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Car bogging with more the half throttle

Hey guys, first time posting to the forum, however I have spent a large portion of my life reading this stuff. But this one I just cannot work out on my own

I bought a 32 skyline that has been converted to an rb25. It had a massive list of problem when I first got it, but it still has one

Whenever you use more then half throttle it makes less power, drives mint using half the accelerator, but get to the second half and it dies in the ass, feels like the car is pulling backwards ..

Otherwise car drives good, idles perfectly and free revs well. Doesn't blow any smoke or do anything it shouldn't.

I have replaced plugs (gapped them to .8),  replaced afm twice, swapped out TPS and adjusted it ( both TPS adjust to ~.045 - .41), replace IACV with a known working one, checked timing, replaced injectors rail and regulator, put a bigger fuel pump in.

Let me know boys. Just want to drive this car properly

 

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Missing some key information here...

- Is it turbo...if so, what boost does it get to with the half throttle and what does it get to before it bogs down under full throttle?

- Factory ECU or aftermarket w/tune?

- Boost controller? If so, what boost is it set to?

If it is turbo, my initial thoughts are that it is related to an inability to build pressure in the manifold causing the ECU to run rich, e.g. a leak or loose hose somewhere in the intake piping, wastegate stuck open, turbo fked etc.

Factory ECU in the 25 does have a rich and retard mode which it will enter if the engine is boosted too high above the factory settings. Those with wastegates stuck shut, a boost controller set too high, or shitty/worn coilpacks will be familiar with this.

As you've replaced TPS and fuel system components, the above is all I can think of that is also affected by throttle position (vacuum).

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9 minutes ago, Birds said:

Missing some key information here...

- Is it turbo...if so, what boost does it get to with the half throttle and what does it get to before it bogs down under full throttle

- Factory ECU or aftermarket w/tune

- Boost controller and if so what boost is it set to

If it is turbo, initial thoughts are that it is related to an inability to build boost, e.g. a leak or loose hose somewhere in the piping causing the ECU to run overly rich, wastegate stuck open, turbo fked etc.

I'm friends with him in real life so can answer a couple of these. 

Is turbo, unsure on the boost answer. 

Factory RB25 ecu in it, swapped that one this afternoon to make sure.

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It is turbo, with FMIC being the only mod. No aftermarket boost controller. The car is building boost, sitting just below the first bar on the factory dash guage. Doesn't look like the car is overboosting according to the dash, but I'll throw a guage on it and have a look tomorrow

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Put a gauge on it as the factory boost gauge is shit and not measured in PSI from memory. Also take note of what boost it gets to at half throttle (when everything is going sweet) and at what boost it starts to turn to shit (full throttle etc.).

Also check if it does this for half and full throttle conditions off boost, e.g. in 5th gear at 60 km/h so you can see if the turbo is involved in the bogging down.

Factory boost is approx 7-10psi, ~0.5-0.7bar max.

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I do not know the RB25 but I would expect it is similar to other RB series engines.

It is not looking like a fuel problem. I would be checking the Alternator output voltage first. Turn on all the eletricals in the car like A/C, Headlights, fan, wipers. The voltage should not go much below 13-14Volts.

If the alternator checks OK the I would suspect the coil driver module. It is not easy to check them under load as it seems that the problem appears under load.

That all I can think of.

I wish you well.

Michael

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I just thought of something. Check that the piping on the FMIC is around the right way. I once bought a Twin Turbo with an aftermarket FMIC and had the same issues. I swapped the hoses over and it was perfect.

Just a thought.

Michael.

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I just thought of something. Check that the piping on the FMIC is around the right way. I once bought a Twin Turbo with an aftermarket FMIC and had the same issues. I swapped the hoses over and it was perfect.
Just a thought.
Michael.
I dont understand how the cooler piping could be around the wrong way?
Airflow in, airflow out. Makes no difference which way it goes
  • Like 1

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Hey guys, sorry I haven't been replying. My job has been pretty flat out of late!

So it was overboosting due to a split hose, I have replaced that and it no longer cuts out. But there is still a hesitation on throttle. Ive recently bought a PFC. So I'm just going to install that and give it to my tuner to sort out as I cant work it out 

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On one of my old s13's, I had a similar issue when i put my foot the whole way down. It turned out the MAF was failing. (that car was non-turbo though so i'm not sure if it applies here sorry)

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21 hours ago, 89CAL said:

I dont understand how the cooler piping could be around the wrong way?
Airflow in, airflow out. Makes no difference which way it goes

I'm struggling to determine why he thinks the alternator could have been linked?

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On 9/19/2017 at 10:50 PM, Birds said:

If it is turbo, my initial thoughts are that it is related to an inability to build pressure in the manifold causing the ECU to run rich, e.g. a leak or loose hose somewhere in the intake piping, wastegate stuck open, turbo fked etc.

As you've replaced TPS and fuel system components, the above is all I can think of that is also affected by throttle position (vacuum).

Factory ECU in the 25 does have a rich and retard mode which it will enter if the engine is boosted too high above the factory settings.

 

12 hours ago, Liam brah said:

Hey guys, sorry I haven't been replying. My job has been pretty flat out of late!

So it was overboosting due to a split hose, I have replaced that and it no longer cuts out. But there is still a hesitation on throttle. Ive recently bought a PFC. So I'm just going to install that and give it to my tuner to sort out as I cant work it out 

Called it! :D

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Ok. Is it twin turbo? If it is not then it might be an ignition problem.

If it is a twin turbo then the single FMIC is actually two separate sections. The top half is one and the bottom half is the second Intercooler. So you have 4 hoses for two turbo's. On my car the previous owner had both upper hoses connected to the inlet of each turbo and the two bottom hoses to the Outlet of each of the turbos effectively choking the turbos.

I just swapped the left side hoses around and that was it. Problem fixed.

 

Michael.

 

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