Shudder on Petrol not LPG

[lunny]

Got an annoying problem, when cruising at 80-90kph in top gear (V6 auto) around 1500rpm. The only way i can describe it is when i take up the slack to maintain speed, just pushing down on the throttle i get a shudder through the whole car, feels like something slack somwhere in the drivetrain, but the thing is it only does it on petrol. I switch over to LPG at same speeds/revs but it wont happen. I've tried to make it happen at lower speeds in 3rd at same revs....doesnt happen. I've started out cheap and changed plugs and leads thinking maybe it could be poor spark at those revs but problem still there. Next thing may be injectors, Anyone else had this??

[anonymousmoose]

How long ago was the LPG installed? On my old car I found it running rough on petrol when I first got LPG installed. They then had to adjust something. Maybe something similar is happening to you?

[andyman]

how often are you using lpg vs petrol, mixer setups and clag up the ends of the injectors if not run on petrol often enough, just something to consider,

they might not be that bad but under the right load conditions things can cause problems

[rokkz]

It's amazing, you have described my problem exactly!

When crusiing on the freeway at 80-90, and you apply more throttle its almost as if there is a flat spot, or another way to describe is it is almost like there is very very slight traction control kicking in. 1/20 the strength of when traction control kicks normally kicks in when on gas, then after the rumble is heard and the revs or sort of lock at 1500rpm the revs break free and no further problems until back at 80-90/1500rpm approx.

I first noticed this problem when first installed, but was only apparent when after switch from gas to petrol (or running out of gas and automatically switching to petrol) then accelerating from 80-90 to 100. This would not go away unless turning the motor off then restarting on petrol only.

I didn't report it as I found if I started the car on petrol and turn gas off, the problem was not there. However I think the problem is noticeable starting on petrol now.

In my opinion I think it definitely a fuel injector signal problem or fuel supply problem and nothing to do with not running it on petrol enough with possibly something to do with the installation of the gas system, as it was not there before.

And like you this problem is NOT apparent when running on gas.

What gas system do you have?

Mine is Tartarini Injected.

Cheers

[Flat_White]

same thing happening to me, VY V6 sprint gas mixer LPG.

[lunny]

Thanks for your responses, the system is MGA/Gastec, was installed june 08. I might try staying with the petrol to see if problem stays or goes, i usually flick from one to other because i was warned about injectors clagging up but obviously the LPG is a favourite because of running costs (got 600ks on gas other day). I'm thinking the problem may be developing further as leaving work today she had a bit of a splutter on petrol when i took off which has not happened before. I'll give the installer a call tomorrow to see if they can explain whether the computer may get confused if running from one to other, and who knows he may have a solution??
Cheers
Lunny

[vxcalais_01]

Sometimes if their is a fault when gas and petrol mix together, it really does nto run happily ! But its probably due to blocked injectors, get soem Techron additive from Safeway/Caltex SErvos. Best fuel additive, proven to help.

[tobydwyer]

I have same problem between 1800rpm and 2300rpm (mainly under load) on petrol only. the car seems to have a flat spot, vibrates, and has noticably less power. from all the post i have read, I am nervous about replacing every electronic sensor and plugs and leads to get no result.

driving in any gear (automatic) outside this range is ok. driving on lpg is always ok. doesn't matter whether starting on petrol, or switching from gas to petrol.

-it can't be fuel filter because over 2300rpm on high load runs fine
-runs on lpg so plugs, leads, coils, must be ok

with my limited knowledge of modern cars, I initially guessed tps, but noone seems to be linking this to similar problems.

have run injections cleaner through on two occasions, first time had improvement (6 months ago). second time, no improvement. ultimate (98oct) fuel makes no difference.

if injectors are dirty, can they perform well below 1500rpm and over 2300rpm, and poorly inbetween?

need help because I don't trust holden dealships - their technicians seem to guess rather than problem solve and it costs too much subsidising their guesswork.

Can anyone help? thanks Toby