First thread, and its a doozy.
This is the first time I've ever had to deal with an EFI Honda and I'm pulling my hair out

Base 1990 hatch, D15B1 believed to be the original motor, just over 300k miles, 4-speed manual, Federal Emissions, Dual Point Fuel Injected, Full exhaust system with a loud fart cannon...

My fiance snagged a riced up hatch to return to stock and use as a project and daily driver car. We have slowly been getting it back to stock but it has had a lot of issues along the way.
Ill break this out into issues, Fixes, and then End with whats still going on.

At best case, It seems to only get 15-18MPG at fairly modest 45-55mph country roads. Not Even my first gen accord with a slush box got economy like this with higher miles...

Initial Issues:

• really rich dumping black smoke on acceleration
• Burning oil on deceleration / high vacuum situations
• High Idle, then Lumpy idle
• TERRIBLE FUEL ECONOMY like 12MPG initially on rural roads.
• Surging idle and surging under light acceleration or steady cruising. Fairly bad afterfires when this happens.
• Failed to run properly if low octane (87) was used. Hard to start.

Fixes Conducted so far

• O2 Sensor replaced, original caked with soot. New one is reading really close to .5 at idle, but will sometimes hop up to .7 when it starts getting a little lumpy
• Map Sensor Replaced : Ecu indicated fault, one on the car did not look like a stock one and had two vac lines, Replaced with one from a 2 year newer honda that appears to have the same voltage readings under idle and load conditions, with only one vac line. ECU seems happy with this, really cleaned up the idle fuel smell.
• removed hot-air intake and replaced with OEM air intake, new filter, OEM breather tube and resonator chamber behind the bumper.
• Water Coolant Sensor for the ECU (2 prong under dizzy) replaced as it was out of spec - Cleaned up idle and low load fuel smells
• Thermostat replaced as it was getting hung open - Ive had hondas in the past and know the cooling system needs to be burped with the little valve on the outlet, burped coolant system after replacement.
• Inlet Air Temp Switch was flakey and would drop out, Replaced. - Further Cleaned up fuel smells.
• Checked Ignition timing - Appears to be spot on when hot, though a little "warbly" when cold.
• Both injectors sound like the are firing when listening with a steth/probe, however they almost sound like they are firing together, not as a primary/secondary. Not sure if this is normal.
• IACV was Sticking, but has been freed up with seafoam, unplugging it and re-plugging it has instant idle change so it appears to be working - Fixed high idle speed
• Secondary Throttle Plate appears (the one that looks like a choke flap) to open when floored after moving the diaphragm manually once or twice Air baffle in the intake surge tank is still in place.
• Dizzy was new from the previous owner : looks brand new, as is the cap, and rotor. No Carbon Tracking inside either.
• Re ran some of the vac lines to the the carbon canister, redid the map lines and put it all back to stock.
• Checked vacuum leaks after all this with carb cleaner : no idle changes at all when wetting the entire intake / vac system
• Injectors DO cut off above about 1500RPM if in gear, off throttle, and coasting down... so TPS appears to be working.
• Temp when running stays just below half way on the interior gauge

AS OF THIS

• Idle is fixed, idles around 1500 RPM when cold. Drops to 800 when warmed up. Verified with Timing Light - car does not have a tach. Occasionally after a hot restart it may stumble a little bit but clears up after about 30 seconds of driving.
• Drives a little better, black smoke has drastically cleared up, After Fires have subsided
• Pulls pretty hard for what it is. Its probably faster than my Nissan that has 25HP on it.

Still On Going

• intermittent idle stumbles or misfires, hard to tell.
• Grey/white Oil smoke out exhaust in high vacuum conditions (Valve guides are my guess here?)
• Poor Fuel Economy

Next on the List

• replace Spark plugs (they were new with the car, but I suspect they may be gapped improperly, might as well replace them if im pulling them out)
• Replace Spark plug leads : they dont feel like they make good contact with the plugs, but they dont arc (cant hear them, dont get popped when touching them)
• recheck spark timing.
• Check Valve Lash to make sure its not hanging valves open and loosing compression (my nissans with solid lash adjust click like a banshee when adjusted to factory lash, and this honda has 0 valve train noise, so i fear it may be too tight)

If anyone has any good ideas, and is way smarter than i am...im all ears.

 

well to start with the bad fuel mileage
id take the fuel filter out then poor that gas into a clear glass and see how clean it is
and if its dirty gas
then replace the fuel filter
doing this should bring you up about 4 mpg or so

and for the stumbling idle after the engines already warmed up
this is because your rpms are to low
these old honda engines when they were new they were soposed to idle at 700rpm

but nowadays you have to raise the rpms by turning the throttle body screw a bit
900 rpm at idle is the sweet spot
doing this should fix those second start up problems

let me know how this goes
it sounds to me like your starting to like the little civic ^_-

 

I like working on it, everything is in reach, without a 3 hour disassembly process like my nissans. Makes me Want a Gen 1 Accord again. It really is just such a easy car to drive.

Followups :
Compression at 6 Cranks across the board from 1-4 as follows - this is on a cold engine that sat all night: 180, 177, 178, 178
So I can probably rule out valve lash being overly adjusted, Did not see a reason to check that given the compression.

New NGK Plugs. Gapped down to split the difference in the spec range. Bumped Timing back up just a hair (degree or two). Plugs in the car had some hard pure white ash deposits, almost like it was run with leaded AVgas at some point. Number 2 was wet with fuel, possibly just not burning well or the tip was too insulated from the buildups.

The engine is no longer rocking at idle, I had supposed it was a bad motor mount, but it may have just been a small misfire or uneven detonation from the plugs.

New Wires installed as well, ones that actually "click" properly when pushed down on the plugs, rather than using a spring seat.

Pulled Idle up to 875 or so per your suggestion, so we will see how it works.

Have not pulled the fuel filter yet, however its brand new and shiny, with the box in the hatch still from the PO. IF we have not solved this with the plugs and wires, Ill probably replace the filter, Check the fuel high side line and make sure its getting enough pressure. Might Take the injectors out and inspect them, make sure they are not fouled up and just shooting a stream instead of a mist.



This is where its sitting now, IACV is unplugged here just to set the base timing.

 

I replied yesterday however it seems to be stuck in moderation Limbo maybe due to pictures linked of the bay?

Compression tested between 176 and 180 on all four cylinders cold. Leak down at 3 minutes had it holding steady. No Valves are hanging open, so that's good. I'm shocked..

Plugs appeared to be lead fouled and improperly gapped... Like someone ran AVgas through it or a ton of antiknock agents.
New NKG Coppers Gapped at .042, New Plug wires that use the old clip style contact instead of a spring in the wire, Pulled Timing back up 2 more degrees.
Pulled idle up to 875 Per your suggestion.

Pulled IACV and totally flushed it with carb cleaner, then seafoam top end oil mist, repeated a few times to free it up until it ran out clear.

Pulled all connections again today on the intake side of the motor, cleaned the sensor contacts (and injectors contacts) with a brass brush. Sprayed a little electronics cleaner and lube in them too.

Idles great now. Put around 100miles on the car today, mixed driving putzing around and some just winding it out for the fun of it. Gauge Still reads out at over 3/4 tank. Before this would have drained it all out and then some.

No more stumbles when decelerating or after coming to a stop after extended running.

Last Oddity : Do the fans not run very often? the cooling fan only seems to run if it idles while hot for more than 5 minutes or so. It then cuts on maybe 1-2 minutes and then cuts off again. Most of my cars still use clutch fans so they are always on to some degree, but they are quite a bit older.

Ill Keep this updated if anything changes or more work is done.

 

one thing about the spark plugs is that they should be gaped to .44 this is the factory setting and its the setting for the best mpg

and as for your electric timing
your setting should be set straight with the middle mark on the 3 lines on your crank pulley
this is normally 16 degrees

but it looks like youve almost got the car working perfect now
normally on a full take you can get about 300-30 miles on a full tank in the city
and about 350-380 on the interstate road trips

those are the number that ive been getting forever!!! ^_-

 

I saw anywhere from .040 to .044 depending on year trim and etc, so thats where the .042 came from to split that difference.

Base times between the center and outer mark on the pully. I figured this cant really hurt to try, 2-4* extra base time on my nissans has always helped fuel economy out but they also have really low base times like 4 instead of 15-16. just a little timing advance and I get 28city 32hwy out of my Nissan rated at 19/24, but I short shift it a lot and keep it in dual spark mode too.

I will probably pick up a filter and drop in it this week too since they are only 7 bucks at autozone. Dropping in a Bosch Tachometer to so she has something to kinda help her not wind it out so bad and get a little better economy..

I'm just happy its running right finally. Before hand i just had no drive to help fix it up but now that its a good economical runner, its time to start cleaning it up. Its been rear ended in the past, but my other half already managed to find and sweetalk someone into getting the entire rear end of the car for like 150. It sat presumably open to the elements for a long time as there is a substantial bit of grime and mildew on everything.

 

New updates.
fuel economy has improved, between 260 and 280 miles per fill up at 8 to 9 gallons each time. Happy with the fuel economy. Its running 87 now just fine. Had to re adjust idle a few times, I suppose after the ecu was relearning?

Hatch has been replaced with a non bent one.

However, now that its driving a lot more we notice its consuming a lot of oil. Compression test was good, so I dont think its ring related. Valve guides maybe?
Pcv valve ? (I'll replace this soon and see) but its drinking probably a quart or more every 600 to 800 miles.

 

https://honda-tech.com/forums/honda-...fixed-3345235/