Vibration/Misfire at High RPM

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BlueReaperX
Posts: 31
Joined: Tue Jun 19, 2018 8:29 pm

Vibration/Misfire at High RPM

Postby BlueReaperX » Tue Jun 11, 2019 8:28 pm

I spent about two weeks hunting for an issue and along the way I might have created a new one. The truck was stalling and losing power at light throttle initially and it was getting worse and dangerous to drive on the road. Trying to fix the issue I have replaced my injectors (ID1300x), spark plugs (NGK LFR7), replaced the O2 sensors and tried another working crank position sensor from a non boosted application (stock ECU, stock motor, etc.). All of which are a direct replacement and didn't require any tune modification except to recalibrate the o2 sensors.

Changing the spark plugs, injectors and o2 sensors did nothing. However, when I installed the crank sensor from the other vehicle, the truck acted normally and didn't stall surprisingly. So I ordered a new crank sensor and 5 minutes after driving the issue came back again almost immediately. We took the transmission out to check if I have a cracked flex-plate (common on this platform at high power levels) or there is an issue with the trigger plate. Everything looked normal so we put everything back again.

Eventually, after looking at the logs closely we noticed vacuum wasn't changing immediately with the throttle pedal. Turns out it was a clogged MAP sensor. I was using liquid nitrogen and forming condensate in my intake manifold. Water + oil = clogged sensor. Replaced with a new one and all is well. Or so I thought.

Cranking, idling, driving all is great. However, I started noticing the truck would lose power at higher RPMs as if 1 or 2 cylinders have stopped working or slightly misfiring as there was a high frequency vibration and sound coming from the engine. It wasn't violent at all, and the truck would still pull like a freight train albeit not as fast as before. Looking at the logs it seemed like the issue was strictly on bank 2 only. Whenever this occurs, bank 2 would get lean (11.5 to 12.5) and it did trigger a "Bank 2 Lean" code a few times. So I thought maybe one of the injectors is bad on Bank 2. I put the old injectors in, no change. Swapped coils one side to the other, no change. New plugs (old ones looked brand new), no change.

Somewhere along the way I noticed that the issue was also happening even while the truck is in neutral. At around 5000-5300 RPM This vibration can be felt and heard coming from the engine and stays all the way to the limiter at 6800. It can be heard very clearly when it happens as if it's on a switch. Below 5000 RPM the sound goes away. This is shown in the logs as a lean spot on both banks however the spike is higher on bank 2. So maybe it's not a single bank issue? I was testing disabling fuel from a single cylinder (using per cylinder correction) and unplugging coils from one cylinder at a time and while revving in neutral the same vibration can be heard in both cases across the rev range. This IMO proves that one or multiple cylinders are misfiring ever so slightly at higher RPMs for some reason. I couldn't identify which as the engine gets really loud at higher RPMs.

I've been looking on this forum for others who have had similar symptoms and almost all seem to point at a trigger/home signal error. Unfortunately, I'll be away from home for a while and I can't test replacing my crank sensor again (but I really doubt it is bad as it's brand new). Removing and installing my transmission again to check if the trigger plate was put back correctly is going to set me back +$500 in labor as well.

For a more clear picture, this is what my trigger plate looks like:
makhovik-3211834010-697180_1 (002).jpeg


36-2 with 10 bolts (36 degrees per bolt).

My TDC was set at 486 degrees by my tuner. With it being a V8 (90 degrees per cylinder?) with a total of 720 degrees, is it possible that my engine would start and fire correctly if the trigger wheel was off by 1 bolt? If so, does that mean my ignition timing table (or TDC) is off by 36 or 18 degrees? 18 would make sense but I think it being 36 degrees off and idles and drives fine is a bit of a stretch. TIA

BlueReaperX
Posts: 31
Joined: Tue Jun 19, 2018 8:29 pm

Re: Vibration/Misfire at High RPM

Postby BlueReaperX » Wed Jun 12, 2019 5:06 pm

I just confirmed that the trigger plate can't be off as it can only be bolted in one way. So I'm back to square one. I'd like to mention that I also didn't get any trigger/home errors at all so the knock sensor being the issue is off as well. Next thing I'm going to try is recalibrating the o2 sensors or get the new Haltech wideband so I don't have to worry about calibration anymore.

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HaltechMatthew
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Re: Vibration/Misfire at High RPM

Postby HaltechMatthew » Thu Jun 13, 2019 10:15 am

Sounds like you are systematically going through everything, but you may have missed some basics.

Fuel Pressure is one. Does the AFR stay constant or near to the Target? You mentioned going lean but this can be either spark or fuel.
And you are certain there are no trigger errors and it stay in sync (Running/Full)?

BlueReaperX
Posts: 31
Joined: Tue Jun 19, 2018 8:29 pm

Re: Vibration/Misfire at High RPM

Postby BlueReaperX » Thu Jun 13, 2019 4:21 pm

Correction, I meant crank not knock sensor in my previous post.

HaltechMatthew wrote:Sounds like you are systematically going through everything, but you may have missed some basics.

Fuel Pressure is one. Does the AFR stay constant or near to the Target? You mentioned going lean but this can be either spark or fuel.
And you are certain there are no trigger errors and it stay in sync (Running/Full)?


Fuel pressure is very stable (first thing I checked) and the pressure sensor is even on bank 2 where it goes lean and trigger is 100% in sync without any errors. AFR is perfect everywhere up to the point when it starts vibrating and missing somewhere around 5000 RPM with and without load. It goes roughly 6-8% lean on bank 2 regardless of load and bank 1 goes 1-2% lean but only without load in neutral or at least it's not noticeable under load.

For clarification, when I'm saying it's 8% lean I mean it needs 8% more fuel on that bank in the LTFT table to stay on target.

I'll try to get a friend to log it for me or send one of my previous logs I have.

Is it possible to be a valve train issue? I broke a valve spring before on another platform and it barely cranked and idled afterwards, granted it was a 4 cylinder FA20 and this is a V8 but there are almost 0 issues idling or cranking and no noise coming from the engine except that vibration at high RPM. And I don't think valve float is possible or extremely rare on a single valve or cylinder, is it?

I would also like to mention that one of the coils shows a hot spot where it could have been shorting. Took that one out and replaced it with a new one and swapped the other 3 on that bank to the other side. There was also a ground strap next to that coil which I removed. The symptoms remain exactly the same. All coils on both banks share the same battery signal and ground so probably not that. The connectors have all been cleaned as well. I checked dwell time and it seems 2.3ms is when it starts vibrating. Lowering it to 2.0 and 1.8 made no difference. Plugs are new as I mentioned and they don't need to be gapped as I have been using them this way for the past 40,000 km without problems and it's clearly not a problem on the other bank and I'm not even running the thing at max boost (25 psi vs Wastegate 14 psi).

One more thing, boost is almost 1 psi off but I'm not sure if it's related to the issue or simple the weather being warm now. I used to get 14-15 psi on the same map but now it rarely goes above 13.5 psi. Boost controller is also adding more duty when targeting higher boost. I don't think I had that issue last summer.

BlueReaperX
Posts: 31
Joined: Tue Jun 19, 2018 8:29 pm

Re: Vibration/Misfire at High RPM

Postby BlueReaperX » Tue Jun 18, 2019 8:32 pm

I checked on the truck last night, recalibrated the o2 sensors, checked on all the wires and other connectors, no sparks flying around or shorts and it still has the same symptoms and the Elite doesn't show any CELs or errors. I'm running out of options and I really don't want to drop the engine to change the valve springs. I found this page that describes my symptoms exactly:

https://www.aa1car.com/library/valve_sp ... gnosis.htm

"Symptoms of Weak Valve Springs

Weak valve springs will typically cause misfiring and a loss of power as engine speed increases. The engine may start and idle fine, or run normally up to 3500 to 4000 RPM. But at higher speeds, it may misfire and lose power because the valves are floating because the springs are weak and unable to keep up with the speed of the valvetrain."

The issue is this engine stock can rev up to 5800 RPM (N/A). I have stiffer springs installed and I barely go over 6500 @ 14 psi while daily driving it and it maybe saw 20 passes at the track at 6700 RPM with 25 psi. Engine has 40,000 km only in the past year. A similar platform (2UR-GSE) has softer springs and those can rev up to 7400 RPM stock. I have a really hard time believing stiffer springs (even if worn out) will float at 5000 RPM.

If we forgot everything and assume it is floating, what symptoms should I see on the log? Vacuum/boost are stable even with boost controller off. When the valve floats would it go lean or rich? As I mentioned before mine goes lean (11.5 to 12.5) on bank 2 at 5000 RPM.

One last thing, I enabled the boost controller last night at 17 psi and in 3rd it would only hit 15.5 psi. As soon as it shifts into 4th it goes up to 17 psi. It is on closed loop though and it added about 5% duty before shifting.


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