Fuel regulator?

[944 S2]

Anyone replaced their regulator? Trying to solve a hard to start issue. Car cranks a little long after feathering the throttle it starts a little rough for 15 seconds and I get some smoke out the tail pipe. After that we're good.
I just had the timing belt replace and the mechanic thought it was a rich fuel mixture and likely the fuel regulator. Oh and I can seem to find one reasonably priced except the dealer and there are none here. Need to ship from Germany!

[mytrplseven]

There's a one year old one on ebay for 59.99 from Reanimation. If it takes time to get your fuel up to where the engine will start, I'd consider the check valve in the fuel pump. What color is the smoke? If it's definitely running rich, it could be other things and you'd see black smoke.

[944 S2]

Smoke is dark, that's why my mechanic thought fuel related.

[Techno Duck]

Check fuel pressure after shut down and after sitting overnight, could be a leaking injector or bad check valve at the fuel pump.

[DannoXYZ]

I helped a friend trouble a weird starting problem on his 635csi that turned out to be the FPR What happened was if he drives the car every day, it starts up fine. But if he lets it sit for 4-days or more, it'll choke and spit out dark-grey/black smoke.

Testing fuel-pressure at start-up on daily-driven cycle shows ~33psi, which is correct. But if we let it sit for 4-days, the start-up fuel-pressure is ~43psi, or way too high and it floods the engine within 5-minutes and it would refuse to start. Would have to let it sit for about 3-4 hours and then it start right up.

I suspect that the rubber diaphragm in the regular was getting crispy with age and would stiffen up when sitting for 4-days. This would then prevent the FPR from decreasing fuel-pressure in relation to intake-vacuum and it would just send full-pressure, which is too much. However, if he drove it and warmed it up every day, the rubber would stay soft & supple and the FPR would reduce pressure correctly to 33psi and the car would start properly.

Anyway, swapping in a replacement FPR fixed this problem for good. Start-up fuel-pressure was reduced to proper ~33psi and it starts up every time.

I would at least test fuel-pressure to see if it's correct. And manifold-vacuum as well, should be 18-22 inHg. If you've got intake vacuum-leak, this would reduce vacuum to FPR and fuel-pressure would then be too high.

[944 S2]

Originally Posted by DannoXYZ

I helped a friend trouble a weird starting problem on his 635csi that turned out to be the FPR What happened was if he drives the car every day, it starts up fine. But if he lets it sit for 4-days or more, it'll choke and spit out dark-grey/black smoke.

Testing fuel-pressure at start-up on daily-driven cycle shows ~33psi, which is correct. But if we let it sit for 4-days, the start-up fuel-pressure is ~43psi, or way too high and it floods the engine within 5-minutes and it would refuse to start. Would have to let it sit for about 3-4 hours and then it start right up.

I suspect that the rubber diaphragm in the regular was getting crispy with age and would stiffen up when sitting for 4-days. This would then prevent the FPR from decreasing fuel-pressure in relation to intake-vacuum and it would just send full-pressure, which is too much. However, if he drove it and warmed it up every day, the rubber would stay soft & supple and the FPR would reduce pressure correctly to 33psi and the car would start properly.

Anyway, swapping in a replacement FPR fixed this problem for good. Start-up fuel-pressure was reduced to proper ~33psi and it starts up every time.

I would at least test fuel-pressure to see if it's correct. And manifold-vacuum as well, should be 18-22 inHg. If you've got intake vacuum-leak, this would reduce vacuum to FPR and fuel-pressure would then be too high.

I like the theory. Seems to make sense. Now I'm wondering if I need to invest in a pressure gage!