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Engine Surging down when Hot

8K views 25 replies 12 participants last post by  thevdeub 
#1 ·
Got an old Westerbeke 40. Worked pretty well, except for contaminated fuel.
Changed the primary filter, secondary, fuel lines from and to the tank, added biocide to fuel (too much).
Now the engine hold 500 rpm steadily, but 1500 rpm (kinda slow cruising speed for my boat) only briefly.

1500 rpm will be stable for few minutes, until the engine reach its running temperature - 180c. (Roughly, seems related, but it could be because of the few minutes spent warming up).

Troubleshooting.
- bypassed secondary filter - still happening
- bypassed fuel tank (from jerrycan of clean diesel) - heard to much biocide could be the cause
- added low pressure 12v lift diesel pump for trucks (0.4mpa). with or without, same issue
- no visible fuel leaks
- tried to bleed various bleeding points on the engine and injector pump during surge without noticeable effect.
- checked the return line flow. it is small and steady. routed it into a jerrycan. still same issue.

I have a fuel sensor switch on the top of the injector pump that trigger an alarm when the fuel reach enough pressure and the alarm stop when engine kicks off and pressure lower.(don't ask me why the previous pwner did that - I know it should be on the oil pressure side).

Anyhow,

Start the pump
Wait 8s - Alarm Ring
Start the engine
Runs fine for few minutes at 1500 rpm
Start to surge
Kill the engine
Wait 60s to hear the fuel alarm ring.
Start the engine again.
within less than a minute engine will surge again until bring back to cold.

Facts:
- Time for the surge depends on the engine beeing warm. this is 100% repro.
- lift Pump takes WAY more time to build pressure into the injector pump AFTER the engine did surge.

Mechanic want to remove and rebuild the injector pump.
My hypothesis is :
- there is a leak of some sort (I find it a coincidence that the pump gave up when I changed my filters)

Questions:
Is it possible to have an intake of air without leak of fuel, and could it be because of metal expansion when hot ? that would explain why the pump takes more time to flush out air after a surge, and the slow building of the air inside the injector pump body.

Video : check around 1:45 https://drive.google.com/open?id=0B3t8KLz_eQTpRzZqUXFIdW9BY2s

This having be driving me nuts for weeks, and I am close to despair.
I can move the boat around but with such low power it becomes dangereous with any swell or breeze.
 
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#2 ·
It is certainly possible to have an air leak without fuel seepage. Double check to make sure the filter change didn't leave any double o-rings in place.

You might want to have the injectors tested because partial clogs in them can cause surging.

I'm a bit confused on your wording - does it only reach 1500rpm? Is 1500 the governed speed? If not, will it rev higher in neutral when cold, but not hot? When you pulled fuel from a jug with the lift pump, did you feed it directly to the injection pump and bypass the rest of the fuel intake system?

You can always temporarily put some clear hose in place of fuel lines to see if air is getting into the system.
 
#4 ·
@ianjoub definitively noise/rpm is going down after 1:45. Believe me :) . Power goes down as well, and boat slows down.
@colemj I used 1500 as a reference, but it goes above, up to 2000 rpm which was around the maximum it was going before. I usually do not try 2000 rpm before the engine is hot, but I could try.

When I pulled from the jug, I bypassed the racor, but not the primary as it is connected with tubes instead of hoses and that was trickier. But yes, I am at the point I am ready to try that, bypassing the primary. I need to find a way to go from hoses to tubes cleanly. clear hoses before the pump is a great idea.
 
#5 ·
What is the manufacturer's governed max rpm for the engine? If much higher, and you can't make it in neutral, then that does suggest a possible injection pump issue, or bad injector or restricted air supply.

That is, if it never went above that. If it is just low now, then air in the fuel could still be a problem.

Mark
 
#9 ·
Hunting, which is what I assume you mean by surging, is a factor of air getting in the lines somewhere. But most often that occurs at idle and slower speeds, but disappears when one throttles up sufficiently that plenty of fuel is flowing.
What you are describing is more of a fuel restriction. Perhaps when you changed the filters a speck of dirt got to the injection pump.
We had that happen just as we were tying up to the St George's Bermuda customs dock. A replacement would have been a fortune out there and nobody on island could fix it. So against a dozen warnings in the manual, we begged aboard a mega yacht and the engineer and I dismantled and cleaned it. One little tiny speck of dirt slid out onto the stainless steel workbench. We both knew right away we had found the problem!
Reassembly was a nervous endeavor but the Eureka moment was when I pushed the throttle and she revved right up. It's still performing admirably more than 5 years later.
I am certainly not saying to tear down the injection pump, but should all else fail, send it out to a shop. But if I were you I'd be looking for a fuel restriction, not air intrusion.
 
#10 ·
"little tiny speck of dirt slid". This sound scary and might be the culprit, as I was battling with pretty bad fuel contamination. However, I don't think I bypassed ever the primary filter. But I thought about fuel restriction as well, however, the fact that this happen only when the engine is 'hot' does seem to match. Why the fuel would be restricted only after few minutes ?
 
#12 ·
Still struggling on this.
I found this post : https://theboatgalley.com/tracking-down-a-fuel-problem/ that have very similar symptoms.
Slow Fuel Starvation, Same engine, no visible leak.

Now, a local mechanic (done that his entire life) who is advising me (atm, to remove the injector pump), is convinced that if there was a leak on the pressure side of the fuel lines, there will be fuel leaking. (remember we have a 12v pump pushing 8 psi before the primary filter).

This seems contrary of what have been said here, of this blog post and what my gut feeling telling me (as I touched the fuel lines and filters, but not the injector pump).

Who to believe ?

ps: I am stuck waiting for parts as I actually caused a real leak on the inlet of the injector pump trying to bypass the secondary filter to check my theory.
 
#16 ·
Now, a local mechanic (done that his entire life) who is advising me (atm, to remove the injector pump), is convinced that if there was a leak on the pressure side of the fuel lines, there will be fuel leaking. (remember we have a 12v pump pushing 8 psi before the primary filter).
We just went through this same thing and it took a LONG time to isolate and solve the problem on our Onan because of the thinking above.
Let me assure you that you can have an air leak after the fuel pump and before the injection pump without any fuel coming out! In our case it was a double whammy, a bad connection on a too small hose barb, so it was an air leak and a fuel restriction.
If you have hoses and barbs, change all the lines after the primary filter (Racor?) including those to the secondary filter on the engine. If metal piping, there could easily be a crack in one of the flare fittings you can't identify.
But if this problem developed right after a filter change, as I believe you said it did, I'd still put my money on a speck of dirt in the injection pump.
 
#13 ·
Any hose that's 10 years or older just needs to be replaced, Just do it even if its not the problem. After reading the post you reference I see no mention of a return line either on yours or in the post referenced. The return line will cover a small leak and its common I think essential there is a return line. And yes if its on the pressure side a leak will, uh leak, and on the suction side it will pull air and with a proper return run fine to a point with a small leak. But ideally you don't want leaks of any kind.
 
#15 ·
Since you said you changed the fuel filters i have to ask if you know you have the right micron filter rating. Did you put in finer filters then the engine specs call for? like a 5 micron? you said you had a fuel contamination problem so how do you know the fuel is clean now and you did not plug the filters again.
 
#18 ·
Just on a whim, check the valve clearance. As they wear they get tighter, and as they get hot they get tighter yet. A tight valve doesn't close completely and can cause a reduction in power. My diesel did that but had an accompanying top end knock that the OP didn't mention. Adjusting the valve clearance fixed it. Needs checking and adjustment periodically anyway.
 
#20 ·
Is there a screen on the pickup in your fuel tank?

I had a similar problem that drove me out of my mind. It turned out there was a mesh screen installed in the fuel pickup about half way up the pipe. The screen and the whole length of pipe below it were clogged with gunk. I couldn't believe the engine had been running at all.

I removed the screen completely - the fuel filter will take care of anything large enough to get caught in the screen - and she's been running great ever since.
 
#24 ·
Try replacing the mechanical lift pump and or checking the gaskets. Pull it apart any way and have a look. I'll put in some STP diesel fuel/injector additive into the bottom of my racors once in awhile, seems to make engine run a bit better.
 
#25 ·
Have you run the lift pump disconnected directly into a container to check for good flow. I agree this should show at any temperature But>>Same for the return, should be good flow returning to the Tank. Blow on the return line to be sure the return is not clogged at or inside the Tank. Return flow will clear air pockets before being pulled into the Injector pump.
Maybe check Valve lash, I always thought clearances would open up rather than close as another poster suggested but its worth a check. Also your return line should leave some back pressure on the injector pump, has the size been changed or anything else changed that might affect this return ratio.
BTW you can buy fittings for hoses that go right on where the flare tubing connects. Ill say again supply and return lines should be replaced entirely on any Boat with this amount of age on it. A good hydraulic/hose shop can get you through this. Let them make the hoses don't barb and clamp let them press the ferrules on.

One more thing to check there may be a fitting on the Tank supply fitting that has a check ball in it, I can hear mine rattle when priming. I would think with a lift pump there needs to be a check somewhere to hold the fuel in the line between runs.

Stay after it you will find something. I had an air vent on top of my Racor work loose and the engine would not idle, it would move enough fuel to overcome the air intrusion at a higher throttle but would shut down at idle. No air ever got into the high pressure side of the system but all systems are diferent and wont react in the same way to air if that's your problem.

Its either air, fuel flow , mechanical or mechanical issue related to fuel.
 
#26 ·
People will certainly tell me : 'I told you so' :)
In a last desperate attempt before pulling the injector, I just changed again the secondary filter. I used before an aftermarket cheap one on Amazon and was wondering if that could be the issue.
Likely the issue was not the filter but the way I did put it, with 3 o-rings.
2 for the mounts (top/botton) , one for the top of the filter (BAAADDD)

What likely happened is that I was limiting the entry of fuel, and when the engine was hot (Maybe) the metal of the filter would expand and limit even more the flow - that's my take on it at least.

Found this on internet.

I am curious why a - ORing there, on top of the filter would limit the flow. I would have expected this part to be sealed with the cap ?


Note that I did not test it in a real situation yet, but the try I did today were very positive. I was able to hold for 5 min at 2000rpm, engine Hot.
 

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