Car runs worse after MSD coils and sparkplug change??

[mike2225]

So a few weeks back I changed out my coils and plugs and havent really driven the car since, Ive been using my girlfriends car mostly for work and errands.. I took the SHO out yesterday and drove a little over 100 miles mostly on the highway. At lower rpms and low boost it runs fine but I noticed the car ran rough at WOT and it was noticeably slower.. For the past 3 years Ive been using sp42s gapped at .028 but decided to switch to the newer plug M-12405-35T since it seems most people are using these now.. Has anyone had any issues like this when swapping out to MSD coils and/or different plugs?

[TopherSho]

Was it tuned with a sct4x ?  See what the spark value is when you are wot in 2ns gear... And see what the turbo pressure is.


When I installed mine I only saw a minimal benefit. And no spark level differences under my AJPTurbo tune.

[Macgyver]

AJP tuned when I had my 2015 SHO. He said just use the OEM plugs. He never saw data logs to say yeah SP42s are so much better when you are not Modding with higher boost etc and just pretty much straight tuning.

Had a 93 tune. E30 tune and a E85 tune.

Try the OEMs maybe ? Gapped accordingly of course.

[mike2225]

Was it tuned with a sct4x ?  See what the spark value is when you are wot in 2ns gear... And see what the turbo pressure is.


When I installed mine I only saw a minimal benefit. And no spark level differences under my AJPTurbo tune.

Yes on the sctx4, I have a 93 tune from AJP and have been running it for 3+ years using sp542s and the car has ran excellent ever since.. I'll record some datalogs later today hopefully and compare them from the original ones and see if there is any difference in spark or turbo pressure

[mike2225]

AJP tuned when I had my 2015 SHO. He said just use the OEM plugs. He never saw data logs to say yeah SP42s are so much better when you are not Modding with higher boost etc and just pretty much straight tuning.

Had a 93 tune. E30 tune and a E85 tune.

Try the OEMs maybe ? Gapped accordingly of course.

I have a feeling its the spark plugs, so im thinking of switching back to the ones I was using before

[TopherSho]

AJP tuned when I had my 2015 SHO. He said just use the OEM plugs. He never saw data logs to say yeah SP42s are so much better when you are not Modding with higher boost etc and just pretty much straight tuning.

Had a 93 tune. E30 tune and a E85 tune.

Try the OEMs maybe ? Gapped accordingly of course.

I have a feeling its the spark plugs, so im thinking of switching back to the ones I was using before

It likely is,  but the logs will point that out if the boost pressure is still the same but you see -3 -4 degrees of spark and or  borderline knock and the spark never ramps up. (I suspect the later)

[ridered74]

I've been running the M-12405's since early last summer. My car runs the same times as with the 542's.


If you had issues immediately after swapping plugs and coils, i would be looking at the connectors on the coils and making sure they are all tight, and if that is not the issue double check the plugs to make sure one of them isn't cracked or the gap is off.

[mike2225]

I did a quick datalog today.. maybe someone can take a look and see whats going on

[TopherSho]

are you spraying meth?

[TopherSho]

Edit .. attaching jpg .. image in post wont scale ??

Here is my 1st reaction,  your spark takes a VERY long time to recover... the vertical red box is the throttle getting floored.. the horizontal is the spark up to the end of the 2nd gear run.  it spends 1/4 of the 2nd gear WOT under or equal to 10' timing.  then slowly increased to 15.. but then flutters between 15-14 degrees.  While at the same time the knock sensor reading begins climbing.

at the same time we see Lambse take a nose dive which prompts my meth question ... if you are running meth there is no way you should be running 10' or less timing for that length of time and my initial reaction is

a) the new coils are HOT, and dropping voltage;  not getting enough voltage from the system and dropping voltage
b) the plugs were not gapped and are VERY open .. like .032  or they got dropped hard in shipping and are way under .026 ..

Swap in the old coils ... 20 minute job and repost a new datalog.

[mike2225]

Edit .. attaching jpg .. image in post wont scale ??

Here is my 1st reaction,  your spark takes a VERY long time to recover... the vertical red box is the throttle getting floored.. the horizontal is the spark up to the end of the 2nd gear run.  it spends 1/4 of the 2nd gear WOT under or equal to 10' timing.  then slowly increased to 15.. but then flutters between 15-14 degrees.  While at the same time the knock sensor reading begins climbing.

at the same time we see Lambse take a nose dive which prompts my meth question ... if you are running meth there is no way you should be running 10' or less timing for that length of time and my initial reaction is

a) the new coils are HOT, and dropping voltage;  not getting enough voltage from the system and dropping voltage
b) the plugs were not gapped and are VERY open .. like .032  or they got dropped hard in shipping and are way under .026 ..

Swap in the old coils ... 20 minute job and repost a new datalog.

Im not running meth, my car is completely stock but with a 93 tune. I gapped all the plugs myself @ .028 before installing them.. Ill try swapping back to the oem coils first and see if that makes a difference. I went ahead and ordered a new set of spark plugs just to switch out incase the plugs are bad, they should be in tomorrow. Thanks for the input

[Macgyver]

Edit .. attaching jpg .. image in post wont scale ??

Here is my 1st reaction,  your spark takes a VERY long time to recover... the vertical red box is the throttle getting floored.. the horizontal is the spark up to the end of the 2nd gear run.  it spends 1/4 of the 2nd gear WOT under or equal to 10' timing.  then slowly increased to 15.. but then flutters between 15-14 degrees.  While at the same time the knock sensor reading begins climbing.

at the same time we see Lambse take a nose dive which prompts my meth question ... if you are running meth there is no way you should be running 10' or less timing for that length of time and my initial reaction is

a) the new coils are HOT, and dropping voltage;  not getting enough voltage from the system and dropping voltage
b) the plugs were not gapped and are VERY open .. like .032  or they got dropped hard in shipping and are way under .026 ..

Swap in the old coils ... 20 minute job and repost a new datalog.

Im not running meth, my car is completely stock but with a 93 tune. I gapped all the plugs myself @ .028 before installing them.. Ill try swapping back to the oem coils first and see if that makes a difference. I went ahead and ordered a new set of spark plugs just to switch out incase the plugs are bad, they should be in tomorrow. Thanks for the input

What plugs ?

[TopherSho]

Edit .. attaching jpg .. image in post wont scale ??

Here is my 1st reaction,  your spark takes a VERY long time to recover... the vertical red box is the throttle getting floored.. the horizontal is the spark up to the end of the 2nd gear run.  it spends 1/4 of the 2nd gear WOT under or equal to 10' timing.  then slowly increased to 15.. but then flutters between 15-14 degrees.  While at the same time the knock sensor reading begins climbing.

at the same time we see Lambse take a nose dive which prompts my meth question ... if you are running meth there is no way you should be running 10' or less timing for that length of time and my initial reaction is

a) the new coils are HOT, and dropping voltage;  not getting enough voltage from the system and dropping voltage
b) the plugs were not gapped and are VERY open .. like .032  or they got dropped hard in shipping and are way under .026 ..

Swap in the old coils ... 20 minute job and repost a new datalog.

Im not running meth, my car is completely stock but with a 93 tune. I gapped all the plugs myself @ .028 before installing them.. Ill try swapping back to the oem coils first and see if that makes a difference. I went ahead and ordered a new set of spark plugs just to switch out incase the plugs are bad, they should be in tomorrow. Thanks for the input

What plugs ?

He mentioned going to M-12405-35T  WITH the new coils.   I just learned to read slower (lol) .. he has them gapped to .028.. he should be good.  This leads me back to Coils and the STFT/LAMBSE readings.

I took a look at my last non meth logs from AJPTurbo,  at no time do i drop to .80 .. I think we need a bigger log like from 3rd gear ..

@Mike2225 - can you safely get a log of a full 3rd gear pull at WoT?  IE 3rd gear at 2500rpm to redline while floored?

[mike2225]

Edit .. attaching jpg .. image in post wont scale ??

Here is my 1st reaction,  your spark takes a VERY long time to recover... the vertical red box is the throttle getting floored.. the horizontal is the spark up to the end of the 2nd gear run.  it spends 1/4 of the 2nd gear WOT under or equal to 10' timing.  then slowly increased to 15.. but then flutters between 15-14 degrees.  While at the same time the knock sensor reading begins climbing.

at the same time we see Lambse take a nose dive which prompts my meth question ... if you are running meth there is no way you should be running 10' or less timing for that length of time and my initial reaction is

a) the new coils are HOT, and dropping voltage;  not getting enough voltage from the system and dropping voltage
b) the plugs were not gapped and are VERY open .. like .032  or they got dropped hard in shipping and are way under .026 ..

Swap in the old coils ... 20 minute job and repost a new datalog.

Im not running meth, my car is completely stock but with a 93 tune. I gapped all the plugs myself @ .028 before installing them.. Ill try swapping back to the oem coils first and see if that makes a difference. I went ahead and ordered a new set of spark plugs just to switch out incase the plugs are bad, they should be in tomorrow. Thanks for the input

What plugs ?

He mentioned going to M-12405-35T  WITH the new coils.   I just learned to read slower (lol) .. he has them gapped to .028.. he should be good.  This leads me back to Coils and the STFT/LAMBSE readings.

I took a look at my last non meth logs from AJPTurbo,  at no time do i drop to .80 .. I think we need a bigger log like from 3rd gear ..

@Mike2225 - can you safely get a log of a full 3rd gear pull at WoT?  IE 3rd gear at 2500rpm to redline while floored?

So I did a 3rd gear pull and it felt aweful. Im going to try and switch back the coils today and do another datalog

[TopherSho]

I'll keep an eye out ..