Spark plug woes on an EFI 2.7

[MrBonus]

My car has always been a hard starter in general since I've had it. Not terrible, but it would frequently take 2-3 attempts to get it to idle. This past winter, I went from Webers to a full EFI, coil-on-plug, ECU Masters setup which is fantastic. However, it still struggles with fully cold starts (i.e. sitting 24 hours or more). Warm starts, even after sitting 4-5 hours, are no problem whatsoever.

Once it has run for 30 seconds and has some heat in the heads, it would idle and run completely fine, just like a modern car. Before it has any temp, a lot of stumbling and some restarting.

Reviewing my records, the car has had the same plugs in it since 2004. They're Champion RN11YC4s gapped to .040 (heat range of 11). I texted the installer/tuner and he recommended I try NGK 6637s (a hotter plug) to alleviate my cold start issues. Now, to add context, I was starting the car wrong post-EFI conversion (giving it too much throttle) and without question partially fouled the plugs as a result. I let them dry off then gave them an Italian tuneup and they have performed fine otherwise, but decided now is the time for new plugs.

Anyway, I installed the 6637 (gapped at .032; heat range of 6) and it's running like my car did after fouling the prior plugs. Very rough, struggling to idle, major throttle stumble and delay off idle. I double checked my coil plugs were on tight and I was certain the plugs were tight in their hole when installed.

Do I just go get another set of RN11YC4s and call it a day? Or should I try a different plug?

I have a hand written build sheet for my 2.7 (from a '77) motor from the mid '90s but it's barely legible. I don't know my exact compression ratio or cams, but I can see Mahle S pistons and can confirm the car made 160 whp on the dyno. I'm not sure this is of any use.

Thanks for any help!

Update: Fixed it. 6637s run like a champ.

[fanaudical]

My 2.7 (mostly stock-ish and running CIS with the stock distributor and CDI) likes NGK BP6ES plugs at 0.032" gap. These are standard plugs, same heat range but no resistor as your iridium plugs.

My opinion (which could be wrong) - At 160 whp, you're probably not running much more compression than stock.

I would try going back to a standard copper spark plug and see if there is a difference (NGK BP6ES or the BPR6ES if you need the resistor).

Are you sure it's a spark issue? How much fuel is the EFI providing at cold start-up/idle?

[MrBonus]

Originally Posted by fanaudical

My 2.7 (mostly stock-ish and running CIS with the stock distributor and CDI) likes NGK BP6ES plugs at 0.032" gap. These are standard plugs, same heat range but no resistor as your iridium plugs.

My opinion (which could be wrong) - At 160 whp, you're probably not running much more compression than stock.

I would try going back to a standard copper spark plug and see if there is a difference (NGK BP6ES or the BPR6ES if you need the resistor).

Are you sure it's a spark issue? How much fuel is the EFI providing at cold start-up/idle?

No, I'm not, but it seemed like low hanging fruit given the issue has been the same from carbs to EFI. I'm not sure regarding how much fuel; I'll need to ask the installer. I'm very much a novice with all of this so I'm kind of clueless with picking plugs.

Thanks for your input! I agree on the compression comment. I am guessing it's stock or close to it.

[pampadori]

With ITBs i assume you don't have any idle control valve. For cold starting, you need a lot more fuel than you'd need after there is some heat in the motor. Can you play around with enrichment tables and fuel trim tables to try and test if it likes more fuel or not when cold? Without an idle control valve you will need to give it about 1-3% throttle for the first 20-30 seconds of running.

I don't know about your ECU masters setup, but with my AEM there are a ton of tables that are only active during cranking and cold start/idle. The other thing i've experienced is the time to fire is dependent on the settings within my crank/cam sync section. It won't fire the injectors or coils until it makes XXX degrees of rotation and sees sync. You can make some changes there and get it to fire a full second or more sooner. But i'm not sure if these settings/tables are AEM specific or not. Maybe something similar exists in ECU Masters.

Another detail to mention - in order for my setup to have a nice 900RPM idle when fully warmed, it only has about a 600-700rpm idle with the same setup when cool. (the fuel atomizes so much easier when some heat is in the engine/intake)

[MrBonus]

Originally Posted by pampadori

With ITBs i assume you don't have any idle control valve. For cold starting, you need a lot more fuel than you'd need after there is some heat in the motor. Can you play around with enrichment tables and fuel trim tables to try and test if it likes more fuel or not when cold? Without an idle control valve you will need to give it about 1-3% throttle for the first 20-30 seconds of running.

I don't know about your ECU masters setup, but with my AEM there are a ton of tables that are only active during cranking and cold start/idle. The other thing i've experienced is the time to fire is dependent on the settings within my crank/cam sync section. It won't fire the injectors or coils until it makes XXX degrees of rotation and sees sync. You can make some changes there and get it to fire a full second or more sooner. But i'm not sure if these settings/tables are AEM specific or not. Maybe something similar exists in ECU Masters.

Another detail to mention - in order for my setup to have a nice 900RPM idle when fully warmed, it only has about a 600-700rpm idle with the same setup when cool. (the fuel atomizes so much easier when some heat is in the engine/intake)

You are correct that there is no idle control valve. However, the issue I'm having when it's bone cold is that any application of throttle would cause it to stumble and die pretty quickly until the 2nd or 3rd start. Then I can give it some light throttle until it will hold idle.

[MrBonus]

Update: Someone, who will remain nameless, checked all of the coils but not the plugs themselves, and the #4 plug wasn't fully seated. Checked the other 5 as a precaution and they were fine. Car is now running better than ever and fired up like a nearly new car.