overboost.

[AUSSIE JIM]

what controls the overboost? i'm assuming it's the apc solenoid. so if you take thet out and put just an mbc in will that get rid of the" screen head" suffering. got to be so carefull at the moment. she's hiting it in second and third nearly every time! or is my only solution to fork out for ecu upgardes?



sorry forgot to say, mine is LH not trionic

[Grentarc]

on pre DI/APC cars, there is a boost pressure switch that activates at a certain pressure and then cuts fuel by disabling the injectors.
on DI/APC i can't remember but still cuts injectors out
on trionic it gets reading from MAP sensor, and cuts injectors and therefore head/steering wheel become one!

Many people run MBC only and still hit fuel cut. it is ecu or switch controlled. on th '87 I had, i adjusted the switch to cut fuel at 24psi, not the standard 16, as I was running up to (had an adjusting knob on the dash) 18 psi with a modded APC.

I would reccomend getting ECU upgrades rather than MBC, but each to their own!

[AUSSIE JIM]

i've got DI/APC on mine, it lets me get to about 18-19 pound before the slam dancing starts. wanted to know if there was a cheap way to disable it coz the missus would go spare if i start spending hundreds on chips and the like... but... don't they say it's easier to say sorry, than to ask in the first place!

[AUSSIE JIM]

grentarc, are all your" soup up bits" aussie bought? or do you send overseas for them?

and where do you find the cut out switch on the 87, coz i've got one of them too!, along with a 900turbo which is the same set up so i'm assuming it would have it also.

[Marrk]

On 1991-1992 2.3 Carlssons I assume the overboost is in the ecu, however whilst people say it should be set at about 1.4 bar or whatever both my cars don't hit overboost until I'm over 2.2 bar. I constantly run 1.7 bar and it doesn't kick in. Mind you this is with a 3 ported mbc valve, maybe the valve is restricting the pressure the ecu is seeing....either way its easier than getting the ecu chipped I would think.

I did go thru a phase where if I was doing say 50mph in 5th and floored it it would hit overboost, but if I went thru the gears wot it didn't. Couldn't fathom it out why but then it went okay on its own. Maybe it got fed up and resigned itself to the fact I wanted more boost so moved itself up to the higher pressures...

[Grentarc]

Originally Posted by AUSSIE JIM

grentarc, are all your" soup up bits" aussie bought? or do you send overseas for them?

and where do you find the cut out switch on the 87, coz i've got one of them too!, along with a 900turbo which is the same set up so i'm assuming it would have it also.

My souped up bits (excluding strut brace) were bought from Elkparts.com as it was easiest for me, strut brace was from the Maptun/ dealer Sammuel Motorsport of ACT and the modified APC was home done (quite simple if you have a soldering iron and a DSE nearby to get resistors)

the overbost cutout on the '87 (and all pre-DI) 9000's is above the driver's feet.. you will see a creamy coloured round thing in the gal sheet. it has 2 screws on it.. screw the centre one (you will know what i mean) in to increase fuel cutout pressure (as in from 14psi to 22psi). unscrew to decrease pressure (as in 22psi to 14psi)
if you need instructions to mod the APC unit, and also to make the distributor retard spark more under boost, just ask and I can send details!

[AUSSIE JIM]

thanks mate, would the apc mod work on a DI/APC unit? or only the the older 87 non DI one?

[Grentarc]

only works on non-DI APC units... need to chip the DI/APC one

will get those mods off the other computer when i start it up next...

[UK9K]

I think mine may be overboosting now too. I just got the new HKS EVC EZ11 fitted, and the guy took it for a run to try set it up. He said if he puts his foot down from standstill, the boost gauge will shoot right over to about 1.4 BAR, even tho the controller is set to only 1.2, and drop down to 1.0 and hold there. It won't go over 1.0 BAR even if he had a really long run. And that it does a ' kangarooing ' motion when trying to floor it. So I am assuming it's the fuel cut off cutting in then.

At first, we thought possibly it was a leak in an air hose, leaking out under certain pressure, but upon inspection, they were all fine. Is the only way around this to get an ECU remap then or get an aftermarket anti-fuel cut device like HKS's FCD?

The car is a 92 with DI and unconnected APC.

[UK9K]

Ok, I am still not quite sure what it is exactly that my car is doing. I havn't been able to try it out myself to the full since the new boost controller got fitted. However, the guy who took it for a test drive said;
a, at standstill, trying to floor it results in a turbo spike, where the boost gauge needle shoots round to 1.4 BAR, then drops right down to about 0.9/1.0 BAR, and goes as normal.
b, when actually running along a long stretch, with the foot down, there isn't what you would call much turbo boosting. The boost gauge shows about 0.9 BAR, but there isn't the turbo ' push ' , and it just feels powerless.

The boost controller was set to 1.2BAR/17.40 psi, but it was 'creeping' past to 1.4BAR. However, if I turned the boost DOWN to 1.0 BAR, then all is fine. I have just been doing some searching for the spiking, and a couple of people have put it down to running too lean with the stock air intake system. The air was getting trapped in the system, and not getting into the engine fast enough, causing it to spike out. Is THIS the cause? Or something else? What have you guys done before to eliminate the problem? 1.0 BAR is not enough for me. I want my 1.2 BAR back.

Has anyone an idea what I am experiencing here? I was checking online for a Fuel Cut Defender, and spoke on the fone to a guy, who said my problem wouldn't be fixed by getting one. He suggested possibly getting an ECU remap, but he would make some enquiries for me. Am I not getting enough fuel or is it something else??