Fuel Pressure Reg rising rate, or fixed rate?

Hi, Car - Saab 900 T16, tweaked APC (turbo charge pressure controller) with 1 bar of boost at moment. Ford Motorsport 30lbs injectors, JR filter, Forge atmo twin-piston dump valve. Timing, mixure all set to spec.

Problem - car at moment has a standard Saab 2.5bar FPR on it. This can't supply enough fuel at high boost, and the APC backs the boost off. I've tried a Saab 3.0bar FPR, this solves the problem of lack of fuel at high boost, but the car runs idles roughly and picks up poorly (until the boost comes in, then it flies) and is really uneconomical.

I've checked the saabcentral and a few other Saabist sites, but there seems to be too much conflicting information - can anyone who knows their stuff tell me whether I should splash out on a rising rate FPR to solve this problem, or can I adjust the one I have? I've heard tales of RRFPRS leaking and all sorts..

cheers Mike

Reply to
Mike P
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Biggest problem with RRFPRs is that they go out of adjustment.

When you been doing so much tweaking BTW? It should indexed against boost anyway, so the 3bar should do it.

Just as a thought, but the Lucas injection models had a higher than normal (2.8bar) I think FPR rather than the standard T16 Bosch 2.5bar.

Also, I think the standard ECU can't handle the bigger injectors with out having it's chip changed.

I think Maptun used to do stuff for the older cars, or Abbott/TrentSaab may know something about this (although Abbott like the throw away the APC and use an MBC (silly people)). Not sure if Partsforsaabs can get BSR stuff for the T16.

Reply to
Sleeker GT Phwoar

Hi Carl, had a couple of weeks off work sick with instructions from the doc to do something totally non-work related, so been doing some fiddling and tweaking. Car was dead a couple of weeks ago, but my diesel passat had some sort of electrical death and mini-fire behind the dash, so I had to get the Saab going again anyway. Fitted a replacement dizzy and fuel pump and away it went.

Already had the injectors as I ordered them last year for the 1st T16 I had. The APC was easy to do, I followed the instructions on 900aero.com, bought the right resistors for 6p each from Maplins and 10 mins with a soldering iron. The dump valve I got with a T16 throttle body I got for £15. Well, I wasn't about to mention what it was, was I??? :-)

Car runs fine with the 2.5 bar reg providing you don't drive like you just nicked it. If you do, blah blah blah

Having just re-read 900.aero.com, and wondering why I didn't spot this before, it says that larger injectors with the standard fuel chip and 3.0bar regulator will cause rich running at idle and low revs. Duh! So, yes, you are spot on. Thanks!!!! I'll have to look into that next I suppose.

I've also bought a leather interior and a set of aero 3 spokes for the car. Lower it 40mm and it'll look fantastic...

thanks for your help Mike

Reply to
Mike P

Easy solution, install the 3bar FPR and wire a 380ohm resistor into the orange signal wire from the AMM.

Regards Matt (who's back)

Reply to
Matt

Cheers Matt. Will do just that. I've already checked that the amm is 380 ohms across pin 3 and 6, I take it this mod does other things..

Mike

Reply to
Mike P

He returns!!! Got any new projects on the go?

Also, got any tips on tuning a PSA 2.0 16v XU lump?

Reply to
Carl Gibbs

In article , snipped-for-privacy@privacy.net spouted forth into uk.rec.cars.modifications...

Incase you aren't sure where the ECU is, it is in the drivers footwell with the fuel relays, under the kick panel carpet.

Feel the carpet, and you will feel a square lump that isn't on the passenger side.

that will look very cool, but make sure you don't get speedbumpitis. Mine wasn't lowered at all, and still used to knock off the exhaust at about 50% of bumps.

Reply to
Sleeker GT Phwoar

In article , snipped-for-privacy@yahoo.co.uk spouted forth into uk.rec.cars.modifications...

Give him chance, he has ultimate Saab day to arrange. The Celica is fun, but I'm missing my 900 already. Why couldn't Saab have built the T16 into a Sonnet shaped/sized body and made it AWD. Damned that would be near perfect.

Reply to
Sleeker GT Phwoar

How does the FPR cause a reduction in fuel at high demand? Normally they just spill excess fuel into the return or have SAAB done something odd? Maybe the 2.5bar is old and has some erosion on the valve so it leaks a bit more fuel or the spring has gone weak? Check it gives the right pressure. You need a remap to use higher fuel pressure.

If the fuel pressure dorps at high load an uprated fuel pump from a

300ZX or a Group A Fuel pump or a Walbro would be the first item for a 200SX with this problem. Then you can be sure it's got enough fuel for the injectors and whatever fuel goes down the FPR.
Reply to
Peter Hill

In article , peter.usenet1 @nospam.demon.co.uk spouted forth into uk.rec.cars.modifications...

Saab fuel pumps can supply plenty of fuel for the injectors he is planning. The stock regulator is fine with some uprated injectors, but runs out of range with the 30lb'ers Problem Mike is having (and you were spot on) is that the ECU doesn't know that he has bigger injectors able to chuck more fuel in less time. Not a simple rempa unfortunatley, need to pay for an updated rom based curcuit board for an old 900/

Reply to
Sleeker GT Phwoar

Yey!! :)

Reply to
Chet

Basicaly LH2.2 runs from a Pre-Set map at WOT and above 3000rpm, it doesn't sample data from the AMM - below 3000 RPM it samples data as skews a map based on this - the maps setup for 21# injectors hence its too rich so by clipping the output of the AMM by a measured amount we can get the ECU to reduce the injector D/C however because the injectors are larger they still flow a similar amount of fuel to the

21's at a lower D/C hence a decent idle/low speed running but still plenty of fuel at high RPM when its running off the 2D map.

Matt

P.S. I'll post a proper hello to everyone this evening ;)

Reply to
Matt

Basicaly LH2.2 runs from a Pre-Set map at WOT and above 3000rpm, it doesn't sample data from the AMM - below 3000 RPM it samples data as skews a map based on this - the maps setup for 21# injectors hence its too rich so by clipping the output of the AMM by a measured amount we can get the ECU to reduce the injector D/C however because the injectors are larger they still flow a similar amount of fuel to the

21's at a lower D/C hence a decent idle/low speed running but still plenty of fuel at high RPM when its running off the 2D map.

Matt

P.S. I'll post a proper hello to everyone this evening ;)

Reply to
Matt

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