Update on Surging Problem with Video - Would Appreciate any Advice!

[KJ-6G75]

Hi guys,

I posted a little while back about a surging problem that’s been driving me crazy. I’d appreciate any advice you may have. I’ve had a lot of parts replaced recently, so I feel like that should narrow down the possibilities. Car is a 2002 Auto KJ Verada with duel fuel.

Description of the problem:

• Rough surging when car is under heavy acceleration. Whole car lurches forward and back.
• Has been occurring for at least 6 months. Doesn’t seem to have gotten much worse over time.
• Car idles normally.
• Only happens when car is warm (been driven for half an hour or so).
• Will happen whether accelerating from a standstill or accelerating from 60 km/h.
• Haven’t noticed the problem while car is running on LPG – Only petrol.
• Revs increase but car goes nowhere. Feels like the transmission is struggling to shift gears.
• When gears change I've been hearing a "whoosh" from the exhaust that's similar to how a blow off valve sounds. Can't remember if it was there before, but it's reasonably loud.
• Car occasionally will backfire while it happens.
• Recently (last few weeks) after the car is driven hard I’ve noticed the exhaust sounding a bit different. Could describe it as sounding more like a “muscle car” while idling. Can be heard in the cabin quite easily.
• Problem has never triggered a check engine light.

Things that have been done in the last two months:

• Automatic transmission flushed/serviced – No problems noted.
• 3.8L 6G75 engine installed about a month ago by Mal and Brendan at Mits-Fix.
• Injectors cleaned.
• Spark plugs and leads replaced.
• Throttle body/TPS checked.
• MAF replaced.
• O2 sensor replaced.
• Entire distributor including ignition coil replaced.
• Intake manifold gasket replaced.
• Fuel pump and filter replaced, fuel lines flushed and tank cleaned. This reduced the problem considerably. It used to happen after 10 minutes of driving, and it now takes around 30 minutes.
• Catalytic converter replaced.

Video of problem:

This is accelerating from a standstill to around 90km/h with just below full throttle. While the revs spike the whole car is surging back and forth. Throughout the video I have my foot in the same position on the accelerator.

https://videobam.com/QjMkU

[KJ-6G75]

Sorry to double post, but here is how the car sounds when started and at idle:

https://videobam.com/moFOT

[KJ-6G75]

Bump. Anyone?

[Spetz]

If the issue is only with petrol then it should be a fuel issue?
Fuel pump going, relay, etc (I don't know what constitutes a fuel system)

[flyboy]

Sounded like a fuel delivery problem from the start.

The fact that work in the fuel system greatly reduced the problem is proof it's not getting enough fuel.

Have you checked the fuel pressure is within specs under all conditions - ie cold, hot, idle, full throttle?

Perhaps when it it really heats up under the bonnet it's opening a small fuel leak somewhere causing a drop in fuel pressure??

If it isn't and hasn't ever occurred on LPG, that's pretty good evidence it's probably a fuel issue.

[KJ-6G75]

Today I noticed that the car is backfiring on LPG when changing gears, so the problem is not limited to petrol. I haven't noticed any surging/jerking when on LPG though. Hmm...

[d1ng0d4n]

All that comes to mind is possibly the fuel pressure regulator. I've got popping and all sorts of crazy crap going on at random times and a strange up/down rev when keeping my foot perfectly level. Not as violent as yours seems to be, and you've replaced more parts than me!