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Hesitation, cutting out at high rpm, cannot solve it

 
Old 05-04-2019, 09:12 PM
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Default Hesitation, cutting out at high rpm, cannot solve it

Hello, this is my first post on this forum so I apologize if this is in the wrong section.

I have looked through many, many of the forums attempting to solve an issue I have had for several months, but now I am out of ideas and need to post my own question.

The issue: The engine is cutting in and out at 5500 rpm. The car will rev to 6500 while sitting still, but will not rev out while driving. The ecu has no way of telling of the car is in gear or not. Below is a link to YouTube of the car showing this issue. Map sensor is reading the same as my boost gauge (7psi), afr at WOT when the issue occurs (5500 rpm) is 12.8. I have it tuned for 11.0 afr, 14 degrees timing, and 14 lbs of boost at 6250 rpm. The car currently is at 7 psi of boost until I get this issue solved.

Youtube link:

Setup: 150k mile Gen 3 5.3, ss2 cam, btr .660 springs, stock everything else. Fitech ultimate LS tuning, 7psi wastegate spring, T56 magnum. Tuned on 93. Bosch 044 fuel pump, 3/8Ē fuel line, deka 80ís at 58psi. Tr6 plugs gapped to .026Ē. 70mm turbo.

What Iíve done to attempt to fix the issue:
New cam and crank sensors
Played with crank shims
Checked fuel pressure (stays at 57-58psi) and filter
Made sure thereís no limits in the tune
Tightened plug gap all the way to .015Ē
Checked all wiring and added more grounds
Swapped coils
New MSD plug wires
Swapped valve springs
Checked pushrods
Free flowing exhaust, 2.25Ē on each bank into 3Ē into turbo

I have found none of these to be the culprit.

One odd thing I have found is if I unplug the cam sensor, it runs exactly the same. I find that odd, but I donít really know what the purpose of that sensor is. The car runs absolutely perfect and has great power up until 5500 rpm and then it cuts out. Afr and map sensors appear to be working as they should. TPS only reads up to 96.5% but I find it hard that it would cause an issue like this.

To me, it feels like a computer issue due to how sudden and repeatable it is, but honestly donít know, it could be anything.

I am absolutely out of ideas at this point and Iím tired of blindly throwing money at it to make it run right. Any input is highly appreciated. Thank you in advance.
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Old 05-05-2019, 09:11 AM
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Speed density or MAF? Maybe a bad MAF?
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Old 05-05-2019, 09:30 AM
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There isnít a MAF sensor in this system.
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Old 05-05-2019, 10:24 AM
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Originally Posted by Notchback5.3 View Post
The issue: The engine is cutting in and out at 5500 rpm. The car will rev to 6500 while sitting still, but will not rev out while driving. The ecu has no way of telling of the car is in gear or not.
Actually it does, It senses load. Free revving has no load so it's easy get it to rev. Putting a load on the engine is where problems if there are any will show themselves.
You seem to have covered most of the possible fixes and I can't think of anything else to replace. Does the Fitech log cam and crank signal?
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Old 05-05-2019, 10:44 AM
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Great input, and the Fitech system does not have the ability to log the cam and crank sensors.
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Old 05-05-2019, 03:50 PM
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0.025 gap is too good if you will not exceed 14lb. what the log shows on the run you make did you log the fuel pressure all the run , the injector duty and the wideband .
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Old 05-05-2019, 03:55 PM
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There's a tune/diagnostic forum, for these types of issues. Also a forced induction forum.
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Old 05-05-2019, 05:19 PM
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I’m not a FI guy yet, but I have to question the fuel pump. Might be fine, but I wonder if you have enough fuel volume, not necessarily pressure. You run that pump inline, or in-tank? How are you filtering your fuel?
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Old 05-05-2019, 05:20 PM
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Originally Posted by Old Geezer View Post
There's a tune/diagnostic forum, for these types of issues. Also a forced induction forum.
Also this^^^^^^^^^^^^^^^^^^^^^^^^....
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Old 05-05-2019, 06:21 PM
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Originally Posted by Chemical Tuner View Post
0.025 gap is too good if you will not exceed 14lb. what the log shows on the run you make did you log the fuel pressure all the run , the injector duty and the wideband .
So youíre saying open the gap up more? Fuel pressure pulls down to 56 psi (set to 58 psi), injector duty cycle hits 41% and wide band is around 12.8:1.

Originally Posted by Che70velle View Post
Iím not a FI guy yet, but I have to question the fuel pump. Might be fine, but I wonder if you have enough fuel volume, not necessarily pressure. You run that pump inline, or in-tank? How are you filtering your fuel?
Bocsh 044 inline, 3/8Ē line. Should be 300 lph at 58psi if I did my math right. Filtering inline with jegs inline fuel filter. I had the same wonder if the pressure is there, but there isnít enough flow. I find it hard to believe that it would hold 56 psi of fuel pressure if there wasnít enough flow. Youíd think it would pull the fuel pressure down a lot more if the flow was insufficient.
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Old 05-05-2019, 06:50 PM
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12.8 afr too lean for boost. Try to target your wideband to 11.5 afr after 105 kpa.
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Old 05-05-2019, 06:56 PM
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Iíll richen it up and report back.
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Old 05-06-2019, 06:01 AM
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Originally Posted by Notchback5.3 View Post
afr at WOT when the issue occurs (5500 rpm) is 12.8. I have it tuned for 11.0 afr.
So you are already commanding 11.0 afr and it is leaning out all the way to 12.8???
That defiantly seems like it could be the problem
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Old 05-06-2019, 08:21 AM
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Itís tuned for 11.0 at 14 lbs. On 7 lbs, itís hitting its target of 12.8. Iím going to richen it up some more per the advice Iíve received.

Also, I got to thinking more about what itís doing, and I wonder if my injectors arenít clogged up. Maybe it has enough injector to run well in low boost, but once the boost comes on they canít keep up. Iím going to pull the injectors hopefully today, but maybe tomorrow and give them a good cleaning and see if that changes anything.
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Old 05-06-2019, 10:15 AM
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If duty cycle was higher I would say dirty injectors but even that is highly unlikely.
What do the plugs look like?
What is battery voltage when under load?
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Old 05-07-2019, 09:38 PM
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Ladies and gentlemen, boys and girls of all ages, I done got it fixed. I was thinking the same thing about the injectors so I took them out and cleaned them. Sure enough, tons of gunk came out of them. I didnít realize my post filter was only a 40 micron and wasnít filtering out the small stuff.

I took it for a rip and it still studdered ever so slightly in first and almost non-existing second gear on. Definitely progress. Iím going to pull them out again and give them another thorough cleaning and Iíd guess my issue is going to be fixed.

I also lowered my injector LB/Hour rating on the Fitech. I read somewhere that the deka 80ís at 58 psi flow 94 lbs. At WOT my fuel pressure is pulled down to 56 psi so I adjusted them down to 90 lbs to ensure Iím not running lean. I might bring that down a little more to be on the safe side.

Also, I richened up the tune per the input Iíve received here. I think thatís a great idea and I didnít notice any adverse affects.

Overall, I am tickled to death with the help Iíve received from you guys. Thereís nothing quite like a turbocharged LS screaming at 6500 rpm and just asking for more. Iím looking forward to making the switch to E85 and turning it up. Thank you guys for your help!
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Old 05-07-2019, 09:43 PM
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Don't forget the 10 micron filter.....
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Old 05-15-2019, 09:40 PM
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So the issue came back, so I looked at a few more things:

I verified my timing with a piston stop. Sloppy mechanics has a great video on how to do this and how to do it correctly, worth the watch. My timing came in 5 degrees ADVANCED on top of what I was commanding. My timing table is really conservative and I never saw any knock from the sensors. I donít think that was my issue, and my octane is actually around 100 (unleaded race gas). I would think it would have blown up by now if it was detonation, but who knows.

Secondly, I switched to BR7EF plugs. Currently on the stock gap (around .027Ē) and I truly believe that was my issue the whole time. For what ever reason my car didnít like the TR6ís no matter what the gap was. I took it for a rip and it ran better than it ever has out of the boost and flat rips in the boost all the way to the rev limiter.

So if your having a cutting out issue at high rpm, Iíd swap over the the BR7EFís and see if there is any change before dumping a bunch of money on things like I did.
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Old 05-16-2019, 10:10 AM
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Awesome glad you got it fixed, thanks for letting us know what it was!
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