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Old 10-16-2008, 03:22 PM   #1
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My new VX is Lacking in mileage

I just did a swap from a CX to a VX.

I'm not getting the mileage I thought, I'm at about 40mpg highway.

My EGR is disconected because it would remain open when starting and of course stall, so I disconected the controler.... attempting to resolve this problem. Now it idles fine... little high sometimes ....

Any sugestions as to why the mileage is so low? anyone?
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Old 10-16-2008, 03:46 PM   #2
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I just did a swap from a CX to a VX.

I'm not getting the mileage I thought, I'm at about 40mpg highway.

My EGR is disconected because it would remain open when starting and of course stall, so I disconected the controler.... attempting to resolve this problem. Now it idles fine... little high sometimes ....

Any sugestions as to why the mileage is so low? anyone?
Bad 02 sensor?
Needs tune up?
Clogged fuel injectors?
Vacuum leak?
Tire pressure?
Any other fuel or emissions related problems?
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Old 10-16-2008, 04:08 PM   #3
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New O2 sensor .... ebay
Looked at plugs, wires & cap and they looked good not too much wear.
cleaned fuel injectors ... soaked in break clean for a day ...
Haven't found a vacuum leak yet.
Tire presure at 39 front 38 rear
No check engine light and there are no emmisions in SC, so no problems that I know of...
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Old 10-16-2008, 05:26 PM   #4
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40 mpg is not too bad if you're accustomed to driving 80 mph. I'm guessing you probably don't drive that fast !!!

My VX gets 49 mpg at 60 mph and about 45 at 70.

Check your VTEC solenoid/spool valve. You could be stuck in full time 4 valve per cylinder operation but that would normally trigger a CEL.

Too bad the VX was OBD1. You could probably track down the issue with OBD2 and a decent scan tool.

Your best bet is trying to monitor the signal from the LAF sensor to see if your engine goes into lean burn. If not - you've found the problem.
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Old 10-17-2008, 05:02 AM   #5
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Your best bet is trying to monitor the signal from the LAF sensor to see if your engine goes into lean burn. If not - you've found the problem.
That is a good start.

Do you have the correct NGK V-Power spark plugs in there? Made a couple mpg difference for me.

I would also work on getting you EGR setup to work properly. When everything on the VX engine is working correctly it will operate more efficiently. Very sensitive little motor........

Are you all freeway driving or more city?

Bump tires up to 40-42psi.
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Old 10-17-2008, 06:27 PM   #6
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I have the correct plugs.
And I do mostly highway driving.
I'm not sure where to start with the egr issue.
I have spare ecu's ... tried that.
There is power going to the EGR controler causing the EGR valve to open... could there be a problem with the EGR vavle?
Or perhaps another sensor telling the controler to stay on when it shouldn't be?
I'm gonna checkout the vtec solenoid this weekend
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Old 10-18-2008, 10:00 AM   #7
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Check the condition of your battery by doing a load test if it is about gone it could be causing the alternator to work overtime trying to keep the battery charged which would result in lower MPG.
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Old 10-18-2008, 12:04 PM   #8
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Originally Posted by Diazo66 View Post
I just did a swap from a CX to a VX. I'm not getting the mileage I thought, I'm at about 40mpg highway.
Any sugestions as to why the mileage is so low? anyone?
I don't accept < 42 mpg hwy as even close to normal for a properly running Fed VX. I'm in the same boat and interested in how this sorts out. My VX has never delivered better than ~41.xx mpg. I believe there is a major malfunction of some kind that prevents the car from getting the additional 25% higher (10 mpg) that these engines are capable of for highway use, expecting ~50 mpg +

My VX is a CA version with a Fed ECU swap, it came with the 5-wire sensor as all the 1992's did. I am second owner who purchased the car in August with 215,200miles on a well maintained engine.

Been there, done that: correct plugs, air filter, rotor, distributor, good clutch, correct tranny, high tire pressure, and good maintenance practice, my VX is perfectly up-to-date on those obvious things that both our cars (and many other's here) have properly handled.

Yet I really think there is a short list of silver bullet items that force the VX to the low 40 mpg number and this is the sign of something seriously out of wack in the engine management area. I am guessing that the short list would look something like this,
*LAF sensor,
*electronic air control valve (EACV),
*intake manifold clogged by EGR carbon choking off intake swirl effect at low rpm.


That's my guess on a short list, though I'm interested in other none maintenance, system related issues that someone before us have found. Did anyone take a VX from low 40's to low 50's in one swoop?
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Old 11-10-2008, 03:16 PM   #9
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I have a 92 VX that I recently purchased, it has had a full tune-up along with a new NTK O2 sensor, tires are at 40 psi, stock 165/70-13. I took on a road trip this weekend, the best mileage (pure highway at 60 to 65mph) was 42 mpg, it should be capable of better. I know there are many possible reasons including those listed above. Can anyone suggest diagnostics?
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Old 11-10-2008, 10:10 PM   #10
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Wow, the silence is deafening! I posted the same question three weeks ago. mrmcg1 and me are asking the same thing (though you did not state if you've got the Federal version). My explaination, (unconfirmed) is that the VX is not obtaining lean burn and the basic tune up is insufficient to solve that issue. So if we have all the basics down, what next? Any VX owners solved this? These cars should just nail 50mpg at 60mph pure highway.

My eom sensor has ~100k on it and no CEL codes. My purchase of a new Bosch o2 sensor immediately threw CEL, so its just been returned. Going to try another plug and play o2 sensor. mrmcg1's got a new NTK o2 and getting crappy mileage, not good, as that is item one on my short list.
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