I’ve recently bought a GC8 running mafless on Syvecs standalone with link 3 bar map sensor, wideband into the ecu and flex fuel. The car has seemingly developed overnight, an issue where it splutters/hesitates very badly under any load aswell as kangarooing quite violently. I used the car Monday night on a spirited run with no issues then, on Tuesday it started doing this. The car has gotten progressively worse since Tuesday, to the point now from cold it will take around 7-8 tries of starting and then stalling before it will even run for more than a few seconds, when it does eventually run its very poor, the idle fluctuates and the vehicle will not pick up properly with any throttle input. I’ve tried swapping the fuel filter, drained the tank in its entirety and put fresh fuel in, it always runs V power regardless, however this has made it no better. I’m a little stumped and I am probably pissing in the wind without pulling live data as I do not have access to a laptop, but wondered if anyone else has had similar issue?

 

Fuel pump. Has it a fuel pressure gauge.

 

yes got a pressure gauge under the bonnet, it runs 3 bar on idle, picks up to around 3.5/4 ish when revving, pump is a walbro 400

 

Your going to have to get a syvecs lead and download the software or else get someone to look at it for you.

 

yes unfortunately it’s looking that way, I just wondered if there was something simple I’ve potentially overlooked, does that fuel pressure sound about right?

 

It does but have seen pumps work 100% at idle but when load is put on them they cannot deliver the correct flow/pressure. Hence why we always run an in car fuel pressure gauge.

 

Any recommendations as to good gauge for inside? Also what should the fuel pressure rise to when driving?

 

Depends what ecu you have mine runs through syvecs x3 via Toucan and Bluetooth module but R Spec performance sell some standalone gauges which aren't bad.

 

Mine is S7, out of interest so you run wideband? Mine is positioned right after the turbo and I’m led to believe this is generally not the best position

 

Well all of ours are in the downpipe just after the turbo.

 

ahh okay, that rules that out too then, that’s exactly where mine is. Are coilpacks common for failing? I’m new to this platform, I’ve only had the car a month

 

They do but there like anything else the vehicle is 21 years+ old. What version is it.

 

It’s a V2, it’s had a lot of work done to it, according to the previous owner it’s on new age coilpacks, grey ones

 

You need to get it plugged in to a laptop. We're only guessing here now.

 

managed to make some sense of the measured values, when looking at fuel pressure and lambda, the car seems to sit around 6-700 relFP (which I think is fuel pressure relative to map) when the car starts to run rough the relFP drops right off and the lambda reading goes above 1, which I believe is lean