Cat 3116 "hunting" after injector change

GnrlPatton

GnrlPatton

Well-Known Member
Jul 12, 2010
719
Maple Valley, WA
Boat Info
Current: 1998 370 Express Cruiser
Sold:1988 230 Weekender
Engines
Twin Cat 3116T
Had a mechanic out in March to replace my injectors on both engines. Starboard side went fine, port side had a bad injector from Cat, and was replaced on warranty. During the sea trial after all the work was done, I noticed that the port motor was hunting while at idle after being fully warmed up - like a good 20 minutes of full cruise after the oil (not just the coolant temp) is at cruise temp. I come down off plane, put engines at idle and then take it out of gear, and it happens,

My mechanic is stumped, he's been back at least 5 times to adjust the fuel rail (several times) clean the fuel supply line, remove the fuel rail and check the bushings (one was indeed loose and he replaced it) and (I did this one myself) replace the fuel filters. So far we've not been able to solve it, and his next idea is to replace the fuel governor, which I understand will be a fairly expensive operation as nobody around here rebuilds them. I thought I would post here to see if my CSR peeps have any ideas on it. Here's a video of it in action the first time around, it's fluctuating about 2-300 RPMs. It's not quite this bad now, maybe 50-100 RPMs, but still very noticeable.


Thanks,
Kevin
 
C sounds more like a pump setting problem than an injector problem to me. There are several adjustments on the 3116 fuel injection pump and resetting one doesn’t require a pump replacement, but it does require access to Cat specs.

If your mechanic cannot reset the pump, I would suggest that get your local caterpillar to check the pump and reset it. He will be able to tell if you need to have the pump rebuilt.
 
douglee25 said:
Check for a binding or worn rack.
Click to expand...
Add that to the list of things he did look at.

I'll ping him about the fuel pump reset, I don't believe he's tried that. He's been in close contact with our local Cat shop here (he used to work there) and they've together walked through all of the troubleshooting steps to get to where we are. Our current crossroads is to do the fuel governor or bring a Cat tech out to help him troubleshoot on site (so far it's all been over the phone). I may ask him to choose that route and see what the tech has to say, as well as suggest a fuel pump reset.

Thanks all, it's been a frustrating experience so far, but I'll give the mechanic credit, he's not billed me for anything past the initial injector install, even though he's probably spent a ton in labor.
 
Out of curiosity. If you give it a little throttle doe it stop?
 
NotHerDecision said:
Out of curiosity. If you give it a little throttle doe it stop?
Click to expand...
It does. It only repros when the engine is fully warmed up, at idle and out of gear. Throttle up and it goes away, put it in gear and it goes away. It's probably still happening in gear, it's just not noticeable as it's under load. The mech was trying to adjust the idle setting last time, and we almost got it to go away by increasing the idle speed, but we felt it was too high so backed it off a bit.
 
fwebster said:
C sounds more like a pump setting problem than an injector problem to me. There are several adjustments on the 3116 fuel injection pump and resetting one doesn’t require a pump replacement, but it does require access to Cat specs.

If your mechanic cannot reset the pump, I would suggest that get your local caterpillar to check the pump and reset it. He will be able to tell if you need to have the pump rebuilt.
Click to expand...
And to add to Franks comment - which I believe he is talking about the governor - did your mechanic set the rack after the injector replacement? Also a couple of other things:
1. Check for air bubbles in the fuel return line - your mechanic if a Cat mechanic knows what this is about and how new injector installation can cause it.
2. Inside of the injector pump housing are a series of little plastic check valves ( I think five) that over time tend to gum up and will cause erratic behavior. They are not expensive and easy to get to for replacement.
3. Check that the throttle arm is hard on the stop and that the stop is set to the idle setting.
 
Thanks for the responses so far guys, I'll compile this and pass it along to discuss with the mechanic. I think he's done some of it, but not all, will confirm and come up with a plan that (hopefully) doesn't include replacing the governor.

Kevin
 
on 3116's I had a few years back with this problem the Cat mechanic set the fuel rail as mentioned above. This takes about 3 hours per engine and requires a special tool and dial indicator. He also set one cylinder a little tight and another a little loose to help with the wear. Ran better than ever.
 
GnrlPatton said:
Had a mechanic out in March to replace my injectors on both engines. Starboard side went fine, port side had a bad injector from Cat, and was replaced on warranty. During the sea trial after all the work was done, I noticed that the port motor was hunting while at idle after being fully warmed up - like a good 20 minutes of full cruise after the oil (not just the coolant temp) is at cruise temp. I come down off plane, put engines at idle and then take it out of gear, and it happens,

My mechanic is stumped, he's been back at least 5 times to adjust the fuel rail (several times) clean the fuel supply line, remove the fuel rail and check the bushings (one was indeed loose and he replaced it) and (I did this one myself) replace the fuel filters. So far we've not been able to solve it, and his next idea is to replace the fuel governor, which I understand will be a fairly expensive operation as nobody around here rebuilds them. I thought I would post here to see if my CSR peeps have any ideas on it. Here's a video of it in action the first time around, it's fluctuating about 2-300 RPMs. It's not quite this bad now, maybe 50-100 RPMs, but still very noticeable.


Thanks,
Kevin
Click to expand...

I had the exact same problem with port 3116 when I bought my boat last year. All it took was to adjust the idle at the fuel pump. It is a straight forward process that someone with basic mechanical knowledge can handle.
There is a web site out there called Boat Diesel. I got the info to correct the idle issue from there.
I highly recommend joining the site. Lots of valuable information on the 3116's.

Here is what I did to solve my issue
1. Run boat and get the engines up to operating temperature. Return to the slip
2. Remove the throttle cable from the throttle arm.
3. On the side of the fuel pump there is a small hole for adjusting the pump. Locate the hole and turn the screw inside of it counter clockwise 2-3 turns.
4. Start the engine and adjust the throttle arm stop adjustment screw so the engine is at 700 rpm's.
5. Turn the pump screw clockwise until the engine rpm is 750.
Viola! Smooth idle

Disclaimer: This is what I did to solve the idle surging issue on my boat. I'm not saying that this will solve your problem.
Just had to throw that out there.
 
Thanks @acman we have done the idle adjustment a few times to no avail. Increasing the idle definitely helps smooth it out, but it doesn't completely eliminate it.

I sent my guy a list of things that you all recommended here. He zeroed in on the return line bubble test and the check valves, he said since those are the easiest things to check we would start with that. He was at the boat on Tuesday and found that one of the check valves was indeed gummed up and wasn't seating properly, so he's going to buy a full set and get them replaced. I'm really hoping that is the problem!

CheckValve.jpg
 
acman said:
I had the exact same problem with port 3116....
5. Turn the pump screw clockwise until the engine rpm is 750. Viola! Smooth idle
Click to expand...

750 seems like a fast idle speed...What is your speed at that rpm? Perhaps that's normal, but I'm already bumping in and out of gear sometime to slow her down...

@GnrlPatton , Good luck...check valves interesting thought...Hope it's something this simple...(Mental note- remember check valves...haha)
 
The one check valve was replaced, to no avail, she's still hunting. I asked my mechanic to reach out to CAT to get a technician scheduled, but they are apparently slammed and haven't been able to find a date for us. I sent him a few more items that I uncovered in my Google searches, mostly from BoatDiesel.com, he was going to look into them. They were things like checking/cleaning the oil filter screen on the governor, checking the rack for binding, and checking the orifice on the dashpot. Seems this issue has happened to others, but I can't find the one thing that they say fixed it. Pretty frustrating for sure!

Kevin
 
Carver370 said:
Did you ever figure this out?
Click to expand...
Nope, we got it to the point where it was acceptable, but it was always there. When I first noticed it and started this thread, it was really bad, with a 2-300rpm fluctuation. We got it down to maybe 20-30rpm, but never to 0. I just got back from a big trip a few weeks ago, and during the trip it got worse, it's probably now 150rpm fluctuation. Another symptom as well is that it's smoking a lot, even after being warmed up.

I reached out to my mechanic when I got back, and he came back with this:

"I'm sorry to hear this. I do have an extra governor and rack for your engine model/HP that I can install. I believe this is the problem with your engine. If it's fine with you we can come up and get these parts changed out. The parts would be of no cost to you and are used.. They came out of an engine with 800 hours that failed due to an oil loss issue about 3 weeks ago."

I'm going to have him do the replacement and see if that is indeed the problem. Last year we considered swapping the rack and governor from the starboard motor over to see if the hunting problem went away, but I was hesitant to touch the good running motor. He said he's booked out a few weeks, so once we're able to make the swap, I'll update this thread with the results.

Kevin
 
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