4000 rpm rev limit AHHHHH!!! - K20A.org .:. The K Series Source . Honda / Acura K20a k24a Engine Forum
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Old 02-08-2011, 05:49 PM   #1
TYFOMOTO/NLM
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Default 4000 rpm rev limit AHHHHH!!!

Can someone help diagnose a small issue I am having?

Car is a 2001 Integra.

Problem: Engine has a 4K rev limit no matter what temperature the engine is at, hot or cold the engine will not rev past 4K. Limp mode?

Issues and facts: Engine is a 2006 K20Z1 RSX-S long block bone stock with a 2004 RSX-S transmission. Managed by a stock PRB ECU with no immobilizer. Engine wiring harness consists of a JDM ITR RSX 2004 harness with RCREW sub harness. NO OBD port to check codes, Engine starts up fine and idles with no issues. Tach and speedo work along with temperature.

The only plug that is not connected is the oil pressure sensor on the VTEC solenoid. The JDM harness does not have this.

I just cant seem to get the car to past 4K.

Any help, insight,theory is welcome. I am open to any advice.

Thanks.
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Old 02-09-2011, 05:04 AM   #2
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Default Re: 4000 rpm rev limit AHHHHH!!!

Do you have any CELs and have you pulled the codes?
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Old 02-09-2011, 05:12 AM   #3
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Default Re: 4000 rpm rev limit AHHHHH!!!

Sounds to me like the PRB ECU does not like the fact it cant see Oil Pressure at the VTEC spool valve, which the JDM Ecu's could careless about, Hence the reason the harness does not have the connector

Just My opinion
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Old 02-09-2011, 06:10 AM   #4
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Default Re: 4000 rpm rev limit AHHHHH!!!

Quote:
Originally Posted by StErN View Post
Do you have any CELs and have you pulled the codes?
THIS..

Quote:
Originally Posted by H23VTECLUDE View Post
Sounds to me like the PRB ECU does not like the fact it cant see Oil Pressure at the VTEC spool valve, which the JDM Ecu's could careless about, Hence the reason the harness does not have the connector

Just My opinion
And this could be what is throwing it in limp mode.

also ive seen this happen with a bad map sensor.
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Old 02-09-2011, 06:18 AM   #5
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Default Re: 4000 rpm rev limit AHHHHH!!!

well said kyle
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Old 02-09-2011, 06:29 AM   #6
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Default Re: 4000 rpm rev limit AHHHHH!!!

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also ive seen this happen with a bad map sensor.
Seen that as well. Another Good possibilty.

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well said kyle
Thanks Buddy.
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Old 02-09-2011, 11:10 AM   #7
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Default Re: 4000 rpm rev limit AHHHHH!!!

Thanks guys for your advice good idea about the map, I too have seen them go bad and completely forgot to possibly check it. Im going to try that right now.

As for the check engine light, I cannot read the code its giving because the RCREW subharness does not have the OBD2 port connector.
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Old 02-09-2011, 11:35 AM   #8
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Default Re: 4000 rpm rev limit AHHHHH!!!

This is most certainly a case of limp mode.

You need to get that sensor wired up.

You should also change out your conversion harness IMO, you don't have kpro or anyway to manage the codes you are clearly throwing. If you had the dataport you would already have answered this question.


Also, you may want to look into a K20R ECU if Kpro is out of the budget. The stock ecu is not doing your swap any favors.
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Old 02-09-2011, 11:48 AM   #9
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Default Re: 4000 rpm rev limit AHHHHH!!!

Yup, I just tried a new MAP sensor and the same thing happend.

Im wondering if there are any other sensors that need to be changed back to 2004 for this motor to work with my ECU.

At this point I may just break down and try and pick up a Kpro just to see whats really going on.
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Old 02-09-2011, 01:03 PM   #10
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Default Re: 4000 rpm rev limit AHHHHH!!!

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Originally Posted by TYFOMOTO/NLM View Post
Yup, I just tried a new MAP sensor and the same thing happend.

Im wondering if there are any other sensors that need to be changed back to 2004 for this motor to work with my ECU.

At this point I may just break down and try and pick up a Kpro just to see whats really going on.
The sensors in the 05-06 K20Z1 motors are the same as 02-04 K20A2. I believe its not a sensor issue on the motor. Same thing would happen with a 05-06 PRB ECU

Pretty much your options are a JDM PRC ECU, Wire up the VTEC oil pressure switch to your PRB ECU, or Get a K-Pro and disable VTEC Oil pressure Input

I would atleast start there
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Old 02-09-2011, 01:32 PM   #11
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Default Re: 4000 rpm rev limit AHHHHH!!!

You are absolutely right.

I just wanted to eliminate anything else that I may have missed.

Thanks you guys for the help, now Im off to go Kpro hunting.
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Old 02-10-2011, 05:28 AM   #12
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Default Re: 4000 rpm rev limit AHHHHH!!!

My luck with bad MAP sensors is the car won't even start. Had one go bad once before and wasn't given a check engine light for it or anything. Had to swap out sensors one by one until I figured out it was bad.

One other thing you could check is your battery voltage at start up. I believe it should be 10V or higher. If its lower than 10V you could be getting a "Daughter Board Communication Error" CEL which can also cause limp mode. I've had this happen to me with bad a battery numerous times.

Like everyone mentioned though, get KPRO and your problems will be a lot simpler.
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Old 02-10-2011, 05:53 AM   #13
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Default Re: 4000 rpm rev limit AHHHHH!!!

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Originally Posted by TYFOMOTO/NLM View Post
You are absolutely right.

I just wanted to eliminate anything else that I may have missed.

Thanks you guys for the help, now Im off to go Kpro hunting.
Glad I could help out. Good luck with your hunt
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Old 03-03-2011, 08:03 PM   #14
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Default Re: 4000 rpm rev limit AHHHHH!!!

Okay so I found out what it was.

The Stock ECU looks for oil pressure from the VTEC solenoid. I ended up buying a Kpro to hunt down the problem. As soon as I turned off the oil pressure signal in Kpro the car REVed the the moon and WOW!!! is this engine strong. Due to the USDM ECU and JDM engine harness it put the ECU in limp.

When I re-flash my ECU's from now on I will make sure to eliminate this for you JDM harness guys that use USDM ECU's.
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Old 03-03-2011, 08:48 PM   #15
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Default Re: 4000 rpm rev limit AHHHHH!!!

Quote:
Originally Posted by TYFOMOTO/NLM View Post
Okay so I found out what it was.

The Stock ECU looks for oil pressure from the VTEC solenoid. I ended up buying a Kpro to hunt down the problem. As soon as I turned off the oil pressure signal in Kpro the car REVed the the moon and WOW!!! is this engine strong. Due to the USDM ECU and JDM engine harness it put the ECU in limp.

When I re-flash my ECU's from now on I will make sure to eliminate this for you JDM harness guys that use USDM ECU's.
Pretty sure thats exactly what I told you it was.

Good stuff, I'm glad your up and runnin now.
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