Lumpy idle

[suzukishrek]

I've got a LandCrusier which I had converted to gas about 5 or 6 years ago. I've only ever had one problem with it when I'd neglected to do a timely service on it and it back fired turning the flap type MAF inside out! Toyota wanted about £500 for a new MAF because my Cruiser is a Middle East destined import, but i got one from the USA for about USD200 including delivery! Needless to say everything was fine... for a while.

Now it idles rough as hell on LPG trying its best to stall and sometimes if succeeds which when you're decelerating to turn a corner means I'm now piloting a 2.5 ton non-turning, non braking missile! If I just leave it alone and stare at stupidly the revs will suddenly pick up from 200 or 300 to normal and run fine - I've not touched a thing, just looked at it.

Well I started to mess about figuring I had an air leak somewhere, so I swapped all the induction tubing out for new and in ran pretty much perfect on LPG but when I switch to petrol it hunts between 300 and 600 at a rate of about 1Hz. If I switch back to LPG sometimes it's fine and sometimes it's back to its old 200 - 300 idle problem. Interestingly if I pump the brakes the revs pick up, but then die off slowly as the pedal pressure releases. If I kill the engine, pump the brakes until they are solid, keep my foot on the brakes, start the engine it runs fine... and the brake pedal drops down to normal operation height.

I believe it's running rich as it stinks of LPG at idle. But the petrol hunting thing has got me, why does it hunt? Would some air restriction cause this or could my MAF unit be set too "tight" - it's a flap type/

I need to check my EGR, PCV, lambda sensors and make sure I've no more leaks anywhere - out with the butane torch I guess and then WD40 to temporarily block whatever minute hole I find.

[dpcwright]

Graham
Have you tried changing the LPG filter usually located below one of the solenoids? Changing this filter cured a lot of my RRC problems and it was black with dirt.
Regards
David

[hiswitsend]

Does it idle OK on petrol?

Just had a problem with my RRC not running on gas and that was due to not getting enough air in, or in my case...ANY!!

Problem was that there was a mechanism to open the flapper type door on the MAF, when on LPG, that had seized and was not opening the door when it switched over.

[suzukishrek]

dpcwright:

Didn't know I had one! I've had a quick look and can't see anything that might look like a filter either! What do they look like, how big are they?

hiswitsend:
No it's worse on petrol if anything! I stripped out all the rubber hosing on the induction side the other day and replaced it all, which seemed to cure it, but then halfway up the M6 the other day I was loosing power something chronic and when I stopped I noticed that the heat from the exhaust had warmed up the hosing and moved it all slightly giving me an air leak. I repositioned it all, tightened it all up and off we went.

So now I'm at the stage where:
- on petrol at idle it "throbs" a little between 500 an 600 rpm.
- on lpg it lumps right down to 200 rpm and mostly stalls. If I pump the brakes up 'til they are hard and then restart the car it idles properly after that. At worst it lumps down to about 400 rpm, seems to realise and alters itself to about 700.
- when motoring along on LPG if I suddenly take my foot off the accelerator the engine suddenly slows as if its been deprived of fuel altogether and is voices its disgust by backfiring (funny to see drivers behind me suddenly pull back as flames leap out the exhaust ). Because I'm motoring along at this point it doesn't stall, just kind of judders and hesitates which confuses the hell out of the auto transmission when you put your foot back down again!

My MAF is a flapper type and I don't have a mechanism to open it! I never have had though so that shouldn't make any difference because it used to work fine.

My system is a Bedini one and uses two stepper motors to control gas flow; one on the regulator and one just before the mixer itself. These are driven from the lambda sensors. I'm going to fit a separate sensor specifically for the LPG system to see if that changes my LPG problems and keeps the petrol ones. I'm also going to check the TPS to see if that is causing me the problem on petrol.

Anyones thoughts on the above would be much appreciated!

[hiswitsend]

If it runs better when the brakes are pumped could it be down to a leak around the brake servo vacuum pipe?

[suzukishrek]

I pulled the pipe off the actual servo and the revs shot up to be more where they should be, perhaps a little too high! If I put my finger over the end of the pipe I pulled off, the revs lump down and it stalls. Does this mean my servo is duff - how would I test this?

[hiswitsend]

Sounds like the engine is not getting enough air on a closed throttle, maybe there is some restriction there, or the MAF isn't operating correctly.

Would inspect the inlet side from the air filter back to the engine, then hopefully someone with more experience on that engine/LPG systems comes a long and says: "Aha, its the doohickey that needs replaced/cleaned!"

Good luck

Dave

PS there is also this forum.....unless you've found it already

http://www.my90.co.uk/cgi-bin/lpgforum/discus.cgi?pg=topics

[Sooty Zooki]

How you getting on with this G? Hope you got it sorted. Just realised your packed in pretty much as you were setting mine up - do you think it is an omen?

[suzukishrek]

[suzukishrek]

Righto, sorted the damn thing.

To cut a long story short, I tracked the fault down to the TPS (Throttle Position Sensor). Needless to say the phone call to Toyota proved to be the worlds most expensive unit, so I cheated.

On my LPG system you have a setup procedure to run through and one of its stages is "spooling of the TPS" which turned out to be Bedini's fancy way of saying "we're checking the value the TPS gives at idle and 3K RPM." Since most modern cars use a potentiometer, rather like a volume control on a radio, you get a variable voltage back from the TPS relative to where the throttle is.

I wondered what the significance of 3K RPM was why not use 2K or 4K even until I realised that it just needed a voltage at idle and a completely different one to indicate off-idle. Well I figured that 0V and 12V would give a definite indication and, more importantly, I could get these two extremes by using a microswitch and a small bulb rigged up to the throttle. Basically, the microswitch closed and supplied 12V at idle and opened, providing 0V, at anything off idle. I had to tweak the exact position of the microswitch so that it went to 0V at about 900 RPM.

The bulb? Oh yeah, just wired in parallel with the switch and ground so that I could see when the microswitch was switching over states and also to provided a current load for the Bedini electronics to recognise - it didn't register a direct connection of 12V into the TPS wire!

So, sorted eventually. Now I hoof the engine out, throw it at next doors rabbit and stuff in the 4.2TDi I've got instead.

[suzukishrek]

Right, after making the initial decision to switch from petrol to diesel having cured my petrol of it's LPG problems, I started to enjoy the joys of petrol and thus decided NOT to swap to diesel. So what happens? My blasted lumpy idle is back again and worse than ever now.

In fact at one point it got so bad I couldn't even start the truck, it just kept dieing on me - cranked for England, but wouldn't catch. I eventually got round it temporarily by pulling the electrically operated LPG solenoids out, replacing one of them with a manual thumb screw type and then leaning the LPG right down to get it to run. Once it was running I could then pic the revs up, switch to petrol and it seemed okay after that although it was back to its problem of stalling on LPG and lumping badly on petrol - at idle that is, off idle it went like a rocket! I've got to have something fubar with my injector wiring somewhere and they are still firing when I'm running on LPG thus making my mixture way too rich as it's actually running on both fuels at the same time.

Think I'm gonna remove the mixer and electronics of the LPG from the truck and see if I can get rid of the problem when running solely on petrol with none of the LPG stuff to interfere. Then I can start putting the LPG back in bit-by-bit to see where the fault returns although I'm not convinced it's an LPG fault, it just shows up worse on LPG!

It was suggested to me that the lambda or O2 sensors (same thing) were duffo, but I didn't think the ECU used the O2 sensors until it was off idle and only upto about 4K RPM or thereabouts. Anyone know?

[Rossko]

[suzukishrek]

The only problem with that Ross is that you can't fix O2 sensors! You have to replace them if they are no longer working and since there are two of them I don't get much change out of £500 - blasted Toyotas attitude to Jap imports I guess.

The idea of putting an extra one in was so that it proved the point inexpensively - if it didn't cure the problem I've not wasted £500.

Anyway, what would the drawbacks be of fitting a separate sensor specifically for the LPG system?

[Rossko]

[webber1982]

what cruiser is it if its the 4.6 streight 6 then they have a 0-1 volt sensor the signal wire is always the black wire at the sensor be aware they ysually change colour in the plug. to check its working simply get a multi meter put one side ot the battery negative and probe the signal wire out of the sensor u should be able to see the voltage scanning between probarbly 0.1 - 0.85 ish of a volt if it is not doing this then it is broken.