The car is a '95 DX Coupe EJ2 (D15B7) with no engine mods.

Since the last time the 02 sensor was changed was unknown (had the car about 20K miles), I obtained a new one (NTK 24542) and installed it. No change in mileage or operation, same as before.

Last Odo Before Fill-up: 208.7
Typical pre-issue mileage: 330-370 (as high 518.84 (or 47.6MPG) hypermiling(!)
Gas Tank Size: 11.9

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Questions you may have:

Do I have any signs of an over-rich condition (black smoke, sooty tailpipe, cooler running temperatures, extra power, etc.) The answer to all of them is no.

Have I looked for a fuel leak under the car. Yes, but I admit, depending on the rate it may evaporate before I can see it. Granted it would have to be a very large leak to cause the kind of drop I'm seeing here.

Oil I run: Mobil One 0w30, Full Synthetic
Manual Gearbox Oil: Royal Purple, High Wear Additive Package, 1.9qts

Do I have a CEL. No.

There are no drivability problems on the vehicle. Aside from sucking gas like a Ford Pick-up, the engine runs seems to run perfectly. No sputtering, erratic idle, surging idle, no AC idle issues, no idle issues of any kind.
No cruising or acceleration issues. Car seems to have all normal HP output available.

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What have I checked (Not Much):

Replaced 02 Sensor
Checked for Vacuum leaks around Manifold, Body, and Lines.
Clutch Slippage

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Items I intend to check:

Fuel pump output pressure
Fuel pressure regulator numbers

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Anyone have any further suggestions? And no, my foot hasn't gotten any heavier

 

Wow...I am at a loss here, you shot down everything I would normally think of...

How about...

tire pressure
Wheel Alignment
Excessive Brake Drag
Fuel leaks from the filter, fuel rail, or pressure regulator
A clogged catalytic converter (your car won't throw a code for this since it is OBDI)
Other exhaust restrictions
Excessive friction in the driveline (long shot here, but just making ideas)

Hope this helps...I know its not much

 

Fuel pressure, exhaust velocity, and timing would be the first things I checked.

Also, running rich doesn't give you more power - it actually robs you of power. If your car felt slower than it usually does, that might be indicative, but we're talking <5%. 5% of 100 is 5, I.E. "Less than you'd be able to notice."

 

- B20DelSol -

TP: @32

Tires: BFGoodrich g-Force™ Sport COMP-2™ (newer than the problem)

Fresh alignment from the tires and suspension (several actually, hey...I said the engine wasn't modified )

Excessive Brake Drag - Possible and will check drag but doubtful. No smell or side to side fade from constant contact, which with how I drive I probably would noticed. Brakes are nothing special, Factory Pads on Brembo standard rotors. Brake upgrade in the works for sure... 4 corner disc & probably move to 5-lug.

No fuel leaks in any of those specific areas, all intake areas checked for vacuum leaks as well with no leaks to eliminate either the possibility of just a pouring leak or a vacuum leak causing a metering problem from unmeasured intake air, causing an over-rich condition. Possible malfunctioning FPR, Possible Malfunctioning FP, thought I would expect them to either die or tank (ha!) in its output which it obviously isn't. In the case of the FPR, there is only about a 10psi difference between high and low. Adding to those two facts that the car runs fine under all operating conditions, It's not making itself easy to track down.

I suppose a plugged cat could be a consideration, but again, I more than likely would be seeing a fairly decent loss of power across the board from incomplete cylinder filling, and the same goes for any other type exhaust issue.

 

Pull your plugs and post a picture of the tips of them. That might be helpful as well.

 

- jbpnoman -

No noticeable change in power anywhere in the power band, regardless of the driving condition.

My plugs are great. They're about 10K miles old now and look brand new. Of course, they are NGK's reviewed Iridium replacements for that engine

The pressure at the service port on the fuel filter was the definite next area to test.

With the FP output, & vacuum to verify the specs on the FPR, I should have all that already.

It's sad and I have no excuse for not having a decent FP Tester. Got too used to borrowing them from other people I guess at the shop. I'm gonna rack it @ the dealership Saturday & do both of the fuel tests wouldn't hurt to put it on the exhaust gas analyzer; see what's up.

Due to the mileage on the vehicle (255,000), a retirement for the cat may be a serious consideration, especially since she's been getting a small amount closer to a fail many years in a row now. Then again, the 02 sensor I pulled was the original, so that might have been all that was.

When I opened this thread It was mostly geared to be a 'Is this a known problem that come out strong around X miles with X part to blame'? Rather than I diagnostic theory discussion. Aside from my own baby, I've only put serious time in on a handful of other Honda's, so as usual our discussion has been illuminating.

If anyone has any other experiences that kind of came out of the blue and what you did to try and chase down the gremlin or any parts you threw at it. Feel free to post them.

Thank you! - B20DelSol & jbpnoman -

 

No problem man...your mpg issue is interesting to say the least.

I wish I could be of more help and just tell you what it is...but you are going through and checking everything just find out they are within spec.

At this point, I am going to point to the cat as the problem....just because!

Keep us updated!

 

Alright, over the last couple of months I have found a few issues:

1) The timing was set incorrectly by the place where I had it smogged last. The did NOT short the service connector to bring the system back to base timing. As a result the timing was set to 0 degrees or exactly TDC. I shorted the connector and set the timing to the proper factory spec which is 16 degrees +-2 degrees BTDC.

Effect: Made problem worse.(!)

2) Distributor cap had cracks in it extending about a 1/4 inch from each terminal. However there is no evidence of any carbon tracking, and there have been no misfire issues. The car runs strong and steady.

3) Upon pulling the spark plugs it is apparent that we are running over-rich, as the plugs have a sooty black base ring (to the point of carbon flaking off) and a white insulator. No abnormal tip or ground strap wear/coloration.

Aside all of that, there still is no solution though the testing seems to indicate that the distributor or the ECM are to blame. There are still no codes for anything. In the next couple of days I intend to pull the distributor, run all diagnostic tests in the service manual, replace the cap and rotor and fill up and map out another tank. If the distributor tests bad I will replace the faulty component(s), if not I guess it's a trip to the junkyard to pull a '95 matching ECM.

I'll report back with anything noteworthy.

Justin

 

Change the fuel filter , get a new gas cap, check physical timing , hollow out the catalytic , do a compression test

 

Have you checked the exhaust manifold for cracks/leaks?

 

Chinochanginc:

- Fuel Filter is new, but the problem is too MUCH fuel, not too little.

- Gas cap just passed California SMOG check, also I'm not sure why it would be relevant.

- Physical Timing is correct

- I cannot 'hollow out' the Catalytic Converter, even if I could it would have no effect. Even if fuel was after-burning in the exhaust, it would continue to do so.

- Compression is near new per Honda specs, I ran a compression test a bit ago. This is the only item I'd consider related to the issue, but it has been checked already.

Telecaster:

- There are no exhaust leaks present anywhere in the system. I performed an inspection at the time I changed the O2 sensor.

Updates:

- New and old distributor caps were heavily different. The old cap terminals were severely worn, I will post comparison pics later. Despite the change problem still exists. (Though power has increased.)

- Removed Distributor and tested all electrical paths per the Honda BGB, everything tested perfectly.

- A TPA (Tail pipe analysis) was done, the car would have passed a smog check with flying colors. Excess fuel or not, it's managing to burn it all as HC levels were very low.

Of note: The distributor o-ring had been leaking some more recently, and after removing the distributor I found that the ECT sensor to the ECM was full of oil, and it is NOT a sealed connector. I completely cleaned everything including the terminals with electronic terminal cleaner, and used dielectric grease on the connector to keep contaminants out. There is an EXTREMELY remote chance it was causing a resistance increase or decrease in the ECT sensor, which could lead to artificial enrichment. I plan on testing it with a few gallons of gas before moving to replacing the computer.

I'm still open to any ideas, but frankly at this point it is looking very much like an Engine Computer.

 

Have you now replaced the plugs, wires, cap, and rotor? If so, now is the time to re-check the ignition timing with a timing gun.

Does the CEL work?

Any visible cracks in the exhaust manifold? Any possible leaks around the newly installed O2 sensor?

Have you resistance tested the ECT sensor? Do you have a high idle problem?

What does the temp gauge in the cluster read when the engine is fully warmed up?

Is the hood 7.5A Back UP fuse blown?

 

RonJ:

Have you now replaced the plugs, wires, cap, and rotor? If so, now is the time to re-check the ignition timing with a timing gun.

- Currently the cap, rotor and plugs have been changed. The wires measure within spec, with the longest coming in somewhere around 8.4ohms (25 maximum permissible)
Timing was set with a high end Snap-On Timing unit to 16 Degrees BTDC +-2 Degrees, stock timing.

Does the CEL work?

- Yes, but there are no codes of any kind being set.

Any visible cracks in the exhaust manifold? Any possible leaks around the newly installed O2 sensor?

- As I said earlier, there are no signs of any leak anywhere pre-cat or post. Tail pipe had become sooty, probable fuel burn in the exhaust system. Possibly fixed with the distributor tune up.

Have you resistance tested the ECT sensor? Do you have a high idle problem?

- I found the ECT Sensor (The one under the distributor) soaked in oil which struck me as a possible problem so it was properly cleaned and sealed with dielectric grease as that connector does not have an environmental seal. No idle problems at all.

What does the temp gauge in the cluster read when the engine is fully warmed up?

- Temperature is as it should be, typically the lowest 1/3rd of the gauge to a maximum of slightly over half. All elements of the cooling system with the exception of the heater core are brand new within the last year (new stock radiator, ALL new hoses, including air and coolant carrying hoses for the Honda's different sensors)

Is the hood 7.5A Back UP fuse blown?

- No, the 7.5 back up fuse was removed during some work yesterday, inspected, and is good. Also its function of dumping and reseting the ECM and Radio appear to be working as designed.

 

Old Cap Terminal Examples:

http://www.flickr.com/photos/30955309@N06/8383602262/http://www.flickr.com/photos/30955309@N06/8383602262/ by http://www.flickr.com/people/30955309@N06/, on Flickr

http://www.flickr.com/photos/30955309@N06/8382506505/http://www.flickr.com/photos/30955309@N06/8382506505/ by http://www.flickr.com/people/30955309@N06/, on Flickr

http://www.flickr.com/photos/30955309@N06/8382506405/http://www.flickr.com/photos/30955309@N06/8382506405/ by http://www.flickr.com/people/30955309@N06/, on Flickr

http://www.flickr.com/photos/30955309@N06/8383589370/http://www.flickr.com/photos/30955309@N06/8383589370/ by http://www.flickr.com/people/30955309@N06/, on Flickr

New Cap Terminal Example (Note the huge amount of material that was missing from the old one.)

http://www.flickr.com/photos/30955309@N06/8382519245/http://www.flickr.com/photos/30955309@N06/8382519245/ by http://www.flickr.com/people/30955309@N06/, on Flickr

Old Rotor Photos:

http://www.flickr.com/photos/30955309@N06/8382506215/http://www.flickr.com/photos/30955309@N06/8382506215/ by http://www.flickr.com/people/30955309@N06/, on Flickr

http://www.flickr.com/photos/30955309@N06/8383589184/http://www.flickr.com/photos/30955309@N06/8383589184/ by http://www.flickr.com/people/30955309@N06/, on Flickr

http://www.flickr.com/photos/30955309@N06/8383589242/http://www.flickr.com/photos/30955309@N06/8383589242/ by http://www.flickr.com/people/30955309@N06/, on Flickr

 

How old are the plug wires? Note that resistance testing would not tell you whether the wires arc spark into the engine bay.

Did you recheck/adjust the ignition timing AFTER all ignition parts were replaced. Was the service connector jumped?

Have you reset the ECU and run a full tank of gas?

In general, the temp gauge in the cluster should never rise above the halfway mark. Doing so suggests an overheating problem.

 

Also, my worse tank of gas has gone down to 167 miles for an entire 11.9 gallon tank. A massive 14.03 MPG!!

 

Do you have a locking gas cap

If your car is running fine you probably have a leaky fuel injector. Car runs fine etc.. Shut car off, fuel left in line bleeds off. If did a lot of short trips I could see it affecting your mileage a lot.

I would run your car on the freeway. Bring it back to your house, shut off car. Turn on (not start) to prime fuel pump, maybe do that ten times. Pull all your plugs or better yet disconnect your fuel pump, ignition and crank it and see if any fuel gushes out your spark plug holes.

 

RonJ:

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How old are the plug wires? Note that resistance testing would not tell you whether the wires arc spark into the engine bay.

- The wires appear to be the original wires, and their jacketing appears in excellent condition, though as you point out I cannot rule out spark energy being shorted to ground. I do doubt the wires are to blame as the car is putting out factory power level at speed, and the idles (both low & high )run extremely strong. A significant cross level would more than likely impact performance, if even momentarily (I would notice it).

Did you recheck/adjust the ignition timing AFTER all ignition parts were replaced.

- No, the timing has not been rechecked since the component replacements, though its place was marked and was re-aligned with the marks match afterward.

Have you reset the ECU and run a full tank of gas?

- I just reset the ECU last night and am currently running through a tank of gas, both to see if retained settings might have been to blame, or the input signal from the ECT.

In general, the temp gauge in the cluster should never rise above the halfway mark. Doing so suggests an overheating problem.

- When I say 'raises slightly above half', I am referring to an outside temperature scenario at or above 115F, with the air conditioner running at full blast (It's been as high as 126F ambient). A slight raise in temp from half in those conditions is fairly normal, and the cooling system quickly makes work of the extra heat whenever it gets an opportuity.

 

Hyyix,

I'm afraid it would take more than one small injector leak to reduce my mileage by half over the course of a whole tank. Though if *all* the injectors were leaking, that could cause the issue.

Thanks for the input though.

-Justin

 

My 2 cents:

Original spark wires? Seriously, just replace them. And why speculate about spark arcing. At night, in a dark place, open the hood and look for spark arcing from the wires.

Have you inspected the color of the new spark plugs?

After you replace the wires (hint), recheck/adjust the ignition timing. Be sure to jump the service connector during the procedure.

I live in a high heat and humidity environment. My Civic temp gauges have NEVER even reached the halfway mark. I think your slightly above halfway temp readings are abnormal.

 

RonJ... Good suggestions. But do you really believe one or two plug wires are going to manage to make a Civic go from 36-40mpg all the way down to 14? It doesn't seem feasable that that is the sole issue. Especially if NONE of them end up being bad.

- The original timing was done with the service connector shorted. As I said earlier, we found it had been set wrong during a SMOG test by a tech.

- The heat issue occurs on one, maybe two drives in the course of an entire year. I seriously doubt there is an issue with that. All cooling system components are new (Honda Dealer Parts), having been installed in the last year.

 

You tend to talk yourself out of ideas without good reasoning. You'll get to the bottom of your problem more quickly if you keep an open mind about suggestions given to you. For example, jbpnoman and hwyix presented some reasonable ideas that you seem to have just dismissed out of hand. Good luck.

 

I have read somewhere on the internet(since I have having this same problem)! The computer is sensing that something is wrong, and is dumping fuel to try to cure the problem. I have not done alot of research on this, I have a cracked exhaust manifold...so, with mine it starts there. I would research it, and try to see if it may be the computer that is causing the problem. All this could just be a bad computer, common issue on the Eg body's.

Sorry if this has already been suggested...thought I would try and throw it out there.

Also, even if the computer is doing this...it wont throw a CEL! just adding this in!

 

Ronj:

I am line mechanic, and have been in consultation with two ASE certified Master Technicians with more that 35 years experience each, so a great many things have already been tried.

- I know how to read my own spark plugs, I don't need to put up pictures of them unless everyone has a special interest in seeing them. (I will put them up later today, along with pictures of the rotor and cap, with comparison to the new as I have already prepared them).

- The 'Leaky Injector' theory is a good one, but it is one we have already investigated.

While it is a plausible theory, several items of evidence rule it out. The only thing I cannot rule out at this point is if ALL the injectors are leaky or otherwise have issues.
Regardless to its inclusion in THIS issue, I feel these are ready to be retired at $255K+ miles or professionally rebuilt and flow matched. I will do that. The real problem takes precidence over that. If a known good ECM fails to fix the problem, the next place I'd be headed was the junkyard.


Ej2guy28:

Out of all of the troubleshooting that has been done on the vehicle (and believe me, it's just about everything that has to do with the fuel and ignition systems), the failure of the distributor, the intermediate wiring between that & ECM, and the ECM itself have been the components that 'we' had narrowed it down to. I believe that you are correct and that it in fact is the ECM, as the 'no codes' despite issue was an important point for us as well. I hand measured everything in the distributor and it's healthy as ever. The only other thing that wouldn't generate codes would be leaky fuel injectors, and the chances of developing ONE injector that leaks SO severely without encountering a drivability issue is highly unlikely. By that same logic, it would be even more unlikely that I managed to aquire '4' leaky injectors at the same time (though as I said, both are POSSIBLE, just very UNPLAUSIBLE). As soon as I have the opportunity to measure the wiring between the ECM and the distributor, I will be swapping out the ECM.

Replacing the ECM is the Honda BGB Service Manual's suggestion in troubleshooting this stage of this issue.

I started this thread to see if anyone threw out anything I HADN'T THOUGHT OF. So far the only idea I hadn't considered was replacing the high-tension spark plug wires, since I had measured them per the service manual and they were all well within there resistance limits. NOW, that doesn't mean one or more of them AREN'T partially grounding out, causing a weaker spark and therefore a possible incomplete burn (thusly making the engine extremely inefficient in its job). I will as a result replace the wires.

Aside from that, nothing so far has come up that hasn't been considered. I continue to look forward to reading some possibly unconventional theories, or other scenarios you have not seen in this page (make sure they are relevant to the problem if you can before hand).

I will always respond, and if I indicate a negative response that only means that your scenario or suggestion of a part in question has already been tested and eliminated, not to put you down or disrespect you. Group brainstorming is important to us here.

Sometimes we run into some truly weird stuff, and all of us thinking about it definitely helps.

-Justin

 

jbpnoman also had a good idea about measuring the fuel pressure and testing the FPR. Was this ever done? You can probably rent a gauge at a local auto parts store.

You should also consider that the low gas mileage may not be caused by a single large problem but instead by a collection of small ones.