Problem with spark above 2800

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A4seen Racer
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Problem with spark above 2800

Post by A4seen Racer »

I'm using the 029q2 code on a v2.2 board. I've got a 60-2 wheel and vr sensor on a 1.8t 20v

Whenever my rpms go past 2800 theres a noticeable loss in power and it will missfire badly if I put load on it above 2800. I have changed from a few different setups because I've been switching from edis to 60-2 wheel decoder. Here's kind of a timeline of when the problem started
1. EDIS - ran fine
2. eids 36-1 wheel and vr sensor in wheel decoder mode with edis coil pack - ran good
3. 60-2 wheel, edis coil pack and wrong version of megatune - one led cut out at about 2800
4. same setup but used right megatune - engine would rev all the way but lose power at 2800 and miss
5. switched to stock coil packs and probelm stayed the same

If anyone can help me out I'd greatly appreciate it. I cant figure out where the problem is at. It definitely started when I went to the 60-2 wheel though. I attached a log of when it happens. I seem to get a reset when it gets real bad.
jsmcortina
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Post by jsmcortina »

Why did you switch from 36-1 to 60-2 ?

Do you have a 390R load resistor across the VR sensor input to the Megasquirt board? This can help with high(er) rpm signal problems.

Please post your settings.

James
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A4seen Racer
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Post by A4seen Racer »

I did some shoddy work when I welded the 36-1 wheel onto the crank pulley and it was noticeably off center so I wanted get it off before it did any damage.

Do you mean a 390R resisitor between the 2 wires from the vr sensor? if so then no
milosch01
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Post by milosch01 »

Have you tried switching from v24X to v25 wheel decoder routine in the wheel decoder page?
daxtojeiro
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Post by daxtojeiro »

the resistor that James mentions is a cure, I did the VR conditioner mod to a TR6 and didnt add the resistor, it wouldnt rev passed 3000, then I fitted the resistor as James says and ts perfect now :)
Phil
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A4seen Racer
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Post by A4seen Racer »

ok i tried the 390 resistor between the vr input but it didnt cure the problem. It actually made it worse. After adding it the stock tach which i kept hooked up would drop to 300 when the actual rpm hit 2800. The rpm still read right in Megatune but it was much more jumpy. I took the resistor off and unhooked the stock tach and it got better but still misfires under load.

I also tried playing with the dwell. I had it set at 1.5 (COP coils) then bumped it up to 1.8 but the misfires got worse. when i lowered it to 1.2 it got better.

It seems to me that im getting a noisy vr signal. Is there any other ways to address this? I already have it shielded all the way into the ms.
JTbo
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Post by JTbo »

I did read somewhere that if VR sensor voltage goes over 5(?) Volts it may be needed to replace input resistor of signal conditioner circuit. LM1815 has protection for over voltage and it may cause troubles.

There seem to be quite few threads with 3000rpm problem and I think it was one of those that has specific details about this, but just can't find now which one it was.
A4seen Racer
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Post by A4seen Racer »

I measured the voltage coming in on the vr signal wire with a multimeter and the highest it got to was 0.15 volts. Thats when it started misfiring. I'm kinda confused as to why its misfiring. Everything seems to be working as it should.
A4seen Racer
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Post by A4seen Racer »

I'm still having a misfire problem. I played with resitors a bit and it got better when I put a 150k resistor inline on the vr signal wire. The only thing wierd now is that is misfires worse under about 3000 rpm and then gets better above that. I'm not sure what to try now and I'm still not sure what is actually happening when it misfires. Sometimes it seems like only 2 cylinders are firing and sometimes it seems like the timing and dwell are way off. One time it backfired out the intake so I know the timing gets off. Could there be a problem with the vr sensor or maybe even the wheel?

I attachted the results from the tooth logger. The first one is at idle and the second one is at about 3000 when it was misfiring. I couldn't interpret it so theres just a screenshot.
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