If you only removed sec.cats maybe the upper cats are a little clogged up, I mean they are the original 30+ year old one s right?
Fox Xtremely high fuel consumption
- Thread starter PonyGTrider
- Start date
Those compression numbers seem low to me. The cylinder to cylinder difference is also concerning. You shouldn't have over 20% variation.
A leakdown test is strongly advised.
gkomo
now i can hopefully expect to receive the shaft
Hows your oil viscosity after a lot of miles and does it smell like fuel?
9.5 mpg just doesn't make sense from a fueling perspective. If we figure your combo for a worst-case 16mpg expected, then you're using ~68% more fuel than you should be. So, where you should be seeing close to stoich at ~14.7:1 during light throttle/cruise operations, you'd actually be seing 8.75:1.
On the load-side of the things, needing 68% more throttle means that instead of needing like 20hp at cruise, you need 33.
Or, it could be somewhere in the middle. If for some reason you were only firing on 6 cylinders (I'd hope this would be something you could feel, but don't discount it just because it isn't obvious), while simultaneously using a badly spec'd MAF, you might be running rich, and might be wasting fuel in 2 cylinders simultaneously.
What a quarterhorse would let you do is to monitor the stock narrow-band O2s' AFRs & fuel trim corrections in real time. You'd also see what the MAF is commanding, timing, and all of the other things that can screw up your tune. I'm not a remote tuner, but if you were in my area of NC, I'd hook up to ya to see what's going on. It would provide the type of data that would really allow you to hone in on your issues.
FWIW, I have a way to monitor fuel pressure & AFR in all 3 of my cars, which REALLY helps me get to the root of whether the issue is fuel or timing related.
On the load-side of the things, needing 68% more throttle means that instead of needing like 20hp at cruise, you need 33.
Or, it could be somewhere in the middle. If for some reason you were only firing on 6 cylinders (I'd hope this would be something you could feel, but don't discount it just because it isn't obvious), while simultaneously using a badly spec'd MAF, you might be running rich, and might be wasting fuel in 2 cylinders simultaneously.
What a quarterhorse would let you do is to monitor the stock narrow-band O2s' AFRs & fuel trim corrections in real time. You'd also see what the MAF is commanding, timing, and all of the other things that can screw up your tune. I'm not a remote tuner, but if you were in my area of NC, I'd hook up to ya to see what's going on. It would provide the type of data that would really allow you to hone in on your issues.
FWIW, I have a way to monitor fuel pressure & AFR in all 3 of my cars, which REALLY helps me get to the root of whether the issue is fuel or timing related.
You’re correct, but I can see thru very good and I can’t see anything unusual just a tan color honeycomb.
Thank you
I just ordered a cheap leak down tester to have at least some reference of what’s going on in all cylinders. I’ll get it tomorrow and jump on that task right away.
Thank you
Yeah something weird is going on I will keep and review all the data you’re sharing against what I have.
An AFR will be the next step before I tear out all the top end.
I ran a cylinder balance test resulting and all cylinders contributing correctly.
It is unfortunate I don’t have a Quarterhorse to pinpoint the root of the problem.
Yeah I know you would drop by if I was close enough.
In the mean time I will run a lead own test, and verify total advance and see if I can find some leads about this.
Thanks a bunch man!
I’ll see about that possibility
I just removed the sparkplugs and they don’t look like overly fueled, but who knows… They are side gapped at 0.040” and they run awesome! I tried from 0.054” down to 0.40” and there is were it runs the best.
In regards to compression I will re do the test and one thing for sure there is no Blow-By, I have an oil watch can and there only appear three or four drops of oil once in a while.
Thank you
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I’ll see about that possibility
I just removed the sparkplugs and they don’t look like overly fueled, but who knows… They are side gapped at 0.040” and they run awesome! I tried from 0.054” down to 0.40” and there is were it runs the best.
In regards to compression I will re do the test and one thing for sure there is no Blow-By, I have an oil watch can and there only appear three or four drops of oil once in a while.
Thank you
Why is the strap cut back on all of those spark plugs?
It is what they call “Side Gap” and the intention is to expose the spark without being hidden under the strap. That is something I followed up to improve the combustion but tuning the plugs with normal ground strap makes no difference on the poor fuel economy, but it kind of make sense to use side gapped plugs so I did that.
Yeah that’s what I thought. So I will narrow my chances to COMPRESSION AND TIMING.
I will get Myles down tester tomorrow and I already removed all the plugs and put No 1 piston at TDC to start checking all cylinders and see where they take me.
Put a new set of properly gapped, unmodified copper plugs in there and re-evaluate.
One of the things that doesn't need help on a fuel injected Fox is the ignition system. It provides hot and fat spark, all by itself when it's in good condition.
If you really want to play with the plugs, index them.
I know I’m running more compression than you are and I’m gapped at 0.050 and my plugs look waaaay better than that. Those look rich if you ask me. This picture is super basic but Inthink you get the idea.
Yep I will do that but first I will run a leak Down test tomorrow as soon as I get the tester I ordered. I’m very suspicious some things are pointing to that or timing.
I want to find what is causing this terrible MPG once and for for all, but yes I will follow your suggestion
Actually I tried indexing the plugs but I’ve must done something wrong because my engine ran like crap!!!! I might try that again.
Thank you
I wouldn't sweat that part too much. Gains are questionable at best.
Understood, so tomorrow I will stick with the plan and I’ll put ani update of any findings on the leak down test. I’m worried I will have to take this thin apart but it is what it is
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