Engine backfiring through throttle body when trying to accelerate

[Scott Danforth]

There are only 2 thread sizes used on engines and every compression tester I have ever used has both threads

Also, just borrow one from you local parts store

 

[badrano]

Not to go down another path here.....I'm still going to do the compression testing..... Did some additional reading and talking to some other folks and they're pointing me to a fuel issue, specifically a lean fuel condition.
Since everything ran fine 2 day prior and the fact that I topped off the tank before heading out, I'm wondering if I got water in the tank or other crap in the tank that might be plugging up the fuel filter.
With a cool fuel 3 module, if I pull the filter out, do I need to replace the o-ring before putting it back together? At least this would be a quick check to see if there's any crap caught in the filter restricting fuel flow.

 

[Scott Danforth]

If you pull the fuel filter, you replace the filter with a new one. because it will cross-contaminate the filter.

you are doing a compression test to rule out a sticking valve

crappy fuel, lean condition, improper timing, running hot all contribute to a motor sneezing.

 

[badrano]

Compression test on a cold engine. Thought this would be the better test without any heat expansion involved. I believe this shows no leaky valves.
#1 158
#3 160
#5 160
#7 170
#2 165
#4 153
#6 147
#8 160

The spark plugs look good. Do I shift my focus over to a fuel issue?

 

[nola mike]

For some reason I thought that the fuel filters were inspected/changed already. You have a water separator on there? But yeah, sorry, water in your fuel or other constriction is definitely something to rule out

 

[jimmbo]

Backfiring could be the Result of Cross Firing due to Inductance from one Plug Wire to another. Often happens after wires are "relocated/rerouted" from original positions, and/or the Insulation is weak. Tying them together, may look tidier, but can create many Ignition Problems

 

[alldodge]

I'm not giving much thought to the surging, many (not all) motors have this issue at a given RPM, it's the backfire issue

Check that the distributor is in correct position


While the compression variation between 7 and 6 is 13.5% don't see this as the issue either, probably a gauge or test issue

The next possibility might be lean mix which is an injector issue and flow testing can verify. Other might be from excessive carbon build up from to much fuel and a hot spot

Be nice to get @muc thoughts

 

[badrano]

If this helps.....the backfiring only occurred a couple times. When I was accelerating, I heard the "pop" noise from under the so called hood/back seat. I backed off to idle, then tried accelerating again, heard another pop....so maybe 3-4 pops total over the whole course of trying accelerate multiple times. It was not a constant/continuous backfire.
I will double check the alignment.

From the fuel perspective,
- Fuel filter gets changed out at the beginning of each season
- Cool fuel 3 module was broken down and rebuilt last year to address the flaking paint issue. Looked like a chuck of paint clogged up the regulator. This fixed the rich condition.
- Fuel injectors were pulled and sent out for flow test/cleaning 2 years ago (first attempt at addressing the rich condition)

How does the Cool fuel 3 module trap water? Is it in that "cup" that the cartridge filter inserts into? Thinking if I pull the fuel filter, would I see water in there assuming this problem is water contamination?

 

[Scott Danforth]

how old is the fuel?

 

[badrano]

how old is the fuel?

Tank was topped off before winterizing back in Oct. I keep the tank like 3/4-7/8 full over the winter.
It looks like I didn't mention in the original post, that I did my un-winterizing check ride the week before all this on the topped off tank and I was out for several hours with no issues. The tstat replacement on Friday was a result of the check ride because the temp was behaving is way that indicated a sticky tstat....the engine did not overheat during the check ride.

 

[alldodge]

How does the Cool fuel 3 module trap water? Is it in that "cup" that the cartridge filter inserts into? Thinking if I pull the fuel filter, would I see water in there assuming this problem is water contamination?

Any water should show up with visual when filter is removed.

 

[Scott Danforth]

Tank was topped off before winterizing back in Oct..

How old was the fuel that was still in the tank?

 

[badrano]

How old was the fuel that was still in the tank?

Basically from last summer after all the different fill ups during the summer.

 

[badrano]

Distributor alignment looks.

Check that the distributor is in correct position

Alignment looks good

 

[badrano]

I think the culprit has been found, picked up some crap gas. Popped the filter out and the fuel at the bottom was cloudy. Dumped the gas out of the filter bowl and dumped it in to a cup and you can see the line.

 

[badrano]

My tank has ~60 gallons in it.....the DIY issue I see is how do I off load 60 gallons......any tips on what I can do as a DIY or at this point is it better to throw in the towel and just take it to a mechanic and pay 1 kidney, 2 legs and maybe a lung.
Called one mechanic and he charges $10 a gallon to offload + the labor to clean out the fuel system.
And not mention now to try and fight with the gas station to get reimbursed.

 

[alldodge]

Look around in your area for places that take used oil, most will also take some gas in the mix. Places like Autozone, O'Reillys, Advance are local and might also look for commercial places like Crystal Clean, Safety-Kleen, Valicor, and GFL Environmental

Get a cheap 12V pump and connect to tank and pump it out in cans. After it's out, than might take to the Mechanic for finishing, but by than you could also do that.

It still don't understand why Merc takes your motor with a Alpha behind it and uses the old Gen 2 cool fuel, and with a Bravo it installs the piece of carp (IMO) pump and filter. The Alpha also gets the old style canister filter

 

[badrano]

Another mechanic i just talked to said to raise the bow of the boat so all the water settles to the back of the tank by the pickup tube and to just pump/syphon the gas out until you see clean gas come out.
In a way I could be lucky in the sense that the pad the trailer is parked on also tilts to the right so theoretically everything would pool to the right lower corner which is right below the fill port....maybe pop the fill line off and shove a pickup hose in or could I just pull from the pickup line?

 

[Lou C]

Another mechanic i just talked to said to raise the bow of the boat so all the water settles to the back of the tank by the pickup tube and to just pump/syphon the gas out until you see clean gas come out.
In a way I could be lucky in the sense that the pad the trailer is parked on also tilts to the right so theoretically everything would pool to the right lower corner which is right below the fill port....maybe pop the fill line off and shove a pickup hose in?

I think if you can do that it would be worth a shot, but here's the issue, if you have water in the fuel and you were using E10 fuel, it could be phase separation in which case you'd be left with low octane fuel that might cause detonation. Also, if you want to get all the way down to the very bottom of the tank, the way to do it is to remove the sending unit cover and go through that. If you were using E0 fuel then yes it might be worth a shot!
Like I said I had a similar problem all last season, it was bad gas as verified by running it on an outboard tank (after checking EVERYTHING ELSE), my situation was:
30 gallons of E-10 that was stabilized, but at that point about 10 months old
my recycling center only takes 5 gallons per week
given my lack of patience at this point, I simply paid "the guy" who pumps out all the fuel tanks for the local marinas, and in 15 min it was done. Given that I fix literally everything on this old boat myself I felt it was worth it. Given the symptoms I was seeing (would not plane, occasional stalling, etc) I thought phase separation was a fairly probable cause.
Also it's good to keep in mind that if you are checking what comes out of the fuel filter, when using E10 fuels, you won't see water in the fuel, until it reaches the point of phase separation. So the fuel can look great, till it ain't!

 

[badrano]

here's the issue, if you have water in the fuel and you were using E10 fuel, it could be phase separation in which case you'd be left with low octane fuel that might cause detonation.

Yeah, I use 87 octane from the local station....not ethanol free.
I think that settles it, pump it off and discard it. I don't want to risk being left with low octane gas.