Black deposit in intake of TB48DE

Hi all,

Over the last month or so, my 4.8 has been idling really rough to the point of stalling on occasion. Seems to be normal when driving at speed but for a significant lag if you put your foot down. It's on LPG and is the mixer type, not injected.
I suspected the air filter as I have not changed this in the 6 months I've owned this Patrol but when I took the old one out, I found a black, carbon like deposit covering everything on the intake manifold side of the filter. Running a finger over any of the internal surfaces would leave it black and clear finger prints in the deposit.
Obviously this isn't going to do the MAF sensor any favours and I will buy some cleaner and clean it up tomorrow but wondering if anyone had seen this type of thing before? A mechanic mate reckons it's probably oil from the PCV but I don't see a PCV connection upstream of where I'm seeing this stuff and the deposit is dry and powdery, almost like smoke damage.
Seems to have been happening for some time or due to an event prior to the last air filter change as the filter I took out was relatively free of the black deposit on its metal parts and the paper element looked pretty much the same as the new one.

Cheers!

Scott

If your model has a MAF sensor I'd be cleaning it and changing all filters as well' is your EGR blocked??

Thanks Threedogs - it's a 4.8 petrol/LPG, I didn't think they used EGR?? Will certainly look at blocking it if it'll help anything. I've got all the filters but I'm trying to get a new set of plugs. I'm sure the MAF will be filthy - will see how it goes on the weekend. Wife has taken it to visit her mother this week... Stalling and rough idle still wont get her back in her own car :)

Cleaned the MAF and changed the air filter. Huge difference running on petrol. Still missing a little bit at idle but the feeling like it's going to stall is gone. Haven't had gas in it for a couple of weeks as it would stall pretty much every time we stopped at traffic lights etc on the gas - Will fill it up today and see how it goes. Piss easy fix if it works - forums are awesome!

As for the black deposit, this seems to have been concentrated towards the filter end of the intake tubing - in the metal grilles on the "clean" side of the filter and in the MAF housing - it's not in the rubber tube that goes from the MAF to the intake manifold. Looks like it was a poor quality air filter and the foam seal at the bottom end was breaking down. Either it was the foam itself making up the deposit or it was letting fine dust through. Anyway, I cleaned it all out - see how it goes.

So I filled it with Gas and switched it over. It stalled pulling out of the servo.. I gave it a few more chances and every time I slowed for a corner or intersection, it'd die. I'd need to turn the ignition off and back on or switch over to Petrol to get it to re-start. Oddly, if I put it in neutral before slowing down it's fine. It'll idle away happily on the gas but I need to do this before RPM drops below about 1100 and RPM need to be brought back above this when putting it back into gear otherwise it'll stall as soon as I do. Once it's moving, it drives like normal. On the Petrol, it's better than ever.

Anyway, it's got me stumped. I'll make a few calls and see if I can find a gas mechanic who'll take a look at it this week.

Possible a stuffed gas converter. Take it to a gas specialist and have it checked.
The black could have been seals and the rough idle is possibly the engine flooding with gas?

Has gas mileage changed much or can you smell the gas?

Kallen Westbrook
Owner of
Westy's Accessories

Hi Kallen,

Thanks for the response - now that you mention it, I have had the odd whiff of gas through the vents in the cabin if the A/C wasn't on recirculate. The LPG system was fitted in VIC and I live in NSW so I had to get it re-complied for rego in October - I mentioned the gas smell at the time but was told it was fairly normal and the system all checked out okay. I also got a gas mechanic to check it over when I first bought it (6 months ago) and it got the okay then as well.

Mileage when I first got it was pretty consistently around the 350km mark for the 90L tank around town and over 400km on the open road. Now it's all over the shop. Over 400K's from a tank on a long trip recently but I also had a tank emptied in under 260km. I'd put that one down to a dodgy fill but there could be more to it. I wouldn't expect to get much more than 300km from a tank around town right now but I can't get an accurate read due to having to change to the Petrol all the time.

Anyway, I'll try and find a decent gas mechanic this week - original setup was done by LPGAS1 in VIC so I might give them a call and see if there's anyone up my way they reccomend that might be familiar with the Landi Renzo system fitted to my patrol.

Cheers!

Scott

Is ask around town at mechanics for a good gas repairman.
But I'd put my money on the converter or maybe the actual regulator on the tank Could be playing up.

A good system going over and a tune should see you straight.
Keep us tuned

Kallen Westbrook
Owner of
Westy's Accessories

I rang LPGAS1 today and got some pointers as to who I can talk to that might be familiar with this system. None are anywhere near me unfortunately - things start getting expensive when it's an $80 cab fare from/to the mechanics so I might have to wait until I can have a day off work.

I also spoke to my regular mechanic who I get to do logbook servicing on our other car for warranty who thought it might be a loose or broken hose or wiring harness. I actually found the setup manual for the type of regulator I have - along with instructions on how to adjust the idle setting (http://honda.concerto.free.fr/file/SE81sic.pdf) but my specific regulator has a stepper motor controlling the adjustment screw rather than just the thumb screw in the manual. This motor is connected to a harness that pisses off into the main wiring loom. The guy that checked it over for me when I got it said it was a very odd setup in that it was a mixer type fitted so recently (2007 - When injected would have been the norm) and that it was a type of regulator he'd not seen before - guess this is what he was talking about.

I'm having the exact same problems with my 4.8L !!!!!!!!!! I have replaced the spark plugs, with iridiums, installed k&n air filter, also, cleaned throttle body (it was filthy black) and it still runs rough!!! My 4.8 doesn't stall on gas, but it wants too!!! It back fires on gas??? Idles like a pig, on gas or petrol. It is a mixer as well. Not injection. Maybe, i should put a kit through the mixer??