Boost Limit

nappo · 03-25-2009, 01:41 PM

I recently bought an '87 951 with a few mods (PO felt mods were higher priority than paint...I happen to agree):

rebuilt K26/8
LSD
Lindsey stage 2 clutch
Lindsey engine rebuild kit w/wide
3" exhaust
Lindsey chips
LBE
3bar FPR

My question concerns overboost protection. When I go to WOT in 4th gear the car simply shuts down around 4000-4200 rpm and something like 15.5 psi. It feels like the fuel is simply cut off. Is this what the overboost protection feels like? What can be done to remedy this situation? How can I tell if this is in fact what is happening?

The primer gray gives it a sleeper look

trivgar · 03-25-2009, 02:08 PM

sounds like overboost. its just a fuel cut as far as i know. be careful as it can damage the engine. cutting fuel results in a prettu extreme lean condition. most people get chips to override or raise the stock limit. i see you have chips. surprised it isnt eliminated. find out what boost levels the chips are mapped for. for now i would turn it down.

trivgar · 03-25-2009, 02:09 PM

also set the boost level in a higher(3rd or 4th) gear. if you set it to 15 in 2nd its gonna hit 18+ in 4th from what i recall.

nize · nize's Garage

are the injectors stock? it sounds like you might be damaging your car;
bypassing cycling valve

nappo · 04:51 AM

As far as I know I have the stock injectors. The only modification I have made is to install the 3bar FPR, I haven't done anything to adjust the boost. What can I do to turn the boost down? I am much more interested in not ruining the engine than having high boost.

Nize, are you suggesting that I have a bad CV?

Edit: I guess this weekend I will try to follow the diagnostics from Clarks Garage for this situation.

nappo · 03-28-2009, 08:10 PM

Poked around under hood a bit today and I didn't see any obvious vacuum leaks bad hoses etc. Then I noticed the LBE...looks like the PO had the LBE really cranked down. I hooked it up to a pressure regulator and a compressor and set it back to the recommended 10psi, seems to have straightened things out. Thanks for the help.

nappo · 03-31-2009, 06:05 AM

Scratch that...turning down the LBE did help, but it did not eliminate the problem. It has just pushed the problem later into the rpm range. Now instead of cutting out at 4000-4200 it did it closer to 5200rpm. I did not get a chance to test the CV, but the boost seems under control in the lower gears. Also this only happens at WOT if I am even just a little backed off it doesn't seem to happen.

nize · nize's Garage

my bet is still that you are over-running the stock injectors, probably damaging the car.

get an aftermarket gauge and monitor your boost levels. let us know what actual boost levels you're seeing on the gauge.

nappo · 03-31-2009, 07:22 AM

I have an aftermarket gauge and once I turned down the LBE the boost is normally controlled around 11-12psi. However it does seem to creep up in 4th and 5th gear, not all the way to 15 but maybe 13-14psi.

nize · nize's Garage

do you have a wideband afr sensor? it might give more clues to what's going on when it cuts out.

nappo · 03-31-2009, 07:40 AM

I am shopping for one right now...I was also thinking along those lines. I saw you had recommended one from innovative motorsports, LC-1?, in another thread and I am trying to decide what parts I need. The PO has welded a bung and installed a 5 wire (I assume to be wideband) O2 sensor, but the lead is just tied up under the car. I was considering installing a narrowband gauge until I saw the pigtail hanging under the car . Hopefully it won't be too much trouble to get a gauge and install it...until then I will just have to not drive it and/or stay out of the throttle.

nize · nize's Garage

you could also take it to a dyno shop and have them monitor afr at the exhaust and datalog while you get on it.

nappo · 03-31-2009, 11:43 AM

Just ordered a wideband kit w/gauge from innovative motorsports. Hopefully it will be here by the end of the week and I will take another stab at nailing this down this weekend.

Rogue_Ant · 03-31-2009, 12:36 PM

You aren't 'over-running' the stock injectors. Not happening on a stock turbo.
Even if he is, the ECU won't shut-down, rather the AFR will simply start to enlean and possibly knock.

You are hitting over-boost protection. This is determined by the DME based on airflow. You turning down the boost simply delayed the onset to a higher RPM.

To fix, you either need to turn down the boost more, or get a chip that is mapped for the boost you want to run (and thus has a higher over-boost threshold).

Also, I would double-check for vacuum/boost leaks, as this can skew the airflow number to the DME resulting in over-boost cutting in to soon.

-Rogue

trivgar · 03-31-2009, 02:12 PM

That's what it sounds like to me. I ran 18psi on my 26/6 for a year and never had any problems. Granted I had chips but, never maxed my injectors out.

Like I said you gotta set the boost in 3rd or even 4th. 12 psi in 3rd even might be too high. Could easily build to 15 in 4th and 5th. As I recall overboost kicks in somewhere around 1 bar? 14.7psi.

I've heard of people setting boost in 1st gear with a mbc. that doesn't work. I have my car set around 18psi right now and I probably hit 8-9 in 1st. My wastegate will barely even open.

nappo · 03-31-2009, 02:23 PM

I don't have an mbc...it seems like the PO had tried to set the boost using LBE. I reset it back down to 10psi. How else could the boost be set? I was told that the car had chips, I guess what I'm going to have to do is open it up and check to see if that is the case. Also I guess look harder for vacuum and boost leaks?

Greendomize · 03-31-2009, 05:33 PM

This concerns me now. Last time I checked I noticed 16psi during a 3rd gear pull. I wish the previous owner would have told me what kind of chip was installed when adjusting the boost. I have a knob below my radio that I can manually lower the boost with, should I drop it to the factory boost level asap? Also, I heard someone mention adusting the boost in individual gears. Is this possible with my setup?

nize · nize's Garage

Quote:

Originally Posted by Greendomize

This concerns me now. Last time I checked I noticed 16psi during a 3rd gear pull. I wish the previous owner would have told me what kind of chip was installed when adjusting the boost. I have a knob below my radio that I can manually lower the boost with, should I drop it to the factory boost level asap? Also, I heard someone mention adusting the boost in individual gears. Is this possible with my setup?

since you don't know what all you have on your car, you should probably lower the boost to factory asap until you sort it all out.

if you want us to comment on the possibility of adjusting boost with your setup, you should list in detail what your setup is. we are not mind readers.

Greendomize · 03-31-2009, 06:05 PM

It's an Autothority Chip, I was told that it raises the fuel cut by about 500rpm. I'm pretty sure the car has a factory wastegate, I have heard that this may cause problems as well.

nappo · 04-01-2009, 01:54 PM

How can I tell stock vs aftermarket chips. The chips in my car appear stock (ie correct part #) however they have a blue dot on them...is this normal or did I get fleeced? The only reason I ask is bc the PO told me he had put chips in from Lindsey Racing.