3.9 Popping back through inlet

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BigErn

New Member
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54
Location
Sunderland.
My Discovery has a problem of being very reluctant to rev up and is flat as a fart as the revs rise. It also pops and bangs back up the inlet and has even blown the rubber pipe from MAF to throttle body to bits :lol:

Its ok to drive at low revs and light throttle but ask for anything more and it is sluggish and starts to pop and bang, on both petrol and LPG.

Its had..... plugs (BCR6ES), leads, cap looks brand new, rotor arm, brand new vac advance, dizzy timing checked, my MAF replaced with a known working one and still no further forward to finding the problem.

Anyone got any suggestions for me to try next??

Cheers :)
 
your symptons do sound like weak spark and or air leaks,as it appears to be back firing ,is it worse on gas, the fact that parts are or look new dosent mean there conductting properly,an old fashioned krypton tuner is the best way of testing component efficency but who has one now. did you check timing with strobe ,is amplifier working properly same with coil ,its usually a good idea to fit new coil ,cap arm ,leads ,plugs at same time
 
Its about the same on gas as it is on petrol and does the popping just the same when revving on the spot.

Timing was checked with a strobe yes. I do agree that it seems to be spark related still. It has a strong spark on idle but was beginning to think it could be the coil breaking down at higher revs. This is going to be my next port of call I think.
 
The symptoms sound like a classic case of wrong ignition timing OR a couple of the HT leads are the wrong way round. Check the firing order is correct.

Other than that, I might be tempted to think in terms of stretched timing chain, gummed up plenum or possibly an air leak somewhere on the inlet side of things.

Best I can think of at the mo.
 
I had a problem where my series was poping back through the inlet,missing and loss of power. Checked all electrics and all fine, did a compression test all fine, it turned out that the camshaft was knackered. Some of the lobes were worn away mainly on the exhaust valves so the valves weren't opening causing it to pop back through the inlet.
It was only when i decided to pull the heads off to have a look inside that I saw the knackered camshaft when I got the inlet manifold off.
Might not be the case with yours but just a thought
 
Going to hopefully get another look at it this weekend. Has anyone got the timing diagram for the engine so I can double check it is timed right? Also the firing order too? I believe it is timing related somehow now. Im hoping its not a knackered cam as I really cant be bothered to take the engine apart to swap it. I've already got an engine in bits in the garage Im rebuilding :lol:
 
Had a look at the weekend, fitted a mates spare dizzy and ignition amp and set the timing bang on to Autodata specification. Its now sweet as a nut and pulls nice and strong right through the revs on petrol with no issues.... still pops on gas at between 3.5 - 4k rpm. Im guessing the gas system needs a service and a re-cal
 
BigErn said:
Had a look at the weekend, fitted a mates spare dizzy and ignition amp and set the timing bang on to Autodata specification. Its now sweet as a nut and pulls nice and strong right through the revs on petrol with no issues.... still pops on gas at between 3.5 - 4k rpm. Im guessing the gas system needs a service and a re-cal
Click to expand...

Hey, is your still running sweet on the petrol ?
I'm having very similar issues to you, I even had a fire bomb fly out of the side of the plenum, inlet this morning.

I'm confused, if you are getting a good spark ? (i.e. from the dizzy cap) how does that point to an ignition amp fault on the dizzy ? What am i missing here ?

Thanks
 
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