Fixing the overboost issues with the MN 2.5HP

[nashy27]

By the sounds of it your reading the Manifold Absolute Pressure (MAP), which is your boost plus atmospheric pressure. Atmospheric pressure uaually sits around 13-14psi. Basically all the air we are sorrounded by has a pressure of around 13-14psi, depending on how high above sea level you are. My Ultra gauge has a readout on it that reads both for me so I can see what my boost pressure is as well as the MAP. So in theory your readout is perfectly normal as it's reading approximately 13psi atmospheric pressure plus 24psi boost when it spikes at 37psi.

[dan_4818]

I still get the overboost code even with the dawes valve mod and the chip it chip. Only when towing though and normally during or just after a hill climb. Gets quite annoying losing all power and holding up traffic, it will cause an accident one day

[Stoneman]

Dawes valve will only control your maximum boost unles your running it with a bleed off valve

I think it's being made more complicated than it actually is

[Redneck198033]

Well, Installed new dump pipe with cat just after the turbo, this sure did quieten up the exhaust sound under big loads.

So this did not fix the issue.

I still had the LIMP mode at 17.7PSI ( 122Kpa in my EDS scan tool 212 - 90, 90Kpa being atmospheric ).

I did notice during this time that the Load was constant at 88 to 90% & then went into LIMP mode .

So plan is to put back my original exhaust & see what happens.

The only fix was to fan the throttle every few seconds to stop LIMP, I was in third & still has a fair bit of power considering how step the hill was.

So I'm thinking that it could be related to Load & not boost as the P1298 fault suggest.

finding myself getting closer to getting rid of this rig, after cooking an engine at 60K & now this issue, no confidence at all.

[Cowboy Dave]

Some of them will overboost even in stock form. I guess you're about to find out if yours is one of them.

There's a post from Tony somewhere that explains that the limp mode kicks in after a set number of seconds. Once you know that you can drive around it by varying the throttle as you've found.

The fact that Tony can usually fix it with a Dawes valve setup suggests it is all about boost. It's something to do with the variable vanes in the vgt turbo as I understand it. Too much exhaust flow from the bigger exhaust takes the whole setup outside its expected parameters.

More than one exhaust seller claims a 200 cell cat is the solution but often (as you've just found) it does not improve the situation.

[Redneck198033]

My setup now has 2 x 200 cell cats. one at the turbo & under the drivers seat, looks like I waisted $200 on the new dump pipe, it does look good though, chrome & shiny.

The problem may of come from the new motor & turbo, might be time to start playing with the VGT control arm.

Will put the stock exhaust on first.

Also I NEVER had this issue with the old motor & standard exhaust when towing the same van.

Has anyone run a chip with standard exhaust?

I will measure the old dump pipe from Genie as I'm sure it's not 3", looks to be 2.75" or there abouts.

[Redneck198033]

Well, very interesting, I put the OEM exhaust back on with chip set to 1, van on the back, went back to the hills I had issues last time & no LIMP mode.
Switched chip to pos 3, still no LIMP mode. Made 3 runs over the same hills no LIMP mode.

Only at pos 3 due to possible temps in the motor & exhaust, will ring Roo systems & Berrima Diesel to see what I should set to if at all.

Also update from Berrima Diesel having a look, they believed it to be the fact that the cat was under the car not at the turbo. So back pressure issue.

I did some measurements of the 2 dump pips, the original from Genie with not cat is a 2.5" pipe all the way to the mounts below the gear box. The newer dump ( same length as 2.5" pipe) with cat is 2.5" to the cat then 3" out. not convinced this is better due to hi flow cat & dump after cat is now 3" not 2.5".

The OEM is so small @ 2" pipe the hole way.

So for me the exhaust is the real issue here, Genie & Roo systems have some thing wrong here.

I did notice on my EDS scan tool that the boost recovers much quicker & settles at 212Kpa ( 212kpa - 90kpa = 122Kpa, so this is 17.7PSI for me at full load for as many seconds as I need, Biggest hill climb was 50 to 60 sec worth of full throttle in third.

Checked vane control arm for movement all good, so should it be its only 10k old.

Where next for me NFI, so frustrating to have $2500 worth of exhaust now sitting in the garage.

You would think that buying gear from a seller it would be setup to handle all issue. well not good for towing.

[coughy]

i have read that you need a 2.5" dump pipe then go to a 3" system after that as this stops the limp from a qld company in burleigh
might be worth a shot??
as i have a stock exhaust and get this limp code bs it is a mitsubishi fault in the programming

i have it with stock car
now i have a mod car with chip and so on it still does it
very disapointing pos

[Redneck198033]

The system I had on for 12months & my first LIMP mode had a 2.5" dump that finished below the gearbox.

On the plus I have a stock exhaust running my chip on setting 3, not even sure what the setting difference on the fuel rail is. 1 to 10 NFI.

Stock exhaust has changed the power a fair bit, if it was not chipped the power would be far down.

I will see how my fuel economy goes.

[coughy]

but where was the cat in the 12 months exhaust
was it up at the turbo or down lower under the car??
so the exhaust and chip is better for power??

[Redneck198033]

but where was the cat in the 12 months exhaust
was it up at the turbo or down lower under the car??
so the exhaust and chip is better for power??

First 3" setup came with the cat under the drivers seat. The reason I had no issues with this was due to the fact I have not towed my van for 12 months. Towed on the October long weekend. This was how I found my LIMP mode issue. I then got a dump pipe with cat at the turbo( still using the cat under the seat) & had the same issues.

As for power & fuel economy, economy was what I was after more, the exhaust with chip set to 5 so middle gave me much better fuel economy as I don't need to plant the foot all the time to get away. Can drive the car more conservatively.

[coughy]

thats what i wont to hear
as for your limp still there??
with both cats mmm seems as tho it isnt back pressure it is after must be turbo run away as they call it
i have noticed that the scan gauge sits on 18.4 psi and my digital gauge reads about 3.2 psi higher when foot to the wall but when lighter throttle used the gauges are similiar up until about the 14 psi mark

the oem ecu reads it slower or not very well at all.
i wonder if i can run a bleed of valve at the oem map sensor to say start bleeding of at 17psi then shut again when drops under again to keep it at the right psi
while my dawes and enterprise keep the car happy??

[Stoneman]

Faulty map sensor?

[Redneck198033]

Limp mode in not happening with stock OEM exhaust.
My unit will site around 18-19 PSI & peak at 24PSI with stock.

But 3" exhaust setup will peak to 30-32PSI, & takes to long to get back to 18PSI. does site around 20PSI for some time once the foot is into it with the van on. at this stage if I don't blip the throttle LIMP mode will tack effect after about 8-10 seconds.

[coughy]

yes it does happen with standard exhaust i have it happening to me mine is stock exhaust

[Cowboy Dave]

Yeah but every car is different. In this case it's the bigger exhaust causing it.

[Monkeyz]

I am interested here as I am looking at a Roo Systems Exhaust and ECU Remap, what im noting in this discussion is most people have a 3" exhaust and Chip (not remap)

A, could that be the issue, big bore exhaust and a chip fooling the computer causing some sort of confusion in the system

B, does anyone here have a fully dyno'd remap & 3" exhaust package and how has it performed ? any limp mode issues ?

c, With an ECU remap it can be tuned/matched to the exhaust and its a complete reprogram not fooling signals, does anyone think this would make a difference.

Cheers,

Mojo..

[motoz]

I am interested here as I am looking at a Roo Systems Exhaust and ECU Remap, what im noting in this discussion is most people have a 3" exhaust and Chip (not remap)

A, could that be the issue, big bore exhaust and a chip fooling the computer causing some sort of confusion in the system

B, does anyone here have a fully dyno'd remap & 3" exhaust package and how has it performed ? any limp mode issues ?

c, With an ECU remap it can be tuned/matched to the exhaust and its a complete reprogram not fooling signals, does anyone think this would make a difference.

Cheers,

Mojo..

Yes.

Currently running with an ECUTEK remap, 3" Scots system and Cross Country front mount intercooler upgrade.

The tuner can retune as required and if you add other upgraded components. I noticed good gains after the fitting of the front mount and no noticeably difference in turbo lag that is often thrown around.

I have fitted a daws valve as with the 3" system mine was prone to overboost issues. Since this has been fitted and set correctly it hasn't happened.

It's taken a couple dyno sessions though I'm really happy.



Recorded at the wheels turning 32's and loaded to the hilt in full touring trim and the sluggish 5spd auto.

[Cowboy Dave]

Are you saying you still needed the Dawes valve? Or the tune meant you could get rid of it?

[gregned]

Yes you still need the cases valve as the ecu isn't fast enough to pull back the boost.
I have the same setup as Motoz and have had it in several times with the same tuner as it was "overboosting" although it wasn't going past the 23 psi limit set.
The issue turned out to be fine tuning of the virtual wastegate, I'll have to take it in to get sorted now that he can get it right, I ran out of patience and was a long way to get to him.

[motoz]

Are you saying you still needed the Dawes valve? Or the tune meant you could get rid of it?

Yes still need it CD. Maybe it's just the 3" dump on the tiny MN turbo but it upsets things somewhat.

Yes you still need the cases valve as the ecu isn't fast enough to pull back the boost.
I have the same setup as Motoz and have had it in several times with the same tuner as it was "overboosting" although it wasn't going past the 23 psi limit set.
The issue turned out to be fine tuning of the virtual wastegate, I'll have to take it in to get sorted now that he can get it right, I ran out of patience and was a long way to get to him.

Mine has taken two sessions to get right. It would randomly over boost on light throttle applications from around 2000 RPM when cruising at 100km/h. You'd pull out to overtake or give it light throttle up a hill... Bam engine light on and limp mode.

Dead set dangerous on the freeway overtaking a semi !!!
Alas it's all sorted now and working really well.

[DynamicDave]

Hi Tony,
you've probably heard this question a million times but will the dawes setup eliminate the limp mode up hill my boost is sitting somewhere between 20 and 30 psi when it goes into limp mode.
If so How do I go about buying the setup

Thanks David

[Tony]

Hi Tony,
you've probably heard this question a million times but will the dawes setup eliminate the limp mode up hill my boost is sitting somewhere between 20 and 30 psi when it goes into limp mode.
If so How do I go about buying the setup

Thanks David

David, I'll answer this briefly for now.

Depends what issue is and we need to know CEL to determine if your chasing Boost and airflow related problems.

The what is labeled overboost (more correctly VGT system discrepancy read by ECU under certain conditions) is CEL P1298 and not read by generic scan tools. (they often can force clear or will show other soft codes that not related to issue)

The way ECU determines this condition is directly related to more airflow, VGT aspect unable to stop at boost target and two sensors then return voltages excessive to ECU's max target safe limits.
The dawes valve does work alone (Set up backing the factory boost solenoid) with some issues and others can require tuning of the Boost sensor and Air flow sensor.

Please email us for more info tony@spvindustries.com

Our system used on the VGT-178HP Triton and Challenger. (we now use genuine hybrid dawes valve with HD spring and ceramic ball for best performance)

Dawes 2.5 hp.jpg

[scumbag]

gee my triton spikes to like 27-29psi all the times and the engine never cracks the shits... pulls it back pretty fast to 20ish... wonder if id be able to get away with a 3" dumpie and no upset ecu?

[coughy]

i very much dout it m8 if 3" is fitted will boost more and faster so a cel would be nilly 100% a given