For stock, street driven cars, the factory D-Jet is pretty well-regarded as a proven system to get smooth operation and good gas mileage for the regular driver. So why dump it? Primarily because of concerns about how a new MPS is $1K and how the advances in aftermarket PEFI are so 'inexpensive' and use modern technology and are ‘better’.
For tinkerers, those with non-stock engines, turbos, etc, PEFI is great and is a great option, but for most of us with stock 914 engines, D-Jet works great.
I have been thinking about this for awhile and wanted to post this for your $9.14 opinions. D-Jet is a fuel-only system, so lets not even discuss any system that does more than D-Jet…no turbos, no ignition control, yada yada. The rhetorical topic is ‘Whats the minimum we need to simply and reliably replace D-Jet when it no longer becomes a viable system?’. I think that D-Jet will only become non-viable when the major parts either become unavailable or when they become more expensive to replace than a replacement EFI system would cost to install. We are not at that point in time yet.
We don’t need to consider costs of the induction manifolds, AAR, throttle body, filter housing, fuel pump, FP regulator, relays, vacuum hoses, gaskets, fuel injectors, TS1 and TS2 sensors, fuel hoses, fuel filters…We are comparing basic D-Jet to some other system and these would be needed with any FI system, do not wear out or are regular maintenance or consumable items.
1. If your D-Jet is functioning well, you have no reason for concern. Enjoy it as long as it lasts.
2. If your D-Jet needs replacement main parts, then here is the magnitude of your potential worries as of today. By simply replacing some or all of these parts, your D-Jet needs no tuning. It is Plug N Play and reliable. These parts are all available:
$200 Rebuilt MPS
$140 New TPS
$140 New Trigger points
$340 New FI harness (less to repair yours if it is repairable)
$820 Total for all the big expensive main parts and chances are you wouldn’t need all these at any one time. Even if you do, for a $1000 you could reinstall that box of removed FI D-Jet parts back on your engine, with all new main parts and hoses, yada yada, have a stock system and be driving today. No tuning. Increase or maintain your 914s resale value with the stock D-Jet.
3. So then I recently looked at SDS which is perhaps the least costly PEFI on the market from a reputable manufacturer. Warranty, tech help, replacement parts, relatively easy to install and program. Other systems from Haltech, Link, etc, are similar, or more sophisticated, cost more and maybe more than needed for a stock engine. SDS is just the baseline example I have used for comparison. The SDS EM-4D is a fuel only, programmable EFI, basically a suitable aftermarket replacement to D-Jet, but you have to program it to your engines specific needs. I like the non-laptop programming add-on box because 10 years from now when you or the next owner needs to reprogram it, you won’t have to worry about that old laptop working. The harnesses it comes with are basic but functional, so add casing and rubber boots at each component for a durable install. This system could be installed to be very stealthy for those wanting a very original looking engine bay.
$850 EM-4D system
$150 TPS and MAP sensors
$150 Shrink tube casing/rubber boots for harness, misc items
$350 LM-1 or equivalent cost for dyno time
So SDS installed and tuned is at least $1500. out of pocket including your full hourly rate of $0 per hour for R&D, adapter bracket fabrication and labor. You will probably need a few days time at least to make it work.
4. MegaSquirt is maybe the most inexpensive system to buy, but fully installed, with dyno or LM-1 tuning costs, with a decent harness, and not including your labor to make it all happen, MS must still be around a Grand. And that for an 'experimental' system with no warranty, and no one to service it if it breaks.
So as I see it we should still be able to keep D-Jet alive for awhile longer. PEFI for a stock 914 engine only becomes reasonable and necessary when the price of the major parts at least doubles from what they are now, or they become completely unavailable and even then, only if your D-Jet needs all those replacement main parts at one time.
Or unless you just WANT it.