Honda DPFI vs MPFI...
 

OK, I have an '88 CRX DX with a D15B2 and DPFI. From a performance and modification standpoint, everybody seems to recommend upgrading to MPFI, but more than a few people have warned me that it will result in a net loss of fuel economy.

But if I'm not mistaken, the CRX HF was equipped with MPFI. So I'm wondering if the loss in FE that I've been warned about has just been a result of heavy right feet in the drivers in question. Does anybody here have any experience with the DPFI to MPFI swap? I'm especially interested in finding out what happens when driven judiciously and with FE in mind....

The conversion appears to be relatively cheap and easy. So my big issue would be whether it will help or hurt me in the FE dept. Any input will be helpful....

I would venture to believe that its the right foot of the driver... Way back when people used to tell me that cars with 4 bbl carbs were the worst on mileage... In my experience my vehicles with 4bbl carbs got better mileage than the ones with 2bbl carbs. It all has to do with the driver's right foot. Even as a teenager driving my 1980 Bonneville wagon with a big block V-8 and a 4bbl carb I used to average 16 MPG. That was with me driving the backroads @ 60 MPH, and not really caring about mileage because gas was under $1/gallon. It was so right on and regular I used that for my fuel gauge, because the one in the car did not work well. I used to write my mileage down when I got fuel. If I was wondering how much was left I would subtract my current mileage from the one written down, and divide by 16. That gave me my fuel used. I'm sure I could have hypermiled that car at least to the low 20's in mixed driving.

Sounds like we have similar driving styles....

Anyway, I kind of figured it was mainly the driving style of the drivers in question (they were looking for more power after all), but since the swap includes a whole new ECU, I figured that there might be some other stuff going on like more aggressive spark curves or richer mixtures....

Oddly enough, my reason for considering the swap is that I might eventually turbocharge the car just to prove/disprove the theory that turbocharged engines are better on fuel under low load/cruise situations.... The stock DPFI just isn't up to the task from what I've heard.

If ANYTHING causes your mileage to drop by going MPFI, it is going to be the ECU. Remember that the PM6 ECU was mapped for a higher performance AND larger displacement engine. So if nothing else, it might waste fuel by dumping 1.6 liter's worth of fuel into a 1.5 liter engine. You might be able to correct for this with an adjustable fuel pressure regulator. Also, it is possible to rechip OBD0 (and OBD1) ECUs and reprogram them on a dyno based on what you are looking for from the engine.

A word of warning about turbos, though. Honda D-series engines are pretty weak internally. And in stock form, they don't stand up too well to turbocharging. Some people don't care about this, since D15 engines can be gotten either super cheap or free if you blow up a bottom end. But if you expect the engine to last, turbocharging on stock internals is not the best idea.

words of wisedom. although i recommend against turning down fuel pressure.... im sure there are penty of ways to rechip to run a decently tuned mpfi setup.

HEARSAY!!!!!!!!! Nothing replaces proper tuning. Unfortunately too many don't understand this and take the term "Bolt-on Turbocharger" too literally.

Have you ever heard about the Epic-Tuning Hatch? Their goal was to take a Stock D Series to it's power limits. Their goal wasn't to blow it up (I can do that). Their goal revolved around reliability. Countless passes down the track and all that happened was warped rods! When something blows up that means improper tuning. When rods warp how they did that's reaching it's power limits.
375 WHP Stock D-Series

Now that they are done with that goal check out what else they got up their sleeve! INSANE!
AWD D-Series Civic

Hmm... I thought that there were other 1.5L D series engines out there with MPFI. I wouldn't swap the FI from a 1.6 to a 1.5L engine anyway. Different displacement engines would definitely have different needs in terms of fuel and spark and its unlikely that the 1.5L would run efficiently unless the donor engine was nearly identical. I'm still looking for the easy improvements and don't need to deal with transporting the car 150 miles to the nearest dyno shop for tuning at this stage in the game.

Yeah, I'm aware of the toothpick size rods that the D series engines have. Not to worry though. Since I'm not going for performance I'm talking about a very low boost setup (maybe 5 psi max.. if that). And with my driving style, I wouldn't expect any real problems. Owning the car for a month now, I've floored the accelerator precisely 1 time (to confirm that the engine was working properly). Aside from that, I have a very light touch with the throttle. As I understand it, the FE gains that a turbo can produce are all at very low throttle settings anyway, so driving the car like my grandma would tend to keep the internal stresses low even in the face of a little bit of boost. If I drove like Mario Andretti I'd be worried about durability, but I'm pretty confident about this plan.

I'm running the DPFI and have no complaints from a FE perspective. Even looking on the EPA website my DPFI Civic has better FE than the other 4th gen MPFI Civics.

On top of this I'm running the STD Civic which has tamed down cam lobes compared to the other civics so. Therefore keep this in mind when comparing that to your DX.

If I were you I wouldn't bother converting to MPFI until you're going Forced Induction unless you want the practice of working on your car. Otherwise you're going to be wasting money on injectors, and an ECU you'll need to replace when you go FI.

The 1988-1991 HF and 1992-1995 DX have non-VTEC motors with MPFI. The 1988-1991 HF ECU will drop right in. But it will not have proper fuel maps for a DX motor with SI MPFI. Also, you will have to use an EGR valve, since it looks for one. This means you will be stuck using the HF intake manifold, which is not the best idea, either. The 1992-1995 DX ECU would actually be the best choice. BUT, it is an OBDI ECU. Not that converting to OBDI is hard. And OBDI WILL get better MPG than OBD0. However, I know that ALOT of people would rather not do this. Also, I have never tried this. But you might have problems bolting the 1992-1995 distributer (which MUCH be used with an OBDI ECU) to the 1988-1991 head. This problem might be best solved by upgrading to a 1992-1995 DX head (which you can get for a song or free these days).

One of the problems with 'proper tuning' is that you are running with a razor-thin margin of error. ANYTHING that might happen to disrupt this could throw your tuning off enough to cause problems. Also, reliabilty may be better with a lightly turbocharged engine that is properly tuned. BUT, don't expect it to be stock-reliable. The way I see it, a boosted D should NEVER be your sole vehicle.

Wow, the opinions are all over the place on this one! Thanks for all the input guys.

Storminmatt, I'm still a relative newbie to Hondas. Can you maybe give me a quick description of the differences between the 88-91 and 92-95 models? Learning what's compatible and what's totally different will help me out a lot I think.