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Old 05-08-2015, 09:35 PM   #26 (permalink)
EcoModding Lurker
Join Date: Oct 2014
Location: California
Posts: 50

Pearl - '92 Honda Civic VX
Thanks: 26
Thanked 5 Times in 5 Posts
Since my last post:
Bought an original shop manual and will find a buddy.
Previous maintenance appeared to have worsened gas mileage by 10 mpgs.

New dealer parts:
Timing belt/water pump
Fuel filter
Air filter
Valve adjustment
Oil change with MOA
Miscellaneous belts, o rings, oil pan gasket
Motor mounts, left and right
Set ignition timing with timing light
New air filter

I already had these:
The major tune up (I actually had one 47 mpg tank after)
Re-built distributor
New thermostat

I began to have trouble with the idle. After several attempts to adjust it I took her in for a dealer diagnostic.
Here's what they did:

Adjusted timing belt tension
Checked timing
Checked idle speed
Removed and cleaned throttle body, removed and cleaned idle adjust screw, adjusted per service manual procedure
They recommended that I replace the idle control valve.
I did but still had fluctuating tachometer readings, bottoming out even with lights out(factory tach, still need mpguino).

More new parts and cleaning with Seafoam
VSS (the speedometer went haywire after an undercarriage wash)
Thermo unit and thermo
Sensor assembly
Five wire o2 sensor (NGK 24300)

I took it back to the mechanic at the dealer tech for more diagnostics as suggested and to adjust that darn idle.

Here's his work and "verdict":
Checked EGR operation
Checked A/F sensor
MAP sensor
T/P sensor
ECT (TW) sensor
Set base ignition to spec (VX spec I hope)
Performed compression test (#1-128 psi, #2-129, #3-120, #4-130)
Re-set base idle 75 rpm higher than spec
Monitored PGMFI dat list with PGM tester and 3 pin data link adapter. All values within expected range
Ensured that PCM is getting A/C request signal

After all of this, he concluded that an engine with nearly 270,000 miles on it couldn't do better. Even though I drove it across the country and for two months in Denver getting 45-48. A quick drop from 47 to 37 leads me to think there's still something else going on.

I changed to Conoco gas and will run a couple tanks of 87, but am working through a tank of 85. Which by the way, I was getting the better mileage pre-cleaning, pre-maintenance on 85, but I will upgrade to what my book says. I don't know if that accounts for 10% ethanol, but the power was better and I got 44 mpgs over 350 miles, 2/3 at 60 mph, 1/3 short highway trips and city commuting.

Then I noticed hesitation when I let off the pedal and re-accelerate around the time the shift indicator light comes on.
It seemed to be worse when the tank was below 1/4. It also took a little longer to turn over. Next part:

New fuel pump.
Checked the clutch (it's fine)
Checked the oil (it's Much, Much cleaner)
Set the tire pressure to 44/40 (I can go higher if you advise)

What about trying this procedure to set the idle speed for 92-95 Civics I found? It involves resetting the ECU to VX spec under load (test load w lights only) 650-700 rpm, no load 550-650. Or does it sound like this was already done? This procedure is at

Full tank.
Any advice before my next experiment?

Thanks folks. Sorry if this is overload information.
This same car here was for sale here in Denver. It was for sale, all stock, Tahitian Green Pearl, just like my car with only 67,000 miles. It sold for $9,000. It is getting average 52.
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