Jump to content
gav-

megasquirt popping/backfiring - random idle and load

Recommended Posts

Hello, 

Does anyone have any advice what to look for when a megasquirt is popping or backfiring, it seems to do this on idle, randomly and rarely. But with some load and the rpm fixed it will pop from the exhaust every now and again. The rest of the time the engine sounds great, wideband is running around 14.7. I am wondering if it could be a plug problem? Any thoughts? 

Share this post


Link to post
Share on other sites

14.7 at idle is too lean, this can give backfiring in exhaust.

Tune idle to around 13.5 and see how you get on.

Share this post


Link to post
Share on other sites

Is it resetting at all? That can cause a misfire.

You can watch the SECL number tick up from 0 to 255 and back round to 0 in the data, if it resets from any other number that's a sign there's a problem, usually wiring related.

Share this post


Link to post
Share on other sites

Out of interest would a head gasket leak cause a misfire/popping(I think it could!)?? 

It runs really well except for the popping!!! 

Share this post


Link to post
Share on other sites

Lots of things could, but looking at a datalog costs nothing, ;) which is less than all the other things it might be.

Share this post


Link to post
Share on other sites

Just an update - it looks like it was lead issue - plugs 2&4 were wrong! 

Thanks for helping! (But need to check more than once it would seem!!) 

  • Like 1

Share this post


Link to post
Share on other sites

I *was* going to suggest wrongly positioned plug leads, but I had assumed that had already been checked ;)

  • Like 1

Share this post


Link to post
Share on other sites

Unfortunately the plug wires didnt fix it! 

I have attached a video of it, that is the sound from the exhaust!!! its not me hitting something. I have tried two different maps and both have the same affect, although disconnecting the map hose made it run awfully, but I dont think there was a popping sound! 

I wondered if the pwm could be faulty or if there was a vacuum leak (i cant hear/find anything though!)

Any ideas where to look next??? (thanks) 

CurrentTune.msq

Share this post


Link to post
Share on other sites

Still reckon your plug wires are wrong. 

 

Share this post


Link to post
Share on other sites
47 minutes ago, gav- said:

Unfortunately the plug wires didnt fix it! 

I have attached a video of it, that is the sound from the exhaust!!! its not me hitting something. I have tried two different maps and both have the same affect, although disconnecting the map hose made it run awfully, but I dont think there was a popping sound! 

I wondered if the pwm could be faulty or if there was a vacuum leak (i cant hear/find anything though!)

Any ideas where to look next??? (thanks)

You can very easily unplug & block off the PWM valve to prove that theory but I doubt an air leak would lead to misfires unless your mixture is waaaaay out.

If you disconnect the MAP hose you're immediately making the ECU think the throttle is wide open (MAP=99kPa) and running right along the top row of the fuel table, that's not really helping owt.

You haven't answered my question about resets.

Or posted a data log file which would be super handy.

Share this post


Link to post
Share on other sites

Thanks, I am not too sure if it’s reseting (oh how to tell to be honest) I can see at the bottom of the rhs of the screen on the video, that there are 3 lights, which are flashing between red and green as it running? Is this what I need to look at? There isn’t anything that comes up as a reset???? 

Share this post


Link to post
Share on other sites

You need to hook it up to a pc and run the log viewer. Catch a good set of data where it's misbehaving.

I'd suspect: resetting issue caused by power supply issue, interference or crank trigger not positioned correctly/out of spec/damaged or incorrect wiring. All of this will be visible in the logs (you can save and post here if you're unsure what you're looking at), but you're very unlikely to see just staring at the dials in TunerStudio or randomly disconnecting stuff. When it's logged and graphed, it's easy to spot what's going wrong. 

Share this post


Link to post
Share on other sites

tsms_realtime_menu.png

tsms_realtime_secl.png

 

SECL value just counts up 0,1,2,3...255,0,1,2,3... over and over as the ECU runs. If it resets it will drop back to 0 unexpectedly. That's a sign that something (wiring fault etc.) is electrically upsetting the ECU enough to make the thing reset.

 

But the most useful thing you can do is...

tsms_logging_menu.png

And post the log file! That way we can SEE all the data of exactly what's going on!

 

Mind you, you've also not said if it's Megasquirt, MegaJolt, which version, if it's running fuel and/or spark, on what system, where you got it from / who built it...

Share this post


Link to post
Share on other sites

Never heard anything like that before, sounds to be running quite nice apart from the pop. The mixture seems to jump at the same time and go rich i think looking at the video. :unsure:

Has it ever run ok or is it a new install. If so did it run ok before the install. IE do you know that the timing and everything is ok on the engine. Some are known for the engine pulley marks to not line up correctly. You need to make sure 0 is actually TDC and the sensor is in the correct place for the EDIS timing. You can physically move the sensor or offset it in the software. For the sake of taking the heads off you can see if TDC is at the right place and if all the valves are opening ok. I didn't find the engine that sensitive to changes in the spark table but worth looking for something stupid. 

Also easy to spray a bit of easy start around the engine to check for leaks, it should run faster if some is getting in.

Are you running petrol or lpg? Are all 8 injectors working evenly, maybe one bank is putting more fuel in than the other and that's making the mixture jump? I put a plastic cup under each injector to measure what was coming out of each one. You just have be be very careful there are no sparks!

Are all the plugs proven to be firing and in the right order, I had real problems with plugs on mine, sometimes they would crack the ceramic and it was almost impossible to see it.

I found it easier to blank off the pwm, get it running nicely then put it back in just to help with the cold running. I found trying to tune it with the PWM in to be really hard. 

Only other problems I had were with the fuel pump losing pressure as it got hot, there is a manual somewhere on here that tells you what the pressure should be, it's a certain amount over manifold pressure, I fitted an oil pressure gauge to the fuel system to monitor it. I also had a fault with the power supply of the board, that caused the engine to play up I didn't find it until it finally died and I had something to track. 

Good luck!

Share this post


Link to post
Share on other sites
2 hours ago, Cynic-al said:

The mixture seems to jump at the same time and go rich i think looking at the video. :unsure:

This is where you have to be careful not to fool yourself - a mis-fire will dump unburnt fuel down the exhaust and trick or smother the lambda sensor, so you can't rely on the O2 reading if it's not running right.

Classic case in point was a certain Range Rover that was burning so much oil it coated the sensor - owner was seeing "lean" EGO2 reading and kept adding fuel despite the fact it absolutely stank of unburnt fuel :rolleyes:

If you enable EGO correction / auto-tune in that sort of situation you'll make things even worse as the computer blindly tries to tune it off into the weeds!

  • Like 1

Share this post


Link to post
Share on other sites

Thanks everyone for your help. I have attached a datalog file, but too be honest i am not sure what i am looking at!

The SEcl number counts from 0 to 255, and then resets, so dont think its that. 

I did play around with the fuelling which seemed to help if I made it leaner? (could it be a stuck injector???)

The ECU was brought about 10years ago, its an ms2 from extra efi (very nice chap), unforunately though due to family, work etc everything got put away and now i have the time to work on it again, so essentially its a new install. I have checked the timing and that is spot on. Its running EDIS, and other than the popping it sounds and runs nice, except i cant run it very long as it sounds like a gunshot going off!!! ITs a wideband lc1 02 sensor too. 

 

 

 

2019-11-28_20.17.09.msl

Share this post


Link to post
Share on other sites

Well nothing glaringly obvious in the datalog, could you point to a time in the log where it was popping / misfiring? I've uploaded a piccy of the graphs for others to gander at;

datalog_screenshot.thumb.png.01b6e9a1790098028e89e082ea7f30a2.png

 

Are you sure it's an MS2 because the logfile header suggests it's an MS1 running the usual 029y4 code...

MS1/Extra format 029y3 *********: MS1/Extra rev 029y4 ************

 

Share this post


Link to post
Share on other sites

This bit is a little odd, the injector duty cycle (bottom yellow trace) jumps up from ~5% to ~8% for seemingly no reason;

datalog_screenshot2.png.64253ed1c980c581c1b8bed998cdf29a.png

 

And this bit is also a bit jumpy for idling - although the very lean mix likely doesn't help;

datalog_screenshot4.png.5b8599c634f8305ee9443da08b2d7e1d.png

Share this post


Link to post
Share on other sites

If that's idle, you are running waaaaay to much advance. It will run like that, but pull it back to 10 as a starter. 

A lean mixture burns more slowly, so it is possible that it is still burning when the exhaust valve opens, causing the popping. Tune idle to 13.5 afr. 

Screen grabs on the ve and spark tables would be handy at this point, or even the msq. 

I'm going with leads or a miss-timed trigger wheel at the moment. 

 

 

Share this post


Link to post
Share on other sites

Thanks for the comments and suggestions. One thing is have realised is that the lc1 wideband switching point is incorrect, it’s set at 0.5xxV and I think it should be 2.432V. So the exhaust measurements are way out. When I get a minute I’ll make the change I’ll  run it again! (Sorry best to check the basics!) 

yes your right it’s an ms1 too! 

Share this post


Link to post
Share on other sites

The switch point shouldn't make any difference to your idling as EGO correction shouldn't be active - unless you've gone wild and are running AFR-target tables rather than normal fuel map.

The key here is "Active Above RPM" which should be above idle.

ego_control.png

 

Share this post


Link to post
Share on other sites

I am using BPR6E spark plugs reading all of the posts on here about spark plugs- should I use BPR6ES? I have some BP6ES plugs would they be worth trying?? 

Share this post


Link to post
Share on other sites

The S is just for the copper core plug, likely make no difference at all. 

Share this post


Link to post
Share on other sites

I very much doubt it's your spark plugs, especially if it ran before.

You say you can't find vacuum leaks, are you 100% sure on that?

What engine is it?

Can you load up someone's "known good" settings MSQ from here and see if that works?

Share this post


Link to post
Share on other sites

Its never been properly ran on mega squirt, I changed over and then my daughters arrived and it sat for 8 years! 
i have tried two different msq, one from hfh and bowie69. On both engine runs fine but still popping away! If I lower the reg fuel it’s gets better but doesn’t go away completely, if I go to far with dropping reg fuel then it just stalls. 
 

i have been listening and looking but can’t find any vac leaks plus it’s so erratic. It’s Very random 

it’s a 3.5 low compression with old Hotwire efi 

 

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...

Important Information

We use cookies to ensure you get the best experience. By using our website you agree to our Cookie Policy