Rpm/tach flutter using digital dash.

[Lofiracingcrx]

hey fellow hondata users,
I'm having a problem and it has me stumped. I have a 91 si with a b16b swap, And above 3k rpm or so, the tach begins to flutter and fluctuate. I've changed every part of the ignition system multiple times including multiple icms. There used to be a slight hesitation once in a while, but re doing the grounds cleaned it up. Here is my calibration and a data log. Watch the flutter, and watch my voltage drop under full throttle. cant find any voltage drops in any grounds. I think it is an alternator issue or a ground issue, but I've been flying blind for a while and thought I would ask for help. im using a rywire harness. Thanks to hondata and the community.

[Spunkster]

The drop in your voltage is strange, also your sensor readings are very jagged as well. I would recommend that you try your ECU on a different vehicle and see if the problem persists or if it is something specific to your vehicle.

[Lofiracingcrx]

Thanks for your help spunkster, unfortunately I'll need a bit more. I ran to the shop that sold me the s300 and told them the sob story. They installed my s300 in one of their p28s and sent me around the block. No change. Than to rule out the s300 itself, one of them gave me their personal s300 and ecu to test. No change. At idle the ecu tells me I'm pulling 14 volts. At the battery I'm reading 14.3 at idle. Some reference somewhere is bad or there is noise and I'm not sure what to test next. Thanks again, this is pretty odd.

[Spunkster]

More than likely this has something to do with the aftermarket harness. You should contact the manufacturer of the harness.

[Lofiracingcrx]

I spoke with one of them and he was asking me questions you would not ask if unfamiliar with our cars. He seemed stumped so I sent him the logs I uploaded here, and he told me he would get back to me if him or one of colleagues thought of anything. Eliminating the 1 percent chance my ecu or s300 was failing leaves me confident it's a wiring issue somewhere. I want to know if the ecu really thinks the rpms are jumping like that, or if I'm erroneously being told that on the display. I guess the next step is to check what's going on between the signal wire on the igniter and the ecu correct?

Quick edit: my vtec would rapidly cut in and out close to the 5700 I have it set at no? That's a pretty solid swing from low to hi.

[Spunkster]

This does not sound like an ECU or s300 related issue. It sounds like a wiring problem as you have stated. The ECU is reporting what it sees.

[Thenameforcorey]

Hey did u ever find a fix for the fluctuation cause I'm having a similar issue but what's happening to me is, with just the key in on position engine off My map ,tps, o2 voltage, battery volt, and eld voltage fluctuates up and Down constantly and cause of this my car runs like crap. So I was curious if u found a fix cause ur prob was similar just not as bad lol?