Engine backfiring through throttle body when trying to accelerate

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

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.

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.

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?

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

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

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

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?

how old is the fuel?

Scott Danforth said:

how old is the fuel?

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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.

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?

Click to expand...

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