Allan-BilletDesign

Hey guys. Looking for some help. I bought my 944 and it seems to have some issues, and the dealer I bought from not being much help, actually any help as they refuse to reply. On the day the car got delivered it had a dead battery. My friend and I jumped it, and took it for a ride. It seemed to stutter everytime it came on boost, and then sometimes pull through. At one point the car would idle, but if you pressed the gas, it would not rev. We popped the hood and noticed some wire had caught fire and we blew it out.
Flash forward to today, and my mechanic has the intake off, and it seems that a wire that wasnt in use had touched the turbo causing it to go. The car has lots of aftermarket things on it seems, like the pic below of the Lindsay racing harness. My question is, there are lots of wires that are not in use, and he wants to start tracing them. Also there is nothing plugged into the Idle valve. Could it have been the car was simply running incorrectly due to low voltage? With a PSC1-001 would that idle valve be disconnected?
Ive been reading online and have seen several people describe the same issue I had as a MAF issue?
https://splitsec.com/…/psc1-001-prog...ignal-calibr…/

bw993

Sounds like you have a Split Second MAF system installed on your 951, which if not setup correctly will cause idle and rev'ing issues. Bottom line is your DME uses the voltages from the SS MAF to control your air/fuel mixture.

Tom M'Guinn

Normally, when these cars run fine but sputter when getting on the boost, it is a sign of a weak ignition (old plugs, arcing wires, worn-out cap and rotor). In your case, it sounds like there is a bunch of things going on, however. Low voltage and bad grounds can cause all sorts of issues, so its worth confirming your battery is holding a good charge and that the charging system is working as intended. A car that won't run past idle without sputtering may be getting a bad MAF voltage and causing the AFR to go out of whack, or it could be as simple as a terrible ignition again. You have the added challenge of not knowing if/how the car was tuned for this set up and/or if it ever ran well on it. You may want to revert to all stock parts, get the car running right, then work from there if you want to add power. There shouldn't be many or any spare wires floating around the engine bay, and definitely none so close to the turbo that the catch fire? That suggest some pretty sloppy mods in the past...

There are a number of guys in your area that know these cars inside and out, including a few rennlisters who work on other cars. I think V2Rocket is in your area and will work for hire? You might tap into that network a bit to get the car sorted. Taking a modded and unsorted 951 it to a typical "german car specialist" or the like can be frustrating and expensive, as they just won't the same level of knowledge about this specific car and how they get modified as someone who obsesses on just these cars...

Allan-BilletDesign

Thanks for the input. Would the idle control valve be disconnected under the intake when using the PSC1?

Tom M'Guinn

Chance are the PSC1 is being used to modify a MAF or AFM signal to alter fueling. Regardless, there is nothing about the PSC1 that should cause someone to disconnect the ISV. If the ISV is disconnected, then someone was probably trying to compensate for something (e.g., the ISV had failed, the DME driver had failed, bad connectors, they needed the car to idle fast due to bad tuning or big cam...etc.).

If you need more evidence, Splitsec.com has wiring instructions online for the PSC1, showing 3 ways to configure it, and none of them mention the ISV...

beamishnz

The above is great advice. I just helped out a guy who bought a modded Silver Rose that was running poorly ... Very difficult to diagnose a car that has been modded and tuned by someone else. I put it all back to stock and go tit running sweetly ... so sweetly that the guy didn't want o put any of the modded stuff back on.

MM951

Years ago I struggled to make my 951 run well with split second stuff..I'm amazed I didn't blow my motor when I had the same symptoms as you. **** poor running, but when it came on it felt very fast. I bought all the harnesses lindsey racing sells, all new vac lines, all new intake, cooling, and fuel hoses, new grounds, plus a supplemental ground, and a Vitesse MAF kit and immediately enjoyed the reliability and drivability of a late 90's Toyota for 180K miles. With also the usual bolt ons (60-1 and all supporting mods.) If you've got those harnesses you have a good starting point, just make sure they are installed correctly (and completely.) With good grounds.

bwp951

The split second stuff is a very old method of adding a MAF to a 951. What you are doing is trying to scale the voltages from the MAF to simulate a AFM signal with very low resolution. Usually their controller is spliced in series between the signal line from the AFM to the DME.

Allan-BilletDesign

So we got the car back together, and it runs ok, except for 2 issues.

The idle, is still lumpy. My mechanic is questioning as to why the Idle valve is still connected mechanically but not electronically ? Should it be disconnected like that?

2nd.. In lower gears, when it comes under hard boost it still has a hesitation, which he suspects is lack of fuel. In upper gears, this hesitation is much less prominent.

Would the PSC1 control this? Can you download the software to tune if off the web or anything? I also saw somewhere that on the original computer there is a button you can switch to richen up the fuel? Is this true?

Very frustrating. The pos dealer will not return calls, and we cannot find who built the car. All we know is that it has that PSC1, some sort of Mass air, full exhaust, a precision 6262 turbo, stage 2 chips, and that Lindsay harness.

Thank you for all your help so far. Feeling very disheartened by the whole situation.

Tom M'Guinn

Sorry about the whole dealer thing. Almost certainly nothing he could do but take the car back or pay some of the repair costs... But to fix the car up, you'll need someone who knows these cars well.

The idle valve (ISV) shouldn't be unplugged. No good reason for that really, other than maybe as a band aide for something that should be fixed.

The PSC1 is made by Split Second in SoCal. Split Second sold old analog fuel controllers for these cars many moons ago, which became outdated when new modern digital controllers started coming out. The PSC1, from what I can see is their version of a digital, programmable, controller but not a particularly popular one for the 951. Regardless, yes you should be able to add/subtract fuel with it. See about it and their software here:

https://splitsec.com/product/psc1-00...al-calibrator/

If lack of fuel on hard boost is indeed causing the hesitation, you are at very high risk of blowing your head gasket. These motors need a relatively rich mixture on boost (no leaner than 12-12.5:1 for sure) to avoid detonation and the resulting head gasket problems. I'm a little suspect of that diagnosis, however, if it was made just by the seat of the pants. If you plan to keep the PSC1 and MAF, you need to get yourself set up with their software so you can map the fuel, and you'll need either a wideband O2 sensor to know your air-fuel ratio, or take it to a dyno so it can be tuned based on the dyno's O2 sensors. Otherwise you really are just shooting in the dark. These cars can "feel" fantastic at 13:1 afr on boost, but it can blow your head gasket in short order. Similarly, they can "feel" terrible with a perfect AFR if something else is amiss.

lart951

I had one of my larts mobiles tuned by split second it had the psc1, I would say i was most disappointing, it would shut off after hard acceleration. I had used all lindsey mafs with much more success than the psc1.

this was the dyno when split second tuned my car


than I played a little bit with it and got these results


and finally my lartmobile #4 with Lindsey racing old maf and piggy back I believe it's the highest HP ever achieved at 16psi by a 2.5L 951