VR ignition problem.

[pungent]

Hi, first post on here but have been looking around for a little while.

Have a problem with my VR 5LT.

Have just done some engine mods, cam,headwork, carb manifold with efi hardware 4 barrel throttlebody, bigger injectors etc etc.

Have had a custom tuned memcal done for the car (still needs to be put on dyno for a retune).

After a lot of other issues, some my own fault some not I am to the stage of hitting my head against a wall.

First problem is the car will not rev smoothly through the rpm range, goes dead and missy so to speak as soon as the secondary's are opened, primary side runs fine. A lot of this could be in the tune so may be solved after retune.

My main issue is after the car is driven normally for around 1/2 an hour or so it develops a miss that after a few more minutes becomes worse and after a few more minutes the car will not even carry it's own weight or rev at all quite often back firing.
After leaving the car sitting for around an hour it then starts fine and runs fine up till the 30min mark again.

If you put the timing light on it the flash is varied between leads as if the ignition is breaking down somewhere.

I have an adjustable fuel pressure reg and guage and the fuel pressure holds solid on 40psi.

I have changed the Ignition module, coil and the leads are almost new eagle series11 eliminaters. Plugs have been changed twice. Have gone through all the wiring multiple times and can not find anything wrong.

Timing is fine and is set on 10 deg in diagnostic mode.

No fault codes ever appear when checked and the engine light never comes on.

Have done a fair amount of work on carby cars and this is my first injected car I have modified and is driving me crazy.

Any help or advise would be much appreciated.

Thanks in advance.

[gsxrdan]

oxygen sensor perhaps, have heard they can clag up over time and alter the computers perception of the airflow. Also check that the catalytic converter is not blocked, that can happen if the engine had a major uck up... and out of left field - our vp had $k's spent chasing gremlins only to discover an electrical connector in the engine bay had decayed, a mechanic found it by accident when he leaned against the plug and the car died.

[VrWagz1]

I've got a feeling that you might be having issues with the sensors on the car. If your running the standard v8 delco computer. You have the MAP sensor, oxy sensors and tps sensor, coolant senor, hall effects sensor, and theres more.
But you'll have the coolant sensor adjusting the mix as the car warms, map sensor monitors air pressure, and the tps sensor moitoring throttle position and the oxy sensor leaning the mix if it see to much raw fuel. The hall effects looks after the engine position to set the firing up.
If you have no engine codes, i would say that the sensors may be ok, it may just be one of them is not reading right anymore due to being in a different environment(eg..map sensor in a new manifold) and throwing out the calculations of the ecu.
My best advice would be to stop pulling your hair out and take it to a dyno shop, and have them whack it on the dyno and they can see all the readings and work out exactly what needs setting up properly. It may cost a few hundred to have them do it, but it will save you alot of time and effort and you can learn a little about the efi system while you are there

[pungent]

Thanks for the replies. Will go to the dyno in the new year but would really like to sort it out before that as I have to travel over 100km to get to closest dyno.

May have to end up trailoring it there.

[pungent]

Have found that the engine is leaning out everytime it plays up.

Have checked all sensors and they all do as they are supposed to when plugged and unplugged except the MAT sensor.

When the MAT sensor is disconnected while engine is running crap it then revs fine again and plugs get some colour back into them.

Drove the car (know it's not an overly good idea)with the MAT disconnected and it feels like it picks up a HUGE amount of HP even though the engine cuts in and out due to it being unplugged.

Replaced the MAT sensor and no difference made so I am now assuming it is in the tune so just gotta wait for Chiptorque to re-open on 5th jan and speak to the tuner to what he has and hasnt done to the memcal.

Thanks for the replies everyone.