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454 XL TBI rpm issue

GAS engine, transmission and generator repair and maintenance discussion forum.
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Bentone23
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Re: 454 XL TBI rpm issue

Postby Bentone23 » November 30th, 2018, 5:47 pm

I pulled apart the Oberg prefilter and it was clean as a whistle. I then opened the fuel valve. About 4 ounces came out and stopped. Aren’t these fuel tanks higher than the engines and therefore gravity fed?
Bruce Bennett
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1996 355 Aft Cabin
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Boating on the Delta and SF Bay

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Re: 454 XL TBI rpm issue

Postby bud37 » November 30th, 2018, 5:57 pm

Anti -siphon valve at the tank outlet seems to be working properly.......its a safety device to keep the bilge from filling with fuel if the line ruptures....... :beergood:
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Re: 454 XL TBI rpm issue

Postby Cooler » November 30th, 2018, 7:12 pm

Hello all, just read this stream and it sounds almost dead on to what has been happening to a number of boaters over here. You guys are all much more accomplished mechanics than me. The common theme was all these guys had burned ethanol gas. If the gas sat in the tanks for even 30 days, the injectors built up a varnish like layer internally. Reduced the gas flow by 20% to 30% in the affected injectors. Therefore, they were starving the engines for gas, resulting in the popping. One guy had piston damage. Sometimes they could clean out the injectors but rebuild was a better long term solution. You could pull a couple injectors and test for required flow rates. A couple guys had to replace their ignition modules and coils also.

Unfortunately, we have some marinas selling only ethanol treated gas, due to the pressure from fishing guides who burn thru gas a lot faster than pleasure boaters. I burn pure gas only. Hope this helps. Cooler
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Bentone23
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Re: 454 XL TBI rpm issue

Postby Bentone23 » December 1st, 2018, 1:06 pm

bud37 wrote:Anti -siphon valve at the tank outlet seems to be working properly.......its a safety device to keep the bilge from filling with fuel if the line ruptures....... :beergood:



So how do I determine if I am getting fuel flow from the tank?
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Re: 454 XL TBI rpm issue

Postby bud37 » December 1st, 2018, 4:34 pm

Get your mechanic to remove the anti-siphon valve to inspect it and clean if necessary......you can google those valves as there are a few slightly different types to see the insides....you are wise to address that end first...once that is sorted you shouldn't have issues getting fuel out of the tank.
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Re: 454 XL TBI rpm issue

Postby Bentone23 » December 2nd, 2018, 12:07 pm

I AM the mechanic, maid, chef, owner and sometimes captain!
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Re: 454 XL TBI rpm issue

Postby 390Express » December 3rd, 2018, 7:49 pm

Bentone23 wrote:Source of the post I AM the mechanic, maid, chef, owner and sometimes captain!


If you have a TBI motor and want to check if you're getting fuel, you can put a fuel pressure gauge on the shrader valve at the top of the motor. Start the motor, the earlier models will have 10-12 PSI (1995/1996), the later models will be higher (I believe there are two versions, 22psi for TBI and around 43 psi for the MPI style). Carb PSI should be around 8-10. If you have a carb motor, you may have to splice in a T fitting at a break in the rubber line, but you shouldn't have to add a break. Just add a small piece of rubber to a nipple and plumb in your gauge temporarily.

Also, the anti-siphon valve is just a plunger with a spring and o-ring on it. You can get new o-rings at Harbor Freight for $5 for a large kit of them. I haven't found another good source for fuel compatible o-rings. I know, I know... Harbor Freight has quality issues, but the o-rings kits are name brand, and fuel rated. I haven't had any problems with mine. Lubricate the O-ring with a little ATF when you install it, per borg warner's advice with their TBI rebuild kits. The plunger is pretty basic and should never wear out, the spring is low tension, and doubtful that it will wear out. It's all held together by a small c-clip that's pretty easy to install and uninstall. I soaked everything in mineral spirits for a day, but I'm sure it would have been good in a couple hours with some light scrubbing.

I ended up replacing my injectors with brand new bosch injectors. They're kind of pricy at $95 each, but they come with a lifetime warranty from O'Riely Auto Parts:

https://www.oreillyauto.com/detail/b/bw ... tors&pos=0

You'll know your injectors are bad if your motor is running rich. I couldn't notice the poor atomization (the spray and pattern both looked fine on mine), but the motor did run less rich with new injectors.

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