Question for the turbo'd guys

lambostealth · Post by **lambostealth** » Thu Feb 14, 2008 3:34 pm

My Neon has been running strong ever since I put on my portfueled Hahn kit.......however.

EVERY ONCE IN AWHILE, I get a P0068 code....(manifold pressure/throttle position correlation)

What do you guys think could cause this??

Wenuden · Post by **Wenuden** » Thu Feb 14, 2008 4:52 pm

part throttle overboost. Very bad stuff, usually acompanied by compressor surge, at least on my boys car. He kept getting that code when we were trying to tune his agp wga in the first time.

lambostealth · Post by **lambostealth** » Thu Feb 14, 2008 5:53 pm

With the size of my turbo (Super16G), I doubt that would be fixable..........I definately don't HEAR any surge, but, I guess that doesn't mean it's not there.....

esteinmaier · Post by **esteinmaier** » Thu Feb 14, 2008 6:34 pm

There you have it folks. The reason I've been saying the Hahn system doesn't work correctly.

The stock ECU has a set range of variance from the standard TPS to MAP relationship for a given RPM. It's an added diagnostic check that was added in the NGC computers.

This feature was added to track down vacuum leaks. What it's supposed to be doing is checking to make sure there's not too much air in the intake manifold for how far the throttle butterfly is open. This works great with N/A cars. If there's -2in/hg in the intake manifold at 30% throttle, that's a dead giveaway that there's a vacuum leak between the throttle body and the head.

Now what's changed with the addition of the turbo? Now it's commonplace for there to be -2in/hg in the intake manifold with only 30% throttle. You're at 4000 RPM, the turbo is spooling, and you're holding it out of boost because you're not laying on the gas pedal. The ECU will in turn interpret this as a massive vacuum leak.

Now here's the kicker. What good would this do just to throw a CEL if you had a massive vacuum leak, and the average housewife is picking up her kids from soccer practice? She'll keep driving, and when she puts it in park, it will sit on the rev limiter, right? Well it would be kinda dumb to go through all the effort to code in this diagnostic if you weren't going to add the failsafe, right? So if the ECU determines the leak is dangerous, it must do something to stop the damage. So it retards timing heavily, to the point where the engine is likely to calmly die instead of spin itself to death.

If you're on the track road racing, the last thing you want to happen is to have this code set off, and have to kill the car, wait a couple seconds, and then start it back up in hopes that it goes back to thinking the leak is gone. Sometimes it will, sometimes it won't.

Now the Portfueler is really a great tool for fuel for those that don't want to do a full standalone. But let's face it. The NGC is a picky computer. The only way to run an NGC engine in a way it wasn't designed to run is to do away with the NGC altogether. I have to give Hahn credit for trying, but the fact is the NGC won't reliably do what Hahn wants it to do.

lambostealth · Post by **lambostealth** » Thu Feb 14, 2008 10:39 pm

It rarely throws the code.....I've seen it twice in six months...........reset code, good to go.

I'm not the least bit concerned with it retarding timing, because I don't get any knock, or pinging, even with our crappy california 91 octane.

By the way, you really hate the Hahn kit don't ya?!

Aside from throwing that code when I'm urging for a bit of boost but not all of it, it performs EXACTLY as it should, transitions to boost VERY smoothly, and makes the car go faster.....which was my initial goal.

It's a good kit, let's just say they probably didn't do a WHOLE lot of homework on the NGC in the 03+ Neon before selling the kits to the general public.

I would have gone megasquirt, but I didn't feel like playing a guessing game if something goes wrong, I know jack s**t about tunig etc. Plus, I can't imagine how many hours were spent by the first guy getting it to run at all.

I kinda like my bolt on kit.

Kevin_GP · Post by **Kevin_GP** » Thu Feb 14, 2008 11:10 pm

Retarding the timing is to prevent the engine from detonating, it also decreases the amount of power you are really putting down. I don't know how much the NGC computer is really retarding the timing to the point of damage, I don't think many people on here know. Thats what I hated so much about the stock computer, it pulled timing so randomly (2002, pre NGC). With our cars there are no real bolt on and go and expect everything to work flawlessly. I am indifferent about the port fueler, however the fuel is only half the battle. A rrfpr can work just as good as the port fueler imo, its the ecu's limitations that are the problem with turbo charging out cars.

lambostealth, just keep track of the codes and reset it when you get it, I have no experience with that code because I don't have NGC. How often do you go into boost, or more importantly part throttle boost? If you are getting the code at part throttle, then the port fueler is really not doing its job thats well.

BlackRoseRacing · Post by **BlackRoseRacing** » Fri Feb 15, 2008 6:55 am

its the ecu's limitations that are the problem with turbo charging out cars

^^^
Exactly, without being able to properly control the pcm due to the lack of being able to reprogram the pcm, we are limited to piggybacks that end up throwing codes anyways. MS is not for everyone, but until someone figures out how to reprogram the pcm, MS is the only viable option for tuning our cars properly.

project 03 R/T · Post by **project 03 R/T** » Sat Apr 17, 2010 6:54 pm

This code is starting to show up on my car now as well. Jumps into limp mode as well. It comes with P0508 at the same time which is a IAC voltage low. funny thing is, I turn off the car, turn it back on and boom I'm good to go and the light goes off. It's not just the hahn kit though. I have a 60MM TB and the way I understand it the R/Ts have this problem all the time. Has anyone come up with a fix?

Post by **occasional demons** » Sat Apr 17, 2010 10:05 pm

project 03 R/T wrote: Has anyone come up with a fix?

Nope.

AFAIK, no one has tried THIS on the MAP sensor to experiment with preventing the MAP/TPS correlation code. The thing is, you would need some kind of window switch so it only changes the MAP voltage where it is needed.

The only other way around it, would be more work than anyone will go through, and that would be an e-throttle. A 60/65mm TB would prolly shine if it was controlled via a PCM program that kept the MAP at optimum vacuum for the given RPM. The PCM would automatically adjust the throttle opening to keep the MAP where it needs to be. This would basically eliminate any "Bog" from too much throttle. A 65mm would prolly rarely see WOT, but when I had it on mine, it did pull harder than the 60mm at the higher rpm's. But it is a PITA to get it right at normal engine speeds.

project 03 R/T wrote:I have a 60MM TB and the way I understand it the R/Ts have this problem all the time.

Are you N/A or boosted?

I doubt any of this would even work with boost.

project 03 R/T · Post by **project 03 R/T** » Sat Apr 17, 2010 10:09 pm

it is boosted but ur idea is still sound. I have the AEM F/IC and can manipulate MAP clamp at will at any voltage. I just need to figure out what voltage corresponds to the correct TPS voltage at a given vacuum.

Post by **occasional demons** » Sat Apr 17, 2010 10:31 pm

project 03 R/T wrote:I just need to figure out what voltage corresponds to the correct TPS voltage at a given vacuum.

Therein lies the trick, and it needs to be a voltage that doesn't piss off the PCM.

project 03 R/T · Post by **project 03 R/T** » Sat Apr 17, 2010 10:38 pm

for sure. The kicker is, at ignition on I'm at 4.37v and max is 5 so I'm sure it can be done as I can change voltage over rpm or just clamp. i

project 03 R/T · Post by **project 03 R/T** » Sun Apr 18, 2010 9:40 am

I was thinking of monitoring MAP voltage over idle, 2K RPM, 3K RPM , and 4K RPM to see how it moves under vaccuum. I will also see where it is at right around th -2 to -0 Vaccum where there seems to be the problem. If I can log this data, I might be able to discern where the problem voltage is and avoid it.

esteinmaier · Post by **esteinmaier** » Sun Apr 18, 2010 2:34 pm

Monitoring MAP won't do it. I'm pretty sure the stock sensor is linear, so all you have to do is measure voltage and kpa at idle, then measure voltage with the car not running but the ignition on.

What you really need to do is observe TPS and MAP voltage at the same time on a steady state dyno. Build a graph with both the stock tps/map relationship and then build one with one that's known to set codes. Then overlay them, and look at the points with the most difference, and you'll find where the problem lies. My guess is you would find the largest difference in the 30% throttle range.

stdlystdmufn · Post by **stdlystdmufn** » Sun Apr 18, 2010 3:57 pm

at idle the TPS (obviously) is around 0.00V and the map is at -0.58 KPA

edit- thats what my SAFC 2 says anyway

project 03 R/T · Post by **project 03 R/T** » Sun Apr 18, 2010 4:16 pm

can't do a stock one as the car is already boosted, but I can log both TPS percentage and MAP voltage at the same time with the F/IC. I'll try to duplicate my CEL situation again by running in third gear ~4K RPM on an on ramp slowly building boost under part throttle and log the entire event. I should be able to pinpoint the instance where the code is thrown, then take note of TPS and MAP correlation at that moment. I also think my TPS could be suspect. I notice I NEVER get above 77% Throttle even at WOT lately in my logs. I've re-configured the F/IC but my progressive nitrous controller is noticing the same issue. It doesn't show me WOT. I have a new TPS coming tomorrow morning. I will swap that in and see what the values tell us.