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Strange low throttle surging / severe lag
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10-05-2017, 12:28 PM | #1 |
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Strange low throttle surging / severe lag
Guys, trying to figure something out and so far unlucky.
When I'm driving I get this strange pulsing "tug". Its very small but feels as if the car power jumps, then dies, then jumps and dies. It almost surges forward and power drops out, surges forward, power drop. Sort of almost like the sensation of hitting fuel cutoff then it kicks right back in. Or something along the lines of bucking that you get when you don't engage the clutch correctly, just not as severe. It happens in almost any gear 1-4 at low throttle. Its so small and quick it doesn't toss any lights, or errors when I scan. Its at the rate of almost 2 a second. Once you get into the higher RPM range on 3rd gear and above its less noticeable. 1st and second gear in almost any RPM range its very noticeable. 3rd and 4th anything below 2500RPM or so and you can still notice it. If I hold it at 2k RPM, the car feels like I am lightly pushing up and down on the throttle, but the RPMs never fluctuate. - HPFP, low pressure sensor, high pressure sensor and 6 index 12 injectors just installed last week (it was doing this before replacement, I was hoping this would correct the issue, and long cranks. Long cranks have since disappeared) - Plugs were changed about 2 years ago, before I tuned anything. - I don't know when/if ever the coils have been changed. - Walnut blast last year - New battery last year - New thermostat and pump last year - New OFHG last year I have a pretty significant amount of oil in the entire intake track. Throttle body had it spilling out, it drips out of my CP everytime I take it off, and the sensor is usually covered in it (the boost pressure sensor sits snug in the CP, but the clip on it was broke by previous owner). The BOV you can always see a ring of oil around the valve on the front from blow-by. I also have an issue where I am not hitting boost targets until 4000RPM. I've checked all lines and replaced with new platinum silicone with the exception of the ones on the wastegates. Solenoids checked out fine, and hold vacuum. I'm just throwing this information out there to see if it could tie into anything else. My feeling at this point (due to the horrific rattle) is that they are on their way out, and may be contributing to the lag. Mods Stett CP, Synapse BOV, JB4 G5, BMS DCI. Anyone have any thoughts or ideas? |
10-24-2017, 08:18 AM | #3 | |
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I literally am just about to check out from ECS with new sets of plugs, coils, PCV valve, and OCC. The amount of oil in the intake track is ridiculous. It coats and slightly seeps out the front of the Synapse BOV. That just seems like a ton of oil. I can only imagine what the IC looks like. I'm hoping it just needs new plugs/coils and that's it, but knowing this thing, it's going to throw me another curve ball. After I just dropped $1400 to do HPFP and all 6 injectors it still runs like shit. |
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10-24-2017, 10:08 AM | #4 |
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Try to log it happening at light throttle. Hold accel pedal as steady as you can. Does it do it under cruise control too?
Also do a WOT log to show boost profile. Reset adaptations and see if things change. Post logs in datazap and link here and we'll take a look! Chris |
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10-24-2017, 10:33 AM | #5 | |
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I haven't checked cruise control. But I can recreate it all day everyday in 3rd gear at 2k RPM. It bucks on and off, like I said, feels almost like a fuel cut and then back on. If I hold steady at 2k it will continue the same on-off, on-off the entire way. WOT on mine is bad news. I have been trying to track down a supposed boost leak, but haven't found anything. I never reach target until about 4k. (We may need to speak about turbo replacement, but having these other issues is preventing me from seeing if it is truly just busted turbo. But gas mileage is good, no smoke, and minimal rattle with updated JB4 FUD) I reset all adaptions after changing out the HPFP, Low and high pressure sensors, and all six injectors. |
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10-24-2017, 11:02 AM | #6 | |
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Don't want to thread jack, so I'll point you over there. I'm wondering if you have any clue where my surging is coming from. My post is the last post, #1477. |
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10-24-2017, 02:23 PM | #7 |
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Chris,
Here is a log from about a month ago. Basically showing how severe the spool lag is. I'll try and get another one with the steady 2k RPM run and post that next. https://datazap.me/u/milfriez/91817?...data=1-3-4-5-8 |
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10-24-2017, 04:28 PM | #8 |
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I solved my problem! The spark plugs helpped but adjusting the user adjustments in the jb4 got rid of my surging. I would check your menu settings for 10,11, and 12 and see what they are at.
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10-25-2017, 12:30 AM | #9 |
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When I had a similar issue, I had to go into bav technic and reset everything except throttle. This problem popped up after I switched to MHD from Cobb; car was fine on Cobb. The reset helped, although the surging is back now several months later (goes away again upon reset of everything). I think it's something in MHD that's different. I'm not sure why this is.
Chris |
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10-25-2017, 07:40 AM | #10 | |
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This morning, driving in though, it seemed to be a lot more calm. It could be due to air temps being in the 40s though and the engine/oil taking longer to warm. Once back at 225F or so, the good old stutter seemed to return. @Chris I can even notice it when accelerating in first and second gear, that it is jerking while accelerating. I tried logging steady throttle, but JB4 wouldn't show anything. I know there is a setting somewhere to log when its not WOT, but couldn't find it at stop lights I'll post my datazaps from this mornings quick pulls to see if it gives any small indication of anything that could be adjusted. |
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10-25-2017, 10:23 AM | #11 |
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Yep, low throttle angles. Here was steady state second gear, 33 mph log showing my A/F spikes and the pulsing. This made the car irritating to drive.
Chris |
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10-25-2017, 12:24 PM | #12 |
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I'd like to note that my surging was and is still present on my stock bin, I flashed back to stock yesterday to troubleshoot this. RSL on the MHD log thread has suggested I swap the intake and exhaust solenoids, which I'm planning on doing to see if it makes a difference.
Chris, that seems very similar to my car. |
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10-25-2017, 12:43 PM | #13 |
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If you have a JB4 uncheck log wot only you log it but often lowering menu 12 is all you need to do. Default is 2800, you can try as low as 1800.
Mike |
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10-25-2017, 03:14 PM | #14 | |
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I was looking for that setting all over the place previously but couldn't find it. There is a setting under Data Logging--> X-Axis --> "Log Heavy Throttle Only" Is that the setting I need to uncheck? |
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10-25-2017, 09:30 PM | #15 | |
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10-26-2017, 12:17 PM | #16 | |
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Menu 10 is set to 3500. Yesterday driving home, I couldn't replicate the jerking. This morning though, the second I pulled out of the driveway it was bucking. It doesn't have a pattern, and doesn't always do it, like the cyclical pulse of the JB4 settings. It is more of a power loss and then right back on. In 4th gear at 1500-2k I could make it jerk non stop, but still no codes. I have a feeling mine is related to either ignition, or fuel, but I just replaced the HPFP and all 6 injectors. I have not read any articles on LPFP going bad, just stuff on upgrading when running E85. But it feels just like it's not getting enough fuel, then jerks, then starved, then jerk forward. But RPM's are not bouncing and no codes. I'm going with new plugs/coils and see if that has any effect. I'm hoping it's not something stupid like one of the injectors or HPFP was faulty from the box, but I would expect codes if that was the issue. I still get the "Fuel Pump Plausible" code, but I've learned that's basically just a tuner code. Has anyone ever had to replace their LPFP because of poor performance, that wasn't due to running E85? I've heard things about LPFP can potentially cause the HPFP to fail. So if I just replaced the HPFP and still having issues, wondering if the LPFP needs attention? But it's just a theory at this point. |
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10-26-2017, 12:25 PM | #17 |
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10-26-2017, 12:50 PM | #18 | |
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Try these settings i found from a member of the n54tech forum that helped me. Did the surging come on randomly? I noticed mine after doing my dp, i heard it before but didn't think anything of it until i took the dp out and it was a lot louder.
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10-26-2017, 03:06 PM | #19 | |
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I fixed the long starts, and haven't gotten a half/engine light yet, but it brought on these strange misfire-esque, jerking movements. If all else fails, I still have plugs/coils coming this weekend hopefully. |
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10-27-2017, 12:27 PM | #20 |
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Well this morning, after the car started bucking again on the way in to work, I changed JB4 to MAP0. The poor driving still existed, which leads me to believe it is not a problem with the JB4, but a mechanical issue.
Coils/Plugs won't arrive until Monday now, so I guess I'll check this weekend to see what condition they are in, and then possibly replace next week. |
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10-27-2017, 10:34 PM | #21 | |
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In MHD, there is a setting for non standard 02 sensors that could be used for single turbo. If you run the car with that setting, it will exhibit "similar" bucking... Just a thought.
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10-29-2017, 07:41 PM | #22 | |
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Something to add today. Much colder out today, engine wasn't very warmed up, and I was holding RPM in 4th gear, there was a sudden BOOST and SHARP drop off. Not a back and forth motion, but as dumb as this sounds, almost like a NOS shot for a second, then just died. Its really making me feel like something is just not measuring correctly and is messing with values. Which values? I couldn't tell ya, fuel pressure? ignition? AFR? boost? Could symptoms like this be from dirty/contaminated MAP sensors? Like I said, it seems like all this bucking was exasperated after replacing HPFP, low pressure sensor, high pressure sensor, and injectors all at once. |
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