spitfiremk2497

Hello

I recently bought a 98 civic hx m/t. I love it, its a great car. I get 48 mpg!

Ever since I bought the car, when I am crusing at a constant speed, I can feel the motor lose or gain power intermittently. I can hold the throttle steady, and the engine may suddenly either gain or lose what feels like aprox 30 horse power. I notice it most during hill climbing, for example I can be driving up an incline and the engine just feels a tad sluggish so I feed it a bit more throttle and I get a disproportionally strong power response from the motor compared to the amount of throttle increase I gave it.

Perhaps a totally unrelated issue, a check engine light came on shortly after I got the car. The code read P116X (either 2 or 3) and it says the 02 sensor is responding slowly. Yet when I read the numbers, the 02 is responding at normal ranges and does not appear to be malfunctioning.

I believe the owner before me really babied the car and there was a lot of carbon buildup in the motor. So I ran seafoam through the fuel system and the engine light turned off by itself without me clearing it. I figured the 02 sensor was just gunked up from the buildup and I was cleaning it out.

BUT the engine light has returned, and I found a scary looking TSB for my car related to this issue:



Here is someone with perhaps a similar issue : http://www.hondacivicforum.com...70307

I was poking around on the internet and came across this thread:
http://www.cleanmpg.com/forums...age=2

And I have confirmed that I have a L31 ECM.

So here is my question- is the L31 ECM the one that is notoriously bad, and does this ECM trouble with the 98-00 civic hx m/t have anything to do with the drivability issue I explained above with the intermittent power loss? Or is what I am experiencing the "lean burn mode?"

Thanks!!!


Modified by spitfiremk2497 at 3:10 PM 11/2/2008

spitfiremk2497

Bump.

I would greatly appreciate the help. Thanks.

Spool This

try reseting ecm or try new o2 if nothing, then replace.

j_polk2008

I think my computer is bad too it does the same thing but i have no check engine light on.

Relic1

lean burn mode exit will feel like a power lull when you press on the throttle after cruising for a little bit. What you described sounds a lot like what I felt with my VX, but not while cruising steady throttle.

the L31 is specific to the 98 HX, it's also cali-spec for emissions... which may mean that lean burn was disabled. (It does for sure on the VX, not sure on the HX)

List of P2N's
A21 = 96 49-state
A22 = 97 49-state
A31 = 98 49-state
A32 = 99-00 49-state (replaced by the A33)
A33 = 99-00 49-state
A61 = 98 49-state CVT
L21 = 96 cali-spec
L22 = 97 cali-spec
L31 = 98 cali-spec
L32 = 99-00 49-state (replaced by the L33)
L33 = 99-00 cali-spec
L61 = 98 cali-spec CVT

IMO, I'd swap the out just to be sure. (P2Ns are cheaper than the O2)
If the problem persists drop in a new O2 sensor.


NOTE: since your L31 uses the same 36531-P2M-A01 O2 as the 49-state version the ECU should be directly swapable between the cali-spec HX and the 49-state spec. This may help you get better mileage.
I'm not sure how picky Cali emissions is, I'd think as long as the first three digit numbers are correct they'd not care if you swap them. (P2N)

ABK

usually when they come out with a TSB it usually the problem. At dealerships we always start with TSBs because it's a known problem. HX uses a wideband o2 right? If so that would be one expensive o2 sensor.

You can mostlikely find that ecu on honda-tech for like $40 because no one has use for it.

spitfiremk2497

Thanks for all of the input everyone!!

The thread I lined above, this one :

http://www.cleanmpg.com/forums...age=2

Some guy wanted to buy a lean burn car, and one guy claims that ALL hx's from these years are lean burn.

The TSB shows that a L31 ecm should be replaced with a 405?

http://www.hondapartsnow.com/d....html

So what is a 405 ecm? is it a L33? or what?


Modified by spitfiremk2497 at 12:05 AM 11/4/2008

spitfiremk2497

Also, I was looking at whole sale prices for 02 sensors, one is under 100 bucks and the other is like 250 or something.

AND, today my check engine like mysteriously turned off. I have made no changes to ANYTHING.


Modified by spitfiremk2497 at 7:24 PM 11/3/2008

Relic1

most people either don't know about, or forget about the cali-spec versions.

the parts system shows the 405 and 406 but doesn't list it as matching with any models. Maybe because it's a replacement not an original equipment item.

spitfiremk2497

That is what I am afraid of. I am hoping this "405" ecm has a oem equivalent. Otherwise its going to be $650....................................

spitfiremk2497

So I just got off the phone with a local dealer.

We looked over the TSB together and my question to them, was if this 405 is a naturally occurring ecm in a different car. They looked it over and found that it is actually a replacement ecm that you can't find in a different honda. So online it costs 650 bucks, their price was 915 something plus 130 bucks of labor to plug it in!! What a joke! haha.

Well this sucks.

Either I decide to live with the check engine light coming on and off, or I can fork over 650 bucks that I don't have... or is it possible that not ALL L31 ECM's have this problem?

What are the chances that I can find a used L31 that won't have this issue?

And if I just leave it alone, do you think this is helping or hurting the fuel economy in my car? Or more importantly, is it safe to continue to drive the car like this for the long term?

Thanks for all of your help, people.

Relic1

pick up a L22 or L21, they will plug right in.
Or you can go with a A31, A22 or A21 if you want to drop the cali-emissions part of the ECU. It will likely give you better mileage but I'm not sure what the test station will say about it. Maybe nothing, maybe something...

Used P2Ns are in the $50 or less rage.

here's a L31 for sale... https://honda-tech.com/zerothread?id=2388852

spitfiremk2497

It may be better to stick with the L models so I can stay closer to being smog legal?

The L22 or L21? Both of these will work with no changes or issues?

Relic1

yes, all though they are an older ECU, Cali emissions doesn't like older engines in newer cars.... not sure how picky they actually are.

Wish someone that knows the cali-inspection process would chime in.


NOTE: with the A series ECUs you should get better mileage.
It may even be worth it to pick up an A series and drive it daily, then drop in the L31 for a few days before testing.