Vehicle: 1990/Honda/CRX HF
Engine: 1.5 Liter I4
Injection: Factory Honda PGM-FI port injection hardware
Description: Also plan on using MS to control ignition timing; the ultimate goal is awesome fuel economy
This statement is a work in progress, I'm not quite finished with it.
Well, this is my first MegaSquirt project. I am hoping that it goes smoothly; I figure the best way to ensure this is to approach the conversion methodically and in as organized of a manner as possible. My victim is a 1990 Honda Civic CRX HF. This is not a â€œfast and furiousâ€ project, more of a â€œslow and benignâ€ one. The goal is to finish with a daily driver that gets excellent fuel economy (I have a 140 mile daily commute, racking up way too many miles on my â€™05 Outback XT) while being reliable and eventually being a bit peppier than the HF currently is. First some basics about the car:
Curb weight: 1967 lbs
Engine: D15B6 8-valve SOHC 1.5 liter inline-4 cylinder (1493 cc)
Honda PGM-FI multi-port fuel injection
9.6:1 CR, redline 6,800 rpm
Horsepower: 70 hp@4500 rpm
Torque: 90 ft-lbs@2000 rpm
Transmission: L3 5-speed manual, 2.95 final drive ratio
Fuel Economy: 49 mpg city / 52 mpg highway
Tires P165/70 R13
Honda thoughtfully supplied the factory service manual free for download at http://www.honda.co.uk/owner/CRXManual/. Unfortunately the manual is not the exactly right one; it is for the UK version, powered by a SOHC 1.6 liter (our 1988-1991 Si motor) or DOHC 1.6 liter (the â€œZCâ€ motor), with the DOHC Vtech 1.6 liter (B16) covered in a supplement. Despite this, the manual has been very helpful; I wish more companies would do this for their older vehicles, since most of them wonâ€™t be serviced at the dealer after a certain age anyway. Not to mention it would be counter-productive to train your employees how to tune carbs and early EFI anyway; the current generation of mechanics is more comfortable with OBD than anything, why distract them from their primary focus? But I digressâ€¦
I have prepared an Excel spreadsheet detailing Honda to MegaSquirt interface; here is an excerpt. The format is as follows:
Honda designation, Honda CPU Pin #, wire color, MS designation, MS Pin #, MS relay board Pin #
Injector 1, A1, NA, Inj #1/2, 32/33 or 34/35, Â½ or Â¾
Injector 2, A3, NA, Inj #1/2, 32/33 or 34/35, Â½ or Â¾
Injector 3, A5, NA, Inj #1/2, 32/33 or 34/35, Â½ or Â¾
Injector 4, A7, NA, Inj #1/2, 32/33 or 34/35, Â½ or Â¾
MAP Sensor, C14, GRN/WHT, MAP
MAP Sensor, C11, WHT
MAP Sensor, C15, YEL/RED
Throttle Angle Sensor, C13, YEL/WHT, TPS, 22, 13
Throttle Angle Sensor, C7, RED/BLU, TPS, 22, 13
Throttle Angle Sensor, C12, ground
TW Sensor, C6, GRN/WHT, CLT, 18, 21
TA Sensor, C5, UNKNOWN, IAT, 16, 20
Tachometer Output, N/A, BLU, Coil/Tach, 15, 24
Oxygen Sensor, C16, WHT, O2, 23, 20
Fast Idle (EACV), A11/A17, BLU/YEL, Fidle, N/A, 6
Fuel Pump Relay, UNKNOWN, YEL/BLK, Fuel Relay, N/A, 5
This is not quite complete, there are a few items I need to clarify before I start slashing wires. The Honda TPS output is apparently through the â€œcenter wireâ€, the RED/BLU one that goes to C7 on the Honda ECU. It is apparently possible to get an engine speed signal through the tachometer by splicing into the tachometer output and placing a 10K resistor inline to the MS (to prevent excessive MS draw from robbing the tachometer of adequate signal to function properly). However, I plan on using the MS to control ignition as well as fuel, so I will probably need a higher resolution signal than the tachometer can provide. Honda uses 3 VR sensors to determine engine position (I have more on this at home, but do not have the source here), separate sensors for TDC, crank position, and cylinder position. All 3 of these feed into the ECU, which then spits out the correct output for ignition timing and tachometer output; if any one is missing the ECU will throw a â€œcheck engineâ€ code. I think I will need to tap into one of these to get a signal; I am not yet certain which one or how I am going to do it. The only other problems are fast idle and the fuel pump relay; at this point I think I will leave control of this up to the Honda ECU, as well as control over the A/C clutch and other engine functions.
As can be seen from the hp / torque ratings, and is confirmed by driving it, the HF makes decent power at low rpm and rapidly drops off, running out of breath at a relatively low rpm for a 4-cylinder (most Honda engines make peak torque higher than the HFâ€™s peak horsepower). There is not much that can be done about this while retaining the key virtues I am building the car for- any changes in cams, head design (DOHC, 16-valve SOHC) or fuel injector size will hurt fuel economy. Perhaps not much, but I am aiming for mpg above all else, not hp. One possibility, which I will explore further down the line, is adding a small turbo to help high-rpm breathing. I intend to use boost-dependant water injection instead of an intercooler; the engine will not spend a lot of time at high-rpm and load, so heat should not be that much of a problem. The main reason for water injection instead of intercooling is the weight-savings, as long as water volume is kept to a few liters. As long as the turbo is sized appropriately, boost should be minimal at cruising rpms.
The super-high gearing in combination with the two overdrive gears results in a remarkably low rpm at highway speeds; in fifth gear at 60 mph the engine is revving at only ~1900 rpm, at 75 mph ~2300 rpm. A correctly sized turbo could be picked to build boost at higher rpm; a problem with my Outback that I think could be remedied here. The drivability cost would be tolerable; in-gear acceleration in the HF will be leisurely at best, but a downshift to fourth or even third gear should result in tolerable pick-up. Cruising at 60 mph in 4th gear occurs at ~2200 rpm, 75 mph is ~2800 rpm; in 3rd gear 60 is ~2800 rpm, 75 mph is ~3500 rpm. Based on these number, a turbo should be sized to start building boost at ~2500 rpm and preferably be at full pressure by ~3000-3500 rpm. Regarding full pressure- well, the compression ratio is quite low, but I would like to retain the ability to use regular fuel (87 octane), and the lack of an intercooler will lead to higher intake temperatures. Not to mention the HFâ€™s injectors are definitely on the small side, limiting the capacity to compensate by richening the mixture. There are three options I can think of right off to remedy this; replace the HFâ€™s injectors with those from an Si (106 hp, more than enough for my power goals), which may hurt fuel economy; replace the intake tract with the intake manifold from a CRX DX, which used a throttle-body injection, and adding the HF injectors in the port position (some fabrication required and heavy, but get a larger throttle body as well as better water distribution); or adding a second set of injectors. I believe the Si injectors are the best option, but I will explore that more in the future.
I still think I'm going to be using the HF as the first project vehicle, but a recent acquisition is giving me second thoughts... I should know better than to skim the "budget wheels" section in the paper by now. Looking through the Grand Rapids Press, and there it was: 1988 Mazda 323 GTX, 87,000 miles, 4wd turbo, garaged since 1998, $1000... Well, this being Michigan, I expected it to be a rust bucket, and sent my brother to check it out (I was flying to Baltimore, so couldn't do it myself). Body is in great shape, little tiny bit of rust in the traditional '80s Japanese car spots (over rear wheel arches, rocker panels, etc), interior was MINT, no rips, not faded at all, dash wasn't cracked. *sigh*. So, what else could I do? I mailed a check to my brother, he picked it up the next day. My family now have one of the most complete late-80s / early-90s Japanese performance econobox collections I know; the GTX, an '89 CRX Si, a '91 Sentra SE-R, 2 Subaru XT turbos (engine donors for my brother's '84 BRAT), the '91 CRX HF (ok, a different kind of performance there). And we plan on acquiring a Mazda RX-7 or RX-7 Turbo II as a donor for the '69 Opel GT, plus we have a '91 Civic hatch in need of an engine, and the '91 323 hatch that has shown itself to be well-nigh indestructible, and one of our friends offered us a Celica-platformed Supra with the non-turbo 5MGE engine for free... Now all we need is time to do the work. Thank goodness our primary vehicles don't require constant maintance!
Of course, I'm once again contemplating using the Nissan SE-R instead of the CRX HF, mainly because the car itself needs less work. If I could find a factory service manual for a reasonable price, I would definitely do the SE-R, but they're all ridiculously expensive, and no one at Nissan has seen fit to provide one online. So I'll probably go with the CRX; guess I'll have to figure that out before transport one of the vehicles the 300 miles from home to here.
1/11/06- Well, ask and ye shall receive. I was able to find a pdf of the Sentra FSM, so it looks like the CRX is going to be #2 on the MS hit list. That'll give me more time to learn on the SE-R, which has a more durable- and performance oriented- engine anyways. Also should give me a chance to implement the WBO2 sensor versus the existing NB.