I have a 96 MX5, 1600 cc. 5 speed, that fried it’s ecu several months ago. The original ecu has part # B6GP 18881C. Since i couldn’t find a source for this particular ecu i tried ecu part # B6HA 18881. Apparently it doesn’t work for my MX5. A shop suggested that i try out ecu part # B63H 18881 but the car would have to go through a few modifications on the wiring harness. After a couple of hours they got the car running smoothly. I did notice though that the air/fuel mixture was very rich. I was told that i’d have to convert my injectors. The reason they cited was that my former ecu was wired for sequential type of fuel injection but with the ecu i’m using now it has been converted to a batch type of fuel injection.
My questions are:
Is there a difference between the two types of injectors?
Aside from the injectors is there anything else i should replace to make the ecu conversion run smoothly?
The spark plugs are very black due to the overly rich mixture.
Your engine is rated at 88 bhp and you now have an ECU that is mapped to fuel an earlier JDM-spec engine rated at 115 - 120 bhp. Unsurprisingly, it is overfuelling.
You could try an adjustable fuel pressure regulator to reduce fuel pressure across the board but it is pot luck if the fuel maps are corrected for the full speed/load range. The issue of the wrong ignition maps will still remain though.
It might be worthwhile posting in the “Wanted:” forum here and also over on mx5nutz, stating that you need a working B6GP ECU (and transponder keys for the immobiliser).
OP is in the Phillippines. I’d imagine the later 1.6 differs from here in that it is not fitted with an immobiliser.Won’t a used UK/Euro 88hp ECU require a set of keys to go with it?
Good point (previous post amended). I had seen this post, also under the “hybrid” username, referring to a UK-spec car and put 2+2 together …
The matching transponder key and loop aerial would indeed also be required to accompany a UK spec ECU, although I would be tempted to tape the donor key transponder and aerial together inside the steering column cowling rather than faffing about replacing steering/ignition locks.
“You’ll need the immobiliser unit from the donor car as well.” …unfortunately i wasn’t able to include the donor key, transponder & aerial when i ordered the ecu from Andrew Stott so now i’ve got a very expensive paperweight.
"Yes, the engine.
Your engine is rated at 88 bhp and you now have an ECU that is mapped
to fuel an earlier JDM-spec engine rated at 115 - 120 bhp.
Unsurprisingly, it is overfuelling.
You could try an adjustable fuel pressure regulator to reduce fuel
pressure across the board but it is pot luck if the fuel maps are
corrected for the full speed/load range. The issue of the wrong ignition
maps will still remain though." … does that mean that if i have the ecu that i’ve got on my MX5 now re-mapped to mimic the program for an 88 hp engine it’ll run fine then? Are the injectors for an 88 hp engine the same as those used for a 115 hp engine?
“OP is in the Phillippines. I’d imagine the later 1.6 differs from here
in that it is not fitted with an immobiliser.Won’t a used UK/Euro 88hp
ECU require a set of keys to go with it?” …you’re right AT. MX5’s in the Philippines don’t have immobilizers fitted on them.
Better still what will i need to do to make my engine put out 115 hp since i’ve already got the ecu for it?
You don’t need the immobiliser, transponder and aerial for the B63H ECU as this is for an earlier JDM car with with the 115bhp 1.6 engine. It is still the wrong ECU for a later 88bhp engine though.
You cannot remap these ECUs. Your “new” ECU is mapped to provide fuel for a 115bhp engine. By lowering fuel pressure across the board you might be able to reduce the fuelling to somewhere approaching that required for 88bhp. The 88bhp engine has lower compression and different camshaft profiles and the volumetric efficiency profiles will still be different to the 115bhp engine. As I said before, the fuel and ignition maps are different for these two engines and the ECU is mapped accordingly.
To convert your 88bhp engine to 115bhp spec. you need the cylinder head, camshafts and pistons from the earlier engine.
Hi Niggle. Thanks so much for the quick reply and valuable info. I really appreciate it.
When i mentioned that i’d need the immobilizer, transponder, etc., i was reffering to the ecu that i purchased from Autolink a few months back. I should’ve ordered the transponder, etc., so i could use the ecu which has part # B6HA 18881C. Unfortunately i didn’t include said parts in my order thus i have an expensive paperweight on my hands.
I’ve got a spare adjustable fuel pressure regulator with me. I’ll try it. Any suggestion on what psi i should set it at? So are the injectors on the 88 hp and 115 hp the same? Is it the mapping that’s just different?
If i can get my hands on a 115 hp spec cylinder head with camshafts then that would be ideal. As per the pistons i’d hold off a bit on them cause my engine has only about 25k kms. on it and it’s still in very good condition. I’d probably shave the head a bit so i could get a bit more compression.
After many months of frustration I was finally able to figure out how to make my miata run on a B61P ecu. What we did was to first order an entire engine wiring harness of a miata that uses the B61P ecu and one by one went thru the difference in wiring pin outs to the different sensors. Then we merely duplicated it and the car instantly ran. Idle was very smooth and the once overly rich mixture was instantly corrected and the spark plugs were burning very cleanly ( light gray in color ). It’s true that the mapping of a 115 hp miata and a 90 hp miata is slightly different cause now the performance increase i feel is very noticeable. Next step is to get myself some 115 hp spec camshafts so i’ll be able to maximize the mapping on the replaced ecu. So from a B6GP ecu, my miata now runs flawlessly on a B61P ecu.
Well done hybrid - you have persevered and solved your problem - many would have fallen by the wayside.
The B6HB ECU, also known as B6HA is totally inactive and unusable without the ASSOCIATED immobiliser bits - thats the box that sits in front of your right knee in a UK car and the ignition bit + the black coil around the key insert. A suitably coded transponder key is also required. I have proved that even the diagnostic will not activate on this ECU without the immob bits.
Wish you the best of luck with the other mods required and hopefully, some time this year I will get my own car back on the road too.
