Boost cut without CEL?

Hi guys,

So I finally got around to installing the Perrin intake, Perrin TMIC, ported manifolds, GS cross pipe, GS Up pipe and VF52. All gaskets are GS 2x metal. All vacuum lines are zip tied. All grounding straps are installed and look good.

I am having a problem that is kinda strange. While doing the tune we are experiencing a boost cut that is temporary. It can happen anytime I am above 4500rpm. Its not consistent.

Could an exhaust leak at the Up pipe cause this? I hear a small tickling like a up pipe gasket that is not torqued fully or is leak lightly. I will re-torque the exhaust today and spray with soapy water to look for a leak.

My crank position sensor and cam position sensors were fine before the upgrade so I don't think that's it?

Any advice is appreciated!

Here is a link to a video of the boost cut.

romraiderlog_20210514_114447.csv

The first few times, when the weather changed in Fall or Spring, my cars would cough once sometimes when in WOT running through the gears like entering a highway.

Neither car has done that for many years now.

But I do run out of MAP sometimes, that's normally in 1st gear. Redline comes pretty fast sometimes. 7300rpm is where the wagons MAP stops.

Even though I am not having an error code for the coil packs I am going to pick one up. I can move it from one cylinder to the next. If that’s the problem it will solve it.

I have not seen many misfits however? So this is a $118 gamble.

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Would this kind of stumble in rpm be caused by lack of fuel pressure?

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The first few times, when the weather changed in Fall or Spring, my cars would cough once sometimes when in WOT running through the gears like entering a highway.

 

Neither car has done that for many years now.

 

But I do run out of MAP sometimes, that's normally in 1st gear. Redline comes pretty fast sometimes. 7300rpm is where the wagons MAP stops.

I wish that was all that was happening. Before with the VF46 I had it tuned and it was running great. Now with the VF52 it’s got this strange cut in power fairly consistently between 4K-5k. The tuner says it could be coil packs or at least start there. I have one coming from Subaru. I would think it would throw a check engine light with the harshness of the cut I am feeling? So strange!

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the connections to the coil packs can go bad. jmp's ideaweb has a link to the amazon posting for them. The oem wires are very small. The one case I had to do this, one wire had very high resistance due to cracking in the connector itself.

I was doing the "swap the coil pack" testing when I discovered the loose connector. You can also buy a replacement harness and skip the whole "did I make the connections correctly" issue.

the connections to the coil packs can go bad. jmp's ideaweb has a link to the amazon posting for them. The oem wires are very small. The one case I had to do this, one wire had very high resistance due to cracking in the connector itself.

 

I was doing the "swap the coil pack" testing when I discovered the loose connector. You can also buy a replacement harness and skip the whole "did I make the connections correctly" issue.

The one thing that is confusing is that I am not getting any misfiring when I log?

I posted a log with the stumble above.

My tuner thinks it is either cam sensors, crank sensor, or fuel pump. I am thinking of replacing all three along with the fuel filter. It’s a bit costly but that’s part of the process.

Should I only use OEM sensors?

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IMO, I would not touch these. I don't see why all of the sudden they would fail.

I just watched your video. Is it a coincidence that your tpms light turned on right before the stumble and then turned off after it? Or was it in a blinking process?

I see you have an automatic. Just to rule it out, did you try to repeat the issue while changing gears yourself?

Edit: actually, I would leave the cam and crank sensors alone. Fuel pump however, could be possible.

The TPMS is blinking and needs to be sorted. One wheel sensor is low battery.

Yes, I tried shifting in manual mode but it still cuts power.

I have ordered the sensors and will replace anyway.

I also ordered an AEM 340lph fuel pump and a fresh fuel filter.

I will also swap the plugs when I check the coil packs.

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I will start with the fuel pump and filter first. I’m hoping I don’t have to do the sensors.

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i'd have spent $200 on a launch or similar odb reader/logger. randomly replacing parts is expensive.

check the wiring and connectors.

I do have a OBD reader. It’s not throwing any codes? I have used Tactrix OP and a tuner. He thinks it’s electrical. So yes I have to dig deeper into the why.

I think starting with the fuel pump isn’t a bad idea if I go larger injectors eventually it will need one anyway.

I really don’t want to put unnecessary parts on the car at all. I was able to get some used but working sensors for a good price. It’s the time and labor that eats the money. So thankfully I can do most of the work myself.

I didn’t have any of these problems until I upgraded to VF52, silicone intake, and ported manifolds.

Yeah it's weird though. IIRC, you did not even reach 'much' higher load levels on the log you provided. It was still less than 3 g/rev. When it's cold outside, I can reach 3.3 g/rev with boost level still below 20 psi (JMP VF52). Also, it seemed you still had some headroom with your injector DC.

Anyway, if you go down the path of changing parts, at least do one at a time and assess performance. I think you are already planning to do that.

Yeah it's weird though. IIRC, you did not even reach 'much' higher load levels on the log you provided. It was still less than 3 g/rev. When it's cold outside, I can reach 3.3 g/rev with boost level still below 20 psi (JMP VF52). Also, it seemed you still had some headroom with your injector DC.

 

 

Anyway, if you go down the path of changing parts, at least do one at a time and assess performance. I think you are already planning to do that.

Yes that’s the plan. First thing I am going to do is checking the electrical connections? Then test run and log.

Then get a boost leak test, smoke test and exhaust leak inspection by a real shop. Just to cover my ass. There was a compression leak down test done last fall. It’s healthy otherwise.

Do you guys think that’s a good starting order?

Then fuel pump and filter.

Then crank and cam sensors.

Then coil packs and new plugs.

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You mentioned "ported manifolds" what was done to the exhaust and or intake manifolds ?

Exhaust manifolds.

I just got my car back from the mechanic. He smoke tested for boost leak, vacuum leak, and exhaust leaks. None were found.

There were no misfire events.

MAF is clean.

The mechanic says it is easily duplicated in 3rd gear only in open loop WOT at rpm as low as 2k. It is fuel cut.

He thinks it’s something in the tune since no mechanical issues are present.

Any ideas from you guys?

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