Goldbox misfire issue at low load

James408

Member
May 18, 2020
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Well winters hear and I’m trying to knock some issues of the to do list on my 1986 GT. It’s the original bottom end with twisted wedge heads and a 93 cobra intake stock ho cam. I have damn near replaced every sensor, vacuum line, full valve grind gasket set with less than 1000 miles sense head swap. Now to preface, this car has had this misfire for years. Earlier this year i found my a9l ecu burned out causing a nasty rough running condition and lean conditions. I replaced it with ms3 gold box and tuned it pretty well via speed density for street use and it started to idle properly for once other than these little pops that seem to be getting worse. intermittently mainly at idle and they happen very little through like 1500 rpms. It pulls great under wot and feels great under load cruising no misses. All new wires plugs and cap and rotor. Coil is still original I tested the spark with a spark spark plug opened the gap way up and spark seemed ok. Not crazy intense like an msd coil but seems ok. Or the old 19lb injectors not doing to well? Vacuum tests great all the vacuum lines are brand new no leaks anywhere. Fuel pressure is good. It also runs very rich. Afr 12 to 12.8 at idle. I tried to lean it out in fuel tables and the pops got significantly worse and throttle response was awful in lower rpms? Like leaning it out made the misfire worse or more noticeable. So I left it rich and seems to run well aside from carbon in everything building up. Compression is around 165 to 170psi all around although it has been burning some oil little blue smoke here or there. I’m stumped. it’s not like it’s stalling or undrivable at all just want it to idle smoothly for once and
figure this Out. I’m thinking Got to be weak spark or failing injectors? Any ideas on something I missed or looking over?
 
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Monkeybutt2000

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Had an 87 lx years back,had a funny idle issue I could not get rid of. Bit the bullet and ordered new injectors. BAM, problem fixed. However,you say you replaced sensors. Did you test them before install? I put a new ect sensor in my car,and it ran rich and reeked of gasoline at idle. I tested it and it was dead,new piece of :poo: right out the box. Ordered another,tested it and it was good to go,problem solved.
 
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James408

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May 18, 2020
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New York
Had an 87 lx years back,had a funny idle issue I could not get rid of. Bit the bullet and ordered new injectors. BAM, problem fixed. However,you say you replaced sensors. Did you test them before install? I put a new ect sensor in my car,and it ran rich and reeked of gasoline at idle. I tested it and it was dead,new piece of :poo: right out the box. Ordered another,tested it and it was good to go,problem solved.
Yeah chasing misfires can be a nightmare im learning. But yeah all my sensors checked out ok tested with dmm and there values in tunerstudio look good too. Im really starting to think injectors too being i never replaced or had them tested now,that i think back. Plus they are from a 1989 lx 5.0 lol. Good to hear injectors fixed your problem though because I'm,really thinking of getting some new 36lb injectors for full hci combo.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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The best way to make a problem harder to diagnose is to toss aftermarket parts on it. And then throw more stuff on it hoping to accidentally fix it. Without know basic stuff like timing, valve adjustments and the like all I can do is ask do you have a data log one of our tuning members can look at.
Also I would advise not to run the engine (you did indicate it it a new build) rich do to cylinder wash that can cause premature wear.
 
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James408

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May 18, 2020
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The best way to make a problem harder to diagnose is to toss aftermarket parts on it. And then throw more stuff on it hoping to accidentally fix it. Without know basic stuff like timing, valve adjustments and the like all I can do is ask do you have a data log one of our tuning members can look at.
Also I would advise not to run the engine (you did indicate it it a new build) rich do to cylinder wash that can cause premature wear.
Thank you for the advice. I got to get a fesh datalog and yeah a bad habit of impulse buying parts to throw at an issue I basically get frustrated sometimes and hope for the best. It is a stock 80k mile bottom end but 500 miles or so on tw 170 heads and cobra intake, still stock cam. Runs pretty good other than this low rpm miss but yea I could really use someones help who has tuning knowledge see if I may have botched anything. Im gonna try and attach my tune file. if anyone who has good knowledge of this and can take a look see if I messed up would really appreciate that. I did the basic stuff locked timing to 20 on the dizzy. Calibrated my coolant temp sensor, tps, and adjusted values to get it idling ok but cold starts are a pain have to hold throttle because no iat. Only thing I could not get working was my idle air control so adjusted fuel and timing some to run off throttle stop only. I also use tune analyze live a lot so maybe that's not best bet right now?
 

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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
20,149
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polk county florida
Thank you for the advice. I got to get a fesh datalog and yeah a bad habit of impulse buying parts to throw at an issue I basically get frustrated sometimes and hope for the best. It is a stock 80k mile bottom end but 500 miles or so on tw 170 heads and cobra intake, still stock cam. Runs pretty good other than this low rpm miss but yea I could really use someones help who has tuning knowledge see if I may have botched anything. Im gonna try and attach my tune file. if anyone who has good knowledge of this and can take a look see if I messed up would really appreciate that. I did the basic stuff locked timing to 20 on the dizzy. Calibrated my coolant temp sensor, tps, and adjusted values to get it idling ok but cold starts are a pain have to hold throttle because no iat. Only thing I could not get working was my idle air control so adjusted fuel and timing some to run off throttle stop only. I also use tune analyze live a lot so maybe that's not best bet right now?
Get over to the digital tuning forums and ask for some help, post the data log, wait, let me ask @a91what do you want to just move this thread over to the digital tuning forums?
Or is this member helpless :jester:
 
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James408

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Shiiit... if I’m helpless with this ecu stuff I’ll just convert to carb and sell all my Efi/ecu stuff to someone smarter lmao seriously though it probably is better moved to tuning forums at this point lol
 

a91what

SendMeUrDataLog
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I will get it moved over to the tuning forum. You say you cannot get the idle valve to function properly so a test of the output will need to be run. A stock cam car should be very easy to tune [relatively speaking if there is not a mechanical issue]. A datalog of the problem will go a long way for me to give you advice.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
A carb swap is not as simple as one would think.
Keep the aftermarket ecu, it can be dealt with, it is a step up from the stock ecu, it's just a learning curve.
I will say if the same problem exists after swapping in the aftermarket ecu than it's likely a wiring problem, that can be dealt with also, just have some patients
 
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a91what

SendMeUrDataLog
Mod Dude
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Thank you for the advice. I got to get a fesh datalog and yeah a bad habit of impulse buying parts to throw at an issue I basically get frustrated sometimes and hope for the best. It is a stock 80k mile bottom end but 500 miles or so on tw 170 heads and cobra intake, still stock cam. Runs pretty good other than this low rpm miss but yea I could really use someones help who has tuning knowledge see if I may have botched anything. Im gonna try and attach my tune file. if anyone who has good knowledge of this and can take a look see if I messed up would really appreciate that. I did the basic stuff locked timing to 20 on the dizzy. Calibrated my coolant temp sensor, tps, and adjusted values to get it idling ok but cold starts are a pain have to hold throttle because no iat. Only thing I could not get working was my idle air control so adjusted fuel and timing some to run off throttle stop only. I also use tune analyze live a lot so maybe that's not best bet right now?
are you sure this is the tune you are running on? I see that it is set for a 5 cylinder engine and using a firmware that to my knowledge is not for the goldbox.
 
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James408

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Damn I think I hit a example file. this should be it and its snowing here now so will have to grab a datalog from idling and low rpms. will at least show rich idle condition.
 

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a91what

SendMeUrDataLog
Mod Dude
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From a quick glance at the tune..

The AFR table is not setup for a street car, you are targeting 13 afr at idle thats rich

The VE table is not scaled properly for an NA car.. it is scaled for 30psi of boost and only has a third of it allocated to NA.

your req fuel is setup for the stock injectors I believe you said you have 30lbers in the car

the ignition table is not setup for a SBF and is commanding too little timing under load and is not scaled properly for a streetcar

the idle valve is not working because it is set to the wrong output, it should be set to idle or fidle depending on the hardware, yours is set to nitrous.

again I am sure there is more but this was the first glance
 
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James408

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May 18, 2020
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From a quick glance at the tune..

The AFR table is not setup for a street car, you are targeting 13 afr at idle thats rich

The VE table is not scaled properly for an NA car.. it is scaled for 30psi of boost and only has a third of it allocated to NA.

your req fuel is setup for the stock injectors I believe you said you have 30lbers in the car

the ignition table is not setup for a SBF and is commanding too little timing under load and is not scaled properly for a streetcar

the idle valve is not working because it is set to the wrong output, it should be set to idle or fidle depending on the hardware, yours is set to nitrous.

again I am sure there is more but this was the first glance
Whoa I really overlooked that VE table being setup for so much boost and the timing too. The original tune from efisource that came on the ecu was setup for a 363. they said it had a stock 5.0 tune but it definitely didn't seem like it but I get very lost when it comes to actually tuning. Mainly let tune analyze live do the work. Its probably why its afr and fueling is way off for a mild 5.0. I am currently running 19lb injectors I meant to say had some 30lbers i want to install in the future but not until i have a good matching combo. Just grabbed a cold start datalog and ran it through warmup to about 180 degrees its cold out so took a while, Also got one with a few revs don't know if they would be any help without driving but the weather isnt cooperating at the moment. The once that shows 8:55 is the datalog of few light throttle revs and wot blips. The one with 8:35 is cold start warmup. At idle I`m nasty rich it seems afr averaging 12s. Is there any NA 302w street friendly ignition and fuel tables I can take a glance at? Just so can get a general idea where I need to go with the tables.
 

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James408

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Well I took a look at the tune did some adjusting and its in need of some reworking for sure but I’m currently waiting better weather a storm just passed through and salts everywhere now. As far as the misfire goes I’m really beginning to think it’s mechanical still but what is the question. I tried leaning it out tried sweeping timing no effect. Maybe spark or fuel don’t know yet but I’m slowly gonna diagnose and test sensors and stuff again weather depending. Here’s a video I took of how it runs so you can hear those misses are bad enough to cause concern but not as bad as could be. View: https://youtu.be/VoK4ltLkvEQ