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Judder on LPG
Posted: Mon Mar 07, 2011 8:50 pm
by ChrisJC
OK, my P38 is exhibiting the most peculiar anomaly:
It's a 4.6 with OMVL Dream 21 LPG.
Runs perfectly on petrol. Runs perfectly on LPG at light to moderate loads. But:
When under heavy load between 3500rpm and 5000rpm, it judders pretty badly. Perhaps not as regular and harsh as a total misfire, but very very jerky nonetheless.
I've done some diagnostics with the LPG software and an OBD-II reader, and the following are true:
1. The Injector times go wild when it judders
2. The MAF reading goes wild (is 80-90 when on petrol, jumps up to 270 when on LPG!)
3. TPS is steady
I can't understand why it should be perfect on petrol, yet not OK on LPG.
Any ideas?
Thanks,
Chris.
Posted: Wed Mar 09, 2011 10:59 am
by bodger
Hi Chris
have you looked at the HT leads for tracking , mine old one used to do that on LPG but not on petrol ..it was tyhe HT leads breaking down as they coped with petrol but not Gas ...
Re: Judder on LPG
Posted: Wed Mar 09, 2011 2:49 pm
by DaveEFI
ChrisJC wrote:OK, my P38 is exhibiting the most peculiar anomaly:
It's a 4.6 with OMVL Dream 21 LPG.
Runs perfectly on petrol. Runs perfectly on LPG at light to moderate loads. But:
When under heavy load between 3500rpm and 5000rpm, it judders pretty badly. Perhaps not as regular and harsh as a total misfire, but very very jerky nonetheless.
I've done some diagnostics with the LPG software and an OBD-II reader, and the following are true:
1. The Injector times go wild when it judders
2. The MAF reading goes wild (is 80-90 when on petrol, jumps up to 270 when on LPG!)
3. TPS is steady
I can't understand why it should be perfect on petrol, yet not OK on LPG.
Any ideas?
Thanks,
Chris.
Any EFI system depends on a reliable tach signal from the ignition. And a good clean supply of battery volts, including the ground. Corruption of either could cause your problems
My guess is the tach signal. Have you a method of logging it?
Posted: Wed Mar 09, 2011 8:15 pm
by ChrisJC
Thanks chaps.
The 'tach' signal is OK. I know this because the rev counter is stable on the gas diagnostic software.
I wondered about the leads. I'm reluctant to fork out for a new set without proof, as they're dear for a Thor engine, and they are less than a year old. Mind you, they were 'pattern' leads rather than super-duper expensive ones. Rimmers want £101.22 for a genuine set!!
I think I'll strap a video camera under the bonnet and go for a drive. See if there's any evidence of tracking.
Chris.
Posted: Sun Mar 13, 2011 4:00 pm
by bodger
buy some copper core cable Chris and pull end off an old set of leads you can then solder them back on the new wire ( don't forget to put the caps on first though ...i forget
)
Posted: Sun Mar 13, 2011 5:31 pm
by ChrisJC
I have ordered a set of super-duper (not Magnecore!) leads from eBay...... Shall see if that makes a difference.
Chris.
Posted: Mon Mar 14, 2011 12:09 pm
by bodger
fingers crossed Chris , when i went to TINLEY TECH a while back he said that even the OE leads only last 6/12 months tops on Range Rover with LPG ... they just eat them appaently
Posted: Thu Apr 07, 2011 7:11 am
by ChrisJC
FIXED!
Turned out to be the MAF.
I'd fitted a £40 eBay pattern MAF. In desparation I bought a genuine part from Rimmers (£140), and it's perfect!
I had tried 3 sets of leads, to no avail in the meantime.
Chris.
Posted: Fri Apr 08, 2011 5:38 pm
by bodger
Glad to hear its sorted , things like thsi can be a right pain to find ....