Idling Problem 280GE
I have a 1989 280 GE converted to run on LPG. Once in a while, one gets a small explosion in the inlet manifold. This usually only results in the air filter housing being pushed off (held by rubber straps for this reason). However, if slightly worse, the air metering housing jumps out of the rubber collar attaching it to the inlet manifold. This results in excess air getting into the inlet manifold and it won't idle. Pushing the air metering housing back into the rubber collar usually sorts this out.
The last time an explosion occurred the usual problem (inability to idle)appeared immediately but the usual cure didn't work. The air metering housing hadn't jumped out but the egine wouldn't idle any more (either on LPG or petrol (gasoline)) - it would start to die just below 1 500rpm.
I have re-seated the rubber collar carefully, checked the rubber by-pass pipe below and made sure the air metering disc is centred and operating freely. However, none of this has made any difference. It still won't idle properly and seems as though it is getting too much air with a tendency to backfire.
Any ideas?
Just before this happened, I was starting to get problems with warm starting. If I stalled not long after starting, it was very difficult to start again.
Greetings
Seamus
Seamus,
Send a private message to Peter Perfect (Ian). He has been running gas converted Gs for a few years now and he might be able to help you. He might be too busy to look at the forum so a private message will get you in touch with him.
Good luck
This could be due to excessive air. If so where from?
Suggest that if you have checked out the fuel metering flap and it appears to be OK the only other possibilities are the throttle butterflies or the idle control valve. Either could have been damaged by the backfires. Easiest to check out is the throttle butterflies, so start there. However excessive air getting past either of these SHOULD open the fuel-metering flap. If this is not happening something could be damaged within the fuel-metering head (bad news) :cry: . So in theory air must be getting in to the system down stream of the fuel-metering flap.
Your symptoms prior to this suggest weak fueling.
As an aside if your LPG system and ignition system are working correctly you should not suffer backfires. Ignition system especially needs to be absolutely perfect. As a preventative measure if you do get backfires there should be a plunger type arrangement to fully open the fuel metering flap when running on gas. Then if it does backfire you reduce the risk of trashing your fuel-metering unit.
Good luck and let us know how you get on.
Russ
You wrote:
- '......... If this is not happening something could be damaged within the fuel-metering head (bad news) . '
How would a backfire damage the fuel metering head?
- 'As an aside if your LPG system and ignition system are working correctly you should not suffer backfires. Ignition system especially needs to be absolutely perfect. As a preventative measure if you do get backfires there should be a plunger type arrangement to fully open the fuel metering flap when running on gas.'
Have you seen such an arrangement? You would have to have a solenoid that pushed the plate down from above when you switched over to gas.
I figured out that there must be excessive unmetered air (ie downstream of the air metering disc) but can't work out where it's coming from. Is thee any thing else in the inlet manifold that could be blown out or displaced by a backfire?
Thanks for your help.
Hi Seamus,
Only guessing here but if the backfire blew past the fuel metering flap with enough force it could have damaged the internals.
This may be the cause of possible weak mixture? So it may not be an air leak down stream. As you say difficult to figure where that would be.
Can you get it on a gas analyser?
My LPG system is multi point so doesn't need the plunger. Think your description is correct but have not seen one fitted. Optional extra that not all installers bother with I think.
BTW where in Wales is your 2nd location? (don't worry don't have any dry matches!!)
Russ
Ideally you should take the car back to your LPG installer as gas idle valve is poss a tad over spec,and as multi point this is not always a problem however can be further amplified by a working but downgraded ignition system (plugs etc).All gas users should be advised to loosen all hoses after the air meter, though not that loose that it affects air/idle mixture.There should also be a blow back valve located in series with the air-flow valve that goes some way to protecting the air meter.
I have had same probs in the past and had to replace the b-back valve as it had been bent out of shape by post ignition snags but it had at least saved my air meter.
Hopefully yours has survived but if there were no bb valve and given the frequency of your problem then it may have just had enough.Usually a cold resistance check can eliminate this item but I have no idea where you might find these figures.
I had the same problem with my 280GE on LPG it would blow the air filter off and lift the metering unit out of the rubber joint. The last time it happened the result was exactly as you discribed, after a long time head scratching I took a small mirror and looked under the inlet manifold as you can't see underthere without removing the whole manifold. What I found was 2 vacuum hoses had blown off the unit they were pluged into (I haven't a clue what it does) so I reconnected them and secured them with tie clips. The car started and idled OK. What I have since done is taken the flap in the metering system off completely, it means I can't run on petrol but it starts and runs better with out it. Hope this helps. :)
I had a BMW 730i with LPG, using the venturi system as opposed to the far better sequential injection.
It did occasionally backfire, the cause being an air leak as diagnosed by board members.
Unfortunately the backfires cracked the circuit board within the air flow meter, so I had to replace that unit. It cost enough to wipe out my LPG savings for a year!
Most air flow meters can be checked with an analogue multimeter. Disconnect the unit, and expose the moving flap. Connect your multimeter to the pins of the air flow meter, and find the pins that change electrical resistance when you physically move the flap within the air flow meter. Check that the resistance changes steadily through the range of flap movement.
After my incident, I nearly bought a pressure-release flap from here, but sold the car instead: http://www.cribbs.freeserve.co.uk/parts_page.html
Good luck,
Tim
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Thanks for the advice - I will try and get in touch with him. Actually, although the problem was caused by a LPG back fire, it is not a LPG specific problem. It affects the petrol running and is there when all the LPG stuff is disconnected.
Seamus