aspengc8

Hi guys!


I'm having a "bucking" issue with my 98 GC8 (ej20g)
Long story short, had to replace my gearbox, so I used a mates one (he went 6 speed) so its a GD Hawkeye box, diff, clutch and flywheel.


After it was installed, I noticed at 1500ish RPMS there was a slight hesitation, so went over everything, made sure no vacuum hoses where nocked off, everything was plugged in etc. all good.
so I changed the coil pack as i thought from possibly leaning on it maybe it could have already been cracked and maybe made it worse, also did leads etc. still the same.


So lately when your driving if you take off with low throttle its fine. but if you give it some when it comes onto boost it starts to buck and wont boost. i have some quiet roads near work so i went for a spin and sometimes it bucks so hard it will hurt your neck.


Also, the other week, I accidently stalled the car. When i went to start it again it would keep turning over but would not start. turned it off, waited, turned it back on still would start. eventually after 40 seconds it started.
to me i would think fuel pump? but fuels pumps that have died on me in the past have pretty much died almost straight away. not lasted for a while.
that being said, if it is on it way out im thinking it cant supply enough fuel pressure when it comes onto boost?


tested the maf last night (with multimeter) seems fine, also pulled the cover off it to check all the solder joints and they are all good as well. (purple label maf)


Im going to get some new vacuum hose tonight and replace it all, as well as test the TPS, re test the MAF and the o2 sensor. i don't have a scan tool so i cant plug into the OBD port.


anyone have any other ideas? ive been working long hours so my brain wont function properly.


mods are:
APS CAI
APS 3" exhaust and dump
APS unichip piggyback
APS intercooler waterspray


thanks guys,
Ben.

aspengc8

Also I forgot to add, Every now and then if your just sitting there stopped, but idling, the RPM will randomly drop from 800ish down to almost stall then just jumps back up to idle.


It did it at the traffic lights yesterday. you don't have to touch the throttle, it just almost stalls then goes back to normal. and it wont do it continually, just the once. then its sweet and wont do it again for a day or so.

ossett2k2

iTrader: (9)

1st thing would be to check for error codes,no need for diagnostic tool,classics have self diagnostics using the black connectors under the steering column.
It's also worth giving the bcs a clean(you can activate it using both black and green connectors to start the ecu reset procedure.

ossett2k2

iTrader: (9)

I have no experience with unichip but I'm guessing it's a generic map on a rom chip so can't be remapped?
What is your boost set at?

aspengc8

This is what's under my column:



I thought it was OBD sorry! So do I have to bridge 2 of the pins or something? Because there isn't anything else there.

Yeah I don't have much experience with unichip as it was in there when I brought it, but it's just a piggyback system. The software to access it isn't available to the public so I have no way of looking at it.

ossett2k2

iTrader: (9)

They put the obd on the v4 but afaik you can't read fault codes from there.
All classics have self diagnostics....
http://www.scoobypedia.co.uk/index.p...eadingECUCodes

aspengc8

Alright so I got code 53. Which according the that page you linked me it could be several:
53 Antenna
53 Anti-Quick Operation Mode
53 Communication Error (Time Over)
53 EGI Control Module EEPROM
53 IMM Circuit Failure (Except Antenna Circuit)
53 IMM Control Module EEPROM
53 Key Communication Failure
53 Reference Code Incompatibility
53 Use of Unregistered Key

The one code that has many haha!

ossett2k2

iTrader: (9)

53 will be an immobilizer fault,could be a stored code from a previous fault or you could have a fault with the factory immobilizer.
You could try the ECU reset procedure to see if it clears the fault.

As the immobilizer cuts the fuel pump then maybe this is causing the bucking?

JDM_Stig

iTrader: (3)

might be worth throwing a boost gauge on and seeing if it all ok there.

aspengc8

So I've done a bit of searching, and on all the "Aussie" forums and pages I've read, code 53 is "fuel pump or circuit.

Jdmstig- I have a turbo timer in the car from the previous owner, max boost is 14 psi. When It comes onto boost and bucks, the boost will drop and move around a bit.
I went for a quick drive today, when I was turning onto one of the back roads near my house, I leaned on it a bit and as it came on boost it back fired. Really loud. Sounded like it was under the bonnet.
I've noticed it will "back fire" every now and then as you back off the throttle.
If I only apply light throttle it will be all normal, so if you ease into it.