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94 Explorer sport and octane requirement

Old 05-26-2004, 07:15 AM
niteowl is offline
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94 Explorer sport and octane requirement

Hi Everyone,
I know the 94 Explorer 4.0 Litre is not known for good gas mileage but mine seems to REQUIRE high octane gas. Anything below 92/93 octane and the engine knocks badly driving down the highway.
Is it normal for this model to require such high octane fuel or is there something I can do to lower it and save some money at the pumps?

Old 05-26-2004, 07:57 AM
mason is offline
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Your Ex shouldn't require high octane. Check out the posts on Sea Foam. Sounds like you might need to decarbonize (lower the compression).

Old 05-26-2004, 12:57 PM
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Lots of things cause ping on the 4.0 OHV. Carbon buildup in the cylinder is one common cause.
The other common causes are from the engine running a little lean. Dirty MAF or vacuum leak (in particular lower intake manifold gasket) are most common.
95% of pinging issues are resolved by one or more of those three items. 1) Decarbon the cylinders, 2) Clean MAF, and 3) tighten lower intake manifold bolts (may need to replace lower intake gasket, but not usually). These have been discussed many times, run a search to find more information.
Old 05-26-2004, 07:21 PM
niteowl is offline
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High octane requirement

Well, I found a vacuum leak. One of the rubber plugs over an unused vacuum connector had come apart. I plugged it and the engine runs much better. The idle is lower and smoother and I have acceleration back without the stutter it was giving me before.
Most interestingly though is that I now have my tachometer working again.
I posted a question a few months back about the tach not working correctly but never figured it out. It would stick just above 2000 rpm and would occasionally break free and go higher but would stick again almost immediately. Now that the vacuum leak is plugged it is working pretty well. It seems hesitant to move in some areas of the gauge so it does not move smoothly but it does move in all rpm ranges now.

I hope to be picking up some Sea Foam tomorrow, the local Advance Auto was out but have a shipment coming in. I also pulled and cleaned the MAF sensor with carb cleaner spray. It was pretty dirty prior to cleaning but looks good now.
I disconnected the battery for a while and then reconnected and let the car idle for about five minutes to let the computer re-detect the air flow with the clean sensor. Now I just have to wait a few days for the gas tank to get low enough to fill with a lower grade gasoline and see how it handles lower octane gas.

Thanks everyone.

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