Hey guys, I recently picked up a real clean 04 Redfire Coupe with 24k on it. The car has a lot of the typical bolt on mods-ported Eaton 2.76 upper only, 60lb injectors (unsure of the fuel pumps), JLT RAI, off road x. It had been tuned but I bought it from a dealer and there was no device or info on who tuned it. It runs really well except for a misfire/stumble at low rpm and really light engine loads. Holding it at 1800rpm in neutral is when it’s the worst. It will pop as it misfires while idling but not as bad. Under higher loads or WOT there is no issue at all and it runs hard. So far I have put in a new fuel filter, checked fuel pressure with a gauge at the rail and with an SCT X4,(pressure drop across injectors), cleaned the MAF and IAC, installed new autolite XP103 plugs gapped at .32, and installed new motorcraft coils. I also did a compression test when I did the plugs/coils, and I’ve searched for vacuum leaks. Do you guys think the tune being slightly off could cause this? One thing I tried to say was disconnecting the DPFE, which made no change, but I did notice when I disconnect the TPS it changes the misfire/stumble-it raised the rpm where the issue happens from idle to 2000rpm to around 2000-3000 rpm with the worst being at 2500. I was watching the spark advance on an unmarried X4 I have and it seemed to me like when the timing hit around 48 degrees or highly it would start to misfire. (I know the time can be advanced really high at light engine loads but 48-50 degrees seems like A LOT. Is there anything else you guys think I should try before I start remote tuning with someone? I searched a read a lot of posts about these cars (especially when modified) having a low rpm stumble like this but I never could figure out why mine is doing it. My old plugs I pulled out were TR6s which I had read some people had rough idle issues with which was why I switched to the XP103 autolite plugs. One thing I suspect is maybe it was tuned for 93 and I have 91 in it because thats all I can get in my area. I have not heard or felt any detonation at WOT though and I’ve been really cautious of that since I don’t know who tuned it. Sorry for the long post, just want to get the car running right so I can enjoy it. I had a mystichrome coupe about ten years ago and regretted selling it ever since. Glad to be back in a Terminator and want to make it last. Thanks guys.
Low RPM Light Load Misfire/Stumble
- Thread starter Smoke92
- Start date
Stop beating on it and reach out to a tuner. A lot of times dealers flash the car back to stock. That will cause issues if you have an aftermarket MAF. Chances are things aren't great at WOT, you just can't feel it. And if you don't have one, get a wideband ASAP.
And I'd switch to copper plugs. Platinum plugs aren't recommended for boosted applications.
And I'd switch to copper plugs. Platinum plugs aren't recommended for boosted applications.
Yeah, get some TR-6 plugs. Pretty sure I have mine gapped at .028. You should see about 18 degrees advanced max at wot on that 91 fuel. 93 can go a tad higher.
I don’t think it was flashed back to stock since it has no cats and there’s no codes being thrown for that. The fuel trims short term and long term look good so I don’t think it’s too far off but I am going to have it retuned for sure. I just want to make sure if this issue is fixed (if it can be first) before I do remote tuning so I’m not trying to make whoever does it working in circles because some thing is wrong on the car. Do you guys recommend the TR6 or the TR6IX plugs? I had just searched the forums and came up with some posts of guys saying they had TR6s and it caused some issues like I was experiencing so that was why I changed to those autolite plugs. Obviously that wasn’t the cause though. Also, I did remote tuning on my S550 in the past with JDM and they took good care of me. I was thinking of going with them again but just curious If there are any other good recommendations for that. Also, I’ve only had it WOT in 2nd twice, once before I bought it and once after I did the plugs and coils etc. I totally agree with you about not beating on it until it’s tuned properly. Don’t want to risk hurting it or anything since it seems be a really solid engine that hasn’t been abused.
The XP103s are an iridium plug. Are those a no go or do iridium plugs work well on these cars? Thanks.
My bad. I thought the XP were the platinums. I've never run iridiums. Some have good luck with them. I haven't had problems with the copper though.
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