elbow ( engine is fresh water cooled) old owner had pointed out prior to sale that the elbow had not been replaced in a while and he suspected it would be due in the near future. other aspects i suspect are the injectors themselves and the injection pump. i have extensive mechanical background but not much in the realm of diesel engines. had a VW diesel car for a while and a pair of detriot 353's but never had a problem with em. i am wondering if the injection pump can fail in such a fashion that it "works right" just not deliver enough fuel under load. i do imagine a bad spray pattern from the injectors would certainly reduce output but would that lead to "black smoke" ? i would also think a fouled prop would give black smoke as well?

whew, that was long winded and a messy run on for sure but i hopefully covered all the bases.

if anyone has suggestions or thoughts on how to proceed i would love to here them. simple and cheep first is my motto so diving in and inspecting the prop is first. then i guess i will pull and inspect the exhaust injection elbow followed by pulling the injectors and the the injection pump if nothing else proves fruitful.

thanks in advance for assistance in reviving my old md6a
kenny

[DeepFrz]

I'm wondering about the air going into the racor instead of fuel coming out. Do you have a vacuum gauge on the filter? It would help clarify this type of situation. I once had a blog of black tar like substance block the fuel line at the 90 deg. angle on the fuel pickup. Filter was clean of course because not much could get through. Usually a fuel starvation situation the engine will rev up just before dying however you could have a situation where you are getting enough fuel in to keep it running at a lower RPM.. I guess its also possible that you picked up something on the prop and shaft. That would explain the sudden drop in RPM as well. Best of luck.

[farm sail]

i dont have a vacuum gauge but after changing the filter and hoses it no longer sucks air in if i crack the drain. i also used lung pressure to pressurize the tank and bleed the system so i am pretty confident i dont have any restrictions between the tank and engine mounted fuel pump.

[DougR]

Get a pressure/vacuum gauge and install it between the electric fuel pump and the injection pump, then run the engine at high throttle setting under load for awhile and see what kind of fuel pressure you have at the entrance to the injection pump. The pressure requirements are given earlier in this thread. If the pressure is good there, then the problem is not in the fuel feed system. If the pressure is not good there, put the gauge on the suction side of the electric pump and see how much vacuum you are pulling. Start working your way back to the tank cleaning all the fittings, elbows, etc.

DougR

[Shawn67]

I think you are running on only 1 cylinder due to a fuel injector sticking.

I have this problem with a MD7A and your symptoms almost exactly match mine. Out of gear the engine will rev up fine, in gear under load you are limited to around 1400-1500RPM.

It is actually insane how well the engine runs on a single cylinder, which is why it is very deceiving. But it does run a little rougher at idle on a single cylinder, doesn't accelerate as well (in or out of gear the throttle response is off) and is limited to about 1400rpm under load.

Get an IR thermometer and under load measure the temp. of the two cylinders. I suspect after the engine warms a bit you will see 20+ degree difference between the cylinders. In my case #2 was not running. If I got the RPMs up occasionally it would free the injector, I'd hear a knock as the second cylinder started firing and then it ran great. I had this off and on all last season but mis-diagnosed it as an air leak in that injector.

This year after converting to fresh water cooled #2 wasn't running at all. I swapped out the injector with a spare from a parts engine and the cylinder came right back and ran great. I took apart the removed injector and the needle valve was stuck solid in the nozzle. The injector was still clicking as it should have but was obviously not firing.

I've read salts build up in the diesel which can cause this sticking of the injectors. I've had it stick slightly even with the replacement injector and had it stick partially open too (LOADs of white smoke and very elevated exhaust riser temps). My guess is the Seafoam knocked some gunk loose (maybe in the high pressure pump) that got into your injector and jammed it closed.

In my case I'm going to drain all my fuel, clean the tank, replace the fuel filter and fill it with seafoam for a heavy duty injector cleaning, refill with fresh diesel and put Opti-Lube XPD in the tank for cleaning as well as increased lubricosity as current diesel has much lower lubricosity than what was around when these engines were current.

Shawn

[Shawn67]

BTW, if you are comfortable working on small things the injectors are pretty easy to open up and clean. I took mine apart and put them in a small ultrasonic jewelry cleaner to get some of the gunk out of them. Just be sure you don't loose anything when you open them up. Including the body sections there are 10 pieces, possibly 11 if an additional spacer is needed to adjust opening pressure.

Shawn

[Cheechako]

It could be a bad injector... or even a bad piston. If the injector is "streaming" instead of atomizing... the raw fuel goes past the rings into the oil. This is quite possible if the boat sat a lot before you got it.... rust etc on the injector tip. Don't ask how I know!


Another possibility is a bent valve pushrod, leaving one cylinder not firing and the raw fuel issue. I have also seen a pushrod simply come off the rocker, and sit there not opening the valve.


It sounds like you are getting sidetracked on a lot of things.... There are only so many things that will make diesel in the sump. Stay focused!

[Shawn67]

If a valve is open (and therefor not producing compression to ignite the diesel) he should be seeing loads of white smoke out the exhaust, ditto an injector streaming. When mine stuck slightly open it was shocking how much white smoke I was getting until the injector started firing normally.

".... There are only so many things that will make diesel in the sump. Stay focused!"

Is this still an issue? That may have already been solved when the lift pump was replaced.

If he has the hand crank he can turn off the fuel and crank it over by hand (without using the compression release) to see if each cylinders compression feels *roughly* the same. If one is much easier to push through he may have low compression and that could keep the cylinder from firing, but it should be smoking white in that case as the unburnt diesel would be in the exhaust.

Shawn

[Cheechako]

Originally Posted by Shawn67

If a valve is open (and therefor not producing compression to ignite the diesel) he should be seeing loads of white smoke out the exhaust, ditto an injector streaming. When mine stuck slightly open it was shocking how much white smoke I was getting until the injector started firing normally.

".... There are only so many things that will make diesel in the sump. Stay focused!"

Is this still an issue? That may have already been solved when the lift pump was replaced.

If he has the hand crank he can turn off the fuel and crank it over by hand (without using the compression release) to see if each cylinders compression feels *roughly* the same. If one is much easier to push through he may have low compression and that could keep the cylinder from firing, but it should be smoking white in that case as the unburnt diesel would be in the exhaust.

Shawn

At this point I cant remember if it was exhaust or intake stuck closed. (pushrod off) 4 cyl perkins. Seemed to run perfect. made 1.25 quarts of diesel in the crankcase in 8 hours motoring. No smoke to speak of. But at idle some raw diesel came out the exhaust staining the water.

[Shawn67]

This is one of the injectors opened up. Can't really see it here but in the round disc in the center there are also two small locating pins that fit into the nozzle housing. One of those pins was also frozen on my bad injector.

Shawn


Sent from my iPhone using Cruisers Sailing Forum

[DeepFrz]

Did you really say that you could pressurize the tank by blowing in to it? If so then your vent hose is blocked and needs to be cleaned out. Unless of course you were blowing into the vent hose.