Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[V6Astra F]

Hi

This is starting to do my head in  . When the car has warmed up to normal operating temprature and you stop and switch off , either for getting something at the shops or for refueling as soon as you get back in and start the car it hesitates like its not getting fuel . And you can smell its overfueling form inside the car , this carries on for about a minute or so then its gone or until you floor it and it gets above 4000 rpm then its fine  :-/ . Fuel pressure is steady at 3.9 bar , have a new fuel filter and pump installed , with the vac pipe on the reg removed it reads 4.3bar . Thinking its the ECT sensor acting up . Its a z32se running a x25xe intake with a motronic 2.8.1 ecu no faults logged . 

Any ideas guys ?

Thank YOu

[Kevin Wood]

Interesting.. The fuel pressure reg. isn't vacuum referenced on these engines normally. The reference port is connected upstream of the throttle.

4.3 bar sounds a little high. X25XE fuel reg. would have been 3 BAR. The same injectors were used on the X30XE so they are sized for 3 bar operation. I know the Y series engines used 3.8 bar. Will have to check the injector flow specs. 

I take it it drives normally at all speeds once it's started and warmed up? Any signs of black smoking on full throttle?

I agree that the coolant temperature sensor must be under suspicion too. If it's using cold start enrichment when hot that would fit nicely.

Worth checking what injectors and regulator you're using, though, and whether they are suited to each other.

Kevin

[V6Astra F]

  Forgot to mention im using a 4.0Bar regulator and the c25xe/x25xe 216cc injectors . After a while its fine , just when you stop and start again . I know the z32se injectors are 200cc but they dont fit the x25xe rail since they are too short . Maybe the 4bar + 216cc injectors are causing it to overfuel to mutch , since the x25xe ones are 216cc @ 3 bar . But I was under the impression that the ecu would shorten the injector pulses to prevent that .

Thanks

[V6Astra F]

Think im going to put back the old 3bar one to test . Anyone know the Brake Specific Fuel Consumption value for the z32se ?

[Kevin Wood]

The ECU can trim the fuelling back but only once the engine is up to temperature, has been running long enough to heat up the Lambda sensors and working "closed loop".

The fuelling during cranking and initial after-start running will be straight out of a lookup table based on, primarily, coolant temperature, air temperature, throttle position and not much else.

Once the engine has accelerated close to idle speed and started to pull a reliable signal through the MAF the intake airflow and RPM will be added to the equation but it will remain open-loop until the Lambda sensors are working.

So, upping the fuel pressure might well give exactly the symptoms you have. Having said that, it's a law of diminishing returns so upping it from 3 to 4.3 BAR would probably give you around 260 odd cc/min based on 216cc/min at 3 BAR. :-/

I would be inclined to try it with a 3 bar regulator and see if it's any better.

Check the coolant temperature sensor though.

Kevin

[V6Astra F]

Will do , got a new one today the old one came from my old 2l motor so it had done about 300000km . Will keep you posted . Think thats why my car was hunting when hot aswell, we had to modify the iac valve to get it to idle correctly . Just getting everything sorted , will put the fpr pipe back to where it should be , since I put it back on the vac line when it started to overfuel badly when cold .

Thanks 

[Kevin Wood]

since I put it back on the vac line when it started to overfuel badly when cold .

As I said, it shouldn't be vacuum referenced on this setup, although that would actually lean the mixture.

Kevin

[V6Astra F]

Yea thats why im going to put it back on the pipe before the butterly in the TB . Theres no vac there the guy I got the 2.5 from connected the fpr to vac line under the TB , last week I found out it was wrong so I corrected it . But I had to put it back since I tought it was overfueling to bad without vacuum on the fpr . I tought all cars used vacuum on the fpr , does the v6 have a special type of fpr then ? . This weekend I will put back the 3bar fpr and connect the pipe to where it should go .

I just love learning new things 

[Kevin Wood]

It's down to how the car is mapped. If the FPR is vacuum referenced it keeps the fuel pressure constant across the injector nozzles (as the injectors are spraying into the manifold, and hence a partial vacuum). This means the injectors always flow fuel at the same rate (they "see" constant pressure).

With the FPR referenced to atmospheric pressure, the fuel is at a constant pressure relative to atmospheric, and because the manifold vacuum varies with engine load, so does the pressure the injectors see and hence their flow rate.

In the latter case, a correction is effectively built into the mapping of the ECU but you can see that if the wrong strategy is used it will result in errors in the fuelling when manifold pressure is lowest (idle and light load).

It's a good idea to have the FPR reference port connected somewhere in the intake tract, because it can leak fuel if the diaphragm fails and this keeps the fuel away from ignition sources.

Kevin

[V6Astra F]

Ah ok .

Just to give you a idea of how he told me to connect it , it was on this pipe under the TB .

If I understand correctly it should be on this one marked in red .

That means that the UnichipQ should be remmaped to get it running 100% . Had the problem of the car overfueling when they did the chip so with the 3bar fpr that should be sorted  8-)

[V6Astra F]

Put back the 3bar fpr and put the reference port where it should be , car feels a bit more responsive . Will just get the piggyback remapped now .

Thanks Kevin