97 Civic EX to HX conversion
 

I'm going to convert my wife's EX with D16Y8 to a lean-burn D16Y5, and thought someone might eventually find this helpful. I do have pictures, and will include them in this thread as I get it going.

Here is the background (non-technical, skip if you'd like):

Both my wife and I have owned Civic EX's for a few years. Mine returned around 38 mpg and hers around 35 mpg, on fuel with ethanol. When mine was wrecked, I went on the hunt for an HX for myself. I've been getting fuel mileage in the 44-47 mpg range consistenly, with no drafting, P&G, etc. This helps out with fuel bills a lot, and we started talking about buying her an HX as well, while their prices are down a little. But she likes her EX's sunroof, and I like it's larger front brake system and the fact that we know it's service history, and we decided to swap out what was necessary to convert her EX to an HX, fuel-efficiency wise.

There are several notable differences between the two cars, and I have also run across a lot of untrue and/or conflicting info while learning about these HX models. So I hope to, in one thread, provide a very complete (and hopefully 100% accurate) guide to what an HX is and isn't, and the hows and whys to an HX conversion from a different model of Civic.

There are also several things I DON'T intend to do in this thread:

1. I do NOT intend to give mileage advice, as I'm only getting average fuel mileage from my HX, and have the same expectations from the conversion which I'll be detailing here. So you'll need to look elsewhere for driving advice.

2. I do NOT intend to explain VTEC-E in detail, as there are several excellent write-ups already here on gassavers.

3. I do NOT intend to get into beyond-stock modifications. I plan to use stock Honda parts and quality-name aftermarket parts where applicable.

I'm just your average Joe (literally, that's my name), who has some mechanical experience in his past. It also helps that I have a complete factory HX already here to go by, and that I have a shop with an auto lift in it. There are several still-unanswered questions I have, which I'll ask as I go along in this thread.

As much as I remember, I'll also detail expenses. At the end, we'll figure out how many miles it'll take to pay back the conversion at current fuel prices.

I hope this thread will be a help to the forum.

Re: 97 Civic EX to HX conversion
 

Here is some pertinent info I've gathered. I realize some is common knowledge, so just skip over it if you already know it.

1. The HX uses a wideband oxygen sensor, with 5 wires instead of 4. The sensor itself is an NTK L1H1, Honda part number 36531-P2M-A01. This part number is good for HX's from 96-00, Federal or CA emissions.

2. The HX uses an EGR Valve, Honda part number 18011-P2M-305. This number is good from 96-00, Federal or CA emissions. You will read elsewhere that CA emissions HX cars do not have an EGR valve. THIS IS FALSE.

3. The HX uses the same throttle body, idle air control valve, VTEC solenoid, and bare head as the EX models. You will read elsewhere that some or all of these items are HX specific. THIS IS FALSE.

4. The HX's engine wiring harness is unique, and breaks down to (3) Honda part numbers as follows: 1996-97 use 32110-P2N-A01. 1998 uses 32110-P2N-A02. 1999-2000 use 32110-P2M-A00. The engine harness part number is the same whether you have CA or Federal emissions. Because the EGR valve and oxygen sensor use the same part numbers across all years of HX's, I've taken a chance and bought a used harness off a 2000 HX, even though the car it's going in is a 97 and so is the D16Y5 engine I've found. If I find it's not plug and play, at least I'll have the proper connectors to add these into my EX harness.

5. ECU (PCM, computer, "brain box"). All HX's use OBD2 programming. Around 1999, Honda switched most Civics from OBD2A connectors to OBD2B connectors at the ECU. However, all info I can find from informed sources says that the 96-2000 HX remained OBD2A, and did not make the switch to OBD2B with the rest of the Civics. Here are the Honda ECU part numbers for 5-speed manual transmission HX's, ordered by year and emissions level:

1996: Federal - 37820-P2N-A21. CA - 37820-P2N-L21.
1997: Federal - 37820-P2N-A22. CA - 37820-P2N-L22.
1998: Federal - 37820-P2N-A31. CA - 37820-P2N-L31.
1999: Federal - 37820-P2N-A32. CA - 37820-P2N-L32.
2000: Federal - 37820-P2N-A33. CA - 37820-P2N-L33.

NOTE: I ran across online rumors that the A32 had problems and was frequently replaced under warranty with the A33. I have no firsthand experience to back this up.

6. Transmission: The HX transmission had a higher, numerically lower final drive ratio compared to the EX, somewhere between 10 and 20 percent. It shared the "B000" casting number with the EX transmission, as opposed to the "A000" casting number on other Civic D-series transmissions. The "B000" casting is said to have larger bearings inside. As far as I know the only way to positively identify an HX trans from an EX is to physically count input and output shaft rotations.

7. The HX had 14" alloy wheels with 8 spokes with a 4x100mm bolt pattern. Stock tire size was 185/65R14, the same as other Civics of the time. These wheels were made for Honda by Enkei and were extremely lightweight, even by today's standards. They use a ball/radius seat lug nut (12 x 1.50mm thread pitch), Honda part number 90304-SA5-013. Do NOT attempt to use conical-seat lug nuts on these wheels, as they will loosen and come off. Ball/radius seat lug nuts are available much cheaper on ebay under the Gorilla brand, part number 38038.

8. Brakes - The HX shared the smaller brakes of the DX, etc. HX wheels won't clear EX brake caliper mounting brackets without the use of either a spacer and extended lugs (bad move in my opinion) or grinding down the caliper mounting brackets. As I found a set of HX wheels with new tires for $300, a deal I couldn't resist, I will be detailing the grinding of the brackets when the time comes.

Some other info I hope will be helpful:

A. If you're looking for Honda part numbers for purchasing or to verify compatibility, look on https://www.hondapartsdeals.com/honda_parts.php. They have the factory parts diagrams and part numbers.

B. A couple of HX VIN numbers I've run across, for reference:

1. 1HGEJ7129VL015731 - 97 HX 5-speed, unknown emissions.
2. 1HGEJ7127YL072403 - 00 HX 5-speed, CA emissions.

I'll move into the parts I've accumulated and plans I have soon (probably tomorrow). -Joe

Re: 97 Civic EX to HX conversion
 

ADDITIONAL HX parts:

9. Intake manifold, to mount the EGR valve.

10. Head parts, including cams, roller rockers, etc.

11. The HX exhaust manifold is the same as the DX, CX, and LX. The EX's manifold is different, and mounts the oxygen sensor and catalytic converter further from the engine.

I chose to buy a complete non-running D16Y5 so I could get all of these parts at one time, and complete. The engine cost me $150, but didn't come with an exhaust manifold. It was a Craigslist find.

Re: 97 Civic EX to HX conversion
 

I own a 97 hx 5sp 373,500 so far ,i changed my header to an ex header and ex cat and it works fine,also changed main dash wire harness to put factory cruise control into my car.works good. I get 30% discount on honda parts at majestic honda .Iknow my hx really good. mike

Re: 97 Civic EX to HX conversion
 

Mike, did you notice a change in fuel mileage or lean-burn when you did this? What fuel mileage averages are you getting? I assume you made an extension for the O2 sensor harness?

I've thought of leaving the EX exhaust manifold and cat on it, but I'm not sure how it will affect lean-burn operation. If you're having good results, I may just leave it on and give it a try. I figure if I need an HX-style manifold I can probably swap a ricer even for my EX system.

Re: 97 Civic EX to HX conversion
 

Sorry, I see the 51 mpg under your name so disregard answering the mpg question. But I would still be interested to know how the EX exhaust swap affected your car.

Re: 97 Civic EX to HX conversion
 

The header i used is powercore header stainless,and a hi flow cat,and yes i had to extend the secondary 02 wires,works great no problem no check eng. light or codes. I will tell you the primary o2 is not cheap for the hx,iv'e replaced it once so far,another thing is the egr system the cover under the fuel rail gives acces to the egr ports on the intake they tend to plug up with carbon and will affect gas milage. I clean mine every 100k.I only fill up with non ethenol 87oct car does not like that crap gas milage drops to like an ex,i run full syn oil eng and transm. I still have the original clutch and radiator. Ex has abs you should be able to keep that and the gage cluster.
Mike

Re: 97 Civic EX to HX conversion
 

Sounds like I need to check the EGR passages in my HX - 190k miles. I'll clean the ones out on this donor engine for the EX also. I run non-ethanol gas and syn eng oil as well. Our 97 EX doesn't have ABS, just the larger front brakes. I need to take some time and figure out how to upload pics to this site so I can get into the meat of this thread.

Re: 97 Civic EX to HX conversion
 

Further HX transmission information:

An HX 5-speed trans can also be identified by the partial VIN tag riveted to the front face of the transmission. If you have already located the "B000" casting number, you know you have a trans from an EX or an HX. You'll see either an "EJ7" or "EJ8" as the beginning 3 characters in the partial VIN number on the tag. The EJ8 means it came out of an EX and has the less-fuel-efficient final drive ratios. The EJ7 was the Civic HX. Note: If you add a "1HG" to the beginning of the partial VIN, you have the complete VIN of the donor Civic.

Re: 97 Civic EX to HX conversion
 

Here are some pics to illustrate EX/HX differences.

1. The EX (D16Y8) engine compartment.

https://www.fuelly.com/attachments/fo...db916a1e58.jpg

2. The HX (D16Y5) engine compartment.

https://www.fuelly.com/attachments/fo...869ce6e3e2.jpg

3. The used D16Y5 I bought for a donor engine.

https://www.fuelly.com/attachments/fo...a91dc2a2cf.jpg

4. The D16Y5 intake manifold with EGR valve (the canister at the left end)

https://www.fuelly.com/attachments/fo...8914d2cb20.jpg

5. The EX (D16Y8) exhaust manifold, also showing primary oxygen sensor location. Yes, I know the valve cover gasket's leaking. :)

https://www.fuelly.com/attachments/fo...2db3890557.jpg

6. The HX/DX/CX/LX exhaust manifold.

https://www.fuelly.com/attachments/fo...83487db634.jpg

7. The location of the riveted-on VIN tag on the transmission. The entire VIN will be on it, but the first 3 digits aren't stamped so can be missing if it's been painted. The plate is at an angle above the clutch slave cylinder.

https://www.fuelly.com/attachments/fo...1e7f24fd46.jpg

Well, that's all the business I have for this thread for now, until I've gathered up more parts.

Re: 97 Civic EX to HX conversion
 

A few more parts gathered:

1. An ECU from a 97 HX Fed emissions 5-spd:

https://www.fuelly.com/attachments/fo...3c0c59f714.jpg

2. The '97 ECU with an engine wiring harness from a '00 HX CA emissions 5-spd:

https://www.fuelly.com/attachments/fo...2241469038.jpg

3. A set of final drive gears, 3.722 ratio (18T on countershaft, 67T on ring gear):

https://www.fuelly.com/attachments/fo...e63b5f5a7b.jpg

4. A pic of where this will be taking place, once I find the rest of the parts.

https://www.fuelly.com/attachments/fo...a2d28ec92c.jpg

Re: 97 Civic EX to HX conversion
 

ECU won't work with that harness (96-98 OBD2A, 99-00 OBD2B) they don't use the same plugs, am I right?

Re: 97 Civic EX to HX conversion
 

Yes, if we were talking about any other Civic from 96-00 you'd be right.

But the HX didn't switch to OBD2b like all the rest - it stayed OBD2a right through 2000. You can find verification of this at other Honda sites with a search. And yes, the wiring harness plugs into the ECU perfectly - already checked that out for just in case.

More updates to come - HX wheels are installed, but waiting on a clutch before doing the tranny teardown and regearing, and waiting on some final bits for the engine before going ahead with that.

Re: 97 Civic EX to HX conversion
 

Great info, jbi. But I'm wondering if a D15 would make more sense. Parts are more readily available and cheaper. I had a 97 HX, which was great. The O2 sensor went out, which cost me $350 at Honda (with a friend discount). Ouch! The exhaust mani cracked as well.

I was getting 46 MPG (mostly all freeway, as I have a 100 mile commute) with no hypermiling stunts. Right now, in my 97 EX, I'm at 37MPG. With a D15, I'm willing to bet I'd be in the low 40's. If you figure in the lower maintenance cost, that would be the way to go, IMO.

Good luck with your swap. I love these Civics and would get another 96-00 Civic if this one gives up the ghost. But only at 190k miles right now.

Re: 97 Civic EX to HX conversion
 

Also should add, with an HX 5-sp transmission, it would close the gap even more. It'd be intereting to see how they would actually compare...

Re: 97 Civic EX to HX conversion
 

Sorry, I don't know if I am able to edit my posts, but can't seem to figure it out.

Digging through my old spreadsheets, it looks like I was getting about 50MPG on the HX, not 46 as I stated above.

Re: 97 Civic EX to HX conversion
 

Sorry for the long time period between posts, but things here have changed. My wife decided she wanted a newer vehicle, so I put the swap on hold after gathering almost all of the necessary parts. The only things left that I need are new parts that go along with the install - clutch, timing belt, etc.

So now I'm left with these parts, and I'm either going to keep them as spares for my HX, or sell them as a lot if anyone is interested. I'm really bummed, as I'd looked forward to this project.

If anyone is interested in buying these parts as a lot, you can post here or PM me. I will be advertising them locally as a lot as well. Sorry, I'm not interested in breaking them up and selling them individually.

If there is real interest, I'll list the contents of the lot and come up with a price. Thanks! -Joe

Re: 97 Civic EX to HX conversion
 

If you need, this might help you. I made it the other day for a friend who is putting a VX in a CRX.

https://eastcoasthondas.com/pictures/ntk-l1h1-pinout.jpg