Converting '86 HF (carb) to fed VX (efi).
 

Well, I've had it with the carb. Fussy and unreliable. Tried a rebuild -- still not acceptable. Going to change out the carb to federal VX efi. If anyone has done a similar conversion, I'd appreciate any advice or warnings.

Thanks!
Colby

Are you replacing the whole engine or just trying to put a VX EFI intake on it? If its a CVCC engine you will have to change over the cylinder head as well

This is going to be a big job- wiring harness, ECU, fuel pump etc.

I have had good luck with my 87 1.5 CVCC carb. I rebuilt it myself last year even though it was running fine then. What is the problem with it? Rough idle, poor acceleration, hard starting when hot/cold?

There are tons of vacuum hoses- it could just be a rotten hose somewhere.

I'm going to go with one more rebuild (since it has a lifetime warranty), and replace all the vacuum lines in case there is a leak or blockage somewhere.

The past carb was dumping too much fuel at low rpm (bad mileage), and the current rebuild bogs hard at anything past 1/3 throttle.

Why would I have to change heads?

I could just fab an intake manifold and mount the injectors in the runners. I know it's a big job but this carb crap is driving me to the breaking point.

If you have a CVCC engine, the cylinder head is special and actually requires two seperate mixtures a rich and a lean mix in order to work correctly- it would be impossible to get a stock ECU to work with this.

The easiest way to tell if you have a CVCC engine is if you have a 3 barrel carb. The tiny carb barrel feeds the extra rich mix to a tiny pre combustion chamber that the spark plug screws into.

Will the engine rev up OK in neutral? Double check the ignition timing and the vacuum hoses. It could be a bad/clogged accelerator pump or a bad power valve in the carb.

It's an '86 HF with stock D15a2 (plastic valve cover).

CRX HF (USA) D15A2 1.5 8V SOHC 2bbl Carb 1488 58hp@4500rpm 80tq@2500rpm

It is unlikely to be a CVCC.

If you're really serious about this, I'd recommend using megasquirt. I doubt that any existing (stock) Honda ECU would be properly tuned for your HF engine once you have done the conversion. The Megasquit will give you the flexibility to tune the engine once you're done.

Check out this section of the online manual. It goes into detail on how to covert a carburated car to EFI. More work then I would want to do, but if you do, lety us know.

https://www.megamanual.com/v22manual/minj.htm

Now that I think about it, you're probably right. The main hurdle I'm seeing is the lack of Vtec for the ECU. However, if it's only an output then perhaps it could just be ignored(?). I'll have to research the VX ECU and see what inputs it is expecting.

The VX ECU probably wouldn't work as it changes the entire fuel map and ignition advance when the vtec kicks in the other 8 intake valves. If you want more info, check out pgmfi.org, these people have dedicated their lives to reverse engineering Honda ECUs.

Yeah, the EFI from the 2nd gen HF would probably be a lot easier. I just wanted to go with the VX for the lean-burn.

Thanks for that link!

The advantage of using the megasquirt is you could program in something similar to a lean burn. The 2nd gen HF ECU is not very easy to rechip so if you were to use one of these, you'd have to hope it would satisfy the ignition and fuel maps for your engine.

I don't know where you got the specs for your '86 crx hf engine from, but I have that exact engine sitting on the bench in the garage right now, and it is a cvcc head, the only 1984-87 crx that didn't have a cvcc head was the 1.3L and the SI modle, the DX and HF both have CVCC heads, so for fuel injection you are going to need a whole head, you are most likely going to need the head off the SI engine to get one fits right, and I'm not sure wha they use for crank shaft position sensor, CPU, and all that.
Who did your carb rebuild?

I'll pop the carb (and valve cover) off this weekend and take pictures so we can get the CVCC question settled. You guys might be right.

This is my first venture into pre-OBD1 land...

If its a CVCC, the 3rd barrel will be a dime sized hole off to the driver's side of top of the carb. After you get the air cleaner off, you will likely need to take the intake screen off the top of the carb to see the small third barrel (if its like my carb).

Another CVCC indicator- when you take off the valve cover, you will actually see 1 tiny valve stem/rocker assembly for each cylinder.

cvcc honda engines also have the spark plugs coming out right over the exaust manifold, on the front side of the head, not the top of the head, about an inche below the lip of the valve cover, they are like this because they are in the prechamber next to that little auxilery valve, it's a great design, and I'm not sure if you can get better gas mileage with fuel injection, not easly at least, but I've rebuilt these carburators a number of times, and I'm a big fan of them, but I know what it's like to have problems.

It's a CVCC alright. Guess I'll just have to keep fussing with the carb and maze of vacuum lines =/