Warm engine, hard starting; cold engine, easy starting

[Badwolf]

So, after tuning up the 1990 Turbo, I still have this nagging issue. I really want to get it squared away, but have no idea where to begin.

Any ideas? Anything jumping out at you?

When the engine is dead cold (sitting overnight, for instance) you put the key in, twist it, and she fires right up; Once warm, the starter engages, everything is normal, but she won't turn over, unless you blip the accelerator a few times - THEN she turns over. Sometimes you have to nurse it along a little when you're first starting it (when it's warm).

Any ideas at all?

Let me know. Thanks.

[JohnJardine]

We had problem and found head gasket had failed. Check for bubbles in cooling overflow bottle with engine running. Check for wet spark plugs. Our failed without much warning

[Badwolf]

When we took out the old spark plugs, they were worn, but did not look like they had any problems other than wear. There was no wetness. There's no smell of coolant at the the exhaust. The hard warm starting was happening before that and the hard starting basically continued unchanged after the tune up. When we changed the oil, we didn't notice any water in the oil - Looked pretty normal - black and smooth. My mechanic friend thinks it could be a fuel delivery issue when the vehicle is warm, or maybe the FI system isn't holding the pressure when it's warm. These are the ideas we've come up with so far.

[s900t8v]

I was always under the impression bad hot starts are from a faulty NTC sensor in the intake manifold. Check the resistance values (quoted in manual)

[Badwolf]

Thanks - We'll start there. I have the Bentley Manual.

[Badwolf]

Okay - came across an idea (theoretical, but maybe?) with regards to clogged or semi-clogged fuel return lines being the cause for difficult starting with an engine that's been recently run. The idea was in a troubleshooting guide for a Datsun P/U that I was reading through while waiting for a friend, and I kind of think this may be a possible reason. Has anyone ever heard of this? Has anyone ever experienced this? This problem has really been on the back-burner since I have other automotive headaches to deal with, and the Saab is still, essentially, fully functional.

[s900t8v]

how would the line get blocked, theres a pump pre filter and a fuel filter, very unlikely.

I wouldn't speculate I'd do real troubleshooting, if the return line is blocked the pressure will end up higher inside the rail despite the fuel regulators best efforts to maintain it at 2.5 bar etc

[Badwolf]

Had a leak at the fuel pump - Had a loose banjo fitting at the fuel rail. Fixed both of those issues and still having the problem. Any other possible ideas? Checking the NTC next....

[Badwolf]

So far...

New fuel pump (it was leaking - had to replace).
New sending check valve (the first replacement was jammed up, broke off during removal, TheSaabSite sent replacement, the second one was "stiff" as well, but we broke it free, and it works fine)
New returning check valve (no problems)
Corrected the fuel rail issues (before)

So we got all that squared away, but now it's running like crap - almost like there's a massive vacuum leak somewhere. Our other thought was the fuel pressure regulator. We've heard that when the fuel pump is replaced, you have to replace the regulator. But we're not in a position to just keep throwing parts at it. The Fuel Pressure Regulator is original (1990 16V Turbo) so I'm figuring there's probably a good reason to replace it (age and fatigue). Any other thoughts or ideas? BTW - the mass air flow sensor appears to be working correctly.

Buddy Holley (one of the wrenches at the shop) went through all the sensors and checked them for voltage and resistance, and they all checked out fine.

Thanks.

[Badwolf]

Another question - has anyone with a 16V Turbo ever messed with a higher PSI fuel pump regulator (3.0 vs 2.5)? My thought is this - I'm eventually going to "increase the output" of said engine, and will likely need a higher fuel delivery - can I use the higher pressure regulator now, or should I wait until everything else is in place?