Xfi help needed

broke

broke
Another check that’s free, is your passenger side header hit the positive battery cable, new fuel filter is also an inexpensive preventative maintenance thing to try. I had a new filter fail, it was a canister type though.
 

Blacky

Drive it like you stole it
Yes sir, I checked the battery cable and didn't see it hitting anything. Also I am going to put that fuel filter on either today or tomorrow. Thank you. I like cheap fixes
 

Blacky

Drive it like you stole it
I think we've nailed down the problem to being a exhaust pressure loss. We just located a crack in the crossover pipe and once that is welded up I believe we will be up and running to BG We just located a crack in the crossover pipe and once that is welded up I believe we will be up and running to BG
 

Blacky

Drive it like you stole it
Well went all the way to bowling Green and I'll tell you it was fantastic. There lots of cars. Lots of people. But the car was still making those exact same squiggly line recordings. The best we had at running was 1089 and that still had squiggly wine recording exactly all the same. That was what 20 lb of boost and 20 lb of booze should have had that car running 10:50s. So I'm back to the drawing board again, help
 

TIMINATOR

Active Member
How about light it off on a lonely road with an observer to watch the boost and FUEL PRESSURE at the RAIL, since you are not logging it! I once had a braided line fail internally next to a fitting. A "flap" of the inside neoprene hose to the carb made a restriction inside the hose. It did NOT have an external leak! Chased my tail for a while on that one!
Try a different fuel pressure gauge too! At the rail with a "T" to a temporary inside or taped to the windshield (known, good,) gauge.
IMHO, a cracked x over causes slow/ lazy and less boost, never had one cause breaking up.
I think u have eliminated the spark issue as a cause....
TIMINATOR
 

Blacky

Drive it like you stole it
Sounds like some more good ideas to think about. Yes, the spark issue seems to be fine. I'll think about your gremlin and see if I can't think of something along those lines. That's a new thing for me to check that I haven't done before and I appreciate your feedback timinator!
 

TIMINATOR

Active Member
You could have broken a valvespring or overrevved it and "sacked" them all. Also, everytime you float valves, they will float just a bit lower next time. More food for thought....
P.S. how much spring pressure are you running?
TIMINATOR
 

Chuck Leeper

Toxic old bastard
Staff member
Yes, the spark issue seems to be fine.
The spark issue is not resolved until you learn to read the plugs.
Read a fresh set? Don't waste your time trying to read them after they've been driven for a while.
Have you tried different gaps?
Tried another heat range?
 

Blacky

Drive it like you stole it
We have tried different gaps and are at 34 I believe. I haven't tried a different heat range because those ones have been used and that engine build for 6ish years and running fantastic before this quirk chuck
 

TurboWh1

Well-Known Member
Hey Steve, spark plugs might be worth a shot. I have mine gapped at .017 currently, that got me the finals on a car that didn't want to run in the heat or higher boost levels.

I went from .025 to .017 on the plug gap. More boost was blowing out the spark. Runs like charm now:)
 

Chuck Leeper

Toxic old bastard
Staff member
those ones have been used and that engine build for 6ish years and running fantastic before this quirk
Same ign system too?
Same springs?
Pull the gap down to .025 on the plugs you have now. See what happens.
Still there?
I'd spend a few $ and do a range colder and leave the gap at .034-5.
Read them after a WFO blast. This includes cutting the threaded part off to look at the fuel ring.
Still there? Repeat with a colder set the same as above, with the gap at .025.
 
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Blacky

Drive it like you stole it
You all have given me a few ideas. I'm going to start with the fuel first and make sure there's no issue there. I would think if I had a broken spring or something I would hear it in the engine and the engine seems to be just fine. As far as the plug and spark, a few people have mentioned tightening the gap. The only thing I'm afraid of is with these GN1 aluminum heads. I think I set the Gap to what Tom had recommended and used the plug. He recommended. Poor Tom
 

Chuck Leeper

Toxic old bastard
Staff member
"The only thing I'm afraid of is with these GN1 aluminum heads. I think I set the Gap to what Tom had recommended and used the plug gap he recommended".
In the "FWIW" dept: ;)
There's no correlation between what plug gap you run, and the fact that the heads are aluminum.
Plug choice, gap, and tuning parameters are based on the engine application.
When changing plugs, go light with the anti seize.
 

Blacky

Drive it like you stole it
Thank you Chuck. That clears up a lot for me. I'll get working on this soon. And I'll post the results sir
 

TIMINATOR

Active Member
True story! No never sieze on the first 2 threads, it vaporizes with the hot shell, and combustion heat and can be deposited on the center insulator causing misfires under load only! Can be hard to find, and see. Once it is there, I toss the plugs, damn near impossible to remove.
TIMINATOR
 

Blacky

Drive it like you stole it
I believe that to be true. We were told by a friend that pulled my plugs that the never sees had gotten too far in. That's kind of why we couldn't. So that is an absolute true story as I've personally witnessed it. I think I'll pull the plugs and do as chuck recommended. Hope other people read this thread and realize what the anti-seize can do if applied too much
 

TIMINATOR

Active Member
Get BIG q tips (industrial size) and clean the threads in the heads too. And then get what you can inside the combustion chamber around the hole. Use a lot of them with brake cleaner on them! Any left in the chamber around the plug hole can revaporize under heavy load, and redeposit on the insulator of the next set of plugs u put in there!
Experience is what you get when you didn't get the results you expected!

We did a new 8-71 boat blower motor that would only run for 45 sec. to a minute and a half, backfire and stop.
We checked a few things, and it kept doing it! All new complete MSD system.
Replaced: coil wire, plugs, wires, coil, rotor, then hot wired it to the battery and MUCH more. About half the times, it would crush a float or two. Being that it was a drag boat, one of us would hit the starter, and the other one of us worked the throttle from outside the boat. We swapped positions after I lost part of my moustasche, and eyebrows from flames out of the backfire plate! Spent several hours dicking with it, wanted to replace the dist. but didnt have another small cap one that cleared the blower.
Bottom line: the terminals in the inside of the cap were 3/8" too short, the air in the cap ionized and the spark crossfired, killing the motor. After a few minutes of checking things out, the air in the cap would de ionize and the motor would again run for a short time. Being anal, and out of ideas, I measured the distance of the rotor to the distributor body, and the then, depth of the cap terminals. I bent the tip of the rotor up about 1/4" and it ran fine. Replaced the cap the next day, and shipped the boat.
MSD said they had never heard of that and didn't replace it!
To this day, I drill two vent holes in dist cap near the bottom, just because....
Trust me, I am too old to be learning this kind of crap!
TIMINATOR
 
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