I have a 2000 Opel/vauxhall tigra 1.6 16v and I have few problems. On a cold start it cranks for a bit and then starts hardly but if I shut it down and try to start it again it starts right up, and then so on. Like it doesn’t build up fuel pressure immediately. Check engine light is on until i floor the gas a bit then it shuts down and turns up again if i let the gas pedal. Sometimes it misfires a bit on lower rpms. Yesterday, after many days it started with a long crank but without check engine and it didn’t stutter but the light came again not so long after. Also seems like it has less power on lower rpms. One thing i forgot to mention is that mostly on cold start there is smoke from the exhaust and petrol can be smelled. I changed the fuel filter recently and fuel pressure regulator (it was pissing fuel). Jerks and misfires started after the fuel pressure regulator change. Also sometimes gas pedal doesn’t react at all and then jerks suddenly. I didn’t measure fuel pressure and didn’t run a diagnostic check, every mechanic in my place is avoiding me 
. I’m pointing at fuel pump relay, because i can’t hear no fuel pump sound when giving contact, but I dunno maybe it shouldn’t even make any sound. If any of you have some advice I’d be glad to hear…
Do both, post diagnostic codes.
The next time you go to start the engine after the car has sat for a while, turn the ignition switch on so the dash lights turn on for two seconds and then turn the ignition switch off.
Repeat this a half dozen times and then try starting the engine.
If the engine starts right up, it points to a problem with the fuel pump assembly.
Tester
@Tester It did crank a bit less but didnt start right up
I’m guessing you have more than one problem. Since you can drive the car the fuel rail pressure must be fairly close to spec, otherwise it wouldn’t run at all. That pressure should be maintained when the engine is off, since there is no place for the fuel to go, injectors are off, and fuel pump has a check valve to prevent flow from fuel rail back to tank. (A faulty pressure regulator can cause fuel rail pressure to leak down, but you say you’ve replaced that part. Make sure there is no fuel in any vacuum hose that goes to it.) Those pump check valves are pretty common failure items , probably what is causing your main symptom. The check valve is probably part of the fuel pump, so your shop will have to replace the fuel pump. That would be a good time to ask your shop to do a basic fuel rail pressure test, could be helpful for diagnosing the other symptoms .
Thanks for the detailed explanation! Once I change the fuel pump I’ll come back to you.
Again! Have the codes read, then post the code numbers.
This needs to be addressed. Code numbers are a starting point for diagnosis.
Will do in a few days!
One question for you guys, I just noticed my fuel pump relay is connected through some wires just on top of a fuel pump and one “pin” is not connected to anything (seems like someone was having fun 
). Do you have any idea why someone would do something like that or that’s how it should be?
Very unlikely that’s the way the car came configured new. No experience w/your car though.
Years ago I had a late 70’s Rabbit. The fuel pump relay would occasionally fail and stall the engine when driving on the freeway. Actually the relay itself didn’t fail, the problem was a bad connection due to overheating in the underlying relay plate, the part the relay plugged into. Known problem, VW fixed this gratis, under warranty. The solution involved bypassing the relay plate’s faulty connection with external wiring. So maybe something like that is going on w/your car too. Not every pin (blade) on a relay is used, so it wouldn’t be unusual to see a blade with nothing connected to it on a relay that’s not installed on a relay plate.
That makes sense, thanks for the explanation!
I had my car diagnosed, the conclusion is the main problem is the crankshaft position sensor which I will change in a few days and then do the diagnostic and then post the codes. Other codes suggested issues with the immobilizer, egr, and throttle body position (could be the tps). After changing the crankshaft position sensor, I will measure fuel pressure and notify you if the problem persists!
@Purebred these are the codes before the crankshaft position sensor change: P0335-0 and P0120-2
Car had detonations on exhaust and blew fire at high rpm 
P0335 was the crankshaft position sensor—which you have now replaced.
P0120 stands for “Throttle/Pedal Position Sensor ‘A’ Circuit.” It is triggered once the powertrain control module (PCM) detects abnormal voltage readings from one of your car’s TP or APP
sensors.