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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?
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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:
The above is strictly my opinion always based on years of doing...remember to support local business , it pays back.
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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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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.
The above is strictly my opinion always based on years of doing...remember to support local business , it pays back.
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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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Boating on the Delta and SF Bay
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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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Re: 454 XL TBI rpm issue

Postby 390Express » June 19th, 2019, 1:41 am

Well, I seem to have two mechanical issues left - erratic idle on my port motor, (which I'm not terribly concerned about, it fluctuates about 200 rpm), and this issue, which remains from last year.

Last year I had an issue where the stbd check engine light would come on, then the motor would run like hell, and then subsequently shut off. The good news is, no more check engine light... the bad news is, it's still shutting off.

Stbd motor starts and runs fine, for about 30-40 seconds, then shuts off. Doesn't seem to matter what I do with the throttle, or fuel. I tried spraying starting fluid down the TBI as it's stalling, and no change. I also checked the fuel pressure and it's fine, a perfect 12psi while cranking, while running, and even briefly as and after the motor stalls, before the regulator allows the system to bleed down, which it's designed to do.

I changed the MAP sensor last year, no change. I knew the distributor wasn't right (timing was jumping around) going into last winter. This spring I installed a new distributor, and adjusted the timing. No change. I had the hard start issue on this motor, and thought that maybe a ground/corroded power lead may be leading to power loss at the ECU, causing the stall. I've since cleaned all of the power leads and grounds, the hard start issue is gone, but the stall issue remains. I know there was some fault codes logged in the ECU last year, evidenced by the check engine light, but never cleared them, as I did not have access to a scanning tool to read or clear the codes. I checked and have power at the coil as its stalling. Tried a new coil, no change. Checked the trigger wire, which seems fine. I have a new set of plugs and wires ready to go, but I was hoping to fix the stalling issue prior to install, so I don't foul the new plugs.

Any ideas as to sensors, safety mechanisms, etc. that could be faulty causing the stall? Oil pressure reads fine at the gauge, is there a 2nd sending unit and shutoff if the oil pressure reads low on that sending unit or due to a faulty sending unit? I'm considering swapping the ECU, but the ECU doesn't seem to be the issue. The fuel pump, spark, etc. is all good, and starts the motor just fine. Next step may be to "rent" a diagnostic tester from Michigan Motorz. They don't rent them, but I talked to their sales rep. They'll sell me a tester, knowing that I plan to return it, and charge me a $50 re-stocking fee.

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Re: 454 XL TBI rpm issue

Postby tomschauer » June 19th, 2019, 1:23 pm

I would try the ECM swap.

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Re: 454 XL TBI rpm issue

Postby Viper » June 19th, 2019, 8:14 pm

So she will stall even if you throttle up past idle?

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