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Discussion Starter · #1 ·
Having recently had a full engine swap from a '90 Carlsson, I am now having boost issues while under heavy acceleration. I have not had much chance to drive the car since getting her back from the garage, and while driving her gently, i did not initially notice that the APC wasnt connected :evil: :evil:

BUT, now that I have reconnected it, and accelerated with a bit more "vigour", I get the boost cutting out at what feels like 3/4 of the way thru the rev range (I've not fitted boost guage yet - another reason for having driven it gently).

Not being an expert on boost systems etc, does anyone have any suggestions as to why the car suddenly slows when under acceleration? ( i know it would be helpful to say at what psi or bar it cuts out, but until ive swapped the dial pods over and fitted the boost guage, sorry)

Ive left the APC disconected for now, so she's jut running base boost as an LPT

Any suggestions would be great
Cheers in advance

G
 

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Likely you are hitting the boost cutout which will be set for your LPT at a lower threshold than an FTP - it can be adjusted or bypassed - plenty of info and opinions on how to do this is you search the archives.
 

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Stock LPT fuel cut is 0.6 bar IIRC. Unless you have bypassed or recalibrated the fuel cut off then you will be hitting it, which will cut the power until you take your foot off the gas.

Edit - what he said ;)
 

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Hitting the cut-out would give a major (nose hitting steering wheel) type of hesitation, are you getting this? or just the APC cutting boost because it's detecting knock??
 

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Discussion Starter · #5 · (Edited)
I wouldnt say that I hit my nose on the steering wheel (I wear my seat belt;) ), but it is along those lines.....

The complete engine was sourced from a Carlsson, and included the FPR.
The work was carried out by a decent garage round these parts, and seeing as tho the APC unit wasnt even plugged in when I picked the car up (should have checked, I know.... but I was driving her gently, so there were no indications). Do you reckon I'd have a case to take it bake and get them to sort the issues, as to all intents and purposes, the job isnt actually finished? Like I said before, I am a comparative novice to all this "boosting" malarchy

Cheers for the input already thos guys
G

.....edit..... by the way, think ive asked this before, but what does everyone mean when they say IIRC?.... call me stoopid but i just cant figure that one out:roll:
 

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Discussion Starter · #8 ·
NIMS (now it makes sense):cheesy:

Cheers matthew - ive wondered about that for over a year........
G
 

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I accidentally reconnected my fuel cut when changing to silicone hoses. Normally I run 1.2 bar boost - my car was originally an LPT. What I found was while driving normally there was a curve coming up so I changed down a gear, came off the clutch and accelerated a little, and suddenly there was a hesitation and loss of power - nothing major, and certainly no wheel headbutting. Ease off teh gas and power came back. It happened again and again until I worked it out (I was feeling a bit dim that day). I reckon if you connect up the fuel cut on a stock LPT you'll just get a hesitation, not a major jolt, because the fuel cut is set so low. IMHO ;)
 

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My fuel cut off is very annoying:x every time i boost for more then 4 seconds in 3 gear it kicks in, i dont try too boost over 15 Psi and at 15.5 it kicks in:roll:

How do you disconnect the fuel cut off? isnt it part of the APC solenoid?

I should not be able to blow air down the APC solenoid right? i think i can a little.
 

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The overboost cut-out switch is behind the dash on the passenger side (UK cars). It's next to the pressure transducer & has vacuum as well as wiring running to them both. Just bridge the 2 wires on the overboost switch & that part of the APC will be disabled.
 

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The fuel cutout on pre-Lucas cars is much more severe - it really is a bonce-meets-steering-wheel moment :eek: And damn dangerous too :evil:

The pre-Lucas cutouts are certainly adjustable - I had to tweak the one on my T16 when I temporarily fitted a Trent APC box :)o :eek:). I think the later cutouts aren't adjustable though.

I think it's a good idea to keep the cutout wired in, to stop the engine going bang at 2bar boost due to something going awry.

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You guys are going to get me into trouble:lol: but i will say for safety reason i will switch off my fuel cut out switch and i will make sure my boost is no more than 15 Psi.

I am thinking about using a bleed valve, the owner before me used one and it made the car wheel spin and the first gears and in the wet third too.

The APC still gives good boost but no wheel spin when i put my foot down with the clutch fully engauged and its a softer power delivery.

If i by pass the APC soleniod that is plumed into the waste gate turbo and intake then i wont have to bypass the fuel cut off right?

Its just my fuel cut off never did when the brass bleed valve was on my car.
 

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Firstly wheelspin will knacker your gearbox quicker than anything. The APC is designed to moderate boost which helps preserve the transmission. Secondly a bleed valve has no knock protection, so you can destroy your engine if you turn it up too high. Thirdly the APC you currently have can give you the same boost as a bleed valve but retaining knock protection. Fourthly the bleed valve has nothing to do with fuel cut - you will still hit it unless you bypass or recalibrate it, but you will just hit it sooner. As long as you're aware of all that then it's fine.
 

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Discussion Starter · #15 ·
COOL
Just spent the evening scrabling around under the dashboard, splicing the wires on the fuel switch and refitting the lower dash etc (gggggrrrrrr:evil: )

but

SHE NOW FLIES :)

Cheers guys
See you all at 2bar
 

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Thanks Jezzadee for the info, dont take it for granted that i know as much as you chaps about the 900, i know for a fact i dont:cheesy:

I though the stress on a gear box from wheel spin was not that bad? just the rapid speed changed heated it up? do you mean when the tyres bite and the stress is loaded onto the gears is damaging?

Believe me am no wheel spin freak:nono;

The only thing i have noticed is my 900 is slower all round since I have tried to make it stockish, the only big thing i have done is replace the bleed valve with the original soleniod and before with the Bleed valve i never knew there was a fuel cut off valve as it never once kicked in, this all changed when i connected the APC soleniod.

Whats the maximium safe boost in Psi, should get from a stock T16 engine?

I want it to be a fine tuned engine running at its best safe level of performance, i honestly believe this is how to make it last a long long time:cheesy: :cheesy:
 

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ShadowWorks said:
do you mean when the tyres bite and the stress is loaded onto the gears is damaging?
Exactly - it's the sudden stress caused by the wheels spinning then abruptly biting that causes the wear.

Like I said earlier, I accidentally reconnected my fuel cut by changing the hose behind the dash that runs through the bulkhead. It is now blocked with a screw, an elegantly high tech solution ;)

Whats the maximium safe boost in Psi, should get from a stock T16 engine?
I want it to be a fine tuned engine running at its best safe level of performance, i honestly believe this is how to make it last a long long time:cheesy: :cheesy:
Dunno really. I've been running 1.2 bar (18 psi) with stock components for some time. I think I might turn it down to stock 0.75 bar just to prolong the life of the car a bit though, until I fit an APC myself. Peaking at 1.3 bar gets a bit mental after a while :cheesy: Best way you could prolong the life of the car is to keep the APC and forget about bleed valves.
 
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