924Board.org

[Velocevito]

Hello all, i just acuired new to me 1982 porsche 924 turbo with 79k original miles
Car had been with previous owner since 1992, and had a top end rebuild back in 2012, also it came with 2 spare 931 cylinder heads,
After that car has done maybe 2k miles in total, but now since i got im trying to get it running nice, but had no luck, cold starts are nice, warm idle is nice now too, but under wot it cuts at 3k rpms, but it freely revs to redline, also can go in gear not under wot to red line no problem..
Things ive done:
Vacuum/boost leaks (smoke tested under 7psi)
Cleaned up fuel system, new filter, new intank pump(had broken hose internally), new orings on cis module and injectors,
New coil, new wires and distributor with rotor are new
Gapped plugs to 0.024
New timing belt (old one was still good)
Suspectes collapsed catalytic converter, so removed o2 sensor and test port plug just before the catalytic converter, more noises and turbo noises, but didnt help with the issue..
I wish Dan was still here in illonois and i could just drive to him

Anyways i need some pointers, what should i look at next. I want this car to run like it should[/img]

[924RACR]

Hmmm, that's strange - in-tank pump would've been my first target... seems like you've hit most or all likely points.

Especially to be able to rev to redline under load below WOT... I wonder if the throttle position switch is not working properly to indicate WOT and creating a problem that way?

On the early/S1 Turbos, there's a circuit that closes once the throttle gets at/above 71 degrees open. While the S2 has a single TPS unit, it's a similar arrangement of microswitches, just all in one housing to simplify adjustment. I'm pretty sure there's one circuit that does the same on the S2.

Ah, yeah, reading up, accel enrichment is triggered when throttle is above 66 degrees or >3500rpm. But not if coolant temp is below 60C/35C (not sure what that means)...

Long story short, I'd wonder is the coolant temp switch - located in the return tube from the back of the head - or the TPS not working properly?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Velocevito]

Also, one of my mechanic friends said that those two open ports might not be enough to make a difference if the cat is clogged..
so to test this theory the only way for me is to just disconnect the exhaust from the turbo and test run it that way

[Mclaren924]

Agreed that the little test port won't be enough to fully rule out a clogged cat but I would expect worse running condition tbh.
_________________
1980 931 "Salt" Bucket wannabe racer (Dreaming)
1979 924 Sebring "Pepper" -Sold

[Velocevito]

can it be overboost protection ? i mean i dont even know how it feels on the 924turbo, my 1989 944 turbo would throw me off the seat when the overboost protection would kick in, felt like the car slammed on the brakes..
this feels different, not full ignition cut but like fuel cut.
i could try bypassing boost switch ? or would disconnecting vacuum hose to wastegate leave it open ?

[924RACR]

Well, yeah on the 931 the overboost protection is fuel cut not ignition...

You can bypass the overboost switch by grounding the lead to it (located on the intake duct) - at your own risk. Would be more helpful if you had a boost gauge installed...

On the plus side, new ones are readily available, and not that expensive... though I think they usually fail open, meaning the engine won't run at all...

I would NOT disconnect the pipe to the wastegate. Sounds like a great way to pop your motor.

Besides, if the wastegate is faulty - that would typically lead to uncontrolled boost, resulting in the overboost switch kicking in, NOT a lack of boost.

However what would lead to a lack of boost is a stuck (jammed, non-spinning) turbo... I'd wondered if that might be a problem, but you indicated you had noises from the turbo evident with the test port etc disconnected... which would imply it is spinning.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Velocevito]

boost is there, not only the turbo is audible, even more now since i removed the o2 sensor to test, and also can feel the boost building, when driving, i really leaning towards overboost protection kicking in

just ordered analog boost gauge for troubleshooting, should have done it probably long time ago,
max boost pressure on 931 s2 is 10psi ?

[924RACR]

OK, good data points.

It should actually be 6.5-7psi, stock.

Again, if the overboost switch is a problem, grounding it to the intake and a quick test drive should rule that out.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Velocevito]

Didnt receive the t to connect to vacuum hose, so boost gauge got delayed,

Tried bypassing boost switch, car running disconnected car dies right away(guess it means its working)
Grounded the wire and took it on my street, still same, 3k+ rpm car loses all power

I guess its all pointing towards catalytic converter

[924RACR]

Yeah, sure looks like that is the next thing to check.

The overboost switch is the ground for the fuel pump relay, apologies for not being clear about that before.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype