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Yamaha F250 Losing Power and Backfiring

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Yamaha F250 Losing Power and Backfiring

Old 09-05-2018, 01:33 AM
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Default Yamaha F250 Losing Power and Backfiring

Long time lurker and first time poster here. I'm hoping to pick the brains of some of the brilliant minds on here.

I have a 2006 Yamaha F250. I started having issues this year with the motor losing power and backfiring. It will be running fine at 4500rpm and then drop RPMs down to 2500 or less. It won't die, but it surges and struggles and often starts backfiring. If I back off the throttle and we pump the primer bulb, it will pick back up and run for a while longer, maybe 15-20 minutes. I have seen a similar issue from a couple other people that had this happen in rough water. That is the case here as well.

Initially this happened on the reserve tank only, then began happening on the main tank. It is intermittent however. A couple weeks ago, we ran 114 miles on an albacore without a hiccup. Two days later, we ran 141 miles and it started doing it on the way home. I suspected that was due to getting low on fuel in the main tank and sucking air. The next week we ran another trip and were full on fuel. It started happening about 15-20 miles out. Fortunately, that was about where we needed to start fishing. We trolled all day at 2300rpm without problems. Once we picked up to run home it started happening again.

We have replaced every fuel line in the boat, drained the reserve and sucked all of the sediment out with a shop vac. We checked the pickup tube and it had no holes or clogged filters. We have replaced every fuel line other than the line from the primer bulb to the motor which was new when we installed the motor 3 months ago. The Racor filter has been changed. The Racor housing has been checked for clogs or debris. Both tanks puke fuel from the breather when full on fuel. We have cracked the fill caps to make sure we do not have vacuums. The VST has been cleaned, but the filters were not replaced. They canister filter on the motor has been bypassed. The low pressure fuel pump has been replaced. We have bypassed the primer bulb. We have disconnected the fuel line to the kicker thinking it may be sucking air from there. The valve to switch tanks has been checked and is clear.

When we changed the low pressure fuel pump and did a sea trial, we ran out on the main tank about 2 miles and thought we may have solved the problem. We switched to the reserve, and it started losing power. We got back in and bypassed the primer bulb and checked the Racor housing. We were maybe back at the dock for two hours. We went for another run and started on the main then switched to the reserve. Same thing. We realized that this only happens when the engine is warmed up. I have two Yamaha mechanics helping me on this and we are all stumped.

One of them suggested that this may be the Oil Control Valves, but that doesn't make sense because the pumping the bulb corrects the problems. Still seems like a fuel delivery issue.

We are also having an issue with making oil, but I'm not sure if that is related. Injectors are out getting cleaned and I have ordered new thermostats. I also have new plugs and VST filters on the way.

Anyone have any ideas on what may be causing this. Especially with different behavior on the main and reserve tanks.
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Old 09-05-2018, 02:20 AM
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I just sold twin 2005 F250's and one was starting to act strange. My mechanic was concerned about vapor lock and the VST filters. Also I have heard that some F250's are affected by the exhaust corrosion issue although I don't know if this would cause your symptoms.
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Old 09-05-2018, 03:39 AM
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VST filters will definately cause RPM loss/fluctuation, Ask how I know. Weren't very expensive to do.
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Old 09-05-2018, 04:57 AM
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Replace the two VST filters.
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Old 09-05-2018, 08:01 AM
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Originally Posted by Capt_Paul View Post
Still seems like a fuel delivery issue.
Agreed.
The VST is the "mini gas tank" that the engine runs on.
Everything between the VST and the boat tank - including the primer bulb -
exists only to keep the VST "topped up".

If, in fact, the symptoms are alleviated by pumping the primer,
then the problem is, that fuel is not getting into the VST fast enough, consistently enough.

There is no problem with the filter inside the VST - that would affect the fuel rail pressure,
and the priming bulb could do nothing to help.

there are many failure modes on the F2xx fuel delivery system;
the one odd thing is this:

Originally Posted by Capt_Paul View Post
if I back off the throttle and we pump the primer bulb,
it will pick back up and run for a while longer, maybe 15-20 minutes.
The VST only holds ~8 ounces. That last a few seconds at cruising speed.
So I'm mystified by how the primer would "get things going again" - for 15-20 minutes.

I see that a great of work has been already done,
but I would still be looking for an air leak or a restriction on the suction side of the LP pump,
or a restriction on the discharge side.

A vacuum gauge Tee'd in on the suction side, and a pressure gauge Tee'd in on the outlet side,
can quantify the performance of the LP pump.

In terms of "throwing parts" that may be the cause
there is a screen "filter" on the outlet side of the LP pump, on top of the VST - #8 below.

There is also a pressure regulating valve on the LP pump output - #3 below.


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Old 09-05-2018, 01:09 PM
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Originally Posted by Fwpratt View Post

If, in fact, the symptoms are alleviated by pumping the primer,
then the problem is, that fuel is not getting into the VST fast enough, consistently enough.
That is why we ended up replacing the low pressure pump. That was an expensive test. Occasionally the primer bulb stays sucked down, but eventually pops back out.

Originally Posted by Fwpratt View Post
There is no problem with the filter inside the VST - that would affect the fuel rail pressure,
and the priming bulb could do nothing to help.
When it runs, it runs well. I don't think it is a fuel rail issue either. It seems to be between the VST and the tank which is why we have focused all of our efforts on that side.

Originally Posted by Fwpratt View Post
the one odd thing is this:

The VST only holds ~8 ounces. That last a few seconds at cruising speed.
So I'm mystified by how the primer would "get things going again" - for 15-20 minutes.
It does. In fact, I have had my deckhand sit back there and continue to pump the bulb and it keeps it going. However, he has to keep pumping it. If I back off the throttle, he only has to pump it a few times before it gets hard and I can pick back up and run. This has all of us mystified as well.

Originally Posted by Fwpratt View Post
I see that a great of work has been already done,
but I would still be looking for an air leak or a restriction on the suction side of the LP pump,
or a restriction on the discharge side.
We'll keep looking at that. I would think that if that was the case, then I would either have problems at low RPMs or I would always have the problem at high RPMs. The issue with the different tanks behaving differently is puzzling. I have run 100-120 miles with no issues of the main tank. Then the next trip it starts losing power after 15-20 miles.

Originally Posted by Fwpratt View Post
A vacuum gauge Tee'd in on the suction side, and a pressure gauge Tee'd in on the outlet side,
can quantify the performance of the LP pump.
I don't have these gauges so I will have to see if my mechanics do. The problem then is trying to run the motor in the ocean without the cowl on it.

Originally Posted by Fwpratt View Post
In terms of "throwing parts" that may be the cause
there is a screen "filter" on the outlet side of the LP pump, on top of the VST - #8 below.
I have one of these on the way in a VST filter kit. It has that filter, the screen in the VST, and a new VST gasket.

Originally Posted by Fwpratt View Post
There is also a pressure regulating valve on the LP pump output - #3 below.
I will get one of these if the other solutions don't resolve the problem.

The injectors came back with no issues and flow tested good. Hopefully, the thermostats fix the making oil issue.

Thanks for your help!
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Old 09-06-2018, 02:08 AM
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Check your ignition coils.
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Old 09-18-2018, 08:26 PM
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Originally Posted by DaveHNL View Post
Check your ignition coils.
What is the best way to check these? Check the resistance?
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Old 09-18-2018, 10:39 PM
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UPDATE:
Last week, I changed the pickup tube on the main tank. There were some issues with the old tube that may have been contributing to the problem. The old barb fitting wouldn’t fit, so I ended up ordering an aluminum anti-siphon valve because they were cheaper than than a straight hose barb. This may have been a mistake. We did a short sea trial and had the same issue after about three miles.

I had an Albacore trip on Thursday and let customers know that we were having the issue that would be an inconvenience but not serious. One of my customers said he had a similar problem and installed a check valve on the kicker fuel line. One of my mechanics suggested a shutoff valve on the kicker line. I kinked the line and zip tied it before we left. We made it 12 miles before losing power. We were able to pump the bulb and continue on. I was convinced that the problem had to be the anti-siphon causing a restriction.

On Friday, I replaced the anti-siphon valve with a straight barb fitting. I added a shutoff valve to the kicker fuel line. I I replaced the Sierra primer bulb with a Yamaha OEM bulb. One of my mechanics also recommended an electric fuel pump in place of the primer bulb to maintain fuel pressure.

On Saturday, we ran another trip offshore for albacore. We made it 3 miles, then 12 miles. i’m Starting to think we have the problem fixed. We made it 20miles before losing power. I had my deckhand pump the primer bulb, but it was hard. I wasn’t able to get the motor to run well at all. I put the electric pump in. That didn’t help. The motor would idle and that’s was it. I couldn’t even run at 2300 which is about where we runt o get 7-9 knots trolling. One of my mechanics thought we may have a heat related issue causing problems with coils or the ECM. There have been no overheat alarms or warnings. I decided to shut the main down and run on the kicker. It was off for 6-8 hours while we trolled on the kicker. When we fired up the main to run home, it didn’t want to run at anymore than idle. We ended up coming home 40 miles on the kicker.

I think we have addressed the fuel related issues between the tank and the VST. I decided I needed to take my boat to a shop. But they are 3 hours away. I called two shops. One wouldn’t let me talk to a tech, the other was very helpful. He suggested not bringing it in, because he didn’t think anything would show up on a diagnostic since I am eating no check engine warning or codes on the gauge. He thought the problem now is the Needle Valve in the VST or the high pressure fuel pump. We are going to try to do a pressure test between the VST and the rail. Not sure if there is a shcrader valve or if we have to tee in somewhere. I have also ordered a high pressure fuel pump.

Any more ideas?
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Old 09-18-2018, 11:54 PM
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Originally Posted by Capt_Paul View Post
What is the best way to check these? Check the resistance?
Yes,
Ignition coil resistance:
Primary coil "A":
1.530–2.070 Ω at 20 °C (68 °F)
Secondary coil "B":
12.50–16.91 kΩ at 20 °C (68 °F)

PS, the above is for a 2006 Yamaha F150 TXR

Last edited by DaveHNL; 09-19-2018 at 12:34 AM.
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Old 09-19-2018, 06:21 AM
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If it's still backfiring, that's the thing to focus on imo. That's usually caused by the engine running really rich, incorrect timing, or bad coils.

Have you inspected the plugs that are in there now? I know you have new ones coming, but looking at the existing plugs now could tell you if it's running really rich (which could be causing the backfiring). If the tips of the plugs look really dark, then it could be a stuck open injector, a faulty MAP sensor or even a faulty ECM.

Definitely test the coils like Dave said.

And maybe just check the timing belt. Very unlikely that would be the problem, but it's possible.
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Old 09-19-2018, 06:40 AM
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Since you pretty much exhausted the fuel delivery system - I'm thinking it might be electrical.

I'd check your spark plug wires. A faulty one might explain it bogging down and backfiring.
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Old 09-19-2018, 07:56 AM
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Subscribed to learn.
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Old 09-19-2018, 10:17 AM
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just went thru this with mine, ended up being the high pressure vst pump. It was acting the same exact way. tried filters first and it was a little better( a little more run time before acting up) but then I replaced the pump and problem solved. Had the same issue on a f115 years back that just the filters fixed after chasing everything from lines, connections and tank fittings. Hope this helps.
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Old 09-20-2018, 11:20 AM
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Originally Posted by rejesterd View Post
If it's still backfiring, that's the thing to focus on imo. That's usually caused by the engine running really rich, incorrect timing, or bad coils.
It only backfires when it has lost power and I give it throttle. The power loss is inconsistent. In some cases, it has gone more than 100 miles. In other cases it has been less than 3 miles. Up until the last trip, it only happened at cruising speed. It would idle or troll fine.

Originally Posted by rejesterd View Post
Have you inspected the plugs that are in there now? I know you have new ones coming, but looking at the existing plugs now could tell you if it's running really rich (which could be causing the backfiring). If the tips of the plugs look really dark, then it could be a stuck open injector, a faulty MAP sensor or even a faulty ECM.
We changed the plugs and the old plugs looked good. My mechanic actually had me save them as backups in case I had fouled a plug.

Originally Posted by rejesterd View Post
Definitely test the coils like Dave said.

And maybe just check the timing belt. Very unlikely that would be the problem, but it's possible.
We are definitely checking the coils. And we will check the timing belt.
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Old 09-20-2018, 11:23 AM
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Originally Posted by HMBJack View Post
Since you pretty much exhausted the fuel delivery system - I'm thinking it might be electrical.

I'd check your spark plug wires. A faulty one might explain it bogging down and backfiring.
There are no wires. The coil is integrated into the boot.
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Old 09-20-2018, 06:19 PM
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Originally Posted by Capt_Paul View Post
There are no wires. The coil is integrated into the boot.
Don't know if you have one of these shop manuals - I'm ordering one for my engine.

https://www.yamahapubs.com/
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Old 09-20-2018, 07:06 PM
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Please check your oil dipstick. We had a similar issue with the same vintage Yamaha F250’s. Our engines were suffering from ring blow by. Essentially we were making oil, aka the oil was being diluted by the fuel blowing by the rings. Once the oil level got very high on the dipstick we would get a loud backfire and a loss of power caused by the crankcase getting over pressurized.
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Old 09-20-2018, 09:58 PM
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Originally Posted by DaveHNL View Post
Don't know if you have one of these shop manuals - I'm ordering one for my engine.
That’s on my list. I have a PDF for a 2003 F225.
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Old 09-20-2018, 10:03 PM
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Originally Posted by Blues Brother View Post
Please check your oil dipstick. We had a similar issue with the same vintage Yamaha F250’s. Our engines were suffering from ring blow by. Essentially we were making oil, aka the oil was being diluted by the fuel blowing by the rings. Once the oil level got very high on the dipstick we would get a loud backfire and a loss of power caused by the crankcase getting over pressurized.
We do have an issue with making oil. This is why we sent the injectors out to get cleaned and changed the thermostats. However, I believe it is caused by the trolling we do. We spend a lot of time trolling. We fish salmon and albacore. With the exception of albacore we don’t have the opportunity to run the motor hard. We fish close to port and it is often too rough to run hard without beating my customers up. We just drained off some of the oil. We are due for anothe oil change this weekend. We will be leaving some room and not topping it off. We have run 350+ hours in the last 4 months.
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