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Hey all, have a recently acquired Miata that was boosted before my ownership that is cutting out under full power. Especially in first gear, sometimes second. The more lively the RPM change the more likely it seems to happen. It supposedly makes 200 whp and was dynotuned professionally at Ohio ECU Solutions. Car is pretty well sorted overall. All gauges work (boost, wideband afr, actual oil press, the usual), only track oriented mods. However, after my first 4 days of driving the car it has developed a violent hesitation that feels like fuel cut. I did some searching and I have a guess as to what's wrong, but I'm like 7 hours into trying to learn megasquirt including building the laptop from spare parts....
I <THINK> it is a loss of sync issue after reading a couple of other threads. I <THINK> the solution is to install a new OEM crank position sensor and gap it correctly to .35-.42. I have also read that electrical noise from running the wrong plugs can cause this type of issue. Also that there are noise reduction settings I could try.
Have uploaded a composite log, which weirdly to me looks like great uniform square waves (altho the first page is oddly mostly empty is that the issue?). Also uploaded a log and the tune. Screenshot is of that same log pointing out what I think is wrong.
The car:
1990 with 1.8 swap. No idea which intake mani yet. MSM turbo/mani/downpipe with mishimoto IC.
MS2 PNP with supposedly a pro dynotune.
Indigo injectors that say Japan on them. I know, I'm working on it.
Have not pulled the fuel pump to identify
Coilpacks do not look like the typical wasted spark two block. Still trying to identify.
Plugs look fine. They are Bosche double iridum gapped to .023-.025
Other:
Idle surges and car dies when warm. AFR bounces between 10.x and 14.x. I think this is unrelated.
The first graph is kind of busy, but you start to see loss of sync events in yellow as RPM dies and AFR doesn't seem to spike until I take my foot out of it. This is a soft launch from first, into WOT. Hesitates, I let off the throttle then shift into second. The pull in second is clean, no hesitation.
Those look like stock 1.6 coils with a BEGi bracket to mount to the 1.8.
Get some NGK BKR7E (4644) plugs and swap them when you change your oil; they're cheap and work great, but don't last long.
When you're losing sync RPMs drop to zero, so you're getting no spark or fuel. That's definitely the issue you're feeling, hopefully just need to tighten the gap on the crank sensor.
In the log, what's your sync loss code?
0 = no problem 1 = init error 2 = missing tooth at wrong time 3 = too many teeth before missing tooth (last) 4 = too few teeth before missing tooth (last) 5 = 1st tooth failed test 6 = nonsense input (last) 7 = nonsense input (mid) 8 = too many teeth before missing tooth (mid) 9 = too few teeth before missing tooth (mid) 10 = too many teeth before end of sequence 11 = too few teeth before second trigger 12 = too many sync errors 13 = dizzy wrong edge 14 = trigger return vane size 15 = EDIS 16 = EDIS
Thanks for the ID. Loss of reason code appears to be 39 (4G63), which is the decoder ring I have selected in ignition settings.
I tried gapping down to .020 to rule out spark blowout, did not seem to help. Altho all of the blowout vids I checked the engine seems to breakup and miss rather than the ECU completely shutting the lights out like what I'm seeing. Will still throw new plugs on my shopping list.
Have an OEM cam and crank position sensor on the way. Also read the following:
- Try adjusting VR conditioning pots.
- Buy a supermiata 36-2 trigger wheel (out of stock)
- Check that the crank position wiring is shielded and grounded to the ECU.
My brain still hasn't adjusted to reading the composite log yet, I may give that another go with a much shorter log.
Well I've learned something tonight. The engine has a "BP" cast into the exhaust side of the block with an adjustable CAS in the rear. No cam sensor on the timing cover. No crank sensor in the usual 4 o'clock position. So I guess I've got an early 1.8, completely different than the NB I'm accustomed to. Dug into the CAS and found a very crusty connector so I flooded with isopropyl, cleaned and greased. All this started by inspecting the stock trigger wheel which apparently has hardly any teeth on it compared to the 36-2 wheel (thanks @emilio700 not sure what happened).
Took it out for about 30 minutes and could not get it to cut out. The AFR's do seem to get down under 10.8 to even out of range at low-rpm/high-load. Flooring it in fifth gear is particularly bad with it missing lightly, which I think it actually spark blowout this time. Not sure how worried I am, lugging at WOT in fifth is probably ill advised anyway. Conclusion, the tune seems conservative.
I'm not going to celebrate because then the car will break again and it will be yet another year without a single track day... and I literally just moved 5 minutes from mid ohio road coarse. Need to pick out some tires and pads and do a bit more sorting, but yeah. It needs to happen.
Interesting, I replied last night but saw a brief message about needing approval. I'm too new to send a PM so... let's see. @18psi@sixshooter any chance my post is sitting in an approval queue? Thanks.
Not sure what's going on with the forum, will try to repost from memory. TLDR: I think it's fixed.
The engine has a "BP" cast into the exhaust side of the block with an adjustable CAS in the rear. No cam sensor on the timing cover. No crank sensor in the usual 4 o'clock position. So I guess I've got an early 1.8, completely different than the NB I'm accustomed to. Dug into the CAS and found a very crusty connector so I flooded with isopropyl, cleaned and greased. All this started by inspecting the stock trigger wheel which apparently has hardly any teeth on it compared to the 36-2 wheel (thanks @emilio700, I see it in stock now).
Have run it hard for a few days now and I can't get it to choke anymore. The AFR's do seem to get down under 10.8 to even out of range at low-rpm/high-load. Flooring it in fifth gear is particularly bad with it missing lightly, which I think is actually spark blowout this time. Anyway, tune seems conservative and car has been running fine for a couple days now.
06-05-2022, 09:12 PM
Fuel cut (or something) under boost
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