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Yamaha F250 Losing Power and Backfiring

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Yamaha F250 Losing Power and Backfiring

Old 09-20-2018, 10:07 PM
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Originally Posted by Capt_Paul View Post
Thatís on my list. I have a PDF for a 2003 F225.
I found one on ebay for my engine - it was only $19 and instantly downloadable.
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Old 09-21-2018, 02:46 AM
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Another possibility could be your needle valve in the VST sticking closed intermittently.

A way to test this might be to run the boat with the cowling off, and when the engine stalls, quickly open the VST drain into a container and see how much gas there was in the VST.

Last edited by DaveHNL; 09-21-2018 at 09:16 PM.
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Old 09-21-2018, 01:59 PM
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Originally Posted by Fwpratt View Post
there is a screen "filter" on the outlet side of the LP pump, on top of the VST - #8 below.
I have seen these filters clog and create issues with the pumps failing (or so we think), and also blowing pump fuses. You should be able to blow through this filter easily, but if it hasn't been replaced recently, replace it.
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Old 09-21-2018, 08:59 PM
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Thatís your problem and please donít make excuses for Yamahas shortcomings. Do you run Ring Free? Try a shock treatment. If that doesnít work take it to Yamaha dealer and have them complete a carbon treatment on the engine. I wish I had seen this post earlier. Sending the injectors out and replacing the thermostats wonít fix the issue. Are you making WOT with the prop on the boat?
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Old 09-23-2018, 03:34 PM
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Originally Posted by tarpononecharter View Post
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.
Changed the VST filters and the High Pressure Fuel Pump. This appears to have fixed the problem.
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Old 09-23-2018, 03:39 PM
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Originally Posted by DaveHNL View Post
Another possibility could be your needle valve in the VST sticking closed intermittently.

A way to test this might be to run the boat with the cowling off, and when the engine stalls, quickly open the VST drain into a container and see how much gas there was in the VST.
The needle valve has been cleaned and was cleaned again the other day. The ocean is usually too rough to to run without the cowling unless we are at the dock. Iím not going to try this 20 miles offshore.
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Old 09-23-2018, 03:42 PM
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Originally Posted by HooHolder View Post
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.
Changed both filters and the pump. Seems like the problem has been fixed. I will know for sure on out next Albacore trip later this week.
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Old 09-23-2018, 03:45 PM
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Originally Posted by ParkRanger View Post
I have seen these filters clog and create issues with the pumps failing (or so we think), and also blowing pump fuses. You should be able to blow through this filter easily, but if it hasn't been replaced recently, replace it.
That filter had not been changed and it was not easy to blow through. When I tried I definitely thought that was contributing to the problem. I replaced both filters and the pump just to make sure. At least I have spare fuel pumps now!
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Old 09-23-2018, 04:21 PM
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Originally Posted by Blues Brother View Post
Thatís your problem and please donít make excuses for Yamahas shortcomings.
That wasnít the problem. The makin oil was a separate problem and not causing the loss of power. It was clearly related to fuel delivery. Donít make excuses for Yamahaís short coming? Really? LOL. Yamaha has plenty of shortcomings. In many cases they either donít admit their own shortcomings or make their own excuses. In my opinion, there is no excuse for their shortcomings especially when they plague various models and multiple years. Not being able to do a fuel pressure test on this motor without a fitting only available to dealers is another shortcoming. There is no Schrader valve on the rails or the VST. I am happy with this motor and wouldnít own another outboard in saltwater, but Yamaha isnít the holy grail and they have their shortcomings.

Originally Posted by Blues Brother View Post
Do you run Ring Free? Try a shock treatment.
Yes, I run Ring Free and we did a shock treatment.

Originally Posted by Blues Brother View Post
If that doesnít work take it to Yamaha dealer and have them complete a carbon treatment on the engine.
That isnít an option. The shops are 3 hours away and booking appoints out 3 weekís. One shop wouldnít let me speak to a tech, the other suggested the high pressure pump and needle valve. It was either the horse shoe filter or the high pressure pump causing the resulting problem and most likely the pump was damaged because of the earlier fuel delivery issues. In any case, the problem has been solved and it wasnít due to making oil.

Originally Posted by Blues Brother View Post
I wish I had seen this post earlier. Sending the injectors out and replacing the thermostats wonít fix the issue.
Leaky injectors and thermostats can both cause making oil. One of the thermostats neededed to be replaced anyway. Having the injectors flow tested was cheap insurance. Both of these were suggested by Yamaha mechanics. However, the most like reason is excessive trolling and idling.

Originally Posted by Blues Brother View Post
Are you making WOT with the prop on the boat?
Yes. 6000 RPM with my 4 blade prop and 5500 RPM with my 3 blade. Yesterday was the first time I was able to run WOT with a light load to test the 3 blade prop.
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Old 09-23-2018, 05:04 PM
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Originally Posted by Capt_Paul View Post
That filter had not been changed and it was not easy to blow through. When I tried I definitely thought that was contributing to the problem. I replaced both filters and the pump just to make sure. At least I have spare fuel pumps now!
Glad to hear your problem may solved!

Hopefully that filter (#8) 69j-24501-10-00 on the parts diagram was the problem - I have a similar filter that's never been changed which I just ordered - I hope this solves my problem as well.

Good luck and let us know what happens.
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Old 04-01-2019, 07:36 PM
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I have good news and bad news. The good news is, after changing the high pressure fuel pump, we believe we resolved the fuel issue we had most of the season last year. We ended up changing everything from the fuel pickups to the high pressure pump. All fuel lines, both fuel pumps, every filter. Thank you so much to the guys that provided input and advice. We ran a salmon trip, rockfish trip, and the first 130 miles of an Albacore trip without issues.

Now for the bad news. On the way home from the Albacore trip, we lost power again. This time it was unlike any of the fuel related issues. We were running nearly full throttle and suddenly, over 3-4 seconds, lost power. RPMs dropped down to 3K and remained there. We tried shutting down and running on the kicker for a while, but we still couldn’t get it to run higher than 3K. It ran a little rough but ran. A mile or two from the harbor, it dropped to 2500 and then 1500. The motor was vibrating like hell and backfiring. At that point, we shut it down and came in on the kicker. Over the next couple months, We tried to resolve the issue with no luck. I bought an older YDS system on a tablet. That showed two codes for cam position sensors, but when those sensors went off really made no sense. One of the, went off a couple days earlier on the rockfish trip, but there was no impact on how the engine ran. The second one went off right before we shut the motor down after the loss of power. We figured both were anomalies. At this point, we thought it was the ECU. I had seen some with low hours on eBay previously, but when I returned, they were gone. One of the mechanics aI had been referred to about 3 hours away said he had one. I had a customer pick it up on the way up to fish. The ECU was too old and the wiring harness didn’t fit. Had to cancel the trip and refund their money. I was frustrated nonetheless. I found another ECU on eBay and bought that one. We also had to install a new lower unit as I had to return the loaner I had on there. We hook up the ECU and head out to break in the lower. The motor didn’t want to start withou a lot of throttle. When it ran it ran very rough, vibrating and backfiring. My buddy thought it might be the ECU learning the new motor and would improve. I ran it for a couple hours but had to come in when I couldn’t increase the RPMs above 1500. At that point I was frustrated and parked the boat. I tried getting an appointment with the mechanic in the Bay Area, but he was too busy. I took a few months off and then recently started looking for another mechanic. This guy is a Yamaha Master Tech. He lives about 5-6 hours from me, but has a yard in near the other mechanic. Two weeks ago I made arrangements to take the boat to him. We put the boat in the water at the ramp and he began troubleshooting. He found water in the oil, and thought we had a bigger issue. I assured him that we had no issues with water in the oil and it was likely condensation from sitting so long. He thought the motor ran rough because we sheared a flywheel key. He was supposed to take it home with him but had another boat to haul and couldn’t leave it at his yard which isn’t secure. He suggested we take it to the other mechanic who has a secure yard. He also said to have them pull the flywheel to check the key. They didn’t want to work on the boat either, because of the water in the oil. But he ended up checking the flywheel key. It wasn’t sheared and the timing was fine. They wanted me to take it home, drain the oil, and run water through the lower unit intake and flush port. When we pulled the plugin drain some oil, there was a little water in there, but it was mostly oil with fuel. We still have the issue with making oil. Before doing the water test, I wanted to do some more running tests. We confirmed that we were only running on two cylinders. But we tested both coils and injectors with the computer and they seemed to be fine. We also did several resistance tests on the coils. We noticed that the fuse for the fuel feed (low pressure) fuse was blown. We replaced it again and it blew again. We replaced it with a 10 amp and it didn’t blow again. We need to chase that down. We noticed the throttle position sensors differed by 2 volts. .77 on #1 and 2.7-2.i on the #2. We thought that was the issue. We checked the resistance which should have been 1.3-1.6. It was at 2. We also found some condensation in. Breather line which confirmed that was where the water in the oil came from. Called one of the mechanics with our findings. He called Yamaha this morning who said the TPS sensors seem fine and not to change the throttle body. Can’t change just sensors and the throttle body is $1100 new, $450 used. The Yamaha tech suggested it was oil control valves. I can’t afford to keep throwing money at parts. Just wondering what the brilliant minds here think.
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Old 04-01-2019, 08:37 PM
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Did you check compression (and leakdown if you can) and check the plugs since the most recent issue? The most recent issue sounds completely different... I donít think that amount of water in the oil will be condensation.
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Old 04-02-2019, 01:04 AM
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Originally Posted by Texas 17 View Post
Did you check compression (and leakdown if you can) and check the plugs since the most recent issue? The most recent issue sounds completely different... I donít think that amount of water in the oil will be condensation.
We did check compression. 182-195. We didnít do leak down. One of the mechanics was supposed to but didnít want to do it until we did the water test. The most recent issue is definitely different. There wasnít much water in the oil. When we lost power in September, we checked the oil and there was no water. The only other time we ran the motor was the the lower unit break in. The water test didnít result in any water from the drain. It is possible it came from the pan gasket, but that will be replaced when we pull the power head to replace a leaking oil seal.
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Old 04-02-2019, 01:33 AM
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You said you're only running on two cylinders, are the other cylinders getting a spark?

Last edited by DaveHNL; 04-02-2019 at 04:06 AM.
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Old 04-02-2019, 03:26 AM
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Change the fuel filter housing before you go much further may have a pinhole leak sucking air
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Old 04-02-2019, 03:56 AM
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question(s)....when the motor loses power, does it backfire at low RPM because you have the throttle up? I am wondering if the backfire is being caused by you trying to compensate for power loss? My F225 was losing power, and if remember correctly, if i tried pushing the throttle up to push through the problem, it started acting up even more. In the end, that issue was floating trash in the VST. It would run fine for hours, and out of the blue it would lose power. Somehow debris would suck up to the VST screen if the conditions were just right.

When the power loss happens, can you shut the motor down for a minute or two, and then when you restart, do you have full power for a spell?
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Old 04-02-2019, 10:35 AM
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Originally Posted by DaveHNL View Post
You said you're only running on two cylinders, are the other cylinders getting a spark?
When we check for spark we have it. If we disconnect coils while running it doesnít change how it is running. We pulled the plugs and replaced with a set for my last service that still looked good. We ran the coil test on each plug and had spark. Another shop last year also said we had spark and thought it was injectors but the injectors had just been sent out a month or so earlier.
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Old 04-02-2019, 10:40 AM
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Originally Posted by Airboat0540 View Post
Change the fuel filter housing before you go much further may have a pinhole leak sucking air
That filter was bypassed last year. That was one of the first things we suspected when we were having the fuel problems. I have a separate Racor filter that Tís off to both the main and kicker.
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Old 04-02-2019, 10:55 AM
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Originally Posted by REGMARINE26FS View Post
question(s)....when the motor loses power, does it backfire at low RPM because you have the throttle up? I am wondering if the backfire is being caused by you trying to compensate for power loss? My F225 was losing power, and if remember correctly, if i tried pushing the throttle up to push through the problem, it started acting up even more.
This motor lost power and never regained it. It won't idle so we have to run it with throttle. It backfires regardless of the amount of throttle.

Originally Posted by REGMARINE26FS View Post
In the end, that issue was floating trash in the VST. It would run fine for hours, and out of the blue it would lose power. Somehow debris would suck up to the VST screen if the conditions were just right.
We have taken the VST apart 4-6 timesThe first time there was some crap in there, but the other times it was clean. The last major change we did was replace the VST filters and high pressure pump so the VST was once again cleaned days before we lost power. The thread lists all of the work we have done.

Originally Posted by REGMARINE26FS View Post
When the power loss happens, can you shut the motor down for a minute or two, and then when you restart, do you have full power for a spell?
No. Once we lost power, it never got better. Only worse. The motor will not run over 1500 RPM in gear.
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Old 04-02-2019, 01:15 PM
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Maybe try swapping the injectors on the cylinders that are firing to the ones that aren't.
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