97 HSE 4.6 on LPG: LPG went POP. Changed MAF but still wont Idle (Single Point)

Why did I change my Classic to a P38???

Did aout 300miles on Petrol - all fine
Did around 500 miles on LPG... pulled up a hill heavy right foot - LPG system went pop.

She still runs on Petrol but will not Idle. Changed the MAF (As I thought that was went pop)...out but still no different.

Any Help. Looking for quick fix As I moving house and stuck now. Currently in London untill the 16th then moving to North Wales.

what do you mean went pop?

does it run smoothly when you rev?

I was pulling up a hill on LPG with a heavy right foot and 1 green light left on the lpg gauge.

Then we had an all mighty loud pop... which I can only assume was a blow back. Not wanting another one I switched over to Petrol and she continued to run at 50mph to 70mph as normal... when we got up into traffic she was very jurcky on the accelerator... then as we approach static traffic (m6) and the revs droped... she stalled. She would restart and rev fine but will not hold the idle - Revs just drop off.

I though that the MAF had been damaged byt the air blow back so changed it for a known working one... but still she will not idle. I have no idea what else to check now.

how is it running under 3000rpm?

When you start her up - She revs on herself... which is something new since the pop. above say 2,000 to 2,500 revs she revs fine with no audible issues...

After start - the revs rise as I said (only for a few seconds) then start to drop. When they get to around the 1,000 and Idle mark she just dies.

If you help her by tapping the accelerator - she will respond above 1,500 to 2,000 but lower than that she's already dieing and sometimes you catch it sometimes you don't. Either way then end result is she will not idle.

I have about 3 days to fix her otherwise I'm completely screwed... with a dead Rangy in London and having to move back to North Wales.

how do your plugs look?

if it was a blow back and the MAF is ok check the other pipes/sensors around the inlet. check any pipes for leaks and disconnect any sensors one by one. if you disconnect a sensor and nothing happens then there is a good possiblilty thats its damaged.



what you discribe sounds like an air leak

POAH said:

how do your plugs look?

if it was a blow back and the MAF is ok check the other pipes/sensors around the inlet. check any pipes for leaks and disconnect any sensors one by one. if you disconnect a sensor and nothing happens then there is a good possiblilty thats its damaged.




what you discribe sounds like an air leak

Click to expand...

As above failing that- gas back fire due to hgf between cylinders not unknown. compression test will pick up

Whipped the plugs out. All where very black with the thread being oily... and the tip being sooted and dry.

What does this mean?

The oily black deposit runs all the way up. Cleaned and replaced and she ran better.

I think I found why she wasn't idling. I have two spring type things (think blow back protection) that sit in the plume chamber. One of these was not sitting right and once I removed, cleaned and reseated correctly along with the plugs. She now idles.


BUT the idle is a little low!!! How can I pick this up?

what us she idling at?

just above the first mark which I think is 500? so I'd say she's grumbeling along at about 550 / 600.

She seams to struggle to maintain this; especialy as you come off accelerator and coast upto a set of lights for example. Somtimes she dies. She doesn't like to idle, brake and stear.

Before all this she was ideling closer to the second mark which I assume is 750?

There is no difference to Park and Drvier now (there was before).

I just don't trust here as she is..... she's dangerous.

have you tried a different MAF now you ahve improved things?

O got a pattern part off ebay.. no difference. Nothing to say that was crap I know.. but don't want to falk out for a genuine one to find its not that you know.

Found the issue on this one... the blow back protection had blown. I have two copper washer type things on springs sitting int the plumb. One had blown out and not returned to the normal closed position... which was sucking in air. Reseated it and now she runs ok.

THANK you to all who Helped.

good news

Simple one to try, i did it last night; find and change the lpg solenoid filter [might look like a bell).
My 3.9 now idles smoothly, pulls without hesitating, doesnt try to stall and holds revs when drop cltuch at junctions...

Also try spending £60 on a new vaporiser, that cured my lpg back fire and improved idling.