• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

MS: Overboost protection?

foggyjames

foggyjames

Procrastinating since 2001!
Joined
Jan 22, 2004
Location
Nottingham, UK
We suddenly seem to have hit some sort of limiter at around 20psi of boost. AFR and spark timing look healthy. It 'feels' like a limiter in the EMS. Changing the kPa value in the overboost limiter does make the cut-off move, but not go away. You can run the highest boost without hitting the limiter with the value set at its minimum (20kPa). You can still run up to 20psi with 20kPa selected. We've previously run 27psi with no such problem. Not sure when this started, as we've only just upped the boost to around 20psi after installing Bosch 680cc injectors in place of the suspect Siemens/Deka 630s. It's much happier now!

I'm tempted to remove the HKS BOV (not an SSQV....something older which barely works) in case it's blowing open.

Other odd thing...after fitting larger injectors we've had to raise all the values in the VE table. Req Fuel hasn't been changed. Weird.

Any thoughts?

cheers

James
 
Just a quick update on this. We tested a few things today like removing the air filter and hose to make sure that was not collapsing, a couple of turns up and down on the mbc and a few hose changes on the BOV but still nothing. The bov is not brill though so I am going to get another and see if that helps.

We have also go through the data log of the event and can see that when the boost hits 20psi, it then drops down to 15 psi and then oscillates between the two. Duty cycle and spark angle also drop up and down in the same area but not down to the numbers where it would be a limited on fuel or spark from our knowledge. I'll try and get a jpg put up with the numbers tomorrow.
 
On reviewing the datalog, MS appears (to my eyes) to be responding to an external influence...i.e. it's doing what it should do, but something else is mucking it around.

Our theories today involve boost control (two questionable MBCs, and a dubious HKS BOV). It doesn't help that we can't find any information for the HKS BOV we're using. It has two pipe connections. With a bit of assistance from Rupert today, we think it's now hooked up correctly - with the main pipe feed connected after the throttle body and the smaller one (on the rear of the diaphragm) connected 'at' the throttle body (i.e. it generates vacuum when the throttle is open, due to the venturi effect). This now (for almost the first time) makes it dump correctly...but...we can't get more than 10psi, no matter how much we wind the MBC in. The question is...is that related to the MBC, or the BOV? I guess we have to part-swap until we find a pattern.

What we haven't tried today is putting the original MBC back on - this would make 20psi without a problem...but would only do so above 4000rpm. It'd spool (and make good power) to 10psi, then above 4k it was like a switch was flicked, and we got 20psi. I'm tempted to stop pissing around with MBCs and fast-track the upgrade to a BCS triggered by MS.

cheers

James
 
Could be....although it does manage 10psi (it's a -31 actuator) no matter what else you do. I'd be interested to pressure-check the actuator...and to try running it without the MBC.

cheers

James
 
IIRC you need to set the overboost KPA to 100 to turn it off.

Which is mildly dangerous, you won't get any more gas for MAP's over 250 kpa, when the sensor tops out. But just set that top row rich, keep an eye on the AFR's.
 
JohnMc said:
IIRC you need to set the overboost KPA to 100 to turn it off.

Which is mildly dangerous, you won't get any more gas for MAP's over 250 kpa, when the sensor tops out. But just set that top row rich, keep an eye on the AFR's.
Click to expand...

Mildly dangerous? That whole plan sounds completely insane. You aren't going to get any additional timing retard past that point either.

Get a different map sensor.
 
Captain Bondo said:
Mildly dangerous? That whole plan sounds completely insane. You aren't going to get any additional timing retard past that point either.

Get a different map sensor.
Click to expand...

It's not *completely* insane, but it is removing a safety net. Most Volvo-sized turbos aren't really going to boost much higher even if the WG hose pops off.

Just mildly insane. I turned it off on mine when the MBC was giving me very brief blips up over 250 kpa before it settled back down. With OB protection on, the car would cut completely off, then kick abruptly back on when the boost fell down. Very violent, not fun. Turning it off let me edge closer to 250 kpa in controlled boost.

If nothing else, trying that could serve as a diagnostic to tell if the cut-off is coming from overboost protection or something else.
 
GOT a different MAP sensor ;-) Even so (before we fitted it), it doesn't freak out when you go over the top...it just doesn't give you any different fuelling. Set the top row of bins high enough and it's fine.

Setting it to 20kPa (the lowest it'll go) or 400kPa (the highest) made no notable difference...in fact 20kPa appeared to allow more boost before cut-off. Of course that could be a conincidence. We'll try setting it to 100kPa (i.e. off) and see how we get on. The map is solid for 30psi, so I'm not worried on that front.

cheers

James
 
Right, new bov has been fitted along (another both seem to have an issue - see the thread in performance) with a different mbc and still the issue remains. Last thing to try is to fit the old plug leads and see if that helps but after that, I'm stuck.
 
I was getting spark blowout when I was close to 20psi on my setup. I had to gap the plug tighter. Could it be what's hapening?
 
Although I suspect it is ignition related, it doesn't feel like the blowout I've experienced on cars before...it's too "slow" for that...although I guess that could be because it's on a car with a bigger turbo. I think the plugs / leads / coil are our next ports of call.

cheers

James
 
Sure...but probably not until tomorrow :) Would the CSV (or whatever it is...) or a screenshot of an 'incident' be better?

It looks (to my eyes) like we have a really slow-acting boost controller...i.e. everything looks "right", just that boost pressure (and duty cycle, etc) is dropping then rising, saw-tooth style, several times a second. In other words...the log, to me, appears to show that MS is behaving itself, and this is something external. I can well believe it's blow-out, the more I think about it.

cheers

James
 
In the end, we found the problem before we got around to pulling the datalog. Ryan checked the plug gaps and found them to be about right, but the problem miraculously went away when we swapped back to the old plug leads. We'll probably look at this in more depth later, but I suspect Ryan will be having words with the supplier of the custom-made 'new' ones...

cheers

James
 
Oh...and 20psi puts us into the next row of load bins, and a whole world of richness...we're in the 9s. That needs looking at, but **** me it's fast, even with the less-than-optimal tune, and at "just" 20psi.

cheers

James
 
Glad you got it covered out! Plug are so cheap, i'm always starting with them for those kind of problem. Also my car totally loses all power when the afr dive into the low 10's, lean that thing and tell us how fast it is.
 
Ok, back with this issue. Anything over 20 psi is causing the same issue again and its now occuring if you let off and then straight back on the throttle at lower boost.

I've gapped all of the new plugs (NGK B8EVX) to 0.5mm and refitted them. Checked all of the connectors on the old leads and they seem to be connecting fine. Below is a couple of screen shots of the log and I have also put links to the data log and the msq.

Anyone got any ideas?

(click for bigger image)


Datalog (as shown above) - http://www.ryanniblett.co.uk/images/744/megalogs/datalog200906162008.xls

MSQ - http://www.ryanniblett.co.uk/images/744/megalogs/megasquirt200906041942.msq
 
Look at the battery voltage,
It's crazy!!
Are you running low impedance injektors?
There is a mod for the latest board.
Concerrning the ground plane.

Otherwise are the ground wires adequate, and the ignition 12 volt side ok.
The log tells it's baad.

BR.

Morten
 
You must log in or register to reply here.
Back
Top