Mogwyth

Mogwyth

New Member
Having a little problem the new engine. Essentially under certain circumstances it feels as if it's going to stall at around 1500 rev, pressing the accelerator overcomes it. It seems less evident on petrol than LPG. Tried dropping into third and it doesn't appear to happen and generally seems smoother, but as the problem only seems to happen under certain circumstances it may be coincidence. Fuel consumption has increased by about 15%. Checked the obvious plugs, leads ect all seem fine. So any thoughts? It wasn't gradual but quite sudden.
 
I just had a thought, does it feel like a "stumble", a kind of mild misfire? That being the case, it may well be an injection misfire. I remember a while ago (2 years?) reading about similar symptoms. If I remember what it was I'll let you know.

Might not be relevent but have you checked your battery and alternator? Both need to be strong and if failing can (and do) cause odd running glitches.
 
Cheers.

Not really a misfire Kev more like fuel starvation. Battery and alternator should be good both are under 5,000 miles old.
 
Mogwyth said:
Cheers.

Not really a misfire Kev more like fuel starvation. Battery and alternator should be good both are under 5,000 miles old.
Click to expand...

Could that be your answer? How old is the fuel filter? Have you checked that you don't have a rusted fuel pipe that is leaking? or perhaps a perished fuel hose.
 
I had a look at my various scribblings and references but couldn't find what I was looking for. I have definately read somewhere there is a known common issue at 1500 rpm cruising speed. I hate it when I know I've seen it and can't find it but never mind.

Have you checked the obvious things like ignition timing and wether the vac advance and mechanical advance are both working properly. It sounds like you're getting a problem on light throttle, so vac advance might be a reasonable possibility.

Failing that, is the plenum and ram housing nice and clean and is the throttle disk set correctly. Might be worth checking the throttle pot as a precaution. Sorry all I have for now. If I find what I'm looking for will let you know unless somebody else gets there first!!
 
classic kev said:
Could that be your answer? How old is the fuel filter? Have you checked that you don't have a rusted fuel pipe that is leaking? or perhaps a perished fuel hose.
Click to expand...

It happens on lpg and petrol.

classic kev said:
I had a look at my various scribblings and references but couldn't find what I was looking for. I have definately read somewhere there is a known common issue at 1500 rpm cruising speed. I hate it when I know I've seen it and can't find it but never mind.

Have you checked the obvious things like ignition timing and wether the vac advance and mechanical advance are both working properly. It sounds like you're getting a problem on light throttle, so vac advance might be a reasonable possibility.

Failing that, is the plenum and ram housing nice and clean and is the throttle disk set correctly. Might be worth checking the throttle pot as a precaution. Sorry all I have for now. If I find what I'm looking for will let you know unless somebody else gets there first!!
Click to expand...

No need to apologies anything it better than nothing and anyway if worse comes to worse the garage can have it back, just want to avoid that if I can.
 
Mogwyth said:
It happens on lpg and petrol.
Click to expand...

Mmmmm....... so something common to both then. Possibilities that spring to mind are ignition timing, so as before vac advance and mechanical advance but also, the inlet side is common(air leak?). For what it takes to do, would it be worth popping off the plenum, clean and bolt back on making sure there are no air leaks. (can also check/set throttle disk at the same time).
 
sounds like mine when it was the TPS , does it only do it when its up to temp?

Thats how mine was, fine for the first 4 trips roud the block but after that it would play up.
 
as it is a d2 then it has a totaly different injection system to the classic have a ecu fault read look at the parameters could be a air leak poor idle valve
 
Thanks for your responses, in-between building a cider press I have had a little play disconnected MAF, no difference checked on or two other bits no obvious problems so she is booked in Tuesday for a diagnostic.

Bill
 
Petrol solved loose lead round the back of the engine but LPG is still playing up but we do know the problem, vaporiser is rated for 120kw the 4.6 is 160plus KW, may have to uprate other parts of the gas system too:(
 
Right it seems the old girl had two separate problems, the falling of in fuel economy on LPG was caused by undersized vaporiser and pipes all sorted now and the strange fuel trim/pressure fluctuations have been cured. However we still have this misfire/stuttering around 1500 revs, it's not showing any fault codes or anything untoward on the diagnostics. The coil packs have been checked and seem fine, the old plugs were cleaned and gapped but we are still getting the problem and track marks on on the plug towers. A new set of plugs has been tried to no avail. Leads are next but they are a set of Magnecors less than 1500 miles old so shouldn't be an issue.

Any thoughts what else to look at? Essentially we are looking for what would cause a misfire at 1500 revs.

This is getting close to box of matches job.
 
Update.

Got her back and she is running fine now, problem was caused by a broken wire from knock sensor to ECU.

Do have another problem though the rear O2 sensors are not working, now from what I understand these are just a backup to the front ones and are of no real consequence if the front ones are working, can OK anyone confirm that?
 
yes when checking the read out of sensor reading the rear sensor will stay on a constant signal if the pre cat fail then the rears work so you know your fronts are faulty
 
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