Odd fart/"Brrrrrrat" sound then timing got ugly (JB4)

[Mr. Tech]

Hey guys, I finally got my timing fixed on my AWD Stinger GT2 running Map 2, then, during a launch control pull down a hill with a low tank (~45 miles left) I hear a fart/"Brrrrrrat" type sound almost immediately after lifting my foot off the brake that lasted about half a second. I got a mediocre 0-60 time, then looked at my logs (attached) and saw that my timing had a huge deviation on all cylinders. The previous few pulls (different days with more fuel in the tank) had almost 0 degrees deviation on all cylinders through the entire run.

Some other useful info, I've been running 93 octane with Lucas oil octane booster for two full tanks before this run. This was the end of my third tank with octane booster. I was doing this to guarantee that octane wouldn't be the issue while I was fixing my timing.

JB4 Map 2, DIY intakes, new Denso plugs gapped to .022 (about 600 miles on the Denso plugs).

I'm guessing it's just because I had a low tank and was on a hill so I couldn't get enough fuel to the cylinders.

I'm just going to stop launching on low tanks and I'm sure it'll be fine, but if anyone else has any other input, I'm all ears.

 

[Terry@BMS]

Fuel pressure seems fine in the log so your guess is as good as mine as to what you were actually hearing.

 

[Mr. Tech]

Fuel pressure seems fine in the log so your guess is as good as mine as to what you were actually hearing.

Thanks for the feedback, Terry! That's interesting. Did you see anything in the logs, outside of the bad timing, that would hint towards anything?

Hopefully it was still, somehow, low fuel related. Not sure what else it could have been. It certainly screwed up my timing, though. Prior to this sound, every run had near perfect timing, with only a deviation in ign1, which, from what I understand, is pretty normal. Below is a snapshot of what my logs looked like before this sound. Every run after the sound has had crazy timing, but no odd sounds. I'm guessing the ECU still needs to learn the timing again. I'll force the issue with an ECU reset tonight to get right back to normal timing. For now, I'll just avoid low fuel launches and see if that "fixes" the issue.

If anyone else has had a similar thing happen, I'd love to hear about it.

 

[Terry@BMS]

Timing looks normal for lower grade fuels, a couple drops in a couple cylinders throughout the run. Bad timing would have every cylinder stepping down relative to RPM.

 

[Mr. Tech]

Timing looks normal for lower grade fuels, a couple drops in a couple cylinders throughout the run. Bad timing would have every cylinder stepping down relative to RPM.

Hi Terry, I just noticed something else, my timing has gone UP, a couple degrees in most cylinders. My previous peak was 14-15 in 1st gear and 15-16 in second gear (see attached log). But since the sound, my timing has a peak of almost 19 in 1st gear and 18 in second (see the log I already posted). Only ign3 has a lower value than the what it used to be. Have you ever seen a random, significant INCREASE in ign?

Edit: "Timing looks normal for lower grade fuels" I was using Shell 93 with Lucas oil octane booster in both logs.

Edit 2: I just noticed that my boost is much lower in the higher ignition timing log. Down to about 12 instead of the usual 15-16.

 

[Mr. Tech]

Just noticed another log with a dip in boost in 3rd gear before recivering (attached). This was a run taken sometime after the odd sound. Lots of interesting things going on...

 

[Terry@BMS]

Boost and timing are also mapped on ambient conditions, expect to see less boost and more timing during colder weather, for example.

 

[Mr. Tech]

Oh, interesting. I didn't realize that about temperature. But the IATs were the same between the run that was just a day before with much higher boost, but lower timing.

Also, any thoughts on boost reaching peak, then dipping a few psi before recovering in 3rd gear? (see the log from my last post).

 

[Terry@BMS]

In terms of the JB4 end it's doing what it should be doing there. If boost is bleeding off between shifts intermittently perhaps one of the diverter valves isn't fully closing/sealing.

 

[Mr. Tech]

Thanks for the diverter valve suggestion. I'll keep an eye on my logs, and if it keeps happening, I'll look more into that.

Also, just an update for everyone else. After almost 200 miles and 8 to 10 pulls later, my timing and boost levels are mostly back to normal.

If anyone else has heard a similar sound, I'd still like to hear about your experience though.

 

[Adamdan]

Hey guys, I finally got my timing fixed on my AWD Stinger GT2 running Map 2, then, during a launch control pull down a hill with a low tank (~45 miles left) I hear a fart/"Brrrrrrat" type sound almost immediately after lifting my foot off the brake that lasted about half a second. I got a mediocre 0-60 time, then looked at my logs (attached) and saw that my timing had a huge deviation on all cylinders. The previous few pulls (different days with more fuel in the tank) had almost 0 degrees deviation on all cylinders through the entire run.

Some other useful info, I've been running 93 octane with Lucas oil octane booster for two full tanks before this run. This was the end of my third tank with octane booster. I was doing this to guarantee that octane wouldn't be the issue while I was fixing my timing.

JB4 Map 2, DIY intakes, new Denso plugs gapped to .022 (about 600 miles on the Denso plugs).

I'm guessing it's just because I had a low tank and was on a hill so I couldn't get enough fuel to the cylinders.

I'm just going to stop launching on low tanks and I'm sure it'll be fine, but if anyone else has any other input, I'm all ears.

View attachment 31842

You mentioned you had a timing issue you fixed. What ended up fixing it?

 

[Cyrus Duong]

If I understand correctly I think he means just doing some hard pulls to let the ECU recalibrate/adjust the timing. It's a dynamic ECU that will add/remove timing to achieve the best possible performance & efficiency depending on a lot of factors - mainly considering the knock sensors I would guess though.

 

[lun471k]

Boost and timing are also mapped on ambient conditions, expect to see less boost and more timing during colder weather, for example.

What are the JB4 working conditions considering variation in temperature ? Will the car work fine at -40C (-40F) this winter with a JB4 installed ?
(Sorry if I'm slightly off-topic)

 

[Mr. Tech]

You mentioned you had a timing issue you fixed. What ended up fixing it?

Sorry for the delay, I'll be putting together a longer write-up with logs a bit later, but it boils down to my spark plugs. I confirmed with Denso that I may have gotten knockoff plugs. Unfortunately, they can't tell for sure because the knockoffs look so much like theirs now. They said to buy direct from Denso if I wanted to be sure, so I did. When I replaced my old plugs, I noticed that some of them had scarring on the top electrode that was caused by the cheap gapper I used. I bought a more expensive gapper with a rounded screw and used that to gap down to exactly .022 on all 6 new plugs. Since putting in the new plugs, and resetting the ECU (unplugged battery for at least 30 minutes), the logs had almost no deviation.

I still think that the issue I ran into here, with that "brrrrattt" sound, was related to low fuel and possibly the octane booster. I'm now on my second tank of regular 93 octane (with no octane booster) and my logs are completely back to normal (almost no deviation between cylinders).

 

[Cyrus Duong]

I also used a cheap gapper to gap my plugs and I'm seeing some deviation (only 1-3 degrees max between all cylinders). Hopefully, the deviation isn't due to the tool... If anything happens as it did to you, I might need to consider new plugs and a proper gap tool from BMS. Luckily nothing yet.

Glad to hear it's worked out.