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loosing Rpm signal and backfiring


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#1 Amonje123

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Posted 08 April 2018 - 07:44 PM

So I started my Mpi project last year April. Got it all assembled in about 6 months bit been having this issue I just can't get fixed.

I am running Mocrosquirt V3 from Scott and his COP Ignition system. Car starts up and idles fine, but when u start giving it throttle is loosing the crank signal and backfires.

It's running a 36-1 trigger wheel and Vr sensor. I've been messaging Scott about my issue and he's been really helpful and helping me out. But can't get this issue resolved.

What I've done so far is add a 10k ohm resistor in the + wire. I've tried putting it on the - side also. Even put then in line with eachother and same problem. After started messing with the Vr sensor gap. Went from .10 all the way to .100. Also took the whole shield wite out of the harness. Incase it was picking up noise. Made no difference.

Nothing will make this backfiring go away. I've sent Scott datalogs and stuff and he says yea the crank signal is loosing signal. We have gone back and forth for a few months now and like 200 emails and still can't get this beast to run right.

If you gradually give it throttle in neutral it will Rev all the way up. If driving on flat ground and nice and easy it runs fine. Start revving it up in neutral and shots fired lol. Driving it and try to accelerate it bucks and backfires.

I hooked it up to a timing light and watched it blink. Just about every time I snap the throttle the light goes away and I get a backfire every here and there. So it loses signal when the engine has a sudden increase in Rpm.

So I'm pretty sure Scott is tired of emailing me now I've been bugging him alot cause of course I want to get this thing running right. I just can't seem to get it and it's starting to drive me to the point of insanity lol.

So I'm posting here to see if anyone else has had this problem and many can help me get my car up and running.





#2 importwarrior

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Posted 08 April 2018 - 07:56 PM

What’s the gap between the trigger wheel and pickup sensor?
Is the pickup sensor vibrating bad?

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#3 speedyquest

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Posted 08 April 2018 - 08:01 PM

Have you read through the megasquirt manual or searched around any of the megasquirt forums? You can't be the first person to have this issue. I'm going to list out a few things id check if I was you but keep two things in mind. I'm not experienced with megasquirt yet, I'm not to the point where I've started tuning my car yet. I've only been reading a ton about it. And secondly I'm guessing anything I suggest Scott has already suggested himself.

That being said here we go...

1) Verify you have a consistent gap on your trigger wheel to your sensor. The manual says that runout over .5mm will cause desync of the rpm signal.

2) Make absolutely sure whatever wire your using for the sensor is as far away from coils, starter, alternator, or any other high amp thing in your engine bay. You can use an AM radio to listen for high interference.

3) Make absolutely sure that your ecu is grounded properly AND that the megasquirt's sensor ground wires are only being used for sensors and not anything else. You can find more info about this in the manual. Poor or incorrect grounding can reek havoc on any inputs or outputs.


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#4 Amonje123

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Posted 08 April 2018 - 10:23 PM

The gap right now on the sensor is .40in. And yes i have read the Manuel over and over again. I have it hooked up 100% how the directions say.

Ecu is grounded to the engine. Vr sensor is grounded at the ecu not the chassis or engine as the Manuel says.

Of course I have done research before posting here. I've read that many ppl have this issue. I've been on the Miata forms, hot rod guys, Honda tech, starquestclub, even Sand rail guy using this set up and run into this issue.

The #1 fix that in the Manuel and a lot of ppl do is add a 10k ohm resister to help clear the signal. That did not work for me. Another fix it the maneul and ppl also do is adjust the noise filters to help clear out the signal. I have done that to no end and can't get it to get better.

Also found ppl say the sensor is tricky and like certain gap specs. I've tried gaps from .10 to .100. Couldn't get it to clear up. But it does seem to run better at gaps .40 and bigger.

Another thing in the Manuel use shield wire and keep away from coils, injectors, fans etc. I'm using shield wire from DIY so it's good wire. I have the wire out of the harness and on the front of the car away from everything so it ain't picking up no noise from anything.

I've even read on the a form that someone had the problem I did and they changed a piece on the ecu itself. Sorderd a piece off and put another one in its place. Forgot what it was but it worked for him.

Same form a guy was having this issue and did the board mod and didn't solve his issue. He never wrote back if he fixed it or not. But I'm not about to take a piece of this ecu and mess it up.

I've read and read over and over so many things these passed few months and it's just weird how I can't fix this. I usually can fix just about anything I come across.

#5 scott87star

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Posted 09 April 2018 - 08:56 AM

I don't think we've tried switching from rising to falling edge capture (or vice versa), see what happens there.
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#6 Amonje123

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Posted 09 April 2018 - 09:42 PM

I switched it from falling edge to rising and same thing. Readjusted the trigger angle to get the timing back at 10degrees. Still have the same issue of backfiring.

Here's one thing I do notice tho. Since we have been doing all these adjustments. The Rpm gauge in the microsquirt doesn't jump around anymore and go at zero and back up.

I took a log and can't see the crank missing any teeth. Maybe I'm reading it wrong. But with the timing light I can see the misfire when the light doesn't flash.

Like at idle or holding it at like 2k 3k rpm the light will skip a blink every now and then but not to bad. Snapping the throttle is not good tho. Light blinks then doesn't blinks and doesn't and every time it stops blinking. Bang backfire.

Maybe I should send u another log Scott maybe I'm getting signal to ecu but losing it through after the ecu idk lol

#7 scott87star

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Posted 10 April 2018 - 08:18 AM

Send me a regular log, tooth log and trigger log.
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#8 Chad

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Posted 10 April 2018 - 11:18 AM

what kind of plug and plug wires are you using?  if you have very low ohm plug wires, you will kill your signal as the engine experiences load.  When a cylinder loads up with pressure, the noise from the spark plug wires increases.  If your sensor or sensor wires are anywhere near the plug wires, you will induce a gerat deal of eelctrical noise into the pickup signal.  

I had this happen with some Moroso Ultra40 plug wires, I had to move my sensor wires around so it was never closer than 8" from the plug wires.  Then I never had a problem again.  THe sensor wires were shielded, but it was still too close.

#9 Amonje123

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Posted 18 April 2018 - 10:14 PM

I have no plug wires. It's Coil On Plug. What I did so far is advance the timing 5° from idle to 3500 rpm. The car doesn't pop anymore when I Rev it up. I copied the stock ignition map from the begining. Drivimg the car fells better to.

But once the rpm start to build while under load car will start to miss around 4k or so. I've I try to get on it quicker. It will cut out faster. Just sounds like I hit a Rev limiter.

Driving around with the laptop tho my rpm doesn't bounce around tho like its losing the signal? Afr are good.

Man been going at this for like 6 months now :( lol


#10 scott87star

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Posted 19 April 2018 - 08:47 AM

What's the history of the motor?  Last compression test?
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#11 speedyquest

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Posted 19 April 2018 - 09:11 AM

View Postscott87star, on 19 April 2018 - 08:47 AM, said:

What's the history of the motor?  Last compression test?

Ah... yea I see what your thinking. Good idea.

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#12 importwarrior

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Posted 19 April 2018 - 07:09 PM

What are your rev limiter setting ? I had an issue when I first setup my base settings and had the setting too low for over boost.

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#13 Amonje123

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Posted 19 April 2018 - 09:39 PM

Haven't done a compression test on this motor since ive rebuilt it. Has about 30k of very abusive miles on it lol. But engine ran totally fine when I parked it and when tbi.
Right now the tbi setup would of walked this mpi setup I have lol.

But I will do a compression test just to rule it out. Maybe it broke sitting for like 5 months who knows. I will do that and post back.

I have the Rev limiter set to 6000 rpm. It will Rev but it just breaks up all over the place at higher rpm or when the boost starts going above 10 lbs.

Which is another problem my tial waste gate isn't working. Some reason doesn't want to open. Car will get to 20psi real fast after 4k rpm. Shouldn't pass 10psi tho.

Another thing I did today was advance the timing a bit on the boost side of the table. Car goes alot faster now and alot less break ups. I had it at 25° from 1psi up to 20psi. Through the whole map. Kinda lame but thought that would be safe for now till I get it tuned.

Now it's at 35° at 1psi-5 psi. 33° at like 7psi. 30° at 10psi. 25° at 20psi. Car runs way better like this. I did that to the while map from 3500 rpm and up.

Edited by Amonje123, 19 April 2018 - 09:44 PM.


#14 scott87star

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Posted 20 April 2018 - 08:43 AM

What do the plugs look like?  I'd do a plug chop when it's breaking up.  Also what gap?
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#15 Amonje123

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Posted 22 April 2018 - 01:58 PM

Go to the car this moron pulled out the plugs not bad. Kinda black but it's cool.  I have the engine running at 12.5 13 and High 10 low 11 when starts hitting boost.

And those plugs have been there a while with a lot of trial and error so they needed to be change anyways.

There gapped at .25 right now. And what's a plug chop?

Got rid of my boost solenoid too. Got the hose straight to the waste gate and still boosting to high. So I'll see what's going on there to. It's hard to Rev up the car without the boost going crazy.

Ooo and I couldn't do a compression test. I guess I let my buddy use it couple months ago and of  course wasn't bright back lol

I'll get back or the car this afternoon to check the wastegate. Compression test and go from there.

#16 Amonje123

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Posted 22 April 2018 - 04:59 PM

Go to the car this moron pulled out the plugs not bad. Kinda black but it's cool.  I have the engine running at 12.5 13 and High 10 low 11 when starts hitting boost.

And those plugs have been there a while with a lot of trial and error so they needed to be change anyways.

There gapped at .25 right now. And what's a plug chop?

Got rid of my boost solenoid too. Got the hose straight to the waste gate and still boosting to high. So I'll see what's going on there to. It's hard to Rev up the car without the boost going crazy.

Ooo and I couldn't do a compression test. I guess I let my buddy use it couple months ago and of  course wasn't bright back lol

I'll get back or the car this afternoon to check the wastegate. Compression test and go from there.

#17 importwarrior

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Posted 23 April 2018 - 07:02 AM


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#18 Amonje123

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Posted 27 April 2018 - 01:23 PM

OK got back to may car ran a comp test and got 100 across the board. And before u guys are like that's too low it was 110 when new these Dnj pistons are just low compression for some reason. Good tho more boost.

Added a nice big squirt of oil in there and they went up like 3psi 5psi. So not bad. Don't know where the other 5psi went but OK lol.

Fixed my waste gate issue so now i can hold 10psi all the way up. Thanks for the waste gate video Import Warrior but that wasn't my problem.

I'm running a hx40 turbo with a .82ar hotside. With Chad tubular header and 38mm wastegate.

So took the car for a drive and I can Rev it all the way up to 5k before it starts breaking up. But car misses a lot while driving at a constant speed holding 20 30 40 50 60mph etc. And i mean it misfires alot. Like every 5 seconds it can miss 10 15 times fells like.

Funny thing if i have a slight load on the car 1 2 psi and speeding up it gives a nice smooth note. No missfires. Kinda weird but yeah that's and issue too.

So have to find out why the car is missing so much. I can now Rev the car up in nertual all the way up to 6k but not under load.

How do I check to see what's causing this. I'm either losing spark or fuel that the only thing that can be doing this. Just have to find out why.



#19 Chad

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Posted 27 April 2018 - 02:02 PM

I'd try a plug gap of .035 to.032.  I've run short gap like yours and found no benefit, and several problems like gap foul and hard starts.  Stock gap is .041.  What heat range are hte plugs?  8's are the coldest you want to go, and most are better off with 7's.

#20 Amonje123

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Posted 27 April 2018 - 02:59 PM

I'm using the ngk 7s. I'll do that and see what happens. I have a question about your intake also sending you a dm.




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