Right, my turn to ask a question... and figured I'd post up here before the 'other place'...
2001, 4.6 Thor engine - petrol and LPG.
If I start it from cold, it runs fine - idles about 1200rpm for 20-30 seconds and then idle drops back to about 1000rpm, and then down to normal (seems to be normal behaviour for the Motronic 'cold start' strategy or that's what the manual said anyway! <br>
My problem is if I then hot start it - say go to the supermarket, and come back 10-15min later. Did it today and it had sat for 5min... It will start fine, and idle for a few seconds and then go lumpy and misfire for about 30-45 seconds (I presume until it goes back into closed loop). Then once it's had it's little tantrum, it will run, and idle sweetly on both petrol and gas. <br>
A brief run down of the engine/what I've done to it over the last few years since I've had it: <br>
First bought it and has misfiring at idle - all the time, petrol and gas. Changed TPS, CKS, HT leads and eventually tracked it down to a faulty MAF sensor. Replaced it with aftermarket and problem solved.. ish. <br>
It then ran fine, but every now and again I'd read the codes and the fuel trims would be jammed to max, I could reset adaptives and it would all be fine but over time would get skewed again. Ended up buying a genuine Bosch MAF and replacing the aftermarket Bearmach one - and problem solved. MAF is now about 2yrs old. <br>
Been poking about with the LPG and injectors/plumbing and all that so ran it on Petrol for a fair amount of time and trims seemed pretty stable, no recurring faults in the ECU. <br>
Over last 6 months or so (bearing in mind I'm away a lot and it doesn't get used - so 6 months is probably 1000 miles tops) it's been doing this when restarting the vehicle hot. <br>
Things that have been replaced in the last few years: <br>
MAF (Bearmach aftermarket, and then genuine Bosch circa 2014) <br>
TPS (aftermarket - 2012) <br>
CKS (Genuine LR - 2012) <br>
Spark Plugs (Changed at regular service Jan 2012 when I bought it, and then circa 2014 I changed them for NGK BPR6ES) <br>
HT Leads (Changed first in 2012 as regular service item, then circa 2014 I changed them for Magnecore KV85 HT Leads) <br>
Coil Packs (Changed circa 2104 with Magnecores and NGK's - Genuine Bosch replacement units) <br>
O2 sensors (Changed 2015 for Genuine Bosch sensors - partly preventative maintenance and partly due to LPG system being tapped into them and I was getting the odd O2 signal missing error in the engine ECU - LPG system had been connected on the sensor wiring side and on one side was just 'twisted and taped' so decided it was worth just replacing them!) <br>
IACV has previously been cleaned but it doesn't coke up like the GEMS one does either. <br>
My current thoughts... <br>
I have another genuine Bosch MAF so thinking about swapping that just to rule it in/out. I don't think it's the MAF as the symptoms of my problems before were bad idle all the time, not just on a hot start. <br>
I haven't yet chopped the O2 sensor wires off that feed the LPG system... now I know they aren't needed for anything the plan is to disconnect them altogether. I don't know if the LPG system is somehow interfering with it - but it feels like the problem is in the 'open loop' fuelling before it switches over to closed loop. <br>
I've looked at live data on Nanocom and the MAF reading looks to be fairly normal - however very quickly after I had reset adaptive values, the 'idle trim' fuel trims had shot from the reset value of 0.00 back up to about 1,46 where they were before. Other fuel trims are looking pretty close to 1.00 <br>
I don't think it's likely to be plugs, leads, coils - and as such haven't yet pulled the plugs out to check them - but if people think it's worth doing, then I'll do that in the next couple of days. <br>
I haven't tested fuel pressure - but I don't think it's the in tank pump as it has no trouble starting, and after it hits closed loop, it runs sweetly. <br>
Any ideas/thoughts/things to try? I've had the upper plenum off a few times when doing the LPG bits - and have resused the tin gasket a couple of times - but it's always been cleaned off and then re-sealed with a thin smear of black RTV. What's best to use if I want to spray something around the inlet to see if there is a vacuum leak into the manifold, post MAF? Easy start or something like that? <br>
I've decided I want to get it sorted this month as I have some time at home and want to catch up on some of the maintenance on it, even though it hasn't done a lot of mileage, but I'm likely to be using it more and it pisses me off when I'm out and about to have it idling so rough when I start it up - even if it is only for a short period of time! <br>
Cheers, <br>
Marty