TheTunedPort

So my '86 Vette since I've had it all of a week, has been hard to start, hot or cold, takes many cranks (3-5 cranks at 3 secs each) and often blows a puff of white/bluish smoke for a few secs upon startup. It runs strong out on the road and has enough torque to take off in 3rd... so it seems to have good compression and the oil is clean no coolant.. 103K original miles, runs like a sewing machine once running
The problem is also not getting worse or better... now I had an old 88 Camaro with a TBI 305 in it and I know all about the valve guides and seals... but the Camaro was never this hard to start I don't think.
This car has a stock L98, but the previous owner has done some sort of bypass of the fuel regulator with a rubber line and turned up the fuel pressure. Why would someone do this, and is this a problem? I feel like if the car was tuned from the factory, computer and all, to run on a regulated amount of fuel, then thats how it should stay.. am I wrong?
Is this a headgasket or a dirty Throttle Body?

PatternDayTrader

This is the problem with modified cars.
In your situation, things sound totally screwed up and I would be putting it back to stock immediately, then worry about whatever else is wrong.

aklim

Have you run a compression and leakdown test to make sure everything is in spec? On the one hand you say it seems to have good compression and on the other hand you are wondering about the headgasket? You can test it to eliminate the issue. Next thing is to get a scanner to see what data the ECM sees for ambient air temp and coolant temp. Hit those sensors with an IR thermometer and see if they are close. If everything so far is good, maybe the valve stem seals cause the smoke? Pressurize the cooling system and test it to be sure. What is the fuel pressure? Does it hold pressure after shutdown? How is the spark? Is it a blue flame? Are the plug wires leaking?

Maybe the cold start injector needs to be serviced? Injectors are the first thing people change when they are wanting more power but the last thing people think will get dirty.

TheTunedPort

Thanks guys I was just about start diggin deeper but the car has since later revealed today that when you run it under about a half a tank, then it will not only be even harder to start, but it will also bog, skip, and miss at anything over 1/4 throttle.....filled it to the brim with fresh fuel and ran great again. So looks like Im gonna be changing the fuel filter this weekend, might drop and clean out the tank too. Car has sat for the better part of a year, and as for the puff of blue smoke.. yeah 36 year old valve seals lmao it is what it is. Thanks again im happy this is easy to fix and not serious. This would have been a tow bill and a $1500 shop fee for my old Jaguar XK8, dash lit up like an xmas tree and a burnt up fuel pump lol. Long live the CORVETTE!!!!!!!!

aklim

Probably need to check the fuel pump assembly and see if the pulsator is FUBAR

TheTunedPort

If it doesnt get fixed with a new fuel filter then Ima drop the tank, clean it out, idk I think that "sock filter" that fits over the pump in the tank is stopped up, plus its got probly a 15-20 year old filter with 60k miles on it dont help it any lol

Tom400CFI

Don't bother with tank "dropping" and cleaning just yet...if it runs good under power, then the problem isn't likely fuel pump/sock/filter.

Can you confirm that your fuel pump runs/primes for ~2 second when your first turn the key on?

Joe C

tuned ports are very touchy when it comes to fuel pressure. before anything, reconfigure the FPR back to stock configuration. follow up with a basic fuel pressure test. do you know if the injectors are stock or correct for a stock L98? just a wild *** guess, but maybe the PO installed the wrong injectors and tried to compensate with increased fuel pressure. curious when you say "...and turned up the fuel pressure" - ??? - or do you mean "bypass the FPR to increase the FP" - can you clarify? too many unknowns, i'd start by verifying that all components are correct for a stock L98 and follow up with a proper tune-up. double check all vacuum lines and clean the TB (optional). service fluids and filters and establish a baseline. IMO, without a known starting point, trying to troubleshoot a "new to you" car with unknowns is, at best, helter-skelter. I mean, do you even know if you have the right spark plugs in this thing? the general designed and developed these cars so everything is in perfect balance. the minute someone modifies one thing, they upset that balance. modify something else, and you start to compound things. it maybe minor at first, but it can snowball into a "WTF" real fast. now throw in the "bubba effect" and you could have real problems (sorry, just venting here). anything else modified - egr valve, smog pump, ???? trying to visualize how you bypass the FPR - ??? did the PO run a piece of fuel line from one fuel rail to another, eliminating the FPR all together - is the FPR even in the system, or just hanging there - what? do you really mean, "pulled the vacuum line, thus bypassing the regulation feature of the FPR?" am I misunderstanding something here?

do you have a FSM? if not, get one before anything! good luck....