rahulsingh

Hi everyone,
​​​​​​928 GTS is having hard start issues, it takes long 5-6 crank while trying for the 1st time of the day... Once it starts then it will be started very easily all the time for the day... Something I have noticed is it that new pump actually never primes with ignition on...
my duramatrics tester registers fault for " engine temperature sensor & knock sensor 2"...
Although my knock sensor is also new.. someone hooked pressure gauge & found that fuel pressure drops to 2 bar withing 30 minutes... Any idea how to identify if leak is there from injectors/ pressure regulator or somewhere else..
spark plug new... New timing belt, new pump, fuel pressure damper...
Thanks to all

FredR

If you have a tester that works and it indicates faults then logic says you should fix the faults otherwise why have the thing?

The temp2 sender is needed to tell the brains how much cold start enrichment to apply. If this sender does not work correctly then either cold starts are difficult or warm running is compromised- I cannot remember from the top of my head which way round it is. Easy thing to do is measure the resistance to earth of both terminals one at a time noting that there are two channels- one pin for the LH circuit and the other one for the EZK. Do this for the cold engine and report back the numbers you measure- they should both be the same. Even better if you can remove the thing and measure the values in a pan of water with increasing temperatures from ambient to boiling in 20 degreeC steps.

The fuel pressure should hold up reasonably well if everything is working as it should and the WSM suggests that fuel pressure should still be above 1 barg after 20 minutes so from that point of view it seems you are in good shape.

Leaky injectors, a leaky fuel pressure regulator, faulty dampers or a faulty check valve on the pump can all cause premature loss of fuel pressure. If the fuel rail loses fuel altogether over night then indeed it takes time [a few seconds] to fill the rail with fuel before it can pressurise- sounds as though that could possibly be happening for one of the afore mentioned reasons but check out the temp2 resistance values first.

Mrmerlin

when was the last time you ran a bottle of techron through the tank?
Pull the vacuum line off the front damper smell for fuel;
if you smell fuel then one of these parts is leaking.
either the regulator on the RR rail,
or the damper on the LR rail ,
or the front damper at the center of the fuel rails

rahulsingh

Today I checked the resistance for temp senaor2.. at cold engine I got 68.9 ohm ( LH control unit pin 13 & 5) & OL ( pin 19 & 18 for ezk control unit)... Checked continuity in wiring, all ok...
I believe this verifies what that sensor is bad..
Further to this I started the car few times... & Then allowed the pressure to drop to approx 0.5 bar... Now as engine was started few times so engine was a bit heated up... It didn't require any fuel enrichment so even with a very low pressure reading( 0.5 bar) ... It started at every time very well...

FredR

With a cold motor you should have seen something in the region of 2k to 4k ohms depending on your ambient temperature. If the LH and EZ units see those values you measured then the brains think the motor is fully warmed up and will not apply any cold start enrichment making it very difficult to start and awful pick up when the motor is cold. Once warmed up there will be no problem if that is the root cause of the problem.

May be a good idea to pull the connector from the temp 2 sensor and make sure you still get those values to earth when each pin is tested separately.

The Forgotten On

A failed check valve on the fuel pump can cause the issue you're having as well. About $20 for a new one, a fair bit cheaper than the dampers or FPR.

Still, fix your other faults, the Temp II sensor should be replaced with every timing belt ~6 years.

Your new knock sensors causing issues is odd. Who did you get them from? There are a lot of Bosch knock offs being sold as genuine. If it is from any of the big 3 you should be fine though.

Wolfman928

mine cranks so fast I cannot count the turns to determine how fast it starts.